Arturas_Druteika:

Many tutorials show how to calculate mean and std after we create loaders, but isn’t it worthless to know these numbers if we already have all loaders created?


I don’t think it’s worthless, as you would then be able to use these calculated stats in your Normalize transformation.
On the other hand you could also try to use e.g. the ImageNet stats, if your data is “similar” to the ImageNet dataset and you expect the mean and stddev to be approx. the same.