Add on from previous post, there’s a strong and weak method to find the mean and standard deviation of your dataset:
View: CoarseNet/preprocess.py at master · Nikronic/CoarseNet · GitHub 23
Running another test with ResNet-18, it can be observe that the Strong Method does give a little performance boost (own == weak, own_strong == strong):

Screenshot from 2021-04-01 14-11-48878×645 64.1 KB

The mean from both methods are the same, the difference is in the calculations for standard deviation.