pngrtran.c

这个刚才那个的源代码

/* pngrtran.c - transforms the data in a row for PNG readers
 *
 * libpng 1.2.1 - December 12, 2001
 * For conditions of distribution and use, see copyright notice in png.h
 * Copyright (c) 1998-2001 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 file contains functions optionally called by an application
 * in order to tell libpng how to handle data when reading a PNG.
 * Transformations that are used in both reading and writing are
 * in pngtrans.c.
 */

#define PNG_INTERNAL
#include "png.h"

/* Set the action on getting a CRC error for an ancillary or critical chunk. */
void PNGAPI
png_set_crc_action(png_structp png_ptr, int crit_action, int ancil_action)
{
   png_debug(1, "in png_set_crc_action\n");
   /* Tell libpng how we react to CRC errors in critical chunks */
   switch (crit_action)
   {
      case PNG_CRC_NO_CHANGE:                        /* leave setting as is */
         break;
      case PNG_CRC_WARN_USE:                               /* warn/use data */
         png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
         png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE;
         break;
      case PNG_CRC_QUIET_USE:                             /* quiet/use data */
         png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
         png_ptr->flags |= PNG_FLAG_CRC_CRITICAL_USE |
                           PNG_FLAG_CRC_CRITICAL_IGNORE;
         break;
      case PNG_CRC_WARN_DISCARD:    /* not a valid action for critical data */
         png_warning(png_ptr, "Can't discard critical data on CRC error.");
      case PNG_CRC_ERROR_QUIT:                                /* error/quit */
      case PNG_CRC_DEFAULT:
      default:
         png_ptr->flags &= ~PNG_FLAG_CRC_CRITICAL_MASK;
         break;
   }

   switch (ancil_action)
   {
      case PNG_CRC_NO_CHANGE:                       /* leave setting as is */
         break;
      case PNG_CRC_WARN_USE:                              /* warn/use data */
         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
         png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE;
         break;
      case PNG_CRC_QUIET_USE:                            /* quiet/use data */
         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
         png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_USE |
                           PNG_FLAG_CRC_ANCILLARY_NOWARN;
         break;
      case PNG_CRC_ERROR_QUIT:                               /* error/quit */
         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
         png_ptr->flags |= PNG_FLAG_CRC_ANCILLARY_NOWARN;
         break;
      case PNG_CRC_WARN_DISCARD:                      /* warn/discard data */
      case PNG_CRC_DEFAULT:
      default:
         png_ptr->flags &= ~PNG_FLAG_CRC_ANCILLARY_MASK;
         break;
   }
}

#if defined(PNG_READ_BACKGROUND_SUPPORTED) && \
    defined(PNG_FLOATING_POINT_SUPPORTED)
/* handle alpha and tRNS via a background color */
void PNGAPI
png_set_background(png_structp png_ptr,
   png_color_16p background_color, int background_gamma_code,
   int need_expand, double background_gamma)
{
   png_debug(1, "in png_set_background\n");
   if (background_gamma_code == PNG_BACKGROUND_GAMMA_UNKNOWN)
   {
      png_warning(png_ptr, "Application must supply a known background gamma");
      return;
   }

   png_ptr->transformations |= PNG_BACKGROUND;
   png_memcpy(&(png_ptr->background), background_color, sizeof(png_color_16));
   png_ptr->background_gamma = (float)background_gamma;
   png_ptr->background_gamma_type = (png_byte)(background_gamma_code);
   png_ptr->transformations |= (need_expand ? PNG_BACKGROUND_EXPAND : 0);

   /* Note:  if need_expand is set and color_type is either RGB or RGB_ALPHA
    * (in which case need_expand is superfluous anyway), the background color
    * might actually be gray yet not be flagged as such. This is not a problem
    * for the current code, which uses PNG_BACKGROUND_IS_GRAY only to
    * decide when to do the png_do_gray_to_rgb() transformation.
    */
   if ((need_expand && !(png_ptr->color_type & PNG_COLOR_MASK_COLOR)) ||
       (!need_expand && background_color->red == background_color->green &&
        background_color->red == background_color->blue))
      png_ptr->mode |= PNG_BACKGROUND_IS_GRAY;
}
#endif

