OpenCV visualization error

[mkisantal]

I built Darknet with OpenCV without a problem, and even imtest works well:
./darknet imtest data/eagle.jpg opens up a number of windows without a problem.

However, when I try to run YOLO object detection, I run into the following error:

data/dog.jpg: Predicted in 0.215194 seconds.
dog: 82%
car: 27%
truck: 65%
bicycle: 85%
OpenCV(3.4.1-dev) Error: Assertion failed ((flags & FIXED_TYPE) != 0) in type, file /opt/opencv/modules/core/src/matrix_wrap.cpp, line 807
terminate called after throwing an instance of 'cv::Exception'
  what():  OpenCV(3.4.1-dev) /opt/opencv/modules/core/src/matrix_wrap.cpp:807: error: (-215) Assertion failed: (flags & FIXED_TYPE) != 0 in function type

Aborted (core dumped)

So the inference runs without any problem, but the program crashes when it tries to show the results... Any idea what might be causing the problems here?

[mkisantal]

This line causes the error, by commenting it out I was able to show the detection results.

darknet/examples/detector.c

Line 619 in 80d9bec

save_image(im, "predictions");

[TheMikeyR]

I can see you are using OpenCV 3.4.1, there is currently a bug in C API: opencv/opencv#10963
Use OpenCV 3.4.0 or lower.

[mkisantal]

Thank you @TheMikeyR it solved my issue!

[maelvls]

Same issue in maelvls/homebrew-amc#4. Looks like cvSaveImage fails but I can't find out why ☹️ Is opencv/opencv#10963 responsible for this bug?

[molyswu]

Hi,mkisantal
How do you solved with this problem?

[maelvls]

I dropped the C headers and used the C++ bindings instead 👍
The C API is broken and isn’t maintained anymore