Python book on computer vision

Hi All, I am looking for a book on computer vision in python. I am relatively new to computer vision but have some experience in AI. I have learnt a fair amount form scikit-image documentation and trying things out, but need some more overview. Most of the books I have found are related to opencv. Does anyone have a book that they can recommend. I am more interested in getting an overview of the different techniques of object recognition and categorisation then code examples. Thanks Simon