I'm not sure I understand your point here.  If you are writing from a .py script, presumably you would opt for making the ImageCorrFunc and pass that as the `noise_pad` parameter for the reasons you suggest.  And from the config stuff, we're kind of stuck with having the value be a string, which gets interpreted as a file name.  

Are you just balking at the possibility of passing in an Image that is already in memory, but isn't yet converted to an ImageCorrFunc?  I guess that just seemed like a logical intermediate option without a specific application in mind.  It's only two lines of code given that the code for doing the other options are already there, so it was easy to add in case there is some good reason to use it.