;; Sharpen effect - sharpens edges
;; @param amount float [0, 5] default 1

(define-effect sharpen
  ((amount 1))
  (let ((kernel (list (list 0 (- amount) 0)
                      (list (- amount) (+ 1 (* 4 amount)) (- amount))
                      (list 0 (- amount) 0))))
    (convolve frame kernel)))