CMake -DOPENCV_ENABLE_NONFREE:BOOL=ON

Thank you, but where should I make it? In xfeatures2d?

You have to build opencv and opencv_contrib (git cloneyourself). it is recommended to use them alongside the master branch or latest releases of OpenCV.

Then you can setOPENCV_ENABLE_NONFREE in cmake-gui or in cmake command line

I built opencv and opencv_contrib, but which cmake file I need?

if you built opencv and and opencv_contrib do it again :

CMake -DOPENCV_ENABLE_NONFREE:BOOL=ON -DOPENCV_EXTRA_MODULES_PATH=.your_path/opencv_contrib/modules

I 'm having the same problem.

I built opencv and opencv_contrib 3.4.3 and I set OPENCV_ENABLE_NONFREE in cmake-gui ON and I checked that the Non-free algorithms were installed.

In the test code of surf, at the following line:

detector = SURF::create(minHessian);

it enters in this parte of code (inside surf.cpp)

else // ! #ifdef OPENCV_ENABLE_NONFREE

Ptr<surf> SURF::create(double, int, int, bool, bool) { CV_Error(Error::StsNotImplemented, "This algorithm is patented and is excluded in this configuration; " "Set OPENCV_ENABLE_NONFREE CMake option and rebuild the library"); }

endif

What can I do to enable #ifdef OPENCV_ENABLE_NONFREE?

Thanks for any help

@carnar delete cmakecache.txt and rebuild opencv with OPENCV_ENABLE_NONFREE:BOOL=ON

I made it, but still it doesn't work.

Here what I have in the cmakecache.txt...I think is correct...

//Enable non-free algorithms OPENCV_ENABLE_NONFREE:BOOL=ON

//Where to look for additional OpenCV modules (can be ;-separated // list of paths) OPENCV_EXTRA_MODULES_PATH:PATH=C:/Codice/OpenCV/opencv_contrib-3.4.3/modules

I've noted that surf.cpp include

#include "precomp.hpp" and #include "surf.hpp". Both are only in the directory  'opencv_contrib-3.4.3\modules\xfeatures2d\src'.

Moreover 'precomp.hpp' include opencv_modules,hpp which has the following lines:

// This definition means that OpenCV is built with enabled non-free code.
// For example, patented algorithms for non-profit/non-commercial use only.
/* #undef OPENCV_ENABLE_NONFREE  */

Should I change anything here to define OPENCV_ENABLE_NONFREE = 1?

No don't change source code. again delete cmakecache an run cmakegui and set OPENCV_ENABLE_NONFEE and after generate you will see in cmake output :

    Unavailable:                 java js python2 python3
    Applications:                tests perf_tests apps
    Documentation:               NO
    Non-free algorithms:         YES

  Windows RT support:            NO