Add support for ICtCp color space

docs/api.md

@@ -1547,6 +1547,7 @@ Mode | Color space | Definition object
 `hsl` | HSL color space | `modeHsl`
 `hsv` | HSV color space | `modeHsv`
 `hwb` | HWB color space | `modeHwb`
+`itp` | IC<sub>t</sub>C<sub>p</sub> color space | `modeItp`
 `jab` | J<sub>z</sub>a<sub>z</sub>b<sub>z</sub> color space | `modeJab`
 `jch` | J<sub>z</sub>a<sub>z</sub>b<sub>z</sub> in cylindrical form | `modeJch`
 `lab` | CIELAB color space (D50 Illuminant) | `modeLab`

docs/color-spaces.md

@@ -438,7 +438,21 @@ It has the default _Chroma from Luma_ adjustment applied (effectively Y is subtr
 | ------- | ------------- | ----------- |
 | `x`       | `[-0.0154, 0.0281]`≈ | Cyan-red component           |
 | `y`       | `[0, 0.8453]`≈     | Luma           |
-| `b`       | `[ -0.2778, 0.3880 ]` ≈ | Blue-yellow component           |
+| `b`       | `[ -0.2778, 0.3880 ]`≈ | Blue-yellow component           |
+
+Does not have gamut limits.
+
+#### `itp`
+
+IC<sub>t</sub>C<sub>p</sub> (or ITP) color space, as defined in ITU-R Recommendation BT.2100.
+
+| Channel | Range             | Description           |
+|---------|-------------------|-----------------------|
+| `i`     | `[0, 0.581]`≈     | Intensity             |
+| `t`    | `[-0.282, 0.278]`≈ | Blue-yellow component |
+| `p`    | `[-0.162, 0.279]`≈ | Green–red component   |
+
+Serialized as `color(--ictcp i t p)`, with the `none` keyword for any missing color channel. An explicit `alpha < 1` is included as ` / alpha`.
 
 Does not have gamut limits.
 

docs/guides/tree-shaking.md

@@ -125,7 +125,7 @@ interpolate(['red', 'green'], 'lch');
 
 Bootstrap all the color spaces available in Culori.
 
