Any recommendation on visualize these flow?

[Zhe Wang]

I tried to re-implement https://arxiv.org/pdf/2004.06704.pdf Figure 5 using code of https://github.com/open-mmlab/mmcv/blob/master/mmcv/visualization/optflow.py, however, default settings give me the single color.

[lizz]

for simple, casual visualization, you may try the png format, by using -st=png

more seriously, there are some python flow visualization packages out there.