emacs/lisp/color.el

;;; color.el --- Color manipulation library -*- lexical-binding:t -*-

;; Copyright (C) 2010-2024 Free Software Foundation, Inc.

;; Authors: Julien Danjou <julien@danjou.info>
;;          Drew Adams <drew.adams@oracle.com>
;; Keywords: lisp, faces, color, hex, rgb, hsv, hsl, cie-lab, background

;; This file is part of GNU Emacs.

;; GNU Emacs is free software: you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.

;;; Commentary:

;; This package provides functions for manipulating colors, including
;; converting between color representations, computing color
;; complements, and computing CIEDE2000 color distances.
;;
;; Supported color representations include RGB (red, green, blue), HSV
;; (hue, saturation, value), HSL (hue, saturation, luminance), sRGB,
;; CIE XYZ, CIE L*a*b* color components, and the Oklab perceptual color
;; space.

;;; Code:

;;;###autoload
(defun color-name-to-rgb (color &optional frame)
  "Convert COLOR string to a list of normalized RGB components.
COLOR should be a color name (e.g. \"white\") or an RGB triplet
string (e.g. \"#ffff1122eecc\").

COLOR can also be the symbol `unspecified' or one of the strings
\"unspecified-fg\" or \"unspecified-bg\", in which case the
return value is nil.

Normally the return value is a list of three floating-point
numbers, (RED GREEN BLUE), each between 0.0 and 1.0 inclusive.

Optional argument FRAME specifies the frame where the color is to be
displayed.  If FRAME is omitted or nil, use the selected frame.
If FRAME cannot display COLOR, return nil."
  ;; `color-values' maximum value is either 65535 or 65280 depending on the
  ;; display system.  So we use a white conversion to get the max value.
  (let ((valmax (float (car (color-values "#ffffffffffff")))))
    (mapcar (lambda (x) (/ x valmax)) (color-values color frame))))

;;;###autoload
(defun color-rgb-to-hex  (red green blue &optional digits-per-component)
  "Return hexadecimal #RGB notation for the color specified by RED GREEN BLUE.
RED, GREEN, and BLUE should be numbers between 0.0 and 1.0, inclusive.
Optional argument DIGITS-PER-COMPONENT can be either 4 (the default)
or 2; use the latter if you need a 24-bit specification of a color."
  (or digits-per-component (setq digits-per-component 4))
  (let* ((maxval (if (= digits-per-component 2) 255 65535))
         (fmt (if (= digits-per-component 2) "#%02x%02x%02x" "#%04x%04x%04x")))
    (format fmt (* red maxval) (* green maxval) (* blue maxval))))

(defun color-complement (color-name)
  "Return the color that is the complement of COLOR-NAME.
COLOR-NAME should be a string naming a color (e.g. \"white\"), or
a string specifying a color's RGB
components (e.g. \"#ffff1212ecec\")."
  (let ((color (color-name-to-rgb color-name)))
    (list (- 1.0 (nth 0 color))
          (- 1.0 (nth 1 color))
          (- 1.0 (nth 2 color)))))

;;;###autoload
(defun color-blend (a b &optional alpha)
  "Blend the two colors A and B in linear space with ALPHA.
A and B should be lists (RED GREEN BLUE), where each element is
between 0.0 and 1.0, inclusive.  ALPHA controls the influence A
has on the result and should be between 0.0 and 1.0, inclusive.

For instance:

   (color-blend \\='(1 0.5 1) \\='(0 0 0) 0.75)
      => (0.75 0.375 0.75)"
  (setq alpha (or alpha 0.5))
  (let (blend)
    (dotimes (i 3)
      (push (+ (* (nth i a) alpha) (* (nth i b) (- 1 alpha))) blend))
    (nreverse blend)))

