* fixed tutorial code of py_matcher

* fixed imread mode

* Fix the bug in case determinant of rotation matrix is -1

* calib3d(test): check det(R) == 1

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

Check for "gutter" around displayed image. there was one row/column missing on the bottom/right.
Might as well set gutter = 0?

* Fix drawMatches and drawKeypoints for BGRA input images

* keep BGRA too

* Combine different input types for drawMatches test