yeah, the NLL_Loss
output:2x640x480
target:640x480
I follow the guidance of official documentation, output should have :NCHW,target:NHW,  I conjecture that’s because the target use pixel-wise class label for calculation.
specificly, I use loss=functional.nll_loss(functional.log_softmax(segmap,dim=1),mask)
this to calculate
the output is .jpg and target is bmp file.
seems not good