Pop\Image\Imagick::contrast PHP Method

    public function contrast($amount)
    {
        if ($amount > 0) {
            for ($i = 1; $i <= $amount; $i++) {
                $this->resource->contrastImage(1);
            }
        } else {
            if ($amount < 0) {
                for ($i = -1; $i >= $amount; $i--) {
                    $this->resource->contrastImage(0);
                }
            }
        }
        return $this;
    }