Transparent gif images show black background when resized

Gif images with transparent backgrounds end up having black backgrounds and animated gif images turn black completely. Any ideas why?

$image_p = imagecreatetruecolor($width, $height);
$image = imagecreatefromgif($filePath);
imagealphablending($image_p,true);
imagesavealpha($image_p,true);
$transparent […]

See original post by invalid@example.com (qwikad.com)