Ciao a tutti, uso questo codice per salvare un'immagine e poi crearne due copie ridimensionate:

Codice PHP:
move_uploaded_file($_FILES["upfile"]["tmp_name"][0], "$upload_dir/$nome_file1")
                or die($_FILES["upfile"]["error"][0]);
                                             
                                
                list($width, $height, $type, $attr) = getimagesize("$upload_dir/$nome_file1");
                if($width>450)
                {
                $newheight=ceil(450*$height/$width);
                $thumb = imagecreatetruecolor(450,$newheight);
                switch($type)
                {
                  case 1: 
                        $source = imagecreatefromgif("$upload_dir/$nome_file1");
                        imagecopyresized($thumb, $source, 0, 0, 0, 0, 450,$newheight, $width, $height);
                        imagegif($thumb, "$upload_dir/$nome_file1", 75);
                        break;
                  case 2: 
                        $source = imagecreatefromjpeg("$upload_dir/$nome_file1");
                        imagecopyresized($thumb, $source, 0, 0, 0, 0, 450,$newheight, $width, $height);
                        imagejpeg($thumb, "$upload_dir/$nome_file1", 75);
                        break;
                  case 4: 
                        $source = imagecreatefromwbmp("$upload_dir/$nome_file1");
                        imagecopyresized($thumb, $source, 0, 0, 0, 0, 450,$newheight, $width, $height);
                        imagewbmp($thumb, "$upload_dir/$nome_file1", 75);
                        break;
                } 
                imagedestroy($thumb);
                }
                list($width, $height, $type, $attr) = getimagesize("$upload_dir/$nome_file1");
                $newheight=ceil(150*$height/$width);
                $thumb = imagecreatetruecolor(150,$newheight);
                switch($type)
                {
                  case 1: 
                        $source = imagecreatefromgif("$upload_dir/$nome_file1");
                        imagecopyresized($thumb, $source, 0, 0, 0, 0, 150,$newheight, $width, $height);
                        imagegif($thumb, "$upload_dir/anteprima/$nome_file1", 75);
                        break;
                  case 2: 
                        $source = imagecreatefromjpeg("$upload_dir/$nome_file1");
                        imagecopyresized($thumb, $source, 0, 0, 0, 0, 150,$newheight, $width, $height);
                        imagejpeg($thumb, "$upload_dir/anteprima/$nome_file1", 75);
                        break;
                  case 4: 
                        $source = imagecreatefromwbmp("$upload_dir/$nome_file1");
                        imagecopyresized($thumb, $source, 0, 0, 0, 0, 150,$newheight, $width, $height);
                        imagewbmp($thumb, "$upload_dir/anteprima/$nome_file1", 75);
                        break;
                  default: copy("$upload_dir/$nome_file1","$upload_dir/anteprima/$nome_file1"); 
                } 
                imagedestroy($thumb); 
Problema: per immagini che sono grandi dal punto di vista della risoluzione e del numero di colori usati il ridimensionamento non funziona: mi crea solo un'immagine nera... mi è stato detto che devo alzare il memory limit, ma non posso farlo... posso migliorare il mio codice?
Grazie