Optimize lab plugin size, fix docs and types for delta method

README.md

@@ -712,18 +712,17 @@ colord("#e60000").isReadable("#ffff47", { level: "AAA", size: "large" }); // tru
 </details>
 
 <details>
-  <summary><b><code>.delta(color2 = "#FFF", options?)</code></b> (<b>lab</b> plugin)</summary>
+  <summary><b><code>.delta(color2 = "#FFF")</code></b> (<b>lab</b> plugin)</summary>
 
 Calculates the perceived color difference between two colors.
 The difference calculated according to [Delta E2000](https://en.wikipedia.org/wiki/Color_difference#CIEDE2000).
-
-Returns the normalized value in range from [0, 1], where 0 is the same color and 1 are completely different.
+The return value is `0` if the colors are equal, `1` if they are entirely different.
 
 ```js
-colord("#3296fa").delta("#197dc8") // 0.099
-colord("#faf0c8").delta("#fff") // 0.148
-colord("#afafaf").delta("#b4b4b4") // 0.014
-colord("#000").delta("#fff") // 1.0
+colord("#3296fa").delta("#197dc8"); // 0.099
+colord("#faf0c8").delta("#ffffff"); // 0.148
+colord("#afafaf").delta("#b4b4b4"); // 0.014
+colord("#000000").delta("#ffffff"); // 1
 ```
 
 </details>
@@ -842,11 +841,11 @@ colord("hwb(210 0% 60% / 50%)").toHex(); // "#00336680"
 </details>
 
 <details>
-  <summary><b><code>lab</code> (CIE LAB color space)</b> <i>1.5 KB</i></summary>
+  <summary><b><code>lab</code> (CIE LAB color space)</b> <i>1.4 KB</i></summary>
 
 Adds support of [CIE LAB](https://en.wikipedia.org/wiki/CIELAB_color_space) color model. The conversion logic is ported from [CSS Color Module Level 4 Specification](https://www.w3.org/TR/css-color-4/#color-conversion-code).
 
-Also plugin provides `.delta` method for perceived color difference calculations.
+Also plugin provides `.delta` method for [perceived color difference calculations](https://en.wikipedia.org/wiki/Color_difference#CIEDE2000).
 
 ```js
 import { colord, extend } from "colord";
@@ -857,8 +856,8 @@ extend([labPlugin]);
 colord({ l: 53.24, a: 80.09, b: 67.2 }).toHex(); // "#ff0000"
 colord("#ffffff").toLab(); // { l: 100, a: 0, b: 0, alpha: 1 }
 
-colord("#afafaf").delta("#b4b4b4") // 0.014
-colord("#000").delta("#fff") // 1.0
+colord("#afafaf").delta("#b4b4b4"); // 0.014
+colord("#000000").delta("#ffffff"); // 1
 ```
 
 </details>

src/constants.ts

@@ -13,13 +13,3 @@ export const ANGLE_UNITS: Record<string, number> = {
   turn: 360,
   rad: 360 / (Math.PI * 2),
 };
-
-/**
- * Radians to degrees multiplier.
- */
-export const rad2deg = 180 / Math.PI;
-
-/**
- * Degrees to radiants multiplier.
- */
-export const deg2rad = Math.PI / 180;

src/get/getPerceivedDifference.ts

@@ -1,4 +1,3 @@
-import { rad2deg, deg2rad } from "../constants";
 import { LabaColor } from "../types";
 
 /**
@@ -14,26 +13,22 @@ import { LabaColor } from "../types";
  *
  * | Delta E | Perception                             |
  * |---------|----------------------------------------|
- * | <= 1.0	 | Not perceptible by human eyes          |
- * | 1 - 2	 | Perceptible through close observation  |
- * | 2 - 10	 | Perceptible at a glance                |
+ * | <= 1.0  | Not perceptible by human eyes          |
+ * | 1 - 2   | Perceptible through close observation  |
+ * | 2 - 10  | Perceptible at a glance                |
  * | 11 - 49 | Colors are more similar than opposite  |
- * | 100	   | Colors are exact opposite              |
+ * | 100     | Colors are exact opposite              |
  *
  * [Source](http://www.brucelindbloom.com/index.html?Eqn_DeltaE_CIE2000.html)
  * [Read about Delta E](https://zschuessler.github.io/DeltaE/learn/#toc-delta-e-2000)
  */
 export function getDeltaE00(color1: LabaColor, color2: LabaColor): number {
-  /**
-   * kl - grafic arts = 1; textiles = 2;
-   * kl - unity factor;
-   * kh - weighting factor;
-   */
-  const [kl, kc, kh] = [1, 1, 1];
-
   const { l: l1, a: a1, b: b1 } = color1;
   const { l: l2, a: a2, b: b2 } = color2;
 
+  const rad2deg = 180 / Math.PI;
+  const deg2rad = Math.PI / 180;
+
   // dc -> delta c;
   // ml -> median l;
   const c1 = (a1 ** 2 + b1 ** 2) ** 0.5;
@@ -55,13 +50,8 @@ export function getDeltaE00(color1: LabaColor, color2: LabaColor): number {
   let h1 = a11 === 0 && b1 === 0 ? 0 : Math.atan2(b1, a11) * rad2deg;
   let h2 = a22 === 0 && b2 === 0 ? 0 : Math.atan2(b2, a22) * rad2deg;
 
-  if (h1 < 0) {
-    h1 += 360;
-  }
-
-  if (h2 < 0) {
-    h2 += 360;
-  }
+  if (h1 < 0) h1 += 360;
+  if (h2 < 0) h2 += 360;
 
   let dh = h2 - h1;
   const dhAbs = Math.abs(h2 - h1);
@@ -99,6 +89,10 @@ export function getDeltaE00(color1: LabaColor, color2: LabaColor): number {
   const Rc = 2 * (c7 / (c7 + 25 ** 7)) ** 0.5;
   const Rt = -Rc * Math.sin(deg2rad * 2 * dTheta);
 
+  const kl = 1; // 1 for graphic arts, 2 for textiles
+  const kc = 1; // unity factor
+  const kh = 1; // weighting factor
+
   return (
     ((dL / kl / sL) ** 2 +
       (dC / kc / sC) ** 2 +

src/plugins/lab.ts

@@ -8,15 +8,16 @@ declare module "../colord" {
   interface Colord {
     /**
      * Converts a color to CIELAB color space and returns an object.
-     * The object always includes `alpha` value [0—1].
+     * The object always includes `alpha` value [0, 1].
      */
     toLab(): LabaColor;
 
     /**
      * Calculates the perceived color difference for two colors according to
      * [Delta E2000](https://en.wikipedia.org/wiki/Color_difference#CIEDE2000).
+     * Returns a value in [0, 1] range.
      */
-    delta(color: AnyColor | Colord): number;
+    delta(color?: AnyColor | Colord): number;
   }
 }
 
@@ -29,7 +30,7 @@ const labPlugin: Plugin = (ColordClass, parsers): void => {
     return roundLaba(rgbaToLaba(this.rgba));
   };
 
-  ColordClass.prototype.delta = function (color) {
+  ColordClass.prototype.delta = function (color = "#FFF") {
     const compared = color instanceof ColordClass ? color : new ColordClass(color);
     const delta = getDeltaE00(this.toLab(), compared.toLab()) / 100;
     return clamp(round(delta, 3));