text: /* pngrtran.c - transforms the data in a row for PNG readers
   *
   * Last changed in libpng 1.6.2 [April 25, 2013]
   * Copyright (c) 1998-2013 Glenn Randers-Pehrson
   * (Version 0.96 Copyright (c) 1996, 1997 Andreas Dilger)
   * (Version 0.88 Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.)
   *
   * This code is released under the libpng license.
   * For conditions of distribution and use, see the disclaimer
   * and license in png.h
   *
   * This file contains functions optionally called by an application
   * in order to tell libpng how to handle data when reading a PNG.
   * Transformations that are used in both reading and writing are
   * in pngtrans.c.
   */
  
  #include "pngpriv.h"
  
  #ifdef PNG_READ_SUPPORTED
  
  /* Set the action on getting a CRC error for an ancillary or critical chunk. */
  void PNGAPI
  png_set_crc_action(png_structrp png_ptr, int crit_action, int ancil_action)
  {
     png_debug(1, "in png_set_crc_action");
  
     if (png_ptr == NULL)
        return;
  
     /* Tell libpng how we react to CRC errors in critical chunks */
     switch (crit_action)
     {
        case PNG_CRC_NO_CHANGE:                        /* Leave setting as is */
           break;
  
        case PNG_CRC_WARN_USE:                               /* Warn/use data */
           png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
           png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE;
           break;
  
        case PNG_CRC_QUIET_USE:                             /* Quiet/use data */
           png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
           png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE |
                             PNG_FLAG_CRC_CRITICAL_IGNORE;
           break;
  
        case PNG_CRC_WARN_DISCARD:    /* Not a valid action for critical data */
           png_warning(png_ptr,
              "Can't discard critical data on CRC error");
        case PNG_CRC_ERROR_QUIT:                                /* Error/quit */
  
        case PNG_CRC_DEFAULT:
        default:
           png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
           break;
     }
  
     /* Tell libpng how we react to CRC errors in ancillary chunks */
     switch (ancil_action)
     {
        case PNG_CRC_NO_CHANGE:                       /* Leave setting as is */
           break;
  
        case PNG_CRC_WARN_USE:                              /* Warn/use data */
           png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
           png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE;
           break;
  
        case PNG_CRC_QUIET_USE:                            /* Quiet/use data */
           png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
           png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE |
                             PNG_FLAG_CRC_ANCILLARY_NOWARN;
           break;
  
        case PNG_CRC_ERROR_QUIT:                               /* Error/quit */
           png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
           png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_NOWARN;
           break;
  
        case PNG_CRC_WARN_DISCARD:                      /* Warn/discard data */
  
        case PNG_CRC_DEFAULT:
        default:
           png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
           break;
     }
  }
  
  #ifdef PNG_READ_TRANSFORMS_SUPPORTED
  /* Is it OK to set a transformation now?  Only if png_start_read_image or
   * png_read_update_info have not been called.  It is not necessary for the IHDR
   * to have been read in all cases, the parameter allows for this check too.
   */
  static int
  png_rtran_ok(png_structrp png_ptr, int need_IHDR)
  {
     if (png_ptr != NULL)
     {
        if (png_ptr->flags & PNG_FLAG_ROW_INIT)
           png_app_error(png_ptr,
              "invalid after png_start_read_image or png_read_update_info");
  
        else if (need_IHDR && (png_ptr->mode & PNG_HAVE_IHDR) == 0)
           png_app_error(png_ptr, "invalid before the PNG header has been read");
  
        else
        {
           /* Turn on failure to initialize correctly for all transforms. */
           png_ptr->flags |= PNG_FLAG_DETECT_UNINITIALIZED;
  
           return 1; /* Ok */
        }
     }
  
     return 0; /* no png_error possible! */
  }
  #endif
  
  #ifdef PNG_READ_BACKGROUND_SUPPORTED
  /* Handle alpha and tRNS via a background color */
  void PNGFAPI
  png_set_background_fixed(png_structrp png_ptr,
      png_const_color_16p background_color, int background_gamma_code,
      int need_expand, png_fixed_point background_gamma)
  {
     png_debug(1, "in png_set_background_fixed");
  
     if (!png_rtran_ok(png_ptr, 0) || background_color == NULL)
        return;
  
     if (background_gamma_code == PNG_BACKGROUND_GAMMA_UNKNOWN)
     {
        png_warning(png_ptr, "Application must supply a known background gamma");
        return;
     }
  
     png_ptr->transformations |= PNG_COMPOSE | PNG_STRIP_ALPHA;
     png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
     png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
  
     png_ptr->background = *background_color;
     png_ptr->background_gamma = background_gamma;
     png_ptr->background_gamma_type = (png_byte)(background_gamma_code);
     if (need_expand)
        png_ptr->transformations |= PNG_BACKGROUND_EXPAND;
     else
        png_ptr->transformations &= ~PNG_BACKGROUND_EXPAND;
  }
  
  #  ifdef PNG_FLOATING_POINT_SUPPORTED
  void PNGAPI
  png_set_background(png_structrp png_ptr,
      png_const_color_16p background_color, int background_gamma_code,
      int need_expand, double background_gamma)
  {
     png_set_background_fixed(png_ptr, background_color, background_gamma_code,
        need_expand, png_fixed(png_ptr, background_gamma, "png_set_background"));
  }
  #  endif  /* FLOATING_POINT */
  #endif /* READ_BACKGROUND */
  
  /* Scale 16-bit depth files to 8-bit depth.  If both of these are set then the
   * one that pngrtran does first (scale) happens.  This is necessary to allow the
   * TRANSFORM and API behavior to be somewhat consistent, and it's simpler.
   */
  #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
  void PNGAPI
  png_set_scale_16(png_structrp png_ptr)
  {
     png_debug(1, "in png_set_scale_16");
  
     if (!png_rtran_ok(png_ptr, 0))
        return;
  
     png_ptr->transformations |= PNG_SCALE_16_TO_8;
  }
  #endif
  
  #ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
  /* Chop 16-bit depth files to 8-bit depth */
  void PNGAPI
  png_set_strip_16(png_structrp png_ptr)
  {
     png_debug(1, "in png_set_strip_16");
  
     if (!png_rtran_ok(png_ptr, 0))
        return;
  
     png_ptr->transformations |= PNG_16_TO_8;
  }
  #endif
  
  #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
  void PNGAPI
  png_set_strip_alpha(png_structrp png_ptr)
  {
     png_debug(1, "in png_set_strip_alpha");
  
     if (!png_rtran_ok(png_ptr, 0))
        return;
  
     png_ptr->transformations |= PNG_STRIP_ALPHA;
  }
  #endif
  
  #if defined(PNG_READ_ALPHA_MODE_SUPPORTED) || defined(PNG_READ_GAMMA_SUPPORTED)
  static png_fixed_point
  translate_gamma_flags(png_structrp png_ptr, png_fixed_point output_gamma,
     int is_screen)
  {
     /* Check for flag values.  The main reason for having the old Mac value as a
      * flag is that it is pretty near impossible to work out what the correct
      * value is from Apple documentation - a working Mac system is needed to
      * discover the value!
      */
     if (output_gamma == PNG_DEFAULT_sRGB ||
        output_gamma == PNG_FP_1 / PNG_DEFAULT_sRGB)
     {
        /* If there is no sRGB support this just sets the gamma to the standard
         * sRGB value.  (This is a side effect of using this function!)
         */
  #     ifdef PNG_READ_sRGB_SUPPORTED
           png_ptr->flags |= PNG_FLAG_ASSUME_sRGB;
  #     else
           PNG_UNUSED(png_ptr)
  #     endif
        if (is_screen)
           output_gamma = PNG_GAMMA_sRGB;
        else
           output_gamma = PNG_GAMMA_sRGB_INVERSE;
     }
  
     else if (output_gamma == PNG_GAMMA_MAC_18 ||
        output_gamma == PNG_FP_1 / PNG_GAMMA_MAC_18)
     {
        if (is_screen)
           output_gamma = PNG_GAMMA_MAC_OLD;
        else
           output_gamma = PNG_GAMMA_MAC_INVERSE;
     }
  
     return output_gamma;
  }
  
  #  ifdef PNG_FLOATING_POINT_SUPPORTED
  static png_fixed_point
  convert_gamma_value(png_structrp png_ptr, double output_gamma)
  {
     /* The following silently ignores cases where fixed point (times 100,000)
      * gamma values are passed to the floating point API.  This is safe and it
      * means the fixed point constants work just fine with the floating point
      * API.  The alternative would just lead to undetected errors and spurious
      * bug reports.  Negative values fail inside the _fixed API unless they
      * correspond to the flag values.
      */
     if (output_gamma > 0 && output_gamma < 128)
        output_gamma *= PNG_FP_1;
  
     /* This preserves -1 and -2 exactly: */
     output_gamma = floor(output_gamma + .5);
  
     if (output_gamma > PNG_FP_MAX || output_gamma < PNG_FP_MIN)
        png_fixed_error(png_ptr, "gamma value");
  
     return (png_fixed_point)output_gamma;
  }
  #  endif
  #endif /* READ_ALPHA_MODE || READ_GAMMA */
  
  #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
  void PNGFAPI
  png_set_alpha_mode_fixed(png_structrp png_ptr, int mode,
     png_fixed_point output_gamma)
  {
     int compose = 0;
     png_fixed_point file_gamma;
  
     png_debug(1, "in png_set_alpha_mode");
  
     if (!png_rtran_ok(png_ptr, 0))
        return;
  
     output_gamma = translate_gamma_flags(png_ptr, output_gamma, 1/*screen*/);
  
     /* Validate the value to ensure it is in a reasonable range. The value
      * is expected to be 1 or greater, but this range test allows for some
      * viewing correction values.  The intent is to weed out users of this API
      * who use the inverse of the gamma value accidentally!  Since some of these
      * values are reasonable this may have to be changed.
      */
     if (output_gamma < 70000 || output_gamma > 300000)
        png_error(png_ptr, "output gamma out of expected range");
  
     /* The default file gamma is the inverse of the output gamma; the output
      * gamma may be changed below so get the file value first:
      */
     file_gamma = png_reciprocal(output_gamma);
  
     /* There are really 8 possibilities here, composed of any combination
      * of:
      *
      *    premultiply the color channels
      *    do not encode non-opaque pixels
      *    encode the alpha as well as the color channels
      *
      * The differences disappear if the input/output ('screen') gamma is 1.0,
      * because then the encoding is a no-op and there is only the choice of
      * premultiplying the color channels or not.
      *
      * png_set_alpha_mode and png_set_background interact because both use
      * png_compose to do the work.  Calling both is only useful when
      * png_set_alpha_mode is used to set the default mode - PNG_ALPHA_PNG - along
      * with a default gamma value.  Otherwise PNG_COMPOSE must not be set.
      */
     switch (mode)
     {
        case PNG_ALPHA_PNG:        /* default: png standard */
           /* No compose, but it may be set by png_set_background! */
           png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
           png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
           break;
  
        case PNG_ALPHA_ASSOCIATED: /* color channels premultiplied */
           compose = 1;
           png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
           png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
           /* The output is linear: */
           output_gamma = PNG_FP_1;
           break;
  
        case PNG_ALPHA_OPTIMIZED:  /* associated, non-opaque pixels linear */
           compose = 1;
           png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
           png_ptr->flags |= PNG_FLAG_OPTIMIZE_ALPHA;
           /* output_gamma records the encoding of opaque pixels! */
           break;
  
        case PNG_ALPHA_BROKEN:     /* associated, non-linear, alpha encoded */
           compose = 1;
           png_ptr->transformations |= PNG_ENCODE_ALPHA;
           png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
           break;
  
        default:
           png_error(png_ptr, "invalid alpha mode");
     }
  
     /* Only set the default gamma if the file gamma has not been set (this has
      * the side effect that the gamma in a second call to png_set_alpha_mode will
      * be ignored.)
      */
     if (png_ptr->colorspace.gamma == 0)
     {
        png_ptr->colorspace.gamma = file_gamma;
        png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
     }
  
     /* But always set the output gamma: */
     png_ptr->screen_gamma = output_gamma;
  
     /* Finally, if pre-multiplying, set the background fields to achieve the
      * desired result.
      */
     if (compose)
     {
        /* And obtain alpha pre-multiplication by composing on black: */
        memset(&png_ptr->background, 0, (sizeof png_ptr->background));
        png_ptr->background_gamma = png_ptr->colorspace.gamma; /* just in case */
        png_ptr->background_gamma_type = PNG_BACKGROUND_GAMMA_FILE;
        png_ptr->transformations &= ~PNG_BACKGROUND_EXPAND;
  
        if (png_ptr->transformations & PNG_COMPOSE)
           png_error(png_ptr,
              "conflicting calls to set alpha mode and background");
  
        png_ptr->transformations |= PNG_COMPOSE;
     }
  }
  
  #  ifdef PNG_FLOATING_POINT_SUPPORTED
  void PNGAPI
  png_set_alpha_mode(png_structrp png_ptr, int mode, double output_gamma)
  {
     png_set_alpha_mode_fixed(png_ptr, mode, convert_gamma_value(png_ptr,
        output_gamma));
  }
  #  endif
  #endif
  
  #ifdef PNG_READ_QUANTIZE_SUPPORTED
  /* Dither file to 8-bit.  Supply a palette, the current number
   * of elements in the palette, the maximum number of elements
   * allowed, and a histogram if possible.  If the current number
   * of colors is greater then the maximum number, the palette will be
   * modified to fit in the maximum number.  "full_quantize" indicates
   * whether we need a quantizing cube set up for RGB images, or if we
   * simply are reducing the number of colors in a paletted image.
   */
  
  typedef struct png_dsort_struct
  {
     struct png_dsort_struct * next;
     png_byte left;
     png_byte right;
  } png_dsort;
  typedef png_dsort *   png_dsortp;
  typedef png_dsort * * png_dsortpp;
  
  void PNGAPI
  png_set_quantize(png_structrp png_ptr, png_colorp palette,
      int num_palette, int maximum_colors, png_const_uint_16p histogram,
      int full_quantize)
  {
     png_debug(1, "in png_set_quantize");
  
     if (!png_rtran_ok(png_ptr, 0))
        return;
  
     png_ptr->transformations |= PNG_QUANTIZE;
  
     if (!full_quantize)
     {
        int i;
  
        png_ptr->quantize_index = (png_bytep)png_malloc(png_ptr,
            (png_uint_32)(num_palette * (sizeof (png_byte))));
        for (i = 0; i < num_palette; i++)
           png_ptr->quantize_index[i] = (png_byte)i;
     }
  
     if (num_palette > maximum_colors)
     {
        if (histogram != NULL)
        {
           /* This is easy enough, just throw out the least used colors.
            * Perhaps not the best solution, but good enough.
            */
  
           int i;
  
           /* Initialize an array to sort colors */
           png_ptr->quantize_sort = (png_bytep)png_malloc(png_ptr,
               (png_uint_32)(num_palette * (sizeof (png_byte))));
  
           /* Initialize the quantize_sort array */
           for (i = 0; i < num_palette; i++)
              png_ptr->quantize_sort[i] = (png_byte)i;
  
           /* Find the least used palette entries by starting a
            * bubble sort, and running it until we have sorted
            * out enough colors.  Note that we don't care about
            * sorting all the colors, just finding which are
            * least used.
            */
  
           for (i = num_palette - 1; i >= maximum_colors; i--)
           {
              int done; /* To stop early if the list is pre-sorted */
              int j;
  
              done = 1;
              for (j = 0; j < i; j++)
              {
                 if (histogram[png_ptr->quantize_sort[j]]
                     < histogram[png_ptr->quantize_sort[j + 1]])
                 {
                    png_byte t;
  
                    t = png_ptr->quantize_sort[j];
                    png_ptr->quantize_sort[j] = png_ptr->quantize_sort[j + 1];
                    png_ptr->quantize_sort[j + 1] = t;
                    done = 0;
                 }
              }
  
              if (done)
                 break;
           }
  
           /* Swap the palette around, and set up a table, if necessary */
           if (full_quantize)
           {
              int j = num_palette;
  
              /* Put all the useful colors within the max, but don't
               * move the others.
               */
              for (i = 0; i < maximum_colors; i++)
              {
                 if ((int)png_ptr->quantize_sort[i] >= maximum_colors)
                 {
                    do
                       j--;
                    while ((int)png_ptr->quantize_sort[j] >= maximum_colors);
  
                    palette[i] = palette[j];
                 }
              }
           }
           else
           {
              int j = num_palette;
  
              /* Move all the used colors inside the max limit, and
               * develop a translation table.
               */
              for (i = 0; i < maximum_colors; i++)
              {
                 /* Only move the colors we need to */
                 if ((int)png_ptr->quantize_sort[i] >= maximum_colors)
                 {
                    png_color tmp_color;
  
                    do
                       j--;
                    while ((int)png_ptr->quantize_sort[j] >= maximum_colors);
  
                    tmp_color = palette[j];
                    palette[j] = palette[i];
                    palette[i] = tmp_color;
                    /* Indicate where the color went */
                    png_ptr->quantize_index[j] = (png_byte)i;
                    png_ptr->quantize_index[i] = (png_byte)j;
                 }
              }
  
              /* Find closest color for those colors we are not using */
              for (i = 0; i < num_palette; i++)
              {
                 if ((int)png_ptr->quantize_index[i] >= maximum_colors)
                 {
                    int min_d, k, min_k, d_index;
  
                    /* Find the closest color to one we threw out */
                    d_index = png_ptr->quantize_index[i];
                    min_d = PNG_COLOR_DIST(palette[d_index], palette[0]);
                    for (k = 1, min_k = 0; k < maximum_colors; k++)
                    {
                       int d;
  
                       d = PNG_COLOR_DIST(palette[d_index], palette[k]);
  
                       if (d < min_d)
                       {
                          min_d = d;
                          min_k = k;
                       }
                    }
                    /* Point to closest color */
                    png_ptr->quantize_index[i] = (png_byte)min_k;
                 }
              }
           }
           png_free(png_ptr, png_ptr->quantize_sort);
           png_ptr->quantize_sort = NULL;
        }
        else
        {
           /* This is much harder to do simply (and quickly).  Perhaps
            * we need to go through a median cut routine, but those
            * don't always behave themselves with only a few colors
            * as input.  So we will just find the closest two colors,
            * and throw out one of them (chosen somewhat randomly).
            * [We don't understand this at all, so if someone wants to
            *  work on improving it, be our guest - AED, GRP]
            */
           int i;
           int max_d;
           int num_new_palette;
           png_dsortp t;
           png_dsortpp hash;
  
           t = NULL;
  
           /* Initialize palette index arrays */
           png_ptr->index_to_palette = (png_bytep)png_malloc(png_ptr,
               (png_uint_32)(num_palette * (sizeof (png_byte))));
           png_ptr->palette_to_index = (png_bytep)png_malloc(png_ptr,
               (png_uint_32)(num_palette * (sizeof (png_byte))));
  
           /* Initialize the sort array */
           for (i = 0; i < num_palette; i++)
           {
              png_ptr->index_to_palette[i] = (png_byte)i;
              png_ptr->palette_to_index[i] = (png_byte)i;
           }
  
           hash = (png_dsortpp)png_calloc(png_ptr, (png_uint_32)(769 *
               (sizeof (png_dsortp))));
  
           num_new_palette = num_palette;
  
           /* Initial wild guess at how far apart the farthest pixel
            * pair we will be eliminating will be.  Larger
            * numbers mean more areas will be allocated, Smaller
            * numbers run the risk of not saving enough data, and
            * having to do this all over again.
            *
            * I have not done extensive checking on this number.
            */
           max_d = 96;
  
           while (num_new_palette > maximum_colors)
           {
              for (i = 0; i < num_new_palette - 1; i++)
              {
                 int j;
  
                 for (j = i + 1; j < num_new_palette; j++)
                 {
                    int d;
  
                    d = PNG_COLOR_DIST(palette[i], palette[j]);
  
                    if (d <= max_d)
                    {
  
                       t = (png_dsortp)png_malloc_warn(png_ptr,
                           (png_uint_32)(sizeof (png_dsort)));
  
                       if (t == NULL)
                           break;
  
                       t->next = hash[d];
                       t->left = (png_byte)i;
                       t->right = (png_byte)j;
                       hash[d] = t;
                    }
                 }
                 if (t == NULL)
                    break;
              }
  
              if (t != NULL)
              for (i = 0; i <= max_d; i++)
              {
                 if (hash[i] != NULL)
                 {
                    png_dsortp p;
  
                    for (p = hash[i]; p; p = p->next)
                    {
                       if ((int)png_ptr->index_to_palette[p->left]
                           < num_new_palette &&
                           (int)png_ptr->index_to_palette[p->right]
                           < num_new_palette)
                       {
                          int j, next_j;
  
