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         return;
      }

      png_crc_read(png_ptr, buf, length);
      png_ptr->num_trans = 1;
      png_ptr->trans_color.red = png_get_uint_16(buf);
      png_ptr->trans_color.green = png_get_uint_16(buf + 2);
      png_ptr->trans_color.blue = png_get_uint_16(buf + 4);
   }

   else if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
   {
      if ((png_ptr->mode & PNG_HAVE_PLTE) == 0)
      {
         /* TODO: is this actually an error in the ISO spec? */
         png_crc_finish(png_ptr, length);
         png_chunk_benign_error(png_ptr, "out of place");
         return;
      }

      if (length > png_ptr->num_palette || length > PNG_MAX_PALETTE_LENGTH ||
         length == 0)
      {
         png_crc_finish(png_ptr, length);
         png_chunk_benign_error(png_ptr, "invalid");
         return;
      }

      png_crc_read(png_ptr, readbuf, length);
      png_ptr->num_trans = (png_uint_16)length;
   }

   else
   {
      png_crc_finish(png_ptr, length);
      png_chunk_benign_error(png_ptr, "invalid with alpha channel");
      return;
   }

   if (png_crc_finish(png_ptr, 0) != 0)
   {
      png_ptr->num_trans = 0;
      return;
   }

   /* TODO: this is a horrible side effect in the palette case because the
    * png_struct ends up with a pointer to the tRNS buffer owned by the
    * png_info.  Fix this.
    */
   png_set_tRNS(png_ptr, info_ptr, readbuf, png_ptr->num_trans,
       &(png_ptr->trans_color));
}
#endif

#ifdef PNG_READ_bKGD_SUPPORTED
void /* PRIVATE */
png_handle_bKGD(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
{
   unsigned int truelen;
   png_byte buf[6];
   png_color_16 background;

   png_debug(1, "in png_handle_bKGD");

   if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
      png_chunk_error(png_ptr, "missing IHDR");

   else if ((png_ptr->mode & PNG_HAVE_IDAT) != 0 ||
       (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE &&
       (png_ptr->mode & PNG_HAVE_PLTE) == 0))
   {
      png_crc_finish(png_ptr, length);
      png_chunk_benign_error(png_ptr, "out of place");
      return;
   }

   else if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_bKGD) != 0)
   {
      png_crc_finish(png_ptr, length);
      png_chunk_benign_error(png_ptr, "duplicate");
      return;
   }

   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
      truelen = 1;

   else if ((png_ptr->color_type & PNG_COLOR_MASK_COLOR) != 0)
      truelen = 6;

   else
      truelen = 2;

   if (length != truelen)
   {
      png_crc_finish(png_ptr, length);
      png_chunk_benign_error(png_ptr, "invalid");
      return;
   }

   png_crc_read(png_ptr, buf, truelen);

   if (png_crc_finish(png_ptr, 0) != 0)
      return;

   /* We convert the index value into RGB components so that we can allow
    * arbitrary RGB values for background when we have transparency, and
    * so it is easy to determine the RGB values of the background color
    * from the info_ptr struct.
    */
   if (png_ptr->color_type == PNG_COLOR_TYPE_PALETTE)
   {
      background.index = buf[0];

      if (info_ptr != NULL && info_ptr->num_palette != 0)
      {
         if (buf[0] >= info_ptr->num_palette)
         {
            png_chunk_benign_error(png_ptr, "invalid index");
            return;
         }

         background.red = (png_uint_16)png_ptr->palette[buf[0]].red;
         background.green = (png_uint_16)png_ptr->palette[buf[0]].green;
         background.blue = (png_uint_16)png_ptr->palette[buf[0]].blue;
      }

      else
         background.red = background.green = background.blue = 0;

      background.gray = 0;
   }

   else if ((png_ptr->color_type & PNG_COLOR_MASK_COLOR) == 0) /* GRAY */
   {
      background.index = 0;
      background.red =
      background.green =
      background.blue =
      background.gray = png_get_uint_16(buf);
   }

   else
   {
      background.index = 0;
      background.red = png_get_uint_16(buf);
      background.green = png_get_uint_16(buf + 2);
      background.blue = png_get_uint_16(buf + 4);
      background.gray = 0;
   }

   png_set_bKGD(png_ptr, info_ptr, &background);
}
#endif

#ifdef PNG_READ_hIST_SUPPORTED
void /* PRIVATE */
png_handle_hIST(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
{
   unsigned int num, i;
   png_uint_16 readbuf[PNG_MAX_PALETTE_LENGTH];

   png_debug(1, "in png_handle_hIST");

   if ((png_ptr->mode & PNG_HAVE_IHDR) == 0)
      png_chunk_error(png_ptr, "missing IHDR");

   else if ((png_ptr->mode & PNG_HAVE_IDAT) != 0 ||
       (png_ptr->mode & PNG_HAVE_PLTE) == 0)
   {
      png_crc_finish(png_ptr, length);
      png_chunk_benign_error(png_ptr, "out of place");
      return;
   }

   else if (info_ptr != NULL && (info_ptr->valid & PNG_INFO_hIST) != 0)
   {
      png_crc_finish(png_ptr, length);
      png_chunk_benign_error(png_ptr, "duplicate");
      return;
   }

   num = length / 2 ;

   if (num != png_ptr->num_palette || num > PNG_MAX_PALETTE_LENGTH)
   {
      png_crc_finish(png_ptr, length);
      png_chunk_benign_error(png_ptr, "invalid");
      return;
   }

   for (i = 0; i < num; i++)
   {
      png_byte buf[2];

      png_crc_read(png_ptr, buf, 2);
      readbuf[i] = png_get_uint_16(buf);
   }

   if (png_crc_finish(png_ptr, 0) != 0)
      return;

   png_set_hIST(png_ptr, info_ptr, readbuf);
}
#endif

#ifdef PNG_READ_pHYs_SUPPORTED
void /* PRIVATE */
png_handle_pHYs(png_structrp png_ptr, png_inforp info_ptr, png_uint_32 length)
{
   png_byte buf[9];
   png_uint_32 res_x, res_y;