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

               trans_gray *= 0x11;
               break;

            default:

            case 8:
               /* FALL THROUGH (Already 8 bits) */

            case 16:
               /* Already a full 16 bits */
               break;
         }

         png_ptr->background.red = png_ptr->background.green =
            png_ptr->background.blue = (png_uint_16)gray;

         if ((png_ptr->transformations & PNG_EXPAND_tRNS) == 0)
         {
            png_ptr->trans_color.red = png_ptr->trans_color.green =
               png_ptr->trans_color.blue = (png_uint_16)trans_gray;
         }
      }
   } /* background expand and (therefore) no alpha association. */
#endif /* READ_EXPAND && READ_BACKGROUND */
}

void /* PRIVATE */
png_init_read_transformations(png_structrp png_ptr)
{
   png_debug(1, "in png_init_read_transformations");

   /* This internal function is called from png_read_start_row in pngrutil.c
    * and it is called before the 'rowbytes' calculation is done, so the code
    * in here can change or update the transformations flags.
    *
    * First do updates that do not depend on the details of the PNG image data
    * being processed.
    */

#ifdef PNG_READ_GAMMA_SUPPORTED
   /* Prior to 1.5.4 these tests were performed from png_set_gamma, 1.5.4 adds
    * png_set_alpha_mode and this is another source for a default file gamma so
    * the test needs to be performed later - here.  In addition prior to 1.5.4
    * the tests were repeated for the PALETTE color type here - this is no
    * longer necessary (and doesn't seem to have been necessary before.)
    */
   {
      /* The following temporary indicates if overall gamma correction is
       * required.
       */
      int gamma_correction = 0;

      if (png_ptr->colorspace.gamma != 0) /* has been set */
      {
         if (png_ptr->screen_gamma != 0) /* screen set too */
            gamma_correction = png_gamma_threshold(png_ptr->colorspace.gamma,
               png_ptr->screen_gamma);

         else
            /* Assume the output matches the input; a long time default behavior
             * of libpng, although the standard has nothing to say about this.
             */
            png_ptr->screen_gamma = png_reciprocal(png_ptr->colorspace.gamma);
      }

      else if (png_ptr->screen_gamma != 0)
         /* The converse - assume the file matches the screen, note that this
          * perhaps undesireable default can (from 1.5.4) be changed by calling
          * png_set_alpha_mode (even if the alpha handling mode isn't required
          * or isn't changed from the default.)
          */
         png_ptr->colorspace.gamma = png_reciprocal(png_ptr->screen_gamma);

      else /* neither are set */
         /* Just in case the following prevents any processing - file and screen
          * are both assumed to be linear and there is no way to introduce a
          * third gamma value other than png_set_background with 'UNIQUE', and,
          * prior to 1.5.4
          */
         png_ptr->screen_gamma = png_ptr->colorspace.gamma = PNG_FP_1;

      /* We have a gamma value now. */
      png_ptr->colorspace.flags |= PNG_COLORSPACE_HAVE_GAMMA;

      /* Now turn the gamma transformation on or off as appropriate.  Notice
       * that PNG_GAMMA just refers to the file->screen correction.  Alpha
       * composition may independently cause gamma correction because it needs
       * linear data (e.g. if the file has a gAMA chunk but the screen gamma
       * hasn't been specified.)  In any case this flag may get turned off in
       * the code immediately below if the transform can be handled outside the
       * row loop.
       */
      if (gamma_correction != 0)
         png_ptr->transformations |= PNG_GAMMA;

      else
         png_ptr->transformations &= ~PNG_GAMMA;
   }
#endif

   /* Certain transformations have the effect of preventing other
    * transformations that happen afterward in png_do_read_transformations;
    * resolve the interdependencies here.  From the code of
    * png_do_read_transformations the order is:
    *
    *  1) PNG_EXPAND (including PNG_EXPAND_tRNS)
    *  2) PNG_STRIP_ALPHA (if no compose)
    *  3) PNG_RGB_TO_GRAY
    *  4) PNG_GRAY_TO_RGB iff !PNG_BACKGROUND_IS_GRAY
    *  5) PNG_COMPOSE
    *  6) PNG_GAMMA
    *  7) PNG_STRIP_ALPHA (if compose)
    *  8) PNG_ENCODE_ALPHA
    *  9) PNG_SCALE_16_TO_8
    * 10) PNG_16_TO_8
    * 11) PNG_QUANTIZE (converts to palette)
    * 12) PNG_EXPAND_16
    * 13) PNG_GRAY_TO_RGB iff PNG_BACKGROUND_IS_GRAY
    * 14) PNG_INVERT_MONO
    * 15) PNG_INVERT_ALPHA
    * 16) PNG_SHIFT