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原生Js Canvas去除視頻綠幕背景的方法實(shí)現(xiàn)

更新時(shí)間：2023年09月07日 15:02:20 作者：Raccom

本文主要介紹了原生Js Canvas去除視頻綠幕背景的方法實(shí)現(xiàn),文中通過(guò)示例代碼介紹的非常詳細(xì),對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值,需要的朋友們下面隨著小編來(lái)一起學(xué)習(xí)學(xué)習(xí)吧

原理

首先使用canvas的 drawImage 方法將video的當(dāng)前幀畫(huà)面繪制到canvas中

然后再通過(guò) getImageData 方法獲取當(dāng)前canvas的所有像素的 rgba 值組成的數(shù)組

獲取到的值為 [r,g,b,a,r,g,b,a,...] ，每一組 rgba 的值就是一個(gè)像素，所以獲取到的數(shù)組長(zhǎng)度是canvas的像素的數(shù)量 * 4

通過(guò)判斷每一組 rgb 的值是否為綠幕像素，然后設(shè)置其透明通道的 alpha 的值為0實(shí)現(xiàn)效果

代碼

因?yàn)閏anvas會(huì)受到跨域的影響導(dǎo)致畫(huà)布被污染，因此首先需要將測(cè)試視頻下載到本地

如果直接本地打開(kāi)html的話同樣會(huì)因?yàn)楸镜芈窂綀?bào)跨域錯(cuò)誤，需要將html，js，測(cè)試視頻放在文件夾中部署一個(gè)本地服務(wù)器

可以使用 http-server

npm i http-server -g
# 切換到存放html，js，測(cè)試視頻的文件夾 運(yùn)行命令即可部署本地服務(wù)器
http-server

或者

vsCode的 Live server 插件均可

<!DOCTYPE html>
<html lang="en">
  <head>
    <style>
        video{
            width: 480px;
            height: 270px;
        }
    </style>
  </head>
  <body>
    <video id="video"  src="./63e1dd7ddd2b0.mp4"  loop autoplay muted></video>
    <canvas id="output-canvas" width="480" height="270" willReadFrequently="true"></canvas>
    <script type="text/javascript" src="processor2.js"></script>
  </body>
</html>

// processor2.js
let video, canvas, ctx, canvas_tmp, ctx_tmp;
function init () {
    video = document.getElementById('video');
    canvas = document.getElementById('output-canvas');
    ctx = canvas.getContext('2d');
	// 創(chuàng)建的canvas寬高最好與顯示圖片的canvas、video寬高一致
    canvas_tmp = document.createElement('canvas');
    canvas_tmp.setAttribute('width', 480);
    canvas_tmp.setAttribute('height', 270);
    ctx_tmp = canvas_tmp.getContext('2d');
    video.addEventListener('play', computeFrame);
}
function computeFrame () {
    if (video) {
        if (video.paused || video.ended) return;
    }
    // 如果視頻比例和canvas比例不正確可能會(huì)出現(xiàn)顯示形變， 調(diào)整除的值進(jìn)行比例調(diào)整
    ctx_tmp.drawImage(video, 0, 0, video.clientWidth / 1, video.clientHeight / 1);
	// 獲取到繪制的canvas的所有像素rgba值組成的數(shù)組
    let frame = ctx_tmp.getImageData(0, 0, video.clientWidth, video.clientHeight);
	// 共有多少像素點(diǎn)
    const pointLens = frame.data.length / 4;
    for (let i = 0; i < pointLens; i++) {
        let r = frame.data[i * 4];
        let g = frame.data[i * 4 + 1];
        let b = frame.data[i * 4 + 2];
        // 判斷如果rgb值在這個(gè)范圍內(nèi)則是綠幕背景，設(shè)置alpha值為0 
        // 同理不同顏色的背景調(diào)整rgb的判斷范圍即可
        if (r < 100 && g > 120 && b < 200) {
            frame.data[i * 4 + 3] = 0;
        }
    }
    // 重新繪制到canvas中顯示
    ctx.putImageData(frame, 0, 0);
    // 遞歸調(diào)用
    setTimeout(computeFrame, 0);
}
document.addEventListener("DOMContentLoaded", () => {
    init();
});

