private static function _createPng( $imageFile ){
        $gd = @imagecreatefrompng( $imageFile );

        if(!$gd){
            throw new \Exception( sprintf('Could not open "%s". Not a valid %s file.', $imageFile, ImageType::PNG) );
        }

        $image = new self( $gd, $imageFile, imagesx( $gd ), imagesy( $gd ), ImageType::PNG );
        $image->fullAlphaMode( true );
        return $image;
    }