;; Threshold effect - converts to black and white
;; @param level int [0, 255] default 128
;; @param invert bool default false

(define-effect threshold
  ((level 128) (invert false))
  (map-pixels frame
    (lambda (x y c)
      (let* ((lum (luminance c))
             (above (if invert (< lum level) (> lum level))))
        (if above
            (rgb 255 255 255)
            (rgb 0 0 0))))))