view release on metacpan or  search on metacpan

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

                        PNG_sRGB_FROM_LINEAR(gray + back_gx),
                        PNG_sRGB_FROM_LINEAR(gray + back_bx), 255, P_sRGB);
                  }
               }

               cmap_entries = i;
               output_processing = PNG_CMAP_GA;
            }
         }
         break;

      case PNG_COLOR_TYPE_RGB:
      case PNG_COLOR_TYPE_RGB_ALPHA:
         /* Exclude the case where the output is gray; we can always handle this
          * with the cases above.
          */
         if ((output_format & PNG_FORMAT_FLAG_COLOR) == 0)
         {
            /* The color-map will be grayscale, so we may as well convert the
             * input RGB values to a simple grayscale and use the grayscale
             * code above.
             *
             * NOTE: calling this apparently damages the recognition of the
             * transparent color in background color handling; call
             * png_set_tRNS_to_alpha before png_set_background_fixed.
             */
            png_set_rgb_to_gray_fixed(png_ptr, PNG_ERROR_ACTION_NONE, -1,
               -1);
            data_encoding = P_sRGB;

            /* The output will now be one or two 8-bit gray or gray+alpha
             * channels.  The more complex case arises when the input has alpha.
             */
            if ((png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
               png_ptr->num_trans > 0) &&
               (output_format & PNG_FORMAT_FLAG_ALPHA) != 0)
            {
               /* Both input and output have an alpha channel, so no background
                * processing is required; just map the GA bytes to the right
                * color-map entry.
                */
               expand_tRNS = 1;

               if (PNG_GA_COLORMAP_ENTRIES > image->colormap_entries)
                  png_error(png_ptr, "rgb[ga] color-map: too few entries");

               cmap_entries = make_ga_colormap(display);
               background_index = PNG_CMAP_GA_BACKGROUND;
               output_processing = PNG_CMAP_GA;
            }

            else
            {
               /* Either the input or the output has no alpha channel, so there
                * will be no non-opaque pixels in the color-map; it will just be
                * grayscale.
                */
               if (PNG_GRAY_COLORMAP_ENTRIES > image->colormap_entries)
                  png_error(png_ptr, "rgb[gray] color-map: too few entries");

               /* Ideally this code would use libpng to do the gamma correction,
                * but if an input alpha channel is to be removed we will hit the
                * libpng bug in gamma+compose+rgb-to-gray (the double gamma
                * correction bug).  Fix this by dropping the gamma correction in
                * this case and doing it in the palette; this will result in
                * duplicate palette entries, but that's better than the
                * alternative of double gamma correction.
                */
               if ((png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
                  png_ptr->num_trans > 0) &&
                  png_gamma_not_sRGB(png_ptr->colorspace.gamma) != 0)
               {
                  cmap_entries = make_gray_file_colormap(display);
                  data_encoding = P_FILE;
               }

               else
                  cmap_entries = make_gray_colormap(display);

               /* But if the input has alpha or transparency it must be removed
                */
               if (png_ptr->color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
                  png_ptr->num_trans > 0)
               {
                  png_color_16 c;
                  png_uint_32 gray = back_g;

                  /* We need to ensure that the application background exists in
                   * the colormap and that completely transparent pixels map to
                   * it.  Achieve this simply by ensuring that the entry
                   * selected for the background really is the background color.
                   */
                  if (data_encoding == P_FILE) /* from the fixup above */
                  {
                     /* The app supplied a gray which is in output_encoding, we
                      * need to convert it to a value of the input (P_FILE)
                      * encoding then set this palette entry to the required
                      * output encoding.
                      */
                     if (output_encoding == P_sRGB)
                        gray = png_sRGB_table[gray]; /* now P_LINEAR */

                     gray = PNG_DIV257(png_gamma_16bit_correct(gray,
                        png_ptr->colorspace.gamma)); /* now P_FILE */

                     /* And make sure the corresponding palette entry contains
                      * exactly the required sRGB value.
                      */
                     png_create_colormap_entry(display, gray, back_g, back_g,
                        back_g, 0/*unused*/, output_encoding);
                  }

                  else if (output_encoding == P_LINEAR)
                  {
                     gray = PNG_sRGB_FROM_LINEAR(gray * 255);

                     /* And make sure the corresponding palette entry matches.
                      */
                     png_create_colormap_entry(display, gray, back_g, back_g,
                        back_g, 0/*unused*/, P_LINEAR);
                  }