純JavaScript實現HTML5 Canvas 6種特效濾鏡

者：前端Q

轉發鏈接：https://mp.weixin.qq.com/s/ewFfXptccFs5KvjUINLGbQ

前端

小試牛刀，實現了六款簡單常見HTML5 Canvas特效濾鏡，并且封裝成一個純JavaScript可調用的API文件gloomyfishfilter.js。支持的特效濾鏡分別為：

1.反色

2.灰色調

3.模糊

4.浮雕

5.雕刻

6.合理

濾鏡原理解釋：

2.灰色調：獲取一個預期點RGB值r，g，b則新的RGB值

newr =（r * 0.272）+（g * 0.534）+（b * 0.131）;

newg =（r * 0.349）+（g * 0.686）+（b * 0.168）;

newb =（r * 0.393）+（g * 0.769）+（b * 0.189）;

3.模糊：基于一個5 * 5的卷積核

4.浮雕與雕刻：

根據當前預期的前一個預期RGB值與它的后一個重新的RGB值之差再加上128

5.總體：模擬了物體在鏡子中與之對應的效果。

雜項準備

1、如何獲取Canvas 2d context對象

var canvas = document.getElementById("target");

canvas.width = source.clientWidth;

canvas.height = source.clientHeight;

**if**(!canvas.getContext) {

   console.log("Canvas not supported. Please install a HTML5compatible browser.");

   **return**;

}

// get 2D context of canvas and draw image

tempContext = canvas.getContext("2d");

2、如何添加一個DOM img對象到Canvas對象中

var source = document.getElementById("source");

tempContext.drawImage(source, 0, 0, canvas.width,canvas.height);

3、如何從Canvas對象中獲取預定數據

var canvas = document.getElementById("target");

var len = canvas.width * canvas.height * 4;

var canvasData = tempContext.getImageData(0, 0, canvas.width, canvas.height);

var binaryData = canvasData.data;

4、如何對DOM對象實現鼠標ClickEvent綁定

function bindButtonEvent(element, type, handler) 
{  

if(element.addEventListener){ 

      element.addEventListener(type, handler,**false**); 

   }else{ 

      element.attachEvent('on'+type, handler);// for IE6,7,8

   } 

}

5、如何調用實現的gfilter API完成濾鏡功能

<scriptsrc=*"gloomyfishfilter.js"*></script> //導入API文件

gfilter.colorInvertProcess(binaryData, len); //調用 API

6、瀏覽器支持：IE，FF，Chrome上測試通過，其中IE上支持通過以下標簽實現：

<meta http-equiv="X-UA-Compatible"*content=*"chrome=IE8">

效果演示：

應用程序源代碼：

CSS部分：

#svgContainer {
  width:800px;
  height:600px;
  background-color:#EEEEEE;
}

#sourceDiv { float: left; border: 2px solid blue} 
#targetDiv { float: right;border: 2px solid red}

filter1.html中HTML源代碼：

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="X-UA-Compatible" content="chrome=IE8">
<meta http-equiv="Content-type" content="text/html;charset=UTF-8">
<title>Canvas Filter Demo</title>
<link href="default.css" rel="stylesheet" />
<script src="gloomyfishfilter.js"></scrip>
</head>
<body>
  <h1>HTML Canvas Image Process - By Gloomy Fish</h1>
  <div id="svgContainer">
    <div id="sourceDiv">
      <img id="source" src="../test.png" />
    </div>
    <div id="targetDiv">
      <canvas id="target"></canvas>
    </div>
  </div>
  <div id="btn-group">
    <button type="button" id="invert-button">反色</button>
    <button type="button" id="adjust-button">灰色調</button>
    <button type="button" id="blur-button">模糊</button>
    <button type="button" id="relief-button">浮雕</button>
    <button type="button" id="diaoke-button">雕刻</button>
    <button type="button" id="mirror-button">鏡像</button>
  </div>
</body>
</html>

filter1.html中JavaScript源代碼：

var tempContext = null; // global variable 2d context
    window.onload = function() {
      var source = document.getElementById("source");
      var canvas = document.getElementById("target");
      canvas.width = source.clientWidth;
      canvas.height = source.clientHeight;

      if (!canvas.getContext) {
          console.log("Canvas not supported. Please install a HTML5 compatible browser.");
          return;
      }