                          if (num_new_palette & 0x01)
                          {
                             j = p->left;
                             next_j = p->right;
                          }
                          else
                          {
                             j = p->right;
                             next_j = p->left;
                          }
  
                          num_new_palette--;
                          palette[png_ptr->index_to_palette[j]]
                              = palette[num_new_palette];
                          if (!full_quantize)
                          {
                             int k;
  
                             for (k = 0; k < num_palette; k++)
                             {
                                if (png_ptr->quantize_index[k] ==
                                    png_ptr->index_to_palette[j])
                                   png_ptr->quantize_index[k] =
                                       png_ptr->index_to_palette[next_j];
  
                                if ((int)png_ptr->quantize_index[k] ==
                                    num_new_palette)
                                   png_ptr->quantize_index[k] =
                                       png_ptr->index_to_palette[j];
                             }
                          }
  
                          png_ptr->index_to_palette[png_ptr->palette_to_index
                              [num_new_palette]] = png_ptr->index_to_palette[j];
  
                          png_ptr->palette_to_index[png_ptr->index_to_palette[j]]
                              = png_ptr->palette_to_index[num_new_palette];
  
                          png_ptr->index_to_palette[j] =
                              (png_byte)num_new_palette;
  
                          png_ptr->palette_to_index[num_new_palette] =
                              (png_byte)j;
                       }
                       if (num_new_palette <= maximum_colors)
                          break;
                    }
                    if (num_new_palette <= maximum_colors)
                       break;
                 }
              }
  
              for (i = 0; i < 769; i++)
              {
                 if (hash[i] != NULL)
                 {
                    png_dsortp p = hash[i];
                    while (p)
                    {
                       t = p->next;
                       png_free(png_ptr, p);
                       p = t;
                    }
                 }
                 hash[i] = 0;
              }
              max_d += 96;
           }
           png_free(png_ptr, hash);
           png_free(png_ptr, png_ptr->palette_to_index);
           png_free(png_ptr, png_ptr->index_to_palette);
           png_ptr->palette_to_index = NULL;
           png_ptr->index_to_palette = NULL;
        }
        num_palette = maximum_colors;
     }
     if (png_ptr->palette == NULL)
     {
        png_ptr->palette = palette;
     }
     png_ptr->num_palette = (png_uint_16)num_palette;
  
     if (full_quantize)
     {
        int i;
        png_bytep distance;
        int total_bits = PNG_QUANTIZE_RED_BITS + PNG_QUANTIZE_GREEN_BITS +
            PNG_QUANTIZE_BLUE_BITS;
        int num_red = (1 << PNG_QUANTIZE_RED_BITS);
        int num_green = (1 << PNG_QUANTIZE_GREEN_BITS);
        int num_blue = (1 << PNG_QUANTIZE_BLUE_BITS);
        png_size_t num_entries = ((png_size_t)1 << total_bits);
  
        png_ptr->palette_lookup = (png_bytep)png_calloc(png_ptr,
            (png_uint_32)(num_entries * (sizeof (png_byte))));
  
        distance = (png_bytep)png_malloc(png_ptr, (png_uint_32)(num_entries *
            (sizeof (png_byte))));
  
        memset(distance, 0xff, num_entries * (sizeof (png_byte)));
  
        for (i = 0; i < num_palette; i++)
        {
           int ir, ig, ib;
           int r = (palette[i].red >> (8 - PNG_QUANTIZE_RED_BITS));
           int g = (palette[i].green >> (8 - PNG_QUANTIZE_GREEN_BITS));
           int b = (palette[i].blue >> (8 - PNG_QUANTIZE_BLUE_BITS));
  
           for (ir = 0; ir < num_red; ir++)
           {
              /* int dr = abs(ir - r); */
              int dr = ((ir > r) ? ir - r : r - ir);
              int index_r = (ir << (PNG_QUANTIZE_BLUE_BITS +
                  PNG_QUANTIZE_GREEN_BITS));
  
              for (ig = 0; ig < num_green; ig++)
              {
                 /* int dg = abs(ig - g); */
                 int dg = ((ig > g) ? ig - g : g - ig);
                 int dt = dr + dg;
                 int dm = ((dr > dg) ? dr : dg);
                 int index_g = index_r | (ig << PNG_QUANTIZE_BLUE_BITS);
  
                 for (ib = 0; ib < num_blue; ib++)
                 {
                    int d_index = index_g | ib;
                    /* int db = abs(ib - b); */
                    int db = ((ib > b) ? ib - b : b - ib);
                    int dmax = ((dm > db) ? dm : db);
                    int d = dmax + dt + db;
  
                    if (d < (int)distance[d_index])
                    {
                       distance[d_index] = (png_byte)d;
                       png_ptr->palette_lookup[d_index] = (png_byte)i;
                    }
                 }
              }
           }
        }
  
        png_free(png_ptr, distance);
     }
  }
  #endif /* PNG_READ_QUANTIZE_SUPPORTED */
  
  #ifdef PNG_READ_GAMMA_SUPPORTED
  void PNGFAPI
  png_set_gamma_fixed(png_structrp png_ptr, png_fixed_point scrn_gamma,
     png_fixed_point file_gamma)
  {
     png_debug(1, "in png_set_gamma_fixed");
  
     if (!png_rtran_ok(png_ptr, 0))
        return;
  
     /* New in libpng-1.5.4 - reserve particular negative values as flags. */
     scrn_gamma = translate_gamma_flags(png_ptr, scrn_gamma, 1/*screen*/);
     file_gamma = translate_gamma_flags(png_ptr, file_gamma, 0/*file*/);
  
     /* Checking the gamma values for being >0 was added in 1.5.4 along with the
      * premultiplied alpha support; this actually hides an undocumented feature
      * of the previous implementation which allowed gamma processing to be
      * disabled in background handling.  There is no evidence (so far) that this
      * was being used; however, png_set_background itself accepted and must still
      * accept '0' for the gamma value it takes, because it isn't always used.
      *
      * Since this is an API change (albeit a very minor one that removes an
      * undocumented API feature) the following checks were only enabled in
      * libpng-1.6.0.
      */
     if (file_gamma <= 0)
        png_error(png_ptr, "invalid file gamma in png_set_gamma");
  
     if (scrn_gamma <= 0)
        png_error(png_ptr, "invalid screen gamma in png_set_gamma");
  
     /* Set the gamma values unconditionally - this overrides the value in the PNG
      * file if a gAMA chunk was present.  png_set_alpha_mode provides a
      * different, easier, way to default the file gamma.
      */
     png_ptr->colorspace.gamma = file_gamma;
     png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
     png_ptr->screen_gamma = scrn_gamma;
  }
  
  #  ifdef PNG_FLOATING_POINT_SUPPORTED
  void PNGAPI
  png_set_gamma(png_structrp png_ptr, double scrn_gamma, double file_gamma)
  {
     png_set_gamma_fixed(png_ptr, convert_gamma_value(png_ptr, scrn_gamma),
        convert_gamma_value(png_ptr, file_gamma));
  }
  #  endif /* FLOATING_POINT_SUPPORTED */
  #endif /* READ_GAMMA */
  
  #ifdef PNG_READ_EXPAND_SUPPORTED
  /* Expand paletted images to RGB, expand grayscale images of
   * less than 8-bit depth to 8-bit depth, and expand tRNS chunks
   * to alpha channels.
   */
  void PNGAPI
  png_set_expand(png_structrp png_ptr)
  {
     png_debug(1, "in png_set_expand");
  
     if (!png_rtran_ok(png_ptr, 0))
        return;
  
     png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
  }
  
  /* GRR 19990627:  the following three functions currently are identical
   *  to png_set_expand().  However, it is entirely reasonable that someone
   *  might wish to expand an indexed image to RGB but *not* expand a single,
   *  fully transparent palette entry to a full alpha channel--perhaps instead
   *  convert tRNS to the grayscale/RGB format (16-bit RGB value), or replace
   *  the transparent color with a particular RGB value, or drop tRNS entirely.
   *  IOW, a future version of the library may make the transformations flag
   *  a bit more fine-grained, with separate bits for each of these three
   *  functions.
   *
   *  More to the point, these functions make it obvious what libpng will be
   *  doing, whereas "expand" can (and does) mean any number of things.
   *
   *  GRP 20060307: In libpng-1.2.9, png_set_gray_1_2_4_to_8() was modified
   *  to expand only the sample depth but not to expand the tRNS to alpha
   *  and its name was changed to png_set_expand_gray_1_2_4_to_8().
   */
  
  /* Expand paletted images to RGB. */
  void PNGAPI
  png_set_palette_to_rgb(png_structrp png_ptr)
  {
     png_debug(1, "in png_set_palette_to_rgb");
  
     if (!png_rtran_ok(png_ptr, 0))
        return;
  
     png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
  }
  
  /* Expand grayscale images of less than 8-bit depth to 8 bits. */
  void PNGAPI
  png_set_expand_gray_1_2_4_to_8(png_structrp png_ptr)
  {
     png_debug(1, "in png_set_expand_gray_1_2_4_to_8");
  
     if (!png_rtran_ok(png_ptr, 0))
        return;
  
     png_ptr->transformations |= PNG_EXPAND;
  }
  
  /* Expand tRNS chunks to alpha channels. */
  void PNGAPI
  png_set_tRNS_to_alpha(png_structrp png_ptr)
  {
     png_debug(1, "in png_set_tRNS_to_alpha");
  
     if (!png_rtran_ok(png_ptr, 0))
        return;
  
     png_ptr->transformations |= (PNG_EXPAND | PNG_EXPAND_tRNS);
  }
  #endif /* defined(PNG_READ_EXPAND_SUPPORTED) */
  
  #ifdef PNG_READ_EXPAND_16_SUPPORTED
  /* Expand to 16-bit channels, expand the tRNS chunk too (because otherwise
   * it may not work correctly.)
   */
  void PNGAPI
  png_set_expand_16(png_structrp png_ptr)
  {
     png_debug(1, "in png_set_expand_16");
  
     if (!png_rtran_ok(png_ptr, 0))
        return;
  
     png_ptr->transformations |= (PNG_EXPAND_16 | PNG_EXPAND | PNG_EXPAND_tRNS);
  }
  #endif
  
  #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
  void PNGAPI
  png_set_gray_to_rgb(png_structrp png_ptr)
  {
     png_debug(1, "in png_set_gray_to_rgb");
  
     if (!png_rtran_ok(png_ptr, 0))
        return;
  
     /* Because rgb must be 8 bits or more: */
     png_set_expand_gray_1_2_4_to_8(png_ptr);
     png_ptr->transformations |= PNG_GRAY_TO_RGB;
  }
  #endif
  
  #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
  void PNGFAPI
  png_set_rgb_to_gray_fixed(png_structrp png_ptr, int error_action,
      png_fixed_point red, png_fixed_point green)
  {
     png_debug(1, "in png_set_rgb_to_gray");
  
     /* Need the IHDR here because of the check on color_type below. */
     /* TODO: fix this */
     if (!png_rtran_ok(png_ptr, 1))
        return;
  
     switch(error_action)
     {
        case PNG_ERROR_ACTION_NONE:
           png_ptr->transformations |= PNG_RGB_TO_GRAY;
           break;
  
        case PNG_ERROR_ACTION_WARN:
           png_ptr->transformations |= PNG_RGB_TO_GRAY_WARN;
           break;
  
        case PNG_ERROR_ACTION_ERROR:
           png_ptr->transformations |= PNG_RGB_TO_GRAY_ERR;
           break;
  
        default:
           png_error(png_ptr, "invalid error action to rgb_to_gray");
           break;
     }
  
     if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
  #ifdef PNG_READ_EXPAND_SUPPORTED
        png_ptr->transformations |= PNG_EXPAND;
  #else
     {
        /* Make this an error in 1.6 because otherwise the application may assume
         * that it just worked and get a memory overwrite.
         */
        png_error(png_ptr,
          "Cannot do RGB_TO_GRAY without EXPAND_SUPPORTED");
  
        /* png_ptr->transformations &= ~PNG_RGB_TO_GRAY; */
     }
  #endif
     {
        if (red >= 0 && green >= 0 && red + green <= PNG_FP_1)
        {
           png_uint_16 red_int, green_int;
  
           /* NOTE: this calculation does not round, but this behavior is retained
            * for consistency, the inaccuracy is very small.  The code here always
            * overwrites the coefficients, regardless of whether they have been
            * defaulted or set already.
            */
           red_int = (png_uint_16)(((png_uint_32)red*32768)/100000);
           green_int = (png_uint_16)(((png_uint_32)green*32768)/100000);
  
           png_ptr->rgb_to_gray_red_coeff   = red_int;
           png_ptr->rgb_to_gray_green_coeff = green_int;
           png_ptr->rgb_to_gray_coefficients_set = 1;
        }
  
        else
        {
           if (red >= 0 && green >= 0)
              png_app_warning(png_ptr,
                 "ignoring out of range rgb_to_gray coefficients");
  
           /* Use the defaults, from the cHRM chunk if set, else the historical
            * values which are close to the sRGB/HDTV/ITU-Rec 709 values.  See
            * png_do_rgb_to_gray for more discussion of the values.  In this case
            * the coefficients are not marked as 'set' and are not overwritten if
            * something has already provided a default.
            */
           if (png_ptr->rgb_to_gray_red_coeff == 0 &&
              png_ptr->rgb_to_gray_green_coeff == 0)
           {
              png_ptr->rgb_to_gray_red_coeff   = 6968;
              png_ptr->rgb_to_gray_green_coeff = 23434;
              /* png_ptr->rgb_to_gray_blue_coeff  = 2366; */
           }
        }
     }
  }
  
  #ifdef PNG_FLOATING_POINT_SUPPORTED
  /* Convert a RGB image to a grayscale of the same width.  This allows us,
   * for example, to convert a 24 bpp RGB image into an 8 bpp grayscale image.
   */
  
  void PNGAPI
  png_set_rgb_to_gray(png_structrp png_ptr, int error_action, double red,
     double green)
  {
     png_set_rgb_to_gray_fixed(png_ptr, error_action,
        png_fixed(png_ptr, red, "rgb to gray red coefficient"),
        png_fixed(png_ptr, green, "rgb to gray green coefficient"));
  }
  #endif /* FLOATING POINT */
  
  #endif /* RGB_TO_GRAY */
  
  #if defined(PNG_READ_USER_TRANSFORM_SUPPORTED) || \
      defined(PNG_WRITE_USER_TRANSFORM_SUPPORTED)
  void PNGAPI
  png_set_read_user_transform_fn(png_structrp png_ptr, png_user_transform_ptr
      read_user_transform_fn)
  {
     png_debug(1, "in png_set_read_user_transform_fn");
  
  #ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
     png_ptr->transformations |= PNG_USER_TRANSFORM;
     png_ptr->read_user_transform_fn = read_user_transform_fn;
  #endif
  }
  #endif
  
  #ifdef PNG_READ_TRANSFORMS_SUPPORTED
  #ifdef PNG_READ_GAMMA_SUPPORTED
  /* In the case of gamma transformations only do transformations on images where
   * the [file] gamma and screen_gamma are not close reciprocals, otherwise it
   * slows things down slightly, and also needlessly introduces small errors.
   */
  static int /* PRIVATE */
  png_gamma_threshold(png_fixed_point screen_gamma, png_fixed_point file_gamma)
  {
     /* PNG_GAMMA_THRESHOLD is the threshold for performing gamma
      * correction as a difference of the overall transform from 1.0
      *
      * We want to compare the threshold with s*f - 1, if we get
      * overflow here it is because of wacky gamma values so we
      * turn on processing anyway.
      */
     png_fixed_point gtest;
     return !png_muldiv(&gtest, screen_gamma, file_gamma, PNG_FP_1) ||
         png_gamma_significant(gtest);
  }
  #endif
  
  /* Initialize everything needed for the read.  This includes modifying
   * the palette.
   */
  
  /*For the moment 'png_init_palette_transformations' and
   * 'png_init_rgb_transformations' only do some flag canceling optimizations.
   * The intent is that these two routines should have palette or rgb operations
   * extracted from 'png_init_read_transformations'.
   */
  static void /* PRIVATE */
  png_init_palette_transformations(png_structrp png_ptr)
  {
     /* Called to handle the (input) palette case.  In png_do_read_transformations
      * the first step is to expand the palette if requested, so this code must
      * take care to only make changes that are invariant with respect to the
      * palette expansion, or only do them if there is no expansion.
      *
      * STRIP_ALPHA has already been handled in the caller (by setting num_trans
      * to 0.)
      */
     int input_has_alpha = 0;
     int input_has_transparency = 0;
  
     if (png_ptr->num_trans > 0)
     {
        int i;
  
        /* Ignore if all the entries are opaque (unlikely!) */
        for (i=0; i<png_ptr->num_trans; ++i)
           if (png_ptr->trans_alpha[i] == 255)
              continue;
           else if (png_ptr->trans_alpha[i] == 0)
              input_has_transparency = 1;
           else
              input_has_alpha = 1;
     }
  
     /* If no alpha we can optimize. */
     if (!input_has_alpha)
     {
        /* Any alpha means background and associative alpha processing is
         * required, however if the alpha is 0 or 1 throughout OPTIIMIZE_ALPHA
         * and ENCODE_ALPHA are irrelevant.
         */
        png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
        png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
  
        if (!input_has_transparency)
           png_ptr->transformations &= ~(PNG_COMPOSE | PNG_BACKGROUND_EXPAND);
     }
  
  #if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
     /* png_set_background handling - deals with the complexity of whether the
      * background color is in the file format or the screen format in the case
      * where an 'expand' will happen.
      */
  
     /* The following code cannot be entered in the alpha pre-multiplication case
      * because PNG_BACKGROUND_EXPAND is cancelled below.
      */
     if ((png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
         (png_ptr->transformations & PNG_EXPAND))
     {
        {
           png_ptr->background.red   =
               png_ptr->palette[png_ptr->background.index].red;
           png_ptr->background.green =
               png_ptr->palette[png_ptr->background.index].green;
           png_ptr->background.blue  =
               png_ptr->palette[png_ptr->background.index].blue;
  
  #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
          if (png_ptr->transformations & PNG_INVERT_ALPHA)
          {
             if (!(png_ptr->transformations & PNG_EXPAND_tRNS))
             {
                /* Invert the alpha channel (in tRNS) unless the pixels are
                 * going to be expanded, in which case leave it for later
                 */
                int i, istop = png_ptr->num_trans;
  
                for (i=0; i<istop; i++)
                   png_ptr->trans_alpha[i] = (png_byte)(255 -
                      png_ptr->trans_alpha[i]);
             }
          }
  #endif /* PNG_READ_INVERT_ALPHA_SUPPORTED */
        }
     } /* background expand and (therefore) no alpha association. */
  #endif /* PNG_READ_EXPAND_SUPPORTED && PNG_READ_BACKGROUND_SUPPORTED */
  }
  
  static void /* PRIVATE */
  png_init_rgb_transformations(png_structrp png_ptr)
  {
     /* Added to libpng-1.5.4: check the color type to determine whether there
      * is any alpha or transparency in the image and simply cancel the
      * background and alpha mode stuff if there isn't.
      */
     int input_has_alpha = (png_ptr->color_type & PNG_COLOR_MASK_ALPHA) != 0;
     int input_has_transparency = png_ptr->num_trans > 0;
  
     /* If no alpha we can optimize. */
     if (!input_has_alpha)
     {
        /* Any alpha means background and associative alpha processing is
         * required, however if the alpha is 0 or 1 throughout OPTIIMIZE_ALPHA
         * and ENCODE_ALPHA are irrelevant.
         */
  #     ifdef PNG_READ_ALPHA_MODE_SUPPORTED
           png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
           png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
  #     endif
  
        if (!input_has_transparency)
           png_ptr->transformations &= ~(PNG_COMPOSE | PNG_BACKGROUND_EXPAND);
     }
  
  #if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
     /* png_set_background handling - deals with the complexity of whether the
      * background color is in the file format or the screen format in the case
      * where an 'expand' will happen.
      */
  
