From 68439672bcb541663cef3bdb57260df78f6a349f Mon Sep 17 00:00:00 2001 From: Dan Burzo Date: Mon, 20 Nov 2023 21:49:54 +0200 Subject: [PATCH] Add rgb gamut parameter to clampChroma(), shorter jnd bypass for toGamut(), fixes #212, #213 --- docs/api.md | 13 +++++++++++-- src/clamp.js | 35 ++++++++++++++++++++++------------- test/clamp.test.js | 19 ++++++++++++++++++- 3 files changed, 51 insertions(+), 16 deletions(-) diff --git a/docs/api.md b/docs/api.md index 92290334..56eec372 100644 --- a/docs/api.md +++ b/docs/api.md @@ -359,7 +359,7 @@ formatCss(toRgb(crimson)); ☞ [src/clamp.js]({{codebase}}/src/clamp.js) -# **clampChroma**(_color_ or _string_, _mode = 'lch'_) → _color_ +# **clampChroma**(_color_ or _string_, _mode = 'lch'_, _rgbGamut = 'rgb'_) → _color_ ☞ [src/clamp.js]({{codebase}}/src/clamp.js) @@ -374,6 +374,8 @@ clampChroma('lab(50% 100 100)'); By default, the color is converted to `lch` to perform the clamping, but any color space that contains a Chroma dimension can be used by sending an explicit `mode` argument. +Likewise, the destination RGB gamut can be overriden with the corresponding parameter. + ```js import { clampChroma } from 'culori'; @@ -414,10 +416,17 @@ toP3(color); // ⇒ { mode: "p3", r: 0.999…, g: 0.696…, b: 0.508… } ``` -To address the shortcomings of `clampChroma`, which can sometimes produce colors more desaturated than necessary, the test used in the binary search is replaced with "is color is roughly in gamut", by comparing the candidate to the clipped version (obtained with `clampGamut`). The test passes if the colors are not to dissimilar, judged by the `delta` color difference function and an associated `jnd` just-noticeable difference value. +To address the shortcomings of `clampChroma`, which can sometimes produce colors more desaturated than necessary, the test used in the binary search is replaced with “is color is roughly in gamut”, by comparing the candidate to the clipped version (obtained with `clampGamut`). The test passes if the colors are not to dissimilar, judged by the `delta` color difference function and an associated `jnd` just-noticeable difference value. The default arguments for this function correspond to [the gamut mapping algorithm](https://drafts.csswg.org/css-color/#css-gamut-mapping) defined in the CSS Color Module Level 4 spec, but the algorithm itself is slightly different. +The “roughly in gamut” aspect of the algorithm can be disabled by passing `null` for the `delta` color difference function: + +```js +import { toGamut } from 'culori'; +const clampToP3 = toGamut('p3', 'oklch', null); +``` + ## Interpolation In any color space, colors occupy positions given by their values for each channel. Interpolating colors means tracing a line through the coordinates of these colors, and figuring out what colors reside on the line at various positions. diff --git a/src/clamp.js b/src/clamp.js index e351a68f..ade4c619 100644 --- a/src/clamp.js +++ b/src/clamp.js @@ -17,6 +17,8 @@ const fixup_rgb = c => { return res; }; +const to_displayable_srgb = c => fixup_rgb(rgb(c)); + const inrange_rgb = c => { return ( c !