The target tensor for a multi-class segmentation use case using nn.CrossEntropyLoss
or nn.NLLLoss
should have the shape [batch_size, height, width]
and contain the class indices in the range [0, nb_classes-1]
.
If your current target is an RGB image containing color codes for each class, you would have to map these colors to class indices first, e.g. by using a lookup table.