Could you please explain how there are 4 channels(classes) in output. Because if we have 3 channels in output and if 3 channels are empty(that means no segmentation).We can automatically consider this case as background.right?So it would work with 3 channels.ie, output can be [batch_size, 3, h, w] for 3 classes + BG class. right? please correct me if iam wrong.