Do we need to subtract mean pixel values when extracting cnn feautre

Hi! I followed this [notebook](https://github.com/dmlc/mxnet-notebooks/blob/master/python/how_to/predict.ipynb) to extract image feature using pre-trained CNN model. I wonder do we need to subtract mean pixel values of imagenet before feature extraction. Other deep learning frameworks usually have this process, but I didn't find it in this notebook.