     /* The following code cannot be entered in the alpha pre-multiplication case
      * because PNG_BACKGROUND_EXPAND is cancelled below.
      */
     if ((png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
         (png_ptr->transformations & PNG_EXPAND) &&
         !(png_ptr->color_type & PNG_COLOR_MASK_COLOR))
         /* i.e., GRAY or GRAY_ALPHA */
     {
        {
           /* Expand background and tRNS chunks */
           int gray = png_ptr->background.gray;
           int trans_gray = png_ptr->trans_color.gray;
  
           switch (png_ptr->bit_depth)
           {
              case 1:
                 gray *= 0xff;
                 trans_gray *= 0xff;
                 break;
  
              case 2:
                 gray *= 0x55;
                 trans_gray *= 0x55;
                 break;
  
              case 4:
                 gray *= 0x11;
                 trans_gray *= 0x11;
                 break;
  
              default:
  
              case 8:
                 /* FALL THROUGH (Already 8 bits) */
  
              case 16:
                 /* Already a full 16 bits */
                 break;
           }
  
           png_ptr->background.red = png_ptr->background.green =
              png_ptr->background.blue = (png_uint_16)gray;
  
           if (!(png_ptr->transformations & PNG_EXPAND_tRNS))
           {
              png_ptr->trans_color.red = png_ptr->trans_color.green =
                 png_ptr->trans_color.blue = (png_uint_16)trans_gray;
           }
        }
     } /* background expand and (therefore) no alpha association. */
  #endif /* PNG_READ_EXPAND_SUPPORTED && PNG_READ_BACKGROUND_SUPPORTED */
  }
  
  void /* PRIVATE */
  png_init_read_transformations(png_structrp png_ptr)
  {
     png_debug(1, "in png_init_read_transformations");
  
     /* This internal function is called from png_read_start_row in pngrutil.c
      * and it is called before the 'rowbytes' calculation is done, so the code
      * in here can change or update the transformations flags.
      *
      * First do updates that do not depend on the details of the PNG image data
      * being processed.
      */
  
  #ifdef PNG_READ_GAMMA_SUPPORTED
     /* Prior to 1.5.4 these tests were performed from png_set_gamma, 1.5.4 adds
      * png_set_alpha_mode and this is another source for a default file gamma so
      * the test needs to be performed later - here.  In addition prior to 1.5.4
      * the tests were repeated for the PALETTE color type here - this is no
      * longer necessary (and doesn't seem to have been necessary before.)
      */
     {
        /* The following temporary indicates if overall gamma correction is
         * required.
         */
        int gamma_correction = 0;
  
        if (png_ptr->colorspace.gamma != 0) /* has been set */
        {
           if (png_ptr->screen_gamma != 0) /* screen set too */
              gamma_correction = png_gamma_threshold(png_ptr->colorspace.gamma,
                 png_ptr->screen_gamma);
  
           else
              /* Assume the output matches the input; a long time default behavior
               * of libpng, although the standard has nothing to say about this.
               */
              png_ptr->screen_gamma = png_reciprocal(png_ptr->colorspace.gamma);
        }
  
        else if (png_ptr->screen_gamma != 0)
           /* The converse - assume the file matches the screen, note that this
            * perhaps undesireable default can (from 1.5.4) be changed by calling
            * png_set_alpha_mode (even if the alpha handling mode isn't required
            * or isn't changed from the default.)
            */
           png_ptr->colorspace.gamma = png_reciprocal(png_ptr->screen_gamma);
  
        else /* neither are set */
           /* Just in case the following prevents any processing - file and screen
            * are both assumed to be linear and there is no way to introduce a
            * third gamma value other than png_set_background with 'UNIQUE', and,
            * prior to 1.5.4
            */
           png_ptr->screen_gamma = png_ptr->colorspace.gamma = PNG_FP_1;
  
        /* We have a gamma value now. */
        png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;
  
        /* Now turn the gamma transformation on or off as appropriate.  Notice
         * that PNG_GAMMA just refers to the file->screen correction.  Alpha
         * composition may independently cause gamma correction because it needs
         * linear data (e.g. if the file has a gAMA chunk but the screen gamma
         * hasn't been specified.)  In any case this flag may get turned off in
         * the code immediately below if the transform can be handled outside the
         * row loop.
         */
        if (gamma_correction)
           png_ptr->transformations |= PNG_GAMMA;
  
        else
           png_ptr->transformations &= ~PNG_GAMMA;
     }
  #endif
  
     /* Certain transformations have the effect of preventing other
      * transformations that happen afterward in png_do_read_transformations,
      * resolve the interdependencies here.  From the code of
      * png_do_read_transformations the order is:
      *
      *  1) PNG_EXPAND (including PNG_EXPAND_tRNS)
      *  2) PNG_STRIP_ALPHA (if no compose)
      *  3) PNG_RGB_TO_GRAY
      *  4) PNG_GRAY_TO_RGB iff !PNG_BACKGROUND_IS_GRAY
      *  5) PNG_COMPOSE
      *  6) PNG_GAMMA
      *  7) PNG_STRIP_ALPHA (if compose)
      *  8) PNG_ENCODE_ALPHA
      *  9) PNG_SCALE_16_TO_8
      * 10) PNG_16_TO_8
      * 11) PNG_QUANTIZE (converts to palette)
      * 12) PNG_EXPAND_16
      * 13) PNG_GRAY_TO_RGB iff PNG_BACKGROUND_IS_GRAY
      * 14) PNG_INVERT_MONO
      * 15) PNG_SHIFT
      * 16) PNG_PACK
      * 17) PNG_BGR
      * 18) PNG_PACKSWAP
      * 19) PNG_FILLER (includes PNG_ADD_ALPHA)
      * 20) PNG_INVERT_ALPHA
      * 21) PNG_SWAP_ALPHA
      * 22) PNG_SWAP_BYTES
      * 23) PNG_USER_TRANSFORM [must be last]
      */
  #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
     if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
        !(png_ptr->transformations & PNG_COMPOSE))
     {
        /* Stripping the alpha channel happens immediately after the 'expand'
         * transformations, before all other transformation, so it cancels out
         * the alpha handling.  It has the side effect negating the effect of
         * PNG_EXPAND_tRNS too:
         */
        png_ptr->transformations &= ~(PNG_BACKGROUND_EXPAND | PNG_ENCODE_ALPHA |
           PNG_EXPAND_tRNS);
        png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
  
        /* Kill the tRNS chunk itself too.  Prior to 1.5.4 this did not happen
         * so transparency information would remain just so long as it wasn't
         * expanded.  This produces unexpected API changes if the set of things
         * that do PNG_EXPAND_tRNS changes (perfectly possible given the
         * documentation - which says ask for what you want, accept what you
         * get.)  This makes the behavior consistent from 1.5.4:
         */
        png_ptr->num_trans = 0;
     }
  #endif /* STRIP_ALPHA supported, no COMPOSE */
  
  #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
     /* If the screen gamma is about 1.0 then the OPTIMIZE_ALPHA and ENCODE_ALPHA
      * settings will have no effect.
      */
     if (!png_gamma_significant(png_ptr->screen_gamma))
     {
        png_ptr->transformations &= ~PNG_ENCODE_ALPHA;
        png_ptr->flags &= ~PNG_FLAG_OPTIMIZE_ALPHA;
     }
  #endif
  
  #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
     /* Make sure the coefficients for the rgb to gray conversion are set
      * appropriately.
      */
     if (png_ptr->transformations & PNG_RGB_TO_GRAY)
        png_colorspace_set_rgb_coefficients(png_ptr);
  #endif
  
  #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
  #if defined(PNG_READ_EXPAND_SUPPORTED) && defined(PNG_READ_BACKGROUND_SUPPORTED)
     /* Detect gray background and attempt to enable optimization for
      * gray --> RGB case.
      *
      * Note:  if PNG_BACKGROUND_EXPAND is set and color_type is either RGB or
      * RGB_ALPHA (in which case need_expand is superfluous anyway), the
      * background color might actually be gray yet not be flagged as such.
      * This is not a problem for the current code, which uses
      * PNG_BACKGROUND_IS_GRAY only to decide when to do the
      * png_do_gray_to_rgb() transformation.
      *
      * TODO: this code needs to be revised to avoid the complexity and
      * interdependencies.  The color type of the background should be recorded in
      * png_set_background, along with the bit depth, then the code has a record
      * of exactly what color space the background is currently in.
      */
     if (png_ptr->transformations & PNG_BACKGROUND_EXPAND)
     {
        /* PNG_BACKGROUND_EXPAND: the background is in the file color space, so if
         * the file was grayscale the background value is gray.
         */
        if (!(png_ptr->color_type & PNG_COLOR_MASK_COLOR))
           png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
     }
  
     else if (png_ptr->transformations & PNG_COMPOSE)
     {
        /* PNG_COMPOSE: png_set_background was called with need_expand false,
         * so the color is in the color space of the output or png_set_alpha_mode
         * was called and the color is black.  Ignore RGB_TO_GRAY because that
         * happens before GRAY_TO_RGB.
         */
        if (png_ptr->transformations & PNG_GRAY_TO_RGB)
        {
           if (png_ptr->background.red == png_ptr->background.green &&
               png_ptr->background.red == png_ptr->background.blue)
           {
              png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
              png_ptr->background.gray = png_ptr->background.red;
           }
        }
     }
  #endif /* PNG_READ_EXPAND_SUPPORTED && PNG_READ_BACKGROUND_SUPPORTED */
  #endif /* PNG_READ_GRAY_TO_RGB_SUPPORTED */
  
     /* For indexed PNG data (PNG_COLOR_TYPE_PALETTE) many of the transformations
      * can be performed directly on the palette, and some (such as rgb to gray)
      * can be optimized inside the palette.  This is particularly true of the
      * composite (background and alpha) stuff, which can be pretty much all done
      * in the palette even if the result is expanded to RGB or gray afterward.
      *
      * NOTE: this is Not Yet Implemented, the code behaves as in 1.5.1 and
      * earlier and the palette stuff is actually handled on the first row.  This
      * leads to the reported bug that the palette returned by png_get_PLTE is not
      * updated.
      */
     if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
        png_init_palette_transformations(png_ptr);
  
     else
        png_init_rgb_transformations(png_ptr);
  
  #if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
     defined(PNG_READ_EXPAND_16_SUPPORTED)
     if ((png_ptr->transformations & PNG_EXPAND_16) &&
        (png_ptr->transformations & PNG_COMPOSE) &&
        !(png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
        png_ptr->bit_depth != 16)
     {
        /* TODO: fix this.  Because the expand_16 operation is after the compose
         * handling the background color must be 8, not 16, bits deep, but the
         * application will supply a 16-bit value so reduce it here.
         *
         * The PNG_BACKGROUND_EXPAND code above does not expand to 16 bits at
         * present, so that case is ok (until do_expand_16 is moved.)
         *
         * NOTE: this discards the low 16 bits of the user supplied background
         * color, but until expand_16 works properly there is no choice!
         */
  #     define CHOP(x) (x)=((png_uint_16)PNG_DIV257(x))
        CHOP(png_ptr->background.red);
        CHOP(png_ptr->background.green);
        CHOP(png_ptr->background.blue);
        CHOP(png_ptr->background.gray);
  #     undef CHOP
     }
  #endif /* PNG_READ_BACKGROUND_SUPPORTED && PNG_READ_EXPAND_16_SUPPORTED */
  
  #if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
     (defined(PNG_READ_SCALE_16_TO_8_SUPPORTED) || \
     defined(PNG_READ_STRIP_16_TO_8_SUPPORTED))
     if ((png_ptr->transformations & (PNG_16_TO_8|PNG_SCALE_16_TO_8)) &&
        (png_ptr->transformations & PNG_COMPOSE) &&
        !(png_ptr->transformations & PNG_BACKGROUND_EXPAND) &&
        png_ptr->bit_depth == 16)
     {
        /* On the other hand, if a 16-bit file is to be reduced to 8-bits per
         * component this will also happen after PNG_COMPOSE and so the background
         * color must be pre-expanded here.
         *
         * TODO: fix this too.
         */
        png_ptr->background.red = (png_uint_16)(png_ptr->background.red * 257);
        png_ptr->background.green =
           (png_uint_16)(png_ptr->background.green * 257);
        png_ptr->background.blue = (png_uint_16)(png_ptr->background.blue * 257);
        png_ptr->background.gray = (png_uint_16)(png_ptr->background.gray * 257);
     }
  #endif
  
     /* NOTE: below 'PNG_READ_ALPHA_MODE_SUPPORTED' is presumed to also enable the
      * background support (see the comments in scripts/pnglibconf.dfa), this
      * allows pre-multiplication of the alpha channel to be implemented as
      * compositing on black.  This is probably sub-optimal and has been done in
      * 1.5.4 betas simply to enable external critique and testing (i.e. to
      * implement the new API quickly, without lots of internal changes.)
      */
  
  #ifdef PNG_READ_GAMMA_SUPPORTED
  #  ifdef PNG_READ_BACKGROUND_SUPPORTED
        /* Includes ALPHA_MODE */
        png_ptr->background_1 = png_ptr->background;
  #  endif
  
     /* This needs to change - in the palette image case a whole set of tables are
      * built when it would be quicker to just calculate the correct value for
      * each palette entry directly.  Also, the test is too tricky - why check
      * PNG_RGB_TO_GRAY if PNG_GAMMA is not set?  The answer seems to be that
      * PNG_GAMMA is cancelled even if the gamma is known?  The test excludes the
      * PNG_COMPOSE case, so apparently if there is no *overall* gamma correction
      * the gamma tables will not be built even if composition is required on a
      * gamma encoded value.
      *
      * In 1.5.4 this is addressed below by an additional check on the individual
      * file gamma - if it is not 1.0 both RGB_TO_GRAY and COMPOSE need the
      * tables.
      */
     if ((png_ptr->transformations & PNG_GAMMA)
        || ((png_ptr->transformations & PNG_RGB_TO_GRAY)
           && (png_gamma_significant(png_ptr->colorspace.gamma) ||
              png_gamma_significant(png_ptr->screen_gamma)))
        || ((png_ptr->transformations & PNG_COMPOSE)
           && (png_gamma_significant(png_ptr->colorspace.gamma)
              || png_gamma_significant(png_ptr->screen_gamma)
  #  ifdef PNG_READ_BACKGROUND_SUPPORTED
              || (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_UNIQUE
                 && png_gamma_significant(png_ptr->background_gamma))
  #  endif
        )) || ((png_ptr->transformations & PNG_ENCODE_ALPHA)
           && png_gamma_significant(png_ptr->screen_gamma))
        )
     {
        png_build_gamma_table(png_ptr, png_ptr->bit_depth);
  
  #ifdef PNG_READ_BACKGROUND_SUPPORTED
        if (png_ptr->transformations & PNG_COMPOSE)
        {
           /* Issue a warning about this combination: because RGB_TO_GRAY is
            * optimized to do the gamma transform if present yet do_background has
            * to do the same thing if both options are set a
            * double-gamma-correction happens.  This is true in all versions of
            * libpng to date.
            */
           if (png_ptr->transformations & PNG_RGB_TO_GRAY)
              png_warning(png_ptr,
                 "libpng does not support gamma+background+rgb_to_gray");
  
           if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
           {
              /* We don't get to here unless there is a tRNS chunk with non-opaque
               * entries - see the checking code at the start of this function.
               */
              png_color back, back_1;
              png_colorp palette = png_ptr->palette;
              int num_palette = png_ptr->num_palette;
              int i;
              if (png_ptr->background_gamma_type == PNG_BACKGROUND_GAMMA_FILE)
              {
  
                 back.red = png_ptr->gamma_table[png_ptr->background.red];
                 back.green = png_ptr->gamma_table[png_ptr->background.green];
                 back.blue = png_ptr->gamma_table[png_ptr->background.blue];
  
                 back_1.red = png_ptr->gamma_to_1[png_ptr->background.red];
                 back_1.green = png_ptr->gamma_to_1[png_ptr->background.green];
                 back_1.blue = png_ptr->gamma_to_1[png_ptr->background.blue];
              }
              else
              {
                 png_fixed_point g, gs;
  
                 switch (png_ptr->background_gamma_type)
                 {
                    case PNG_BACKGROUND_GAMMA_SCREEN:
                       g = (png_ptr->screen_gamma);
                       gs = PNG_FP_1;
                       break;
  
                    case PNG_BACKGROUND_GAMMA_FILE:
                       g = png_reciprocal(png_ptr->colorspace.gamma);
                       gs = png_reciprocal2(png_ptr->colorspace.gamma,
                          png_ptr->screen_gamma);
                       break;
  
                    case PNG_BACKGROUND_GAMMA_UNIQUE:
                       g = png_reciprocal(png_ptr->background_gamma);
                       gs = png_reciprocal2(png_ptr->background_gamma,
                          png_ptr->screen_gamma);
                       break;
                    default:
                       g = PNG_FP_1;    /* back_1 */
                       gs = PNG_FP_1;   /* back */
                       break;
                 }
  
                 if (png_gamma_significant(gs))
                 {
                    back.red = png_gamma_8bit_correct(png_ptr->background.red,
                        gs);
                    back.green = png_gamma_8bit_correct(png_ptr->background.green,
                        gs);
                    back.blue = png_gamma_8bit_correct(png_ptr->background.blue,
                        gs);
                 }
  
                 else
                 {
                    back.red   = (png_byte)png_ptr->background.red;
                    back.green = (png_byte)png_ptr->background.green;
                    back.blue  = (png_byte)png_ptr->background.blue;
                 }
  
                 if (png_gamma_significant(g))
                 {
                    back_1.red = png_gamma_8bit_correct(png_ptr->background.red,
                       g);
                    back_1.green = png_gamma_8bit_correct(
                       png_ptr->background.green, g);
                    back_1.blue = png_gamma_8bit_correct(png_ptr->background.blue,
                       g);
                 }
  
                 else
                 {
                    back_1.red   = (png_byte)png_ptr->background.red;
                    back_1.green = (png_byte)png_ptr->background.green;
                    back_1.blue  = (png_byte)png_ptr->background.blue;
                 }
              }
  
              for (i = 0; i < num_palette; i++)
              {
                 if (i < (int)png_ptr->num_trans &&
                     png_ptr->trans_alpha[i] != 0xff)
                 {
                    if (png_ptr->trans_alpha[i] == 0)
                    {
                       palette[i] = back;
                    }
                    else /* if (png_ptr->trans_alpha[i] != 0xff) */
                    {
                       png_byte v, w;
  
                       v = png_ptr->gamma_to_1[palette[i].red];
                       png_composite(w, v, png_ptr->trans_alpha[i], back_1.red);
                       palette[i].red = png_ptr->gamma_from_1[w];
  
                       v = png_ptr->gamma_to_1[palette[i].green];
                       png_composite(w, v, png_ptr->trans_alpha[i], back_1.green);
                       palette[i].green = png_ptr->gamma_from_1[w];
  
                       v = png_ptr->gamma_to_1[palette[i].blue];
                       png_composite(w, v, png_ptr->trans_alpha[i], back_1.blue);
                       palette[i].blue = png_ptr->gamma_from_1[w];
                    }
                 }
                 else
                 {
                    palette[i].red = png_ptr->gamma_table[palette[i].red];
                    palette[i].green = png_ptr->gamma_table[palette[i].green];
                    palette[i].blue = png_ptr->gamma_table[palette[i].blue];
                 }
              }
  
              /* Prevent the transformations being done again.
               *
               * NOTE: this is highly dubious; it removes the transformations in
               * place.  This seems inconsistent with the general treatment of the
               * transformations elsewhere.
               */
              png_ptr->transformations &= ~(PNG_COMPOSE | PNG_GAMMA);
           } /* color_type == PNG_COLOR_TYPE_PALETTE */
  
           /* if (png_ptr->background_gamma_type!=PNG_BACKGROUND_GAMMA_UNKNOWN) */
           else /* color_type != PNG_COLOR_TYPE_PALETTE */
           {
              int gs_sig, g_sig;
              png_fixed_point g = PNG_FP_1;  /* Correction to linear */
              png_fixed_point gs = PNG_FP_1; /* Correction to screen */
  
              switch (png_ptr->background_gamma_type)
              {
                 case PNG_BACKGROUND_GAMMA_SCREEN:
                    g = png_ptr->screen_gamma;
                    /* gs = PNG_FP_1; */
                    break;
  
                 case PNG_BACKGROUND_GAMMA_FILE:
                    g = png_reciprocal(png_ptr->colorspace.gamma);
                    gs = png_reciprocal2(png_ptr->colorspace.gamma,
                       png_ptr->screen_gamma);
                    break;
  
                 case PNG_BACKGROUND_GAMMA_UNIQUE:
                    g = png_reciprocal(png_ptr->background_gamma);
                    gs = png_reciprocal2(png_ptr->background_gamma,
                        png_ptr->screen_gamma);
                    break;
  
                 default:
                    png_error(png_ptr, "invalid background gamma type");
              }
  
              g_sig = png_gamma_significant(g);
              gs_sig = png_gamma_significant(gs);
  
              if (g_sig)
                 png_ptr->background_1.gray = png_gamma_correct(png_ptr,
                     png_ptr->background.gray, g);
  
              if (gs_sig)
                 png_ptr->background.gray = png_gamma_correct(png_ptr,
                     png_ptr->background.gray, gs);
  
              if ((png_ptr->background.red != png_ptr->background.green) ||
                  (png_ptr->background.red != png_ptr->background.blue) ||
                  (png_ptr->background.red != png_ptr->background.gray))
              {
                 /* RGB or RGBA with color background */
                 if (g_sig)
                 {
                    png_ptr->background_1.red = png_gamma_correct(png_ptr,
                        png_ptr->background.red, g);
  
                    png_ptr->background_1.green = png_gamma_correct(png_ptr,
                        png_ptr->background.green, g);
  
                    png_ptr->background_1.blue = png_gamma_correct(png_ptr,
                        png_ptr->background.blue, g);
                 }
  
                 if (gs_sig)
                 {
                    png_ptr->background.red = png_gamma_correct(png_ptr,
                        png_ptr->background.red, gs);
  
                    png_ptr->background.green = png_gamma_correct(png_ptr,
                        png_ptr->background.green, gs);
  
                    png_ptr->background.blue = png_gamma_correct(png_ptr,
                        png_ptr->background.blue, gs);
                 }
              }
  
              else
              {
                 /* GRAY, GRAY ALPHA, RGB, or RGBA with gray background */
                 png_ptr->background_1.red = png_ptr->background_1.green
                     = png_ptr->background_1.blue = png_ptr->background_1.gray;
  
                 png_ptr->background.red = png_ptr->background.green
                     = png_ptr->background.blue = png_ptr->background.gray;
              }
  
