how to prepare the custom datasets?

[slowlypasser]

I use the mask images as label(background is 0，foreground is 255),but it can not work when "--label_nc"==2 or == 256.Only when I change the mask images(background is 0，foreground is 1) ,and set "--label_nc"==2,it works.I don't know why it can works.
Is it the problem of the custom datasets?