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src/dlib/external/libpng/pngread.c  view on Meta::CPAN

   return f;
}

/* NOTE: E_LINEAR values to this routine must be 16-bit, but E_FILE values must
 * be 8-bit.
 */
static void
png_create_colormap_entry(png_image_read_control *display,
   png_uint_32 ip, png_uint_32 red, png_uint_32 green, png_uint_32 blue,
   png_uint_32 alpha, int encoding)
{
   png_imagep image = display->image;
   const int output_encoding = (image->format & PNG_FORMAT_FLAG_LINEAR) ?
      E_LINEAR : E_sRGB;
   const int convert_to_Y = (image->format & PNG_FORMAT_FLAG_COLOR) == 0 &&
      (red != green || green != blue);

   if (ip > 255)
      png_error(image->opaque->png_ptr, "color-map index out of range");

   /* Update the cache with whether the file gamma is significantly different
    * from sRGB.
    */
   if (encoding == E_FILE)
   {
      if (display->file_encoding == E_NOTSET)
         set_file_encoding(display);

      /* Note that the cached value may be E_FILE too, but if it is then the
       * gamma_to_linear member has been set.
       */
      encoding = display->file_encoding;
   }

   if (encoding == E_FILE)
   {
      png_fixed_point g = display->gamma_to_linear;

      red = png_gamma_16bit_correct(red*257, g);
      green = png_gamma_16bit_correct(green*257, g);
      blue = png_gamma_16bit_correct(blue*257, g);

      if (convert_to_Y || output_encoding == E_LINEAR)
      {
         alpha *= 257;
         encoding = E_LINEAR;
      }

      else
      {
         red = PNG_sRGB_FROM_LINEAR(red * 255);
         green = PNG_sRGB_FROM_LINEAR(green * 255);
         blue = PNG_sRGB_FROM_LINEAR(blue * 255);
         encoding = E_sRGB;
      }
   }

   else if (encoding == E_LINEAR8)
   {
      /* This encoding occurs quite frequently in test cases because PngSuite
       * includes a gAMA 1.0 chunk with most images.
       */
      red *= 257;
      green *= 257;
      blue *= 257;
      alpha *= 257;
      encoding = E_LINEAR;
   }

   else if (encoding == E_sRGB && (convert_to_Y || output_encoding == E_LINEAR))
   {
      /* The values are 8-bit sRGB values, but must be converted to 16-bit
       * linear.
       */
      red = png_sRGB_table[red];
      green = png_sRGB_table[green];
      blue = png_sRGB_table[blue];
      alpha *= 257;
      encoding = E_LINEAR;
   }

   /* This is set if the color isn't gray but the output is. */
   if (encoding == E_LINEAR)
   {
      if (convert_to_Y)
      {
         /* NOTE: these values are copied from png_do_rgb_to_gray */
         png_uint_32 y = (png_uint_32)6968 * red  + (png_uint_32)23434 * green +
            (png_uint_32)2366 * blue;

         if (output_encoding == E_LINEAR)
            y = (y + 16384) >> 15;

         else
         {
            /* y is scaled by 32768, we need it scaled by 255: */
            y = (y + 128) >> 8;
            y *= 255;
            y = PNG_sRGB_FROM_LINEAR((y + 64) >> 7);
            encoding = E_sRGB;
         }

         blue = red = green = y;
      }

      else if (output_encoding == E_sRGB)
      {
         red = PNG_sRGB_FROM_LINEAR(red * 255);
         green = PNG_sRGB_FROM_LINEAR(green * 255);
         blue = PNG_sRGB_FROM_LINEAR(blue * 255);
         alpha = PNG_DIV257(alpha);
         encoding = E_sRGB;
      }
   }

   if (encoding != output_encoding)
      png_error(image->opaque->png_ptr, "bad encoding (internal error)");

   /* Store the value. */
   {