              /* The background is now in screen gamma: */
              png_ptr->background_gamma_type = PNG_BACKGROUND_GAMMA_SCREEN;
           } /* color_type != PNG_COLOR_TYPE_PALETTE */
        }/* png_ptr->transformations & PNG_BACKGROUND */
  
        else
        /* Transformation does not include PNG_BACKGROUND */
  #endif /* PNG_READ_BACKGROUND_SUPPORTED */
        if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE
  #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
           /* RGB_TO_GRAY needs to have non-gamma-corrected values! */
           && ((png_ptr->transformations & PNG_EXPAND) == 0 ||
           (png_ptr->transformations & PNG_RGB_TO_GRAY) == 0)
  #endif
           )
        {
           png_colorp palette = png_ptr->palette;
           int num_palette = png_ptr->num_palette;
           int i;
  
           /* NOTE: there are other transformations that should probably be in
            * here too.
            */
           for (i = 0; i < num_palette; i++)
           {
              palette[i].red = png_ptr->gamma_table[palette[i].red];
              palette[i].green = png_ptr->gamma_table[palette[i].green];
              palette[i].blue = png_ptr->gamma_table[palette[i].blue];
           }
  
           /* Done the gamma correction. */
           png_ptr->transformations &= ~PNG_GAMMA;
        } /* color_type == PALETTE && !PNG_BACKGROUND transformation */
     }
  #ifdef PNG_READ_BACKGROUND_SUPPORTED
     else
  #endif
  #endif /* PNG_READ_GAMMA_SUPPORTED */
  
  #ifdef PNG_READ_BACKGROUND_SUPPORTED
     /* No GAMMA transformation (see the hanging else 4 lines above) */
     if ((png_ptr->transformations & PNG_COMPOSE) &&
         (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE))
     {
        int i;
        int istop = (int)png_ptr->num_trans;
        png_color back;
        png_colorp palette = png_ptr->palette;
  
        back.red   = (png_byte)png_ptr->background.red;
        back.green = (png_byte)png_ptr->background.green;
        back.blue  = (png_byte)png_ptr->background.blue;
  
        for (i = 0; i < istop; i++)
        {
           if (png_ptr->trans_alpha[i] == 0)
           {
              palette[i] = back;
           }
  
           else if (png_ptr->trans_alpha[i] != 0xff)
           {
              /* The png_composite() macro is defined in png.h */
              png_composite(palette[i].red, palette[i].red,
                  png_ptr->trans_alpha[i], back.red);
  
              png_composite(palette[i].green, palette[i].green,
                  png_ptr->trans_alpha[i], back.green);
  
              png_composite(palette[i].blue, palette[i].blue,
                  png_ptr->trans_alpha[i], back.blue);
           }
        }
  
        png_ptr->transformations &= ~PNG_COMPOSE;
  	  
    	  //png_ptr->flags |= PNG_FLAG_STRIP_ALPHA; /* Add by Sunliang.Liu */
     }
  #endif /* PNG_READ_BACKGROUND_SUPPORTED */
  
  #ifdef PNG_READ_SHIFT_SUPPORTED
     if ((png_ptr->transformations & PNG_SHIFT) &&
        !(png_ptr->transformations & PNG_EXPAND) &&
         (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE))
     {
        int i;
        int istop = png_ptr->num_palette;
        int shift = 8 - png_ptr->sig_bit.red;
  
        png_ptr->transformations &= ~PNG_SHIFT;
  
        /* significant bits can be in the range 1 to 7 for a meaninful result, if
         * the number of significant bits is 0 then no shift is done (this is an
         * error condition which is silently ignored.)
         */
        if (shift > 0 && shift < 8) for (i=0; i<istop; ++i)
        {
           int component = png_ptr->palette[i].red;
  
           component >>= shift;
           png_ptr->palette[i].red = (png_byte)component;
        }
  
        shift = 8 - png_ptr->sig_bit.green;
        if (shift > 0 && shift < 8) for (i=0; i<istop; ++i)
        {
           int component = png_ptr->palette[i].green;
  
           component >>= shift;
           png_ptr->palette[i].green = (png_byte)component;
        }
  
        shift = 8 - png_ptr->sig_bit.blue;
        if (shift > 0 && shift < 8) for (i=0; i<istop; ++i)
        {
           int component = png_ptr->palette[i].blue;
  
           component >>= shift;
           png_ptr->palette[i].blue = (png_byte)component;
        }
     }
  #endif  /* PNG_READ_SHIFT_SUPPORTED */
  }
  
  /* Modify the info structure to reflect the transformations.  The
   * info should be updated so a PNG file could be written with it,
   * assuming the transformations result in valid PNG data.
   */
  void /* PRIVATE */
  png_read_transform_info(png_structrp png_ptr, png_inforp info_ptr)
  {
     png_debug(1, "in png_read_transform_info");
  
  #ifdef PNG_READ_EXPAND_SUPPORTED
     if (png_ptr->transformations & PNG_EXPAND)
     {
        if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
        {
           /* This check must match what actually happens in
            * png_do_expand_palette; if it ever checks the tRNS chunk to see if
            * it is all opaque we must do the same (at present it does not.)
            */
           if (png_ptr->num_trans > 0)
              info_ptr->color_type = PNG_COLOR_TYPE_RGB_ALPHA;
  
           else
              info_ptr->color_type = PNG_COLOR_TYPE_RGB;
  
           info_ptr->bit_depth = 8;
           info_ptr->num_trans = 0;
        }
        else
        {
           if (png_ptr->num_trans)
           {
              if (png_ptr->transformations & PNG_EXPAND_tRNS)
                 info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
           }
           if (info_ptr->bit_depth < 8)
              info_ptr->bit_depth = 8;
  
           info_ptr->num_trans = 0;
        }
     }
  #endif
  
  #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
     defined(PNG_READ_ALPHA_MODE_SUPPORTED)
     /* The following is almost certainly wrong unless the background value is in
      * the screen space!
      */
     if (png_ptr->transformations & PNG_COMPOSE)
        info_ptr->background = png_ptr->background;
  #endif
  
  #ifdef PNG_READ_GAMMA_SUPPORTED
     /* The following used to be conditional on PNG_GAMMA (prior to 1.5.4),
      * however it seems that the code in png_init_read_transformations, which has
      * been called before this from png_read_update_info->png_read_start_row
      * sometimes does the gamma transform and cancels the flag.
      *
      * TODO: this looks wrong; the info_ptr should end up with a gamma equal to
      * the screen_gamma value.  The following probably results in weirdness if
      * the info_ptr is used by the app after the rows have been read.
      */
     info_ptr->colorspace.gamma = png_ptr->colorspace.gamma;
  #endif
  
     if (info_ptr->bit_depth == 16)
     {
  #  ifdef PNG_READ_16BIT_SUPPORTED
  #     ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
           if (png_ptr->transformations & PNG_SCALE_16_TO_8)
              info_ptr->bit_depth = 8;
  #     endif
  
  #     ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
           if (png_ptr->transformations & PNG_16_TO_8)
              info_ptr->bit_depth = 8;
  #     endif
  
  #  else
        /* No 16 bit support: force chopping 16-bit input down to 8, in this case
         * the app program can chose if both APIs are available by setting the
         * correct scaling to use.
         */
  #     ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
           /* For compatibility with previous versions use the strip method by
            * default.  This code works because if PNG_SCALE_16_TO_8 is already
            * set the code below will do that in preference to the chop.
            */
           png_ptr->transformations |= PNG_16_TO_8;
           info_ptr->bit_depth = 8;
  #     else
  
  #        ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
              png_ptr->transformations |= PNG_SCALE_16_TO_8;
              info_ptr->bit_depth = 8;
  #        else
  
              CONFIGURATION ERROR: you must enable at least one 16 to 8 method
  #        endif
  #    endif
  #endif /* !READ_16BIT_SUPPORTED */
     }
  
  #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
     if (png_ptr->transformations & PNG_GRAY_TO_RGB)
        info_ptr->color_type = (png_byte)(info_ptr->color_type |
           PNG_COLOR_MASK_COLOR);
  #endif
  
  #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
     if (png_ptr->transformations & PNG_RGB_TO_GRAY)
        info_ptr->color_type = (png_byte)(info_ptr->color_type &
           ~PNG_COLOR_MASK_COLOR);
  #endif
  
  #ifdef PNG_READ_QUANTIZE_SUPPORTED
     if (png_ptr->transformations & PNG_QUANTIZE)
     {
        if (((info_ptr->color_type == PNG_COLOR_TYPE_RGB) ||
            (info_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA)) &&
            png_ptr->palette_lookup && info_ptr->bit_depth == 8)
        {
           info_ptr->color_type = PNG_COLOR_TYPE_PALETTE;
        }
     }
  #endif
  
  #ifdef PNG_READ_EXPAND_16_SUPPORTED
     if (png_ptr->transformations & PNG_EXPAND_16 && info_ptr->bit_depth == 8 &&
        info_ptr->color_type != PNG_COLOR_TYPE_PALETTE)
     {
        info_ptr->bit_depth = 16;
     }
  #endif
  
  #ifdef PNG_READ_PACK_SUPPORTED
     if ((png_ptr->transformations & PNG_PACK) && (info_ptr->bit_depth < 8))
        info_ptr->bit_depth = 8;
  #endif
  
     if (info_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
        info_ptr->channels = 1;
  
     else if (info_ptr->color_type & PNG_COLOR_MASK_COLOR)
        info_ptr->channels = 3;
  
     else
        info_ptr->channels = 1;
  
  #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
     if (png_ptr->transformations & PNG_STRIP_ALPHA)
     {
        info_ptr->color_type = (png_byte)(info_ptr->color_type &
           ~PNG_COLOR_MASK_ALPHA);
        info_ptr->num_trans = 0;
     }
  #endif
  
     if (info_ptr->color_type & PNG_COLOR_MASK_ALPHA)
        info_ptr->channels++;
  
  #ifdef PNG_READ_FILLER_SUPPORTED
     /* STRIP_ALPHA and FILLER allowed:  MASK_ALPHA bit stripped above */
     if ((png_ptr->transformations & PNG_FILLER) &&
         ((info_ptr->color_type == PNG_COLOR_TYPE_RGB) ||
         (info_ptr->color_type == PNG_COLOR_TYPE_GRAY)))
     {
        info_ptr->channels++;
        /* If adding a true alpha channel not just filler */
        if (png_ptr->transformations & PNG_ADD_ALPHA)
           info_ptr->color_type |= PNG_COLOR_MASK_ALPHA;
     }
  #endif
  
  #if defined(PNG_USER_TRANSFORM_PTR_SUPPORTED) && \
  defined(PNG_READ_USER_TRANSFORM_SUPPORTED)
     if (png_ptr->transformations & PNG_USER_TRANSFORM)
     {
        if (info_ptr->bit_depth < png_ptr->user_transform_depth)
           info_ptr->bit_depth = png_ptr->user_transform_depth;
  
        if (info_ptr->channels < png_ptr->user_transform_channels)
           info_ptr->channels = png_ptr->user_transform_channels;
     }
  #endif
  
     info_ptr->pixel_depth = (png_byte)(info_ptr->channels *
         info_ptr->bit_depth);
  
     info_ptr->rowbytes = PNG_ROWBYTES(info_ptr->pixel_depth, info_ptr->width);
  
     /* Adding in 1.5.4: cache the above value in png_struct so that we can later
      * check in png_rowbytes that the user buffer won't get overwritten.  Note
      * that the field is not always set - if png_read_update_info isn't called
      * the application has to either not do any transforms or get the calculation
      * right itself.
      */
     png_ptr->info_rowbytes = info_ptr->rowbytes;
  
  #ifndef PNG_READ_EXPAND_SUPPORTED
     if (png_ptr)
        return;
  #endif
  }
  
  /* Transform the row.  The order of transformations is significant,
   * and is very touchy.  If you add a transformation, take care to
   * decide how it fits in with the other transformations here.
   */
  void /* PRIVATE */
  png_do_read_transformations(png_structrp png_ptr, png_row_infop row_info)
  {
     png_debug(1, "in png_do_read_transformations");
  
     if (png_ptr->row_buf == NULL)
     {
        /* Prior to 1.5.4 this output row/pass where the NULL pointer is, but this
         * error is incredibly rare and incredibly easy to debug without this
         * information.
         */
        png_error(png_ptr, "NULL row buffer");
     }
  
     /* The following is debugging; prior to 1.5.4 the code was never compiled in;
      * in 1.5.4 PNG_FLAG_DETECT_UNINITIALIZED was added and the macro
      * PNG_WARN_UNINITIALIZED_ROW removed.  In 1.6 the new flag is set only for
      * all transformations, however in practice the ROW_INIT always gets done on
      * demand, if necessary.
      */
     if ((png_ptr->flags & PNG_FLAG_DETECT_UNINITIALIZED) != 0 &&
        !(png_ptr->flags & PNG_FLAG_ROW_INIT))
     {
        /* Application has failed to call either png_read_start_image() or
         * png_read_update_info() after setting transforms that expand pixels.
         * This check added to libpng-1.2.19 (but not enabled until 1.5.4).
         */
        png_error(png_ptr, "Uninitialized row");
     }
  
  #ifdef PNG_READ_EXPAND_SUPPORTED
     if (png_ptr->transformations & PNG_EXPAND)
     {
        if (row_info->color_type == PNG_COLOR_TYPE_PALETTE)
        {
           png_do_expand_palette(row_info, png_ptr->row_buf + 1,
               png_ptr->palette, png_ptr->trans_alpha, png_ptr->num_trans);
        }
  
        else
        {
           if (png_ptr->num_trans &&
               (png_ptr->transformations & PNG_EXPAND_tRNS))
              png_do_expand(row_info, png_ptr->row_buf + 1,
                  &(png_ptr->trans_color));
  
           else
              png_do_expand(row_info, png_ptr->row_buf + 1,
                  NULL);
        }
     }
  #endif
  
  #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
     if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
        !(png_ptr->transformations & PNG_COMPOSE) &&
        (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
        row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA))
        png_do_strip_channel(row_info, png_ptr->row_buf + 1,
           0 /* at_start == false, because SWAP_ALPHA happens later */);
  #endif
  
  #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
     if (png_ptr->transformations & PNG_RGB_TO_GRAY)
     {
        int rgb_error =
            png_do_rgb_to_gray(png_ptr, row_info,
                png_ptr->row_buf + 1);
  
        if (rgb_error)
        {
           png_ptr->rgb_to_gray_status=1;
           if ((png_ptr->transformations & PNG_RGB_TO_GRAY) ==
               PNG_RGB_TO_GRAY_WARN)
              png_warning(png_ptr, "png_do_rgb_to_gray found nongray pixel");
  
           if ((png_ptr->transformations & PNG_RGB_TO_GRAY) ==
               PNG_RGB_TO_GRAY_ERR)
              png_error(png_ptr, "png_do_rgb_to_gray found nongray pixel");
        }
     }
  #endif
  
  /* From Andreas Dilger e-mail to png-implement, 26 March 1998:
   *
   *   In most cases, the "simple transparency" should be done prior to doing
   *   gray-to-RGB, or you will have to test 3x as many bytes to check if a
   *   pixel is transparent.  You would also need to make sure that the
   *   transparency information is upgraded to RGB.
   *
   *   To summarize, the current flow is:
   *   - Gray + simple transparency -> compare 1 or 2 gray bytes and composite
   *                                   with background "in place" if transparent,
   *                                   convert to RGB if necessary
   *   - Gray + alpha -> composite with gray background and remove alpha bytes,
   *                                   convert to RGB if necessary
   *
   *   To support RGB backgrounds for gray images we need:
   *   - Gray + simple transparency -> convert to RGB + simple transparency,
   *                                   compare 3 or 6 bytes and composite with
   *                                   background "in place" if transparent
   *                                   (3x compare/pixel compared to doing
   *                                   composite with gray bkgrnd)
   *   - Gray + alpha -> convert to RGB + alpha, composite with background and
   *                                   remove alpha bytes (3x float
   *                                   operations/pixel compared with composite
   *                                   on gray background)
   *
   *  Greg's change will do this.  The reason it wasn't done before is for
   *  performance, as this increases the per-pixel operations.  If we would check
   *  in advance if the background was gray or RGB, and position the gray-to-RGB
   *  transform appropriately, then it would save a lot of work/time.
   */
  
  #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
     /* If gray -> RGB, do so now only if background is non-gray; else do later
      * for performance reasons
      */
     if ((png_ptr->transformations & PNG_GRAY_TO_RGB) &&
         !(png_ptr->mode & PNG_BACKGROUND_IS_GRAY))
        png_do_gray_to_rgb(row_info, png_ptr->row_buf + 1);
  #endif
  
  #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
     defined(PNG_READ_ALPHA_MODE_SUPPORTED)
     if (png_ptr->transformations & PNG_COMPOSE)
        png_do_compose(row_info, png_ptr->row_buf + 1, png_ptr);
  #endif
  
  #ifdef PNG_READ_GAMMA_SUPPORTED
     if ((png_ptr->transformations & PNG_GAMMA) &&
  #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
        /* Because RGB_TO_GRAY does the gamma transform. */
        !(png_ptr->transformations & PNG_RGB_TO_GRAY) &&
  #endif
  #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
     defined(PNG_READ_ALPHA_MODE_SUPPORTED)
        /* Because PNG_COMPOSE does the gamma transform if there is something to
         * do (if there is an alpha channel or transparency.)
         */
         !((png_ptr->transformations & PNG_COMPOSE) &&
         ((png_ptr->num_trans != 0) ||
         (png_ptr->color_type & PNG_COLOR_MASK_ALPHA))) &&
  #endif
        /* Because png_init_read_transformations transforms the palette, unless
         * RGB_TO_GRAY will do the transform.
         */
         (png_ptr->color_type != PNG_COLOR_TYPE_PALETTE))
        png_do_gamma(row_info, png_ptr->row_buf + 1, png_ptr);
  #endif
  
  #ifdef PNG_READ_STRIP_ALPHA_SUPPORTED
     if ((png_ptr->transformations & PNG_STRIP_ALPHA) &&
        (png_ptr->transformations & PNG_COMPOSE) &&
        (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
        row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA))
        png_do_strip_channel(row_info, png_ptr->row_buf + 1,
           0 /* at_start == false, because SWAP_ALPHA happens later */);
  #endif
  
  #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
     if ((png_ptr->transformations & PNG_ENCODE_ALPHA) &&
        (row_info->color_type & PNG_COLOR_MASK_ALPHA))
        png_do_encode_alpha(row_info, png_ptr->row_buf + 1, png_ptr);
  #endif
  
  #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
     if (png_ptr->transformations & PNG_SCALE_16_TO_8)
        png_do_scale_16_to_8(row_info, png_ptr->row_buf + 1);
  #endif
  
  #ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
     /* There is no harm in doing both of these because only one has any effect,
      * by putting the 'scale' option first if the app asks for scale (either by
      * calling the API or in a TRANSFORM flag) this is what happens.
      */
     if (png_ptr->transformations & PNG_16_TO_8)
        png_do_chop(row_info, png_ptr->row_buf + 1);
  #endif
  
  #ifdef PNG_READ_QUANTIZE_SUPPORTED
     if (png_ptr->transformations & PNG_QUANTIZE)
     {
        png_do_quantize(row_info, png_ptr->row_buf + 1,
            png_ptr->palette_lookup, png_ptr->quantize_index);
  
        if (row_info->rowbytes == 0)
           png_error(png_ptr, "png_do_quantize returned rowbytes=0");
     }
  #endif /* PNG_READ_QUANTIZE_SUPPORTED */
  
