private static final String BLURRED_IMG_PATH = "blurred_image.png";
private static final int TOP_HEIGHT = 700;
private ListView mList;
private ImageView mBlurredImage;
private View headerView;
private ImageView mNormalImage;
private ScrollableImageView mBlurredImageHeader;
private Switch mSwitch;
private float alpha;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
    setContentView(R.layout.activity_main);

    // Get the screen width
    final int screenWidth = ImageUtils.getScreenWidth(this);

    // Find the view
    mBlurredImage = (ImageView) findViewById(R.id.blurred_image);
    mNormalImage = (ImageView) findViewById(R.id.normal_image);
    mBlurredImageHeader = (ScrollableImageView) findViewById(R.id.blurred_image_header);
    mSwitch = (Switch) findViewById(R.id.background_switch);
    mList = (ListView) findViewById(R.id.list);

    // prepare the header ScrollableImageView
    mBlurredImageHeader.setScreenWidth(screenWidth);

    // Action for the switch
    mSwitch.setOnCheckedChangeListener(new OnCheckedChangeListener() {

        @Override
        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
            if (isChecked) {
                mBlurredImage.setAlpha(alpha);
            } else {
                mBlurredImage.setAlpha(0f);

            }

        }
    });

    // Try to find the blurred image
    final File blurredImage = new File(getFilesDir() + BLURRED_IMG_PATH);
    if (!blurredImage.exists()) {

        // launch the progressbar in ActionBar
        setProgressBarIndeterminateVisibility(true);

        new Thread(new Runnable() {

            @Override
            public void run() {

                // No image found => let's generate it!
                BitmapFactory.Options options = new BitmapFactory.Options();
                options.inSampleSize = 2;
                Bitmap image = BitmapFactory.decodeResource(getResources(), R.drawable.image, options);
                Bitmap newImg = Blur.fastblur(MainActivity.this, image, 12);
                ImageUtils.storeImage(newImg, blurredImage);
                runOnUiThread(new Runnable() {

                    @Override
                    public void run() {
                        updateView(screenWidth);

                        // And finally stop the progressbar
                        setProgressBarIndeterminateVisibility(false);
                    }
                });

            }
        }).start();

    } else {

        // The image has been found. Let's update the view
        updateView(screenWidth);

    }

    String[] strings = getResources().getStringArray(R.array.list_content);

    // Prepare the header view for our list
    headerView = new View(this);
    headerView.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT, TOP_HEIGHT));
    mList.addHeaderView(headerView);
    mList.setAdapter(new ArrayAdapter<String>(this, R.layout.list_item, strings));
    mList.setOnScrollListener(new OnScrollListener() {

        @Override
        public void onScrollStateChanged(AbsListView view, int scrollState) {

        }

        /**
         * Listen to the list scroll. This is where magic happens ;)
         */
        @Override
        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {

            // Calculate the ratio between the scroll amount and the list
            // header weight to determinate the top picture alpha
            alpha = (float) -headerView.getTop() / (float) TOP_HEIGHT;
            // Apply a ceil
            if (alpha > 1) {
                alpha = 1;
            }

            // Apply on the ImageView if needed
            if (mSwitch.isChecked()) {
                mBlurredImage.setAlpha(alpha);
            }

            // Parallax effect : we apply half the scroll amount to our
            // three views
            mBlurredImage.setTop(headerView.getTop() / 2);
            mNormalImage.setTop(headerView.getTop() / 2);
            mBlurredImageHeader.handleScroll(headerView.getTop() / 2);

        }
    });
}

private void updateView(final int screenWidth) {
    Bitmap bmpBlurred = BitmapFactory.decodeFile(getFilesDir() + BLURRED_IMG_PATH);
    bmpBlurred = Bitmap.createScaledBitmap(bmpBlurred, screenWidth, (int) (bmpBlurred.getHeight()
            * ((float) screenWidth) / (float) bmpBlurred.getWidth()), false);

    mBlurredImage.setImageBitmap(bmpBlurred);

    mBlurredImageHeader.setoriginalImage(bmpBlurred);
}

implementation 'com.github.mirrajabi:view-effects:e355a1bac4'

ViewFilter.getInstance(this)
        .setRenderer(  BlurRenderer(20))
        .applyFilterOnView(  root_constraintLayout,
            root_constraintLayout    )