Grayscale image: Difference between revisions

=={{header|Racket}}==

<lang racket>

#lang racket

(require racket/draw)

(define (gray->color gray-bm)

(define gray-dc (new bitmap-dc% [bitmap gray-bm]))

(define-values (w h) (send gray-dc get-size))

(define width (exact-floor w))

(define height (exact-floor h))

(define color-bm (make-bitmap width height))

(define color-dc (new bitmap-dc% [bitmap color-bm]))

(define pixels (make-bytes (* 4 width height)))

(send gray-dc get-argb-pixels 0 0 width height pixels)

(send color-dc set-argb-pixels 0 0 width height pixels)

color-bm)

(define (color->gray color-bm)

(define color-dc (new bitmap-dc% [bitmap color-bm]))

(define-values (w h) (send color-dc get-size))

(define width (exact-floor w))

(define height (exact-floor h))

(define gray-bm (make-bitmap width height))

(define gray-dc (new bitmap-dc% [bitmap gray-bm]))

(define pixels (make-bytes (* 4 width height)))

(send color-dc get-argb-pixels 0 0 width height pixels)

(for ([i (in-range 0 (* 4 width height) 4)])

(define α (bytes-ref pixels i))

(define r (bytes-ref pixels (+ i 1)))

(define g (bytes-ref pixels (+ i 2)))

(define b (bytes-ref pixels (+ i 3)))

(define l (exact-floor (+ (* 0.2126 r) (* 0.7152 g) (* 0.0722 b))))

(bytes-set! pixels (+ i 1) l)

(bytes-set! pixels (+ i 2) l)

(bytes-set! pixels (+ i 3) l))

(send gray-dc set-argb-pixels 0 0 width height pixels)

gray-bm)

(require images/icons/symbol)

(define rosetta (text-icon "Rosetta Code" #:color "red" #:height 80))

rosetta

(color->gray rosetta)

(gray->color (color->gray rosetta))

</lang>