index.js

const path = require('path');
const fs = require('fs');
const { createCanvas, loadImage } = require('canvas');

function filterImageData(data) {
    let res = new Array(8 * 8 * 8 * 8).fill(0);
    let device = val => {
        let mapVal = 0;
        if (val > 223) {
            // [224 ~ 255]
            mapVal = 7;
        } else if (val > 191) {
            // [192 ~ 223]
            mapVal = 6;
        } else if (val > 159) {
            // [160 ~ 191]
            mapVal = 5;
        } else if (val > 127) {
            // [128 ~ 159]
            mapVal = 4;
        } else if (val > 95) {
            // [96 ~ 127]
            mapVal = 3;
        } else if (val > 63) {
            // [64 ~ 95]
            mapVal = 2;
        } else if (val > 31) {
            // [32 ~ 63]
            mapVal = 1;
        } else {
            // [0 ~ 31]
            mapVal = 0;
        }
        return mapVal;
    };
    for (let index = 0; index < data.length; index += 4) {
        let key =
            device(data[index]) * 8 * 8 * 8 +
            device(data[index + 1]) * 8 * 8 +
            device(data[index + 2]) * 8 +
            device(data[index + 3]);

        res[key] += 1;
    }
    return res;
}
// 余玄相似度
function vectorCosine(p1, p2) {
    if (p1.length != p2.length) return false;

    let fenzi = 0,
        sqrt1 = 0,
        sqrt2 = 0;
    for (let i = 0; i < p1.length; i++) {
        fenzi += p1[i] * p2[i];
        sqrt1 += p1[i] * p1[i];
        sqrt2 += Math.pow(p2[i], 2);
    }

    let res = fenzi / (Math.sqrt(sqrt1) * Math.sqrt(sqrt2));
    return res;
}

module.exports = function(image1, image2) {
    let img1Path = path.isAbsolute(image1) ? image1 : path.resolve(process.cwd(), image1);
    let img2Path = path.isAbsolute(image2) ? image2 : path.resolve(process.cwd(), image2);

    if (!fs.existsSync(img1Path) || !fs.existsSync(img2Path)) {
        return Promise.reject('输入的图片不存在');
    }

    return Promise.all(
        [img1Path, img2Path].map(src => {
            return loadImage(src).then(image => {
                const canvas = createCanvas(image.width, image.height);
                const ctx = canvas.getContext('2d');
                ctx.drawImage(image, 0, 0, image.width, image.height);
                let imageData = ctx.getImageData(0, 0, image.width, image.height);
                return filterImageData(imageData.data);
            });
        })
    ).then(res => {
        return vectorCosine(res[0], res[1]);
    });
};