How to blur an image using Renderscript

RenderScript is a framework for running computationally intensive tasks at high performance on Android. RenderScript is primarily oriented for use with data-parallel computation, although serial workloads can benefit as well. The RenderScript runtime parallelizes work across processors available on a device, such as multi-core CPUs and GPUs.
RenderScript is especially useful for applications performing image processing, computational photography, or computer vision.
Let's see how you can use Renderscript to effectively blur an image.

Blurred image

Integrating Renderscript with Gradle

To add the Renderscript support library to your Android Studio project just add the following lines to build.gradle (module: app).

android {
    ...
    defaultConfig {
        renderscriptTargetApi 19
        renderscriptSupportModeEnabled true
    }
    ...
}

Code to blur the image

Now create the utility class BlurBuilder that uses RenderScript to blur the image:

/*
 * Copyright (c) - Software developed by iClaude.
 */

package com.flingsoftware.personalbudget.utilita;


import android.content.Context;
import android.graphics.Bitmap;
import android.support.v8.renderscript.Allocation;
import android.support.v8.renderscript.Element;
import android.support.v8.renderscript.RenderScript;
import android.support.v8.renderscript.ScriptIntrinsicBlur;


/**
 * This class is used to blur a Bitmap.
 * The static method blur takes a Bitmap as input e returns a blurred version of if.
 */
public class BlurBuilder {
    private static final float BITMAP_SCALE = 0.4f;
    private static final float BLUR_RADIUS = 7.5f;


    public static Bitmap blur(Context context, Bitmap image) {
        int width = Math.round(image.getWidth() * BITMAP_SCALE);
        int height = Math.round(image.getHeight() * BITMAP_SCALE);

        Bitmap inputBitmap = Bitmap.createScaledBitmap(image, width, height, false);
        Bitmap outputBitmap = Bitmap.createBitmap(inputBitmap);

        RenderScript rs = RenderScript.create(context);
        ScriptIntrinsicBlur theIntrinsic = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
        Allocation tmpIn = Allocation.createFromBitmap(rs, inputBitmap);
        Allocation tmpOut = Allocation.createFromBitmap(rs, outputBitmap);
        theIntrinsic.setRadius(BLUR_RADIUS);
        theIntrinsic.setInput(tmpIn);
        theIntrinsic.forEach(tmpOut);
        tmpOut.copyTo(outputBitmap);

        return outputBitmap;
    }
}

As you can see the class exposes a static method, "blur", that takes the original Bitmap as a parameter and returns the blurred version of the image.
You can adjust the constants BITMAP_SCALE and BLUR_RADIUS to control the amount of blurriness.

Blurring the image

Now, if you have a Bitmap you can blur it using the following code (remeber to do this in a separate thread to avoid locking the UI):

Bitmap origBitmap = ...
Bitmap blurredBitmap = BlurBuilder.blur(mContext, origBitmap);
myImageView.setImageBitmap(blurredBitmap );