code: public static Observable<Bitmap> getThumbnailFromPath(String filePath) {
      final Bitmap sourceBitmap = BitmapFactory.decodeFile(filePath);
      return Observable.fromCallable(new Func0<Bitmap>() {
        @Override
        public Bitmap call() {
          return ThumbnailUtils.
              extractThumbnail(sourceBitmap, sourceBitmap.getWidth(), sourceBitmap.getHeight());
        }
      });
    }
docs: /*
  Get image thumbnail from an image file, by path.