RGB space

Basics

There are four representations of an RGB color in dufy:

• lrgb: linear RGB. The range depends on RGB space but is typically [0, 1].
  • accepted type of lrgb-to- converters: real real real
  • return type of -to-lrgb converters: (values double-float double-float double-float &optional)
• rgb: gamma-corrected RGB. The range depends on RGB space but is typically [0, 1].
  • accepted type of rgb-to- converters: real real real
  • return type of -to-rgb converters: (values double-float double-float double-float &optional)
• qrgb: quantized RGB. The range depends on bits per channel but is typically {0, 1, ..., 255}.
  • accepted type of qrgb-to- converters: fixnum fixnum fixnum
  • return type of -to-qrgb converters: (values fixnum fixnum fixnum &optional)
• rgbpack: RGB value packed to an integer. The range depends on bits per channel but is typically {#x000000, #x000001, ..., #xFFFFFF}.
  • accepted type of rgbpack-to- converters: integer
  • return type of -to-rgbpack converters: (values integer &optional)

The followings are the simplest examples:

(dufy:rgbpack-to-lrgb #xFF8800)
;; => 1.0d0               ; linear R value
;; 0.24620132670783548d0  ; linear G value
;; 0.0d0                  ; linear B value
(dufy:hsv-to-qrgb 120 0.5 1) ; Hue = 120°, Saturation = 0.5, Value = 1
;; => 128 ; quantized R value
;; 255    ; quantized G value
;; 128    ; quantized B value
(dufy:xyz-to-rgb 0.9505d0 1 1.0889d0) ; white point of illuminant D65
;; => 1.000053479346423d0 ; gamma-corrected R value
;; 0.9999860875272101d0   ; gamma-corrected G value
;; 0.9999802745645446d0   ; gamma-corrected B value

Most converters regard the implicit RGB space as sRGB. You can specify it explicitly.

(dufy:xyz-to-qrgb 0.37314 0.70144 1.0601 :rgbspace dufy:+srgb+ :clamp nil)  ; sRGB
;; => -169
;;    255
;;    255

(dufy:xyz-to-qrgb 0.37314 0.70144 1.0601 :rgbspace dufy:+adobe+ :clamp nil) ; Adobe RGB
;; => 2
;;    255
;;    255

Predefined RGB spaces

All the following symbols are exported by dufy/core and reexported by dufy.

Name	Symbol	Illuminant	bpc	Range of linear val.
sRGB	+SRGB+	D65	8	[0.0, 1.0]
Adobe RGB	+ADOBE+	D65	8	[0.0, 1.0]
Adobe RGB	+ADOBE-16+	D65	16	[0.0, 1.0]
scRGB	+SCRGB-16+	D65	16	[-0.5, 7.4999]
scRGB-nl	+SCRGB-NL+	D65	12	[-0.6038, 7.5913]
bg-sRGB	+BG-SRGB-16+	D65	16	[-0.53, 1.68]
bg-sRGB	+BG-SRGB-12+	D65	12	[-0.53, 1.68]
bg-sRGB	+BG-SRGB-10+	D65	10	[-0.53, 1.68]
ProPhoto RGB	+PROPHOTO+	D50	8	[0.0, 1.0]
ProPhoto RGB	+PROPHOTO-12+	D50	12	[0.0, 1.0]
ProPhoto RGB	+PROPHOTO-16+	D50	16	[0.0, 1.0]
PAL/SECAM RGB	+PAL/SECAM+	D65	8	[0.0, 1.0]
CIE RGB	+CIE-RGB+	E	8	[0.0, 1.0]
NTSC RGB	+NTSC1953+	C	8	[0.0, 1.0]
Wide Gamut RGB	+WIDE-GAMUT+	D50	8	[0.0, 1.0]

Define your own RGB space

Function: MAKE-RGBSPACE XR YR XG YG XB YB &KEY (ILLUMINANT +ILLUM-D65+) (LMIN 0.0d0) (LMAX 1.0d0) (LINEARIZER (RCURRY #'FLOAT 1.0d0)) (DELINEARIZER (RCURRY #'FLOAT 1.0d0)) (BIT-PER-CHANNEL 8) (FORCE-NORMAL NIL)

In the following example, CIE RGB is defined with gamma value 2.2. (That of the predefined one is 1.0.)

(defparameter +my-cie-rgb+
  (dufy:make-rgbspace 0.7347d0 0.2653d0 0.2738d0 0.7174d0 0.1666d0 0.0089d0
                     :linearizer (dufy:gen-linearizer 2.2d0)
                     :delinearizer (dufy:gen-delinearizer 2.2d0)
                     :illuminant dufy:+illum-e+))