(defun color-gradient (start stop step-number)
  "Return a list with STEP-NUMBER colors from START to STOP.
The color list builds a color gradient starting at color START to
color STOP.  It does not include the START and STOP color in the
resulting list."
  (let* ((r (nth 0 start))
	 (g (nth 1 start))
	 (b (nth 2 start))
         (interval (float (1+ step-number)))
	 (r-step (/ (- (nth 0 stop) r) interval))
	 (g-step (/ (- (nth 1 stop) g) interval))
	 (b-step (/ (- (nth 2 stop) b) interval))
	 result)
    (dotimes (_ step-number)
      (push (list (setq r (+ r r-step))
		  (setq g (+ g g-step))
		  (setq b (+ b b-step)))
	    result))
    (nreverse result)))

(defun color-hue-to-rgb (v1 v2 h)
  "Compute hue from V1 and V2 H.
Used internally by `color-hsl-to-rgb'."
  (cond
   ((< h (/ 6.0))     (+ v1 (* (- v2 v1) h 6.0)))
   ((< h 0.5)         v2)
   ((< h (/ 2.0 3))   (+ v1 (* (- v2 v1) (- (/ 2.0 3) h) 6.0)))
   (t                 v1)))

(defun color-hsl-to-rgb (H S L)
  "Convert hue, saturation and luminance to their RGB representation.
H, S, and L should each be numbers between 0.0 and 1.0, inclusive.
Return a list (RED GREEN BLUE), where each element is between 0.0 and 1.0,
inclusive."
  (if (= S 0.0)
      (list L L L)
    (let* ((m2 (if (<= L 0.5)
		   (* L (+ 1.0 S))
		 (- (+ L S) (* L S))))
	   (m1 (- (* 2.0 L) m2)))
      (list
       (color-hue-to-rgb m1 m2 (mod (+ H (/ 3.0)) 1))
       (color-hue-to-rgb m1 m2 H)
       (color-hue-to-rgb m1 m2 (mod (- H (/ 3.0)) 1))))))

(defun color-complement-hex (color)
  "Return the color that is the complement of COLOR, in hexadecimal format."
  (apply 'color-rgb-to-hex (color-complement color)))

(defun color-rgb-to-hsv (red green blue)
  "Convert RGB color components to HSV.
RED, GREEN, and BLUE should each be numbers between 0.0 and 1.0,
inclusive.  Return a list (HUE SATURATION VALUE), where HUE is
in radians and both SATURATION and VALUE are between 0.0 and 1.0,
inclusive."
  (let* ((r (float red))
	 (g (float green))
	 (b (float blue))
	 (max (max r g b))
	 (min (min r g b)))
    (if (< (- max min) 1e-8)
	(list 0.0 0.0 min)
      (list
       (/ (* 2 float-pi
	     (cond ((and (= r g) (= g b)) 0)
		   ((and (= r max)
			 (>= g b))
		    (* 60 (/ (- g b) (- max min))))
		   ((and (= r max)
			 (< g b))
		    (+ 360 (* 60 (/ (- g b) (- max min)))))
		   ((= max g)
		    (+ 120 (* 60 (/ (- b r) (- max min)))))
		   ((= max b)
		    (+ 240 (* 60 (/ (- r g) (- max min)))))))
	  360)
       (if (= max 0) 0 (- 1 (/ min max)))
       max))))

(defun color-rgb-to-hsl (red green blue)
  "Convert RGB colors to their HSL representation.
RED, GREEN, and BLUE should each be numbers between 0.0 and 1.0,
inclusive.  Return a list (HUE SATURATION LUMINANCE), where
each element is between 0.0 and 1.0, inclusive."
  (let* ((r red)
         (g green)
         (b blue)
         (max (max r g b))
         (min (min r g b))
         (delta (- max min))
         (l (/ (+ max min) 2.0)))
    (if (= delta 0)
	(list 0.0 0.0 l)
      (let* ((s (if (<= l 0.5) (/ delta (+ max min))
		  (/ delta (- 2.0 max min))))
	     (rc (/ (- max r) delta))
	     (gc (/ (- max g) delta))
	     (bc (/ (- max b) delta))
	     (h  (mod
		  (/
		   (cond
		    ((= r max)      (- bc gc))
		    ((= g max)      (+ 2.0 rc (- bc)))
		    (t              (+ 4.0 gc (- rc))))
		   6.0)
                  1.0)))
	(list h s l)))))

