imghash/index.js

Image perceptual hash calculation for node

"use strict";

const fs = require("fs");
const blockhash = require("blockhash-core");
const { imageFromBuffer, getImageData } = require("@canvas/image");
const imageType = require("image-type");
const jpeg = require("jpeg-js");

function hash(filepath, bits, format) {
  format = format || "hex";
  if (format !== "hex" && format !== "binary")
    throw new Error("Unsupported format");

  bits = bits || 8;
  if (bits % 4 !== 0) throw new Error("Invalid bitlength");

  return new Promise((resolve, reject) => {
    if (Buffer.isBuffer(filepath)) {
      return resolve(filepath);
    }

    fs.readFile(filepath, (err, content) => {
      if (err) return reject(err);
      resolve(content);
    });
  })
    .then((fdata) => {
      return imageFromBuffer(fdata)
        .then((image) => {
          return getImageData(image);
        })
        .catch((err) => {
          const ftype = imageType(fdata);
          if (ftype.mime === "image/jpeg") {
            return jpeg.decode(fdata, { maxMemoryUsageInMB: 1024 });
          } else {
            throw err;
          }
        });
    })
    .then((data) => hashRaw(data, bits))
    .then((hexHash) => {
      if (format === "hex") return hexHash;
      if (format === "binary") return hexToBinary(hexHash);
    });
}

function hashRaw(data, bits) {
  return blockhash.bmvbhash(data, bits);
}

function hexToBinary(s) {
  const lookup = {
    0: "0000",
    1: "0001",
    2: "0010",
    3: "0011",
    4: "0100",
    5: "0101",
    6: "0110",
    7: "0111",
    8: "1000",
    9: "1001",
    a: "1010",
    b: "1011",
    c: "1100",
    d: "1101",
    e: "1110",
    f: "1111",
    A: "1010",
    B: "1011",
    C: "1100",
    D: "1101",
    E: "1110",
    F: "1111",
  };
  let ret = "";
  for (let i = 0; i < s.length; i++) {
    ret += lookup[s[i]];
  }
  return ret;
}

function binaryToHex(s) {
  const lookup = {
    "0000": "0",
    "0001": "1",
    "0010": "2",
    "0011": "3",
    "0100": "4",
    "0101": "5",
    "0110": "6",
    "0111": "7",
    1000: "8",
    1001: "9",
    1010: "a",
    1011: "b",
    1100: "c",
    1101: "d",
    1110: "e",
    1111: "f",
  };
  let ret = "";
  for (let i = 0; i < s.length; i += 4) {
    let chunk = s.slice(i, i + 4);
    ret += lookup[chunk];
  }
  return ret;
}

module.exports = {
  hash,
  hashRaw,
  hexToBinary,
  binaryToHex,
};