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[deltaE] Speedup of 7th powers in DeltaE2000 #340

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Nov 14, 2023
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[deltaE] Speedup of 7th powers in DeltaE2000 #340

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13 changes: 11 additions & 2 deletions src/deltaE/deltaE2000.js
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,15 @@ const π = Math.PI;
const r2d = 180 / π;
const d2r = π / 180;

function pow7 (x) {
// Faster than x ** 7 or Math.pow(x, 7)

const x2 = x * x;
const x7 = x2 * x2 * x2 * x;

return x7;
}

export default function (color, sample, {kL = 1, kC = 1, kH = 1} = {}) {
// Given this color as the reference
// and the function parameter as the sample,
Expand Down Expand Up @@ -46,7 +55,7 @@ export default function (color, sample, {kL = 1, kC = 1, kH = 1} = {}) {

// calculate a-axis asymmetry factor from mean Chroma
// this turns JND ellipses for near-neutral colors back into circles
let C7 = Cbar ** 7;
let C7 = pow7(Cbar);

let G = 0.5 * (1 - Math.sqrt(C7/(C7 + Gfactor)));

Expand Down Expand Up @@ -107,7 +116,7 @@ export default function (color, sample, {kL = 1, kC = 1, kH = 1} = {}) {
// calculate mean Lightness and Chroma
let Ldash = (L1 + L2)/2;
let Cdash = (Cdash1 + Cdash2)/2;
let Cdash7 = Math.pow(Cdash, 7);
let Cdash7 = pow7(Cdash);

// Compensate for non-linearity in the blue region of Lab.
// Four possibilities for hue weighting factor,
Expand Down