text: 
  /* pngwutil.c - utilities to write a PNG file
   *
   * Last changed in libpng 1.6.26 [October 20, 2016]
   * Copyright (c) 1998-2002,2004,2006-2016 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
   */
  
  #include "pngpriv.h"
  
  #ifdef PNG_WRITE_SUPPORTED
  
  #ifdef PNG_WRITE_INT_FUNCTIONS_SUPPORTED
  /* Place a 32-bit number into a buffer in PNG byte order.  We work
   * with unsigned numbers for convenience, although one supported
   * ancillary chunk uses signed (two's complement) numbers.
   */
  void PNGAPI
  png_save_uint_32(png_bytep buf, png_uint_32 i)
  {
     buf[0] = (png_byte)((i >> 24) & 0xffU);
     buf[1] = (png_byte)((i >> 16) & 0xffU);
     buf[2] = (png_byte)((i >>  8) & 0xffU);
     buf[3] = (png_byte)( i        & 0xffU);
  }
  
  /* Place a 16-bit number into a buffer in PNG byte order.
   * The parameter is declared unsigned int, not png_uint_16,
   * just to avoid potential problems on pre-ANSI C compilers.
   */
  void PNGAPI
  png_save_uint_16(png_bytep buf, unsigned int i)
  {
     buf[0] = (png_byte)((i >> 8) & 0xffU);
     buf[1] = (png_byte)( i       & 0xffU);
  }
  #endif
  
  /* Simple function to write the signature.  If we have already written
   * the magic bytes of the signature, or more likely, the PNG stream is
   * being embedded into another stream and doesn't need its own signature,
   * we should call png_set_sig_bytes() to tell libpng how many of the
   * bytes have already been written.
   */
  void PNGAPI
  png_write_sig(png_structrp png_ptr)
  {
     png_byte png_signature[8] = {137, 80, 78, 71, 13, 10, 26, 10};
  
  #ifdef PNG_IO_STATE_SUPPORTED
     /* Inform the I/O callback that the signature is being written */
     png_ptr->io_state = PNG_IO_WRITING | PNG_IO_SIGNATURE;
  #endif
  
     /* Write the rest of the 8 byte signature */
     png_write_data(png_ptr, &png_signature[png_ptr->sig_bytes],
         (png_size_t)(8 - png_ptr->sig_bytes));
  
     if (png_ptr->sig_bytes < 3)
        png_ptr->mode |= PNG_HAVE_PNG_SIGNATURE;
  }
  
  /* Write the start of a PNG chunk.  The type is the chunk type.
   * The total_length is the sum of the lengths of all the data you will be
   * passing in png_write_chunk_data().
   */
  static void
  png_write_chunk_header(png_structrp png_ptr, png_uint_32 chunk_name,
      png_uint_32 length)
  {
     png_byte buf[8];
  
  #if defined(PNG_DEBUG) && (PNG_DEBUG > 0)
     PNG_CSTRING_FROM_CHUNK(buf, chunk_name);
     png_debug2(0, "Writing %s chunk, length = %lu", buf, (unsigned long)length);
  #endif
  
     if (png_ptr == NULL)
        return;
  
  #ifdef PNG_IO_STATE_SUPPORTED
     /* Inform the I/O callback that the chunk header is being written.
      * PNG_IO_CHUNK_HDR requires a single I/O call.
      */
     png_ptr->io_state = PNG_IO_WRITING | PNG_IO_CHUNK_HDR;
  #endif
  
     /* Write the length and the chunk name */
     png_save_uint_32(buf, length);
     png_save_uint_32(buf + 4, chunk_name);
     png_write_data(png_ptr, buf, 8);
  
     /* Put the chunk name into png_ptr->chunk_name */
     png_ptr->chunk_name = chunk_name;
  
     /* Reset the crc and run it over the chunk name */
     png_reset_crc(png_ptr);
  
     png_calculate_crc(png_ptr, buf + 4, 4);
  
  #ifdef PNG_IO_STATE_SUPPORTED
     /* Inform the I/O callback that chunk data will (possibly) be written.
      * PNG_IO_CHUNK_DATA does NOT require a specific number of I/O calls.
      */
     png_ptr->io_state = PNG_IO_WRITING | PNG_IO_CHUNK_DATA;
  #endif
  }
  
  void PNGAPI
  png_write_chunk_start(png_structrp png_ptr, png_const_bytep chunk_string,
      png_uint_32 length)
  {
     png_write_chunk_header(png_ptr, PNG_CHUNK_FROM_STRING(chunk_string), length);
  }
  
  /* Write the data of a PNG chunk started with png_write_chunk_header().
   * Note that multiple calls to this function are allowed, and that the
   * sum of the lengths from these calls *must* add up to the total_length
   * given to png_write_chunk_header().
   */
  void PNGAPI
  png_write_chunk_data(png_structrp png_ptr, png_const_bytep data,
      png_size_t length)
  {
     /* Write the data, and run the CRC over it */
     if (png_ptr == NULL)
        return;
  
     if (data != NULL && length > 0)
     {
        png_write_data(png_ptr, data, length);
  
        /* Update the CRC after writing the data,
         * in case the user I/O routine alters it.
         */
        png_calculate_crc(png_ptr, data, length);
     }
  }
  
  /* Finish a chunk started with png_write_chunk_header(). */
  void PNGAPI
  png_write_chunk_end(png_structrp png_ptr)
  {
     png_byte buf[4];
  
     if (png_ptr == NULL) return;
  
  #ifdef PNG_IO_STATE_SUPPORTED
     /* Inform the I/O callback that the chunk CRC is being written.
      * PNG_IO_CHUNK_CRC requires a single I/O function call.
      */
     png_ptr->io_state = PNG_IO_WRITING | PNG_IO_CHUNK_CRC;
  #endif
  
     /* Write the crc in a single operation */
     png_save_uint_32(buf, png_ptr->crc);
  
     png_write_data(png_ptr, buf, (png_size_t)4);
  }
  
  /* Write a PNG chunk all at once.  The type is an array of ASCII characters
   * representing the chunk name.  The array must be at least 4 bytes in
   * length, and does not need to be null terminated.  To be safe, pass the
   * pre-defined chunk names here, and if you need a new one, define it
   * where the others are defined.  The length is the length of the data.
   * All the data must be present.  If that is not possible, use the
   * png_write_chunk_start(), png_write_chunk_data(), and png_write_chunk_end()
   * functions instead.
   */
  static void
  png_write_complete_chunk(png_structrp png_ptr, png_uint_32 chunk_name,
      png_const_bytep data, png_size_t length)
  {
     if (png_ptr == NULL)
        return;
  
     /* On 64-bit architectures 'length' may not fit in a png_uint_32. */
     if (length > PNG_UINT_31_MAX)
        png_error(png_ptr, "length exceeds PNG maximum");
  
     png_write_chunk_header(png_ptr, chunk_name, (png_uint_32)length);
     png_write_chunk_data(png_ptr, data, length);
     png_write_chunk_end(png_ptr);
  }
  
  /* This is the API that calls the internal function above. */
  void PNGAPI
  png_write_chunk(png_structrp png_ptr, png_const_bytep chunk_string,
      png_const_bytep data, png_size_t length)
  {
     png_write_complete_chunk(png_ptr, PNG_CHUNK_FROM_STRING(chunk_string), data,
         length);
  }
  
  /* This is used below to find the size of an image to pass to png_deflate_claim,
   * so it only needs to be accurate if the size is less than 16384 bytes (the
   * point at which a lower LZ window size can be used.)
   */
  static png_alloc_size_t
  png_image_size(png_structrp png_ptr)
  {
     /* Only return sizes up to the maximum of a png_uint_32; do this by limiting
      * the width and height used to 15 bits.
      */
     png_uint_32 h = png_ptr->height;
  
     if (png_ptr->rowbytes < 32768 && h < 32768)
     {
        if (png_ptr->interlaced != 0)
        {
           /* Interlacing makes the image larger because of the replication of
            * both the filter byte and the padding to a byte boundary.
            */
           png_uint_32 w = png_ptr->width;
           unsigned int pd = png_ptr->pixel_depth;
           png_alloc_size_t cb_base;
           int pass;
  
           for (cb_base=0, pass=0; pass<=6; ++pass)
           {
              png_uint_32 pw = PNG_PASS_COLS(w, pass);
  
              if (pw > 0)
                 cb_base += (PNG_ROWBYTES(pd, pw)+1) * PNG_PASS_ROWS(h, pass);
           }
  
           return cb_base;
        }
  
        else
           return (png_ptr->rowbytes+1) * h;
     }
  
     else
        return 0xffffffffU;
  }
  
  #ifdef PNG_WRITE_OPTIMIZE_CMF_SUPPORTED
     /* This is the code to hack the first two bytes of the deflate stream (the
      * deflate header) to correct the windowBits value to match the actual data
      * size.  Note that the second argument is the *uncompressed* size but the
      * first argument is the *compressed* data (and it must be deflate
      * compressed.)
      */
  static void
  optimize_cmf(png_bytep data, png_alloc_size_t data_size)
  {
     /* Optimize the CMF field in the zlib stream.  The resultant zlib stream is
      * still compliant to the stream specification.
      */
     if (data_size <= 16384) /* else windowBits must be 15 */
     {
        unsigned int z_cmf = data[0];  /* zlib compression method and flags */
  
        if ((z_cmf & 0x0f) == 8 && (z_cmf & 0xf0) <= 0x70)
        {
           unsigned int z_cinfo;
           unsigned int half_z_window_size;
  
           z_cinfo = z_cmf >> 4;
           half_z_window_size = 1U << (z_cinfo + 7);
  
           if (data_size <= half_z_window_size) /* else no change */
           {
              unsigned int tmp;
  
              do
              {
                 half_z_window_size >>= 1;
                 --z_cinfo;
              }
              while (z_cinfo > 0 && data_size <= half_z_window_size);
  
              z_cmf = (z_cmf & 0x0f) | (z_cinfo << 4);
  
              data[0] = (png_byte)z_cmf;
              tmp = data[1] & 0xe0;
              tmp += 0x1f - ((z_cmf << 8) + tmp) % 0x1f;
              data[1] = (png_byte)tmp;
           }
        }
     }
  }
  #endif /* WRITE_OPTIMIZE_CMF */
  
  /* Initialize the compressor for the appropriate type of compression. */
  static int
  png_deflate_claim(png_structrp png_ptr, png_uint_32 owner,
      png_alloc_size_t data_size)
  {
     if (png_ptr->zowner != 0)
     {
  #if defined(PNG_WARNINGS_SUPPORTED) || defined(PNG_ERROR_TEXT_SUPPORTED)
        char msg[64];
  
        PNG_STRING_FROM_CHUNK(msg, owner);
        msg[4] = ':';
        msg[5] = ' ';
        PNG_STRING_FROM_CHUNK(msg+6, png_ptr->zowner);
        /* So the message that results is "<chunk> using zstream"; this is an
         * internal error, but is very useful for debugging.  i18n requirements
         * are minimal.
         */
        (void)png_safecat(msg, (sizeof msg), 10, " using zstream");
  #endif
  #if PNG_RELEASE_BUILD
           png_warning(png_ptr, msg);
  
