A lot of the input layers for pretrained networks (e.g. say ResNet-50) have the normalization parameters stored in the imageInputLayer properties. For example, for ResNet-50, the Mean is stored from the time it was trained on the ImageNet dataset, while properties like Standard Deviation, Min and Max are obtained from the training images on which we are performing the Transfer learning. This documentation captures more information on this topic.
In case we want to add normalization of input data to an existing deep learning model for transfer learning, we can replace the original image input layer from the model with a new image input layer. This will enable the normalization properties and we can change them accordingly.
We can open the network in Deep Network Designer:
Then we can delete the image input layer from the network and replace this with the image Input layer from the Layer Library.