尽管设置了标志 DOPENCV_ENABLE_NONFREE=ON，但运行 opencv 获得专利的 SIFT 和 SURF 的问题

Question

I'm currently working on opencv vers. 4.5.1 and I want to use SIFT and SURF but I run into the well known problem that they're patented. I already know that under 4.5.1 there is the possibility to use the flags DOPENCV_ENABLE_NONFREE=ON and DBUILD_opencv_xfeatures2d=ON . But when I use the following command for cmake

cmake -DOPENCV_EXTRA_MODULES_PATH=home/myname/opencv_build/opencv_contrib/modules/xfeatures2d/src -DOPENCV_ENABLE_NONFREE=ON -DBUILD_opencv_xfeatures2d=ON .

I run into the following problem:

-- The C compiler identification is GNU 9.3.0
-- The CXX compiler identification is GNU 9.3.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found OpenCV: /usr/local (found version "4.5.1") 
-- OpenCV library status:
--     config: /usr/local/lib/cmake/opencv4
--     version: 4.5.1
--     libraries: opencv_calib3d;opencv_core;opencv_dnn;opencv_features2d;opencv_flann;opencv_gapi;opencv_highgui;opencv_imgcodecs;opencv_imgproc;opencv_ml;opencv_objdetect;opencv_photo;opencv_stitching;opencv_video;opencv_videoio;opencv_aruco;opencv_bgsegm;opencv_bioinspired;opencv_ccalib;opencv_datasets;opencv_dnn_objdetect;opencv_dnn_superres;opencv_dpm;opencv_face;opencv_freetype;opencv_fuzzy;opencv_hfs;opencv_img_hash;opencv_intensity_transform;opencv_line_descriptor;opencv_mcc;opencv_optflow;opencv_phase_unwrapping;opencv_plot;opencv_quality;opencv_rapid;opencv_reg;opencv_rgbd;opencv_saliency;opencv_shape;opencv_stereo;opencv_structured_light;opencv_superres;opencv_surface_matching;opencv_text;opencv_tracking;opencv_videostab;opencv_wechat_qrcode;opencv_xfeatures2d;opencv_ximgproc;opencv_xobjdetect;opencv_xphoto
--     include path: /usr/local/include/opencv4
-- Configuring done
-- Generating done
CMake Warning:
  Manually-specified variables were not used by the project:

    BUILD_opencv_xfeatures2d
    OPENCV_ENABLE_NONFREE
    OPENCV_EXTRA_MODULES_PATH


-- Build files have been written to: /home/myname/Dokumente/test/project

The output in clion is:

terminate called after throwing an instance of 'cv::Exception'
  what():  OpenCV(4.5.1-dev) /home/myname/opencv_build/opencv_contrib/modules/xfeatures2d/src/surf.cpp:1027: error: (-213:The function/feature is not implemented) This algorithm is patented and is excluded in this configuration; Set OPENCV_ENABLE_NONFREE CMake option and rebuild the library in function 'create'

For hours I have been desperately trying to get the program running and the algorithms (SIFT, SURF) to be executed and have now reached the point where I (very, very reluctantly) want to downgrade opencv. (I simultaneously need this version of opencv for another project).

Does anyone have a tip for me on how I can still get the algorithms under 5.4.1 to work here. And otherwise, which OpenCV version (c++) should I use in order to use SIFT and SURF without problems. I did not find anything how I can downgrade the version in case of c++. All I found was in case of python.

Help would be very much appreciated!!!

Answer 1

Build OpenCV with the following command:

cmake -D CMAKE_BUILD_TYPE=Release \
      -D CMAKE_INSTALL_PREFIX=/usr/local \
      -D OPENCV_EXTRA_MODULES_PATH=path/to/opencv_contrib/modules \
      -D OPENCV_ENABLE_NONFREE=ON \
      path/to/opencv

Answer 2

There is no need to build OpenCV again to use SIFT algorithm, just use a version above 4.4.0.

Release highlights:

• SIFT (Scale-Invariant Feature Transform) algorithm has been moved to the main repository (patent expired)

for python:

pip install opencv-python==4.4.0.46

And access it directly ( no more xfeatures2d )

import cv2
sift = cv2.SIFT_create()