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Stucki.cxx

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/*
 * @(#)src/Stucki.cxx  1.0  2002-08-27 16:24
 *
 * Copyright (C)  2002  Daniel Léonard
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */

#include "Stucki.h"

namespace halftoner
{

//---------------------------
// Constructor
//---------------------------

   Stucki::Stucki()
   {
   // nothing
   }


//---------------------------
// Destructor
//---------------------------

   Stucki::~Stucki()
   {
   // nothing
   }


//---------------------------
// Implemented methods from ErrorDiffusionHalftoner
//---------------------------

   int Stucki::halftoneToRight(float* source, int i, int j, int offset, int width, int height, int threshold) throw()
   {
      float grey = source[offset];
      int bw = (grey < threshold) ? 0 : 1;
      float diff = grey - 255.0f * bw;

   // first diffusion ( (x+1,y) -> 7)
      bool one_on_right = (i + 1) < width;
      if (one_on_right)
      {
         float* pixel = source + offset + 1;
         *pixel += diff * (8.0f / 42.0f);
      }
   // second diffusion ( (x+2,y) -> 5)
      bool two_on_right = (i + 2) < width;
      if (two_on_right)
      {
         float* pixel = source + offset + 2;
         *pixel += diff * (4.0f / 42.0f);
      }
      if (j + 1 < height)
      {
         float* pixel = source + offset + width - 2;
      // third diffusion ( (x-2,y+1) -> 3)
         if ((i - 2) >= 0)
         {
            *pixel += diff * (2.0f / 42.0f);
         }
         pixel++;

      // fourth diffusion ( (x-1,y+1) -> 5)
         if (i - 1 >= 0)
         {
            *pixel += diff * (4.0f / 42.0f);
         }
         pixel++;

      // fifth diffusion ( (x,y+1) -> 7)
         *pixel += diff * (8.0f / 42.0f);

      // sixth diffusion ( (x+1,y+1) -> 5)
         if (one_on_right)
         {
            pixel++;
            *pixel += diff * (4.0f / 42.0f);
         }

      // seventh diffusion ( (x+2,y+1) -> 3)
         if (two_on_right)
         {
            pixel++;
            *pixel += diff * (2.0f / 42.0f);
         }
      }
      if (j + 2 < height)
      {
         float* pixel = source + offset + width + width - 2;
      // eightth diffusion ( (x-2,y+2) -> 1)
         if (i - 2 >= 0)
         {
            *pixel += diff * (1.0f / 42.0f);
         }
         pixel++;

      // ninth diffusion ( (x-1,y+2) -> 3)
         if (i - 1 >= 0)
         {
            *pixel += diff * (2.0f / 42.0f);
         }
         pixel++;

      // tenth diffusion ( (x,y+2) -> 5)
         *pixel += diff * (4.0f / 42.0f);

      // eleventh diffusion ( (x+1,y+2) -> 3)
         if (one_on_right)
         {
            pixel++;
            *pixel += diff * (2.0f / 42.0f);
         }
      // twelfth diffusion ( (x+2,y+2) -> 1)
         if (two_on_right)
         {
            pixel++;
            *pixel += diff * (1.0f / 42.0f);
         }
      }

      return bw;
   }

   int Stucki::halftoneToLeft(float* source, int i, int j, int offset, int width, int height, int threshold) throw()
   {
      float grey = source[offset];
      int bw = (grey < threshold) ? 0 : 1;
      float diff = grey - 255.0f * bw;

   // first diffusion ( (x+1,y) -> 7)
      bool one_on_left = (i - 1) >= 0;
      if (one_on_left)
      {
         float* pixel = source + offset - 1;
         *pixel += diff * (8.0f / 42.0f);
      }
   // second diffusion ( (x+2,y) -> 5)
      bool two_on_left = (i - 2) >= 0;
      if (two_on_left)
      {
         float* pixel = source + offset - 2;
         *pixel += diff * (4.0f / 42.0f);
      }
      if (j + 1 < height)
      {
         float* pixel = source + offset + width + 2;
      // third diffusion ( (x-2,y+1) -> 3)
         if ((i + 2) < width)
         {
            *pixel += diff * (2.0f / 42.0f);
         }
         pixel--;

      // fourth diffusion ( (x-1,y+1) -> 5)
         if ((i + 1) < width)
         {
            *pixel += diff * (4.0f / 42.0f);
         }
         pixel--;

      // fifth diffusion ( (x,y+1) -> 7)
         *pixel += diff * (8.0f / 42.0f);

      // sixth diffusion ( (x+1,y+1) -> 5)
         if (one_on_left)
         {
            pixel--;
            *pixel += diff * (4.0f / 42.0f);
         }

      // seventh diffusion ( (x+2,y+1) -> 3)
         if (two_on_left)
         {
            pixel--;
            *pixel += diff * (2.0f / 42.0f);
         }
      }
      if (j + 2 < height)
      {
         float* pixel = source + offset + width + width + 2;
      // eightth diffusion ( (x-2,y+2) -> 1)
         if ((i + 2) < width)
         {
            *pixel += diff * (1.0f / 42.0f);
         }
         pixel--;

      // ninth diffusion ( (x-1,y+2) -> 3)
         if ((i + 1) < width)
         {
            *pixel += diff * (2.0f / 42.0f);
         }
         pixel--;

      // tenth diffusion ( (x,y+2) -> 5)
         *pixel += diff * (4.0f / 42.0f);

      // eleventh diffusion ( (x+1,y+2) -> 3)
         if (one_on_left)
         {
            pixel--;
            *pixel += diff * (2.0f / 42.0f);
         }
      // twelfth diffusion ( (x+2,y+2) -> 1)
         if (two_on_left)
         {
            pixel--;
            *pixel += diff * (1.0f / 42.0f);
         }
      }

      return bw;
   }

}

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