RxJava convert byte array to Bitmap

Sorry for my english. Now i learning rxJava 1 and try convert byte[] to Bitmap and set it to imageview. But it work slowly. Do i right work whith rxJava? ps: i chek and asynkTask work fater than rxJava, how it possible?

Observable.just(data)
                .map(new Func1<byte[], Bitmap>() {
                    @Override
                    public Bitmap call(byte[] bytes) {
                        BitmapFactory.Options options = new BitmapFactory.Options();
                        options.inJustDecodeBounds = false;
                        options.inPreferredConfig = Bitmap.Config.RGB_565;
                        options.inDither = true;
                        options.inMutable = true;

                        Bitmap largeBitmap = BitmapFactory.decodeByteArray(data, 0, data.length, options);
                        Bitmap bitmap = Bitmap.createScaledBitmap(largeBitmap
                                , (int) ((float) largeBitmap.getWidth() / 10)
                                , (int) ((float) largeBitmap.getHeight() / 10)
                                , true);

                        if (bitmap.getWidth() > bitmap.getHeight()) {
                            Matrix matrix = new Matrix();
                            matrix.postRotate(90); // anti-clockwise by 90 degrees

                            bitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), matrix, true);
                        }

                        float k = (float) bitmap.getWidth() / (float) w_target;

                        if (w_target < bitmap.getWidth()) {
                            bitmap = Bitmap.createScaledBitmap(bitmap, w_target, (int) ((float) bitmap.getHeight() / k), true);
                        }

                        return createBlackAndWhite(bitmap);
                    }
                })
                .observeOn(Schedulers.io())
                .subscribeOn(AndroidSchedulers.mainThread())
                .subscribe(new Action1<Bitmap>() {
                    @Override
                    public void call(Bitmap bitmap) {
                        imageview.setImageBitmap(bitmap);
                    }
                });