* Add version of descr_of function taking vector of Mat

* Overload descr_of function for cv::Mat

* Add template function instead of copypasting and change tests a little

* GAPI: document GCall's recursive behavior

* Move documentation outside the class

Improve stitching detailed (#13584)

* Added block size getter/setters

* Added a bunch of new features to the stitching_detailed sample

* Do not required XFEATURES2D for default use

* Add support for akaze features in stitching_detailed

* Improved sample logs

Add Matplotlib Perceptually Uniform Sequential colormaps (viridis, plasma, inferno, magma, cividis, twilight and twilight shifted).

Fix a bug in cv :: merge when array of 3-channel mat is input (#13544)

* Mat merge function bug fix - Bug fix of merge function of 3-channel vector <Mat> of 3 or 4 matrices

* Add Core_merge test for opencv#13544

* fixups

Channels exposure compensators (#13532)

* feed compatible with single channel images

* Simplified BlockGainCompensator::apply

* ChannelsCompensator

* BlocksChannelsCompensator

* Make source level compatibility detector happy