canvas像素點操作影片綠幕摳圖

本文介紹了canvas像素點操作之影片綠幕摳圖，分享給大家，具體如下：

用法：

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

下面的栗子簡單實現了幾個簡單的濾鏡效果，具體演算法參考的這裡，學過《數位影像處理》的同學應該對此理解更深刻。

demo

該栗子純屬為了示範功能而做，如果只強調效果而不在乎數據的話，用CSS3的filter屬性便能高效又輕鬆地搞定。

部分程式碼

 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();}}

上週跟同學去了一趟溧陽天目湖的南山竹海，在景區被忽悠拍了一張照片，就是這張-

然後被朋友圈吐槽摳圖。其實當時就是站在一塊綠幕前拍的:joy: 。

PS中魔法棒工具可以把圖片中一定容差下的相近像素都選中、清空，輕鬆做到一鍵摳圖，前提是主體一定要與背景有大的差異，即像素值差值越大，摳圖效果越好。

Canvas同樣可以做到，並且可以處理視頻幀，其中的原理是一樣的- 將每個視頻幀中綠幕的像素塊透明度置0即可。像這樣-

demo

部分程式碼

 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);}}

Manipulating video using canvas

Pixel manipulation with canvas

Canvas and images and pixels