private ImageDecoder createRegionDecoder(int left, int top, int right, int bottom) {
    return new RegionDecoder(
        Fresco.getImagePipelineFactory().getPlatformDecoder(), new Rect(left, top, right, bottom));
  }
Simple region decoding example that renders the original image and a selected region.
samples/showcase/src/main/java/com/facebook/fresco/samples/showcase/imagepipeline/ImagePipelineRegionDecodingFragment.java