使用 JavaScript Canvas 实现高斯模糊效果

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<html lang="zh">
<head>
 <meta charset="UTF-8">
 <meta name="viewport" content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
 <meta http-equiv="X-UA-Compatible" content="ie=edge">
 <title>canvas画布的高斯模糊效果</title>
</head>
<body>
<canvas id="canvas"></canvas>
</body>
<script>
 var canvas = document.getElementById('canvas');
 var ctx = canvas.getContext('2d');
 let img = new Image();
 //这里直接修改图片的路径
 img.src = "636753681750720000/Block/preview.jpg";
 img.onload = function () {
 //设置canvas的宽高
 canvas.height = img.height;
 canvas.width = img.width;
 //将图像绘制到canvas上面
 ctx.drawImage(img, 0, 0, img.width, img.height);
 //从画布获取一半图像
 var data = ctx.getImageData(0, 0, img.width/2, img.height);
 //将图像数据进行高斯模糊 data.data是一个数组，每四个值代表一个像素点的rgba的值，data.width data.height 分别代表图像数据的宽高
 var emptyData = gaussBlur(data);
 //将模糊的图像数据再渲染到画布上面
 ctx.putImageData(emptyData, 0, 0);
 };

 function gaussBlur(imgData) {
 var pixes = imgData.data;
 var width = imgData.width;
 var height = imgData.height;
 var gaussMatrix = [],
  gaussSum = 0,
  x, y,
  r, g, b, a,
  i, j, k, len;

 var radius = 10;
 var sigma = 5;

 a = 1 / (Math.sqrt(2 * Math.PI) * sigma);
 b = -1 / (2 * sigma * sigma);
 //生成高斯矩阵
 for (i = 0, x = -radius; x <= radius; x++, i++) {
  g = a * Math.exp(b * x * x);
  gaussMatrix[i] = g;
  gaussSum += g;

 }

 //归一化, 保证高斯矩阵的值在[0,1]之间
 for (i = 0, len = gaussMatrix.length; i < len; i++) {
  gaussMatrix[i] /= gaussSum;
 }
 //x 方向一维高斯运算
 for (y = 0; y < height; y++) {
  for (x = 0; x < width; x++) {
  r = g = b = a = 0;
  gaussSum = 0;
  for (j = -radius; j <= radius; j++) {
   k = x + j;
   if (k >= 0 && k < width) {//确保 k 没超出 x 的范围
   //r,g,b,a 四个一组
   i = (y * width + k) * 4;
   r += pixes[i] * gaussMatrix[j + radius];
   g += pixes[i + 1] * gaussMatrix[j + radius];
   b += pixes[i + 2] * gaussMatrix[j + radius];
   // a += pixes[i + 3] * gaussMatrix[j];
   gaussSum += gaussMatrix[j + radius];
   }
  }
  i = (y * width + x) * 4;
  // 除以 gaussSum 是为了消除处于边缘的像素, 高斯运算不足的问题
  // console.log(gaussSum)
  pixes[i] = r / gaussSum;
  pixes[i + 1] = g / gaussSum;
  pixes[i + 2] = b / gaussSum;
  // pixes[i + 3] = a ;
  }
 }
 //y 方向一维高斯运算
 for (x = 0; x < width; x++) {
  for (y = 0; y < height; y++) {
  r = g = b = a = 0;
  gaussSum = 0;
  for (j = -radius; j <= radius; j++) {
   k = y + j;
   if (k >= 0 && k < height) {//确保 k 没超出 y 的范围
   i = (k * width + x) * 4;
   r += pixes[i] * gaussMatrix[j + radius];
   g += pixes[i + 1] * gaussMatrix[j + radius];
   b += pixes[i + 2] * gaussMatrix[j + radius];
   // a += pixes[i + 3] * gaussMatrix[j];
   gaussSum += gaussMatrix[j + radius];
   }
  }
  i = (y * width + x) * 4;
  pixes[i] = r / gaussSum;
  pixes[i + 1] = g / gaussSum;
  pixes[i + 2] = b / gaussSum;
  }
 }
 return imgData;
 }
</script>
</html>