html5利用canvas实现颜色容差抠图功能

let canvas = document.querySelector('#canvas');
let context = canvas.getContext('2d');
let img = document.createElement('img');
img.src = './head2.png';
img.onload = function () {
    canvas.height = img.height;
    canvas.width = img.width;
    context.drawImage(img, 0, 0);
    cutout(canvas, [255, 255, 255], 0.2); // 对白色进行抠除，容差为0.2
}
function cutout(canvas, color, range = 0) {
    let context = canvas.getContext('2d');
    let imageInfo = context.getImageData(0, 0, canvas.width, canvas.height);
    // pixiArr是一个数组，每四个数组元素代表一个像素点，这四个数组元素分别对应一个像素的r，g，b，a值。
    let pixiArr = imageInfo.data;
    for (let i = 0; i < pixiArr.length; i += 4) {
    // 匹配到目标像素就将目标像素的alpha设为0
        if (testColor([pixiArr[i], pixiArr[i + 1], pixiArr[i + 2]], color, range)) pixiArr[i + 3] = 0;
    }
    context.putImageData(imageInfo, 0, 0);
}
function testColor(current, target, range) {
    for (let i = 0; i < 3; i++) {
        if (!((1 - range) * target[i] <= current[i] && (1 + range) * target[i] >= current[i])) return false;
    }
    return true;
}

function cutout(canvas, color, range = 0) {
    let context = canvas.getContext('2d');
    let imageInfo = context.getImageData(0, 0, canvas.width, canvas.height);
    let pixiArr = imageInfo.data;
    for (let row = 0; row < canvas.height; row++) {
        let left = row * 4 * canvas.width; // 指向行首像素
        let right = left + 4 * canvas.width - 1 - 3; // 指向行尾像素
        let leftF = false; // 左指针是否碰到边界的标识
        let rightF = false; // 右指针是否碰到边界的标识
        while (!leftF || !rightF) { // 当左右指针都为true，即都碰到边界时结束
            if (!leftF) {
                if (testColor([pixiArr[left], pixiArr[left + 1], pixiArr[left + 2]], color, range)) {
                    pixiArr[left + 3] = 0; // 此像素的alpha设为0
                    left += 4; // 移到下一个像素
                } else leftF = true; // 碰到边界
            }
            if (!rightF) {
                if (testColor([pixiArr[right], pixiArr[right + 1], pixiArr[right + 2]], color, range)) {
                    pixiArr[right + 3] = 0;
                    right -= 4;
                } else rightF = true;
            }
            if (left == right) { // 左右指针重合
                leftF = true;
                rightF = true;
            };
        }
    }
    context.putImageData(imageInfo, 0, 0);
}

function cutout(canvas, color, range = 0) {
    let context = canvas.getContext('2d');
    let imageInfo = context.getImageData(0, 0, canvas.width, canvas.height);
    let pixiArr = imageInfo.data;
    for (let row = 0; row < canvas.height; row++) {
        let left = row * 4 * canvas.width;
        let right = left + 4 * canvas.width - 1 - 3;
        let leftF = false;
        let rightF = false;
        while (!leftF || !rightF) {
            if (!leftF) {
                if (testColor([pixiArr[left], pixiArr[left + 1], pixiArr[left + 2]], color, range)) {
                    pixiArr[left + 3] = 0;
                    left += 4;
                } else leftF = true;
            }
            if (!rightF) {
                if (testColor([pixiArr[right], pixiArr[right + 1], pixiArr[right + 2]], color, range)) {
                    pixiArr[right + 3] = 0;
                    right -= 4;
                } else rightF = true;
            }
            if (left == right) {
                leftF = true;
                rightF = true;
            };
        }
    }
    // 同理进行列扫描
    for (let col = 0; col < canvas.width; col++) {
        let top = col * 4; // 指向列头
        let bottom = top + (canvas.height - 2) * canvas.width * 4 + canvas.width * 4; // 指向列尾
        let topF = false;
        let bottomF = false;
        while (!topF || !bottomF) {
            if (!topF) {
                if (testColor([pixiArr[top], pixiArr[top + 1], pixiArr[top + 2]], color, range)) {
                    pixiArr[top + 3] = 0;
                    top += canvas.width * 4;
                } else topF = true;
            }
            if (!bottomF) {
                if (testColor([pixiArr[bottom], pixiArr[bottom + 1], pixiArr[bottom + 2]], color, range)) {
                    pixiArr[bottom + 3] = 0;
                    bottom -= canvas.width * 4;
                } else bottomF = true;
            }

            if (top == bottom) {
                topF = true;
                bottomF = true;
            };
        }
    }

    context.putImageData(imageInfo, 0, 0);
}

[
    [{r: 255, g: 255, b: 255, a: 1}, {r: 255, g: 255, b: 255, a: 1}, {r: 255, g: 255, b: 255, a: 1}],
    [{r: 255, g: 255, b: 255, a: 1}, {r: 255, g: 255, b: 255, a: 1}, {r: 255, g: 255, b: 255, a: 1}]
    [{r: 255, g: 255, b: 255, a: 1}, {r: 255, g: 255, b: 255, a: 1}, {r: 255, g: 255, b: 255, a: 1}]
]