      // get 2D context of canvas and draw image
      tempContext = canvas.getContext("2d");
      tempContext.drawImage(source, 0, 0, canvas.width, canvas.height);

          // initialization actions
          var inButton = document.getElementById("invert-button");
          var adButton = document.getElementById("adjust-button");
          var blurButton = document.getElementById("blur-button");
          var reButton = document.getElementById("relief-button");
          var dkButton = document.getElementById("diaoke-button");
          var mirrorButton = document.getElementById("mirror-button");

          // bind mouse click event
          bindButtonEvent(inButton, "click", invertColor);
          bindButtonEvent(adButton, "click", adjustColor);
          bindButtonEvent(blurButton, "click", blurImage);
          bindButtonEvent(reButton, "click", fudiaoImage);
          bindButtonEvent(dkButton, "click", kediaoImage);
          bindButtonEvent(mirrorButton, "click", mirrorImage);
    }

    function bindButtonEvent(element, type, handler)  
{  
      if(element.addEventListener) {  
         element.addEventListener(type, handler, false);  
      } else {  
         element.attachEvent('on'+type, handler); // for IE6,7,8
      }  
    }  

    function invertColor() {
      var canvas = document.getElementById("target");
      var len = canvas.width * canvas.height * 4;
      var canvasData = tempContext.getImageData(0, 0, canvas.width, canvas.height);
      var binaryData = canvasData.data;

          // Processing all the pixels
          gfilter.colorInvertProcess(binaryData, len);

          // Copying back canvas data to canvas
          tempContext.putImageData(canvasData, 0, 0);
    }

    function adjustColor() {
      var canvas = document.getElementById("target");
      var len = canvas.width * canvas.height * 4;
      var canvasData = tempContext.getImageData(0, 0, canvas.width, canvas.height);
          var binaryData = canvasData.data;

          // Processing all the pixels
          gfilter.colorAdjustProcess(binaryData, len);

          // Copying back canvas data to canvas
          tempContext.putImageData(canvasData, 0, 0);
    }

    function blurImage() 
{
      var canvas = document.getElementById("target");
      var len = canvas.width * canvas.height * 4;
      var canvasData = tempContext.getImageData(0, 0, canvas.width, canvas.height);

          // Processing all the pixels
          gfilter.blurProcess(tempContext, canvasData);

          // Copying back canvas data to canvas
          tempContext.putImageData(canvasData, 0, 0);
    }

    function fudiaoImage() 
{
      var canvas = document.getElementById("target");
      var len = canvas.width * canvas.height * 4;
      var canvasData = tempContext.getImageData(0, 0, canvas.width, canvas.height);

          // Processing all the pixels
          gfilter.reliefProcess(tempContext, canvasData);

          // Copying back canvas data to canvas
          tempContext.putImageData(canvasData, 0, 0);
    }

    function kediaoImage() 
{
      var canvas = document.getElementById("target");
      var len = canvas.width * canvas.height * 4;
      var canvasData = tempContext.getImageData(0, 0, canvas.width, canvas.height);

          // Processing all the pixels
          gfilter.diaokeProcess(tempContext, canvasData);

          // Copying back canvas data to canvas
          tempContext.putImageData(canvasData, 0, 0);
    }

    function mirrorImage() 
{
      var canvas = document.getElementById("target");
      var len = canvas.width * canvas.height * 4;
      var canvasData = tempContext.getImageData(0, 0, canvas.width, canvas.height);

          // Processing all the pixels
          gfilter.mirrorProcess(tempContext, canvasData);

          // Copying back canvas data to canvas
          tempContext.putImageData(canvasData, 0, 0);
    }

濾鏡源代碼（gloomyfishfilter.js）：

var gfilter = {
    type: "canvas",
    name: "filters",
    author: "zhigang",
    getInfo: function () {
        return this.author + ' ' + this.type + ' ' + this.name;
    },

    /**
     * invert color value of pixel, new pixel = RGB(255-r, 255-g, 255 - b)
     * 
     * @param binaryData - canvas's imagedata.data
     * @param l - length of data (width * height of image data)
     */
   colorInvertProcess: function(binaryData, l) {
    for (var i = 0; i < l; i += 4) {
          var r = binaryData[i];
          var g = binaryData[i + 1];
          var b = binaryData[i + 2];

          binaryData[i] = 255-r;
          binaryData[i + 1] = 255-g;
          binaryData[i + 2] = 255-b;
      }
   },

