Optimization ximgproc::thinning

[sturkmen72]

Pull Request Readiness Checklist

credits @ulikoehler https://github.com/ulikoehler/cv_algorithms

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

[ulikoehler]

@sturkmen72 Thanks for crediting me! I'm fine with releasing this code under another license if that's useful. Apache License v2.0 appears to be the same though.

In any case, I fully support this merge request :-)

[sturkmen72]

@ulikoehler Performance increase almost doubled. let me try to find out why GUOHALL gives different result

[----------] 2 tests from ximgproc_Thinning
[ RUN      ] ximgproc_Thinning.simple_ZHANGSUEN
[       OK ] ximgproc_Thinning.simple_ZHANGSUEN (14 ms)
[ RUN      ] ximgproc_Thinning.simple_GUOHALL
/build/precommit-contrib_linux64/4.x/opencv_contrib/modules/ximgproc/test/test_thinning.cpp:28: Failure
Expected equality of these values:
  0
  cvtest::norm(src, dst, NORM_INF)
    Which is: 255
[  FAILED  ] ximgproc_Thinning.simple_GUOHALL (13 ms)
[----------] 2 tests from ximgproc_Thinning (27 ms total)

[sturkmen72]

@vrabaud could you take a look

[vrabaud]

Nice clean-up ! And faster too.

[sturkmen72]

Please merge the PR #3750 (tested manually) before this PR to give proper credit, as this PR is based on it.

[sturkmen72]

@asmorkalov what is your opinion merging the PR #3750 (tested manually) before this PR to give proper credit, as this PR is based on it.