Maskrcnn_resnet50_fpn normalization

It looks like the images are not normalized when training maskrcnn_resnet50_fpn. See vision/ at main · pytorch/vision · GitHub where hflip is the default argument for the training recipe defined here vision/references/detection at main · pytorch/vision · GitHub

Is it intentional? Why is normalization not applied?

Edit: I also see it mentioned here

Note that these models don’t require the images to be normalized, so we don’t need to use the normalized batch

but still not sure why.