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src/Source/LibPNG/pngrtran.c  view on Meta::CPAN

                  /* Find the closest color to one we threw out */
                  d_index = png_ptr->quantize_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->quantize_index[i] = (png_byte)min_k;
               }
            }
         }
         png_free(png_ptr, png_ptr->quantize_sort);
         png_ptr->quantize_sort = NULL;
      }
      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_dsortp t;
         png_dsortpp hash;

         t = NULL;

         /* Initialize palette index arrays */
         png_ptr->index_to_palette = (png_bytep)png_malloc(png_ptr,
             (png_uint_32)(num_palette * (sizeof (png_byte))));
         png_ptr->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++)
         {
            png_ptr->index_to_palette[i] = (png_byte)i;
            png_ptr->palette_to_index[i] = (png_byte)i;
         }

         hash = (png_dsortpp)png_calloc(png_ptr, (png_uint_32)(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)
                  {

                     t = (png_dsortp)png_malloc_warn(png_ptr,
                         (png_uint_32)(sizeof (png_dsort)));

                     if (t == NULL)
                         break;

                     t->next = hash[d];
                     t->left = (png_byte)i;
                     t->right = (png_byte)j;
                     hash[d] = t;
                  }
               }
               if (t == NULL)
                  break;
            }

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

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

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

src/Source/LibPNG/pngrtran.c  view on Meta::CPAN

            while (bp < bp_end)
            {
               int b = *bp >> shift[channel];
               if (++channel >= channels)
                  channel = 0;
               *bp++ = (png_byte)b;
            }
            break;
         }

#ifdef PNG_READ_16BIT_SUPPORTED
         case 16:
         /* Double byte components, G, GA, RGB, RGBA */
         {
            png_bytep bp = row;
            png_bytep bp_end = bp + row_info->rowbytes;
            int channel = 0;

            while (bp < bp_end)
            {
               int value = (bp[0] << 8) + bp[1];

               value >>= shift[channel];
               if (++channel >= channels)
                  channel = 0;
               *bp++ = (png_byte)(value >> 8);
               *bp++ = (png_byte)(value & 0xff);
            }
            break;
         }
#endif
      }
   }
}
#endif

#ifdef PNG_READ_SCALE_16_TO_8_SUPPORTED
/* Scale rows of bit depth 16 down to 8 accurately */
static void
png_do_scale_16_to_8(png_row_infop row_info, png_bytep row)
{
   png_debug(1, "in png_do_scale_16_to_8");

   if (row_info->bit_depth == 16)
   {
      png_bytep sp = row; /* source */
      png_bytep dp = row; /* destination */
      png_bytep ep = sp + row_info->rowbytes; /* end+1 */

      while (sp < ep)
      {
         /* The input is an array of 16 bit components, these must be scaled to
          * 8 bits each.  For a 16 bit value V the required value (from the PNG
          * specification) is:
          *
          *    (V * 255) / 65535
          *
          * This reduces to round(V / 257), or floor((V + 128.5)/257)
          *
          * Represent V as the two byte value vhi.vlo.  Make a guess that the
          * result is the top byte of V, vhi, then the correction to this value
          * is:
          *
          *    error = floor(((V-vhi.vhi) + 128.5) / 257)
          *          = floor(((vlo-vhi) + 128.5) / 257)
          *
          * This can be approximated using integer arithmetic (and a signed
          * shift):
          *
          *    error = (vlo-vhi+128) >> 8;
          *
          * The approximate differs from the exact answer only when (vlo-vhi) is
          * 128; it then gives a correction of +1 when the exact correction is
          * 0.  This gives 128 errors.  The exact answer (correct for all 16 bit
          * input values) is:
          *
          *    error = (vlo-vhi+128)*65535 >> 24;
          *
          * An alternative arithmetic calculation which also gives no errors is:
          *
          *    (V * 255 + 32895) >> 16
          */

         png_int_32 tmp = *sp++; /* must be signed! */
         tmp += (((int)*sp++ - tmp + 128) * 65535) >> 24;
         *dp++ = (png_byte)tmp;
      }

      row_info->bit_depth = 8;
      row_info->pixel_depth = (png_byte)(8 * row_info->channels);
      row_info->rowbytes = row_info->width * row_info->channels;
   }
}
#endif

#ifdef PNG_READ_STRIP_16_TO_8_SUPPORTED
static void
/* Simply discard the low byte.  This was the default behavior prior
 * to libpng-1.5.4.
 */
png_do_chop(png_row_infop row_info, png_bytep row)
{
   png_debug(1, "in png_do_chop");

   if (row_info->bit_depth == 16)
   {
      png_bytep sp = row; /* source */
      png_bytep dp = row; /* destination */
      png_bytep ep = sp + row_info->rowbytes; /* end+1 */

      while (sp < ep)
      {
         *dp++ = *sp;
         sp += 2; /* skip low byte */
      }

      row_info->bit_depth = 8;
      row_info->pixel_depth = (png_byte)(8 * row_info->channels);
      row_info->rowbytes = row_info->width * row_info->channels;
   }