include/filters/GP_Dither.h

   1 /*****************************************************************************
   2  * This file is part of gfxprim library.                                     *
   3  *                                                                           *
   4  * Gfxprim is free software; you can redistribute it and/or                  *
   5  * modify it under the terms of the GNU Lesser General Public                *
   6  * License as published by the Free Software Foundation; either              *
   7  * version 2.1 of the License, or (at your option) any later version.        *
   8  *                                                                           *
   9  * Gfxprim is distributed in the hope that it will be useful,                *
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of            *
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU         *
  12  * Lesser General Public License for more details.                           *
  13  *                                                                           *
  14  * You should have received a copy of the GNU Lesser General Public          *
  15  * License along with gfxprim; if not, write to the Free Software            *
  16  * Foundation, Inc., 51 Franklin Street, Fifth Floor,                        *
  17  * Boston, MA  02110-1301  USA                                               *
  18  *                                                                           *
  19  * Copyright (C) 2009-2013 Cyril Hrubis <metan@ucw.cz>                       *
  20  *                                                                           *
  21  *****************************************************************************/
  22
  23 /*
  24
  25   Dithering algorithms.
  26
  27  */
  28
  29 #ifndef FILTERS_GP_DITHER_H
  30 #define FILTERS_GP_DITHER_H
  31
  32 #include "GP_Filter.h"
  33
  34 /*
  35  * Classical Floyd-Steinberg. Produces good results and is a little faster than
  36  * the Hilbert-Peano dithering.
  37  *
  38  * The error is distributed to the neighbor pixels as follows:
  39  * (X denotes current position)
  40  *
  41  *
  42  *          |       |
  43  *          |   X   |  7/16
  44  *          |       |
  45  *   -----------------------
  46  *          |       |
  47  *     3/16 |  5/16 |  1/16
  48  *          |       |
  49  *
  50  */
  51
  52 /*
  53  * Converts RGB888 24bit image to any RGB or Grayscale bitmap.
  54  *
  55  * The source pixel_type MUST BE GP_PIXEL_RGB888.
  56  *
  57  * The destination must be at least as large as source.
  58  *
  59  * If operation was aborted from within a callback, non-zero is returned.
  60  */
  61 int GP_FilterFloydSteinberg(const GP_Pixmap *src,
  62                             GP_Pixmap *dst,
  63                             GP_ProgressCallback *callback);
  64
  65 /*
  66  * If malloc() has failed, or operation was aborted by a callback, NULL is
  67  * returned.
  68  */
  69 GP_Pixmap *GP_FilterFloydSteinbergAlloc(const GP_Pixmap *src,
  70                                          GP_PixelType pixel_type,
  71                                          GP_ProgressCallback *callback);
  72
  73 /*
  74  * Hilbert-Peano space filling curve based dithering.
  75  *
  76  * The error value is distributed around the Hilbert curve.
  77  *
  78  * This dithering introduces a little more noisy result but doesn't create
  79  * repeating patterns like Floyd-Steinberg which looks generally better to
  80  * human eye. On the other hand edges tend to be less sharp.
  81  */
  82
  83 /*
  84  * Converts RGB888 24bit image to any RGB or Grayscale bitmap.
  85  *
  86  * The source pixel_type MUST BE GP_PIXEL_RGB888.
  87  *
  88  * The destination must be at least as large as source.
  89  *
  90  * If the operation was aborted from within a callback, non-zero is returned.
  91  */
  92 int GP_FilterHilbertPeano(const GP_Pixmap *src,
  93                           GP_Pixmap *dst,
  94                           GP_ProgressCallback *callback);
  95
  96 /*
  97  * If malloc() has failed, or operation was aborted by a callback, NULL is
  98  * returned.
  99  */
 100 GP_Pixmap *GP_FilterHilbertPeanoAlloc(const GP_Pixmap *src,
 101                                        GP_PixelType pixel_type,
 102                                        GP_ProgressCallback *callback);
 103
 104 #endif /* FILTERS_GP_DITHER_H */