;; Sharpen effect - sharpens edges

(define-effect sharpen
  :params (
    (amount :type int :default 1 :range [0 5])
  )
  (let ((kernel (list (list 0 (- amount) 0)
                      (list (- amount) (+ 1 (* 4 amount)) (- amount))
                      (list 0 (- amount) 0))))
    (convolve frame kernel)))