ptrblck:

preds = torch.argmax(output, dim=1)


Thanks @ptrblck
Yes, I do have the shape shape [batch_size, nb_classes=3, height, width].which seems I am in the right direction.
preds = torch.argmax(output, dim=1) will give me the prediction values (or probabilties). Will I need to use a softmax  or a sigmoid for thresholding?