Problema watermark

[kepal]

Ciao a tutti!
ho un problemino! ho uno script che mi permette di creare un'immagine con un logo sopra (watermark) ma ho un problema.

con un file PNG lo sfondo del wm diventa bianco, invece di lasciarlo trasparente.
con una GIF, le sfumature del wm non vengono trasferite nella trasformazione da PNG a GIF.

lo script è:

class img 
{    
    var $thumb_w =640; // larghezza thumb
    var $thumb_h =480; // altezza thumb
    var $max_w = 720; // larghezza max
    var $max_h = 540; // altezza max
    var $pos_x = "CENTER"; // posizione logo
    var $pos_y = "MIDDLE"; // posizione logo
    var $img_folder = ""; // cartella immagine grande
    var $thumb_folder = ""; // cartella immagine thumb
    var $saveBIG = 1; //salvare immagine grande
    var $saveTHUMB = 0; //salvare thumb
    var $name = ""; //nome immagine senza estensione

    function AddLogo($image, $logo = NULL)
    {
        $this->im = $this->createImgage($image);
        $this->im_width = imagesx($this->im);
        $this->im_height = imagesy($this->im);
        $this->wt_x = $this->calc_pos_x($this->pos_x);
        $this->wt_y = $this->calc_pos_y($this->pos_y);
        
        $this->new_image = $this->resizeImg();
        $this->resizeForThumb();
        
        if($logo != NULL)
        {
            $this->createTheLogo($logo);                
        }
        if($this->name==""){
            $this->name = substr($image, 0 , strrpos($image, "."));
        }
        if($this->saveBIG == 1)
        {
            imagejpeg($this->new_image, $this->img_folder.$this->name."_logo.jpg");
        }
        if($this->saveTHUMB == 1)
        {
            imagejpeg($this->thumb, $this->thumb_folder.$this->name."_small.jpg");
        }
        
    }
    
    function createImgage($image){
        $type = strtolower(substr($image, strrpos($image, "."), strlen($image)-strrpos($image, ".")));
        if($type==".jpeg" || $type==".jpg"){
            return imagecreatefromjpeg($image);
        }elseif($type==".gif"){
            return imagecreatefromgif($image);
        }elseif($type==".png"){
            return imagecreatefrompng($image);
        }else{
            die("Immagine non valida");
        }
    }
    
    function createTheLogo($logo)
    {
        $this->logo = $this->createImgage($logo);
        $this->logo_width = imagesx($this->logo);
        $this->logo_height = imagesy($this->logo);
        $this->wt_x = $this->calc_pos_x($this->pos_x);
        $this->wt_y = $this->calc_pos_y($this->pos_y);
        imagecopymerge($this->new_image, $this->logo, $this->wt_x, $this->wt_y, 0, 0, $this->logo_width, $this->logo_height, 100);
    }
        
        
    function resizeImg()
    {

        if($this->im_width > $this->max_w && $this->im_height < $this->max_h)
        {
        
            $rapporto = $this->max_w / $this->im_width;
            
            $this->new_im_w = $this->im_width * $rapporto;
            $this->new_im_h = $this->im_height * $rapporto;
            
        }
        
        else if($this->im_width < $this->max_w && $this->im_height > $this->max_h)
        {
        
            $rapporto = $this->max_h / $this->im_height;
            
            $this->new_im_w = $this->im_width * $rapporto;
            $this->new_im_h = $this->im_height * $rapporto;
        
        }
        else if($this->im_width > $this->max_w && $this->im_height > $this->max_h)
        {
        
            $rapporto_1 = $this->max_w / $this->im_width;
            $rapporto_2 = $this->max_h / $this->im_height;
                if($rapporto_1 > $rapporto_2)
                {
                    $rapporto = $rapporto_2;
                }
                else
                {
                    $rapporto = $rapporto_1;
                }
                    
                    $this->new_im_w = $this->im_width * $rapporto;
                    $this->new_im_h = $this->im_height * $rapporto;
        
        }
        
        else
        {
            $this->new_im_w = $this->im_width;
            $this->new_im_h = $this->im_height;
        }
        
        $this->new_image = imagecreatetruecolor($this->new_im_w, $this->new_im_h);
        imagecopyresized($this->new_image, $this->im, 0, 0, 0, 0, $this->new_im_w, $this->new_im_h, $this->im_width, $this->im_height);
        
        return $this->new_image;

    }
        function resizeForThumb()
        {
            $thumb_w = $this->thumb_w;
            $thumb_h = $this->thumb_h;
            if($this->im_width > $this->im_height)
            {
                $rapporto = $this->im_height / $this->im_width;
                $thumb_h = $this->thumb_w * $rapporto;
            }    
            else if($this->im_width < $this->im_height)
            {
                $rapporto = $this->im_width / $this->im_height;
                $thumb_w = $this->thumb_h * $rapporto;
            }
            else
            {
                $thumb_w = $this->thumb_w;
                $thumb_h = $this->thumb_h;
            }
            $this->thumb = imagecreatetruecolor($thumb_w, $thumb_h);
            imagecopyresized($this->thumb, $this->new_image, 0, 0, 0, 0, $thumb_w, $thumb_h, $this->new_im_w, $this->new_im_h);

        }
        
    function calc_pos_x($position_x)
        {
        $x = 0;
        switch($position_x)
        {
            case 'LEFT':
                $x = 0;
                break;
            case 'CENTER':
                $x = @$this->new_im_w / 2 - @$this->logo_width / 2;
                break;
            case 'RIGHT':
                $x = @$this->new_im_w - @$this->logo_width;
                break;
            default:
                $x = 0;
        }
            return $x;
        
        }
        
        function calc_pos_y($position_y)
        {
        $y = 0;
        switch($position_y)
        {
            case 'TOP':
                $y = 0;
                break;
            case 'MIDDLE':
                $y = @$this->new_im_h / 2 - @$this->logo_height / 2;
                break;
            case 'BOTTOM':
                $y = @$this->new_im_h - @$this->logo_height;
                break;
            default:
                $y = 0;
        }
    return $y;
        
        }
        
}
    
?> 

nella mia pagina, chiamo la funzione Addlogo().
é possibile far "leggere" allo script un PNG giusto? oppure, è possibile convertire una GIF esattamente?

grazie a tutti, spero di essermi spiegato!

SImo