== undefined && @@ -66,7 +68,7 @@ export function clampRgb(color) { // keep track of color's original mode let conv = converter(color.mode); - return conv(fixup_rgb(rgb(color))); + return conv(to_displayable_srgb(color)); } /* @@ -106,21 +108,25 @@ export function clampGamut(mode = 'rgb') { } /* - Obtain a color that's in the sRGB gamut - by first converting it to `mode` and then - finding the the greatest chroma value - that fits the gamut. + Obtain a color that’s in a RGB gamut (by default sRGB) + by first converting it to `mode` and then finding + the greatest chroma value that fits the gamut. By default, the CIELCh color space is used, but any color that has a chroma component will do. The result is returned in the color's original color space. */ -export function clampChroma(color, mode = 'lch') { +export function clampChroma(color, mode = 'lch', rgbGamut = 'rgb') { color = prepare(color); + let inDestinationGamut = + rgbGamut === 'rgb' ? displayable : inGamut(rgbGamut); + let clipToGamut = + rgbGamut === 'rgb' ? to_displayable_srgb : clampGamut(rgbGamut); + // if the color is undefined or displayable, return it directly - if (color === undefined || displayable(color)) return color; + if (color === undefined || inDestinationGamut(color)) return color; // keep track of color's original mode let conv = converter(color.mode); @@ -133,8 +139,8 @@ export function clampChroma(color, mode = 'lch') { // if not even chroma = 0 is displayable // fall back to RGB clamping - if (!displayable(clamped)) { - return conv(fixup_rgb(rgb(clamped))); + if (!inDestinationGamut(clamped)) { + return conv(clipToGamut(clamped)); } // By this time we know chroma = 0 is displayable and our current chroma is not. @@ -147,7 +153,7 @@ export function clampChroma(color, mode = 'lch') { while (end - start > resolution) { clamped.c = start + (end - start) * 0.5; - if (displayable(clamped)) { + if (inDestinationGamut(clamped)) { _last_good_c = clamped.c; start = clamped.c; } else { @@ -156,7 +162,7 @@ export function clampChroma(color, mode = 'lch') { } return conv( - displayable(clamped) ? clamped : { ...clamped, c: _last_good_c } + inDestinationGamut(clamped) ? clamped : { ...clamped, c: _last_good_c } ); } @@ -173,13 +179,16 @@ export function clampChroma(color, mode = 'lch') { the test used in the binary search is replaced with "is color is roughly in gamut", by comparing the candidate to the clipped version (obtained with `clampGamut`). - The test passes if the colors are not to dissimilar, + The test passes if the colors are not too dissimilar, judged by the `delta` color difference function and an associated `jnd` just-noticeable difference value. The default arguments for this function correspond to the gamut mapping algorithm defined in CSS Color Level 4: https://drafts.csswg.org/css-color/#css-gamut-mapping + + To disable the “roughly in gamut” part, pass either + `null` for the `delta` parameter, or zero for `jnd`. */ export function toGamut( dest = 'rgb', @@ -234,7 +243,7 @@ export function toGamut( clipped = clipToGamut(candidate); if ( inDestinationGamut(candidate) || - (jnd > 0 && delta(candidate, clipped) <= jnd) + (delta && jnd > 0 && delta(candidate, clipped) <= jnd) ) { start = candidate.c; } else { diff --git a/test/clamp.test.js b/test/clamp.test.js index 9c0fec6a..36a209ca 100644 --- a/test/clamp.test.js +++ b/test/clamp.test.js @@ -5,7 +5,8 @@ import { inGamut, clampGamut, formatCss, - toGamut + toGamut, + lch } from '../src/index.js'; tape('RGB', function (test) { @@ -67,6 +68,12 @@ tape('Issue #129', function (test) { clampChroma({ mode: 'oklch', l: 0.5, c: 0.16, h: 180 }, 'oklch'), { mode: 'oklch', l: 0.5, c: 0.090703125, h: 180 } ); + + test.equal( + formatCss(clampChroma('lch(80% 150 60)', 'lch', 'p3')), + 'lch(80 60.040283203125 60)', + 'with p3 gamut' + ); test.end(); }); @@ -157,5 +164,15 @@ tape('toGamut()', t => { 'color(display-p3 0.9999999999999994 0.6969234154991887 0.5084794582132421)', 'api docs example' ); + + const likeClampChroma = toGamut('rgb', 'lch', null); + + t.deepEqual(lch(likeClampChroma('lch(50% 120 5)')), { + mode: 'lch', + l: 50.00519612994975, + c: 77.47625128342412, + h: 5.006331789592595 + }); + t.end(); });