code about flow-based generate motion mask method

[tb2-sy]

Nice work! In the part of the motion mask in the readme, you mentioned that flow-base masks are too noisy. I also have the same feeling when using the code to generate the motion mask in Dynamic nerf, but I have some problems with the code of generate motion mask. In utils/generate_motion_mask.py line 128-131, why do h and w have to be divided by 2, which confuses me very much.