php图片像素点2进制的相反值

$img = imagecreatefromjpeg("timg.jpg");
for ($x=0;$x<imagesx($img);$x++){
    for ($y=0;$y<imagesy($img);$y++){
        $old_color = imagecolorat($img,$x,$y);
        $new_color = (~$old_color)&0xFFFFFF;
        imagesetpixel($img,$x,$y,$new_color);
    }
}
header("content-type:image/jpeg");
imagejpeg($img);