表面模糊

这个功能可以在保留边缘的情况下对图像平坦区域进行模糊滤波，这个功能可以实现很好的磨皮效果，它的算法如下：

 /*
                表面模糊滤波
            */
        function surface(imgData, radius, threshold) {
            var width = imgData.width,
                height = imgData.height,
                pixelData = tempData = imgData.data;
            for (var i = 0; i < height; i++) {
                for (var j = 0; j < width; j++) {
                    pos = (i * width + j) * 4;
                    sumr = sumrw = sumg = sumgw = sumb = sumbw = 0;
                    for (var n = -radius; n <= radius; n++) {
                        for (var m = -radius; m <= radius; m++) {
                            var x = CLIP3(i + n, 0, height - 1);
                            var y = CLIP3(j + m, 0, width - 1);
                            pos0 = (x * width + y) * 4;
                            k = 1.0 - Math.abs(tempData[pos0] - tempData[pos]) / (2.5 * threshold);
                            sumr += k * tempData[pos0];
                            sumrw += k;

                            k = 1.0 - Math.abs(tempData[pos0 + 1] - tempData[pos + 1]) / (2.5 * threshold);
                            sumg += k * tempData[pos0 + 1];
                            sumgw += k;

                            k = 1.0 - Math.abs(tempData[pos0 + 2] - tempData[pos + 2]) / (2.5 * threshold);
                            sumb += k * tempData[pos0 + 2];
                            sumbw += k;
                        }
                    }
                    pixelData[pos] = CLIP2((sumr / sumrw) >> 0, pixelData[pos]);
                    pixelData[pos + 1] = CLIP2((sumg / sumgw) >> 0, pixelData[pos + 1]);
                    pixelData[pos + 2] = CLIP2((sumb / sumbw) >> 0, pixelData[pos + 2]);
                }
            }

            function CLIP2(a, b) {
                if (a < 0 || a > 255) {
                    return b
                } else {
                    return a
                }
            }

            function CLIP3(a, b, c) {
                return Math.min(Math.max(a, b), c)
            }
            imgData.data = pixelData;
            return imgData;
        }