I learned OpenCV using the O'Reilly book by Bradski and Kaehler (back when it was OpenCV 2). I found it well-structured and it worked for me. They have an updated version for OpenCV 3.
However, I can't tell you if OpenCV is still the framework of choice and/or widely used in the field you want to go into.
However, I can't tell you if OpenCV is still the framework of choice and/or widely used in the field you want to go into.