public function vignette($amount = 20, $background = 'white', $blurmode = 'gaussian')
    {
        $options = [
            'a' => $amount,
            'b' => $background,
            'm' => $blurmode
        ];

        // call TransformationMixin function
        $this->setTransformUrl('vignette', $options);

        return $this;
    }