高斯模糊
高斯模糊就是將指定像素變換爲其與周邊像素加權平均後的值，權重就是高斯分佈函數計算出來的值。
一種實現
點擊打開鏈接<-這裏是一片關於高斯模糊算法的介紹，我們需要首先根據高斯分佈函數計算權重值，爲了提高效率我們採用一維高斯分佈函數，然後處理圖像的時候在橫向和縱向進行兩次計算得到結果。下面是一種實現
public static void gaussBlur(int[] data, int width, int height, int radius,
float sigma) {
float pa = (float) (1 / (Math.sqrt(2 * Math.PI) * sigma));
float pb = -1.0f / (2 * sigma * sigma);
// generate the Gauss Matrix
float[] gaussMatrix = new float[radius * 2 + 1];
float gaussSum = 0f;
for (int i = 0, x = -radius; x <= radius; ++x, ++i) {
float g = (float) (pa * Math.exp(pb * x * x));
gaussMatrix[i] = g;
gaussSum += g;
}
for (int i = 0, length = gaussMatrix.length; i < length; ++i) {
gaussMatrix[i] /= gaussSum;
}
// x direction
for (int y = 0; y < height; ++y) {
for (int x = 0; x < width; ++x) {
float r = 0, g = 0, b = 0;
gaussSum = 0;
for (int j = -radius; j <= radius; ++j) {
int k = x + j;
if (k >= 0 && k < width) {
int index = y * width + k;
int color = data[index];
int cr = (color & 0x00ff0000) >> 16;
int cg = (color & 0x0000ff00) >> 8;
int cb = (color & 0x000000ff);
r += cr * gaussMatrix[j + radius];
g += cg * gaussMatrix[j + radius];
b += cb * gaussMatrix[j + radius];
gaussSum += gaussMatrix[j + radius];
}
}
int index = y * width + x;
int cr = (int) (r / gaussSum);
int cg = (int) (g / gaussSum);
int cb = (int) (b / gaussSum);
data[index] = cr << 16 | cg << 8 | cb | 0xff000000;
}
}
// y direction
for (int x = 0; x < width; ++x) {
for (int y = 0; y < height; ++y) {
float r = 0, g = 0, b = 0;
gaussSum = 0;
for (int j = -radius; j <= radius; ++j) {
int k = y + j;
if (k >= 0 && k < height) {
int index = k * width + x;
int color = data[index];
int cr = (color & 0x00ff0000) >> 16;
int cg = (color & 0x0000ff00) >> 8;
int cb = (color & 0x000000ff);
r += cr * gaussMatrix[j + radius];
g += cg * gaussMatrix[j + radius];
b += cb * gaussMatrix[j + radius];
gaussSum += gaussMatrix[j + radius];
}
}
int index = y * width + x;
int cr = (int) (r / gaussSum);
int cg = (int) (g / gaussSum);
int cb = (int) (b / gaussSum);
data[index] = cr << 16 | cg << 8 | cb | 0xff000000;
}
}
}實際測試會發現這種計算方式是很耗時間的，而且模糊半徑越大，從原理也可以看到計算量是平方增長的，所以計算時間也越長。
RenderScript
RenderScript是Android在API 11之後加入的，用於高效的圖片處理，包括模糊、混合、矩陣卷積計算等，代碼示例如下
public Bitmap blurBitmap(Bitmap bitmap){
//Let's create an empty bitmap with the same size of the bitmap we want to blur
Bitmap outBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), Config.ARGB_8888);
//Instantiate a new Renderscript
RenderScript rs = RenderScript.create(getApplicationContext());
//Create an Intrinsic Blur Script using the Renderscript
ScriptIntrinsicBlur blurScript = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
//Create the Allocations (in/out) with the Renderscript and the in/out bitmaps
Allocation allIn = Allocation.createFromBitmap(rs, bitmap);
Allocation allOut = Allocation.createFromBitmap(rs, outBitmap);
//Set the radius of the blur
blurScript.setRadius(25.f);
//Perform the Renderscript
blurScript.setInput(allIn);
blurScript.forEach(allOut);
//Copy the final bitmap created by the out Allocation to the outBitmap
allOut.copyTo(outBitmap);
//recycle the original bitmap
bitmap.recycle();
//After finishing everything, we destroy the Renderscript.
rs.destroy();
return outBitmap;
}（示例來源 https://gist.github.com/Mariuxtheone/903c35b4927c0df18cf8）
FastBlur
public class FastBlur {
public static Bitmap doBlur(Bitmap sentBitmap, int radius, boolean canReuseInBitmap) {
// Stack Blur v1.0 from
// http://www.quasimondo.com/StackBlurForCanvas/StackBlurDemo.html
//
// Java Author: Mario Klingemann <mario at quasimondo.com>
// http://incubator.quasimondo.com
// created Feburary 29, 2004
// Android port : Yahel Bouaziz <yahel at kayenko.com>
// http://www.kayenko.com
// ported april 5th, 2012
// This is a compromise between Gaussian Blur and Box blur
// It creates much better looking blurs than Box Blur, but is
// 7x faster than my Gaussian Blur implementation.
//
// I called it Stack Blur because this describes best how this
// filter works internally: it creates a kind of moving stack
// of colors whilst scanning through the image. Thereby it
// just has to add one new block of color to the right side
// of the stack and remove the leftmost color. The remaining
// colors on the topmost layer of the stack are either added on
// or reduced by one, depending on if they are on the right or
// on the left side of the stack.
//
// If you are using this algorithm in your code please add
// the following line:
//
// Stack Blur Algorithm by Mario Klingemann <[email protected]>
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);
}這裏的方法也可以實現高斯模糊的效果，但使用了特殊的算法，比第一種可以快很多，但比起RenderScript還是慢一些
（示例來源
Android高級模糊技術）
實現YAHOO天氣的動態模糊效果
YAHOO天氣中的背景會隨着手指上滑模糊程度加深，實際使用中發現怎麼都達不到那樣流暢的效果，因爲手勢刷新的速度很快，每一幀都去重新模糊計算一遍，還是會有延遲，造成頁面卡頓。後來在一次偶然的開發中發現其實不需要每一幀都重新去模糊一遍，而是將圖片最大程度模糊一次，之後和原圖疊加，通過改變疊加的模糊圖片的alpha值來達到不同程度的模糊效果。下面是一個例子，可以看到隨着模糊圖片alpha值的變化，疊加後產生不同程度的模糊效果。
隨滑動變換alpha值的代碼如下
mBlurImage.setOnTouchListener(new OnTouchListener() {
private float mLastY;
@Override
public boolean onTouch(View v, MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN:
mLastY = event.getY();
break;
case MotionEvent.ACTION_MOVE:
float y = event.getY();
float alphaDelt = (y - mLastY) / 1000;
float alpha = mBlurImage.getAlpha() + alphaDelt;
if (alpha > 1.0) {
alpha = 1.0f;
} else if (alpha < 0.0) {
alpha = 0.0f;
}
mTextView.setText(String.valueOf(alpha));
mBlurImage.setAlpha(alpha);
break;
case MotionEvent.ACTION_UP:
break;
}
return true;
}
});示例代碼下載 http://download.csdn.net/detail/xu_fu/7628139
