Error redimensionando imagenes png subidas al servidor.. funcion imagecolorsforindex

[HackGhost]

Estoy haciendo una pagina web donde se suben imagenes desde un administrador (creado por mi), estas imagenes son redimensionadas para ser mostradas en distintas partes de la pagina.. el problema que tengo es que me aparece un error (o mas bien una advertencia) al momento en que una imagen .png es redimensionado..

Este es el mensaje:

Warning: imagecolorsforindex() [function.imagecolorsforindex]: Color index -1 out of range in C:\xampp\htdocs\educador\admin\upload.class.php on line 105


upload.class.php

Código PHP:

<?php
class upload
{
    var $directory_name;
    var $max_filesize;
    var $error;
 
    var $user_tmp_name;
    var $user_file_name;
    var $user_file_size;
    var $user_file_type;
    var $user_full_name;
    var $thumb_name;
 
    function set_directory($dir_name = "")
    {
     $this->directory_name = $dir_name;
    }
 
    function set_max_size($max_file = 300000)
    {
     $this->max_filesize = $max_file;
    }
 
    function error()
    {
     return $this->error;
    }
 
    function is_ok()
    {
     if(isset($this->error))
      return FALSE;
     else
      return TRUE;
    }
 
    function set_tmp_name($temp_name)
    {
     $this->user_tmp_name = $temp_name;  
    }
 
    function set_file_size($file_size)
    {
     $this->user_file_size = $file_size;
    }
 
    function set_file_type($file_type)
    {
     $this->user_file_type = $file_type;     
    }
 
    function set_file_name($file)
    {
        $this->user_file_name = $file;
        $this->user_full_name = $this->directory_name."/".$this->user_file_name;
    }
 
    function resize($max_width = 0, $max_height = 0 )
    {
    if(eregi("\.png$",$this->user_full_name))
    {
     $img = imagecreatefrompng($this->user_full_name);
    }
    
    if(eregi("\.(jpg|jpeg)$",$this->user_full_name))
    {
     $img = imagecreatefromjpeg($this->user_full_name);
    }
    
    if(eregi("\.gif$",$this->user_full_name))
    {
     $img = imagecreatefromgif($this->user_full_name);
    }
 
        $FullImage_width = imagesx ($img);    
        $FullImage_height = imagesy ($img);   
 
        if(isset($max_width) && isset($max_height) && $max_width != 0 && $max_height != 0)
        {
         $new_width = $max_width;
         $new_height = $max_height;
        }
        else if(isset($max_width) && $max_width != 0)
        {
         $new_width = $max_width;
         $new_height = ((int)($new_width * $FullImage_height) / $FullImage_width);
        }
        else if(isset($max_height) && $max_height != 0)
        {
         $new_height = $max_height;
         $new_width = ((int)($new_height * $FullImage_width) / $FullImage_height);
        }       
        else
        {
         $new_height = $FullImage_height;
         $new_width = $FullImage_width;
        }   
 
        $full_id =  imagecreatetruecolor( $new_width , $new_height );
        // Check transparent gif and pngs
    if(eregi("\.png$",$this->user_full_name) || eregi("\.gif$",$this->user_full_name))
        {
            $trnprt_indx = imagecolortransparent($img);
            $trnprt_color = imagecolorsforindex($img, $trnprt_indx);
            $trnprt_indx = imagecolorallocate($full_id, $trnprt_color['red'], $trnprt_color['green'], $trnprt_color['blue']);
            imagefill($full_id, 0, 0, $trnprt_indx);
            imagecolortransparent($full_id, $trnprt_indx);
        }
        imagecopyresampled( $full_id, $img, 0,0,0,0, $new_width, $new_height, $FullImage_width, $FullImage_height );
        
 
        if(eregi("\.(jpg|jpeg)$",$this->user_full_name))
        {
         $full = imagejpeg( $full_id, $this->user_full_name,100);
        }
        
        if(eregi("\.png$",$this->user_full_name))
        {
         $full = imagepng( $full_id, $this->user_full_name);
        }
        
        if(eregi("\.gif$",$this->user_full_name))
        {
         $full = imagegif($full_id, $this->user_full_name);
        }
        imagedestroy( $full_id );
        unset($max_width);
        unset($max_height);
    }
 