           /* Attempt sane error recovery */
           if (png_ptr->zowner == png_IDAT) /* don't steal from IDAT */
           {
              png_ptr->zstream.msg = PNGZ_MSG_CAST("in use by IDAT");
              return Z_STREAM_ERROR;
           }
  
           png_ptr->zowner = 0;
  #else
           png_error(png_ptr, msg);
  #endif
     }
  
     {
        int level = png_ptr->zlib_level;
        int method = png_ptr->zlib_method;
        int windowBits = png_ptr->zlib_window_bits;
        int memLevel = png_ptr->zlib_mem_level;
        int strategy; /* set below */
        int ret; /* zlib return code */
  
        if (owner == png_IDAT)
        {
           if ((png_ptr->flags & PNG_FLAG_ZLIB_CUSTOM_STRATEGY) != 0)
              strategy = png_ptr->zlib_strategy;
  
           else if (png_ptr->do_filter != PNG_FILTER_NONE)
              strategy = PNG_Z_DEFAULT_STRATEGY;
  
           else
              strategy = PNG_Z_DEFAULT_NOFILTER_STRATEGY;
        }
  
        else
        {
  #ifdef PNG_WRITE_CUSTOMIZE_ZTXT_COMPRESSION_SUPPORTED
              level = png_ptr->zlib_text_level;
              method = png_ptr->zlib_text_method;
              windowBits = png_ptr->zlib_text_window_bits;
              memLevel = png_ptr->zlib_text_mem_level;
              strategy = png_ptr->zlib_text_strategy;
  #else
              /* If customization is not supported the values all come from the
               * IDAT values except for the strategy, which is fixed to the
               * default.  (This is the pre-1.6.0 behavior too, although it was
               * implemented in a very different way.)
               */
              strategy = Z_DEFAULT_STRATEGY;
  #endif
        }
  
        /* Adjust 'windowBits' down if larger than 'data_size'; to stop this
         * happening just pass 32768 as the data_size parameter.  Notice that zlib
         * requires an extra 262 bytes in the window in addition to the data to be
         * able to see the whole of the data, so if data_size+262 takes us to the
         * next windowBits size we need to fix up the value later.  (Because even
         * though deflate needs the extra window, inflate does not!)
         */
        if (data_size <= 16384)
        {
           /* IMPLEMENTATION NOTE: this 'half_window_size' stuff is only here to
            * work round a Microsoft Visual C misbehavior which, contrary to C-90,
            * widens the result of the following shift to 64-bits if (and,
            * apparently, only if) it is used in a test.
            */
           unsigned int half_window_size = 1U << (windowBits-1);
  
           while (data_size + 262 <= half_window_size)
           {
              half_window_size >>= 1;
              --windowBits;
           }
        }
  
        /* Check against the previous initialized values, if any. */
        if ((png_ptr->flags & PNG_FLAG_ZSTREAM_INITIALIZED) != 0 &&
           (png_ptr->zlib_set_level != level ||
           png_ptr->zlib_set_method != method ||
           png_ptr->zlib_set_window_bits != windowBits ||
           png_ptr->zlib_set_mem_level != memLevel ||
           png_ptr->zlib_set_strategy != strategy))
        {
           if (deflateEnd(&png_ptr->zstream) != Z_OK)
              png_warning(png_ptr, "deflateEnd failed (ignored)");
  
           png_ptr->flags &= ~PNG_FLAG_ZSTREAM_INITIALIZED;
        }
  
        /* For safety clear out the input and output pointers (currently zlib
         * doesn't use them on Init, but it might in the future).
         */
        png_ptr->zstream.next_in = NULL;
        png_ptr->zstream.avail_in = 0;
        png_ptr->zstream.next_out = NULL;
        png_ptr->zstream.avail_out = 0;
  
        /* Now initialize if required, setting the new parameters, otherwise just
         * do a simple reset to the previous parameters.
         */
        if ((png_ptr->flags & PNG_FLAG_ZSTREAM_INITIALIZED) != 0)
           ret = deflateReset(&png_ptr->zstream);
  
        else
        {
           ret = deflateInit2(&png_ptr->zstream, level, method, windowBits,
               memLevel, strategy);
  
           if (ret == Z_OK)
              png_ptr->flags |= PNG_FLAG_ZSTREAM_INITIALIZED;
        }
  
        /* The return code is from either deflateReset or deflateInit2; they have
         * pretty much the same set of error codes.
         */
        if (ret == Z_OK)
           png_ptr->zowner = owner;
  
        else
           png_zstream_error(png_ptr, ret);
  
        return ret;
     }
  }
  
  /* Clean up (or trim) a linked list of compression buffers. */
  void /* PRIVATE */
  png_free_buffer_list(png_structrp png_ptr, png_compression_bufferp *listp)
  {
     png_compression_bufferp list = *listp;
  
     if (list != NULL)
     {
        *listp = NULL;
  
        do
        {
           png_compression_bufferp next = list->next;
  
           png_free(png_ptr, list);
           list = next;
        }
        while (list != NULL);
     }
  }
  
  #ifdef PNG_WRITE_COMPRESSED_TEXT_SUPPORTED
  /* This pair of functions encapsulates the operation of (a) compressing a
   * text string, and (b) issuing it later as a series of chunk data writes.
   * The compression_state structure is shared context for these functions
   * set up by the caller to allow access to the relevant local variables.
   *
   * compression_buffer (new in 1.6.0) is just a linked list of zbuffer_size
   * temporary buffers.  From 1.6.0 it is retained in png_struct so that it will
   * be correctly freed in the event of a write error (previous implementations
   * just leaked memory.)
   */
  typedef struct
  {
     png_const_bytep      input;        /* The uncompressed input data */
     png_alloc_size_t     input_len;    /* Its length */
     png_uint_32          output_len;   /* Final compressed length */
     png_byte             output[1024]; /* First block of output */
  } compression_state;
  
  static void
  png_text_compress_init(compression_state *comp, png_const_bytep input,
      png_alloc_size_t input_len)
  {
     comp->input = input;
     comp->input_len = input_len;
     comp->output_len = 0;
  }
  
  /* Compress the data in the compression state input */
  static int
  png_text_compress(png_structrp png_ptr, png_uint_32 chunk_name,
      compression_state *comp, png_uint_32 prefix_len)
  {
     int ret;
  
     /* To find the length of the output it is necessary to first compress the
      * input. The result is buffered rather than using the two-pass algorithm
      * that is used on the inflate side; deflate is assumed to be slower and a
      * PNG writer is assumed to have more memory available than a PNG reader.
      *
      * IMPLEMENTATION NOTE: the zlib API deflateBound() can be used to find an
      * upper limit on the output size, but it is always bigger than the input
      * size so it is likely to be more efficient to use this linked-list
      * approach.
      */
     ret = png_deflate_claim(png_ptr, chunk_name, comp->input_len);
  
     if (ret != Z_OK)
        return ret;
  
     /* Set up the compression buffers, we need a loop here to avoid overflowing a
      * uInt.  Use ZLIB_IO_MAX to limit the input.  The output is always limited
      * by the output buffer size, so there is no need to check that.  Since this
      * is ANSI-C we know that an 'int', hence a uInt, is always at least 16 bits
      * in size.
      */
     {
        png_compression_bufferp *end = &png_ptr->zbuffer_list;
        png_alloc_size_t input_len = comp->input_len; /* may be zero! */
        png_uint_32 output_len;
  
        /* zlib updates these for us: */
        png_ptr->zstream.next_in = PNGZ_INPUT_CAST(comp->input);
        png_ptr->zstream.avail_in = 0; /* Set below */
        png_ptr->zstream.next_out = comp->output;
        png_ptr->zstream.avail_out = (sizeof comp->output);
  
        output_len = png_ptr->zstream.avail_out;
  
        do
        {
           uInt avail_in = ZLIB_IO_MAX;
  
           if (avail_in > input_len)
              avail_in = (uInt)input_len;
  
           input_len -= avail_in;
  
           png_ptr->zstream.avail_in = avail_in;
  
           if (png_ptr->zstream.avail_out == 0)
           {
              png_compression_buffer *next;
  
              /* Chunk data is limited to 2^31 bytes in length, so the prefix
               * length must be counted here.
               */
              if (output_len + prefix_len > PNG_UINT_31_MAX)
              {
                 ret = Z_MEM_ERROR;
                 break;
              }
  
              /* Need a new (malloc'ed) buffer, but there may be one present
               * already.
               */
              next = *end;
              if (next == NULL)
              {
                 next = png_voidcast(png_compression_bufferp, png_malloc_base
                    (png_ptr, PNG_COMPRESSION_BUFFER_SIZE(png_ptr)));
  
                 if (next == NULL)
                 {
                    ret = Z_MEM_ERROR;
                    break;
                 }
  
                 /* Link in this buffer (so that it will be freed later) */
                 next->next = NULL;
                 *end = next;
              }
  
              png_ptr->zstream.next_out = next->output;
              png_ptr->zstream.avail_out = png_ptr->zbuffer_size;
              output_len += png_ptr->zstream.avail_out;
  
              /* Move 'end' to the next buffer pointer. */
              end = &next->next;
           }
  
           /* Compress the data */
           ret = deflate(&png_ptr->zstream,
               input_len > 0 ? Z_NO_FLUSH : Z_FINISH);
  
           /* Claw back input data that was not consumed (because avail_in is
            * reset above every time round the loop).
            */
           input_len += png_ptr->zstream.avail_in;
           png_ptr->zstream.avail_in = 0; /* safety */
        }
        while (ret == Z_OK);
  
        /* There may be some space left in the last output buffer. This needs to
         * be subtracted from output_len.
         */
        output_len -= png_ptr->zstream.avail_out;
        png_ptr->zstream.avail_out = 0; /* safety */
        comp->output_len = output_len;
  
        /* Now double check the output length, put in a custom message if it is
         * too long.  Otherwise ensure the z_stream::msg pointer is set to
         * something.
         */
        if (output_len + prefix_len >= PNG_UINT_31_MAX)
        {
           png_ptr->zstream.msg = PNGZ_MSG_CAST("compressed data too long");
           ret = Z_MEM_ERROR;
        }
  
        else
           png_zstream_error(png_ptr, ret);
  
        /* Reset zlib for another zTXt/iTXt or image data */
        png_ptr->zowner = 0;
  
        /* The only success case is Z_STREAM_END, input_len must be 0; if not this
         * is an internal error.
         */
        if (ret == Z_STREAM_END && input_len == 0)
        {
  #ifdef PNG_WRITE_OPTIMIZE_CMF_SUPPORTED
           /* Fix up the deflate header, if required */
           optimize_cmf(comp->output, comp->input_len);
  #endif
           /* But Z_OK is returned, not Z_STREAM_END; this allows the claim
            * function above to return Z_STREAM_END on an error (though it never
            * does in the current versions of zlib.)
            */
           return Z_OK;
        }
  
        else
           return ret;
     }
  }
  
  /* Ship the compressed text out via chunk writes */
  static void
  png_write_compressed_data_out(png_structrp png_ptr, compression_state *comp)
  {
     png_uint_32 output_len = comp->output_len;
     png_const_bytep output = comp->output;
     png_uint_32 avail = (sizeof comp->output);
     png_compression_buffer *next = png_ptr->zbuffer_list;
  
     for (;;)
     {
        if (avail > output_len)
           avail = output_len;
  
        png_write_chunk_data(png_ptr, output, avail);
  
        output_len -= avail;
  
        if (output_len == 0 || next == NULL)
           break;
  
        avail = png_ptr->zbuffer_size;
        output = next->output;
        next = next->next;
     }
  
     /* This is an internal error; 'next' must have been NULL! */
     if (output_len > 0)
        png_error(png_ptr, "error writing ancillary chunked compressed data");
  }
  #endif /* WRITE_COMPRESSED_TEXT */
  
  /* Write the IHDR chunk, and update the png_struct with the necessary
   * information.  Note that the rest of this code depends upon this
   * information being correct.
   */
  void /* PRIVATE */
  png_write_IHDR(png_structrp png_ptr, png_uint_32 width, png_uint_32 height,
      int bit_depth, int color_type, int compression_type, int filter_type,
      int interlace_type)
  {
     png_byte buf[13]; /* Buffer to store the IHDR info */
  
     png_debug(1, "in png_write_IHDR");
  
