protected function postEffect($image)
    {
        if (!function_exists('imagefilter')) {
            return;
        }

        if ($this->backgroundColor != null || $this->textColor != null) {
            return;
        }

        // Negate ?
        if ($this->rand(0, 1) == 0) {
            imagefilter($image, IMG_FILTER_NEGATE);
        }

        // Edge ?
        if ($this->rand(0, 10) == 0) {
            imagefilter($image, IMG_FILTER_EDGEDETECT);
        }

        // Contrast
        imagefilter($image, IMG_FILTER_CONTRAST, $this->rand(-50, 10));

        // Colorize
        if ($this->rand(0, 5) == 0) {
            imagefilter($image, IMG_FILTER_COLORIZE, $this->rand(-80, 50), $this->rand(-80, 50), $this->rand(-80, 50));
        }
    }