   /**
    * adjust color values and make it more darker and gray...
    * 
    * @param binaryData
    * @param l
    */
  colorAdjustProcess: function(binaryData, l) {
    for (var i = 0; i < l; i += 4) {
          var r = binaryData[i];
          var g = binaryData[i + 1];
          var b = binaryData[i + 2];

          binaryData[i] = (r * 0.272) + (g * 0.534) + (b * 0.131);
          binaryData[i + 1] = (r * 0.349) + (g * 0.686) + (b * 0.168);
          binaryData[i + 2] = (r * 0.393) + (g * 0.769) + (b * 0.189);
      }
  },

  /**
   * deep clone image data of canvas
   * 
   * @param context
   * @param src
   * @returns
   */
  copyImageData: function(context, src)
  {
      var dst = context.createImageData(src.width, src.height);
      dst.data.set(src.data);
      return dst;
  },

  /**
   * convolution - keneral size 5*5 - blur effect filter(模糊效果)
   * 
   * @param context
   * @param canvasData
   */
  blurProcess: function(context, canvasData) {
    console.log("Canvas Filter - blur process");
    var tempCanvasData = this.copyImageData(context, canvasData);
    var sumred = 0.0, sumgreen = 0.0, sumblue = 0.0;
    for ( var x = 0; x < tempCanvasData.width; x++) {    
            for ( var y = 0; y < tempCanvasData.height; y++) {    

                // Index of the pixel in the array    
                var idx = (x + y * tempCanvasData.width) * 4;       
                for(var subCol=-2; subCol<=2; subCol++) {
                  var colOff = subCol + x;
                  if(colOff <0 || colOff >= tempCanvasData.width) {
                    colOff = 0;
                  }
                  for(var subRow=-2; subRow<=2; subRow++) {
                    var rowOff = subRow + y;
                    if(rowOff < 0 || rowOff >= tempCanvasData.height) {
                      rowOff = 0;
                    }
                    var idx2 = (colOff + rowOff * tempCanvasData.width) * 4;    
                      var r = tempCanvasData.data[idx2 + 0];    
                      var g = tempCanvasData.data[idx2 + 1];    
                      var b = tempCanvasData.data[idx2 + 2];
                      sumred += r;
                      sumgreen += g;
                      sumblue += b;
                  }
                }

                // calculate new RGB value
                var nr = (sumred / 25.0);
                var ng = (sumgreen / 25.0);
                var nb = (sumblue / 25.0);

                // clear previous for next pixel point
                sumred = 0.0;
                sumgreen = 0.0;
                sumblue = 0.0;

                // assign new pixel value    
                canvasData.data[idx + 0] = nr; // Red channel    
                canvasData.data[idx + 1] = ng; // Green channel    
                canvasData.data[idx + 2] = nb; // Blue channel    
                canvasData.data[idx + 3] = 255; // Alpha channel    
            }
    }
  },

  /**
   * after pixel value - before pixel value + 128
   * 浮雕效果
   */
  reliefProcess: function(context, canvasData) {
    console.log("Canvas Filter - relief process");
    var tempCanvasData = this.copyImageData(context, canvasData);
    for ( var x = 1; x < tempCanvasData.width-1; x++) 
    {    
            for ( var y = 1; y < tempCanvasData.height-1; y++)
            {    

                // Index of the pixel in the array    
                var idx = (x + y * tempCanvasData.width) * 4;       
        var bidx = ((x-1) + y * tempCanvasData.width) * 4;
        var aidx = ((x+1) + y * tempCanvasData.width) * 4;

                // calculate new RGB value
                var nr = tempCanvasData.data[aidx + 0] - tempCanvasData.data[bidx + 0] + 128;
                var ng = tempCanvasData.data[aidx + 1] - tempCanvasData.data[bidx + 1] + 128;
                var nb = tempCanvasData.data[aidx + 2] - tempCanvasData.data[bidx + 2] + 128;
                nr = (nr < 0) ? 0 : ((nr >255) ? 255 : nr);
                ng = (ng < 0) ? 0 : ((ng >255) ? 255 : ng);
                nb = (nb < 0) ? 0 : ((nb >255) ? 255 : nb);