     /* Check that we have valid input data from the application info */
     switch (color_type)
     {
        case PNG_COLOR_TYPE_GRAY:
           switch (bit_depth)
           {
              case 1:
              case 2:
              case 4:
              case 8:
  #ifdef PNG_WRITE_16BIT_SUPPORTED
              case 16:
  #endif
                 png_ptr->channels = 1; break;
  
              default:
                 png_error(png_ptr,
                     "Invalid bit depth for grayscale image");
           }
           break;
  
        case PNG_COLOR_TYPE_RGB:
  #ifdef PNG_WRITE_16BIT_SUPPORTED
           if (bit_depth != 8 && bit_depth != 16)
  #else
           if (bit_depth != 8)
  #endif
              png_error(png_ptr, "Invalid bit depth for RGB image");
  
           png_ptr->channels = 3;
           break;
  
        case PNG_COLOR_TYPE_PALETTE:
           switch (bit_depth)
           {
              case 1:
              case 2:
              case 4:
              case 8:
                 png_ptr->channels = 1;
                 break;
  
              default:
                 png_error(png_ptr, "Invalid bit depth for paletted image");
           }
           break;
  
        case PNG_COLOR_TYPE_GRAY_ALPHA:
           if (bit_depth != 8 && bit_depth != 16)
              png_error(png_ptr, "Invalid bit depth for grayscale+alpha image");
  
           png_ptr->channels = 2;
           break;
  
        case PNG_COLOR_TYPE_RGB_ALPHA:
  #ifdef PNG_WRITE_16BIT_SUPPORTED
           if (bit_depth != 8 && bit_depth != 16)
  #else
           if (bit_depth != 8)
  #endif
              png_error(png_ptr, "Invalid bit depth for RGBA image");
  
           png_ptr->channels = 4;
           break;
  
        default:
           png_error(png_ptr, "Invalid image color type specified");
     }
  
     if (compression_type != PNG_COMPRESSION_TYPE_BASE)
     {
        png_warning(png_ptr, "Invalid compression type specified");
        compression_type = PNG_COMPRESSION_TYPE_BASE;
     }
  
     /* Write filter_method 64 (intrapixel differencing) only if
      * 1. Libpng was compiled with PNG_MNG_FEATURES_SUPPORTED and
      * 2. Libpng did not write a PNG signature (this filter_method is only
      *    used in PNG datastreams that are embedded in MNG datastreams) and
      * 3. The application called png_permit_mng_features with a mask that
      *    included PNG_FLAG_MNG_FILTER_64 and
      * 4. The filter_method is 64 and
      * 5. The color_type is RGB or RGBA
      */
     if (
  #ifdef PNG_MNG_FEATURES_SUPPORTED
         !((png_ptr->mng_features_permitted & PNG_FLAG_MNG_FILTER_64) != 0 &&
         ((png_ptr->mode & PNG_HAVE_PNG_SIGNATURE) == 0) &&
         (color_type == PNG_COLOR_TYPE_RGB ||
          color_type == PNG_COLOR_TYPE_RGB_ALPHA) &&
         (filter_type == PNG_INTRAPIXEL_DIFFERENCING)) &&
  #endif
         filter_type != PNG_FILTER_TYPE_BASE)
     {
        png_warning(png_ptr, "Invalid filter type specified");
        filter_type = PNG_FILTER_TYPE_BASE;
     }
  
  #ifdef PNG_WRITE_INTERLACING_SUPPORTED
     if (interlace_type != PNG_INTERLACE_NONE &&
         interlace_type != PNG_INTERLACE_ADAM7)
     {
        png_warning(png_ptr, "Invalid interlace type specified");
        interlace_type = PNG_INTERLACE_ADAM7;
     }
  #else
     interlace_type=PNG_INTERLACE_NONE;
  #endif
  
     /* Save the relevant information */
     png_ptr->bit_depth = (png_byte)bit_depth;
     png_ptr->color_type = (png_byte)color_type;
     png_ptr->interlaced = (png_byte)interlace_type;
  #ifdef PNG_MNG_FEATURES_SUPPORTED
     png_ptr->filter_type = (png_byte)filter_type;
  #endif
     png_ptr->compression_type = (png_byte)compression_type;
     png_ptr->width = width;
     png_ptr->height = height;
  
     png_ptr->pixel_depth = (png_byte)(bit_depth * png_ptr->channels);
     png_ptr->rowbytes = PNG_ROWBYTES(png_ptr->pixel_depth, width);
     /* Set the usr info, so any transformations can modify it */
     png_ptr->usr_width = png_ptr->width;
     png_ptr->usr_bit_depth = png_ptr->bit_depth;
     png_ptr->usr_channels = png_ptr->channels;
  
     /* Pack the header information into the buffer */
     png_save_uint_32(buf, width);
     png_save_uint_32(buf + 4, height);
     buf[8] = (png_byte)bit_depth;
     buf[9] = (png_byte)color_type;
     buf[10] = (png_byte)compression_type;
     buf[11] = (png_byte)filter_type;
     buf[12] = (png_byte)interlace_type;
  
     /* Write the chunk */
     png_write_complete_chunk(png_ptr, png_IHDR, buf, (png_size_t)13);
  
     if ((png_ptr->do_filter) == PNG_NO_FILTERS)
     {
        if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE ||
            png_ptr->bit_depth < 8)
           png_ptr->do_filter = PNG_FILTER_NONE;
  
        else
           png_ptr->do_filter = PNG_ALL_FILTERS;
     }
  
     png_ptr->mode = PNG_HAVE_IHDR; /* not READY_FOR_ZTXT */
  }
  
  /* Write the palette.  We are careful not to trust png_color to be in the
   * correct order for PNG, so people can redefine it to any convenient
   * structure.
   */
  void /* PRIVATE */
  png_write_PLTE(png_structrp png_ptr, png_const_colorp palette,
      png_uint_32 num_pal)
  {
     png_uint_32 max_palette_length, i;
     png_const_colorp pal_ptr;
     png_byte buf[3];
  
     png_debug(1, "in png_write_PLTE");
  
     max_palette_length = (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE) ?
        (1 << png_ptr->bit_depth) : PNG_MAX_PALETTE_LENGTH;
  
     if ((
  #ifdef PNG_MNG_FEATURES_SUPPORTED
         (png_ptr->mng_features_permitted & PNG_FLAG_MNG_EMPTY_PLTE) == 0 &&
  #endif
         num_pal == 0) || num_pal > max_palette_length)
     {
        if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
        {
           png_error(png_ptr, "Invalid number of colors in palette");
        }
  
        else
        {
           png_warning(png_ptr, "Invalid number of colors in palette");
           return;
        }
     }
  
     if ((png_ptr->color_type & PNG_COLOR_MASK_COLOR) == 0)
     {
        png_warning(png_ptr,
            "Ignoring request to write a PLTE chunk in grayscale PNG");
  
        return;
     }
  
     png_ptr->num_palette = (png_uint_16)num_pal;
     png_debug1(3, "num_palette = %d", png_ptr->num_palette);
  
     png_write_chunk_header(png_ptr, png_PLTE, (png_uint_32)(num_pal * 3));
  #ifdef PNG_POINTER_INDEXING_SUPPORTED
  
     for (i = 0, pal_ptr = palette; i < num_pal; i++, pal_ptr++)
     {
        buf[0] = pal_ptr->red;
        buf[1] = pal_ptr->green;
        buf[2] = pal_ptr->blue;
        png_write_chunk_data(png_ptr, buf, (png_size_t)3);
     }
  
  #else
     /* This is a little slower but some buggy compilers need to do this
      * instead
      */
     pal_ptr=palette;
  
     for (i = 0; i < num_pal; i++)
     {
        buf[0] = pal_ptr[i].red;
        buf[1] = pal_ptr[i].green;
        buf[2] = pal_ptr[i].blue;
        png_write_chunk_data(png_ptr, buf, (png_size_t)3);
     }
  
  #endif
     png_write_chunk_end(png_ptr);
     png_ptr->mode |= PNG_HAVE_PLTE;
  }
  
  /* This is similar to png_text_compress, above, except that it does not require
   * all of the data at once and, instead of buffering the compressed result,
   * writes it as IDAT chunks.  Unlike png_text_compress it *can* png_error out
   * because it calls the write interface.  As a result it does its own error
   * reporting and does not return an error code.  In the event of error it will
   * just call png_error.  The input data length may exceed 32-bits.  The 'flush'
   * parameter is exactly the same as that to deflate, with the following
   * meanings:
   *
   * Z_NO_FLUSH: normal incremental output of compressed data
   * Z_SYNC_FLUSH: do a SYNC_FLUSH, used by png_write_flush
   * Z_FINISH: this is the end of the input, do a Z_FINISH and clean up
   *
   * The routine manages the acquire and release of the png_ptr->zstream by
   * checking and (at the end) clearing png_ptr->zowner; it does some sanity
   * checks on the 'mode' flags while doing this.
   */
  void /* PRIVATE */
  png_compress_IDAT(png_structrp png_ptr, png_const_bytep input,
      png_alloc_size_t input_len, int flush)
  {
     if (png_ptr->zowner != png_IDAT)
     {
        /* First time.   Ensure we have a temporary buffer for compression and
         * trim the buffer list if it has more than one entry to free memory.
         * If 'WRITE_COMPRESSED_TEXT' is not set the list will never have been
         * created at this point, but the check here is quick and safe.
         */
        if (png_ptr->zbuffer_list == NULL)
        {
           png_ptr->zbuffer_list = png_voidcast(png_compression_bufferp,
               png_malloc(png_ptr, PNG_COMPRESSION_BUFFER_SIZE(png_ptr)));
           png_ptr->zbuffer_list->next = NULL;
        }
  
        else
           png_free_buffer_list(png_ptr, &png_ptr->zbuffer_list->next);
  
        /* It is a terminal error if we can't claim the zstream. */
        if (png_deflate_claim(png_ptr, png_IDAT, png_image_size(png_ptr)) != Z_OK)
           png_error(png_ptr, png_ptr->zstream.msg);
  
        /* The output state is maintained in png_ptr->zstream, so it must be
         * initialized here after the claim.
         */
        png_ptr->zstream.next_out = png_ptr->zbuffer_list->output;
        png_ptr->zstream.avail_out = png_ptr->zbuffer_size;
     }
  
     /* Now loop reading and writing until all the input is consumed or an error
      * terminates the operation.  The _out values are maintained across calls to
      * this function, but the input must be reset each time.
      */
     png_ptr->zstream.next_in = PNGZ_INPUT_CAST(input);
     png_ptr->zstream.avail_in = 0; /* set below */
     for (;;)
     {
        int ret;
  
        /* INPUT: from the row data */
        uInt avail = ZLIB_IO_MAX;
  
        if (avail > input_len)
           avail = (uInt)input_len; /* safe because of the check */
  
        png_ptr->zstream.avail_in = avail;
        input_len -= avail;
  
        ret = deflate(&png_ptr->zstream, input_len > 0 ? Z_NO_FLUSH : flush);
  
        /* Include as-yet unconsumed input */
        input_len += png_ptr->zstream.avail_in;
        png_ptr->zstream.avail_in = 0;
  
        /* OUTPUT: write complete IDAT chunks when avail_out drops to zero. Note
         * that these two zstream fields are preserved across the calls, therefore
         * there is no need to set these up on entry to the loop.
         */
        if (png_ptr->zstream.avail_out == 0)
        {
           png_bytep data = png_ptr->zbuffer_list->output;
           uInt size = png_ptr->zbuffer_size;
  
           /* Write an IDAT containing the data then reset the buffer.  The
            * first IDAT may need deflate header optimization.
            */
  #ifdef PNG_WRITE_OPTIMIZE_CMF_SUPPORTED
              if ((png_ptr->mode & PNG_HAVE_IDAT) == 0 &&
                  png_ptr->compression_type == PNG_COMPRESSION_TYPE_BASE)
                 optimize_cmf(data, png_image_size(png_ptr));
  #endif
  
           png_write_complete_chunk(png_ptr, png_IDAT, data, size);
           png_ptr->mode |= PNG_HAVE_IDAT;
  
           png_ptr->zstream.next_out = data;
           png_ptr->zstream.avail_out = size;
  