  #ifdef PNG_READ_EXPAND_16_SUPPORTED
     /* Do the expansion now, after all the arithmetic has been done.  Notice
      * that previous transformations can handle the PNG_EXPAND_16 flag if this
      * is efficient (particularly true in the case of gamma correction, where
      * better accuracy results faster!)
      */
     if (png_ptr->transformations & PNG_EXPAND_16)
        png_do_expand_16(row_info, png_ptr->row_buf + 1);
  #endif
  
  #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
     /* NOTE: moved here in 1.5.4 (from much later in this list.) */
     if ((png_ptr->transformations & PNG_GRAY_TO_RGB) &&
         (png_ptr->mode & PNG_BACKGROUND_IS_GRAY))
        png_do_gray_to_rgb(row_info, png_ptr->row_buf + 1);
  #endif
  
  #ifdef PNG_READ_INVERT_SUPPORTED
     if (png_ptr->transformations & PNG_INVERT_MONO)
        png_do_invert(row_info, png_ptr->row_buf + 1);
  #endif
  
  #ifdef PNG_READ_SHIFT_SUPPORTED
     if (png_ptr->transformations & PNG_SHIFT)
        png_do_unshift(row_info, png_ptr->row_buf + 1,
            &(png_ptr->shift));
  #endif
  
  #ifdef PNG_READ_PACK_SUPPORTED
     if (png_ptr->transformations & PNG_PACK)
        png_do_unpack(row_info, png_ptr->row_buf + 1);
  #endif
  
  #ifdef PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED
     /* Added at libpng-1.5.10 */
     if (row_info->color_type == PNG_COLOR_TYPE_PALETTE &&
         png_ptr->num_palette_max >= 0)
        png_do_check_palette_indexes(png_ptr, row_info);
  #endif
  
  #ifdef PNG_READ_BGR_SUPPORTED
     if (png_ptr->transformations & PNG_BGR)
        png_do_bgr(row_info, png_ptr->row_buf + 1);
  #endif
  
  #ifdef PNG_READ_PACKSWAP_SUPPORTED
     if (png_ptr->transformations & PNG_PACKSWAP)
        png_do_packswap(row_info, png_ptr->row_buf + 1);
  #endif
  
  #ifdef PNG_READ_FILLER_SUPPORTED
     if (png_ptr->transformations & PNG_FILLER)
        png_do_read_filler(row_info, png_ptr->row_buf + 1,
            (png_uint_32)png_ptr->filler, png_ptr->flags);
  #endif
  
  #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
     if (png_ptr->transformations & PNG_INVERT_ALPHA)
        png_do_read_invert_alpha(row_info, png_ptr->row_buf + 1);
  #endif
  
  #ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
     if (png_ptr->transformations & PNG_SWAP_ALPHA)
        png_do_read_swap_alpha(row_info, png_ptr->row_buf + 1);
  #endif
  
  #ifdef PNG_READ_16BIT_SUPPORTED
  #ifdef PNG_READ_SWAP_SUPPORTED
     if (png_ptr->transformations & PNG_SWAP_BYTES)
        png_do_swap(row_info, png_ptr->row_buf + 1);
  #endif
  #endif
  
  #ifdef PNG_READ_USER_TRANSFORM_SUPPORTED
     if (png_ptr->transformations & PNG_USER_TRANSFORM)
      {
        if (png_ptr->read_user_transform_fn != NULL)
           (*(png_ptr->read_user_transform_fn)) /* User read transform function */
               (png_ptr,     /* png_ptr */
               row_info,     /* row_info: */
                  /*  png_uint_32 width;       width of row */
                  /*  png_size_t rowbytes;     number of bytes in row */
                  /*  png_byte color_type;     color type of pixels */
                  /*  png_byte bit_depth;      bit depth of samples */
                  /*  png_byte channels;       number of channels (1-4) */
                  /*  png_byte pixel_depth;    bits per pixel (depth*channels) */
               png_ptr->row_buf + 1);    /* start of pixel data for row */
  #ifdef PNG_USER_TRANSFORM_PTR_SUPPORTED
        if (png_ptr->user_transform_depth)
           row_info->bit_depth = png_ptr->user_transform_depth;
  
        if (png_ptr->user_transform_channels)
           row_info->channels = png_ptr->user_transform_channels;
  #endif
        row_info->pixel_depth = (png_byte)(row_info->bit_depth *
            row_info->channels);
  
        row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_info->width);
     }
  #endif
  }
  
  #ifdef PNG_READ_PACK_SUPPORTED
  /* Unpack pixels of 1, 2, or 4 bits per pixel into 1 byte per pixel,
   * without changing the actual values.  Thus, if you had a row with
   * a bit depth of 1, you would end up with bytes that only contained
   * the numbers 0 or 1.  If you would rather they contain 0 and 255, use
   * png_do_shift() after this.
   */
  void /* PRIVATE */
  png_do_unpack(png_row_infop row_info, png_bytep row)
  {
     png_debug(1, "in png_do_unpack");
  
     if (row_info->bit_depth < 8)
     {
        png_uint_32 i;
        png_uint_32 row_width=row_info->width;
  
        switch (row_info->bit_depth)
        {
           case 1:
           {
              png_bytep sp = row + (png_size_t)((row_width - 1) >> 3);
              png_bytep dp = row + (png_size_t)row_width - 1;
              png_uint_32 shift = 7 - (int)((row_width + 7) & 0x07);
              for (i = 0; i < row_width; i++)
              {
                 *dp = (png_byte)((*sp >> shift) & 0x01);
  
                 if (shift == 7)
                 {
                    shift = 0;
                    sp--;
                 }
  
                 else
                    shift++;
  
                 dp--;
              }
              break;
           }
  
           case 2:
           {
  
              png_bytep sp = row + (png_size_t)((row_width - 1) >> 2);
              png_bytep dp = row + (png_size_t)row_width - 1;
              png_uint_32 shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
              for (i = 0; i < row_width; i++)
              {
                 *dp = (png_byte)((*sp >> shift) & 0x03);
  
                 if (shift == 6)
                 {
                    shift = 0;
                    sp--;
                 }
  
                 else
                    shift += 2;
  
                 dp--;
              }
              break;
           }
  
           case 4:
           {
              png_bytep sp = row + (png_size_t)((row_width - 1) >> 1);
              png_bytep dp = row + (png_size_t)row_width - 1;
              png_uint_32 shift = (int)((1 - ((row_width + 1) & 0x01)) << 2);
              for (i = 0; i < row_width; i++)
              {
                 *dp = (png_byte)((*sp >> shift) & 0x0f);
  
                 if (shift == 4)
                 {
                    shift = 0;
                    sp--;
                 }
  
                 else
                    shift = 4;
  
                 dp--;
              }
              break;
           }
  
           default:
              break;
        }
        row_info->bit_depth = 8;
        row_info->pixel_depth = (png_byte)(8 * row_info->channels);
        row_info->rowbytes = row_width * row_info->channels;
     }
  }
  #endif
  
  #ifdef PNG_READ_SHIFT_SUPPORTED
  /* Reverse the effects of png_do_shift.  This routine merely shifts the
   * pixels back to their significant bits values.  Thus, if you have
   * a row of bit depth 8, but only 5 are significant, this will shift
   * the values back to 0 through 31.
   */
  void /* PRIVATE */
  png_do_unshift(png_row_infop row_info, png_bytep row,
      png_const_color_8p sig_bits)
  {
     int color_type;
  
     png_debug(1, "in png_do_unshift");
  
     /* The palette case has already been handled in the _init routine. */
     color_type = row_info->color_type;
  
     if (color_type != PNG_COLOR_TYPE_PALETTE)
     {
        int shift[4];
        int channels = 0;
        int bit_depth = row_info->bit_depth;
  
        if (color_type & PNG_COLOR_MASK_COLOR)
        {
           shift[channels++] = bit_depth - sig_bits->red;
           shift[channels++] = bit_depth - sig_bits->green;
           shift[channels++] = bit_depth - sig_bits->blue;
        }
  
        else
        {
           shift[channels++] = bit_depth - sig_bits->gray;
        }
  
        if (color_type & PNG_COLOR_MASK_ALPHA)
        {
           shift[channels++] = bit_depth - sig_bits->alpha;
        }
  
        {
           int c, have_shift;
  
           for (c = have_shift = 0; c < channels; ++c)
           {
              /* A shift of more than the bit depth is an error condition but it
               * gets ignored here.
               */
              if (shift[c] <= 0 || shift[c] >= bit_depth)
                 shift[c] = 0;
  
              else
                 have_shift = 1;
           }
  
           if (!have_shift)
              return;
        }
  
        switch (bit_depth)
        {
           default:
           /* Must be 1bpp gray: should not be here! */
              /* NOTREACHED */
              break;
  
           case 2:
           /* Must be 2bpp gray */
           /* assert(channels == 1 && shift[0] == 1) */
           {
              png_bytep bp = row;
              png_bytep bp_end = bp + row_info->rowbytes;
  
              while (bp < bp_end)
              {
                 int b = (*bp >> 1) & 0x55;
                 *bp++ = (png_byte)b;
              }
              break;
           }
  
           case 4:
           /* Must be 4bpp gray */
           /* assert(channels == 1) */
           {
              png_bytep bp = row;
              png_bytep bp_end = bp + row_info->rowbytes;
              int gray_shift = shift[0];
              int mask =  0xf >> gray_shift;
  
              mask |= mask << 4;
  
              while (bp < bp_end)
              {
                 int b = (*bp >> gray_shift) & mask;
                 *bp++ = (png_byte)b;
              }
              break;
           }
  
           case 8:
           /* Single byte components, G, GA, RGB, RGBA */
           {
              png_bytep bp = row;
              png_bytep bp_end = bp + row_info->rowbytes;
              int channel = 0;
  
              while (bp < bp_end)
              {
                 int b = *bp >> shift[channel];
                 if (++channel >= channels)
                    channel = 0;
                 *bp++ = (png_byte)b;
              }
              break;
           }
  
  #ifdef PNG_READ_16BIT_SUPPORTED
           case 16:
           /* Double byte components, G, GA, RGB, RGBA */
           {
              png_bytep bp = row;
              png_bytep bp_end = bp + row_info->rowbytes;
              int channel = 0;
  
              while (bp < bp_end)
              {
                 int value = (bp[0] << 8) + bp[1];
  
                 value >>= shift[channel];
                 if (++channel >= channels)
                    channel = 0;
                 *bp++ = (png_byte)(value >> 8);
                 *bp++ = (png_byte)(value & 0xff);
              }
              break;
           }
  #endif
        }
     }
  }
  #endif
  
  #ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
  /* Scale rows of bit depth 16 down to 8 accurately */
  void /* PRIVATE */
  png_do_scale_16_to_8(png_row_infop row_info, png_bytep row)
  {
     png_debug(1, "in png_do_scale_16_to_8");
  
     if (row_info->bit_depth == 16)
     {
        png_bytep sp = row; /* source */
        png_bytep dp = row; /* destination */
        png_bytep ep = sp + row_info->rowbytes; /* end+1 */
  
        while (sp < ep)
        {
           /* The input is an array of 16 bit components, these must be scaled to
            * 8 bits each.  For a 16 bit value V the required value (from the PNG
            * specification) is:
            *
            *    (V * 255) / 65535
            *
            * This reduces to round(V / 257), or floor((V + 128.5)/257)
            *
            * Represent V as the two byte value vhi.vlo.  Make a guess that the
            * result is the top byte of V, vhi, then the correction to this value
            * is:
            *
            *    error = floor(((V-vhi.vhi) + 128.5) / 257)
            *          = floor(((vlo-vhi) + 128.5) / 257)
            *
            * This can be approximated using integer arithmetic (and a signed
            * shift):
            *
            *    error = (vlo-vhi+128) >> 8;
            *
            * The approximate differs from the exact answer only when (vlo-vhi) is
            * 128; it then gives a correction of +1 when the exact correction is
            * 0.  This gives 128 errors.  The exact answer (correct for all 16 bit
            * input values) is:
            *
            *    error = (vlo-vhi+128)*65535 >> 24;
            *
            * An alternative arithmetic calculation which also gives no errors is:
            *
            *    (V * 255 + 32895) >> 16
            */
  
           png_int_32 tmp = *sp++; /* must be signed! */
           tmp += (((int)*sp++ - tmp + 128) * 65535) >> 24;
           *dp++ = (png_byte)tmp;
        }
  
        row_info->bit_depth = 8;
        row_info->pixel_depth = (png_byte)(8 * row_info->channels);
        row_info->rowbytes = row_info->width * row_info->channels;
     }
  }
  #endif
  
  #ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
  void /* PRIVATE */
  /* Simply discard the low byte.  This was the default behavior prior
   * to libpng-1.5.4.
   */
  png_do_chop(png_row_infop row_info, png_bytep row)
  {
     png_debug(1, "in png_do_chop");
  
     if (row_info->bit_depth == 16)
     {
        png_bytep sp = row; /* source */
        png_bytep dp = row; /* destination */
        png_bytep ep = sp + row_info->rowbytes; /* end+1 */
  
        while (sp < ep)
        {
           *dp++ = *sp;
           sp += 2; /* skip low byte */
        }
  
        row_info->bit_depth = 8;
        row_info->pixel_depth = (png_byte)(8 * row_info->channels);
        row_info->rowbytes = row_info->width * row_info->channels;
     }
  }
  #endif
  
  #ifdef PNG_READ_SWAP_ALPHA_SUPPORTED
  void /* PRIVATE */
  png_do_read_swap_alpha(png_row_infop row_info, png_bytep row)
  {
     png_debug(1, "in png_do_read_swap_alpha");
  
     {
        png_uint_32 row_width = row_info->width;
        if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
        {
           /* This converts from RGBA to ARGB */
           if (row_info->bit_depth == 8)
           {
              png_bytep sp = row + row_info->rowbytes;
              png_bytep dp = sp;
              png_byte save;
              png_uint_32 i;
  
              for (i = 0; i < row_width; i++)
              {
                 save = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = save;
              }
           }
  
  #ifdef PNG_READ_16BIT_SUPPORTED
           /* This converts from RRGGBBAA to AARRGGBB */
           else
           {
              png_bytep sp = row + row_info->rowbytes;
              png_bytep dp = sp;
              png_byte save[2];
              png_uint_32 i;
  
              for (i = 0; i < row_width; i++)
              {
                 save[0] = *(--sp);
                 save[1] = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = save[0];
                 *(--dp) = save[1];
              }
           }
  #endif
        }
  
        else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
        {
           /* This converts from GA to AG */
           if (row_info->bit_depth == 8)
           {
              png_bytep sp = row + row_info->rowbytes;
              png_bytep dp = sp;
              png_byte save;
              png_uint_32 i;
  
              for (i = 0; i < row_width; i++)
              {
                 save = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = save;
              }
           }
  
  #ifdef PNG_READ_16BIT_SUPPORTED
           /* This converts from GGAA to AAGG */
           else
           {
              png_bytep sp = row + row_info->rowbytes;
              png_bytep dp = sp;
              png_byte save[2];
              png_uint_32 i;
  
              for (i = 0; i < row_width; i++)
              {
                 save[0] = *(--sp);
                 save[1] = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = save[0];
                 *(--dp) = save[1];
              }
           }
  #endif
        }
     }
  }
  #endif
  
  #ifdef PNG_READ_INVERT_ALPHA_SUPPORTED
  void /* PRIVATE */
  png_do_read_invert_alpha(png_row_infop row_info, png_bytep row)
  {
     png_uint_32 row_width;
     png_debug(1, "in png_do_read_invert_alpha");
  
     row_width = row_info->width;
     if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
     {
        if (row_info->bit_depth == 8)
        {
           /* This inverts the alpha channel in RGBA */
           png_bytep sp = row + row_info->rowbytes;
           png_bytep dp = sp;
           png_uint_32 i;
  
           for (i = 0; i < row_width; i++)
           {
              *(--dp) = (png_byte)(255 - *(--sp));
  
  /*          This does nothing:
              *(--dp) = *(--sp);
              *(--dp) = *(--sp);
              *(--dp) = *(--sp);
              We can replace it with:
  */
              sp-=3;
              dp=sp;
           }
        }
  
  #ifdef PNG_READ_16BIT_SUPPORTED
        /* This inverts the alpha channel in RRGGBBAA */
        else
        {
           png_bytep sp = row + row_info->rowbytes;
           png_bytep dp = sp;
           png_uint_32 i;
  
           for (i = 0; i < row_width; i++)
           {
              *(--dp) = (png_byte)(255 - *(--sp));
              *(--dp) = (png_byte)(255 - *(--sp));
  
  /*          This does nothing:
              *(--dp) = *(--sp);
              *(--dp) = *(--sp);
              *(--dp) = *(--sp);
              *(--dp) = *(--sp);
              *(--dp) = *(--sp);
              *(--dp) = *(--sp);
              We can replace it with:
  */
              sp-=6;
              dp=sp;
           }
        }
  #endif
     }
     else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
     {
        if (row_info->bit_depth == 8)
        {
           /* This inverts the alpha channel in GA */
           png_bytep sp = row + row_info->rowbytes;
           png_bytep dp = sp;
           png_uint_32 i;
  
           for (i = 0; i < row_width; i++)
           {
              *(--dp) = (png_byte)(255 - *(--sp));
              *(--dp) = *(--sp);
           }
        }
  
  #ifdef PNG_READ_16BIT_SUPPORTED
        else
        {
           /* This inverts the alpha channel in GGAA */
           png_bytep sp  = row + row_info->rowbytes;
           png_bytep dp = sp;
           png_uint_32 i;
  
           for (i = 0; i < row_width; i++)
           {
              *(--dp) = (png_byte)(255 - *(--sp));
              *(--dp) = (png_byte)(255 - *(--sp));
  /*
              *(--dp) = *(--sp);
              *(--dp) = *(--sp);
  */
              sp-=2;
              dp=sp;
           }
        }
  #endif
     }
  }
  #endif
  
  #ifdef PNG_READ_FILLER_SUPPORTED
  /* Add filler channel if we have RGB color */
  void /* PRIVATE */
  png_do_read_filler(png_row_infop row_info, png_bytep row,
      png_uint_32 filler, png_uint_32 flags)
  {
     png_uint_32 i;
     png_uint_32 row_width = row_info->width;
  
  #ifdef PNG_READ_16BIT_SUPPORTED
     png_byte hi_filler = (png_byte)((filler>>8) & 0xff);
  #endif
     png_byte lo_filler = (png_byte)(filler & 0xff);
  
     png_debug(1, "in png_do_read_filler");
  
     if (
         row_info->color_type == PNG_COLOR_TYPE_GRAY)
     {
        if (row_info->bit_depth == 8)
        {
           if (flags & PNG_FLAG_FILLER_AFTER)
           {
              /* This changes the data from G to GX */
              png_bytep sp = row + (png_size_t)row_width;
              png_bytep dp =  sp + (png_size_t)row_width;
              for (i = 1; i < row_width; i++)
              {
                 *(--dp) = lo_filler;
                 *(--dp) = *(--sp);
              }
              *(--dp) = lo_filler;
              row_info->channels = 2;
              row_info->pixel_depth = 16;
              row_info->rowbytes = row_width * 2;
           }
  
           else
           {
              /* This changes the data from G to XG */
              png_bytep sp = row + (png_size_t)row_width;
              png_bytep dp = sp  + (png_size_t)row_width;
              for (i = 0; i < row_width; i++)
              {
                 *(--dp) = *(--sp);
                 *(--dp) = lo_filler;
              }
              row_info->channels = 2;
              row_info->pixel_depth = 16;
              row_info->rowbytes = row_width * 2;
           }
        }
  
  #ifdef PNG_READ_16BIT_SUPPORTED
        else if (row_info->bit_depth == 16)
        {
           if (flags & PNG_FLAG_FILLER_AFTER)
           {
              /* This changes the data from GG to GGXX */
              png_bytep sp = row + (png_size_t)row_width * 2;
              png_bytep dp = sp  + (png_size_t)row_width * 2;
              for (i = 1; i < row_width; i++)
              {
                 *(--dp) = hi_filler;
                 *(--dp) = lo_filler;
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
              }
              *(--dp) = hi_filler;
              *(--dp) = lo_filler;
              row_info->channels = 2;
              row_info->pixel_depth = 32;
              row_info->rowbytes = row_width * 4;
           }
  
           else
           {
              /* This changes the data from GG to XXGG */
              png_bytep sp = row + (png_size_t)row_width * 2;
              png_bytep dp = sp  + (png_size_t)row_width * 2;
              for (i = 0; i < row_width; i++)
              {
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = hi_filler;
                 *(--dp) = lo_filler;
              }
              row_info->channels = 2;
              row_info->pixel_depth = 32;
              row_info->rowbytes = row_width * 4;
           }
        }
  #endif
     } /* COLOR_TYPE == GRAY */
     else if (row_info->color_type == PNG_COLOR_TYPE_RGB)
     {
        if (row_info->bit_depth == 8)
        {
           if (flags & PNG_FLAG_FILLER_AFTER)
           {
              /* This changes the data from RGB to RGBX */
              png_bytep sp = row + (png_size_t)row_width * 3;
              png_bytep dp = sp  + (png_size_t)row_width;
              for (i = 1; i < row_width; i++)
              {
                 *(--dp) = lo_filler;
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
              }
              *(--dp) = lo_filler;
              row_info->channels = 4;
              row_info->pixel_depth = 32;
              row_info->rowbytes = row_width * 4;
           }
  
           else
           {
              /* This changes the data from RGB to XRGB */
              png_bytep sp = row + (png_size_t)row_width * 3;
              png_bytep dp = sp + (png_size_t)row_width;
              for (i = 0; i < row_width; i++)
              {
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = lo_filler;
              }
              row_info->channels = 4;
              row_info->pixel_depth = 32;
              row_info->rowbytes = row_width * 4;
           }
        }
  
