javascript - js高斯模糊算法问题

Question

{代码...} 最近看了阮一峰老师关于实现高斯模糊效果的博客，自己就用js和canvas写了这么一个效果 无奈执行时间太长，看stackblur的源码，又看不太懂 希望大家指教一下

迷茫 · Answer

高斯模糊有两种方案做：

直接用二维公式进行二重循环，复杂度为O(xy(2r)^2)
用一维公式分别对x、y循环，复杂度为O(2xy(2r))

测试结果：

用二重循环：（500*800,20） 4566ms
分别循环：（500*800,20） 237ms

可以发现刚好差20倍左右，也就是radius模糊半径的值

结果图：

实现代码如下：

代码较长，建议移步到我的博客看代码

html:

html


    
    test

javascript:

gaussBlur : 二重循环
gaussBlur1 : 分别循环

javascript/**
 * Created by zhaofengmiao on 15/3/22.
 */
window.onload = function(){
    var img = document.getElementById("imgSource"),
        canvas = document.getElementById('canvas'),
        width = img.width,
        height = img.height;

    // console.log(width);

    canvas.width = width;
    canvas.height = height;

    var context = canvas.getContext("2d");
    context.drawImage(img, 0, 0);

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

    //console.log(canvasData);

    // 开始
    var startTime = +new Date();

    var tempData = gaussBlur(canvasData, 20);


    context.putImageData(tempData,0,0);

    var endTime = +new Date();
    console.log(" 一共经历时间：" + (endTime - startTime) + "ms");
}

/**
 * 此函数为二重循环
 */
function gaussBlur(imgData, radius, sigma) {
    var pixes = imgData.data,
        width = imgData.width,
        height = imgData.height;

    radius = radius || 5;
    sigma = sigma || radius / 3;

    var gaussEdge = radius * 2 + 1;    // 高斯矩阵的边长

    var gaussMatrix = [],
        gaussSum = 0,
        a = 1 / (2 * sigma * sigma * Math.PI),
        b = -a * Math.PI;

    for (var i=-radius; i<=radius; i++) {
        for (var j=-radius; j<=radius; j++) {
            var gxy = a * Math.exp((i * i + j * j) * b);
            gaussMatrix.push(gxy);
            gaussSum += gxy;    // 得到高斯矩阵的和，用来归一化
        }
    }
    var gaussNum = (radius + 1) * (radius + 1);
    for (var i=0; i= w) {
        m = w + i - x;
    }
    return m;
}

/**
 * 此函数为分别循环
 */
function gaussBlur1(imgData,radius, sigma) {
    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;


    radius = Math.floor(radius) || 3;
    sigma = sigma || radius / 3;

    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;
            // pixes[i] = r ;
            // pixes[i + 1] = g ;
            // pixes[i + 2] = b ;
            // pixes[i + 3] = a ;
        }
    }
    //end
    imgData.data = pixes;
    return imgData;
}

怪我咯 · Answer

有人写过高斯模糊的jQuery插件 https://github.com/finom/jQuery-Gaussian-Blur 里面用的是svg

PHPz · Answer

你好，我最近也正在纠结高斯模糊这个问题，之前一直在用stackblur，但是貌似对透明的处理不是很理想，如果启用模糊alpha通道，就会把透明处理成白色，如果不模糊，就会是黑色，然后圆角图标模糊出来的边缘就很不好看。最近也在思考是否自己写一个方法实现。
大致看了你的方法，可否考虑把宽度和高度分开模糊，而不是双重的循环。望交流。

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结果图：

实现代码如下：