PHP - 如何在不损失动画质量的情况下在GIF图像上附加文本？

I am using the below code to append text on JPEG image...

imagettftext( $png, $size, 0,$textx+2, $texty+2, $shadow_color, $fontfile, $textval );

imagettftext( $png, $size, 0,$textx, $texty, $tx, $fontfile, $textval );

imagejpeg($png, $medium_card_file_path);

imagedestroy($png);

But while trying to do the same thing using gif images, the quality of the animation gets affected.

Thanks in advance for your help.