feat(image): add extractColors (#33)

## Summary

<!-- Please summarize your changes. -->

<!-- Please link to any applicable information (forum posts, bug
reports, etc.). -->

a new feature in `@fepack/image` which allows users to extract a palette
of colors from a given image URL. The extraction can be customized based
on user-defined parameters such as the number of colors to extract and
the quality of extraction.


![code](https://github.com/fepack/image/assets/77133565/0038c307-971d-417b-8f1e-df54b4957a83)

<img width="789" alt="스크린샷 2023-09-22 오전 12 56 18"
src="https://github.com/fepack/image/assets/77133565/24d2fa38-1749-4b51-8f4e-0b1ca36a204b">



## Checks

<!-- For completed items, change [ ] to [x]. -->

<!-- If you leave this checklist empty, your PR will very likely be
closed. -->

Please check the following:

- [x] I have written documents and tests, if needed.

---------

Co-authored-by: Jonghyeon Ko <[email protected]>

.changeset/fuzzy-impalas-applaud.md

@@ -0,0 +1,5 @@
+---
+"@fepack/image": minor
+---
+
+feat: add add extractRGBAs

configs/eslint-config-js/noimport.js

@@ -18,4 +18,8 @@ module.exports = {
       extends: ["plugin:vitest/recommended"],
     },
   ],
+  rules: {
+    "arrow-body-style": ["warn", "as-needed"],
+    "newline-before-return": "warn",
+  },
 };

packages/image/src/extractRGBAs.spec.ts

@@ -0,0 +1,28 @@
+import { describe, expect, it } from "vitest";
+import { extractRGBAs } from ".";
+
+const load = (src: HTMLImageElement["src"]) =>
+  new Promise<HTMLImageElement>((resolve, reject) => {
+    const image = new Image();
+    image.onload = () => resolve(image);
+    image.onerror = () => reject();
+    image.src = src;
+  });
+
+describe("extractRGBAs", () => {
+  it("should return an array of colors", async () => {
+    const image = await load("src/images/test.png");
+    const result = extractRGBAs(image, { quality: 10 });
+    expect(result.length).toBeGreaterThan(0);
+  });
+
+  it("should throw an error if quality is out of range", async () => {
+    const image = await load("src/images/test.png");
+    expect(() => extractRGBAs(image, { quality: 101 })).toThrow(
+      "options.quality should be between 1 and 100",
+    );
+    expect(() => extractRGBAs(image, { quality: 0 })).toThrow(
+      "options.quality should be between 1 and 100",
+    );
+  });
+});

packages/image/src/extractRGBAs.ts

@@ -0,0 +1,61 @@
+type RGBA = readonly [number, number, number, number];
+type ExtractRGBAsOptions = { quality: number };
+const initialOptions: ExtractRGBAsOptions = { quality: 100 };
+/**
+ * Filters and extracts relevant pixels from image data based on quality setting.
+ */
+export const extractRGBAs = (
+  /**
+   * The image pixel data.
+   */
+  image: HTMLImageElement,
+  /**
+   * Quality setting for filtering pixels. Higher values mean more pixels are processed. Range: [1, 100]
+   */
+  options = initialOptions,
+) => {
+  if (options.quality < 1 || options.quality > 100) {
+    throw new Error("options.quality should be between 1 and 100");
+  }
+  const uint8ClampedArray = extractUint8ClampedArray(image);
+  const step = Math.ceil(100 / options.quality);
+
+  return Array.from({
+    length: Math.ceil(uint8ClampedArray.length / (4 * step)),
+  }).map((_, index) => {
+    const rIndex = index * 4 * step;
+
+    return [
+      uint8ClampedArray[rIndex],
+      uint8ClampedArray[rIndex + 1],
+      uint8ClampedArray[rIndex + 2],
+      uint8ClampedArray[rIndex + 3],
+    ] as RGBA;
+  });
+};
+
+/**
+ * Extracts pixel data from an image.
+ */
+const extractUint8ClampedArray = (
+  /**
+   * The image element
+   */
+  image: HTMLImageElement,
+) => {
+  const canvas = document.createElement("canvas");
+  const canvasRenderingContext2D = canvas.getContext("2d");
+  if (!canvasRenderingContext2D) {
+    throw new Error("canvasRenderingContext2D is not supported");
+  }
+  canvas.width = image.naturalWidth;
+  canvas.height = image.naturalHeight;
+  canvasRenderingContext2D.drawImage(image, 0, 0);
+
+  return canvasRenderingContext2D.getImageData(
+    0,
+    0,
+    canvas.width,
+    canvas.height,
+  ).data;
+};

packages/image/src/index.ts

@@ -1,3 +1,4 @@
 export { checkWebPSupport } from "./checkWebPSupport";
 export { detect } from "./detect";
+export { extractRGBAs } from "./extractRGBAs";
 export { load, type ImageSource } from "./load";