Chyba v třídě pro tvorbu obrázků

class Canvas {
  protected $canvas = null;
  protected $width, $height = 0;
  protected $created = false;
  
  protected $textFont = null;
  protected $textSize = 12;
  
  private $qualityPng = 0;
  private $qualityJpg = 75;
  
  
  /**
   * Create graphic canvas, class constructor
   * @param int $width canvas width
   * @param int $height canvas height
   */
  public function __construct($width, $height) {
    $c = @imagecreatetruecolor($width, $height);
    if(!$c) {$this->created = false;} else {
      $this->canvas = $c;
      $this->created = true;
      $this->width = $width;
      $this->height = $height;
      $this->color = $this->color(0, 0, 0);
    }
  }
  
  
  /**
   * Destroy graphic canvas, free alocated memory
   */
  public function __destruct() {
    imagedestroy($this->canvas);
  }
  
  
  /**
   * Return image string resource
   * @return String image resource
   */
  public final function getCanvas() {
    return $this->canvas;
  }
  
  
  /**
   * Get image width
   * @return int image width   
   */
  public final function getWidth() {
    return $this->width;
  }
  
  
  /**
   * Get image height
   * @param int image height   
   */
  public final function getHeight() {
    return $this->height;
  }
  
  
  /**
   * Output image to browser
   * @param String $type image type (png|jpg|gif)
   * @param bool $header send header to the browser
   */     
  public function createImage($type, $header = false) {
    if((bool)$header) $this->sendHeader($type);
    switch(strtolower($type)) {
      case 'png': imagepng($this->canvas); break;
      case 'jpeg':
      case 'jpg': imagejpeg($this->canvas); break;
      case 'gif': imagegif($this->canvas); break;
    }
  }
  
  
  /**
   * Save image to server
   * @param String $path URL path to the image for save image
   * @return bool true if was saved
   */
  public function saveImage($path) {    
    $type = explode('.', $path);
    $type = end($type);
    switch(strtolower($type)) {
      case 'png': {return (bool)imagepng($this->canvas, $path, $this->qualityPng); break;}
      case 'jpeg':
      case 'jpg': {return (bool)imagejpeg($this->canvas, $path, $this->qualityJpg); break;}
      case 'gif': {return (bool)imagegif($this->canvas, $path); break;}
    }
  }

public function sendHeader($type) { 
    switch(strtolower($type)) { 
      case 'png': header('Content-Type: image/png'); break; 
      case 'jpeg': 
      case 'jpg': header('Content-Type: image/jpg'); break; 
      case 'gif': header('Content-Type: image/gif'); break; 
    } 
  }

public function color($red, $green, $blue) { 
    $this->color = imagecolorallocate($this->canvas, $red, $green, $blue); 
}