setup_png_transformations(png_structp png_read_ptr, png_infop png_info_ptr,
                          gboolean *fatal_error_occurred,
                          png_uint_32* width_p, png_uint_32* height_p,
                          int* color_type_p)
{
        png_uint_32 width, height;
        int bit_depth, color_type, interlace_type, compression_type, filter_type;
        int channels;
        
        /* Get the image info */

        png_get_IHDR (png_read_ptr, png_info_ptr,
                      &width, &height,
                      &bit_depth,
                      &color_type,
                      &interlace_type,
                      &compression_type,
                      &filter_type);

        /* set_expand() basically needs to be called unless
           we are already in RGB/RGBA mode
        */
        if (color_type == PNG_COLOR_TYPE_PALETTE &&
            bit_depth <= 8) {

                /* Convert indexed images to RGB */
                png_set_expand (png_read_ptr);

        } else if (color_type == PNG_COLOR_TYPE_GRAY &&
                   bit_depth < 8) {

                /* Convert grayscale to RGB */
                png_set_expand (png_read_ptr);

        } else if (png_get_valid (png_read_ptr, 
                                  png_info_ptr, PNG_INFO_tRNS)) {

                /* If we have transparency header, convert it to alpha
                   channel */
                png_set_expand(png_read_ptr);
                
        } else if (bit_depth < 8) {

                /* If we have < 8 scale it up to 8 */
                png_set_expand(png_read_ptr);


                /* Conceivably, png_set_packing() is a better idea;
                 * God only knows how libpng works
                 */
        }

        /* If we are 16-bit, convert to 8-bit */
        if (bit_depth == 16) {
                png_set_strip_16(png_read_ptr);
        }

        /* If gray scale, convert to RGB */
        if (color_type == PNG_COLOR_TYPE_GRAY ||
            color_type == PNG_COLOR_TYPE_GRAY_ALPHA) {
                png_set_gray_to_rgb(png_read_ptr);
        }
        
        /* If interlaced, handle that */
        if (interlace_type != PNG_INTERLACE_NONE) {
                png_set_interlace_handling(png_read_ptr);
        }
        
        /* Update the info the reflect our transformations */
        png_read_update_info(png_read_ptr, png_info_ptr);
        
        png_get_IHDR (png_read_ptr, png_info_ptr,
                      &width, &height,
                      &bit_depth,
                      &color_type,
                      &interlace_type,
                      &compression_type,
                      &filter_type);

        *width_p = width;
        *height_p = height;
        *color_type_p = color_type;
        
#ifndef G_DISABLE_CHECKS
        /* Check that the new info is what we want */
        
        if (bit_depth != 8) {
                g_warning("Bits per channel of transformed PNG is %d, not 8.", bit_depth);
                *fatal_error_occurred = TRUE;
                return;
        }

        if ( ! (color_type == PNG_COLOR_TYPE_RGB ||
                color_type == PNG_COLOR_TYPE_RGB_ALPHA) ) {
                g_warning("Transformed PNG not RGB or RGBA.");
                *fatal_error_occurred = TRUE;
                return;
        }

        channels = png_get_channels(png_read_ptr, png_info_ptr);
        if ( ! (channels == 3 || channels == 4) ) {
                g_warning("Transformed PNG has %d channels, must be 3 or 4.", channels);
                *fatal_error_occurred = TRUE;
                return;
        }
#endif
}