-It provides the following named exports: `a98`, `cubehelix`, `dlab`, `dlch`, `hsi`, `hsl`, `hsv`, `hwb`, `jab`, `jch`, `lab`, `lab65`, `lch`, `lch65`, `lchuv`, `lrgb`, `luv`, `okhsl`, `okhsv`, `oklab`, `oklch`, `p3`, `prophoto`, `rec2020`, `rgb`, `xyb`, `xyz50`, `xyz65`, and `yiq`.
+It provides the following named exports: `a98`, `cubehelix`, `dlab`, `dlch`, `hsi`, `hsl`, `hsv`, `hwb`, `itp`, `jab`, `jch`, `lab`, `lab65`, `lch`, `lch65`, `lchuv`, `lrgb`, `luv`, `okhsl`, `okhsv`, `oklab`, `oklch`, `p3`, `prophoto`, `rec2020`, `rgb`, `xyb`, `xyz50`, `xyz65`, and `yiq`.
 
 ```js
 import 'culori/all';

src/bootstrap/all.js

@@ -7,6 +7,7 @@ import modeHsi from '../hsi/definition.js';
 import modeHsl from '../hsl/definition.js';
 import modeHsv from '../hsv/definition.js';
 import modeHwb from '../hwb/definition.js';
+import modeItp from '../itp/definition.js';
 import modeJab from '../jab/definition.js';
 import modeJch from '../jch/definition.js';
 import modeLab from '../lab/definition.js';
@@ -38,6 +39,7 @@ export const hsi = useMode(modeHsi);
 export const hsl = useMode(modeHsl);
 export const hsv = useMode(modeHsv);
 export const hwb = useMode(modeHwb);
+export const itp = useMode(modeItp);
 export const jab = useMode(modeJab);
 export const jch = useMode(modeJch);
 export const lab = useMode(modeLab);

src/index-fn.js

@@ -7,6 +7,7 @@ export { default as modeHsi } from './hsi/definition.js';
 export { default as modeHsl } from './hsl/definition.js';
 export { default as modeHsv } from './hsv/definition.js';
 export { default as modeHwb } from './hwb/definition.js';
+export { default as modeItp } from './itp/definition.js';
 export { default as modeJab } from './jab/definition.js';
 export { default as modeJch } from './jch/definition.js';
 export { default as modeLab } from './lab/definition.js';
@@ -171,6 +172,7 @@ export { default as convertHsiToRgb } from './hsi/convertHsiToRgb.js';
 export { default as convertHslToRgb } from './hsl/convertHslToRgb.js';
 export { default as convertHsvToRgb } from './hsv/convertHsvToRgb.js';
 export { default as convertHwbToRgb } from './hwb/convertHwbToRgb.js';
+export { default as convertItpToXyz65 } from './itp/convertItpToXyz65.js';
 export { default as convertJabToJch } from './jch/convertJabToJch.js';
 export { default as convertJabToRgb } from './jab/convertJabToRgb.js';
 export { default as convertJabToXyz65 } from './jab/convertJabToXyz65.js';
@@ -212,6 +214,7 @@ export { default as convertRgbToYiq } from './yiq/convertRgbToYiq.js';
 export { default as convertRgbToXyb } from './xyb/convertRgbToXyb.js';
 export { default as convertXybToRgb } from './xyb/convertXybToRgb.js';
 export { default as convertXyz65ToA98 } from './a98/convertXyz65ToA98.js';
+export { default as convertXyz65ToItp } from './itp/convertXyz65ToItp.js';
 export { default as convertXyz65ToJab } from './jab/convertXyz65ToJab.js';
 export { default as convertXyz65ToLab65 } from './lab65/convertXyz65ToLab65.js';
 export { default as convertXyz65ToP3 } from './p3/convertXyz65ToP3.js';

src/index.js

@@ -7,6 +7,7 @@ import modeHsi from './hsi/definition.js';
 import modeHsl from './hsl/definition.js';
 import modeHsv from './hsv/definition.js';
 import modeHwb from './hwb/definition.js';
+import modeItp from './itp/definition.js';
 import modeJab from './jab/definition.js';
 import modeJch from './jch/definition.js';
 import modeLab from './lab/definition.js';
@@ -172,6 +173,7 @@ export { default as convertHsiToRgb } from './hsi/convertHsiToRgb.js';