           /* For SYNC_FLUSH or FINISH it is essential to keep calling zlib with
            * the same flush parameter until it has finished output, for NO_FLUSH
            * it doesn't matter.
            */
           if (ret == Z_OK && flush != Z_NO_FLUSH)
              continue;
        }
  
        /* The order of these checks doesn't matter much; it just affects which
         * possible error might be detected if multiple things go wrong at once.
         */
        if (ret == Z_OK) /* most likely return code! */
        {
           /* If all the input has been consumed then just return.  If Z_FINISH
            * was used as the flush parameter something has gone wrong if we get
            * here.
            */
           if (input_len == 0)
           {
              if (flush == Z_FINISH)
                 png_error(png_ptr, "Z_OK on Z_FINISH with output space");
  
              return;
           }
        }
  
        else if (ret == Z_STREAM_END && flush == Z_FINISH)
        {
           /* This is the end of the IDAT data; any pending output must be
            * flushed.  For small PNG files we may still be at the beginning.
            */
           png_bytep data = png_ptr->zbuffer_list->output;
           uInt size = png_ptr->zbuffer_size - png_ptr->zstream.avail_out;
  
  #ifdef PNG_WRITE_OPTIMIZE_CMF_SUPPORTED
           if ((png_ptr->mode & PNG_HAVE_IDAT) == 0 &&
               png_ptr->compression_type == PNG_COMPRESSION_TYPE_BASE)
              optimize_cmf(data, png_image_size(png_ptr));
  #endif
  
           png_write_complete_chunk(png_ptr, png_IDAT, data, size);
           png_ptr->zstream.avail_out = 0;
           png_ptr->zstream.next_out = NULL;
           png_ptr->mode |= PNG_HAVE_IDAT | PNG_AFTER_IDAT;
  
           png_ptr->zowner = 0; /* Release the stream */
           return;
        }
  
        else
        {
           /* This is an error condition. */
           png_zstream_error(png_ptr, ret);
           png_error(png_ptr, png_ptr->zstream.msg);
        }
     }
  }
  
  /* Write an IEND chunk */
  void /* PRIVATE */
  png_write_IEND(png_structrp png_ptr)
  {
     png_debug(1, "in png_write_IEND");
  
     png_write_complete_chunk(png_ptr, png_IEND, NULL, (png_size_t)0);
     png_ptr->mode |= PNG_HAVE_IEND;
  }
  
  #ifdef PNG_WRITE_gAMA_SUPPORTED
  /* Write a gAMA chunk */
  void /* PRIVATE */
  png_write_gAMA_fixed(png_structrp png_ptr, png_fixed_point file_gamma)
  {
     png_byte buf[4];
  
     png_debug(1, "in png_write_gAMA");
  
     /* file_gamma is saved in 1/100,000ths */
     png_save_uint_32(buf, (png_uint_32)file_gamma);
     png_write_complete_chunk(png_ptr, png_gAMA, buf, (png_size_t)4);
  }
  #endif
  
  #ifdef PNG_WRITE_sRGB_SUPPORTED
  /* Write a sRGB chunk */
  void /* PRIVATE */
  png_write_sRGB(png_structrp png_ptr, int srgb_intent)
  {
     png_byte buf[1];
  
     png_debug(1, "in png_write_sRGB");
  
     if (srgb_intent >= PNG_sRGB_INTENT_LAST)
        png_warning(png_ptr,
            "Invalid sRGB rendering intent specified");
  
     buf[0]=(png_byte)srgb_intent;
     png_write_complete_chunk(png_ptr, png_sRGB, buf, (png_size_t)1);
  }
  #endif
  
  #ifdef PNG_WRITE_iCCP_SUPPORTED
  /* Write an iCCP chunk */
  void /* PRIVATE */
  png_write_iCCP(png_structrp png_ptr, png_const_charp name,
      png_const_bytep profile)
  {
     png_uint_32 name_len;
     png_uint_32 profile_len;
     png_byte new_name[81]; /* 1 byte for the compression byte */
     compression_state comp;
     png_uint_32 temp;
  
     png_debug(1, "in png_write_iCCP");
  
     /* These are all internal problems: the profile should have been checked
      * before when it was stored.
      */
     if (profile == NULL)
        png_error(png_ptr, "No profile for iCCP chunk"); /* internal error */
  
     profile_len = png_get_uint_32(profile);
  
     if (profile_len < 132)
        png_error(png_ptr, "ICC profile too short");
  
     temp = (png_uint_32) (*(profile+8));
     if (temp > 3 && (profile_len & 0x03))
        png_error(png_ptr, "ICC profile length invalid (not a multiple of 4)");
  
     {
        png_uint_32 embedded_profile_len = png_get_uint_32(profile);
  
        if (profile_len != embedded_profile_len)
           png_error(png_ptr, "Profile length does not match profile");
     }
  
     name_len = png_check_keyword(png_ptr, name, new_name);
  
     if (name_len == 0)
        png_error(png_ptr, "iCCP: invalid keyword");
  
     new_name[++name_len] = PNG_COMPRESSION_TYPE_BASE;
  
     /* Make sure we include the NULL after the name and the compression type */
     ++name_len;
  
     png_text_compress_init(&comp, profile, profile_len);
  
     /* Allow for keyword terminator and compression byte */
     if (png_text_compress(png_ptr, png_iCCP, &comp, name_len) != Z_OK)
        png_error(png_ptr, png_ptr->zstream.msg);
  
     png_write_chunk_header(png_ptr, png_iCCP, name_len + comp.output_len);
  
     png_write_chunk_data(png_ptr, new_name, name_len);
  
     png_write_compressed_data_out(png_ptr, &comp);
  
     png_write_chunk_end(png_ptr);
  }
  #endif
  
  #ifdef PNG_WRITE_sPLT_SUPPORTED
  /* Write a sPLT chunk */
  void /* PRIVATE */
  png_write_sPLT(png_structrp png_ptr, png_const_sPLT_tp spalette)
  {
     png_uint_32 name_len;
     png_byte new_name[80];
     png_byte entrybuf[10];
     png_size_t entry_size = (spalette->depth == 8 ? 6 : 10);
     png_size_t palette_size = entry_size * (png_size_t)spalette->nentries;
     png_sPLT_entryp ep;
  #ifndef PNG_POINTER_INDEXING_SUPPORTED
     int i;
  #endif
  
     png_debug(1, "in png_write_sPLT");
  
     name_len = png_check_keyword(png_ptr, spalette->name, new_name);
  
     if (name_len == 0)
        png_error(png_ptr, "sPLT: invalid keyword");
  
     /* Make sure we include the NULL after the name */
     png_write_chunk_header(png_ptr, png_sPLT,
         (png_uint_32)(name_len + 2 + palette_size));
  
     png_write_chunk_data(png_ptr, (png_bytep)new_name,
         (png_size_t)(name_len + 1));
  
     png_write_chunk_data(png_ptr, &spalette->depth, (png_size_t)1);
  
     /* Loop through each palette entry, writing appropriately */
  #ifdef PNG_POINTER_INDEXING_SUPPORTED
     for (ep = spalette->entries; ep<spalette->entries + spalette->nentries; ep++)
     {
        if (spalette->depth == 8)
        {
           entrybuf[0] = (png_byte)ep->red;
           entrybuf[1] = (png_byte)ep->green;
           entrybuf[2] = (png_byte)ep->blue;
           entrybuf[3] = (png_byte)ep->alpha;
           png_save_uint_16(entrybuf + 4, ep->frequency);
        }
  
        else
        {
           png_save_uint_16(entrybuf + 0, ep->red);
           png_save_uint_16(entrybuf + 2, ep->green);
           png_save_uint_16(entrybuf + 4, ep->blue);
           png_save_uint_16(entrybuf + 6, ep->alpha);
           png_save_uint_16(entrybuf + 8, ep->frequency);
        }
  
        png_write_chunk_data(png_ptr, entrybuf, entry_size);
     }
  #else
     ep=spalette->entries;
     for (i = 0; i>spalette->nentries; i++)
     {
        if (spalette->depth == 8)
        {
           entrybuf[0] = (png_byte)ep[i].red;
           entrybuf[1] = (png_byte)ep[i].green;
           entrybuf[2] = (png_byte)ep[i].blue;
           entrybuf[3] = (png_byte)ep[i].alpha;
           png_save_uint_16(entrybuf + 4, ep[i].frequency);
        }
  
        else
        {
           png_save_uint_16(entrybuf + 0, ep[i].red);
           png_save_uint_16(entrybuf + 2, ep[i].green);
           png_save_uint_16(entrybuf + 4, ep[i].blue);
           png_save_uint_16(entrybuf + 6, ep[i].alpha);
           png_save_uint_16(entrybuf + 8, ep[i].frequency);
        }
  
        png_write_chunk_data(png_ptr, entrybuf, entry_size);
     }
  #endif
  
     png_write_chunk_end(png_ptr);
  }
  #endif
  
  #ifdef PNG_WRITE_sBIT_SUPPORTED
  /* Write the sBIT chunk */
  void /* PRIVATE */
  png_write_sBIT(png_structrp png_ptr, png_const_color_8p sbit, int color_type)
  {
     png_byte buf[4];
     png_size_t size;
  
     png_debug(1, "in png_write_sBIT");
  
     /* Make sure we don't depend upon the order of PNG_COLOR_8 */
     if ((color_type & PNG_COLOR_MASK_COLOR) != 0)
     {
        png_byte maxbits;
  
        maxbits = (png_byte)(color_type==PNG_COLOR_TYPE_PALETTE ? 8 :
            png_ptr->usr_bit_depth);
  
        if (sbit->red == 0 || sbit->red > maxbits ||
            sbit->green == 0 || sbit->green > maxbits ||
            sbit->blue == 0 || sbit->blue > maxbits)
        {
           png_warning(png_ptr, "Invalid sBIT depth specified");
           return;
        }
  
        buf[0] = sbit->red;
        buf[1] = sbit->green;
        buf[2] = sbit->blue;
        size = 3;
     }
  
     else
     {
        if (sbit->gray == 0 || sbit->gray > png_ptr->usr_bit_depth)
        {
           png_warning(png_ptr, "Invalid sBIT depth specified");
           return;
        }
  
        buf[0] = sbit->gray;
        size = 1;
     }
  
     if ((color_type & PNG_COLOR_MASK_ALPHA) != 0)
     {
        if (sbit->alpha == 0 || sbit->alpha > png_ptr->usr_bit_depth)
        {
           png_warning(png_ptr, "Invalid sBIT depth specified");
           return;
        }
  
        buf[size++] = sbit->alpha;
     }
  
     png_write_complete_chunk(png_ptr, png_sBIT, buf, size);
  }
  #endif
  
  #ifdef PNG_WRITE_cHRM_SUPPORTED
  /* Write the cHRM chunk */
  void /* PRIVATE */
  png_write_cHRM_fixed(png_structrp png_ptr, const png_xy *xy)
  {
     png_byte buf[32];
  
     png_debug(1, "in png_write_cHRM");
  
