Are there more examples about how to use ImageDataBunch?

I am trying to load the real MNIST data.
Here is the source code from keras: https://github.com/keras-team/keras/blob/master/keras/datasets/mnist.py
I want to fit the data into ImageDataBunch type, tried several apis, like from_folder, from_df, cannot make it work.
Any tips?
Thanks for the help in advance.