We have an OpenCV problem of opening (and writing) file paths that contain non-ASCII characters on Windows. Affected functions are: cv::imread(), cv::imwrite(), ...
As far as I saw in the OpenCV source code, it uses fopen even on Windows (instead of _wfopen) and AFAIK fopen does not handle non-ASCII characters on Windows.
I saw questions OpenCV imread with foreign characters and imread(openCV),QString unicodes but still didn't understand a proper way of solving the problem. From the questions above I saw that there could be some trick using QStrings, but if it works what does it exactly do? How does it transform a unicode string to a character array that will be accepted by Windows' fopen()?
P.S. We don't use QT
The way to do this without hacking the OpenCV source code is to use _wfopen (as Remy suggested) to read the whole file into a memory buffer. Then use OpenCV's function imdecode to create a cv::Mat from that buffer.
You can do the reverse too, if necessary - i.e. use imencode to write an image to a memory buffer, then use _wfopen to open a file with a UNICODE name and write the buffer to it (alternatively, you could just imwrite to a temporary file and then move/rename it using the appropriate API function).