     /* Each value is saved in 1/100,000ths */
     png_save_int_32(buf,      xy->whitex);
     png_save_int_32(buf +  4, xy->whitey);
  
     png_save_int_32(buf +  8, xy->redx);
     png_save_int_32(buf + 12, xy->redy);
  
     png_save_int_32(buf + 16, xy->greenx);
     png_save_int_32(buf + 20, xy->greeny);
  
     png_save_int_32(buf + 24, xy->bluex);
     png_save_int_32(buf + 28, xy->bluey);
  
     png_write_complete_chunk(png_ptr, png_cHRM, buf, 32);
  }
  #endif
  
  #ifdef PNG_WRITE_tRNS_SUPPORTED
  /* Write the tRNS chunk */
  void /* PRIVATE */
  png_write_tRNS(png_structrp png_ptr, png_const_bytep trans_alpha,
      png_const_color_16p tran, int num_trans, int color_type)
  {
     png_byte buf[6];
  
     png_debug(1, "in png_write_tRNS");
  
     if (color_type == PNG_COLOR_TYPE_PALETTE)
     {
        if (num_trans <= 0 || num_trans > (int)png_ptr->num_palette)
        {
           png_app_warning(png_ptr,
               "Invalid number of transparent colors specified");
           return;
        }
  
        /* Write the chunk out as it is */
        png_write_complete_chunk(png_ptr, png_tRNS, trans_alpha,
            (png_size_t)num_trans);
     }
  
     else if (color_type == PNG_COLOR_TYPE_GRAY)
     {
        /* One 16-bit value */
        if (tran->gray >= (1 << png_ptr->bit_depth))
        {
           png_app_warning(png_ptr,
               "Ignoring attempt to write tRNS chunk out-of-range for bit_depth");
  
           return;
        }
  
        png_save_uint_16(buf, tran->gray);
        png_write_complete_chunk(png_ptr, png_tRNS, buf, (png_size_t)2);
     }
  
     else if (color_type == PNG_COLOR_TYPE_RGB)
     {
        /* Three 16-bit values */
        png_save_uint_16(buf, tran->red);
        png_save_uint_16(buf + 2, tran->green);
        png_save_uint_16(buf + 4, tran->blue);
  #ifdef PNG_WRITE_16BIT_SUPPORTED
        if (png_ptr->bit_depth == 8 && (buf[0] | buf[2] | buf[4]) != 0)
  #else
        if ((buf[0] | buf[2] | buf[4]) != 0)
  #endif
        {
           png_app_warning(png_ptr,
               "Ignoring attempt to write 16-bit tRNS chunk when bit_depth is 8");
           return;
        }
  
        png_write_complete_chunk(png_ptr, png_tRNS, buf, (png_size_t)6);
     }
  
     else
     {
        png_app_warning(png_ptr, "Can't write tRNS with an alpha channel");
     }
  }
  #endif
  
  #ifdef PNG_WRITE_bKGD_SUPPORTED
  /* Write the background chunk */
  void /* PRIVATE */
  png_write_bKGD(png_structrp png_ptr, png_const_color_16p back, int color_type)
  {
     png_byte buf[6];
  
     png_debug(1, "in png_write_bKGD");
  
     if (color_type == PNG_COLOR_TYPE_PALETTE)
     {
        if (
  #ifdef PNG_MNG_FEATURES_SUPPORTED
            (png_ptr->num_palette != 0 ||
            (png_ptr->mng_features_permitted & PNG_FLAG_MNG_EMPTY_PLTE) == 0) &&
  #endif
           back->index >= png_ptr->num_palette)
        {
           png_warning(png_ptr, "Invalid background palette index");
           return;
        }
  
        buf[0] = back->index;
        png_write_complete_chunk(png_ptr, png_bKGD, buf, (png_size_t)1);
     }
  
     else if ((color_type & PNG_COLOR_MASK_COLOR) != 0)
     {
        png_save_uint_16(buf, back->red);
        png_save_uint_16(buf + 2, back->green);
        png_save_uint_16(buf + 4, back->blue);
  #ifdef PNG_WRITE_16BIT_SUPPORTED
        if (png_ptr->bit_depth == 8 && (buf[0] | buf[2] | buf[4]) != 0)
  #else
        if ((buf[0] | buf[2] | buf[4]) != 0)
  #endif
        {
           png_warning(png_ptr,
               "Ignoring attempt to write 16-bit bKGD chunk "
               "when bit_depth is 8");
  
           return;
        }
  
        png_write_complete_chunk(png_ptr, png_bKGD, buf, (png_size_t)6);
     }
  
     else
     {
        if (back->gray >= (1 << png_ptr->bit_depth))
        {
           png_warning(png_ptr,
               "Ignoring attempt to write bKGD chunk out-of-range for bit_depth");
  
           return;
        }
  
        png_save_uint_16(buf, back->gray);
        png_write_complete_chunk(png_ptr, png_bKGD, buf, (png_size_t)2);
     }
  }
  #endif
  
  #ifdef PNG_WRITE_hIST_SUPPORTED
  /* Write the histogram */
  void /* PRIVATE */
  png_write_hIST(png_structrp png_ptr, png_const_uint_16p hist, int num_hist)
  {
     int i;
     png_byte buf[3];
  
     png_debug(1, "in png_write_hIST");
  
     if (num_hist > (int)png_ptr->num_palette)
     {
        png_debug2(3, "num_hist = %d, num_palette = %d", num_hist,
            png_ptr->num_palette);
  
        png_warning(png_ptr, "Invalid number of histogram entries specified");
        return;
     }
  
     png_write_chunk_header(png_ptr, png_hIST, (png_uint_32)(num_hist * 2));
  
     for (i = 0; i < num_hist; i++)
     {
        png_save_uint_16(buf, hist[i]);
        png_write_chunk_data(png_ptr, buf, (png_size_t)2);
     }
  
     png_write_chunk_end(png_ptr);
  }
  #endif
  
  #ifdef PNG_WRITE_tEXt_SUPPORTED
  /* Write a tEXt chunk */
  void /* PRIVATE */
  png_write_tEXt(png_structrp png_ptr, png_const_charp key, png_const_charp text,
      png_size_t text_len)
  {
     png_uint_32 key_len;
     png_byte new_key[80];
  
     png_debug(1, "in png_write_tEXt");
  
     key_len = png_check_keyword(png_ptr, key, new_key);
  
     if (key_len == 0)
        png_error(png_ptr, "tEXt: invalid keyword");
  
     if (text == NULL || *text == '\0')
        text_len = 0;
  
     else
        text_len = strlen(text);
  
     if (text_len > PNG_UINT_31_MAX - (key_len+1))
        png_error(png_ptr, "tEXt: text too long");
  
     /* Make sure we include the 0 after the key */
     png_write_chunk_header(png_ptr, png_tEXt,
         (png_uint_32)/*checked above*/(key_len + text_len + 1));
     /*
      * We leave it to the application to meet PNG-1.0 requirements on the
      * contents of the text.  PNG-1.0 through PNG-1.2 discourage the use of
      * any non-Latin-1 characters except for NEWLINE.  ISO PNG will forbid them.
      * The NUL character is forbidden by PNG-1.0 through PNG-1.2 and ISO PNG.
      */
     png_write_chunk_data(png_ptr, new_key, key_len + 1);
  
     if (text_len != 0)
        png_write_chunk_data(png_ptr, (png_const_bytep)text, text_len);
  
     png_write_chunk_end(png_ptr);
  }
  #endif
  
  #ifdef PNG_WRITE_zTXt_SUPPORTED
  /* Write a compressed text chunk */
  void /* PRIVATE */
  png_write_zTXt(png_structrp png_ptr, png_const_charp key, png_const_charp text,
      int compression)
  {
     png_uint_32 key_len;
     png_byte new_key[81];
     compression_state comp;
  
     png_debug(1, "in png_write_zTXt");
  
     if (compression == PNG_TEXT_COMPRESSION_NONE)
     {
        png_write_tEXt(png_ptr, key, text, 0);
        return;
     }
  
     if (compression != PNG_TEXT_COMPRESSION_zTXt)
        png_error(png_ptr, "zTXt: invalid compression type");
  
     key_len = png_check_keyword(png_ptr, key, new_key);
  
     if (key_len == 0)
        png_error(png_ptr, "zTXt: invalid keyword");
  
     /* Add the compression method and 1 for the keyword separator. */
     new_key[++key_len] = PNG_COMPRESSION_TYPE_BASE;
     ++key_len;
  
     /* Compute the compressed data; do it now for the length */
     png_text_compress_init(&comp, (png_const_bytep)text,
         text == NULL ? 0 : strlen(text));
  
     if (png_text_compress(png_ptr, png_zTXt, &comp, key_len) != Z_OK)
        png_error(png_ptr, png_ptr->zstream.msg);
  
     /* Write start of chunk */
     png_write_chunk_header(png_ptr, png_zTXt, key_len + comp.output_len);
  
     /* Write key */
     png_write_chunk_data(png_ptr, new_key, key_len);
  
     /* Write the compressed data */
     png_write_compressed_data_out(png_ptr, &comp);
  
     /* Close the chunk */
     png_write_chunk_end(png_ptr);
  }
  #endif
  
  #ifdef PNG_WRITE_iTXt_SUPPORTED
  /* Write an iTXt chunk */
  void /* PRIVATE */
  png_write_iTXt(png_structrp png_ptr, int compression, png_const_charp key,
      png_const_charp lang, png_const_charp lang_key, png_const_charp text)
  {
     png_uint_32 key_len, prefix_len;
     png_size_t lang_len, lang_key_len;
     png_byte new_key[82];
     compression_state comp;
  
     png_debug(1, "in png_write_iTXt");
  
     key_len = png_check_keyword(png_ptr, key, new_key);
  
     if (key_len == 0)
        png_error(png_ptr, "iTXt: invalid keyword");
  
     /* Set the compression flag */
     switch (compression)
     {
        case PNG_ITXT_COMPRESSION_NONE:
        case PNG_TEXT_COMPRESSION_NONE:
           compression = new_key[++key_len] = 0; /* no compression */
           break;
  
        case PNG_TEXT_COMPRESSION_zTXt:
        case PNG_ITXT_COMPRESSION_zTXt:
           compression = new_key[++key_len] = 1; /* compressed */
           break;
  
        default:
           png_error(png_ptr, "iTXt: invalid compression");
     }
  
     new_key[++key_len] = PNG_COMPRESSION_TYPE_BASE;
     ++key_len; /* for the keywod separator */
  
     /* We leave it to the application to meet PNG-1.0 requirements on the
      * contents of the text.  PNG-1.0 through PNG-1.2 discourage the use of
      * any non-Latin-1 characters except for NEWLINE.  ISO PNG, however,
      * specifies that the text is UTF-8 and this really doesn't require any
      * checking.
      *
      * The NUL character is forbidden by PNG-1.0 through PNG-1.2 and ISO PNG.
      *
      * TODO: validate the language tag correctly (see the spec.)
      */
     if (lang == NULL) lang = ""; /* empty language is valid */
     lang_len = strlen(lang)+1;
     if (lang_key == NULL) lang_key = ""; /* may be empty */
     lang_key_len = strlen(lang_key)+1;
     if (text == NULL) text = ""; /* may be empty */
  
     prefix_len = key_len;
     if (lang_len > PNG_UINT_31_MAX-prefix_len)
        prefix_len = PNG_UINT_31_MAX;
     else
        prefix_len = (png_uint_32)(prefix_len + lang_len);
  
     if (lang_key_len > PNG_UINT_31_MAX-prefix_len)
        prefix_len = PNG_UINT_31_MAX;
     else
        prefix_len = (png_uint_32)(prefix_len + lang_key_len);
  
     png_text_compress_init(&comp, (png_const_bytep)text, strlen(text));
  
     if (compression != 0)
     {
        if (png_text_compress(png_ptr, png_iTXt, &comp, prefix_len) != Z_OK)
           png_error(png_ptr, png_ptr->zstream.msg);
     }
  
     else
     {
        if (comp.input_len > PNG_UINT_31_MAX-prefix_len)
           png_error(png_ptr, "iTXt: uncompressed text too long");
  