    function start_copy()
    {
        if(!isset($this->user_file_name))
         $this->error = "You must define filename!";
 
        if ($this->user_file_size <= 0)
         $this->error = "File size error (0): $this->user_file_size KB<br>";
 
        if ($this->user_file_size > $this->max_filesize)
         $this->error = "File size error (1): $this->user_file_size KB<br>";
 
        if (!isset($this->error))
        {
            $filename = basename($this->user_file_name);
 
            if (!empty($this->directory_name)) 
                $destination = $this->user_full_name;
            else 
                $destination = $filename;
                
            if(!is_uploaded_file($this->user_tmp_name))
             $this->error = "File ".$this->user_tmp_name." is not uploaded correctly.";
      
            if (!@move_uploaded_file ($this->user_tmp_name,$destination))
             $this->error = "Impossible to copy ".$this->user_file_name." from $userfile to destination directory.";
        }
    }
    
    function set_thumbnail_name($thumbname)
    {
    if(eregi("\.png$",$this->user_full_name))
     $this->thumb_name = $this->directory_name."/".$thumbname;
    if(eregi("\.(jpg|jpeg)$",$this->user_full_name))
     $this->thumb_name = $this->directory_name."/".$thumbname;
    if(eregi("\.gif$",$this->user_full_name))
     $this->thumb_name = $this->directory_name."/".$thumbname;
    }
    
    function create_thumbnail()
    {
     if (!copy($this->user_full_name, $this->thumb_name))
      {
      echo "<br>".$this->user_full_name.", ".$this->thumb_name."<br>";
       echo "failed to copy $file...<br />\n";
      }
    }
    
    function set_thumbnail_size($max_width = 0, $max_height = 0 )
    {
    if(eregi("\.png$",$this->thumb_name))
    {
     $img = ImageCreateFromPNG ($this->thumb_name);
    }
    
    if(eregi("\.(jpg|jpeg)$",$this->thumb_name))
    {
     $img = ImageCreateFromJPEG ($this->thumb_name);
    }
    
    if(eregi("\.gif$",$this->thumb_name))
    {
     $img = ImageCreateFromGif ($this->thumb_name);
    }
 
        $FullImage_width = imagesx ($img);    
        $FullImage_height = imagesy ($img); 
        
        if(isset($max_width) && isset($max_height) && $max_width != 0 && $max_height != 0)
        {
         $new_width = $max_width;
         $new_height = $max_height;
        }
        else if(isset($max_width) && $max_width != 0)
        {
         $new_width = $max_width;
         $new_height = ((int)($new_width * $FullImage_height) / $FullImage_width);
        }
        else if(isset($max_height) && $max_height != 0)
        {
         $new_height = $max_height;
         $new_width = ((int)($new_height * $FullImage_width) / $FullImage_height);
        }       
        else
        {
         $new_height = $FullImage_height;
         $new_width = $FullImage_width;
        }   
        $full_id =  ImageCreateTrueColor ( $new_width , $new_height );
 
        // Check transparent gif and pngs
        if(eregi("\.png$",$this->user_full_name) || eregi("\.gif$",$this->user_full_name))
            {
                $trnprt_indx = imagecolortransparent($img);
                $trnprt_color = imagecolorsforindex($img, $trnprt_indx);
                $trnprt_indx = imagecolorallocate($full_id, $trnprt_color['red'], $trnprt_color['green'], $trnprt_color['blue']);
                imagefill($full_id, 0, 0, $trnprt_indx);
                imagecolortransparent($full_id, $trnprt_indx);
            }
        ImageCopyResampled ( $full_id, $img, 0,0,0,0, $new_width, $new_height, $FullImage_width, $FullImage_height );
        
 
        if(eregi("\.(jpg|jpeg)$",$this->thumb_name))
        {
         $full = ImageJPEG( $full_id, $this->thumb_name,100);
        }
        
        if(eregi("\.png$",$this->thumb_name))
        {
         $full = ImagePNG( $full_id, $this->thumb_name);
        }
        
        if(eregi("\.gif$",$this->thumb_name))
        {
         $full = ImageGIF($full_id, $this->thumb_name);
        }
        ImageDestroy( $full_id );
        unset($max_width);
        unset($max_height);
    }
}
?>