Should just be able to use the ImageFolder or some other dataloader to iterate over imagenet and then use the standard formulas to compute mean and std. at the channel level E.g., for mean keep 3 running sums, one for the R, G, and B channel values as well as a total pixel count (if you are using Python2 watch for int overflow on the pixel count, could need a different strategy). Then simply divide the running sums by the pixel count