per la tipologia del file salvato ho risolto così:
codice:
function SaveProportionateImage($filename, $quality, $height){
$dest_height = $height;
$ratio = $this->src_height / $dest_height;
$dest_image = imagecreatetruecolor( $this->src_width / $ratio,$dest_height);
imagecopyresampled($dest_image, $this->src_image, 0, 0, 0, 0,
$this->src_width / $ratio,
$this->src_height / $ratio,
$this->src_width,
$this->src_height);
switch($this->src_type){
case 1:
imagegif($dest_image, $filename.'.gif', $quality);
break;
case 2:
imagejpeg($dest_image, $filename.'.jpg', $quality);
break;
case 3:
imagepng($dest_image, $filename.'.png', $quality);
break;
default: return false;
}
imagedestroy($dest_image);
}