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Ensure Okhsl and Okhsv return undefined hues for achromatic colors #517

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merged 3 commits into from
May 29, 2024
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Ensure Okhsl and Okhsv return undefined hues for achromatic colors #517

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32a8324
Ensure Okhsl and Okhsv return undefined hues for achromatic colors
facelessuser May 16, 2024
79007c5
Provide variables for epsilon values
facelessuser May 22, 2024
ce85731
Update to use null and rework Okhsl saturation handling
facelessuser May 28, 2024
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9 changes: 4 additions & 5 deletions package-lock.json
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25 changes: 22 additions & 3 deletions src/spaces/okhsl.js
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Original file line number Diff line number Diff line change
Expand Up @@ -376,8 +376,8 @@ function okhslToOklab (hsl, lmsToRgb, okCoeff) {

let [h, s, l] = hsl;
let L = toeInv(l);
let a = 0.0;
let b = 0.0;
let a = null;
let b = null;
h = constrain(h) / 360.0;

if (L !== 0.0 && L !== 1.0 && s !== 0) {
Expand Down Expand Up @@ -423,6 +423,10 @@ function okhslToOklab (hsl, lmsToRgb, okCoeff) {
function oklabToOkhsl (lab, lmsToRgb, okCoeff) {
// Oklab to Okhsl.

// Epsilon for lightness should approach close to 32 bit lightness
// Epsilon for saturation just needs to be sufficiently close when denoting achromatic
let εL = 1e-7;
let εS = 1e-4;
let L = lab[0];
let s = 0.0;
let l = toe(L);
Expand Down Expand Up @@ -458,7 +462,22 @@ function oklabToOkhsl (lab, lmsToRgb, okCoeff) {
}
}

return [constrain(h * 360), s, l];
const achromatic = Math.abs(s) < εS;
if (achromatic || l === 0.0 || Math.abs(1 - l) < εL) {
h = null;
// Due to floating point imprecision near lightness of 1, we can end up
// with really high around white, this is to provide consistency as
// saturation can be really high for white due this imprecision.
if (!achromatic) {
s = 0.0;
}
}

else {
h = constrain(h * 360);
}

return [h, s, l];
}


Expand Down
16 changes: 13 additions & 3 deletions src/spaces/okhsv.js
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Original file line number Diff line number Diff line change
Expand Up @@ -47,8 +47,8 @@ function okhsvToOklab (hsv, lmsToRgb, okCoeff) {
h = constrain(h) / 360.0;

let l = toeInv(v);
let a = 0.0;
let b = 0.0;
let a = null;
let b = null;

// Avoid processing gray or colors with undefined hues
if (l !== 0.0 && s !== 0.0) {
Expand Down Expand Up @@ -95,6 +95,8 @@ function okhsvToOklab (hsv, lmsToRgb, okCoeff) {
function oklabToOkhsv (lab, lmsToRgb, okCoeff) {
// Oklab to Okhsv.

// Epsilon for saturation just needs to be sufficiently close when denoting achromatic
let ε = 1e-4;
let l = lab[0];
let s = 0.0;
let v = toe(l);
Expand Down Expand Up @@ -134,7 +136,15 @@ function oklabToOkhsv (lab, lmsToRgb, okCoeff) {
s = (s0 + tMax) * cv / ((tMax * s0) + tMax * k * cv);
}

return [constrain(h * 360), s, v];
if (Math.abs(s) < ε || v === 0.0) {
h = null;
}

else {
h = constrain(h * 360);
}

return [h, s, v];
}


Expand Down
8 changes: 4 additions & 4 deletions test/conversions.js
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Original file line number Diff line number Diff line change
Expand Up @@ -965,7 +965,7 @@ const tests = {
{
name: "sRGB white to Okhsl",
args: "white",
expect: [180, 0.6519721306444567, 1.0000000000000002],
expect: [ null, 0.0, 1.0000000000000002 ],
},
{
name: "sRGB red to Okhsl",
Expand Down Expand Up @@ -1000,7 +1000,7 @@ const tests = {
{
name: "sRGB black to Okhsl",
args: "black",
expect: [0.0, 0.0, 0.0],
expect: [ null, 0.0, 0.0 ],
},
],
},
Expand All @@ -1013,7 +1013,7 @@ const tests = {
{
name: "sRGB white to Okhsv",
args: "white",
expect: [ 180, 1.3189507366749435e-15, 1.0000000000000007 ],
expect: [ null, 1.3189507366749435e-15, 1.0000000000000007 ],
},
{
name: "sRGB red to Okhsv",
Expand Down Expand Up @@ -1048,7 +1048,7 @@ const tests = {
{
name: "sRGB black to Okhsv",
args: "black",
expect: [0.0, 0.0, 0.0],
expect: [ null, 0.0, 0.0],
},
],
},
Expand Down
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