        /* So the string will fit in a chunk: */
        comp.output_len = (png_uint_32)/*SAFE*/comp.input_len;
     }
  
     png_write_chunk_header(png_ptr, png_iTXt, comp.output_len + prefix_len);
  
     png_write_chunk_data(png_ptr, new_key, key_len);
  
     png_write_chunk_data(png_ptr, (png_const_bytep)lang, lang_len);
  
     png_write_chunk_data(png_ptr, (png_const_bytep)lang_key, lang_key_len);
  
     if (compression != 0)
        png_write_compressed_data_out(png_ptr, &comp);
  
     else
        png_write_chunk_data(png_ptr, (png_const_bytep)text, comp.output_len);
  
     png_write_chunk_end(png_ptr);
  }
  #endif
  
  #ifdef PNG_WRITE_oFFs_SUPPORTED
  /* Write the oFFs chunk */
  void /* PRIVATE */
  png_write_oFFs(png_structrp png_ptr, png_int_32 x_offset, png_int_32 y_offset,
      int unit_type)
  {
     png_byte buf[9];
  
     png_debug(1, "in png_write_oFFs");
  
     if (unit_type >= PNG_OFFSET_LAST)
        png_warning(png_ptr, "Unrecognized unit type for oFFs chunk");
  
     png_save_int_32(buf, x_offset);
     png_save_int_32(buf + 4, y_offset);
     buf[8] = (png_byte)unit_type;
  
     png_write_complete_chunk(png_ptr, png_oFFs, buf, (png_size_t)9);
  }
  #endif
  #ifdef PNG_WRITE_pCAL_SUPPORTED
  /* Write the pCAL chunk (described in the PNG extensions document) */
  void /* PRIVATE */
  png_write_pCAL(png_structrp png_ptr, png_charp purpose, png_int_32 X0,
      png_int_32 X1, int type, int nparams, png_const_charp units,
      png_charpp params)
  {
     png_uint_32 purpose_len;
     png_size_t units_len, total_len;
     png_size_tp params_len;
     png_byte buf[10];
     png_byte new_purpose[80];
     int i;
  
     png_debug1(1, "in png_write_pCAL (%d parameters)", nparams);
  
     if (type >= PNG_EQUATION_LAST)
        png_error(png_ptr, "Unrecognized equation type for pCAL chunk");
  
     purpose_len = png_check_keyword(png_ptr, purpose, new_purpose);
  
     if (purpose_len == 0)
        png_error(png_ptr, "pCAL: invalid keyword");
  
     ++purpose_len; /* terminator */
  
     png_debug1(3, "pCAL purpose length = %d", (int)purpose_len);
     units_len = strlen(units) + (nparams == 0 ? 0 : 1);
     png_debug1(3, "pCAL units length = %d", (int)units_len);
     total_len = purpose_len + units_len + 10;
  
     params_len = (png_size_tp)png_malloc(png_ptr,
         (png_alloc_size_t)((png_alloc_size_t)nparams * (sizeof (png_size_t))));
  
     /* Find the length of each parameter, making sure we don't count the
      * null terminator for the last parameter.
      */
     for (i = 0; i < nparams; i++)
     {
        params_len[i] = strlen(params[i]) + (i == nparams - 1 ? 0 : 1);
        png_debug2(3, "pCAL parameter %d length = %lu", i,
            (unsigned long)params_len[i]);
        total_len += params_len[i];
     }
  
     png_debug1(3, "pCAL total length = %d", (int)total_len);
     png_write_chunk_header(png_ptr, png_pCAL, (png_uint_32)total_len);
     png_write_chunk_data(png_ptr, new_purpose, purpose_len);
     png_save_int_32(buf, X0);
     png_save_int_32(buf + 4, X1);
     buf[8] = (png_byte)type;
     buf[9] = (png_byte)nparams;
     png_write_chunk_data(png_ptr, buf, (png_size_t)10);
     png_write_chunk_data(png_ptr, (png_const_bytep)units, (png_size_t)units_len);
  
     for (i = 0; i < nparams; i++)
     {
        png_write_chunk_data(png_ptr, (png_const_bytep)params[i], params_len[i]);
     }
  
     png_free(png_ptr, params_len);
     png_write_chunk_end(png_ptr);
  }
  #endif
  
  #ifdef PNG_WRITE_sCAL_SUPPORTED
  /* Write the sCAL chunk */
  void /* PRIVATE */
  png_write_sCAL_s(png_structrp png_ptr, int unit, png_const_charp width,
      png_const_charp height)
  {
     png_byte buf[64];
     png_size_t wlen, hlen, total_len;
  
     png_debug(1, "in png_write_sCAL_s");
  
     wlen = strlen(width);
     hlen = strlen(height);
     total_len = wlen + hlen + 2;
  
     if (total_len > 64)
     {
        png_warning(png_ptr, "Can't write sCAL (buffer too small)");
        return;
     }
  
     buf[0] = (png_byte)unit;
     memcpy(buf + 1, width, wlen + 1);      /* Append the '\0' here */
     memcpy(buf + wlen + 2, height, hlen);  /* Do NOT append the '\0' here */
  
     png_debug1(3, "sCAL total length = %u", (unsigned int)total_len);
     png_write_complete_chunk(png_ptr, png_sCAL, buf, total_len);
  }
  #endif
  
  #ifdef PNG_WRITE_pHYs_SUPPORTED
  /* Write the pHYs chunk */
  void /* PRIVATE */
  png_write_pHYs(png_structrp png_ptr, png_uint_32 x_pixels_per_unit,
      png_uint_32 y_pixels_per_unit,
      int unit_type)
  {
     png_byte buf[9];
  
     png_debug(1, "in png_write_pHYs");
  
     if (unit_type >= PNG_RESOLUTION_LAST)
        png_warning(png_ptr, "Unrecognized unit type for pHYs chunk");
  
     png_save_uint_32(buf, x_pixels_per_unit);
     png_save_uint_32(buf + 4, y_pixels_per_unit);
     buf[8] = (png_byte)unit_type;
  
     png_write_complete_chunk(png_ptr, png_pHYs, buf, (png_size_t)9);
  }
  #endif
  
  #ifdef PNG_WRITE_tIME_SUPPORTED
  /* Write the tIME chunk.  Use either png_convert_from_struct_tm()
   * or png_convert_from_time_t(), or fill in the structure yourself.
   */
  void /* PRIVATE */
  png_write_tIME(png_structrp png_ptr, png_const_timep mod_time)
  {
     png_byte buf[7];
  
     png_debug(1, "in png_write_tIME");
  
     if (mod_time->month  > 12 || mod_time->month  < 1 ||
         mod_time->day    > 31 || mod_time->day    < 1 ||
         mod_time->hour   > 23 || mod_time->second > 60)
     {
        png_warning(png_ptr, "Invalid time specified for tIME chunk");
        return;
     }
  
     png_save_uint_16(buf, mod_time->year);
     buf[2] = mod_time->month;
     buf[3] = mod_time->day;
     buf[4] = mod_time->hour;
     buf[5] = mod_time->minute;
     buf[6] = mod_time->second;
  
     png_write_complete_chunk(png_ptr, png_tIME, buf, (png_size_t)7);
  }
  #endif
  
  /* Initializes the row writing capability of libpng */
  void /* PRIVATE */
  png_write_start_row(png_structrp png_ptr)
  {
  #ifdef PNG_WRITE_INTERLACING_SUPPORTED
     /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */
  
     /* Start of interlace block */
     static PNG_CONST png_byte png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};
  
     /* Offset to next interlace block */
     static PNG_CONST png_byte png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
  
     /* Start of interlace block in the y direction */
     static PNG_CONST png_byte png_pass_ystart[7] = {0, 0, 4, 0, 2, 0, 1};
  
     /* Offset to next interlace block in the y direction */
     static PNG_CONST png_byte png_pass_yinc[7] = {8, 8, 8, 4, 4, 2, 2};
  #endif
  
     png_alloc_size_t buf_size;
     int usr_pixel_depth;
  
  #ifdef PNG_WRITE_FILTER_SUPPORTED
     png_byte filters;
  #endif
  
     png_debug(1, "in png_write_start_row");
  
     usr_pixel_depth = png_ptr->usr_channels * png_ptr->usr_bit_depth;
     buf_size = PNG_ROWBYTES(usr_pixel_depth, png_ptr->width) + 1;
  
     /* 1.5.6: added to allow checking in the row write code. */
     png_ptr->transformed_pixel_depth = png_ptr->pixel_depth;
     png_ptr->maximum_pixel_depth = (png_byte)usr_pixel_depth;
  
     /* Set up row buffer */
     png_ptr->row_buf = png_voidcast(png_bytep, png_malloc(png_ptr, buf_size));
  
     png_ptr->row_buf[0] = PNG_FILTER_VALUE_NONE;
  
  #ifdef PNG_WRITE_FILTER_SUPPORTED
     filters = png_ptr->do_filter;
  
     if (png_ptr->height == 1)
        filters &= 0xff & ~(PNG_FILTER_UP|PNG_FILTER_AVG|PNG_FILTER_PAETH);
  
     if (png_ptr->width == 1)
        filters &= 0xff & ~(PNG_FILTER_SUB|PNG_FILTER_AVG|PNG_FILTER_PAETH);
  
     if (filters == 0)
        filters = PNG_FILTER_NONE;
  
     png_ptr->do_filter = filters;
  
     if (((filters & (PNG_FILTER_SUB | PNG_FILTER_UP | PNG_FILTER_AVG |
         PNG_FILTER_PAETH)) != 0) && png_ptr->try_row == NULL)
     {
        int num_filters = 0;
  
        png_ptr->try_row = png_voidcast(png_bytep, png_malloc(png_ptr, buf_size));
  
        if (filters & PNG_FILTER_SUB)
           num_filters++;
  
        if (filters & PNG_FILTER_UP)
           num_filters++;
  
        if (filters & PNG_FILTER_AVG)
           num_filters++;
  
        if (filters & PNG_FILTER_PAETH)
           num_filters++;
  
        if (num_filters > 1)
           png_ptr->tst_row = png_voidcast(png_bytep, png_malloc(png_ptr,
               buf_size));
     }
  
     /* We only need to keep the previous row if we are using one of the following
      * filters.
      */
     if ((filters & (PNG_FILTER_AVG | PNG_FILTER_UP | PNG_FILTER_PAETH)) != 0)
        png_ptr->prev_row = png_voidcast(png_bytep,
            png_calloc(png_ptr, buf_size));
  #endif /* WRITE_FILTER */
  
  #ifdef PNG_WRITE_INTERLACING_SUPPORTED
     /* If interlaced, we need to set up width and height of pass */
     if (png_ptr->interlaced != 0)
     {
        if ((png_ptr->transformations & PNG_INTERLACE) == 0)
        {
           png_ptr->num_rows = (png_ptr->height + png_pass_yinc[0] - 1 -
               png_pass_ystart[0]) / png_pass_yinc[0];
  
           png_ptr->usr_width = (png_ptr->width + png_pass_inc[0] - 1 -
               png_pass_start[0]) / png_pass_inc[0];
        }
  
        else
        {
           png_ptr->num_rows = png_ptr->height;
           png_ptr->usr_width = png_ptr->width;
        }
     }
  
     else
  #endif
     {
        png_ptr->num_rows = png_ptr->height;
        png_ptr->usr_width = png_ptr->width;
     }
  }
  
  /* Internal use only.  Called when finished processing a row of data. */
  void /* PRIVATE */
  png_write_finish_row(png_structrp png_ptr)
  {
  #ifdef PNG_WRITE_INTERLACING_SUPPORTED
     /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */
  
     /* Start of interlace block */
     static PNG_CONST png_byte png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};
  
     /* Offset to next interlace block */
     static PNG_CONST png_byte png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
  
     /* Start of interlace block in the y direction */
     static PNG_CONST png_byte png_pass_ystart[7] = {0, 0, 4, 0, 2, 0, 1};
  