(defun color-srgb-to-xyz (red green blue)
  "Convert RED GREEN BLUE colors from the sRGB color space to CIE XYZ.
RED, GREEN and BLUE should be between 0.0 and 1.0, inclusive."
  (let ((r (if (<= red 0.04045)
               (/ red 12.95)
             (expt (/ (+ red 0.055) 1.055) 2.4)))
        (g (if (<= green 0.04045)
               (/ green 12.95)
             (expt (/ (+ green 0.055) 1.055) 2.4)))
        (b (if (<= blue 0.04045)
               (/ blue 12.95)
             (expt (/ (+ blue 0.055) 1.055) 2.4))))
    (list (+ (* 0.4124564 r) (* 0.3575761 g) (* 0.1804375 b))
          (+ (* 0.21266729 r) (* 0.7151522 g) (* 0.0721750 b))
          (+ (* 0.0193339 r) (* 0.1191920 g) (* 0.9503041 b)))))

(defun color-xyz-to-srgb (X Y Z)
  "Convert CIE X Y Z colors to sRGB color space."
  (let ((r (+ (* 3.2404542 X) (* -1.5371385 Y) (* -0.4985314 Z)))
        (g (+ (* -0.9692660 X) (* 1.8760108 Y) (* 0.0415560 Z)))
        (b (+ (* 0.0556434 X) (* -0.2040259 Y) (* 1.0572252 Z))))
    (list (if (<= r 0.0031308)
              (* 12.92 r)
            (- (* 1.055 (expt r (/ 2.4))) 0.055))
          (if (<= g 0.0031308)
              (* 12.92 g)
            (- (* 1.055 (expt g (/ 2.4))) 0.055))
          (if (<= b 0.0031308)
              (* 12.92 b)
            (- (* 1.055 (expt b (/ 2.4))) 0.055)))))

(defconst color-d75-xyz '(0.9497 1.0 1.2264)
  "D75 white point in CIE XYZ.")

(defconst color-d65-xyz '(0.950455 1.0 1.088753)
  "D65 white point in CIE XYZ.")

(defconst color-d55-xyz '(0.9568 1.0 0.9215)
  "D55 white point in CIE XYZ.")

(defconst color-d50-xyz '(0.9642 1.0 0.8249)
  "D50 white point in CIE XYZ.")

(defconst color-cie-ε (/ 216 24389.0))
(defconst color-cie-κ (/ 24389 27.0))

(defun color-xyz-to-lab (X Y Z &optional white-point)
  "Convert CIE XYZ to CIE L*a*b*.
WHITE-POINT specifies the (X Y Z) white point for the
conversion.  If omitted or nil, use `color-d65-xyz'."
  (pcase-let* ((`(,Xr ,Yr ,Zr) (or white-point color-d65-xyz))
               (xr (/ X Xr))
             (yr (/ Y Yr))
             (zr (/ Z Zr))
             (fx (if (> xr color-cie-ε)
                     (expt xr (/ 3.0))
                   (/ (+ (* color-cie-κ xr) 16) 116.0)))
             (fy (if (> yr color-cie-ε)
                     (expt yr (/ 3.0))
                   (/ (+ (* color-cie-κ yr) 16) 116.0)))
             (fz (if (> zr color-cie-ε)
                     (expt zr (/ 3.0))
                   (/ (+ (* color-cie-κ zr) 16) 116.0))))
        (list
         (- (* 116 fy) 16)                  ; L
         (* 500 (- fx fy))                  ; a
     (* 200 (- fy fz)))))             ; b