 export { default as convertHslToRgb } from './hsl/convertHslToRgb.js';
 export { default as convertHsvToRgb } from './hsv/convertHsvToRgb.js';
 export { default as convertHwbToRgb } from './hwb/convertHwbToRgb.js';
+export { default as convertItpToXyz65 } from './itp/convertItpToXyz65.js';
 export { default as convertJabToJch } from './jch/convertJabToJch.js';
 export { default as convertJabToRgb } from './jab/convertJabToRgb.js';
 export { default as convertJabToXyz65 } from './jab/convertJabToXyz65.js';
@@ -218,6 +220,7 @@ export { default as convertXyz50ToProphoto } from './prophoto/convertXyz50ToProp
 export { default as convertXyz50ToRgb } from './xyz50/convertXyz50ToRgb.js';
 export { default as convertXyz50ToXyz65 } from './xyz65/convertXyz50ToXyz65.js';
 export { default as convertXyz65ToA98 } from './a98/convertXyz65ToA98.js';
+export { default as convertXyz65ToItp } from './itp/convertXyz65ToItp.js';
 export { default as convertXyz65ToJab } from './jab/convertXyz65ToJab.js';
 export { default as convertXyz65ToLab65 } from './lab65/convertXyz65ToLab65.js';
 export { default as convertXyz65ToP3 } from './p3/convertXyz65ToP3.js';
@@ -235,6 +238,7 @@ export {
 	modeHsl,
 	modeHsv,
 	modeHwb,
+	modeItp,
 	modeJab,
 	modeJch,
 	modeLab,
@@ -266,6 +270,7 @@ export const hsi = useMode(modeHsi);
 export const hsl = useMode(modeHsl);
 export const hsv = useMode(modeHsv);
 export const hwb = useMode(modeHwb);
+export const itp = useMode(modeItp);
 export const jab = useMode(modeJab);
 export const jch = useMode(modeJch);
 export const lab = useMode(modeLab);

src/itp/constants.js

@@ -0,0 +1,16 @@
+// PQ Constants
+// https://en.wikipedia.org/wiki/High-dynamic-range_video#Perceptual_quantizer
+export const M1 = 2610 / 16384;
+export const M2 = 2523 / 32;
+export const IM1 = 16384 / 2610;
+export const IM2 = 32 / 2523;
+export const C1 = 3424 / 4096;
+export const C2 = 2413 / 128;
+export const C3 = 2392 / 128;
+
+// Maximum luminance in PQ is 10,000 cd/m^2
+// Relative XYZ has Y=1 for media white
+// BT.2048 says media white Y=203 at PQ 58
+//
+// This is confirmed here: https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.2408-3-2019-PDF-E.pdf
+export const YW = 203;

src/itp/convertItpToXyz65.js

@@ -0,0 +1,30 @@
+import { YW } from './constants.js';
+import { pq_st2084_eotf } from './utils.js';
+
+const convertItpToXyz65 = ({ i, t, p, alpha }) => {
+	const [l, m, s] = [
+		i + 0.008609037037932761 * t + 0.11102962500302593 * p,
+		i - 0.00860903703793275 * t - 0.11102962500302599 * p,
+		i + 0.5600313357106791 * t - 0.32062717498731885 * p
+	].map(pq_st2084_eotf);
+	const [x, y, z] = [
+		2.0701522183894223 * l -
+			1.3263473389671556 * m +
+			0.20665104762940512 * s,
+		0.36473852097480713 * l +
+			0.6805660249472276 * m -
+			0.04530454592203474 * s,
+		-0.04974720753581203 * l -
+			0.04926096669661379 * m +
+			1.1880659249923042 * s
+	].map(c => Math.max(c / YW, 0));
+
+	const res = { mode: 'xyz65', x, y, z };
+	if (alpha !== undefined) {
+		res.alpha = alpha;
+	}
+
+	return res;
+};
+
+export default convertItpToXyz65;

src/itp/convertXyz65ToItp.js

@@ -0,0 +1,30 @@
+import { YW } from './constants.js';
+import { pq_st2084_oetf } from './utils.js';
+
+const convertXyz65ToItp = ({ x, y, z, alpha }) => {
+	const [absX, absY, absZ] = [x, y, z].map(c => Math.max(c * YW, 0));
+	const [l, m, s] = [
+		0.3592832590121218 * absX +
+			0.6976051147779497 * absY -
+			0.0358915932320289 * absZ,