     /* Offset to next interlace block in the y direction */
     static PNG_CONST png_byte png_pass_yinc[7] = {8, 8, 8, 4, 4, 2, 2};
  #endif
  
     png_debug(1, "in png_write_finish_row");
  
     /* Next row */
     png_ptr->row_number++;
  
     /* See if we are done */
     if (png_ptr->row_number < png_ptr->num_rows)
        return;
  
  #ifdef PNG_WRITE_INTERLACING_SUPPORTED
     /* If interlaced, go to next pass */
     if (png_ptr->interlaced != 0)
     {
        png_ptr->row_number = 0;
        if ((png_ptr->transformations & PNG_INTERLACE) != 0)
        {
           png_ptr->pass++;
        }
  
        else
        {
           /* Loop until we find a non-zero width or height pass */
           do
           {
              png_ptr->pass++;
  
              if (png_ptr->pass >= 7)
                 break;
  
              png_ptr->usr_width = (png_ptr->width +
                  png_pass_inc[png_ptr->pass] - 1 -
                  png_pass_start[png_ptr->pass]) /
                  png_pass_inc[png_ptr->pass];
  
              png_ptr->num_rows = (png_ptr->height +
                  png_pass_yinc[png_ptr->pass] - 1 -
                  png_pass_ystart[png_ptr->pass]) /
                  png_pass_yinc[png_ptr->pass];
  
              if ((png_ptr->transformations & PNG_INTERLACE) != 0)
                 break;
  
           } while (png_ptr->usr_width == 0 || png_ptr->num_rows == 0);
  
        }
  
        /* Reset the row above the image for the next pass */
        if (png_ptr->pass < 7)
        {
           if (png_ptr->prev_row != NULL)
              memset(png_ptr->prev_row, 0,
                  (png_size_t)(PNG_ROWBYTES(png_ptr->usr_channels*
                  png_ptr->usr_bit_depth, png_ptr->width)) + 1);
  
           return;
        }
     }
  #endif
  
     /* If we get here, we've just written the last row, so we need
        to flush the compressor */
     png_compress_IDAT(png_ptr, NULL, 0, Z_FINISH);
  }
  
  #ifdef PNG_WRITE_INTERLACING_SUPPORTED
  /* Pick out the correct pixels for the interlace pass.
   * The basic idea here is to go through the row with a source
   * pointer and a destination pointer (sp and dp), and copy the
   * correct pixels for the pass.  As the row gets compacted,
   * sp will always be >= dp, so we should never overwrite anything.
   * See the default: case for the easiest code to understand.
   */
  void /* PRIVATE */
  png_do_write_interlace(png_row_infop row_info, png_bytep row, int pass)
  {
     /* Arrays to facilitate easy interlacing - use pass (0 - 6) as index */
  
     /* Start of interlace block */
     static PNG_CONST png_byte png_pass_start[7] = {0, 4, 0, 2, 0, 1, 0};
  
     /* Offset to next interlace block */
     static PNG_CONST png_byte  png_pass_inc[7] = {8, 8, 4, 4, 2, 2, 1};
  
     png_debug(1, "in png_do_write_interlace");
  
     /* We don't have to do anything on the last pass (6) */
     if (pass < 6)
     {
        /* Each pixel depth is handled separately */
        switch (row_info->pixel_depth)
        {
           case 1:
           {
              png_bytep sp;
              png_bytep dp;
              unsigned int shift;
              int d;
              int value;
              png_uint_32 i;
              png_uint_32 row_width = row_info->width;
  
              dp = row;
              d = 0;
              shift = 7;
  
              for (i = png_pass_start[pass]; i < row_width;
                 i += png_pass_inc[pass])
              {
                 sp = row + (png_size_t)(i >> 3);
                 value = (int)(*sp >> (7 - (int)(i & 0x07))) & 0x01;
                 d |= (value << shift);
  
                 if (shift == 0)
                 {
                    shift = 7;
                    *dp++ = (png_byte)d;
                    d = 0;
                 }
  
                 else
                    shift--;
  
              }
              if (shift != 7)
                 *dp = (png_byte)d;
  
              break;
           }
  
           case 2:
           {
              png_bytep sp;
              png_bytep dp;
              unsigned int shift;
              int d;
              int value;
              png_uint_32 i;
              png_uint_32 row_width = row_info->width;
  
              dp = row;
              shift = 6;
              d = 0;
  
              for (i = png_pass_start[pass]; i < row_width;
                 i += png_pass_inc[pass])
              {
                 sp = row + (png_size_t)(i >> 2);
                 value = (*sp >> ((3 - (int)(i & 0x03)) << 1)) & 0x03;
                 d |= (value << shift);
  
                 if (shift == 0)
                 {
                    shift = 6;
                    *dp++ = (png_byte)d;
                    d = 0;
                 }
  
                 else
                    shift -= 2;
              }
              if (shift != 6)
                 *dp = (png_byte)d;
  
              break;
           }
  
           case 4:
           {
              png_bytep sp;
              png_bytep dp;
              unsigned int shift;
              int d;
              int value;
              png_uint_32 i;
              png_uint_32 row_width = row_info->width;
  
              dp = row;
              shift = 4;
              d = 0;
              for (i = png_pass_start[pass]; i < row_width;
                  i += png_pass_inc[pass])
              {
                 sp = row + (png_size_t)(i >> 1);
                 value = (*sp >> ((1 - (int)(i & 0x01)) << 2)) & 0x0f;
                 d |= (value << shift);
  
                 if (shift == 0)
                 {
                    shift = 4;
                    *dp++ = (png_byte)d;
                    d = 0;
                 }
  
                 else
                    shift -= 4;
              }
              if (shift != 4)
                 *dp = (png_byte)d;
  
              break;
           }
  
           default:
           {
              png_bytep sp;
              png_bytep dp;
              png_uint_32 i;
              png_uint_32 row_width = row_info->width;
              png_size_t pixel_bytes;
  
              /* Start at the beginning */
              dp = row;
  
              /* Find out how many bytes each pixel takes up */
              pixel_bytes = (row_info->pixel_depth >> 3);
  
              /* Loop through the row, only looking at the pixels that matter */
              for (i = png_pass_start[pass]; i < row_width;
                 i += png_pass_inc[pass])
              {
                 /* Find out where the original pixel is */
                 sp = row + (png_size_t)i * pixel_bytes;
  
                 /* Move the pixel */
                 if (dp != sp)
                    memcpy(dp, sp, pixel_bytes);
  
                 /* Next pixel */
                 dp += pixel_bytes;
              }
              break;
           }
        }
        /* Set new row width */
        row_info->width = (row_info->width +
            png_pass_inc[pass] - 1 -
            png_pass_start[pass]) /
            png_pass_inc[pass];
  
        row_info->rowbytes = PNG_ROWBYTES(row_info->pixel_depth,
            row_info->width);
     }
  }
  #endif
  
  
  /* This filters the row, chooses which filter to use, if it has not already
   * been specified by the application, and then writes the row out with the
   * chosen filter.
   */
  static void /* PRIVATE */
  png_write_filtered_row(png_structrp png_ptr, png_bytep filtered_row,
      png_size_t row_bytes);
  
  #ifdef PNG_WRITE_FILTER_SUPPORTED
  static png_size_t /* PRIVATE */
  png_setup_sub_row(png_structrp png_ptr, const png_uint_32 bpp,
      const png_size_t row_bytes, const png_size_t lmins)
  {
     png_bytep rp, dp, lp;
     png_size_t i;
     png_size_t sum = 0;
     unsigned int v;
  
     png_ptr->try_row[0] = PNG_FILTER_VALUE_SUB;
  
     for (i = 0, rp = png_ptr->row_buf + 1, dp = png_ptr->try_row + 1; i < bpp;
          i++, rp++, dp++)
     {
        v = *dp = *rp;
  #ifdef PNG_USE_ABS
        sum += 128 - abs((int)v - 128);
  #else
        sum += (v < 128) ? v : 256 - v;
  #endif
     }
  
     for (lp = png_ptr->row_buf + 1; i < row_bytes;
        i++, rp++, lp++, dp++)
     {
        v = *dp = (png_byte)(((int)*rp - (int)*lp) & 0xff);
  #ifdef PNG_USE_ABS
        sum += 128 - abs((int)v - 128);
  #else
        sum += (v < 128) ? v : 256 - v;
  #endif
  
        if (sum > lmins)  /* We are already worse, don't continue. */
          break;
     }
  
     return (sum);
  }
  
  static void /* PRIVATE */
  png_setup_sub_row_only(png_structrp png_ptr, const png_uint_32 bpp,
      const png_size_t row_bytes)
  {
     png_bytep rp, dp, lp;
     png_size_t i;
  
     png_ptr->try_row[0] = PNG_FILTER_VALUE_SUB;
  
     for (i = 0, rp = png_ptr->row_buf + 1, dp = png_ptr->try_row + 1; i < bpp;
          i++, rp++, dp++)
     {
        *dp = *rp;
     }
  
     for (lp = png_ptr->row_buf + 1; i < row_bytes;
        i++, rp++, lp++, dp++)
     {
        *dp = (png_byte)(((int)*rp - (int)*lp) & 0xff);
     }
  }
  
  static png_size_t /* PRIVATE */
  png_setup_up_row(png_structrp png_ptr, const png_size_t row_bytes,
      const png_size_t lmins)
  {
     png_bytep rp, dp, pp;
     png_size_t i;
     png_size_t sum = 0;
     unsigned int v;
  
     png_ptr->try_row[0] = PNG_FILTER_VALUE_UP;
  
     for (i = 0, rp = png_ptr->row_buf + 1, dp = png_ptr->try_row + 1,
         pp = png_ptr->prev_row + 1; i < row_bytes;
         i++, rp++, pp++, dp++)
     {
        v = *dp = (png_byte)(((int)*rp - (int)*pp) & 0xff);
  #ifdef PNG_USE_ABS
        sum += 128 - abs((int)v - 128);
  #else
        sum += (v < 128) ? v : 256 - v;
  #endif
  
        if (sum > lmins)  /* We are already worse, don't continue. */
          break;
     }
  
     return (sum);
  }
  static void /* PRIVATE */
  png_setup_up_row_only(png_structrp png_ptr, const png_size_t row_bytes)
  {
     png_bytep rp, dp, pp;
     png_size_t i;
  
     png_ptr->try_row[0] = PNG_FILTER_VALUE_UP;
  
     for (i = 0, rp = png_ptr->row_buf + 1, dp = png_ptr->try_row + 1,
         pp = png_ptr->prev_row + 1; i < row_bytes;
         i++, rp++, pp++, dp++)
     {
        *dp = (png_byte)(((int)*rp - (int)*pp) & 0xff);
     }
  }
  
  static png_size_t /* PRIVATE */
  png_setup_avg_row(png_structrp png_ptr, const png_uint_32 bpp,
      const png_size_t row_bytes, const png_size_t lmins)
  {
     png_bytep rp, dp, pp, lp;
     png_uint_32 i;
     png_size_t sum = 0;
     unsigned int v;
  
     png_ptr->try_row[0] = PNG_FILTER_VALUE_AVG;
  
     for (i = 0, rp = png_ptr->row_buf + 1, dp = png_ptr->try_row + 1,
         pp = png_ptr->prev_row + 1; i < bpp; i++)
     {
        v = *dp++ = (png_byte)(((int)*rp++ - ((int)*pp++ / 2)) & 0xff);
  
  #ifdef PNG_USE_ABS
        sum += 128 - abs((int)v - 128);
  #else
        sum += (v < 128) ? v : 256 - v;
  #endif
     }
  
     for (lp = png_ptr->row_buf + 1; i < row_bytes; i++)
     {
        v = *dp++ = (png_byte)(((int)*rp++ - (((int)*pp++ + (int)*lp++) / 2))
            & 0xff);
  
