[GSoC 2019]Alphamatting

[muskaankularia]

Merge with extra: opencv/opencv_extra#668

Adding functionality of alphamatting algorithm - Implementation of "Designing Effective Inter-Pixel Information Flow for Natural Image Matting"

code in src file can be run by - g++ -std=c++11 alphac.cpp pkg-config --cflags --libs opencv
by giving appropriate input.

third party libraries used for

• KDtree(nanoflann)
• Eigen library for conjugate gradient method for Sparse matrices.

I have added the tests

• yet to run them and resolve the build errors.

opencv_extra=master

[alalek]

Files changed 323
+120,465

Lets avoid placing of 3rdparty libraries into OpenCV code base.
Assume that Eigen is installed and properly detected by CMake automatically.
For custom Eigen installation (e.g., on Windows) use:

cmake -DHAVE_EIGEN=1 -DEIGEN_INCLUDE_PATH=<path_to_eigen> ...

On Linux install Eigen via package manager - it will be detected automatically.

Add check for HAVE_EIGEN value and disable module if not available.