(defun color-lab-to-xyz (L a b &optional white-point)
  "Convert CIE L*a*b* to CIE XYZ.
WHITE-POINT specifies the (X Y Z) white point for the
conversion.  If omitted or nil, use `color-d65-xyz'."
  (pcase-let* ((`(,Xr ,Yr ,Zr) (or white-point color-d65-xyz))
               (fy (/ (+ L 16) 116.0))
             (fz (- fy (/ b 200.0)))
             (fx (+ (/ a 500.0) fy))
             (xr (if (> (expt fx 3.0) color-cie-ε)
                     (expt fx 3.0)
               (/ (- (* fx 116) 16) color-cie-κ)))
             (yr (if (> L (* color-cie-κ color-cie-ε))
                     (expt (/ (+ L 16) 116.0) 3.0)
                   (/ L color-cie-κ)))
             (zr (if (> (expt fz 3) color-cie-ε)
                     (expt fz 3.0)
                   (/ (- (* 116 fz) 16) color-cie-κ))))
        (list (* xr Xr)                 ; X
              (* yr Yr)                 ; Y
          (* zr Zr))))                ; Z

(defun color-srgb-to-lab (red green blue)
  "Convert RGB to CIE L*a*b*."
  (apply 'color-xyz-to-lab (color-srgb-to-xyz red green blue)))

(defun color-lab-to-srgb (L a b)
  "Convert CIE L*a*b* to RGB."
  (apply 'color-xyz-to-srgb (color-lab-to-xyz L a b)))

(defun color-xyz-to-xyy (X Y Z)
  "Convert CIE XYZ to xyY."
  (let ((d (float (+ X Y Z))))
    (list (/ X d) (/ Y d) Y)))

(defun color-xyy-to-xyz (x y Y)
  "Convert CIE xyY to XYZ."
  (let ((y (float y)))
   (list (/ (* Y x) y) Y (/ (* Y (- 1 x y)) y))))

(defun color-lab-to-lch (L a b)
  "Convert CIE L*a*b* to L*C*h*."
  (list L (sqrt (+ (* a a) (* b b))) (atan b a)))

(defun color-lch-to-lab (L C h)
  "Convert CIE L*a*b* to L*C*h*."
  (list L (* C (cos h)) (* C (sin h))))

