Lab, Luv and XYZ conversions rewritten to wide intrinsics (#14106)
* rgb2xyz<float> re-vectorized
* rgb2xyz_i vectorized for ushort and uchar
* xyz2rgb<float> vectorized
* xyz2rgb_i vectorized for both uchar and ushort
* intermediate conversions (int->float) rewritten
* packed rgb2luv rewritten
* (some) float conversions rewritten
* burnt volatile int _3 and similar
* RGB2Lab_b rewritten
* tests: logging made better
* RGB2Lab_f (LRGB path) rewritten
* Lab2RGBfloat rewritten
* Lab2RGBinteger and Lab2RGB_b rewritten to wide universal intrinsics
* Luv2RGBinteger wide vectorized
* RGB2Lab_b fixed: v_sub_wrap instead of saturated sub
* warnings fixed
* trying to fix compilation on older compilers
* using 16x8 registers for 8-element dot product
* cleanup added
* splineInterpolate: loop unrolled, perf fix for f32x4
* Lab2RGBfloat: grab 2x more data to process on f32x4
* nrepeats for Luv2RGBfloat, +20% perf
* minor
* nrepeats to RGB2Lab_f
* Lab2RGBinteger: no tab for linear BGR
* nrepeats for RGB2Luvfloat
* Luv2RGBinteger: no tab for linear RGB
* +10% more to perf of Luv2RGBfloat
* nrepeats for 256-simd for Lab2RGBfloat
* less warnings
* BOM removed
* CV_SIMD_WIDTH used for lanes number checking
* trilinearPackedInterpolate: 128-bit specialization added
* fix build; no vx_cleanup(), instrumentation instead
Extend optical flow tutorial (#14314)
* extend python optical flow tutorial with cpp example code and add it to general tutorial directory
* remove unused parameters, fix comparison between signed and unsigned int
* fix hsv range problem
* switch to samples::findFile for sample file location
* switch to command line parameter for path
* remove old tutorial as in 14393
* minor fixes
Extend meanshift tutorial (#14393)
* copy original tutorial and python code
* add cpp code, fix python code
* add camshift cpp code, fix bug in meanshift code
* add description to ToC page
* fix shadowing previous local declaration
* fix grammar: with -> within
* docs: remove content of old py_meanshift tutorial, add link
* docs: replace meanshift tutorial subpage in Python tutorials
* switch to ref to fix wrong breadcrumb navigation
* switch to cmdline for path as in #14314
* Apply suggestions from code review
* order programming languages alphabetically
