renderscriptTargetApi 18
renderscriptSupportModeEnabled true

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
 xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:padding="20dp">

 <FrameLayout
  android:layout_width="300dp"
  android:layout_height="300dp"
  android:layout_centerInParent="true">

  <ImageView
   android:id="@+id/image"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:scaleType="centerCrop"
   android:src="@drawable/img"/>

  <TextView
   android:id="@+id/text"
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:layout_gravity="center"
   android:text="Melody"
   android:textColor="@android:color/white"
   android:textSize="45sp"/>

 </FrameLayout>

</RelativeLayout>

public class MainActivity extends Activity implements Runnable {

 private static final String TAG = "MainActivity";

 private ImageView mImage;
 private TextView mText;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  mImage = (ImageView) findViewById(R.id.image);
  mText = (TextView) findViewById(R.id.text);
  // onCreate()内无法到ImageView的背景，所以需要 post 到消息队列内稍后执行
  mImage.post(this);
 }

 @Override
 public void run() {
  blur(getImageViewBitmap(mImage), mText);
 }

 /**
  * 取出一个imageView的bitmap背景
  */
 public Bitmap getImageViewBitmap(ImageView imageView) {
  imageView.setDrawingCacheEnabled(true);
  // 取出ImageView的Bitmap
  Bitmap bitmap = imageView.getDrawingCache();
  // 拷贝一份bitmap用作模糊
  Bitmap bitmapCopy = bitmap.copy(bitmap.getConfig(), true);
  imageView.setDrawingCacheEnabled(false);
  return bitmapCopy;
 }

 /**
  * 模糊的具体实现
  *
  * @param inputBitmap 要模糊的 bitmap
  * @param targetView 需要被模糊背景的 View
  */
 public void blur(Bitmap inputBitmap, View targetView) {
  // 创建一个和目标View(需要背景被模糊的View)宽高一样的空的 outputBitmap
  Bitmap outputBitmap = Bitmap.createBitmap((int) (targetView.getMeasuredWidth()),
    (int) (targetView.getMeasuredHeight()), Bitmap.Config.ARGB_8888);
  // 将 outputBitmap 关联在 canvas 上
  Canvas canvas = new Canvas(outputBitmap);
  // 画布移动到目标 View 在父布局中的位置
  canvas.translate(-targetView.getLeft(), -targetView.getTop());
  Paint paint = new Paint();
  paint.setFlags(Paint.FILTER_BITMAP_FLAG);
  // 将要模糊的 inputBitmap 绘制到 outputBitmap 上
  // 因为刚才做了 translate 操作，这样就可以裁剪到目标 View 在父布局内的那一块背景到 outputBitmap 上
  canvas.drawBitmap(inputBitmap, 0, 0, paint);

  // ----接下来做模糊 outputBitmap 处理操作----

  // 创建 RenderScript
  RenderScript rs = RenderScript.create(this);
  Allocation input = Allocation.createFromBitmap(rs, outputBitmap);
  Allocation output = Allocation.createTyped(rs, input.getType());
  // 使用 ScriptIntrinsicBlur 类来模糊图片
  ScriptIntrinsicBlur blur = ScriptIntrinsicBlur.create(
    rs, Element.U8_4(rs));
  // 设置模糊半径 ( 取值范围为( 0.0f , 25f ] ，半径越大，模糊效果也越大)
  blur.setRadius(25f);
  blur.setInput(input);
  // 模糊计算
  blur.forEach(output);
  // 模糊 outputBitmap
  output.copyTo(outputBitmap);
  // 将模糊后的 outputBitmap 设为目标 View 的背景
  targetView.setBackground(new BitmapDrawable(getResources(), outputBitmap));
  rs.destroy()；
 }

}

import android.support.v8.renderscript.Allocation;
import android.support.v8.renderscript.Element;
import android.support.v8.renderscript.RenderScript;
import android.support.v8.renderscript.ScriptIntrinsicBlur;

...
<TextView
 android:id="@+id/text"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:gravity="center"
 android:text="Melody"
 android:textColor="@android:color/white"
 android:textSize="45sp"/>
...

10-09 17:04:23.664 23665-23665/com.melodyxxx.blurdemo2 E/MainActivity: spend: 120ms

...
Bitmap outputBitmap = Bitmap.createBitmap((int) (mTargetView.getMeasuredWidth() / scaleFactor),
  (int) (mTargetView.getMeasuredHeight() / scaleFactor), Bitmap.Config.ARGB_8888);
Canvas canvas = new Canvas(outputBitmap);
canvas.translate(-mTargetView.getLeft() / scaleFactor, -mTargetView.getTop() / scaleFactor);
canvas.scale(1 / scaleFactor, 1 / scaleFactor);
Paint paint = new Paint();
paint.setFlags(Paint.FILTER_BITMAP_FLAG);
canvas.drawBitmap(mInputBitmap, 0, 0, paint);
...