一、实现
实现Blur效果主要有两种方式，一个是通过RenderScript来做，另一种是通过直接对像素点来进行算法处理。
RenderScript是API11之后才引入的，所以对版本有限制，而且RenderScript确实挺复杂的，虽然使用他的Blur功能很简单，但是要真正搞懂，不是一天两天的事。
本文主要介绍另一种算法来实现Blur，这个算法是目前市面上对Blur效果处理比较好的一种算法了

二、算法

import android.graphics.Bitmap;  

/** 
 * Created by paveld on 3/6/14. 
 */  
public class FastBlur {  

    public static Bitmap doBlur(Bitmap sentBitmap, int radius, boolean canReuseInBitmap) {  
        Bitmap bitmap;  
        if (canReuseInBitmap) {  
            bitmap = sentBitmap;  
        } else {  
            bitmap = sentBitmap.copy(sentBitmap.getConfig(), true);  
        }  

        if (radius < 1) {  
            return (null);  
        }  

        int w = bitmap.getWidth();  
        int h = bitmap.getHeight();  

        int[] pix = new int[w * h];  
        bitmap.getPixels(pix, 0, w, 0, 0, w, h);  

        int wm = w - 1;  
        int hm = h - 1;  
        int wh = w * h;  
        int div = radius + radius + 1;  

        int r[] = new int[wh];  
        int g[] = new int[wh];  
        int b[] = new int[wh];  
        int rsum, gsum, bsum, x, y, i, p, yp, yi, yw;  
        int vmin[] = new int[Math.max(w, h)];  

        int divsum = (div + 1) >> 1;  
        divsum *= divsum;  
        int dv[] = new int[256 * divsum];  
        for (i = 0; i < 256 * divsum; i++) {  
            dv[i] = (i / divsum);  
        }  

        yw = yi = 0;  

        int[][] stack = new int[div][3];  
        int stackpointer;  
        int stackstart;  
        int[] sir;  
        int rbs;  
        int r1 = radius + 1;  
        int routsum, goutsum, boutsum;  
        int rinsum, ginsum, binsum;  

        for (y = 0; y < h; y++) {  
            rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;  
            for (i = -radius; i <= radius; i++) {  
                p = pix[yi + Math.min(wm, Math.max(i, 0))];  
                sir = stack[i + radius];  
                sir[0] = (p & 0xff0000) >> 16;  
                sir[1] = (p & 0x00ff00) >> 8;  
                sir[2] = (p & 0x0000ff);  
                rbs = r1 - Math.abs(i);  
                rsum += sir[0] * rbs;  
                gsum += sir[1] * rbs;  
                bsum += sir[2] * rbs;  
                if (i > 0) {  
                    rinsum += sir[0];  
                    ginsum += sir[1];  
                    binsum += sir[2];  
                } else {  
                    routsum += sir[0];  
                    goutsum += sir[1];  
                    boutsum += sir[2];  
                }  
            }  
            stackpointer = radius;  

            for (x = 0; x < w; x++) {  

                r[yi] = dv[rsum];  
                g[yi] = dv[gsum];  
                b[yi] = dv[bsum];  

                rsum -= routsum;  
                gsum -= goutsum;  
                bsum -= boutsum;  

                stackstart = stackpointer - radius + div;  
                sir = stack[stackstart % div];  

                routsum -= sir[0];  
                goutsum -= sir[1];  
                boutsum -= sir[2];  

                if (y == 0) {  
                    vmin[x] = Math.min(x + radius + 1, wm);  
                }  
                p = pix[yw + vmin[x]];  

                sir[0] = (p & 0xff0000) >> 16;  
                sir[1] = (p & 0x00ff00) >> 8;  
                sir[2] = (p & 0x0000ff);  

                rinsum += sir[0];  
                ginsum += sir[1];  
                binsum += sir[2];  

                rsum += rinsum;  
                gsum += ginsum;  
                bsum += binsum;  

                stackpointer = (stackpointer + 1) % div;  
                sir = stack[(stackpointer) % div];  

                routsum += sir[0];  
                goutsum += sir[1];  
                boutsum += sir[2];  

                rinsum -= sir[0];  
                ginsum -= sir[1];  
                binsum -= sir[2];  

                yi++;  
            }  
            yw += w;  
        }  
        for (x = 0; x < w; x++) {  
            rinsum = ginsum = binsum = routsum = goutsum = boutsum = rsum = gsum = bsum = 0;  
            yp = -radius * w;  
            for (i = -radius; i <= radius; i++) {  
                yi = Math.max(0, yp) + x;  

                sir = stack[i + radius];  

                sir[0] = r[yi];  
                sir[1] = g[yi];  
                sir[2] = b[yi];  

                rbs = r1 - Math.abs(i);  

                rsum += r[yi] * rbs;  
                gsum += g[yi] * rbs;  
                bsum += b[yi] * rbs;  

                if (i > 0) {  
                    rinsum += sir[0];  
                    ginsum += sir[1];  
                    binsum += sir[2];  
                } else {  
                    routsum += sir[0];  
                    goutsum += sir[1];  
                    boutsum += sir[2];  
                }  

                if (i < hm) {  
                    yp += w;  
                }  
            }  
            yi = x;  
            stackpointer = radius;  
            for (y = 0; y < h; y++) {  
                // Preserve alpha channel: ( 0xff000000 & pix[yi] )  
                pix[yi] = (0xff000000 & pix[yi]) | (dv[rsum] << 16) | (dv[gsum] << 8) | dv[bsum];  

                rsum -= routsum;  
                gsum -= goutsum;  
                bsum -= boutsum;  

                stackstart = stackpointer - radius + div;  
                sir = stack[stackstart % div];  

                routsum -= sir[0];  
                goutsum -= sir[1];  
                boutsum -= sir[2];  

                if (x == 0) {  
                    vmin[y] = Math.min(y + r1, hm) * w;  
                }  
                p = x + vmin[y];  

                sir[0] = r[p];  
                sir[1] = g[p];  
                sir[2] = b[p];  

                rinsum += sir[0];  
                ginsum += sir[1];  
                binsum += sir[2];  

                rsum += rinsum;  
                gsum += ginsum;  
                bsum += binsum;  

                stackpointer = (stackpointer + 1) % div;  
                sir = stack[stackpointer];  

                routsum += sir[0];  
                goutsum += sir[1];  
                boutsum += sir[2];  

                rinsum -= sir[0];  
                ginsum -= sir[1];  
                binsum -= sir[2];  

                yi += w;  
            }  
        }  

        bitmap.setPixels(pix, 0, w, 0, 0, w, h);  

        return (bitmap);  
    }  
}  

三、使用

Bitmap overlay = FastBlur.doBlur(overlay, (int) radius, true);
view.setImageBitmap(overlay);