                // assign new pixel value    
                canvasData.data[idx + 0] = nr; // Red channel    
                canvasData.data[idx + 1] = ng; // Green channel    
                canvasData.data[idx + 2] = nb; // Blue channel    
                canvasData.data[idx + 3] = 255; // Alpha channel    
            }
    }
  },

  /**
   *   before pixel value - after pixel value + 128
   *  雕刻效果
   * 
   * @param canvasData
   */
  diaokeProcess: function(context, canvasData) {
    console.log("Canvas Filter - process");
    var tempCanvasData = this.copyImageData(context, canvasData);
    for ( var x = 1; x < tempCanvasData.width-1; x++) 
    {    
            for ( var y = 1; y < tempCanvasData.height-1; y++)
            {    

                // Index of the pixel in the array    
                var idx = (x + y * tempCanvasData.width) * 4;       
        var bidx = ((x-1) + y * tempCanvasData.width) * 4;
        var aidx = ((x+1) + y * tempCanvasData.width) * 4;

                // calculate new RGB value
                var nr = tempCanvasData.data[bidx + 0] - tempCanvasData.data[aidx + 0] + 128;
                var ng = tempCanvasData.data[bidx + 1] - tempCanvasData.data[aidx + 1] + 128;
                var nb = tempCanvasData.data[bidx + 2] - tempCanvasData.data[aidx + 2] + 128;
                nr = (nr < 0) ? 0 : ((nr >255) ? 255 : nr);
                ng = (ng < 0) ? 0 : ((ng >255) ? 255 : ng);
                nb = (nb < 0) ? 0 : ((nb >255) ? 255 : nb);

                // assign new pixel value    
                canvasData.data[idx + 0] = nr; // Red channel    
                canvasData.data[idx + 1] = ng; // Green channel    
                canvasData.data[idx + 2] = nb; // Blue channel    
                canvasData.data[idx + 3] = 255; // Alpha channel    
            }
    }
  },

  /**
   * mirror reflect
   * 
   * @param context
   * @param canvasData
   */
  mirrorProcess : function(context, canvasData) {
    console.log("Canvas Filter - process");
    var tempCanvasData = this.copyImageData(context, canvasData);
    for ( var x = 0; x < tempCanvasData.width; x++) // column
    {    
            for ( var y = 0; y < tempCanvasData.height; y++) // row
            {    

                // Index of the pixel in the array    
                var idx = (x + y * tempCanvasData.width) * 4;       
        var midx = (((tempCanvasData.width -1) - x) + y * tempCanvasData.width) * 4;

                // assign new pixel value    
                canvasData.data[midx + 0] = tempCanvasData.data[idx + 0]; // Red channel    
                canvasData.data[midx + 1] = tempCanvasData.data[idx + 1]; ; // Green channel    
                canvasData.data[midx + 2] = tempCanvasData.data[idx + 2]; ; // Blue channel    
                canvasData.data[midx + 3] = 255; // Alpha channel    
            }
    }
  },
};

總結

感謝閱讀，如果你覺得我今天分享的內容，不錯，請點一個贊，謝謝?。?/p>

TML5 Canvas是HTML5新增的一個元素，它提供了一個可執行JavaScript腳本繪制圖形的區域。Canvas元素通過使用JavaScript API，可以在瀏覽器上繪制圖形、渲染動畫和實現交互效果等。

使用原理：
HTML5 Canvas通過使用JavaScript API在瀏覽器中創建一塊畫布（Canvas），然后可以使用腳本語言（通常是JavaScript）在畫布上繪制各種形狀、線條、圖像和文本等。Canvas使用像素渲染，可以直接操作像素數據，因此在性能方面相比其他圖形技術（如SVG）更具優勢。

場景：
HTML5 Canvas可以應用于各種需要圖形繪制、動畫渲染和交互效果的場景，例如：

游戲開發：Canvas可以用來開發2D或3D游戲，通過繪制游戲場景、角色和動畫等實現游戲效果。
數據可視化：Canvas可以用來繪制各種圖表和圖形，實現數據可視化效果。
圖像處理：Canvas可以對圖像進行像素級別的操作，實現圖像處理功能，例如濾鏡、裁剪和合成等。
實時視頻處理：Canvas可以結合WebRTC等技術實現實時視頻處理，例如在視頻通話中添加特效和濾鏡等。

