Scale the image based on the target view's dimension while keeping its ratio, and then make the cropped part blurred.

BlurEffect

private void refreshAvatar(File file) {
    /***
     * Note: the current Fragment has been created once entering the home Activity.
     * So the dimension of avatarParent is determinate already.
     */
    if (file != null && file.exists()) {
        avatarParent.setBackground(defaultBackground);

        Glide.with(this).load(file.getAbsoluteFile())
                .asBitmap()
                .skipMemoryCache(true)
                .diskCacheStrategy(DiskCacheStrategy.NONE)
                .into(new SimpleTarget<Bitmap>() {
                    @Override
                    public void onResourceReady(Bitmap resource, GlideAnimation<? super Bitmap> glideAnimation) {
                        // origin bitmap
                        int bmpWidth = resource.getWidth();
                        int bmpHeight = resource.getHeight();

                        int width = avatarParent.getWidth();
                        int height = avatarParent.getHeight();
                        
                        showBlurredBitmap(resource, bmpWidth, bmpHeight, width, height);
                    }
                });
    }
}

private void showBlurredBitmap(Bitmap resource, final int bmpWidth, final int bmpHeight, final int width, final int height) {
    Observable.just(resource)
            .map(bitmap -> {
                // scale the image while keeping its ratio
                int scaledHeight = (int) (bmpHeight * 1.0f * width / bmpWidth);
                Bitmap scaledBmp = Bitmap.createScaledBitmap(bitmap, width, scaledHeight, false);

                // center vertically
                Bitmap dstBitmap = Bitmap.createBitmap(scaledBmp, 0, (scaledHeight - height) / 2, width, height);
                
                // scale down bitmap first
                // http://trickyandroid.com/advanced-blurring-techniques/
                float scaleFactor = 8;
                int radius = 20;
                Bitmap overlay = Bitmap.createBitmap((int) (width * 1.0f / scaleFactor),
                        (int) (height * 1.0f / scaleFactor), Bitmap.Config.ARGB_8888);
                Canvas canvas = new Canvas(overlay);
                canvas.scale(1 / scaleFactor, 1 / scaleFactor);

                Paint paint = new Paint();
                paint.setFlags(Paint.FILTER_BITMAP_FLAG);
                canvas.drawBitmap(dstBitmap, 0, 0, paint);

                Timber.i(">>> new bmp size w:%d|h:%d", dstBitmap.getWidth(), dstBitmap.getHeight());

                Timber.i(">>> blurring started");
                dstBitmap = FastBlurUtil.doBlur(overlay, radius, true);
                Timber.i(">>> blurring end");
                
                return dstBitmap;
            })
            .subscribeOn(RxSchedulerProvider.getInstance().computation())
            .observeOn(RxSchedulerProvider.getInstance().ui())
            .subscribe(bitmap -> {
                Drawable[] drawables = new Drawable[]{
                        new BitmapDrawable(getResources(), bitmap), alphaDrawable};
                avatarParent.setBackground(new LayerDrawable(drawables));

            }, throwable -> {
                Timber.e(throwable.getMessage());
            });
}