[gd] problema con bmp

[sonounostrinato]

ecco ho trovato una classe per fare thumbnail al volo e funziona da dio ma ha un problema

questo è il codice

<?php
class thumbnail
    {
        var $sourceFile; // We use this file to create the thumbnail
        var $originalFilename; // We use this to get the extension of the filename
        var $destinationDirectory; // The Directory in question
        var $destinationDirectoryFilename; // The destination filename
        
        var $createImageFunction = '';
        var $outputImageFunction = '';
        
        function generate($sourceFile = "", $originalFilename = "", $destinationDirectory = "", $destinationDirectoryFilename = "", $width = -1, $height = -1)
        {
      if (!empty($sourceFile))
        $this->sourceFile = $sourceFile;
      
      if (!empty($originalFilename))
        $this->originalFilename = $originalFilename;
       
      if (!empty($destinationDirectory))
        $this->destinationDirectory = $destinationDirectory;
       
      if (!empty($destinationDirectoryFilename))
        $this->destinationDirectoryFilename = $destinationDirectoryFilename;
      
      if (!empty($width))
        $this->width = $width;
      
      if (!empty($height))
        $this->height = $height;

      list(, $this->extension) = explode('.', $this->originalFilename);
            
            switch ($this->extension)
            {
                case 'gif' :
                    $createImageFunction = 'imagecreatefromgif';
                    $outputImageFunction = 'imagegif';
                  break;
                
                case 'png' :
                    $createImageFunction = 'imagecreatefrompng';
                    $outputImageFunction = 'imagepng';
                  break;
                
                case 'bmp' :
                    $createImageFunction = 'imagecreatefromwbmp';
                    $outputImageFunction = 'image2wbmp';
                  break;
                
                case 'jpg': case 'jpeg':
                    $createImageFunction = 'imagecreatefromjpeg';
                    $outputImageFunction = 'imagejpeg';
                  break;
                
                default : 
                    exit("Sorry: The format '{$this->extension}' is unsuported");
                  break;
            }
            
            $this->img  = $createImageFunction($this->sourceFile);
            
            list($this->org_width, $this->org_height) = getimagesize($this->sourceFile);
            
            if ($this->height == -1)
            {
                $this->height = round($this->org_height * $this->width / $this->org_width);
            }
            
            if ($this->width == -1)
            {
                $this->width = round($this->org_width * $this->height / $this->org_height);
            }     
            
            $this->xoffset = 0;
            $this->yoffset = 0;
            
            $this->img_new = imagecreatetruecolor($this->width, $this->height);    
            
            if ($this->img_new)
            {
                imagecopyresampled($this->img_new, $this->img, 0, 0, $this->xoffset, $this->yoffset, $this->width, $this->height, $this->org_width, $this->org_height);
                
                list($this->newFilename) = explode('.', $this->destinationDirectoryFilename);
                
                $this->fullDestination = ($this->destinationDirectory.'/'.$this->newFilename.'.'.$this->extension);
                
                $outputImageFunction($this->img_new, $this->fullDestination);
            }
            else
            {
                $this->failed = true;
            }
            
            if ($this->failed == false)
            {
                return $this->fullDestination;
            }
        }
    }
?>

l'ho presa da html.it e non capisco perchè al momento di fare la thumb di una bitmap sputi fuori questi errori:

Warning: imagecreatefromwbmp() [function.imagecreatefromwbmp]: '/tmp/phpcZp4zI' is not a valid WBMP file in /newhome/puglfabr/public_html/meta/thumb/thumbnail.class.php on line 86

Warning: imagecopyresampled(): supplied argument is not a valid Image resource in /newhome/puglfabr/public_html/meta/thumb/thumbnail.class.php on line 107

le righe incriminate sono queste: VVoVe:

$this->img  = $createImageFunction($this->sourceFile); <= riga 86
imagecopyresampled($this->img_new, $this->img, 0, 0, $this->xoffset, $this->yoffset, $this->width, $this->height, $this->org_width, $this->org_height); <= riga 107

vi chiedo aiuto....