question about header

[czb2133]

I found the RGBHeader
edsr.MeanShift(0, (0., 0., 0.), (128., 128., 128.))
and the pixel values of the image in dataloader are between 0-255. So what's the perpose of using it while it only turn the value to 0-2.
And how should i set the mean and std if i use a dataset whose image is 12-bit?