Sorry to bother you , I read the document and

torchvision.transforms.ToTensor : Converts a PIL Image or numpy.ndarray (H x W x C) in the range [0, 255] to a torch.FloatTensor of shape (C x H x W) in the range [0.0, 1.0].

well, my flow matrix various from negative number to positive number, I use cv2.calcOpticalFlowFarneback fuction to calculate it, how can I fix this?
Thanks for your reply!