public function fitResize($max_width = 150, $max_height = 150, $min_width = 20, $min_height = 20) {
        $kw = $max_width / $this->width();
        $kh = $max_height / $this->height();
        if($kw > $kh) {
            $new_h = $max_height;
            $new_w = round($kh * $this->width());
        } else {
            $new_w = $max_width;
            $new_h = round($kw * $this->height());
        }
        $this->resize($new_w, $new_h);

        // Method chaining
        return $this;
    }