Mike42\Escpos\EscposImage::getRasterFormatFromFile PHP Method

protected getRasterFormatFromFile ( string $filename = null ) : string \| null
$filename	string	Filename to load from
return	string \| null	Raster format data, or NULL if no optimised renderer is available in this implementation.

    protected function getRasterFormatFromFile($filename = null)
    {
        // No optimised implementation to provide
        return null;
    }

EscposImage