protected function _convert_gif_to_png($image_url) {
		if ( !function_exists("imagecreatefromgif") ) {
			throw new DOMPDF_Exception("Function imagecreatefromgif() not found.  Cannot convert gif image: $image_url.  Please install the image PHP extension.");
		}

		$old_err = set_error_handler("record_warnings");

		$tmp_img = getImageSize($img_url);
		if ($tmp_img[2] == '1') {
			$img = imagecreatefromgif($img_url);
			if ($img) {
				imageinterlace($img, 0);
				$tmp_filename = tempnam(DOMPDF_TEMP_DIR, "dompdf_img_");
				imagepng($img, $tmp_filename);
				rename($tmp_filename, $tmp_filename.'.png');
				$img_url = $tmp_filename.'.png';
			}
			else {
				$img_url = "../../lib/res/broken_image.png";
			}
		}

		restore_error_handler();

		$this->_image_cache[] = $img_url;

		return $img_url;
	}