bug#70963: [PATCH] Add Oklab color space utility functions in color.el.

bug#70963: [PATCH] Add Oklab color space utility functions in color.el.

[Robert Church]

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This patch adds functions to convert to and from the Oklab perceptual color
space to color.el. Oklab preserves the perceived brightness ot a color as
the hue and saturation change. It is especially useful for programmatically
generating color schemes, and can be used directly in CSS in current web
browsers.

Oklab is described here: https://bottosson.github.io/posts/oklab/

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From 8a4c94047ba26c04e2692271e1475c70244fc6d0 Mon Sep 17 00:00:00 2001
From: Robert Church <chrchr@gmail.com>
Date: Mon, 13 May 2024 17:28:28 -0700
Subject: [PATCH] Add Oklab color space utility functions in color.el.

---
 lisp/color.el            | 41 +++++++++++++++++++++++++++++++++++++++-
 test/lisp/color-tests.el | 33 ++++++++++++++++++++++++++++++++
 2 files changed, 73 insertions(+), 1 deletion(-)

diff --git a/lisp/color.el b/lisp/color.el
index 078c12fbf47..5ba73f4a879 100644
--- a/lisp/color.el
+++ b/lisp/color.el
@@ -29,7 +29,8 @@
 ;;
 ;; Supported color representations include RGB (red, green, blue), HSV
 ;; (hue, saturation, value), HSL (hue, saturation, luminance), sRGB,
-;; CIE XYZ, and CIE L*a*b* color components.
+;; CIE XYZ, CIE L*a*b* color components, and the Oklab perceptual color
+;; space.
 
 ;;; Code:
 
@@ -368,6 +369,44 @@ color-cie-de2000
                  (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)))
diff --git a/test/lisp/color-tests.el b/test/lisp/color-tests.el
index 9b6b8c1f8dc..0f53e4332a4 100644
--- a/test/lisp/color-tests.el
+++ b/test/lisp/color-tests.el
@@ -247,5 +247,38 @@ color-tests-darken-name
   (should (equal (color-darken-name "red" 0) "#ffff00000000"))
   (should (equal (color-darken-name "red" 10) "#e66500000000")))
 
+(ert-deftest color-tests-oklab-to-xyz ()
+  (should (color-tests--approx-equal (color-oklab-to-xyz 0 0 0) '(0.0 0.0 0.0)))
+  (should (color-tests--approx-equal (color-oklab-to-xyz 1.0 0.0 0.0)
+                                     '(0.95047005 1.0 1.0883001)))
+  (should (color-tests--approx-equal (color-oklab-to-xyz 0.450 1.236 -0.019) '(1.000604 -0.000008 -0.000038)))
+  (should (color-tests--approx-equal (color-oklab-to-xyz 0.922 -0.671 0.263) '(0.000305 1.000504 0.000898)))
+  (should (color-tests--approx-equal (color-oklab-to-xyz 0.153 -1.415 -0.449) '(0.000590 0.000057 1.001650))))
+
+(ert-deftest color-tests-xyz-to-oklab ()
+  (should (color-tests--approx-equal (color-xyz-to-oklab 0 0 0) '(0.0 0.0 0.0)))
+  (should (color-tests--approx-equal (color-xyz-to-oklab 0.95 1.0 1.089)
+                                     '(0.999969 -0.000258 -0.000115)))
+  (should (color-tests--approx-equal (color-xyz-to-oklab 1.0 0.0 0.0)
+                                     '(0.449932 1.235710 -0.019028)))
+  (should (color-tests--approx-equal (color-xyz-to-oklab 0.0 1.0 0.0)
+                                     '(0.921817 -0.671238 0.263324)))
+  (should (color-tests--approx-equal (color-xyz-to-oklab 0.0 0.0 1.0)
+                                     '(0.152603 -1.414997 -0.448927))))
+
+(ert-deftest color-tests-srgb-to-oklab ()
+  (should (equal (color-srgb-to-oklab 0 0 0) '(0.0 0.0 0.0)))
+  (should
+   (color-tests--approx-equal (color-srgb-to-oklab 0 0 1) '(0.451978 -0.032430 -0.311611)))
+  (should
+   (color-tests--approx-equal (color-srgb-to-oklab 0.1 0.2 0.3) '(0.313828 -0.019091 -0.052561))))
+
+(ert-deftest color-tests-oklab-to-srgb ()
+  (should (equal (color-oklab-to-srgb 0 0 0) '(0.0 0.0 0.0)))
+  (should
+   (color-tests--approx-equal (color-oklab-to-srgb 0.451978 -0.032430 -0.311611) '(0.0 0.0 1.0)))
+  (should
+   (color-tests--approx-equal (color-oklab-to-srgb 0.313828 -0.019091 -0.052561) '(0.1 0.2 0.3))))
+
 (provide 'color-tests)
 ;;; color-tests.el ends here
-- 
2.39.2

bug#70963: [PATCH] Add Oklab color space utility functions in color.el.