代碼示例：
以下是一個簡單的HTML5 Canvas代碼示例，用于在畫布上繪制一個矩形和一個圓形：

<!DOCTYPE html>  
<html>  
    <head>  
     			<title>HTML5 Canvas示例</title>  
    </head>  
      <body>  
           <canvas id="myCanvas" width="400" height="400"></canvas>  
             <script>  
                 // 獲取Canvas元素和繪圖上下文  
                 var canvas = document.getElementById("myCanvas");  
                 var ctx = canvas.getContext("2d");  
                 // 繪制矩形  
                 ctx.fillStyle = "blue";  
                 ctx.fillRect(50, 50, 100, 100);  
                 // 繪制圓形  
                 ctx.beginPath();  
                 ctx.arc(200, 200, 50, 0, Math.PI * 2);  
                 ctx.fillStyle = "red";  
                 ctx.fill();  
             </script>  
      </body>  
</html>

在上述代碼中，我們首先獲取了Canvas元素和繪圖上下文（Context），然后使用fillRect()方法繪制了一個藍色的矩形，使用arc()方法繪制了一個紅色的圓形。最后，我們使用fill()方法填充了圓形的顏色。

動設備和桌面電腦上的客戶端API起初并不是同步的。最初總是移動設備上先擁有某些功能和相應的API，但慢慢的，這些API會出現在桌面電腦上。其中一個應用接口技術就是getUserMedia API，它能讓應用開發者訪問用戶的攝像頭或內置相機。下面就讓我展示一下如何通過瀏覽器來訪問你的攝像頭，并提取截屏圖形。下面的代碼里我寫了一部分注釋，請閱讀：

<videoid="video"width="640"height="480" autoplay></video>
<buttonid="snap">Snap Photo</button>
<canvasid="canvas"width="640"height="480"></canvas>

在寫出上面這些標記前應該判斷用戶的客戶端是否有攝像頭支持，但這里為了不那么麻煩，這里直接寫出了這些HTML標記，需要注意的是我們這里使用的長寬是640×480。

JavaScript代碼

因為我們是手工寫出的HTML，所以下面的js代碼會比你想象的要簡單了很多。

// Put event listeners into place
window.addEventListener("DOMContentLoaded", function() {
// Grab elements, create settings, etc.
var canvas = document.getElementById("canvas"),
context = canvas.getContext("2d"),
video = document.getElementById("video"),
videoObj = { "video": true },
errBack = function(error) {
console.log("Video capture error: ", error.code);
};
// Put video listeners into place
if(navigator.getUserMedia) { // Standard
navigator.getUserMedia(videoObj, function(stream) {
video.src = stream;
video.play();
}, errBack);
} elseif(navigator.webkitGetUserMedia) { // WebKit-prefixed
navigator.webkitGetUserMedia(videoObj, function(stream){
video.src = window.webkitURL.createObjectURL(stream);
video.play();
}, errBack);
}
elseif(navigator.mozGetUserMedia) { // Firefox-prefixed
navigator.mozGetUserMedia(videoObj, function(stream){
video.src = window.URL.createObjectURL(stream);
video.play();
}, errBack);
}
}, false);
一旦判斷出用戶瀏覽器支持getUserMedia ，下面就非常簡單了，只需要將那個video元素的src設置為用戶的攝像頭視頻直播連接。這就是用瀏覽器訪問攝像頭需要做的所有的事情!
拍照的功能只能說是稍微復雜一點點。我們在按鈕上加入一個監聽器，將視頻畫面畫到畫布上。
// 觸發拍照動作
document.getElementById("snap")
.addEventListener("click", function() {
context.drawImage(video, 0, 0, 640, 480);
});
當然，你還可以在圖片上加一些濾鏡效果….我還是把這些技術放到以后里再說吧。但至少你可以將這個畫布圖像轉換成一張圖片。
以前我們需要使用第三方的插件才能從瀏覽器里訪問用戶的攝像頭，這不免有些復雜。現在只需要HTML5的畫布技術和javaScript，我們就能簡單快速的操作用戶的攝像頭。不僅僅還是訪問攝像頭，而且是因為HTML5的畫布技術及其強大，我們可以給圖片上加入各種迷人的濾鏡效果?，F在，在瀏覽器里用自己的攝像頭給自己拍張照片吧!

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