+		-0.1920808463704992 * absX +
+			1.1004767970374318 * absY +
+			0.07537486585191187 * absZ,
+		0.007079784460747716 * absX +
+			0.07483966621863658 * absY +
+			0.8433265453898765 * absZ
+	].map(pq_st2084_oetf);
+
+	const i = 0.5 * l + 0.5 * m;
+	const t = 1.61376953125 * l + -3.323486328125 * m + 1.709716796875 * s;
+	const p = 4.378173828125 * l + -4.24560546875 * m + -0.132568359375 * s;
+
+	const res = { mode: 'itp', i, t, p };
+	if (alpha !== undefined) {
+		res.alpha = alpha;
+	}
+
+	return res;
+};
+
+export default convertXyz65ToItp;

src/itp/definition.js

@@ -0,0 +1,44 @@
+import { interpolatorLinear } from '../interpolate/linear.js';
+import { fixupAlpha } from '../fixup/alpha.js';
+import convertItpToXyz65 from './convertItpToXyz65.js';
+import convertXyz65ToItp from './convertXyz65ToItp.js';
+import { convertRgbToXyz65, convertXyz65ToRgb } from '../index.js';
+
+/*
+  ICtCp (or ITP) color space, as defined in ITU-R Recommendation BT.2100.
+
+  ICtCp is drafted to be supported in CSS within
+  [CSS Color HDR Module Level 1](https://drafts.csswg.org/css-color-hdr/#ICtCp) spec.
+*/
+
+const definition = {
+	mode: 'itp',
+	channels: ['i', 't', 'p', 'alpha'],
+	parse: ['--ictcp'],
+	serialize: '--ictcp',
+
+	toMode: {
+		xyz65: convertItpToXyz65,
+		rgb: color => convertXyz65ToRgb(convertItpToXyz65(color))
+	},
+
+	fromMode: {
+		xyz65: convertXyz65ToItp,
+		rgb: color => convertXyz65ToItp(convertRgbToXyz65(color))
+	},
+
+	ranges: {
+		i: [0, 0.581],
+		t: [-0.369, 0.272],
+		p: [-0.164, 0.331]
+	},
+
+	interpolate: {
+		i: interpolatorLinear,
+		t: interpolatorLinear,
+		p: interpolatorLinear,
+		alpha: { use: interpolatorLinear, fixup: fixupAlpha }
+	}
+};
+
+export default definition;

src/itp/utils.js

@@ -0,0 +1,17 @@
+import { C1, C2, C3, IM1, IM2, M1, M2 } from './constants.js';
+
+function npow(base, exp) {
+	return Math.sign(base) * Math.pow(Math.abs(base), exp);
+}
+
+export function pq_st2084_oetf(c) {
+	const powC = npow(c / 10000, M1);
+	const r = (C1 + C2 * powC) / (1 + C3 * powC);
+	return npow(r, M2);
+}
+
+export function pq_st2084_eotf(c) {
+	const powC = npow(c, IM2);
+	const r = (powC - C1) / (C2 - C3 * powC);
+	return 10000 * npow(r, IM1);
+}

test/api.test.js

@@ -27,6 +27,7 @@ const API_FULL = [
 	'convertHslToRgb',
 	'convertHsvToRgb',
 	'convertHwbToRgb',
+	'convertItpToXyz65',
 	'convertJabToJch',
 	'convertJabToRgb',
 	'convertJabToXyz65',
@@ -73,6 +74,7 @@ const API_FULL = [
 	'convertXyz50ToRgb',
 	'convertXyz50ToXyz65',
 	'convertXyz65ToA98',
+	'convertXyz65ToItp',
 	'convertXyz65ToJab',
 	'convertXyz65ToLab65',
 	'convertXyz65ToP3',
@@ -125,6 +127,7 @@ const API_FULL = [
 	'hsl',
 	'hsv',
 	'hwb',
+	'itp',
 	'inGamut',
 	'interpolate',
 	'interpolateWith',
@@ -161,6 +164,7 @@ const API_FULL = [
 	'modeHsl',
 	'modeHsv',
 	'modeHwb',
+	'modeItp',
 	'modeJab',
 	'modeJch',
 	'modeLab',
@@ -253,6 +257,7 @@ const API_ALL = [
 	'hsl',
 	'hsv',
 	'hwb',
+	'itp',
 	'jab',
 	'jch',
 	'lab',
@@ -294,6 +299,7 @@ const API_FN = [
 	'convertHslToRgb',
 	'convertHsvToRgb',
 	'convertHwbToRgb',
+	'convertItpToXyz65',
 	'convertJabToJch',
 	'convertJabToRgb',
 	'convertJabToXyz65',
@@ -340,6 +346,7 @@ const API_FN = [
 	'convertXyz50ToRgb',
 	'convertXyz50ToXyz65',
 	'convertXyz65ToA98',
+	'convertXyz65ToItp',
 	'convertXyz65ToJab',
 	'convertXyz65ToLab65',
 	'convertXyz65ToP3',
@@ -412,6 +419,7 @@ const API_FN = [
 	'modeHsl',
 	'modeHsv',
 	'modeHwb',
+	'modeItp',
 	'modeJab',
 	'modeJch',
 	'modeLab',