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FloydSteinberg.cxx

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/*
 * @(#)src/FloydSteinberg.cxx  1.0  2002-08-27 13:27
 *
 * 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 "FloydSteinberg.h"

namespace halftoner
{

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

   FloydSteinberg::FloydSteinberg()
   {
   // nothing
   }


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

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


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

   int FloydSteinberg::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 * (7.0f / 16.0f);
      }

   // other diffusion
      if ((j + 1) < height)
      {
         float* pixel = source + offset + width - 1;
      // second diffusion ( (x-1,y+1) -> 3)
         if (i > 0)
         {
            *pixel += diff * (3.0f / 16.0f);
         }
         pixel++;

      // third diffusion ( (x,y+1) -> 5)
         *pixel += diff * (5.0f / 16.0f);
         pixel++;

      // fourth diffusion ( (x+1,y+1) -> 1)
         if (one_on_right)
         {
            *pixel += diff * (1.0f / 16.0f);
         }
      }

      return bw;
   }

   int FloydSteinberg::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 * (7.0f / 16.0f);
      }

   // other diffusion
      if ((j + 1) < height)
      {
         float* pixel = source + offset + width + 1;
      // second diffusion ( (x+1,y+1) -> 3)
         if (i + 1 < width)
         {
            *pixel += diff * (3.0f / 16.0f);
         }
         pixel--;

      // third diffusion ( (x,y+1) -> 5)
         *pixel += diff * (5.0f / 16.0f);
         pixel--;

      // fourth diffusion ( (x-1,y+1) -> 1)
         if (one_on_left)
         {
            *pixel += diff * (1.0f / 16.0f);
         }
      }

      return bw;
   }

}

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