ToTensor transforms the image to a tensor with range [0,1].
Thus it already implies some kind of normalization. If you want to use the normalization transform afterwards you should keep in mind that a range of [0,1] usually implies mean and std to be around 0.5 (the real values depend on your data). These are the values you should pass to the normalization transform as mean and std.



 pytorch docs:

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].


Which means you need to have your image in range of [0,255] before. Maybe your loaded image already lies in a range of [0,1]?