the means of Avg. flow in fig.6 of paper

[famt0531]

Thanks for your wonderful work, and i want to know the meaning of Avg. flow which is written in the caption of fig6. Moreover, the last decoder results flows with the channel number of 3 in AMT-S, but in the process of visualizing optical flow, the channel number are needed to be 2, how do you deal with that?

looking forward to your reply, thanks again