  #ifdef PNG_USE_ABS
        sum += 128 - abs((int)v - 128);
  #else
        sum += (v < 128) ? v : 256 - v;
  #endif
  
        if (sum > lmins)  /* We are already worse, don't continue. */
          break;
     }
  
     return (sum);
  }
  static void /* PRIVATE */
  png_setup_avg_row_only(png_structrp png_ptr, const png_uint_32 bpp,
      const png_size_t row_bytes)
  {
     png_bytep rp, dp, pp, lp;
     png_uint_32 i;
  
     png_ptr->try_row[0] = PNG_FILTER_VALUE_AVG;
  
     for (i = 0, rp = png_ptr->row_buf + 1, dp = png_ptr->try_row + 1,
         pp = png_ptr->prev_row + 1; i < bpp; i++)
     {
        *dp++ = (png_byte)(((int)*rp++ - ((int)*pp++ / 2)) & 0xff);
     }
  
     for (lp = png_ptr->row_buf + 1; i < row_bytes; i++)
     {
        *dp++ = (png_byte)(((int)*rp++ - (((int)*pp++ + (int)*lp++) / 2))
            & 0xff);
     }
  }
  
  static png_size_t /* PRIVATE */
  png_setup_paeth_row(png_structrp png_ptr, const png_uint_32 bpp,
      const png_size_t row_bytes, const png_size_t lmins)
  {
     png_bytep rp, dp, pp, cp, lp;
     png_size_t i;
     png_size_t sum = 0;
     unsigned int v;
  
     png_ptr->try_row[0] = PNG_FILTER_VALUE_PAETH;
  
     for (i = 0, rp = png_ptr->row_buf + 1, dp = png_ptr->try_row + 1,
         pp = png_ptr->prev_row + 1; i < bpp; i++)
     {
        v = *dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);
  
  #ifdef PNG_USE_ABS
        sum += 128 - abs((int)v - 128);
  #else
        sum += (v < 128) ? v : 256 - v;
  #endif
     }
  
     for (lp = png_ptr->row_buf + 1, cp = png_ptr->prev_row + 1; i < row_bytes;
          i++)
     {
        int a, b, c, pa, pb, pc, p;
  
        b = *pp++;
        c = *cp++;
        a = *lp++;
  
        p = b - c;
        pc = a - c;
  
  #ifdef PNG_USE_ABS
        pa = abs(p);
        pb = abs(pc);
        pc = abs(p + pc);
  #else
        pa = p < 0 ? -p : p;
        pb = pc < 0 ? -pc : pc;
        pc = (p + pc) < 0 ? -(p + pc) : p + pc;
  #endif
  
        p = (pa <= pb && pa <=pc) ? a : (pb <= pc) ? b : c;
  
        v = *dp++ = (png_byte)(((int)*rp++ - p) & 0xff);
  
  #ifdef PNG_USE_ABS
        sum += 128 - abs((int)v - 128);
  #else
        sum += (v < 128) ? v : 256 - v;
  #endif
  
        if (sum > lmins)  /* We are already worse, don't continue. */
          break;
     }
  
     return (sum);
  }
  static void /* PRIVATE */
  png_setup_paeth_row_only(png_structrp png_ptr, const png_uint_32 bpp,
      const png_size_t row_bytes)
  {
     png_bytep rp, dp, pp, cp, lp;
     png_size_t i;
  
     png_ptr->try_row[0] = PNG_FILTER_VALUE_PAETH;
  
     for (i = 0, rp = png_ptr->row_buf + 1, dp = png_ptr->try_row + 1,
         pp = png_ptr->prev_row + 1; i < bpp; i++)
     {
        *dp++ = (png_byte)(((int)*rp++ - (int)*pp++) & 0xff);
     }
  
     for (lp = png_ptr->row_buf + 1, cp = png_ptr->prev_row + 1; i < row_bytes;
          i++)
     {
        int a, b, c, pa, pb, pc, p;
  
        b = *pp++;
        c = *cp++;
        a = *lp++;
  
        p = b - c;
        pc = a - c;
  
  #ifdef PNG_USE_ABS
        pa = abs(p);
        pb = abs(pc);
        pc = abs(p + pc);
  #else
        pa = p < 0 ? -p : p;
        pb = pc < 0 ? -pc : pc;
        pc = (p + pc) < 0 ? -(p + pc) : p + pc;
  #endif
  
        p = (pa <= pb && pa <=pc) ? a : (pb <= pc) ? b : c;
  
        *dp++ = (png_byte)(((int)*rp++ - p) & 0xff);
     }
  }
  #endif /* WRITE_FILTER */
  
  void /* PRIVATE */
  png_write_find_filter(png_structrp png_ptr, png_row_infop row_info)
  {
  #ifndef PNG_WRITE_FILTER_SUPPORTED
     png_write_filtered_row(png_ptr, png_ptr->row_buf, row_info->rowbytes+1);
  #else
     unsigned int filter_to_do = png_ptr->do_filter;
     png_bytep row_buf;
     png_bytep best_row;
     png_uint_32 bpp;
     png_size_t mins;
     png_size_t row_bytes = row_info->rowbytes;
  
     png_debug(1, "in png_write_find_filter");
  
     /* Find out how many bytes offset each pixel is */
     bpp = (row_info->pixel_depth + 7) >> 3;
  
     row_buf = png_ptr->row_buf;
     mins = PNG_SIZE_MAX - 256/* so we can detect potential overflow of the
                                 running sum */;
  
     /* The prediction method we use is to find which method provides the
      * smallest value when summing the absolute values of the distances
      * from zero, using anything >= 128 as negative numbers.  This is known
      * as the "minimum sum of absolute differences" heuristic.  Other
      * heuristics are the "weighted minimum sum of absolute differences"
      * (experimental and can in theory improve compression), and the "zlib
      * predictive" method (not implemented yet), which does test compressions
      * of lines using different filter methods, and then chooses the
      * (series of) filter(s) that give minimum compressed data size (VERY
      * computationally expensive).
      *
      * GRR 980525:  consider also
      *
      *   (1) minimum sum of absolute differences from running average (i.e.,
      *       keep running sum of non-absolute differences & count of bytes)
      *       [track dispersion, too?  restart average if dispersion too large?]
      *
      *  (1b) minimum sum of absolute differences from sliding average, probably
      *       with window size <= deflate window (usually 32K)
      *
      *   (2) minimum sum of squared differences from zero or running average
      *       (i.e., ~ root-mean-square approach)
      */
  
  
     /* We don't need to test the 'no filter' case if this is the only filter
      * that has been chosen, as it doesn't actually do anything to the data.
      */
     best_row = png_ptr->row_buf;
  
     if (PNG_SIZE_MAX/128 <= row_bytes)
     {
        /* Overflow can occur in the calculation, just select the lowest set
         * filter.
         */
        filter_to_do &= 0U-filter_to_do;
     }
     else if ((filter_to_do & PNG_FILTER_NONE) != 0 &&
           filter_to_do != PNG_FILTER_NONE)
     {
        /* Overflow not possible and multiple filters in the list, including the
         * 'none' filter.
         */
        png_bytep rp;
        png_size_t sum = 0;
        png_size_t i;
        unsigned int v;
  
        {
           for (i = 0, rp = row_buf + 1; i < row_bytes; i++, rp++)
           {
              v = *rp;
  #ifdef PNG_USE_ABS
              sum += 128 - abs((int)v - 128);
  #else
              sum += (v < 128) ? v : 256 - v;
  #endif
           }
        }
  
        mins = sum;
     }
  
     /* Sub filter */
     if (filter_to_do == PNG_FILTER_SUB)
     /* It's the only filter so no testing is needed */
     {
        png_setup_sub_row_only(png_ptr, bpp, row_bytes);
        best_row = png_ptr->try_row;
     }
  
     else if ((filter_to_do & PNG_FILTER_SUB) != 0)
     {
        png_size_t sum;
        png_size_t lmins = mins;
  
        sum = png_setup_sub_row(png_ptr, bpp, row_bytes, lmins);
  
        if (sum < mins)
        {
           mins = sum;
           best_row = png_ptr->try_row;
           if (png_ptr->tst_row != NULL)
           {
              png_ptr->try_row = png_ptr->tst_row;
              png_ptr->tst_row = best_row;
           }
        }
     }
  
     /* Up filter */
     if (filter_to_do == PNG_FILTER_UP)
     {
        png_setup_up_row_only(png_ptr, row_bytes);
        best_row = png_ptr->try_row;
     }
  
     else if ((filter_to_do & PNG_FILTER_UP) != 0)
     {
        png_size_t sum;
        png_size_t lmins = mins;
  
        sum = png_setup_up_row(png_ptr, row_bytes, lmins);
  
        if (sum < mins)
        {
           mins = sum;
           best_row = png_ptr->try_row;
           if (png_ptr->tst_row != NULL)
           {
              png_ptr->try_row = png_ptr->tst_row;
              png_ptr->tst_row = best_row;
           }
        }
     }
  
     /* Avg filter */
     if (filter_to_do == PNG_FILTER_AVG)
     {
        png_setup_avg_row_only(png_ptr, bpp, row_bytes);
        best_row = png_ptr->try_row;
     }
  
     else if ((filter_to_do & PNG_FILTER_AVG) != 0)
     {
        png_size_t sum;
        png_size_t lmins = mins;
  
        sum= png_setup_avg_row(png_ptr, bpp, row_bytes, lmins);
  
        if (sum < mins)
        {
           mins = sum;
           best_row = png_ptr->try_row;
           if (png_ptr->tst_row != NULL)
           {
              png_ptr->try_row = png_ptr->tst_row;
              png_ptr->tst_row = best_row;
           }
        }
     }
  
     /* Paeth filter */
     if (filter_to_do == PNG_FILTER_PAETH)
     {
        png_setup_paeth_row_only(png_ptr, bpp, row_bytes);
        best_row = png_ptr->try_row;
     }
  
     else if ((filter_to_do & PNG_FILTER_PAETH) != 0)
     {
        png_size_t sum;
        png_size_t lmins = mins;
  
        sum = png_setup_paeth_row(png_ptr, bpp, row_bytes, lmins);
  
        if (sum < mins)
        {
           best_row = png_ptr->try_row;
           if (png_ptr->tst_row != NULL)
           {
              png_ptr->try_row = png_ptr->tst_row;
              png_ptr->tst_row = best_row;
           }
        }
     }
  
     /* Do the actual writing of the filtered row data from the chosen filter. */
     png_write_filtered_row(png_ptr, best_row, row_info->rowbytes+1);
  
  #endif /* WRITE_FILTER */
  }
  
  
  /* Do the actual writing of a previously filtered row. */
  static void
  png_write_filtered_row(png_structrp png_ptr, png_bytep filtered_row,
      png_size_t full_row_length/*includes filter byte*/)
  {
     png_debug(1, "in png_write_filtered_row");
  
     png_debug1(2, "filter = %d", filtered_row[0]);
  
     png_compress_IDAT(png_ptr, filtered_row, full_row_length, Z_NO_FLUSH);
  
  #ifdef PNG_WRITE_FILTER_SUPPORTED
     /* Swap the current and previous rows */
     if (png_ptr->prev_row != NULL)
     {
        png_bytep tptr;
  
        tptr = png_ptr->prev_row;
        png_ptr->prev_row = png_ptr->row_buf;
        png_ptr->row_buf = tptr;
     }
  #endif /* WRITE_FILTER */
  
     /* Finish row - updates counters and flushes zlib if last row */
     png_write_finish_row(png_ptr);
  
  #ifdef PNG_WRITE_FLUSH_SUPPORTED
     png_ptr->flush_rows++;
  
     if (png_ptr->flush_dist > 0 &&
         png_ptr->flush_rows >= png_ptr->flush_dist)
     {
        png_write_flush(png_ptr);
     }
  #endif /* WRITE_FLUSH */
  }
  #endif /* WRITE */
  