;; Posterize effect - reduces color levels

(define-effect posterize
  :params (
    (levels :type int :default 8 :range [2 32])
  )
  (let ((step (floor (/ 256 levels))))
    (map-pixels frame
      (lambda (x y c)
        (rgb (* (floor (/ (red c) step)) step)
             (* (floor (/ (green c) step)) step)
             (* (floor (/ (blue c) step)) step))))))