It's just a realtime blurring overlay like iOS UIVisualEffectView.

Just put the view in the layout xml, no Java code is required.

// Views to be blurred
<ImageView ../>

<com.github.mmin18.widget.RealtimeBlurView
	android:layout_width="match_parent"
	android:layout_height="match_parent"
	app:realtimeBlurRadius="20dp"
	app:realtimeOverlayColor="#8000" />

// Views above blurring overlay
<Button ../>

Try the sample apk: blurring.apk

Add dependencies in your build.gradle:

	dependencies {
	    compile 'com.github.mmin18:realtimeblurview:1.0.3'
	}
	android {
		buildToolsVersion '23.0.3'                 // Use 23.0.3 or higher
		defaultConfig {
			minSdkVersion 15
			renderscriptTargetApi 19
			renderscriptSupportModeEnabled true    // Enable RS support
		}
	}

RealtimeBlurView use RenderScript to blur the bitmap, just like 500px-android-blur.

Everytime your window draw, it will render a blurred bitmap, so there is a performance cost. Set downsampleFactor>=4 will significantly reduce the render cost. However, if you just want to blur a static view, 500px-android-blur is good enough.

I've run the sample on some old phones like Samsung Galaxy S2, Samsung Galaxy S3, it runs at full FPS. Here is a performance chart while scrolling the list on Nexus 5.