I want to convert PNG32 to PNG8 via the php Object Imagick. but I used setImageDepth and setImageFormat setting param to 8bit, it didn't take effect. the code like this: $im = new Imagick($image); $im->cropImage($cutWidth,$cutHeight,$x,$y); $im->thumbnailImage($maxWidth, $maxHeight); $im->setImageDepth(8); $im->setImageFormat('PNG8'); $im->writeImage($filename); inputfile is PNG32, but output abov