使用本地服務(wù)器訪問(wèn)html即可看到效果，可以看到邊緣仍有綠色像素閃爍

一般情況這種就可以了，使用算法進(jìn)行處理的話效果會(huì)更好，但相應(yīng)的資源的消耗也會(huì)提升，造成幀率下降

下面展示通過(guò)一些算法進(jìn)行羽化和顏色過(guò)渡

羽化

// 返回canvas中第num個(gè)像素點(diǎn)所在的坐標(biāo)  12 -> [1, 12]
function numToPoint (num, width) {
    let col = num % width;
    let row = Math.floor(num / width);
    row = col === 0 ? row : row + 1;
    col = col === 0 ? width : col;
    return [row, col];
}
// 返回canvas中所在坐標(biāo)的num(index + 1)值  [1, 12] -> 12
function pointToNum (point, width) {
    let [row, col] = point;
    return (row - 1) * width + col
}
// 獲取輸入的坐標(biāo)周?chē)?像素內(nèi)的所有像素的坐標(biāo)組成的數(shù)組 [1, 1] -> [[1, 2], [2, 1], [2, 2]]
function getAroundPoint (point, width, height, area) {
    let [row, col] = point;
    let allAround = [];
    if (row > height || col > width || row < 0 || col < 0) return allAround;
    for (let i = 0; i < area; i++) {
        let pRow = row - 1 + i;
        for (let j = 0; j < area; j++) {
            let pCol = col - 1 + j;
            if (i === area % 2 && j === area % 2) continue;
            allAround.push([pRow, pCol]);
        }
    }
    return allAround.filter(([iRow, iCol]) => {
        return (iRow > 0 && iCol > 0) && (iRow <= height && iCol <= width);
    })
}

通過(guò)上面的函數(shù)獲取到一個(gè)選定的不透明的像素周?chē)南袼睾螅袛嘀車(chē)南袼氐腶lpha值

如果周?chē)南袼赜写嬖谕该鞯南袼?，則重新計(jì)算選定像素的alpha值

顏色過(guò)渡

計(jì)算修改alpha值連帶計(jì)算周?chē)袼刂衦gb的各項(xiàng)平均值給選定像素

最終處理結(jié)果如下

代碼

// 新增羽化和顏色過(guò)渡
// processor2.js
let video, canvas, ctx, canvas_tmp, ctx_tmp;
function init () {
    video = document.getElementById('video');
    canvas = document.getElementById('output-canvas');
    ctx = canvas.getContext('2d');
	// 創(chuàng)建的canvas寬高最好與顯示圖片的canvas、video寬高一致
    canvas_tmp = document.createElement('canvas');
    canvas_tmp.setAttribute('width', 480);
    canvas_tmp.setAttribute('height', 270);
    ctx_tmp = canvas_tmp.getContext('2d');
    video.addEventListener('play', computeFrame);
}
function numToPoint (num, width) {
    let col = num % width;
    let row = Math.floor(num / width);
    row = col === 0 ? row : row + 1;
    col = col === 0 ? width : col;
    return [row, col];
}
function pointToNum (point, width) {
    let [row, col] = point;
    return (row - 1) * width + col
}
function getAroundPoint (point, width, height, area) {
    let [row, col] = point;
    let allAround = [];
    if (row > height || col > width || row < 0 || col < 0) return allAround;
    for (let i = 0; i < area; i++) {
        let pRow = row - 1 + i;
        for (let j = 0; j < area; j++) {
            let pCol = col - 1 + j;
            if (i === area % 2 && j === area % 2) continue;
            allAround.push([pRow, pCol]);
        }
    }
    return allAround.filter(([iRow, iCol]) => {
        return (iRow > 0 && iCol > 0) && (iRow <= height && iCol <= width);
    })
}
function computeFrame () {
    if (video) {
        if (video.paused || video.ended) return;
    }
    ctx_tmp.drawImage(video, 0, 0, video.clientWidth, video.clientHeight);
    let frame = ctx_tmp.getImageData(0, 0, video.clientWidth, video.clientHeight);
    //----- emergence ----------
    const height = frame.height;
    const width = frame.width;
    const pointLens = frame.data.length / 4;
    for (let i = 0; i < pointLens; i++) {
        let r = frame.data[i * 4];
        let g = frame.data[i * 4 + 1];
        let b = frame.data[i * 4 + 2];
        if (r < 150 && g > 200 && b < 150) {
            frame.data[i * 4 + 3] = 0;
        }
    }
    const tempData = [...frame.data]
    for (let i = 0; i < pointLens; i++) {
        if (frame.data[i * 4 + 3] === 0) continue
        const currentPoint = numToPoint(i + 1, width);
        const arroundPoint = getAroundPoint(currentPoint, width, height, 3);
        let opNum = 0;
        let rSum = 0;
        let gSum = 0;
        let bSum = 0;
        arroundPoint.forEach((position) => {
            const index = pointToNum(position, width);
            rSum = rSum + tempData[(index - 1) * 4];
            gSum = gSum + tempData[(index - 1) * 4 + 1];
            bSum = bSum + tempData[(index - 1) * 4 + 2];
            if (tempData[(index - 1) * 4 + 3] !== 255) opNum++;
        })
        let alpha = (255 / arroundPoint.length) * (arroundPoint.length - opNum);
        if (alpha !== 255) {
            // debugger
            frame.data[i * 4] = parseInt(rSum / arroundPoint.length);
            frame.data[i * 4 + 1] = parseInt(gSum / arroundPoint.length);
            frame.data[i * 4 + 2] = parseInt(bSum / arroundPoint.length);
            frame.data[i * 4 + 3] = parseInt(alpha);
        }
    }
    //------------------------
    ctx.putImageData(frame, 0, 0);
    setTimeout(computeFrame, 0);
}
document.addEventListener("DOMContentLoaded", () => {
    init();
});

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