some questions about training input

[kidcats]

Thank you for your very good work!
now i hava one question.

    def forward(self, iteration, save, viz_split,
                xs, ys, **kwargs):

i know xs is original image and mask,but i can not understand ys mean what. and i see ys in calculate loss as gt.
could you tell more detail about dateset pre-processing?
thanks