(defun color-cie-de2000 (color1 color2 &optional kL kC kH)
  "Return the CIEDE2000 color distance between COLOR1 and COLOR2.
Both COLOR1 and COLOR2 should be in CIE L*a*b* format, as
returned by `color-srgb-to-lab' or `color-xyz-to-lab'."
  (pcase-let*
      ((`(,L₁ ,a₁ ,b₁) color1)
       (`(,L₂ ,a₂ ,b₂) color2)
       (kL (or kL 1))
       (kC (or kC 1))
       (kH (or kH 1))
       (C₁ (sqrt (+ (expt a₁ 2.0) (expt b₁ 2.0))))
       (C₂ (sqrt (+ (expt a₂ 2.0) (expt b₂ 2.0))))
       (C̄ (/ (+ C₁ C₂) 2.0))
       (G (* 0.5 (- 1 (sqrt (/ (expt C̄ 7.0)
                               (+ (expt C̄ 7.0) (expt 25 7.0)))))))
       (a′₁ (* (+ 1 G) a₁))
       (a′₂ (* (+ 1 G) a₂))
       (C′₁ (sqrt (+ (expt a′₁ 2.0) (expt b₁ 2.0))))
       (C′₂ (sqrt (+ (expt a′₂ 2.0) (expt b₂ 2.0))))
       (h′₁ (if (and (= b₁ 0) (= a′₁ 0))
                0
              (let ((v (atan b₁ a′₁)))
                (if (< v 0)
                    (+ v (* 2 float-pi))
                  v))))
       (h′₂ (if (and (= b₂ 0) (= a′₂ 0))
                0
              (let ((v (atan b₂ a′₂)))
                (if (< v 0)
                    (+ v (* 2 float-pi))
                  v))))
       (ΔL′ (- L₂ L₁))
       (ΔC′ (- C′₂ C′₁))
       (Δh′ (cond ((= (* C′₁ C′₂) 0)
                   0)
                  ((<= (abs (- h′₂ h′₁)) float-pi)
                   (- h′₂ h′₁))
                  ((> (- h′₂ h′₁) float-pi)
                   (- (- h′₂ h′₁) (* 2 float-pi)))
                  ((< (- h′₂ h′₁) (- float-pi))
                   (+ (- h′₂ h′₁) (* 2 float-pi)))))
       (ΔH′ (* 2 (sqrt (* C′₁ C′₂)) (sin (/ Δh′ 2.0))))
       (L̄′ (/ (+ L₁ L₂) 2.0))
       (C̄′ (/ (+ C′₁ C′₂) 2.0))
       (h̄′ (cond ((= (* C′₁ C′₂) 0)
                  (+ h′₁ h′₂))
                 ((<= (abs (- h′₁ h′₂)) float-pi)
                  (/ (+ h′₁ h′₂) 2.0))
                 ((< (+ h′₁ h′₂) (* 2 float-pi))
                  (/ (+ h′₁ h′₂ (* 2 float-pi)) 2.0))
                 ((>= (+ h′₁ h′₂) (* 2 float-pi))
                  (/ (+ h′₁ h′₂ (* -2 float-pi)) 2.0))))
       (T (+ 1
             (- (* 0.17 (cos (- h̄′ (degrees-to-radians 30)))))
             (* 0.24 (cos (* h̄′ 2)))
             (* 0.32 (cos (+ (* h̄′ 3) (degrees-to-radians 6))))
             (- (* 0.20 (cos (- (* h̄′ 4) (degrees-to-radians 63)))))))
       (Δθ (* (degrees-to-radians 30)
              (exp (- (expt (/ (- h̄′ (degrees-to-radians 275))
                               (degrees-to-radians 25)) 2.0)))))
       (Rc (* 2 (sqrt (/ (expt C̄′ 7.0) (+ (expt C̄′ 7.0) (expt 25.0 7.0))))))
       (Sl (+ 1 (/ (* 0.015 (expt (- L̄′ 50) 2.0))
                   (sqrt (+ 20 (expt (- L̄′ 50) 2.0))))))
       (Sc (+ 1 (* C̄′ 0.045)))
       (Sh (+ 1 (* 0.015 C̄′ T)))
       (Rt (- (* (sin (* Δθ 2)) Rc))))
        (sqrt (+ (expt (/ ΔL′ (* Sl kL)) 2.0)
                 (expt (/ ΔC′ (* Sc kC)) 2.0)
                 (expt (/ ΔH′ (* Sh kH)) 2.0)
                 (* Rt (/ ΔC′ (* Sc kC)) (/ ΔH′ (* Sh kH)))))))

(defun color-oklab-to-xyz (l a b)
  "Convert the OkLab color represented by L A B to CIE XYZ.
Oklab is a perceptual color space created by Björn Ottosson
<https://bottosson.github.io/posts/oklab/>.  It has the property that
changes in the hue and saturation of a color can be made while maintaining
the same perceived lightness."
  (let ((ll (expt (+ (* 1.0 l) (* 0.39633779 a) (* 0.21580376 b)) 3))
        (mm (expt (+ (* 1.00000001 l) (* -0.10556134 a) (* -0.06385417 b)) 3))
        (ss (expt (+ (* 1.00000005 l) (* -0.08948418 a) (* -1.29148554 b)) 3)))
    (list (+ (* ll 1.22701385) (* mm -0.55779998) (* ss 0.28125615))
          (+ (* ll -0.04058018) (* mm 1.11225687) (* ss -0.07167668))
          (+ (* ll -0.07638128) (* mm -0.42148198) (* ss 1.58616322)))))

