现在许多app中都应用到了对图片的模糊处理，图片高斯模糊备受设计师的青睐，在各大知名APP中，如微信、手机QQ、网易云音乐等等都有对背景高斯图模糊的设计，还有今日头条、内涵段子等。
在Android 中，现在常用的图片高斯模糊技术的根本有两种：RenderScript 、fastBlur
1.RenderScript
RenderScript是在Android上的高性能运行密集型运算的框架。
是在Android3.0（API 11）引入的。而Android图片高斯模糊处理，通常也是用这个库来完成。它提供了我们Java层调用的API,实际上是在c/c++ 层来处理的，所以它的效率和性能通常是最高的。
缺点是：但是它只能在API 17或者更高的版本使用。当然也可以引用兼容包，但是会增加一点包的体积。并且模糊度有有限。
public class RSBlur {
@TargetApi(Build.VERSION_CODES.JELLY_BEAN_MR2)
private static Bitmap rsBlur(Context context,Bitmap source,int radius){
Bitmap inputBmp = source;
//(1)初始化一个RenderScript Context：RenderScript 上下文环境通过create(Context)方法来创建，它保证RenderScript的使用并且提供一个控制后续所有RenderScript对象
RenderScript renderScript = RenderScript.create(context);
//(2)通过Script至少创建一个Allocation：一个Allocation是提供存储大量可变数据的RenderScript 对象。
final Allocation input = Allocation.createFromBitmap(renderScript,inputBmp);
final Allocation output = Allocation.createTyped(renderScript,input.getType());
//(3)创建ScriptIntrinsic：它内置了RenderScript 的一些通用操作，如高斯模糊、扭曲变换、图像混合等等
ScriptIntrinsicBlur scriptIntrinsicBlur = ScriptIntrinsicBlur.create(renderScript, Element.U8_4(renderScript));
//(4)填充数据到Allocations：除了使用方法createFromBitmap创建的Allocation外，其它的第一次创建时都是填充的空数据。
scriptIntrinsicBlur.setInput(input);
//(5)设置模糊半径 (0---25)
scriptIntrinsicBlur.setRadius(radius);
//(6)启动内核，调用方法处理：调用forEach 方法模糊处理。
scriptIntrinsicBlur.forEach(output);
//(7)从Allocation 中拷贝数据：为了能在Java层访问Allocation的数据，用Allocation其中一个copy方法来拷贝数据。
output.copyTo(inputBmp);
//(8)销毁RenderScript对象
renderScript.destroy();
return inputBmp;
}
}
2.fastBlur
fastBlur算法它直接在Java层做图片的模糊处理。对每个像素点应用高斯模糊计算、最后在合成Bitmap。就一个方法,使用这种方式不会有兼容性问题，也不会引入jar包导致APK变大。但是这种方法的效率是非常低的，想想也知道，因为是在Java 层处理，速度会更慢。将Bitmap全部加载到内存，较大图片容易OOM。
源码
public class FastBlur {
public static Bitmap blur(Bitmap sentBitmap, int radius, boolean canReuseInBitmap) {
// Stack Blur v1.0 from
// http://www.quasimondo.com/StackBlurForCanvas/StackBlurDemo.html
//
// Java Author: Mario Klingemann
// http://incubator.quasimondo.com
// created Feburary 29, 2004
// Android port : Yahel Bouaziz
// 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
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);
}
}
使用中需要考虑的问题：
- sdk版本，如果是17或以下，就不能使用RenderScript
- 模糊前应该对源bitmap进行缩放,图片缩小后再进行模糊处理，需要处理的像素点和半径都变小，从而使得模糊处理速度加快。（缩小的系数应该为2的整数次幂 ，即上面代码中的scale应该为1/2、1/4、1/8 ... 参考BitmapFactory.Options 对图片缩放 的inSample系数）
两者结合使用
public Bitmap blurBitmap(Context context,Bitmap source,int radius){
//缩放
int width = source.getWidth();
int height = source.getHeight();
int scaledWidth = width / 4;
int scaledHeight = height / 4;
Bitmap bitmap = Bitmap.createBitmap(scaledWidth, scaledHeight, Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(bitmap);
canvas.scale(1.0F / (float)this.mSampling, 1.0F / (float)this.mSampling);
Paint paint = new Paint();
paint.setFlags(2);
