Android图片实现模糊的一些方法

高斯模糊

高斯模糊就是将指定像素变换为其与周边像素加权平均后的值，权重就是高斯分布函数计算出来的值。

最近去网上找了找实现图片模糊的一些办法。首先找到一个关于高斯模糊算法的介绍。需要首先根据高斯分布函数计算权重值，为了提高效率我们采用一维高斯分布函数，然后处理图像的时候在横向和纵向进行两次计算得到结果。但是因为大图片转换太慢，所以不太建议使用。

radius越大，图片效果越模糊。以下三种方法都是

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 <mario@quasimondo.com>
<span style="white-space:pre"> </span>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);
}RenderScript是Android在API 11之后加入的，用于高效的图片处理，包括模糊、混合、矩阵卷积计算等，转换挺快的。代码示例如下：

public static void blur(Context context,Bitmap bkg, ImageView view, float radius) {
Bitmap overlay = Bitmap.createBitmap(view.getMeasuredWidth(), view.getMeasuredHeight(), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(overlay);
canvas.drawBitmap(bkg, -view.getLeft(), -view.getTop(), null);
RenderScript rs = RenderScript.create(context);
Allocation overlayAlloc = Allocation.createFromBitmap(rs, overlay);
ScriptIntrinsicBlur blur = ScriptIntrinsicBlur.create(rs, overlayAlloc.getElement());
blur.setInput(overlayAlloc);
blur.setRadius(radius);
blur.forEach(overlayAlloc);
overlayAlloc.copyTo(overlay);
view.setImageDrawable(new BitmapDrawable(context.getResources(), overlay));
rs.destroy();
}

还有一种gaussBlur，也是计算的，我没用过。不知道效果怎么样。不过看介绍，转换效果也很慢。

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;
}
}
}