Function: color-cie-de2000

color-cie-de2000 is a byte-compiled function defined in color.el.gz.

Signature

(color-cie-de2000 COLOR1 COLOR2 &optional KL KC KH)

Documentation

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.

Source Code

;; Defined in /usr/src/emacs/lisp/color.el.gz
(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)))))))