So far, you have learned several ways to control the camera, blend images, detect and classify objects, compare images, and apply geometric transformations. These skills can help you solve countless problems in your iOS applications.
Next, you might want to study a collection of advanced OpenCV projects. As of May 2016, there are no other books on OpenCV 3 for iOS. However, with your iOS skills, you can adapt code from any OpenCV 3 book that uses C++. Consider the following options from Packt Publishing:
OpenCV 3 Computer Vision Application Programming Cookbook, Third Edition: This new edition will be published later in 2016. The book provides extensive coverage of OpenCV's C++ API with more than 100 practical samples of reusable code.
Learning Image Processing with OpenCV: This book is a great choice if you are specifically interested in computational photography or videography. The projects use C++ and OpenCV 3.
OpenCV 3 Blueprints: This book...