[Andrea Corallo]

Robert Church <chrchr@gmail.com> writes:

> This patch adds functions to convert to and from the Oklab perceptual color space to color.el. Oklab preserves the
> perceived brightness ot a color as the hue and saturation change. It is especially useful for programmatically generating
> color schemes, and can be used directly in CSS in current web browsers.
>
> Oklab is described here: https://bottosson.github.io/posts/oklab/

Hi Robert,

thanks for the patch.  Unless I'm wrong you have not the FSF copyright
paperwork done, would you be willg to do it in order to contrubute to
Emacs?

Thanks

  Andrea

bug#70963: [PATCH] Add Oklab color space utility functions in color.el.

[Eli Zaretskii]

> From: Robert Church <chrchr@gmail.com>
> Date: Wed, 15 May 2024 09:58:27 -0700
> 
> This patch adds functions to convert to and from the Oklab perceptual color space to color.el. Oklab
> preserves the perceived brightness ot a color as the hue and saturation change. It is especially useful for
> programmatically generating color schemes, and can be used directly in CSS in current web browsers.
> 
> Oklab is described here: https://bottosson.github.io/posts/oklab/

Thanks.

Would you be willing to assign the copyright for your contribution to
the FSF?  We need this to accept contributions of this size.  If you
agree, I will send you the form to fill and the instructions to go
with the form.

bug#70963: [PATCH] Add Oklab color space utility functions in color.el.

[Robert Church]

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Hi Andrea. I submitted the copyright paperwork to the FSF last month.

On Wed, May 15, 2024, 11:00 AM Andrea Corallo <acorallo@gnu.org> wrote:

> Robert Church <chrchr@gmail.com> writes:
>
> > This patch adds functions to convert to and from the Oklab perceptual
> color space to color.el. Oklab preserves the
> > perceived brightness ot a color as the hue and saturation change. It is
> especially useful for programmatically generating
> > color schemes, and can be used directly in CSS in current web browsers.
> >
> > Oklab is described here: https://bottosson.github.io/posts/oklab/
>
> Hi Robert,
>
> thanks for the patch.  Unless I'm wrong you have not the FSF copyright
> paperwork done, would you be willg to do it in order to contrubute to
> Emacs?
>
> Thanks
>
>   Andrea
>

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bug#70963: [PATCH] Add Oklab color space utility functions in color.el.

[Stefan Kangas]

Robert Church <chrchr@gmail.com> writes:

> Hi Andrea. I submitted the copyright paperwork to the FSF last month.

The paperwork has been finalized according to an email from the
FSF copyright clerk on Thu, 16 May 2024 15:56:58 -0400.

bug#70963: [PATCH] Add Oklab color space utility functions in color.el.

[Eli Zaretskii]

> From: Robert Church <chrchr@gmail.com>
> Date: Wed, 15 May 2024 09:58:27 -0700
> 
> This patch adds functions to convert to and from the Oklab perceptual color space to color.el. Oklab
> preserves the perceived brightness ot a color as the hue and saturation change. It is especially useful for
> programmatically generating color schemes, and can be used directly in CSS in current web browsers.
> 
> Oklab is described here: https://bottosson.github.io/posts/oklab/

Thanks, I installed this on the master branch.

For the future, please try to observe our conventions for patch
submissions:

  . accompany the patches with suitable ChangeLog-style commit log
    messages (you can see the examples in what I actually committed,
    and the instructions are in CONTRIBUTE)
  . leave 2 spaces between sentences in doc strings and comments
  . announce any worthy changes in NEWS and propose changes for the
    manuals when appropriate

I'm closing the bug report with this message.

bug#70963: [PATCH] Add Oklab color space utility functions in color.el.

[Eli Zaretskii]

> Cc: 70963@debbugs.gnu.org
> From: Stefan Kangas <stefankangas@gmail.com>
> Date: Sat, 18 May 2024 22:16:34 +0000
> 
> Robert Church <chrchr@gmail.com> writes:
> 
> > Hi Andrea. I submitted the copyright paperwork to the FSF last month.
> 
> The paperwork has been finalized according to an email from the
> FSF copyright clerk on Thu, 16 May 2024 15:56:58 -0400.

Right, and so I installed the changes.