#if defined(PNG_READ_16_TO_8_SUPPORTED)
/* strip 16 bit depth files to 8 bit depth */
void PNGAPI
png_set_strip_16(png_structp png_ptr)
{
   png_debug(1, "in png_set_strip_16\n");
   png_ptr->transformations |= PNG_16_TO_8;
}
#endif

#if defined(PNG_READ_STRIP_ALPHA_SUPPORTED)
void PNGAPI
png_set_strip_alpha(png_structp png_ptr)
{
   png_debug(1, "in png_set_strip_alpha\n");
   png_ptr->transformations |= PNG_STRIP_ALPHA;
}
#endif

#if defined(PNG_READ_DITHER_SUPPORTED)
/* Dither file to 8 bit.  Supply a palette, the current number
 * of elements in the palette, the maximum number of elements
 * allowed, and a histogram if possible.  If the current number
 * of colors is greater then the maximum number, the palette will be
 * modified to fit in the maximum number.  "full_dither" indicates
 * whether we need a dithering cube set up for RGB images, or if we
 * simply are reducing the number of colors in a paletted image.
 */

typedef struct png_dsort_struct
{
   struct png_dsort_struct FAR * next;
   png_byte left;
   png_byte right;
} png_dsort;
typedef png_dsort FAR *       png_dsortp;
typedef png_dsort FAR * FAR * png_dsortpp;

void PNGAPI
png_set_dither(png_structp png_ptr, png_colorp palette,
   int num_palette, int maximum_colors, png_uint_16p histogram,
   int full_dither)
{
   png_debug(1, "in png_set_dither\n");
   png_ptr->transformations |= PNG_DITHER;

   if (!full_dither)
   {
      int i;

      png_ptr->dither_index = (png_bytep)png_malloc(png_ptr,
         (png_uint_32)(num_palette * sizeof (png_byte)));
      for (i = 0; i < num_palette; i++)
         png_ptr->dither_index[i] = (png_byte)i;
   }

   if (num_palette > maximum_colors)
   {
      if (histogram != NULL)
      {
         /* This is easy enough, just throw out the least used colors.
            Perhaps not the best solution, but good enough. */

         int i;
         png_bytep sort;

         /* initialize an array to sort colors */
         sort = (png_bytep)png_malloc(png_ptr, (png_uint_32)(num_palette
            * sizeof (png_byte)));

         /* initialize the sort array */
         for (i = 0; i < num_palette; i++)
            sort[i] = (png_byte)i;

         /* Find the least used palette entries by starting a
            bubble sort, and running it until we have sorted
            out enough colors.  Note that we don't care about
            sorting all the colors, just finding which are
            least used. */

         for (i = num_palette - 1; i >= maximum_colors; i--)
         {
            int done; /* to stop early if the list is pre-sorted */
            int j;

            done = 1;
            for (j = 0; j < i; j++)
            {
               if (histogram[sort[j]] < histogram[sort[j + 1]])
               {
                  png_byte t;

                  t = sort[j];
                  sort[j] = sort[j + 1];
                  sort[j + 1] = t;
                  done = 0;
               }
            }
            if (done)
               break;
         }

         /* swap the palette around, and set up a table, if necessary */
         if (full_dither)
         {
            int j = num_palette;

            /* put all the useful colors within the max, but don't
               move the others */
            for (i = 0; i < maximum_colors; i++)
            {
               if ((int)sort[i] >= maximum_colors)
               {
                  do
                     j--;
                  while ((int)sort[j] >= maximum_colors);
                  palette[i] = palette[j];
               }
            }
         }
         else
         {
            int j = num_palette;

            /* move all the used colors inside the max limit, and
               develop a translation table */
            for (i = 0; i < maximum_colors; i++)
            {
               /* only move the colors we need to */
               if ((int)sort[i] >= maximum_colors)
               {
                  png_color tmp_color;

                  do
                     j--;
                  while ((int)sort[j] >= maximum_colors);

                  tmp_color = palette[j];
                  palette[j] = palette[i];
                  palette[i] = tmp_color;
                  /* indicate where the color went */
                  png_ptr->dither_index[j] = (png_byte)i;
                  png_ptr->dither_index[i] = (png_byte)j;
               }
            }

