;; Posterize effect - reduces color levels
;; @param levels int [2, 32] default 8

(define-effect posterize
  ((levels 8))
  (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))))))