OpenCV numpy to cv::Mat conversion

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I inherited an application with opencv, shiboken and pyside and my first task was to update to qt6, pyside6 and opencv 4.5.5. This has gone well so far, I can import the module and make class instances etc. However I have a crash when passing numpy arrays:

I am passing images in the form of numpy arrays through python to opencv and I am using pyopencv_to to convert from the array to cv::Mat. This worked in a previous version of opencv (4.5.3), but with 4.5.5 it seems to be broken.

When I try to pass an array through pyopencv_to, I get the exception opencv_ARRAY_API was nullptr. My predecessor solved this by directly calling PyInit_cv2(), which was apparently previously included via a header. But I cannot find any header in the git under the tag 4.5.3 that defines this function. Is this a file that is generated? I can see there is a pycompat.hpp, but that does not include the function either.

Is there a canonical way to initialize everything so that numpy arrays can be passed properly? Or a tutorial anyone can point me to? My searches have so far not produced any useful hints.

Thanks a lot in advance! :)

opencv numpy python c++
1 Answers

I finally found a solution. I dont know if this is the correct way of doing it, but it works.

I made a header file that contains

PyMODINIT_FUNC PyInit_cv2();

as a forward declaration and then copied over everything in the modules/python/src2 directory. I assumed this was already happening in the cv2.cpp file, because there is already exactly that line (in cv2.cpp).

But just adding that include works perfectly fine, apparently. Now I can call the init function when my own module is initialized and it seems to properly set all the needed state.

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