text: 
  /*
     Copyright (c) 2003-2007 Clarence Dang <dang@kde.org>
     Copyright (c) 2011 Martin Koller <kollix@aon.at>
     Modified by Maikel Diaz <ariguanabosoft@gmail.com>
     Copyright (c) 2015-2018
     All rights reserved.
  
     Redistribution and use in source and binary forms, with or without
     modification, are permitted provided that the following conditions
     are met:
  
     1. Redistributions of source code must retain the above copyright
        notice, this list of conditions and the following disclaimer.
     2. Redistributions in binary form must reproduce the above copyright
        notice, this list of conditions and the following disclaimer in the
        documentation and/or other materials provided with the distribution.
  
     THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
     IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
     INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
     NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
  
  
  #define DEBUG_KP_EFFECT_REDUCE_COLORS 0
  
  
  #include <kpEffectReduceColors.h>
  
  #include <qdebug.h>
  
  //---------------------------------------------------------------------
  
  static QImage::Format DepthToFormat (int depth)
  {
      // These values are QImage's supported depths.
      switch (depth)
      {
      case 1:
          // (can be MSB instead, I suppose)
          return QImage::Format_MonoLSB;
  
      case 8:
          return QImage::Format_Indexed8;
  
      case 16:
          return QImage::Format_ARGB4444_Premultiplied;
  
      case 24:
          return QImage::Format_ARGB6666_Premultiplied;
  
      case 32:
          return QImage::Format_ARGB32_Premultiplied;
  
      default:
          Q_ASSERT (!"unknown depth");
          return QImage::Format_Invalid;
      }
  }
  
  //---------------------------------------------------------------------
  
  // public static
  QImage kpEffectReduceColors::convertImageDepth (const QImage &image, int depth, bool dither)
  {
  #if DEBUG_KP_EFFECT_REDUCE_COLORS
      kDebug () << "kpeffectreducecolors.cpp:ConvertImageDepth() changing image (w=" << image.width ()
                 << ",h=" << image.height ()
                 << ") depth from " << image.depth ()
                  << " to " << depth
                  << " (dither=" << dither << ")"
                  << endl;
  #endif
  
      if (image.isNull ())
          return image;
  
      if (depth == image.depth ())
          return image;
  
  
  #if DEBUG_KP_EFFECT_REDUCE_COLORS && 0
      for (int y = 0; y < image.height (); y++)
      {
          for (int x = 0; x < image.width (); x++)
          {
              fprintf (stderr, " %08X", image.pixel (x, y));
          }
          fprintf (stderr, "\n");
      }
  #endif
  
  
      // Hack around Qt's braindead QImage::convertToFormat(QImage::Format_MonoLSB, ...)
      // (with dithering off) which produces pathetic results with an image that
      // only has 2 colors - sometimes it just gives a completely black
      // result (try yellow and white as input).  Instead, we simply preserve
      // the 2 colours.
      //
      // One use case is resaving a "color monochrome" image (<= 2 colors but
      // not necessarily black & white).
      if (depth == 1 && !dither)
      {
      #if DEBUG_KP_EFFECT_REDUCE_COLORS
          kDebug () << "\tinvoking convert-to-depth 1 hack";
      #endif
          QRgb color0 = 0, color1 = 0;
          bool color0Valid = false, color1Valid = false;
  
          bool moreThan2Colors = false;
  
          QImage monoImage (image.width (), image.height (), QImage::Format_MonoLSB);
          monoImage.setColorCount (2);
      #if DEBUG_KP_EFFECT_REDUCE_COLORS
          kDebug () << "\t\tinitialising output image w=" << monoImage.width ()
                     << ",h=" << monoImage.height ()
                     << ",d=" << monoImage.depth ()
                     << endl;
      #endif
          for (int y = 0; y < image.height (); y++)
          {
              for (int x = 0; x < image.width (); x++)
              {
                  // (this can be transparent)
                  QRgb imagePixel = image.pixel (x, y);
  
                  if (color0Valid && imagePixel == color0)
                      monoImage.setPixel (x, y, 0);
                  else if (color1Valid && imagePixel == color1)
                      monoImage.setPixel (x, y, 1);
                  else if (!color0Valid)
                  {
                      color0 = imagePixel;
                      color0Valid = true;
                      monoImage.setPixel (x, y, 0);
                  #if DEBUG_KP_EFFECT_REDUCE_COLORS
                      kDebug () << "\t\t\tcolor0=" << (int *) color0
                                 << " at x=" << x << ",y=" << y << endl;
                  #endif
                  }
                  else if (!color1Valid)
                  {
                      color1 = imagePixel;
                      color1Valid = true;
                      monoImage.setPixel (x, y, 1);
                  #if DEBUG_KP_EFFECT_REDUCE_COLORS
                      kDebug () << "\t\t\tcolor1=" << (int *) color1
                                 << " at x=" << x << ",y=" << y << endl;
                  #endif
                  }
                  else
                  {
                  #if DEBUG_KP_EFFECT_REDUCE_COLORS
                      kDebug () << "\t\t\timagePixel=" << (int *) imagePixel
                                 << " at x=" << x << ",y=" << y
                                 << " moreThan2Colors - abort hack" << endl;
                  #endif
                      moreThan2Colors = true;
  
                      // Dijkstra, this is clearer than double break'ing or
                      // a check in both loops
                      goto exit_loop;
                  }
              }
          }
      exit_loop:
  
          if (!moreThan2Colors)
          {
              monoImage.setColor (0, color0Valid ? color0 : 0xFFFFFF);
              monoImage.setColor (1, color1Valid ? color1 : 0x000000);
              return monoImage;
          }
      }
  
      QImage retImage = image.convertToFormat (::DepthToFormat (depth),
          Qt::AutoColor |
          (dither ? Qt::DiffuseDither : Qt::ThresholdDither) |
          Qt::ThresholdAlphaDither |
          (dither ? Qt::PreferDither : Qt::AvoidDither));
  #if DEBUG_KP_EFFECT_REDUCE_COLORS
      kDebug () << "\tformat: before=" << image.format ()
                << "after=" << retImage.format ();
  #endif
  
  #if DEBUG_KP_EFFECT_REDUCE_COLORS && 0
      kDebug () << "After colour reduction:";
      for (int y = 0; y < image.height (); y++)
      {
          for (int x = 0; x < image.width (); x++)
          {
              fprintf (stderr, " %08X", image.pixel (x, y));
          }
          fprintf (stderr, "\n");
      }
  #endif
  
      return retImage;
  }
  
  //---------------------------------------------------------------------
  
  // public static
  void kpEffectReduceColors::applyEffect (QImage *destPtr, int depth, bool dither)
  {
      if (!destPtr)
          return;
  
      // You can't "reduce" to 32-bit since it's the highest depth.
      if (depth != 1 && depth != 8)
          return;
  
      *destPtr = convertImageDepth(*destPtr, depth, dither);
  
      // internally we always use QImage::Format_ARGB32_Premultiplied and
      // this effect is just an "effect" in that it changes the image (the look) somehow
      // When one wants a different depth on the file, then he needs to save the image
      // in that depth
      *destPtr = destPtr->convertToFormat(QImage::Format_ARGB32_Premultiplied);
  }
  
  //---------------------------------------------------------------------
  
  QImage kpEffectReduceColors::applyEffect (const QImage &pm, int depth, bool dither)
  {
      QImage ret = pm;
      applyEffect (&ret, depth, dither);
      return ret;
  }
  
  //---------------------------------------------------------------------
  