(defun color-xyz-to-oklab (x y z)
  "Convert the CIE XYZ color represented by X Y Z to Oklab."
  (let ((ll (+ (* x 0.8189330101) (* y 0.3618667424) (* z -0.1288597137)))
        (mm (+ (* x 0.0329845436) (* y 0.9293118715) (* z 0.0361456387)))
        (ss (+ (* x 0.0482003018) (* y 0.2643662691) (* z 0.6338517070))))
    (let*
        ((cube-root (lambda (f)
                      (if (< f 0)
	                  (- (expt (- f) (/ 1.0 3.0)))
                        (expt f (/ 1.0 3.0)))))
         (lll (funcall cube-root ll))
         (mmm (funcall cube-root mm))
         (sss (funcall cube-root ss)))
      (list (+ (* lll 0.2104542553) (* mmm 0.7936177850) (* sss -0.0040720468))
            (+ (* lll 1.9779984951) (* mmm -2.4285922050) (* sss 0.4505937099))
            (+ (* lll 0.0259040371) (* mmm 0.7827717662) (* sss -0.8086757660))))))

(defun color-oklab-to-srgb (l a b)
  "Convert the Oklab color represented by L A B to sRGB."
  (apply #'color-xyz-to-srgb (color-oklab-to-xyz l a b)))

(defun color-srgb-to-oklab (r g b)
  "Convert the sRGB color R G B to Oklab."
  (apply #'color-xyz-to-oklab (color-srgb-to-xyz r g b)))

(defun color-clamp (value)
  "Make sure VALUE is a number between 0.0 and 1.0 inclusive."
  (min 1.0 (max 0.0 value)))

(defun color-saturate-hsl (H S L percent)
  "Make a color more saturated by a specified amount.
Given a color defined in terms of hue, saturation, and luminance
\(arguments H, S, and L), return a color that is PERCENT more
saturated.  Returns a list (HUE SATURATION LUMINANCE)."
  (list H (color-clamp (+ S (/ percent 100.0))) L))

(defun color-saturate-name (name percent)
  "Make a color with a specified NAME more saturated by PERCENT.
See `color-saturate-hsl'."
  (apply 'color-rgb-to-hex
	 (apply 'color-hsl-to-rgb
		(apply 'color-saturate-hsl
		       (append
			(apply 'color-rgb-to-hsl
			       (color-name-to-rgb name))
			(list percent))))))

(defun color-desaturate-hsl (H S L percent)
  "Make a color less saturated by a specified amount.
Given a color defined in terms of hue, saturation, and luminance
\(arguments H, S, and L), return a color that is PERCENT less
saturated.  Returns a list (HUE SATURATION LUMINANCE)."
  (color-saturate-hsl H S L (- percent)))

(defun color-desaturate-name (name percent)
  "Make a color with a specified NAME less saturated by PERCENT.
See `color-desaturate-hsl'."
  (color-saturate-name name (- percent)))

(defun color-lighten-hsl (H S L percent)
  "Make a color lighter by a specified amount.
Given a color defined in terms of hue, saturation, and luminance
\(arguments H, S, and L), return a color that is PERCENT lighter.
Returns a list (HUE SATURATION LUMINANCE)."
  (let ((p (/ percent 100.0)))
    (if (> p 0.0)
        (setq L (* L (- 1.0 p)))
      (setq p (- (* L (abs p)))))
    (list H S (color-clamp (+ L p)))))

(defun color-lighten-name (name percent)
  "Make a color with a specified NAME lighter by PERCENT.
See `color-lighten-hsl'."
  (apply 'color-rgb-to-hex
	 (apply 'color-hsl-to-rgb
		(apply 'color-lighten-hsl
		       (append
			(apply 'color-rgb-to-hsl
			       (color-name-to-rgb name))
			(list percent))))))

(defun color-darken-hsl (H S L percent)
    "Make a color darker by a specified amount.
Given a color defined in terms of hue, saturation, and luminance
\(arguments H, S, and L), return a color that is PERCENT darker.
Returns a list (HUE SATURATION LUMINANCE)."
  (color-lighten-hsl H S L (- percent)))

(defun color-darken-name (name percent)
  "Make a color with a specified NAME darker by PERCENT.
See `color-darken-hsl'."
  (color-lighten-name name (- percent)))

(provide 'color)

;;; color.el ends here