@Override
  public void process(Bitmap bitmap) {
    final int w = bitmap.getWidth();
    final int h = bitmap.getHeight();

    for (int x = 0; x < w; x++) {
      for (int y = 0; y < h; y++) {
        /*
         * Using {@link Bitmap#getPixel} when iterating about an entire bitmap is inefficient as it
         * causes many JNI calls. This is only done here to provide a comparison to
         * {@link FasterGreyScalePostprocessor}.
         */
        final int color = bitmap.getPixel(x, y);
        bitmap.setPixel(x, y, SlowGreyScalePostprocessor.getGreyColor(color));
      }
    }
  }
Applies a grey-scale effect on the bitmap using the slow {@link Bitmap#setPixel(int, int, int)}
method.
samples/showcase/src/main/java/com/facebook/fresco/samples/showcase/postprocessor/SlowGreyScalePostprocessor.java