  #ifdef PNG_READ_16BIT_SUPPORTED
        else if (row_info->bit_depth == 16)
        {
           if (flags & PNG_FLAG_FILLER_AFTER)
           {
              /* This changes the data from RRGGBB to RRGGBBXX */
              png_bytep sp = row + (png_size_t)row_width * 6;
              png_bytep dp = sp  + (png_size_t)row_width * 2;
              for (i = 1; i < row_width; i++)
              {
                 *(--dp) = hi_filler;
                 *(--dp) = lo_filler;
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
              }
              *(--dp) = hi_filler;
              *(--dp) = lo_filler;
              row_info->channels = 4;
              row_info->pixel_depth = 64;
              row_info->rowbytes = row_width * 8;
           }
  
           else
           {
              /* This changes the data from RRGGBB to XXRRGGBB */
              png_bytep sp = row + (png_size_t)row_width * 6;
              png_bytep dp = sp  + (png_size_t)row_width * 2;
              for (i = 0; i < row_width; i++)
              {
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = *(--sp);
                 *(--dp) = hi_filler;
                 *(--dp) = lo_filler;
              }
  
              row_info->channels = 4;
              row_info->pixel_depth = 64;
              row_info->rowbytes = row_width * 8;
           }
        }
  #endif
     } /* COLOR_TYPE == RGB */
  }
  #endif
  
  #ifdef PNG_READ_GRAY_TO_RGB_SUPPORTED
  /* Expand grayscale files to RGB, with or without alpha */
  void /* PRIVATE */
  png_do_gray_to_rgb(png_row_infop row_info, png_bytep row)
  {
     png_uint_32 i;
     png_uint_32 row_width = row_info->width;
  
     png_debug(1, "in png_do_gray_to_rgb");
  
     if (row_info->bit_depth >= 8 &&
         !(row_info->color_type & PNG_COLOR_MASK_COLOR))
     {
        if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
        {
           if (row_info->bit_depth == 8)
           {
              /* This changes G to RGB */
              png_bytep sp = row + (png_size_t)row_width - 1;
              png_bytep dp = sp  + (png_size_t)row_width * 2;
              for (i = 0; i < row_width; i++)
              {
                 *(dp--) = *sp;
                 *(dp--) = *sp;
                 *(dp--) = *(sp--);
              }
           }
  
           else
           {
              /* This changes GG to RRGGBB */
              png_bytep sp = row + (png_size_t)row_width * 2 - 1;
              png_bytep dp = sp  + (png_size_t)row_width * 4;
              for (i = 0; i < row_width; i++)
              {
                 *(dp--) = *sp;
                 *(dp--) = *(sp - 1);
                 *(dp--) = *sp;
                 *(dp--) = *(sp - 1);
                 *(dp--) = *(sp--);
                 *(dp--) = *(sp--);
              }
           }
        }
  
        else if (row_info->color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
        {
           if (row_info->bit_depth == 8)
           {
              /* This changes GA to RGBA */
              png_bytep sp = row + (png_size_t)row_width * 2 - 1;
              png_bytep dp = sp  + (png_size_t)row_width * 2;
              for (i = 0; i < row_width; i++)
              {
                 *(dp--) = *(sp--);
                 *(dp--) = *sp;
                 *(dp--) = *sp;
                 *(dp--) = *(sp--);
              }
           }
  
           else
           {
              /* This changes GGAA to RRGGBBAA */
              png_bytep sp = row + (png_size_t)row_width * 4 - 1;
              png_bytep dp = sp  + (png_size_t)row_width * 4;
              for (i = 0; i < row_width; i++)
              {
                 *(dp--) = *(sp--);
                 *(dp--) = *(sp--);
                 *(dp--) = *sp;
                 *(dp--) = *(sp - 1);
                 *(dp--) = *sp;
                 *(dp--) = *(sp - 1);
                 *(dp--) = *(sp--);
                 *(dp--) = *(sp--);
              }
           }
        }
        row_info->channels = (png_byte)(row_info->channels + 2);
        row_info->color_type |= PNG_COLOR_MASK_COLOR;
        row_info->pixel_depth = (png_byte)(row_info->channels *
            row_info->bit_depth);
        row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
     }
  }
  #endif
  
  #ifdef PNG_READ_RGB_TO_GRAY_SUPPORTED
  /* Reduce RGB files to grayscale, with or without alpha
   * using the equation given in Poynton's ColorFAQ of 1998-01-04 at
   * <http://www.inforamp.net/~poynton/>  (THIS LINK IS DEAD June 2008 but
   * versions dated 1998 through November 2002 have been archived at
   * http://web.archive.org/web/20000816232553/http://www.inforamp.net/
   * ~poynton/notes/colour_and_gamma/ColorFAQ.txt )
   * Charles Poynton poynton at poynton.com
   *
   *     Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
   *
   *  which can be expressed with integers as
   *
   *     Y = (6969 * R + 23434 * G + 2365 * B)/32768
   *
   * Poynton's current link (as of January 2003 through July 2011):
   * <http://www.poynton.com/notes/colour_and_gamma/>
   * has changed the numbers slightly:
   *
   *     Y = 0.2126*R + 0.7152*G + 0.0722*B
   *
   *  which can be expressed with integers as
   *
   *     Y = (6966 * R + 23436 * G + 2366 * B)/32768
   *
   *  Historically, however, libpng uses numbers derived from the ITU-R Rec 709
   *  end point chromaticities and the D65 white point.  Depending on the
   *  precision used for the D65 white point this produces a variety of different
   *  numbers, however if the four decimal place value used in ITU-R Rec 709 is
   *  used (0.3127,0.3290) the Y calculation would be:
   *
   *     Y = (6968 * R + 23435 * G + 2366 * B)/32768
   *
   *  While this is correct the rounding results in an overflow for white, because
   *  the sum of the rounded coefficients is 32769, not 32768.  Consequently
   *  libpng uses, instead, the closest non-overflowing approximation:
   *
   *     Y = (6968 * R + 23434 * G + 2366 * B)/32768
   *
   *  Starting with libpng-1.5.5, if the image being converted has a cHRM chunk
   *  (including an sRGB chunk) then the chromaticities are used to calculate the
   *  coefficients.  See the chunk handling in pngrutil.c for more information.
   *
   *  In all cases the calculation is to be done in a linear colorspace.  If no
   *  gamma information is available to correct the encoding of the original RGB
   *  values this results in an implicit assumption that the original PNG RGB
   *  values were linear.
   *
   *  Other integer coefficents can be used via png_set_rgb_to_gray().  Because
   *  the API takes just red and green coefficients the blue coefficient is
   *  calculated to make the sum 32768.  This will result in different rounding
   *  to that used above.
   */
  int /* PRIVATE */
  png_do_rgb_to_gray(png_structrp png_ptr, png_row_infop row_info, png_bytep row)
  
  {
     int rgb_error = 0;
  
     png_debug(1, "in png_do_rgb_to_gray");
  
     if (!(row_info->color_type & PNG_COLOR_MASK_PALETTE) &&
         (row_info->color_type & PNG_COLOR_MASK_COLOR))
     {
        PNG_CONST png_uint_32 rc = png_ptr->rgb_to_gray_red_coeff;
        PNG_CONST png_uint_32 gc = png_ptr->rgb_to_gray_green_coeff;
        PNG_CONST png_uint_32 bc = 32768 - rc - gc;
        PNG_CONST png_uint_32 row_width = row_info->width;
        PNG_CONST int have_alpha =
           (row_info->color_type & PNG_COLOR_MASK_ALPHA) != 0;
  
        if (row_info->bit_depth == 8)
        {
  #ifdef PNG_READ_GAMMA_SUPPORTED
           /* Notice that gamma to/from 1 are not necessarily inverses (if
            * there is an overall gamma correction).  Prior to 1.5.5 this code
            * checked the linearized values for equality; this doesn't match
            * the documentation, the original values must be checked.
            */
           if (png_ptr->gamma_from_1 != NULL && png_ptr->gamma_to_1 != NULL)
           {
              png_bytep sp = row;
              png_bytep dp = row;
              png_uint_32 i;
  
              for (i = 0; i < row_width; i++)
              {
                 png_byte red   = *(sp++);
                 png_byte green = *(sp++);
                 png_byte blue  = *(sp++);
  
                 if (red != green || red != blue)
                 {
                    red = png_ptr->gamma_to_1[red];
                    green = png_ptr->gamma_to_1[green];
                    blue = png_ptr->gamma_to_1[blue];
  
                    rgb_error |= 1;
                    *(dp++) = png_ptr->gamma_from_1[
                        (rc*red + gc*green + bc*blue + 16384)>>15];
                 }
  
                 else
                 {
                    /* If there is no overall correction the table will not be
                     * set.
                     */
                    if (png_ptr->gamma_table != NULL)
                       red = png_ptr->gamma_table[red];
  
                    *(dp++) = red;
                 }
  
                 if (have_alpha)
                    *(dp++) = *(sp++);
              }
           }
           else
  #endif
           {
              png_bytep sp = row;
              png_bytep dp = row;
              png_uint_32 i;
  
              for (i = 0; i < row_width; i++)
              {
                 png_byte red   = *(sp++);
                 png_byte green = *(sp++);
                 png_byte blue  = *(sp++);
  
                 if (red != green || red != blue)
                 {
                    rgb_error |= 1;
                    /* NOTE: this is the historical approach which simply
                     * truncates the results.
                     */
                    *(dp++) = (png_byte)((rc*red + gc*green + bc*blue)>>15);
                 }
  
                 else
                    *(dp++) = red;
  
                 if (have_alpha)
                    *(dp++) = *(sp++);
              }
           }
        }
  
        else /* RGB bit_depth == 16 */
        {
  #ifdef PNG_READ_GAMMA_SUPPORTED
           if (png_ptr->gamma_16_to_1 != NULL && png_ptr->gamma_16_from_1 != NULL)
           {
              png_bytep sp = row;
              png_bytep dp = row;
              png_uint_32 i;
  
              for (i = 0; i < row_width; i++)
              {
                 png_uint_16 red, green, blue, w;
  
                 red   = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
                 green = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
                 blue  = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
  
                 if (red == green && red == blue)
                 {
                    if (png_ptr->gamma_16_table != NULL)
                       w = png_ptr->gamma_16_table[(red&0xff)
                           >> png_ptr->gamma_shift][red>>8];
  
                    else
                       w = red;
                 }
  
                 else
                 {
                    png_uint_16 red_1   = png_ptr->gamma_16_to_1[(red&0xff)
                        >> png_ptr->gamma_shift][red>>8];
                    png_uint_16 green_1 =
                        png_ptr->gamma_16_to_1[(green&0xff) >>
                        png_ptr->gamma_shift][green>>8];
                    png_uint_16 blue_1  = png_ptr->gamma_16_to_1[(blue&0xff)
                        >> png_ptr->gamma_shift][blue>>8];
                    png_uint_16 gray16  = (png_uint_16)((rc*red_1 + gc*green_1
                        + bc*blue_1 + 16384)>>15);
                    w = png_ptr->gamma_16_from_1[(gray16&0xff) >>
                        png_ptr->gamma_shift][gray16 >> 8];
                    rgb_error |= 1;
                 }
  
                 *(dp++) = (png_byte)((w>>8) & 0xff);
                 *(dp++) = (png_byte)(w & 0xff);
  
                 if (have_alpha)
                 {
                    *(dp++) = *(sp++);
                    *(dp++) = *(sp++);
                 }
              }
           }
           else
  #endif
           {
              png_bytep sp = row;
              png_bytep dp = row;
              png_uint_32 i;
  
              for (i = 0; i < row_width; i++)
              {
                 png_uint_16 red, green, blue, gray16;
  
                 red   = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
                 green = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
                 blue  = (png_uint_16)(((*(sp))<<8) | *(sp + 1)); sp += 2;
  
                 if (red != green || red != blue)
                    rgb_error |= 1;
  
                 /* From 1.5.5 in the 16 bit case do the accurate conversion even
                  * in the 'fast' case - this is because this is where the code
                  * ends up when handling linear 16 bit data.
                  */
                 gray16  = (png_uint_16)((rc*red + gc*green + bc*blue + 16384) >>
                    15);
                 *(dp++) = (png_byte)((gray16>>8) & 0xff);
                 *(dp++) = (png_byte)(gray16 & 0xff);
  
                 if (have_alpha)
                 {
                    *(dp++) = *(sp++);
                    *(dp++) = *(sp++);
                 }
              }
           }
        }
  
        row_info->channels = (png_byte)(row_info->channels - 2);
        row_info->color_type = (png_byte)(row_info->color_type &
            ~PNG_COLOR_MASK_COLOR);
        row_info->pixel_depth = (png_byte)(row_info->channels *
            row_info->bit_depth);
        row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
     }
     return rgb_error;
  }
  #endif
  #endif /* PNG_READ_TRANSFORMS_SUPPORTED */
  
  #ifdef PNG_BUILD_GRAYSCALE_PALETTE_SUPPORTED
  /* Build a grayscale palette.  Palette is assumed to be 1 << bit_depth
   * large of png_color.  This lets grayscale images be treated as
   * paletted.  Most useful for gamma correction and simplification
   * of code.  This API is not used internally.
   */
  void PNGAPI
  png_build_grayscale_palette(int bit_depth, png_colorp palette)
  {
     int num_palette;
     int color_inc;
     int i;
     int v;
  
     png_debug(1, "in png_do_build_grayscale_palette");
  
     if (palette == NULL)
        return;
  
     switch (bit_depth)
     {
        case 1:
           num_palette = 2;
           color_inc = 0xff;
           break;
  
        case 2:
           num_palette = 4;
           color_inc = 0x55;
           break;
  
        case 4:
           num_palette = 16;
           color_inc = 0x11;
           break;
  
        case 8:
           num_palette = 256;
           color_inc = 1;
           break;
  
        default:
           num_palette = 0;
           color_inc = 0;
           break;
     }
  
     for (i = 0, v = 0; i < num_palette; i++, v += color_inc)
     {
        palette[i].red = (png_byte)v;
        palette[i].green = (png_byte)v;
        palette[i].blue = (png_byte)v;
     }
  }
  #endif
  
  
  #ifdef PNG_READ_TRANSFORMS_SUPPORTED
  #if defined(PNG_READ_BACKGROUND_SUPPORTED) ||\
     defined(PNG_READ_ALPHA_MODE_SUPPORTED)
  /* Replace any alpha or transparency with the supplied background color.
   * "background" is already in the screen gamma, while "background_1" is
   * at a gamma of 1.0.  Paletted files have already been taken care of.
   */
  void /* PRIVATE */
  png_do_compose(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
  {
  #ifdef PNG_READ_GAMMA_SUPPORTED
     png_const_bytep gamma_table = png_ptr->gamma_table;
     png_const_bytep gamma_from_1 = png_ptr->gamma_from_1;
     png_const_bytep gamma_to_1 = png_ptr->gamma_to_1;
     png_const_uint_16pp gamma_16 = png_ptr->gamma_16_table;
     png_const_uint_16pp gamma_16_from_1 = png_ptr->gamma_16_from_1;
     png_const_uint_16pp gamma_16_to_1 = png_ptr->gamma_16_to_1;
     int gamma_shift = png_ptr->gamma_shift;
     int optimize = (png_ptr->flags & PNG_FLAG_OPTIMIZE_ALPHA) != 0;
  #endif
  
     png_bytep sp;
     png_uint_32 i;
     png_uint_32 row_width = row_info->width;
     int shift;
  
     png_debug(1, "in png_do_compose");
  
     {
        switch (row_info->color_type)
        {
           case PNG_COLOR_TYPE_GRAY:
           {
              switch (row_info->bit_depth)
              {
                 case 1:
                 {
                    sp = row;
                    shift = 7;
                    for (i = 0; i < row_width; i++)
                    {
                       if ((png_uint_16)((*sp >> shift) & 0x01)
                          == png_ptr->trans_color.gray)
                       {
                          unsigned int tmp = *sp & (0x7f7f >> (7 - shift));
                          tmp |= png_ptr->background.gray << shift;
                          *sp = (png_byte)(tmp & 0xff);
                       }
  
                       if (!shift)
                       {
                          shift = 7;
                          sp++;
                       }
  
                       else
                          shift--;
                    }
                    break;
                 }
  
                 case 2:
                 {
  #ifdef PNG_READ_GAMMA_SUPPORTED
                    if (gamma_table != NULL)
                    {
                       sp = row;
                       shift = 6;
                       for (i = 0; i < row_width; i++)
                       {
                          if ((png_uint_16)((*sp >> shift) & 0x03)
                              == png_ptr->trans_color.gray)
                          {
                             unsigned int tmp = *sp & (0x3f3f >> (6 - shift));
                             tmp |= png_ptr->background.gray << shift;
                             *sp = (png_byte)(tmp & 0xff);
                          }
  
                          else
                          {
                             unsigned int p = (*sp >> shift) & 0x03;
                             unsigned int g = (gamma_table [p | (p << 2) |
                                 (p << 4) | (p << 6)] >> 6) & 0x03;
                             unsigned int tmp = *sp & (0x3f3f >> (6 - shift));
                             tmp |= g << shift;
                             *sp = (png_byte)(tmp & 0xff);
                          }
  
                          if (!shift)
                          {
                             shift = 6;
                             sp++;
                          }
  
                          else
                             shift -= 2;
                       }
                    }
  
                    else
  #endif
                    {
                       sp = row;
                       shift = 6;
                       for (i = 0; i < row_width; i++)
                       {
                          if ((png_uint_16)((*sp >> shift) & 0x03)
                              == png_ptr->trans_color.gray)
                          {
                             unsigned int tmp = *sp & (0x3f3f >> (6 - shift));
                             tmp |= png_ptr->background.gray << shift;
                             *sp = (png_byte)(tmp & 0xff);
                          }
  
                          if (!shift)
                          {
                             shift = 6;
                             sp++;
                          }
  
                          else
                             shift -= 2;
                       }
                    }
                    break;
                 }
  
                 case 4:
                 {
  #ifdef PNG_READ_GAMMA_SUPPORTED
                    if (gamma_table != NULL)
                    {
                       sp = row;
                       shift = 4;
                       for (i = 0; i < row_width; i++)
                       {
                          if ((png_uint_16)((*sp >> shift) & 0x0f)
                              == png_ptr->trans_color.gray)
                          {
                             unsigned int tmp = *sp & (0xf0f >> (4 - shift));
                             tmp |= png_ptr->background.gray << shift;
                             *sp = (png_byte)(tmp & 0xff);
                          }
  
                          else
                          {
                             unsigned int p = (*sp >> shift) & 0x0f;
                             unsigned int g = (gamma_table[p | (p << 4)] >> 4) &
                                0x0f;
                             unsigned int tmp = *sp & (0xf0f >> (4 - shift));
                             tmp |= g << shift;
                             *sp = (png_byte)(tmp & 0xff);
                          }
  
                          if (!shift)
                          {
                             shift = 4;
                             sp++;
                          }
  
                          else
                             shift -= 4;
                       }
                    }
  
                    else
  #endif
                    {
                       sp = row;
                       shift = 4;
                       for (i = 0; i < row_width; i++)
                       {
                          if ((png_uint_16)((*sp >> shift) & 0x0f)
                              == png_ptr->trans_color.gray)
                          {
                             unsigned int tmp = *sp & (0xf0f >> (4 - shift));
                             tmp |= png_ptr->background.gray << shift;
                             *sp = (png_byte)(tmp & 0xff);
                          }
  
                          if (!shift)
                          {
                             shift = 4;
                             sp++;
                          }
  
                          else
                             shift -= 4;
                       }
                    }
                    break;
                 }
  
                 case 8:
                 {
  #ifdef PNG_READ_GAMMA_SUPPORTED
                    if (gamma_table != NULL)
                    {
                       sp = row;
                       for (i = 0; i < row_width; i++, sp++)
                       {
                          if (*sp == png_ptr->trans_color.gray)
                             *sp = (png_byte)png_ptr->background.gray;
  