            /* find closest color for those colors we are not using */
            for (i = 0; i < num_palette; i++)
            {
               if ((int)png_ptr->dither_index[i] >= maximum_colors)
               {
                  int min_d, k, min_k, d_index;

                  /* find the closest color to one we threw out */
                  d_index = png_ptr->dither_index[i];
                  min_d = PNG_COLOR_DIST(palette[d_index], palette[0]);
                  for (k = 1, min_k = 0; k < maximum_colors; k++)
                  {
                     int d;

                     d = PNG_COLOR_DIST(palette[d_index], palette[k]);

                     if (d < min_d)
                     {
                        min_d = d;
                        min_k = k;
                     }
                  }
                  /* point to closest color */
                  png_ptr->dither_index[i] = (png_byte)min_k;
               }
            }
         }
         png_free(png_ptr, sort);
      }
      else
      {
         /* This is much harder to do simply (and quickly).  Perhaps
            we need to go through a median cut routine, but those
            don't always behave themselves with only a few colors
            as input.  So we will just find the closest two colors,
            and throw out one of them (chosen somewhat randomly).
            [We don't understand this at all, so if someone wants to
             work on improving it, be our guest - AED, GRP]
            */
         int i;
         int max_d;
         int num_new_palette;
         png_dsortpp hash;
         png_bytep index_to_palette;
            /* where the original index currently is in the palette */
         png_bytep palette_to_index;
            /* which original index points to this palette color */

         /* initialize palette index arrays */
         index_to_palette = (png_bytep)png_malloc(png_ptr,
            (png_uint_32)(num_palette * sizeof (png_byte)));
         palette_to_index = (png_bytep)png_malloc(png_ptr,
            (png_uint_32)(num_palette * sizeof (png_byte)));

         /* initialize the sort array */
         for (i = 0; i < num_palette; i++)
         {
            index_to_palette[i] = (png_byte)i;
            palette_to_index[i] = (png_byte)i;
         }

         hash = (png_dsortpp)png_malloc(png_ptr, (png_uint_32)(769 *
            sizeof (png_dsortp)));
         for (i = 0; i < 769; i++)
            hash[i] = NULL;
/*         png_memset(hash, 0, 769 * sizeof (png_dsortp)); */

         num_new_palette = num_palette;

         /* initial wild guess at how far apart the farthest pixel
            pair we will be eliminating will be.  Larger
            numbers mean more areas will be allocated, Smaller
            numbers run the risk of not saving enough data, and
            having to do this all over again.

            I have not done extensive checking on this number.
            */
         max_d = 96;

         while (num_new_palette > maximum_colors)
         {
            for (i = 0; i < num_new_palette - 1; i++)
            {
               int j;

               for (j = i + 1; j < num_new_palette; j++)
               {
                  int d;

                  d = PNG_COLOR_DIST(palette[i], palette[j]);

                  if (d <= max_d)
                  {
                     png_dsortp t;

                     t = (png_dsortp)png_malloc(png_ptr, (png_uint_32)(sizeof
                         (png_dsort)));
                     t->next = hash[d];
                     t->left = (png_byte)i;
                     t->right = (png_byte)j;
                     hash[d] = t;
                  }
               }
            }

            for (i = 0; i <= max_d; i++)
            {
               if (hash[i] != NULL)
               {
                  png_dsortp p;

                  for (p = hash[i]; p; p = p->next)
                  {
                     if ((int)index_to_palette[p->left] < num_new_palette &&
                        (int)index_to_palette[p->right] < num_new_palette)
                     {
                        int j, next_j;

                        if (num_new_palette & 0x01)
                        {
                           j = p->left;
                           next_j = p->right;
                        }
                        else
                        {
                           j = p->right;
                           next_j = p->left;
                        }