canvas.drawBitmap(source, 0.0F, 0.0F, paint);
//模糊处理
Bitmap newBitmap;
if(Build.VERSION.SDK_INT >= 18) {
newBitmap = RSBlur.blur(context, bitmap, radius)；
} else {
newBitmap = FastBlur.blur(bitmap,radius, true);
}
return newBitmap;
}
【分割线】
大量加载and优化
当我们的需求只有对一张图片进行模糊当做背景这种情况，直接进行上面所述的模糊就好，不需要做缓存等处理。
然而当我们要在列表中加载大量的模糊图片时（就像内涵段子首页视频展示），就要考虑优化，缓存，不应该过多重复的进行模糊。否则对造成滑动卡顿。
通常我们用Glide加载一张图片，在Glide基础上也有了一个开源库glide-transformations，可以进行模糊处理，并增加缓存，对模糊类也做了封装，方便使用。
一个小demo
compile 'jp.wasabeef:glide-transformations:2.0.1'
xml
public class MainActivity extends AppCompatActivity {
private Context context;
private ImageView iv_blur;
private ImageView iv_origin;
private String url ="http://mvimg2.meitudata.com/583bc2f76f58a6875.jpg";
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
context=this;
setContentView(R.layout.activity_main);
this.iv_blur = (ImageView) findViewById(R.id.iv_blur);
this.iv_origin = (ImageView) findViewById(R.id.iv_origin);
Glide.with(context).load(url)
.bitmapTransform(new BlurTransformation(context, 23, 4)).into(new SimpleTarget() {
@Override
public void onResourceReady(final GlideDrawable glideDrawable, GlideAnimation glideAnimation) {
Glide.with(context).load(url)
.asBitmap().into(new SimpleTarget() {
@Override
public void onResourceReady(Bitmap resource, GlideAnimation glideAnimation) {
//resource为原图 glideDrawable为模糊处理后得到的
//为了不改变原图的宽高，对原图resource进行等比例缩放
Matrix matrix = new Matrix();
float scale=resource.getHeight()/360 * context.getResources().getDisplayMetrics().density;
matrix.postScale(scale, scale);
Bitmap newResource=Bitmap.createBitmap(resource, 0, 0, resource.getWidth(), resource.getHeight(), matrix,
true);
iv_origin.setImageBitmap(resource);
iv_blur.setImageDrawable(glideDrawable);
}
});
}
});
}
}
效果如下：
继续优化 可以看出我们进行了两次图片加载，一次用作背景模糊，一次用作原图显示，整体显得臃肿，还增加的请求的次数，所以我们可以重写自己的转换类，做我们自己的操作，把这两张图片进行合成。
如下：
public class MyBlurTransformation implements Transformation {
private static int MAX_RADIUS = 25;
private static int DEFAULT_DOWN_SAMPLING = 1;
private Context mContext;
private BitmapPool mBitmapPool;
private int mRadius;
private int mSampling;
private int bitmapWidth;
private int bitmapHeight;
public MyBlurTransformation(Context context, BitmapPool pool, int radius, int sampling
,int bitmapWidth,int bitmapHeight){
this.mContext = context.getApplicationContext();
this.mBitmapPool = pool;
this.mRadius = radius;
this.mSampling = sampling;
this.bitmapHeight=bitmapHeight;
this.bitmapWidth=bitmapWidth;
}
public MyBlurTransformation(Context context, int radius, int sampling
,int bitmapWidth,int bitmapHeight) {
this(context, Glide.get(context).getBitmapPool(), radius, sampling,bitmapWidth,bitmapHeight);
}
@Override
public Resource transform(Resource resource, int outWidth, int outHeight) {
//source为原图 glide 的url
Bitmap source = (Bitmap)resource.get();