                          else
                             *sp = gamma_table[*sp];
                       }
                    }
                    else
  #endif
                    {
                       sp = row;
                       for (i = 0; i < row_width; i++, sp++)
                       {
                          if (*sp == png_ptr->trans_color.gray)
                             *sp = (png_byte)png_ptr->background.gray;
                       }
                    }
                    break;
                 }
  
                 case 16:
                 {
  #ifdef PNG_READ_GAMMA_SUPPORTED
                    if (gamma_16 != NULL)
                    {
                       sp = row;
                       for (i = 0; i < row_width; i++, sp += 2)
                       {
                          png_uint_16 v;
  
                          v = (png_uint_16)(((*sp) << 8) + *(sp + 1));
  
                          if (v == png_ptr->trans_color.gray)
                          {
                             /* Background is already in screen gamma */
                             *sp = (png_byte)((png_ptr->background.gray >> 8)
                                  & 0xff);
                             *(sp + 1) = (png_byte)(png_ptr->background.gray
                                  & 0xff);
                          }
  
                          else
                          {
                             v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                             *sp = (png_byte)((v >> 8) & 0xff);
                             *(sp + 1) = (png_byte)(v & 0xff);
                          }
                       }
                    }
                    else
  #endif
                    {
                       sp = row;
                       for (i = 0; i < row_width; i++, sp += 2)
                       {
                          png_uint_16 v;
  
                          v = (png_uint_16)(((*sp) << 8) + *(sp + 1));
  
                          if (v == png_ptr->trans_color.gray)
                          {
                             *sp = (png_byte)((png_ptr->background.gray >> 8)
                                  & 0xff);
                             *(sp + 1) = (png_byte)(png_ptr->background.gray
                                  & 0xff);
                          }
                       }
                    }
                    break;
                 }
  
                 default:
                    break;
              }
              break;
           }
  
           case PNG_COLOR_TYPE_RGB:
           {
              if (row_info->bit_depth == 8)
              {
  #ifdef PNG_READ_GAMMA_SUPPORTED
                 if (gamma_table != NULL)
                 {
                    sp = row;
                    for (i = 0; i < row_width; i++, sp += 3)
                    {
                       if (*sp == png_ptr->trans_color.red &&
                           *(sp + 1) == png_ptr->trans_color.green &&
                           *(sp + 2) == png_ptr->trans_color.blue)
                       {
                          *sp = (png_byte)png_ptr->background.red;
                          *(sp + 1) = (png_byte)png_ptr->background.green;
                          *(sp + 2) = (png_byte)png_ptr->background.blue;
                       }
  
                       else
                       {
                          *sp = gamma_table[*sp];
                          *(sp + 1) = gamma_table[*(sp + 1)];
                          *(sp + 2) = gamma_table[*(sp + 2)];
                       }
                    }
                 }
                 else
  #endif
                 {
                    sp = row;
                    for (i = 0; i < row_width; i++, sp += 3)
                    {
                       if (*sp == png_ptr->trans_color.red &&
                           *(sp + 1) == png_ptr->trans_color.green &&
                           *(sp + 2) == png_ptr->trans_color.blue)
                       {
                          *sp = (png_byte)png_ptr->background.red;
                          *(sp + 1) = (png_byte)png_ptr->background.green;
                          *(sp + 2) = (png_byte)png_ptr->background.blue;
                       }
                    }
                 }
              }
              else /* if (row_info->bit_depth == 16) */
              {
  #ifdef PNG_READ_GAMMA_SUPPORTED
                 if (gamma_16 != NULL)
                 {
                    sp = row;
                    for (i = 0; i < row_width; i++, sp += 6)
                    {
                       png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
  
                       png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
                           + *(sp + 3));
  
                       png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
                           + *(sp + 5));
  
                       if (r == png_ptr->trans_color.red &&
                           g == png_ptr->trans_color.green &&
                           b == png_ptr->trans_color.blue)
                       {
                          /* Background is already in screen gamma */
                          *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
                          *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
                          *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
                                  & 0xff);
                          *(sp + 3) = (png_byte)(png_ptr->background.green
                                  & 0xff);
                          *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
                                  & 0xff);
                          *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                       }
  
                       else
                       {
                          png_uint_16 v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                          *sp = (png_byte)((v >> 8) & 0xff);
                          *(sp + 1) = (png_byte)(v & 0xff);
  
                          v = gamma_16[*(sp + 3) >> gamma_shift][*(sp + 2)];
                          *(sp + 2) = (png_byte)((v >> 8) & 0xff);
                          *(sp + 3) = (png_byte)(v & 0xff);
  
                          v = gamma_16[*(sp + 5) >> gamma_shift][*(sp + 4)];
                          *(sp + 4) = (png_byte)((v >> 8) & 0xff);
                          *(sp + 5) = (png_byte)(v & 0xff);
                       }
                    }
                 }
  
                 else
  #endif
                 {
                    sp = row;
                    for (i = 0; i < row_width; i++, sp += 6)
                    {
                       png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
  
                       png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
                           + *(sp + 3));
  
                       png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
                           + *(sp + 5));
  
                       if (r == png_ptr->trans_color.red &&
                           g == png_ptr->trans_color.green &&
                           b == png_ptr->trans_color.blue)
                       {
                          *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
                          *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
                          *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
                                  & 0xff);
                          *(sp + 3) = (png_byte)(png_ptr->background.green
                                  & 0xff);
                          *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
                                  & 0xff);
                          *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                       }
                    }
                 }
              }
              break;
           }
  
           case PNG_COLOR_TYPE_GRAY_ALPHA:
           {
              if (row_info->bit_depth == 8)
              {
  #ifdef PNG_READ_GAMMA_SUPPORTED
                 if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
                     gamma_table != NULL)
                 {
                    sp = row;
                    for (i = 0; i < row_width; i++, sp += 2)
                    {
                       png_uint_16 a = *(sp + 1);
  
                       if (a == 0xff)
                          *sp = gamma_table[*sp];
  
                       else if (a == 0)
                       {
                          /* Background is already in screen gamma */
                          *sp = (png_byte)png_ptr->background.gray;
                       }
  
                       else
                       {
                          png_byte v, w;
  
                          v = gamma_to_1[*sp];
                          png_composite(w, v, a, png_ptr->background_1.gray);
                          if (!optimize)
                             w = gamma_from_1[w];
                          *sp = w;
                       }
                    }
                 }
                 else
  #endif
                 {
                    sp = row;
                    for (i = 0; i < row_width; i++, sp += 2)
                    {
                       png_byte a = *(sp + 1);
  
                       if (a == 0)
                          *sp = (png_byte)png_ptr->background.gray;
  
                       else if (a < 0xff)
                          png_composite(*sp, *sp, a, png_ptr->background.gray);
                    }
                 }
              }
              else /* if (png_ptr->bit_depth == 16) */
              {
  #ifdef PNG_READ_GAMMA_SUPPORTED
                 if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
                     gamma_16_to_1 != NULL)
                 {
                    sp = row;
                    for (i = 0; i < row_width; i++, sp += 4)
                    {
                       png_uint_16 a = (png_uint_16)(((*(sp + 2)) << 8)
                           + *(sp + 3));
  
                       if (a == (png_uint_16)0xffff)
                       {
                          png_uint_16 v;
  
                          v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                          *sp = (png_byte)((v >> 8) & 0xff);
                          *(sp + 1) = (png_byte)(v & 0xff);
                       }
  
                       else if (a == 0)
                       {
                          /* Background is already in screen gamma */
                          *sp = (png_byte)((png_ptr->background.gray >> 8)
                                  & 0xff);
                          *(sp + 1) = (png_byte)(png_ptr->background.gray & 0xff);
                       }
  
                       else
                       {
                          png_uint_16 g, v, w;
  
                          g = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
                          png_composite_16(v, g, a, png_ptr->background_1.gray);
                          if (optimize)
                             w = v;
                          else
                             w = gamma_16_from_1[(v&0xff) >> gamma_shift][v >> 8];
                          *sp = (png_byte)((w >> 8) & 0xff);
                          *(sp + 1) = (png_byte)(w & 0xff);
                       }
                    }
                 }
                 else
  #endif
                 {
                    sp = row;
                    for (i = 0; i < row_width; i++, sp += 4)
                    {
                       png_uint_16 a = (png_uint_16)(((*(sp + 2)) << 8)
                           + *(sp + 3));
  
                       if (a == 0)
                       {
                          *sp = (png_byte)((png_ptr->background.gray >> 8)
                                  & 0xff);
                          *(sp + 1) = (png_byte)(png_ptr->background.gray & 0xff);
                       }
  
                       else if (a < 0xffff)
                       {
                          png_uint_16 g, v;
  
                          g = (png_uint_16)(((*sp) << 8) + *(sp + 1));
                          png_composite_16(v, g, a, png_ptr->background.gray);
                          *sp = (png_byte)((v >> 8) & 0xff);
                          *(sp + 1) = (png_byte)(v & 0xff);
                       }
                    }
                 }
              }
              break;
           }
  
           case PNG_COLOR_TYPE_RGB_ALPHA:
           {
              if (row_info->bit_depth == 8)
              {
  #ifdef PNG_READ_GAMMA_SUPPORTED
                 if (gamma_to_1 != NULL && gamma_from_1 != NULL &&
                     gamma_table != NULL)
                 {
                    sp = row;
                    for (i = 0; i < row_width; i++, sp += 4)
                    {
                       png_byte a = *(sp + 3);
  
                       if (a == 0xff)
                       {
                          *sp = gamma_table[*sp];
                          *(sp + 1) = gamma_table[*(sp + 1)];
                          *(sp + 2) = gamma_table[*(sp + 2)];
                       }
  
                       else if (a == 0)
                       {
                          /* Background is already in screen gamma */
                          *sp = (png_byte)png_ptr->background.red;
                          *(sp + 1) = (png_byte)png_ptr->background.green;
                          *(sp + 2) = (png_byte)png_ptr->background.blue;
                       }
  
                       else
                       {
                          png_byte v, w;
  
                          v = gamma_to_1[*sp];
                          png_composite(w, v, a, png_ptr->background_1.red);
                          if (!optimize) w = gamma_from_1[w];
                          *sp = w;
  
                          v = gamma_to_1[*(sp + 1)];
                          png_composite(w, v, a, png_ptr->background_1.green);
                          if (!optimize) w = gamma_from_1[w];
                          *(sp + 1) = w;
  
                          v = gamma_to_1[*(sp + 2)];
                          png_composite(w, v, a, png_ptr->background_1.blue);
                          if (!optimize) w = gamma_from_1[w];
                          *(sp + 2) = w;
                       }
                    }
                 }
                 else
  #endif
                 {
                    sp = row;
                    for (i = 0; i < row_width; i++, sp += 4)
                    {
                       png_byte a = *(sp + 3);
  
                       if (a == 0)
                       {
                          *sp = (png_byte)png_ptr->background.red;
                          *(sp + 1) = (png_byte)png_ptr->background.green;
                          *(sp + 2) = (png_byte)png_ptr->background.blue;
                       }
  
                       else if (a < 0xff)
                       {
                          png_composite(*sp, *sp, a, png_ptr->background.red);
  
                          png_composite(*(sp + 1), *(sp + 1), a,
                              png_ptr->background.green);
  
                          png_composite(*(sp + 2), *(sp + 2), a,
                              png_ptr->background.blue);
                       }
                    }
                 }
              }
              else /* if (row_info->bit_depth == 16) */
              {
  #ifdef PNG_READ_GAMMA_SUPPORTED
                 if (gamma_16 != NULL && gamma_16_from_1 != NULL &&
                     gamma_16_to_1 != NULL)
                 {
                    sp = row;
                    for (i = 0; i < row_width; i++, sp += 8)
                    {
                       png_uint_16 a = (png_uint_16)(((png_uint_16)(*(sp + 6))
                           << 8) + (png_uint_16)(*(sp + 7)));
  
                       if (a == (png_uint_16)0xffff)
                       {
                          png_uint_16 v;
  
                          v = gamma_16[*(sp + 1) >> gamma_shift][*sp];
                          *sp = (png_byte)((v >> 8) & 0xff);
                          *(sp + 1) = (png_byte)(v & 0xff);
  
                          v = gamma_16[*(sp + 3) >> gamma_shift][*(sp + 2)];
                          *(sp + 2) = (png_byte)((v >> 8) & 0xff);
                          *(sp + 3) = (png_byte)(v & 0xff);
  
                          v = gamma_16[*(sp + 5) >> gamma_shift][*(sp + 4)];
                          *(sp + 4) = (png_byte)((v >> 8) & 0xff);
                          *(sp + 5) = (png_byte)(v & 0xff);
                       }
  
                       else if (a == 0)
                       {
                          /* Background is already in screen gamma */
                          *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
                          *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
                          *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
                                  & 0xff);
                          *(sp + 3) = (png_byte)(png_ptr->background.green
                                  & 0xff);
                          *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
                                  & 0xff);
                          *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                       }
  
                       else
                       {
                          png_uint_16 v, w;
  
                          v = gamma_16_to_1[*(sp + 1) >> gamma_shift][*sp];
                          png_composite_16(w, v, a, png_ptr->background_1.red);
                          if (!optimize)
                             w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >>
                                  8];
                          *sp = (png_byte)((w >> 8) & 0xff);
                          *(sp + 1) = (png_byte)(w & 0xff);
  
                          v = gamma_16_to_1[*(sp + 3) >> gamma_shift][*(sp + 2)];
                          png_composite_16(w, v, a, png_ptr->background_1.green);
                          if (!optimize)
                             w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >>
                                  8];
  
                          *(sp + 2) = (png_byte)((w >> 8) & 0xff);
                          *(sp + 3) = (png_byte)(w & 0xff);
  
                          v = gamma_16_to_1[*(sp + 5) >> gamma_shift][*(sp + 4)];
                          png_composite_16(w, v, a, png_ptr->background_1.blue);
                          if (!optimize)
                             w = gamma_16_from_1[((w&0xff) >> gamma_shift)][w >>
                                  8];
  
                          *(sp + 4) = (png_byte)((w >> 8) & 0xff);
                          *(sp + 5) = (png_byte)(w & 0xff);
                       }
                    }
                 }
  
                 else
  #endif
                 {
                    sp = row;
                    for (i = 0; i < row_width; i++, sp += 8)
                    {
                       png_uint_16 a = (png_uint_16)(((png_uint_16)(*(sp + 6))
                           << 8) + (png_uint_16)(*(sp + 7)));
  
                       if (a == 0)
                       {
                          *sp = (png_byte)((png_ptr->background.red >> 8) & 0xff);
                          *(sp + 1) = (png_byte)(png_ptr->background.red & 0xff);
                          *(sp + 2) = (png_byte)((png_ptr->background.green >> 8)
                                  & 0xff);
                          *(sp + 3) = (png_byte)(png_ptr->background.green
                                  & 0xff);
                          *(sp + 4) = (png_byte)((png_ptr->background.blue >> 8)
                                  & 0xff);
                          *(sp + 5) = (png_byte)(png_ptr->background.blue & 0xff);
                       }
  
                       else if (a < 0xffff)
                       {
                          png_uint_16 v;
  
                          png_uint_16 r = (png_uint_16)(((*sp) << 8) + *(sp + 1));
                          png_uint_16 g = (png_uint_16)(((*(sp + 2)) << 8)
                              + *(sp + 3));
                          png_uint_16 b = (png_uint_16)(((*(sp + 4)) << 8)
                              + *(sp + 5));
  
                          png_composite_16(v, r, a, png_ptr->background.red);
                          *sp = (png_byte)((v >> 8) & 0xff);
                          *(sp + 1) = (png_byte)(v & 0xff);
  
                          png_composite_16(v, g, a, png_ptr->background.green);
                          *(sp + 2) = (png_byte)((v >> 8) & 0xff);
                          *(sp + 3) = (png_byte)(v & 0xff);
  
                          png_composite_16(v, b, a, png_ptr->background.blue);
                          *(sp + 4) = (png_byte)((v >> 8) & 0xff);
                          *(sp + 5) = (png_byte)(v & 0xff);
                       }
                    }
                 }
              }
              break;
           }
  
           default:
              break;
        }
     }
  }
  #endif /* PNG_READ_BACKGROUND_SUPPORTED || PNG_READ_ALPHA_MODE_SUPPORTED */
  
  #ifdef PNG_READ_GAMMA_SUPPORTED
  /* Gamma correct the image, avoiding the alpha channel.  Make sure
   * you do this after you deal with the transparency issue on grayscale
   * or RGB images. If your bit depth is 8, use gamma_table, if it
   * is 16, use gamma_16_table and gamma_shift.  Build these with
   * build_gamma_table().
   */
  void /* PRIVATE */
  png_do_gamma(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
  {
     png_const_bytep gamma_table = png_ptr->gamma_table;
     png_const_uint_16pp gamma_16_table = png_ptr->gamma_16_table;
     int gamma_shift = png_ptr->gamma_shift;
  
     png_bytep sp;
     png_uint_32 i;
     png_uint_32 row_width=row_info->width;
  
     png_debug(1, "in png_do_gamma");
  
     if (((row_info->bit_depth <= 8 && gamma_table != NULL) ||
         (row_info->bit_depth == 16 && gamma_16_table != NULL)))
     {
        switch (row_info->color_type)
        {
           case PNG_COLOR_TYPE_RGB:
           {
              if (row_info->bit_depth == 8)
              {
                 sp = row;
                 for (i = 0; i < row_width; i++)
                 {
                    *sp = gamma_table[*sp];
                    sp++;
                    *sp = gamma_table[*sp];
                    sp++;
                    *sp = gamma_table[*sp];
                    sp++;
                 }
              }
  
              else /* if (row_info->bit_depth == 16) */
              {
                 sp = row;
                 for (i = 0; i < row_width; i++)
                 {
                    png_uint_16 v;
  
                    v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                    *sp = (png_byte)((v >> 8) & 0xff);
                    *(sp + 1) = (png_byte)(v & 0xff);
                    sp += 2;
  
                    v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                    *sp = (png_byte)((v >> 8) & 0xff);
                    *(sp + 1) = (png_byte)(v & 0xff);
                    sp += 2;
  
                    v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                    *sp = (png_byte)((v >> 8) & 0xff);
                    *(sp + 1) = (png_byte)(v & 0xff);
                    sp += 2;
                 }
              }
              break;
           }
  
           case PNG_COLOR_TYPE_RGB_ALPHA:
           {
              if (row_info->bit_depth == 8)
              {
                 sp = row;
                 for (i = 0; i < row_width; i++)
                 {
                    *sp = gamma_table[*sp];
                    sp++;
  
                    *sp = gamma_table[*sp];
                    sp++;
  
                    *sp = gamma_table[*sp];
                    sp++;
  
                    sp++;
                 }
              }
  
              else /* if (row_info->bit_depth == 16) */
              {
                 sp = row;
                 for (i = 0; i < row_width; i++)
                 {
                    png_uint_16 v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                    *sp = (png_byte)((v >> 8) & 0xff);
                    *(sp + 1) = (png_byte)(v & 0xff);
                    sp += 2;
  
                    v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                    *sp = (png_byte)((v >> 8) & 0xff);
                    *(sp + 1) = (png_byte)(v & 0xff);
                    sp += 2;
  
                    v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                    *sp = (png_byte)((v >> 8) & 0xff);
                    *(sp + 1) = (png_byte)(v & 0xff);
                    sp += 4;
                 }
              }
              break;
           }
  
           case PNG_COLOR_TYPE_GRAY_ALPHA:
           {
              if (row_info->bit_depth == 8)
              {
                 sp = row;
                 for (i = 0; i < row_width; i++)
                 {
                    *sp = gamma_table[*sp];
                    sp += 2;
                 }
              }
  
              else /* if (row_info->bit_depth == 16) */
              {
                 sp = row;
                 for (i = 0; i < row_width; i++)
                 {
                    png_uint_16 v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                    *sp = (png_byte)((v >> 8) & 0xff);
                    *(sp + 1) = (png_byte)(v & 0xff);
                    sp += 4;
                 }
              }
              break;
           }
  
           case PNG_COLOR_TYPE_GRAY:
           {
              if (row_info->bit_depth == 2)
              {
                 sp = row;
                 for (i = 0; i < row_width; i += 4)
                 {
                    int a = *sp & 0xc0;
                    int b = *sp & 0x30;
                    int c = *sp & 0x0c;
                    int d = *sp & 0x03;
  
