Why no normalization ?

Hi, 
In order to use vgg19, the following normalizing step has to be used:
(Values of the input image being between 0 and 1)
`normalize = transforms.Normalize(mean=[0.485, 0.456, 0.406],
                                     std=[0.229, 0.224, 0.225])`
cf : https://github.com/pytorch/vision#models
Why arn't you using here, not needed ?
Thx :)