add ΔE_ITP color difference as differenceItp()

Author: danburzo

docs/api.md

@@ -29,6 +29,7 @@ codebase: 'https://github.com/evercoder/culori/blob/main'
 <li><a href='#differenceHueSaturation'>differenceHueSaturation</a></li>
 <li><a href='#differenceHyab'>differenceHyab</a></li>
 <li><a href='#differenceKotsarenkoRamos'>differenceKotsarenkoRamos</a></li>
+<li><a href='#differenceItp'>differenceItp</a></li>
 <li><a href='#displayable'>displayable</a></li>
 <li><a href='#color-spaces'>dlab</a></li>
 <li><a href='#color-spaces'>dlch</a></li>
@@ -1097,7 +1098,7 @@ These methods are concerned to finding the [distance between two colors](https:/
 
 Returns a [Euclidean distance](https://en.wikipedia.org/wiki/Color_difference#Euclidean) function in a certain color space.
 
-You can optionally assign different weights to the channels in the color space. See, for example, the [Kotsarenko/Ramos distance](#differenceKotsarenkoRamos).
+You can optionally assign different weights to the channels in the color space. See, for example, the [Kotsarenko/Ramos distance](#differenceKotsarenkoRamos) or [ΔE<sub>ITP</sub>](#differenceItp).
 
 The default weights `[1, 1, 1, 0]` mean that the _alpha_, which is the fourth channel in all the color spaces Culori defines, is not taken into account. Send `[1, 1, 1, 1]` as the weights to include it in the computation.
 
@@ -1175,6 +1176,12 @@ Computes the [DIN99o][din99ode] ΔE\*<sub>99o</sub> color difference between the
 
 Computes the [Kotsarenko/Ramos][kotsarekno-ramos] color difference between the colors _a_ and _b_. This is a weighted Euclidean distance in the `yiq` color space.
 
+<a id="differenceItp" href="#differenceItp">#</a> **differenceItp**()
+
+<span aria-label='Source:'>☞</span> [src/difference.js]({{codebase}}/src/difference.js)
+
+Computes the [ΔE<sub>ITP</sub>][eitp-difference] color difference metric between the colors _a_ and _b_. This is a weighted Euclidean distance in the `itp` color space, scaled by a factor of 720 so that a the just-noticeable difference (<abbr>JND</abbr>) corresponds to a value of 1.
+
 ### Nearest color(s)
 
 <a id="nearest" href="#nearest">#</a> **nearest**(_colors_, _metric = differenceEuclidean()_, _accessor = identity_) → _function(color, n = 1, τ = Infinity)_
@@ -1898,3 +1905,4 @@ __convertYiqToRgb__(_color_) → _color_ | `yiq` → `rgb`
 [kotsarekno-ramos]: http://www.progmat.uaem.mx:8080/artVol2Num2/Articulo3Vol2Num2.pdf
 [din99ode]: https://de.wikipedia.org/wiki/DIN99-Farbraum#Farbabstandsformel
 [midpoint]: https://github.com/w3c/csswg-drafts/issues/3935
+[eitp-difference]: https://www.itu.int/rec/R-REC-BT.2124/en

docs/color-spaces.md

@@ -458,6 +458,8 @@ Serialized as `color(--ictcp i t p)`, with the `none` keyword for any missing co
 
 Does not have gamut limits.
 
+The `itp` color space is the basis of the [ΔE<sub>ITP</sub> color difference](/api/#differenceItp) metric defined in _Objective metric for the assessment of the potential visibility of colour differences in television_ ([Rec. ITU-R BT.2124](https://www.itu.int/rec/R-REC-BT.2124/en)).
+
 ### Cubehelix
 
 [The Cubehelix color scheme](https://www.mrao.cam.ac.uk/~dag/CUBEHELIX/) was described by Dave Green in this paper:

docs/resources.md

@@ -35,9 +35,9 @@ _Does your product/project use Culori? Create a PR and add yourself to this list
 
 ### Specifications
 
-- [CSS Color Module Level 4](https://drafts.csswg.org/css-color-4/)
-- [CSS Color Module Level 5](https://drafts.csswg.org/css-color-5/)
-- [CSS Color HDR Module Level 1](https://drafts.csswg.org/css-color-hdr/)
+- [CSS Color Module Level 4](https://drafts.csswg.org/css-color-4/) [[changelog](https://github.com/w3c/csswg-drafts/commits/main/css-color-4)]
+- [CSS Color Module Level 5](https://drafts.csswg.org/css-color-5/) [[changelog](https://github.com/w3c/csswg-drafts/commits/main/css-color-5)]
+- [CSS Color HDR Module Level 1](https://drafts.csswg.org/css-color-hdr/) [[changelog](https://github.com/w3c/csswg-drafts/commits/main/css-color-hdr)]
 
 ### Websites
 

src/difference.js

@@ -292,6 +292,14 @@ const differenceHyab = () => {
 const differenceKotsarenkoRamos = () =>
 	differenceEuclidean('yiq', [0.5053, 0.299, 0.1957]);
 
+/*
+	ΔE_ITP, as defined in Rec. ITU-R BT.2124:
+
+	https://www.itu.int/rec/R-REC-BT.2124/en
+*/
+const differenceItp = () =>
+	differenceEuclidean('itp', [518400, 129600, 518400]);
+
 export {
 	differenceHueChroma,
 	differenceHueSaturation,
@@ -302,5 +310,6 @@ export {
 	differenceCiede2000,
 	differenceCmc,
 	differenceHyab,
-	differenceKotsarenkoRamos
+	differenceKotsarenkoRamos,
+	differenceItp
 };

src/index-fn.js

@@ -118,7 +118,8 @@ export {
 	differenceHueSaturation,
 	differenceHueChroma,
 	differenceHueNaive,
-	differenceKotsarenkoRamos
+	differenceKotsarenkoRamos,
+	differenceItp
 } from './difference.js';
 
 export {

src/index.js

@@ -119,7 +119,8 @@ export {
 	differenceHueSaturation,
 	differenceHueChroma,
 	differenceHueNaive,
-	differenceKotsarenkoRamos
+	differenceKotsarenkoRamos,
+	differenceItp
 } from './difference.js';
 
 export {

test/api.test.js

@@ -93,6 +93,7 @@ const API_FULL = [
 	'differenceHueSaturation',
 	'differenceHyab',
 	'differenceKotsarenkoRamos',
+	'differenceItp',
 	'displayable',
 	'dlab',
 	'dlch',
@@ -364,6 +365,7 @@ const API_FN = [
 	'differenceHueSaturation',
 	'differenceHyab',
 	'differenceKotsarenkoRamos',
+	'differenceItp',
 	'displayable',
 	'easingGamma',
 	'easingInOutSine',

test/difference.test.js

@@ -7,6 +7,7 @@ import {
 	differenceCmc,
 	differenceHyab,
 	differenceKotsarenkoRamos,
+	differenceItp,
 	rgb,
 	lab65,
 	round,
@@ -187,3 +188,8 @@ tape('differenceHyab', t => {
 	t.equal(differenceHyab()('red', 'green'), 139.92805737622862);
 	t.end();
 });
+
+tape('differenceItp', t => {
+	t.equal(differenceItp()('red', 'green'), 238.28868759957626);
+	t.end();
+});