                    *sp = (png_byte)(
                        ((((int)gamma_table[a|(a>>2)|(a>>4)|(a>>6)])   ) & 0xc0)|
                        ((((int)gamma_table[(b<<2)|b|(b>>2)|(b>>4)])>>2) & 0x30)|
                        ((((int)gamma_table[(c<<4)|(c<<2)|c|(c>>2)])>>4) & 0x0c)|
                        ((((int)gamma_table[(d<<6)|(d<<4)|(d<<2)|d])>>6) ));
                    sp++;
                 }
              }
  
              if (row_info->bit_depth == 4)
              {
                 sp = row;
                 for (i = 0; i < row_width; i += 2)
                 {
                    int msb = *sp & 0xf0;
                    int lsb = *sp & 0x0f;
  
                    *sp = (png_byte)((((int)gamma_table[msb | (msb >> 4)]) & 0xf0)
                        | (((int)gamma_table[(lsb << 4) | lsb]) >> 4));
                    sp++;
                 }
              }
  
              else if (row_info->bit_depth == 8)
              {
                 sp = row;
                 for (i = 0; i < row_width; i++)
                 {
                    *sp = gamma_table[*sp];
                    sp++;
                 }
              }
  
              else if (row_info->bit_depth == 16)
              {
                 sp = row;
                 for (i = 0; i < row_width; i++)
                 {
                    png_uint_16 v = gamma_16_table[*(sp + 1) >> gamma_shift][*sp];
                    *sp = (png_byte)((v >> 8) & 0xff);
                    *(sp + 1) = (png_byte)(v & 0xff);
                    sp += 2;
                 }
              }
              break;
           }
  
           default:
              break;
        }
     }
  }
  #endif
  
  #ifdef PNG_READ_ALPHA_MODE_SUPPORTED
  /* Encode the alpha channel to the output gamma (the input channel is always
   * linear.)  Called only with color types that have an alpha channel.  Needs the
   * from_1 tables.
   */
  void /* PRIVATE */
  png_do_encode_alpha(png_row_infop row_info, png_bytep row, png_structrp png_ptr)
  {
     png_uint_32 row_width = row_info->width;
  
     png_debug(1, "in png_do_encode_alpha");
  
     if (row_info->color_type & PNG_COLOR_MASK_ALPHA)
     {
        if (row_info->bit_depth == 8)
        {
           PNG_CONST png_bytep table = png_ptr->gamma_from_1;
  
           if (table != NULL)
           {
              PNG_CONST int step =
                 (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 4 : 2;
  
              /* The alpha channel is the last component: */
              row += step - 1;
  
              for (; row_width > 0; --row_width, row += step)
                 *row = table[*row];
  
              return;
           }
        }
  
        else if (row_info->bit_depth == 16)
        {
           PNG_CONST png_uint_16pp table = png_ptr->gamma_16_from_1;
           PNG_CONST int gamma_shift = png_ptr->gamma_shift;
  
           if (table != NULL)
           {
              PNG_CONST int step =
                 (row_info->color_type & PNG_COLOR_MASK_COLOR) ? 8 : 4;
  
              /* The alpha channel is the last component: */
              row += step - 2;
  
              for (; row_width > 0; --row_width, row += step)
              {
                 png_uint_16 v;
  
                 v = table[*(row + 1) >> gamma_shift][*row];
                 *row = (png_byte)((v >> 8) & 0xff);
                 *(row + 1) = (png_byte)(v & 0xff);
              }
  
              return;
           }
        }
     }
  
     /* Only get to here if called with a weird row_info; no harm has been done,
      * so just issue a warning.
      */
     png_warning(png_ptr, "png_do_encode_alpha: unexpected call");
  }
  #endif
  
  #ifdef PNG_READ_EXPAND_SUPPORTED
  /* Expands a palette row to an RGB or RGBA row depending
   * upon whether you supply trans and num_trans.
   */
  void /* PRIVATE */
  png_do_expand_palette(png_row_infop row_info, png_bytep row,
     png_const_colorp palette, png_const_bytep trans_alpha, int num_trans)
  {
     int shift, value;
     png_bytep sp, dp;
     png_uint_32 i;
     png_uint_32 row_width=row_info->width;
  
     png_debug(1, "in png_do_expand_palette");
  
     if (row_info->color_type == PNG_COLOR_TYPE_PALETTE)
     {
        if (row_info->bit_depth < 8)
        {
           switch (row_info->bit_depth)
           {
              case 1:
              {
                 sp = row + (png_size_t)((row_width - 1) >> 3);
                 dp = row + (png_size_t)row_width - 1;
                 shift = 7 - (int)((row_width + 7) & 0x07);
                 for (i = 0; i < row_width; i++)
                 {
                    if ((*sp >> shift) & 0x01)
                       *dp = 1;
  
                    else
                       *dp = 0;
  
                    if (shift == 7)
                    {
                       shift = 0;
                       sp--;
                    }
  
                    else
                       shift++;
  
                    dp--;
                 }
                 break;
              }
  
              case 2:
              {
                 sp = row + (png_size_t)((row_width - 1) >> 2);
                 dp = row + (png_size_t)row_width - 1;
                 shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
                 for (i = 0; i < row_width; i++)
                 {
                    value = (*sp >> shift) & 0x03;
                    *dp = (png_byte)value;
                    if (shift == 6)
                    {
                       shift = 0;
                       sp--;
                    }
  
                    else
                       shift += 2;
  
                    dp--;
                 }
                 break;
              }
  
              case 4:
              {
                 sp = row + (png_size_t)((row_width - 1) >> 1);
                 dp = row + (png_size_t)row_width - 1;
                 shift = (int)((row_width & 0x01) << 2);
                 for (i = 0; i < row_width; i++)
                 {
                    value = (*sp >> shift) & 0x0f;
                    *dp = (png_byte)value;
                    if (shift == 4)
                    {
                       shift = 0;
                       sp--;
                    }
  
                    else
                       shift += 4;
  
                    dp--;
                 }
                 break;
              }
  
              default:
                 break;
           }
           row_info->bit_depth = 8;
           row_info->pixel_depth = 8;
           row_info->rowbytes = row_width;
        }
  
        if (row_info->bit_depth == 8)
        {
           {
              if (num_trans > 0)
              {
                 sp = row + (png_size_t)row_width - 1;
                 dp = row + (png_size_t)(row_width << 2) - 1;
  
                 for (i = 0; i < row_width; i++)
                 {
                    if ((int)(*sp) >= num_trans)
                       *dp-- = 0xff;
  
                    else
                       *dp-- = trans_alpha[*sp];
  
                    *dp-- = palette[*sp].blue;
                    *dp-- = palette[*sp].green;
                    *dp-- = palette[*sp].red;
                    sp--;
                 }
                 row_info->bit_depth = 8;
                 row_info->pixel_depth = 32;
                 row_info->rowbytes = row_width * 4;
                 row_info->color_type = 6;
                 row_info->channels = 4;
              }
  
              else
              {
                 sp = row + (png_size_t)row_width - 1;
                 dp = row + (png_size_t)(row_width * 3) - 1;
  
                 for (i = 0; i < row_width; i++)
                 {
                    *dp-- = palette[*sp].blue;
                    *dp-- = palette[*sp].green;
                    *dp-- = palette[*sp].red;
                    sp--;
                 }
  
                 row_info->bit_depth = 8;
                 row_info->pixel_depth = 24;
                 row_info->rowbytes = row_width * 3;
                 row_info->color_type = 2;
                 row_info->channels = 3;
              }
           }
        }
     }
  }
  
  /* If the bit depth < 8, it is expanded to 8.  Also, if the already
   * expanded transparency value is supplied, an alpha channel is built.
   */
  void /* PRIVATE */
  png_do_expand(png_row_infop row_info, png_bytep row,
      png_const_color_16p trans_color)
  {
     int shift, value;
     png_bytep sp, dp;
     png_uint_32 i;
     png_uint_32 row_width=row_info->width;
  
     png_debug(1, "in png_do_expand");
  
     {
        if (row_info->color_type == PNG_COLOR_TYPE_GRAY)
        {
           unsigned int gray = trans_color ? trans_color->gray : 0;
  
           if (row_info->bit_depth < 8)
           {
              switch (row_info->bit_depth)
              {
                 case 1:
                 {
                    gray = (gray & 0x01) * 0xff;
                    sp = row + (png_size_t)((row_width - 1) >> 3);
                    dp = row + (png_size_t)row_width - 1;
                    shift = 7 - (int)((row_width + 7) & 0x07);
                    for (i = 0; i < row_width; i++)
                    {
                       if ((*sp >> shift) & 0x01)
                          *dp = 0xff;
  
                       else
                          *dp = 0;
  
                       if (shift == 7)
                       {
                          shift = 0;
                          sp--;
                       }
  
                       else
                          shift++;
  
                       dp--;
                    }
                    break;
                 }
  
                 case 2:
                 {
                    gray = (gray & 0x03) * 0x55;
                    sp = row + (png_size_t)((row_width - 1) >> 2);
                    dp = row + (png_size_t)row_width - 1;
                    shift = (int)((3 - ((row_width + 3) & 0x03)) << 1);
                    for (i = 0; i < row_width; i++)
                    {
                       value = (*sp >> shift) & 0x03;
                       *dp = (png_byte)(value | (value << 2) | (value << 4) |
                          (value << 6));
                       if (shift == 6)
                       {
                          shift = 0;
                          sp--;
                       }
  
                       else
                          shift += 2;
  
                       dp--;
                    }
                    break;
                 }
  
                 case 4:
                 {
                    gray = (gray & 0x0f) * 0x11;
                    sp = row + (png_size_t)((row_width - 1) >> 1);
                    dp = row + (png_size_t)row_width - 1;
                    shift = (int)((1 - ((row_width + 1) & 0x01)) << 2);
                    for (i = 0; i < row_width; i++)
                    {
                       value = (*sp >> shift) & 0x0f;
                       *dp = (png_byte)(value | (value << 4));
                       if (shift == 4)
                       {
                          shift = 0;
                          sp--;
                       }
  
                       else
                          shift = 4;
  
                       dp--;
                    }
                    break;
                 }
  
                 default:
                    break;
              }
  
              row_info->bit_depth = 8;
              row_info->pixel_depth = 8;
              row_info->rowbytes = row_width;
           }
  
           if (trans_color != NULL)
           {
              if (row_info->bit_depth == 8)
              {
                 gray = gray & 0xff;
                 sp = row + (png_size_t)row_width - 1;
                 dp = row + (png_size_t)(row_width << 1) - 1;
  
                 for (i = 0; i < row_width; i++)
                 {
                    if (*sp == gray)
                       *dp-- = 0;
  
                    else
                       *dp-- = 0xff;
  
                    *dp-- = *sp--;
                 }
              }
  
              else if (row_info->bit_depth == 16)
              {
                 unsigned int gray_high = (gray >> 8) & 0xff;
                 unsigned int gray_low = gray & 0xff;
                 sp = row + row_info->rowbytes - 1;
                 dp = row + (row_info->rowbytes << 1) - 1;
                 for (i = 0; i < row_width; i++)
                 {
                    if (*(sp - 1) == gray_high && *(sp) == gray_low)
                    {
                       *dp-- = 0;
                       *dp-- = 0;
                    }
  
                    else
                    {
                       *dp-- = 0xff;
                       *dp-- = 0xff;
                    }
  
                    *dp-- = *sp--;
                    *dp-- = *sp--;
                 }
              }
  
              row_info->color_type = PNG_COLOR_TYPE_GRAY_ALPHA;
              row_info->channels = 2;
              row_info->pixel_depth = (png_byte)(row_info->bit_depth << 1);
              row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,
                 row_width);
           }
        }
        else if (row_info->color_type == PNG_COLOR_TYPE_RGB && trans_color)
        {
           if (row_info->bit_depth == 8)
           {
              png_byte red = (png_byte)(trans_color->red & 0xff);
              png_byte green = (png_byte)(trans_color->green & 0xff);
              png_byte blue = (png_byte)(trans_color->blue & 0xff);
              sp = row + (png_size_t)row_info->rowbytes - 1;
              dp = row + (png_size_t)(row_width << 2) - 1;
              for (i = 0; i < row_width; i++)
              {
                 if (*(sp - 2) == red && *(sp - 1) == green && *(sp) == blue)
                    *dp-- = 0;
  
                 else
                    *dp-- = 0xff;
  
                 *dp-- = *sp--;
                 *dp-- = *sp--;
                 *dp-- = *sp--;
              }
           }
           else if (row_info->bit_depth == 16)
           {
              png_byte red_high = (png_byte)((trans_color->red >> 8) & 0xff);
              png_byte green_high = (png_byte)((trans_color->green >> 8) & 0xff);
              png_byte blue_high = (png_byte)((trans_color->blue >> 8) & 0xff);
              png_byte red_low = (png_byte)(trans_color->red & 0xff);
              png_byte green_low = (png_byte)(trans_color->green & 0xff);
              png_byte blue_low = (png_byte)(trans_color->blue & 0xff);
              sp = row + row_info->rowbytes - 1;
              dp = row + (png_size_t)(row_width << 3) - 1;
              for (i = 0; i < row_width; i++)
              {
                 if (*(sp - 5) == red_high &&
                     *(sp - 4) == red_low &&
                     *(sp - 3) == green_high &&
                     *(sp - 2) == green_low &&
                     *(sp - 1) == blue_high &&
                     *(sp    ) == blue_low)
                 {
                    *dp-- = 0;
                    *dp-- = 0;
                 }
  
                 else
                 {
                    *dp-- = 0xff;
                    *dp-- = 0xff;
                 }
  
                 *dp-- = *sp--;
                 *dp-- = *sp--;
                 *dp-- = *sp--;
                 *dp-- = *sp--;
                 *dp-- = *sp--;
                 *dp-- = *sp--;
              }
           }
           row_info->color_type = PNG_COLOR_TYPE_RGB_ALPHA;
           row_info->channels = 4;
           row_info->pixel_depth = (png_byte)(row_info->bit_depth << 2);
           row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
        }
     }
  }
  #endif
  
  #ifdef PNG_READ_EXPAND_16_SUPPORTED
  /* If the bit depth is 8 and the color type is not a palette type expand the
   * whole row to 16 bits.  Has no effect otherwise.
   */
  void /* PRIVATE */
  png_do_expand_16(png_row_infop row_info, png_bytep row)
  {
     if (row_info->bit_depth == 8 &&
        row_info->color_type != PNG_COLOR_TYPE_PALETTE)
     {
        /* The row have a sequence of bytes containing [0..255] and we need
         * to turn it into another row containing [0..65535], to do this we
         * calculate:
         *
         *  (input / 255) * 65535
         *
         *  Which happens to be exactly input * 257 and this can be achieved
         *  simply by byte replication in place (copying backwards).
         */
        png_byte *sp = row + row_info->rowbytes; /* source, last byte + 1 */
        png_byte *dp = sp + row_info->rowbytes;  /* destination, end + 1 */
        while (dp > sp)
           dp[-2] = dp[-1] = *--sp, dp -= 2;
  
        row_info->rowbytes *= 2;
        row_info->bit_depth = 16;
        row_info->pixel_depth = (png_byte)(row_info->channels * 16);
     }
  }
  #endif
  
  #ifdef PNG_READ_QUANTIZE_SUPPORTED
  void /* PRIVATE */
  png_do_quantize(png_row_infop row_info, png_bytep row,
      png_const_bytep palette_lookup, png_const_bytep quantize_lookup)
  {
     png_bytep sp, dp;
     png_uint_32 i;
     png_uint_32 row_width=row_info->width;
  
     png_debug(1, "in png_do_quantize");
  
     if (row_info->bit_depth == 8)
     {
        if (row_info->color_type == PNG_COLOR_TYPE_RGB && palette_lookup)
        {
           int r, g, b, p;
           sp = row;
           dp = row;
           for (i = 0; i < row_width; i++)
           {
              r = *sp++;
              g = *sp++;
              b = *sp++;
  
              /* This looks real messy, but the compiler will reduce
               * it down to a reasonable formula.  For example, with
               * 5 bits per color, we get:
               * p = (((r >> 3) & 0x1f) << 10) |
               *    (((g >> 3) & 0x1f) << 5) |
               *    ((b >> 3) & 0x1f);
               */
              p = (((r >> (8 - PNG_QUANTIZE_RED_BITS)) &
                  ((1 << PNG_QUANTIZE_RED_BITS) - 1)) <<
                  (PNG_QUANTIZE_GREEN_BITS + PNG_QUANTIZE_BLUE_BITS)) |
                  (((g >> (8 - PNG_QUANTIZE_GREEN_BITS)) &
                  ((1 << PNG_QUANTIZE_GREEN_BITS) - 1)) <<
                  (PNG_QUANTIZE_BLUE_BITS)) |
                  ((b >> (8 - PNG_QUANTIZE_BLUE_BITS)) &
                  ((1 << PNG_QUANTIZE_BLUE_BITS) - 1));
  
              *dp++ = palette_lookup[p];
           }
  
           row_info->color_type = PNG_COLOR_TYPE_PALETTE;
           row_info->channels = 1;
           row_info->pixel_depth = row_info->bit_depth;
           row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
        }
  
        else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA &&
           palette_lookup != NULL)
        {
           int r, g, b, p;
           sp = row;
           dp = row;
           for (i = 0; i < row_width; i++)
           {
              r = *sp++;
              g = *sp++;
              b = *sp++;
              sp++;
  
              p = (((r >> (8 - PNG_QUANTIZE_RED_BITS)) &
                  ((1 << PNG_QUANTIZE_RED_BITS) - 1)) <<
                  (PNG_QUANTIZE_GREEN_BITS + PNG_QUANTIZE_BLUE_BITS)) |
                  (((g >> (8 - PNG_QUANTIZE_GREEN_BITS)) &
                  ((1 << PNG_QUANTIZE_GREEN_BITS) - 1)) <<
                  (PNG_QUANTIZE_BLUE_BITS)) |
                  ((b >> (8 - PNG_QUANTIZE_BLUE_BITS)) &
                  ((1 << PNG_QUANTIZE_BLUE_BITS) - 1));
  
              *dp++ = palette_lookup[p];
           }
  
           row_info->color_type = PNG_COLOR_TYPE_PALETTE;
           row_info->channels = 1;
           row_info->pixel_depth = row_info->bit_depth;
           row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth, row_width);
        }
  
        else if (row_info->color_type == PNG_COLOR_TYPE_PALETTE &&
           quantize_lookup)
        {
           sp = row;
  
           for (i = 0; i < row_width; i++, sp++)
           {
              *sp = quantize_lookup[*sp];
           }
        }
     }
  }
  #endif /* PNG_READ_QUANTIZE_SUPPORTED */
  #endif /* PNG_READ_TRANSFORMS_SUPPORTED */
  
  #ifdef PNG_MNG_FEATURES_SUPPORTED
  /* Undoes intrapixel differencing  */
  void /* PRIVATE */
  png_do_read_intrapixel(png_row_infop row_info, png_bytep row)
  {
     png_debug(1, "in png_do_read_intrapixel");
  
     if (
         (row_info->color_type & PNG_COLOR_MASK_COLOR))
     {
        int bytes_per_pixel;
        png_uint_32 row_width = row_info->width;
  
        if (row_info->bit_depth == 8)
        {
           png_bytep rp;
           png_uint_32 i;
  
           if (row_info->color_type == PNG_COLOR_TYPE_RGB)
              bytes_per_pixel = 3;
  
           else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
              bytes_per_pixel = 4;
  
           else
              return;
  
           for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
           {
              *(rp) = (png_byte)((256 + *rp + *(rp + 1)) & 0xff);
              *(rp+2) = (png_byte)((256 + *(rp + 2) + *(rp + 1)) & 0xff);
           }
        }
        else if (row_info->bit_depth == 16)
        {
           png_bytep rp;
           png_uint_32 i;
  
           if (row_info->color_type == PNG_COLOR_TYPE_RGB)
              bytes_per_pixel = 6;
  
           else if (row_info->color_type == PNG_COLOR_TYPE_RGB_ALPHA)
              bytes_per_pixel = 8;
  
           else
              return;
  
           for (i = 0, rp = row; i < row_width; i++, rp += bytes_per_pixel)
           {
              png_uint_32 s0   = (*(rp    ) << 8) | *(rp + 1);
              png_uint_32 s1   = (*(rp + 2) << 8) | *(rp + 3);
              png_uint_32 s2   = (*(rp + 4) << 8) | *(rp + 5);
              png_uint_32 red  = (s0 + s1 + 65536) & 0xffff;
              png_uint_32 blue = (s2 + s1 + 65536) & 0xffff;
              *(rp    ) = (png_byte)((red >> 8) & 0xff);
              *(rp + 1) = (png_byte)(red & 0xff);
              *(rp + 4) = (png_byte)((blue >> 8) & 0xff);
              *(rp + 5) = (png_byte)(blue & 0xff);
           }
        }
     }
  }
  #endif /* PNG_MNG_FEATURES_SUPPORTED */
  #endif /* PNG_READ_SUPPORTED */
  