node_modules/@jimp/plugin-hash/src/index.ts

import { JimpClass } from "@jimp/types";
import anyBase from "any-base";

import ImagePHash from "./phash.js";

// an array storing the maximum string length of hashes at various bases
// 0 and 1 do not exist as possible hash lengths
// prettier-ignore
const alphabet =
  "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$_";

// an array storing the maximum string length of hashes at various bases
// 0 and 1 do not exist as possible hash lengths
const maxHashLength = [NaN, NaN];

for (let i = 2; i < 65; i++) {
  const maxHash = anyBase(
    anyBase.BIN,
    alphabet.slice(0, i),
  )(new Array(64 + 1).join("1"));
  maxHashLength.push(maxHash.length);
}

export const methods = {
  /**
   * Calculates the perceptual hash
   * @returns the perceptual hash
   * @example
   * ```ts
   * import { Jimp } from "jimp";
   *
   * const image = await Jimp.read("test/image.png");
   *
   * image.hash();
   * ```
   */
  pHash<I extends JimpClass>(image: I) {
    const pHash = new ImagePHash();
    return pHash.getHash(image);
  },

  /**
   * Generates a perceptual hash of the image <https://en.wikipedia.org/wiki/Perceptual_hashing>. And pads the string. Can configure base.
   * @param base A number between 2 and 64 representing the base for the hash (e.g. 2 is binary, 10 is decimal, 16 is hex, 64 is base 64). Defaults to 64.
   * @example
   * ```ts
   * import { Jimp } from "jimp";
   *
   * const image = await Jimp.read("test/image.png");
   *
   * image.hash(2); // binary
   * image.hash(64); // base 64
   * ```
   */
  hash<I extends JimpClass>(image: I, base = 64) {
    if (base < 2 || base > 64) {
      throw new Error("base must be a number between 2 and 64");
    }

    const subAlphabet = alphabet.slice(0, base);
    const pHash = this.pHash(image);
    const maxLength = maxHashLength[base]!;

    return anyBase(anyBase.BIN, subAlphabet)(pHash).padStart(maxLength, "0");
  },

  /**
   * Calculates the hamming distance of the current image and a hash based on their perceptual hash
   * @param compareHash hash to compare to
   * @returns  a number ranging from 0 to 1, 0 means they are believed to be identical
   * @example
   * ```ts
   * import { Jimp } from "jimp";
   *
   * const image = await Jimp.read("test/image.png");
   *
   * image.distanceFromHash(image.pHash());
   * ```
   */
  distanceFromHash<I extends JimpClass>(image: I, compareHash: string) {
    const pHash = new ImagePHash();
    const currentHash = pHash.getHash(image);

    return pHash.distance(currentHash, compareHash);
  },
};

/**
 * Calculates the hamming distance of two images based on their perceptual hash
 * @param img1 A Jimp image to compare
 * @param img2 A Jimp image to compare
 * @returns A number ranging from 0 to 1, 0 means they are believed to be identical
 * @example
 * ```ts
 * import { Jimp, distance } from "jimp";
 *
 * const image1 = await Jimp.read("test/image.png");
 * const image2 = await Jimp.read("test/image.png");
 *
 * distance(image1, image2); // 0.5
 * ```
 */
export function distance<I extends JimpClass>(img1: I, img2: I) {
  const phash = new ImagePHash();
  const hash1 = phash.getHash(img1);
  const hash2 = phash.getHash(img2);

  return phash.distance(hash1, hash2);
}

/**
 * Calculates the hamming distance of two images based on their perceptual hash
 * @param hash1 A pHash
 * @param hash2 A pHash
 * @returns A number ranging from 0 to 1, 0 means they are believed to be identical
 * @example
 * ```ts
 * import { Jimp, compareHashes } from "jimp";
 *
 * const image1 = await Jimp.read("test/image.png");
 * const image2 = await Jimp.read("test/image.png");
 *
 * compareHashes(image1.pHash(), image2.pHash()); // 0.5
 * ```
 */
export function compareHashes(hash1: string, hash2: string) {
  const phash = new ImagePHash();
  return phash.distance(hash1, hash2);
}