public function asPng($compression = 9)
    {
        ob_start();

        $im = $this->output();
        imagepng($im, null, $compression);

        return ob_get_clean();
    }
public function asPng($compression = 9)
    {
        ob_start();

        $im = $this->output();
        imagepng($im, null, $compression);

        return ob_get_clean();
    }
public function asPng ( $ compression = 9 ) { ob_start ( ) ; $ im = $ this -> output ( ) ; imagepng ( $ im , null , $ compression ) ; return ob_get_clean ( ) ; }
Return image as PNG string

@param int $compression

@return string
Return image as PNG string