Bitmap composeBitmap= this.mBitmapPool.get(source.getWidth()/this.mSampling, source.getHeight()/this.mSampling, Bitmap.Config.ARGB_8888);
if (composeBitmap==null){
composeBitmap= composeBitmap(source);
}
return BitmapResource.obtain(composeBitmap, this.mBitmapPool);
}
private Bitmap composeBitmap(Bitmap source) {
int width = source.getWidth();
int height = source.getHeight();
int scaledWidth = width / this.mSampling;
int scaledHeight = height / this.mSampling;
Bitmap bitmap = this.mBitmapPool.get(scaledWidth, scaledHeight, Bitmap.Config.ARGB_8888);
if(bitmap == null) {
bitmap = Bitmap.createBitmap(scaledWidth, scaledHeight, Bitmap.Config.ARGB_8888);
}
Canvas canvas = new Canvas(bitmap);
canvas.scale(1.0F / (float)this.mSampling, 1.0F / (float)this.mSampling);
Paint paint = new Paint();
paint.setFlags(2);
canvas.drawBitmap(source, 0.0F, 0.0F, paint);
if(Build.VERSION.SDK_INT >= 18) {
try {
bitmap = RSBlur.blur(this.mContext, bitmap, this.mRadius);
} catch (RSRuntimeException var13) {
bitmap = FastBlur.blur(bitmap, this.mRadius, true);
}
} else {
bitmap = FastBlur.blur(bitmap, this.mRadius, true);
}
Bitmap scaleGlideBitmap=scaleBlurBitmap(bitmap);
Bitmap scaleResourceBitmap=scaleOriginBitmap(source);
Bitmap newBitmap=Bitmap.createBitmap(bitmapWidth,bitmapHeight,scaleResourceBitmap.getConfig());
Canvas canvasnew=new Canvas(newBitmap);
canvasnew.drawBitmap(scaleGlideBitmap,0,0,null);
canvasnew.drawBitmap(scaleResourceBitmap,(bitmapWidth-scaleResourceBitmap.getWidth())/2,0,null);
canvasnew.save(Canvas.ALL_SAVE_FLAG);//保存
canvasnew.restore();//存储
return newBitmap;
}
private Bitmap scaleOriginBitmap(Bitmap bkg) {
int originHeight = bkg.getHeight();
float scaleWidth = ((float) bitmapHeight) / originHeight;
Matrix matrix = new Matrix();
matrix.postScale(scaleWidth, scaleWidth);
return Bitmap.createBitmap(bkg, 0, 0, bkg.getWidth(), bkg.getHeight(), matrix,
true);
}
private Bitmap scaleBlurBitmap(Bitmap bitmap) {
float scaleWidth=(float) bitmapWidth/bitmap.getWidth();
float scaleHeight=(float) bitmapHeight/bitmap.getHeight();
Matrix matrix = new Matrix();
matrix.postScale(scaleWidth, scaleHeight);
return Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix,
true);
}
@Override
public String getId() {
return "BlurTransformation(radius=" + this.mRadius + ", sampling=" + this.mSampling + ")";
}
}
然后MainActivity使用就可以如下这么写 （去掉iv_origin，用一张图显示）
传入 也就是imageview的宽高，用作对原图的缩放
bitmapWidth =
bitmapHeight= 自己获取
Glide.with(mContext).load(url).bitmapTransform(new MyBlurTransformation(mContext,23, 4,bitmapWidth,bitmapHeight)).into(new SimpleTarget(){
@Override
public void onResourceReady(GlideDrawable resource, GlideAnimation glideAnimation) {
if (url.equals(vertical_view.getTag())) {
blur_iv.setImageDrawable(resource);
}
}
});
以上例子只展示显示一张图，当然可以把它用在列表中，也已经做了缓存。