Learning OpenCV 4 Computer Vision with Python 3 - Third Edition

Masking a copy operation

The rects module is implemented in rects.py. We already saw a call to the rects.swapRects function in the previous section. However, before we consider the implementation of swapRects, we first need to a more basic copyRect function.

As far back as Chapter 2, Handling Files, Cameras, and GUIs, we learned how to copy data from one rectangular region of interest (ROI) to another using NumPy's slicing syntax. Outside the ROIs, the source and destination images were unaffected. Now, we want to apply further limits to this copy operation. We want to use a given mask that has the same dimensions as the source rectangle.

We shall copy only those pixels in the source rectangle where the mask's value is not zero. Other pixels ...