本文介绍了canvas像素点操作之视频绿幕抠图，分享给大家，具体如下：

用法：

context.putImageData(imgData, x, y, dX, dY, dWidth, dHeight);

下面的栗子简单实现了几个简单的滤镜效果，具体算法参考的这里，学过《数字图像处理》的同学应该对此理解更深刻。

demo

该栗子纯属为了演示功能而做，如果只强调效果而不在乎数据的话，用CSS3的filter属性便能高效又轻松地搞定。

部分代码

import imgUrl from ./component/sample.jpg;export default {data () {return {imgUrl: imgUrl}},methods: {onOperate1 () {this.ctx.putImageData(this.onCompute1(), 0, 0);},onOperate2 () {this.ctx.putImageData(this.onCompute2(), 0, 0);},...onCancel () {this.reload();},onCompute1 () {let data = this.frameData.data;        for (let i = 0; i < this.imgDataLength; i += 4) {          let r = data[i + 0],          g = data[i + 1],          b = data[i + 2];                    data[i + 0] = 255 - r;          data[i + 1] = 255 - g;          data[i + 2] = 255 - b;        }        return this.frameData;},onCompute2 () {let data = this.frameData.data;        for (let i = 0; i < this.imgDataLength; i += 4) {          data[i] = Math.abs(data[i + 1] - data[i + 2] + data[i + 1] + data[i]) * data[i] / 256;              data[i + 1] = Math.abs(data[i + 2] - data[i + 1] + data[i + 2] + data[i]) * data[i] / 256;              data[i + 2] = Math.abs(data[i + 2] - data[i + 1] + data[i + 2] + data[i]) * data[i + 1] / 256;        }        return this.frameData;},...},mounted () {        this.canvas = this.$refs[canvas];        this.ctx = this.canvas.getContext(2d);        this.reload();}}

上周跟同学去了一趟溧阳天目湖的南山竹海，在景区被忽悠拍了一张照片，就是这张 ——

然后被朋友圈吐槽抠图。其实当时就是站在一块绿幕前拍的:joy: 。

PS中魔法棒工具可以把图片中一定容差下的相近像素都选中、清空，轻松做到一键“抠图”，前提是主体一定要与背景有大的差异，即像素值差值越大，抠图效果越好。

Canvas同样可以做到，并且可以处理视频帧，其中的原理是一样的 —— 将每个视频帧中绿幕的像素块透明度置0即可。像这样 ——

demo

部分代码

import videoUrl from ./component/video.ogv;import imgUrl from ./component/sample.jpg;const TOLERANCE = 5;export default {data () {return {videoUrl: videoUrl,imgUrl: imgUrl}},methods: {draw () {if (this.video.paused || this.video.ended) {          return;        }this.ctx.drawImage(this.video, 0, 0, this.width, this.height);this.ctx.putImageData(this.cutOut(), 0, 0);},cutOut () {let frameData = this.ctx.getImageData(0, 0, this.width, this.height),len = frameData.data.length / 4;        for (let i = 0; i < len; i++) {          let r = frameData.data[i * 4 + 0],          g = frameData.data[i * 4 + 1],          b = frameData.data[i * 4 + 2];          if (r - 100 >= TOLERANCE            && g - 100 >= TOLERANCE            && b - 43 <= TOLERANCE) {            frameData.data[i * 4 + 3] = 0;          }        }        return frameData;}},mounted () {this.video = this.$refs[video];        this.canvas = this.$refs[canvas];        this.ctx = this.canvas.getContext(2d);        this.timer = null;        this.video.addEventListener(play, () => {            this.width = this.video.videoWidth;            this.height = this.video.videoHeight;            this.timer && clearInterval(this.timer);            this.timer = setInterval(() => {            this.draw();            }, 50);        }, false);}}

参考资料

Manipulating video using canvas

 Pixel manipulation with canvas

Canvas and images and pixels