Lab/XYZ modes have been postponed (color_lab.cpp):
- need to split code for tables initialization and for pixels processing first
- no significant performance improvements for switching between SSE42 / AVX2 code generation

Do not try to process empty inputs.

color.cpp split (#10869)

* initial split is done

* files renamed (these names are excluded during compilation)

* IPP code moved to corresponding files

* splineBuild, splineInterpolate -> color_lab.cpp

* Lab, Luv: little refactored

* it compiles (didn't check work); Lab OCL code moved to color_lab.cpp

* cvtcolor.cl: Lab/Luv part moved to color_lab.cl

* cvtcolor.cl: color_rgb.cl extracted

* cvtcolor.cl: color_yuv.cl separated

* cvtcolor.cl: color_hsv.cl extracted

* cvtcolor.cl: extracted to color_lab.cl and color_rgb.cl

* helper functions moved to hpp file

* Lab, Luv: moved to color_lab.cpp

* CPU XYZ: to color_lab.cpp

* OCL XYZ: to color_lab.cpp

* warning fixed

* CvtHelper added

* CPU YUV: to color_yuv.cpp, helpers to color.hpp

* CPU HLS/HSV: to color_hsv.cpp

* CPU BGR2BGR: to color_rgb.cpp

* CPU RGB: to color_rgb.cpp

* extra arg removed

* CPU YUV: to color_yuv.cpp

* color code decoded

* OclHelper added, some funcs rewritten

* color_lab.cpp: refactored to use OclHelper

* OCL RGB: to color_rgb.cpp

* OCL HLS/HSV: to color_hsv.cpp

* OCL YUV: to color_yuv.cpp

* OCL YUV planes: to color_yuv.cpp

* OCL: color code reduced

* licence to demosaicing.cpp

* IPP func tables to color_rgb.cpp

* code cleanup

* HAVE_OPENCL ifdefs added

* helpers made more common

* fixed two plane YUV with separate mats

* fixed warning in gcc7.2.0

* precomp header fixed

* color space classification functions fixed

* helpers fixed

* rename: isSRGB -> is_sRGB

* add (untested) JavaCamera2View class

* initial fixes

* minor cleanup

* exclude JavaCamera2View from build for older SDK version

* fix method name typo

* add asserts + sanity checks

* fix preview format checks

* fix the memory leak

* export cvtTwoPlaneYUVtoBGR for Java usage

* add handling for two-plane YUV frames (C wrapper still missing)

* add two-plane cvtColor helper function

* fix warnings

* actually use the new cvtColorTwoPlane helper func

* fix wrong output matrix size

* fix wrong conversion type

* simplify method signature, add error condition

* minor fixes to Mat types

* remove leftover semaphore from camera api 1

* android: JavaCamera2View minor refactoring

- re-apply Java code style
- imports cleanup
- dump exceptions information

* android: JavaCamera2View: pause/resume fixes

* android: JavaCamera2View: fix mScale

Found via `codespell`

* lab_tetra squashed

* initial version is almost written

* unfinished work

* compilation fixed, to be debugged

* Lab test removed

* more fixes

* Luv2RGBinteger: channels order fixed

* Lab structs removed

* good trilinear interpolation added

* several fixes

* removed Luv2RGB interpolations, XYZ tables; 8-cell LUT added

* no_interpolate made 8-cell

* interpolations rewritten to 8-cell, minor fixes

* packed interpolation added for RGB2Luv

* tetra implemented

* removing unnecessary code

* LUT building merged

* changes ported to color.cpp

* minor fixes; try to suppress warnings

* fixed v range of Luv

* fixed incorrect src channel number

* minor fixes

* preliminary version of Luv2RGBinteger is done

* Luv2RGB_b is in progress

* XYZ color constants converted to softfloat

* Luv test: precision fixed

* Luv bit-exactness test added

* warnings fixed

* compilation fixed, error message fixed

* Luv check is limited to [0-2,0-2,0-2] by XYZ

* L->Y generation moved to LUT

* LUTs added for up and vp of Luv2RGB_b

* still works

* fixed-point is done, works at maxerr 2

* vectorized code is done, 2x slower than original

* perf improved by 10%

* extra comments removed

* code moved to color.cpp

* test_lab.cpp updated

* minor refactoring

* test added for Luv2RGB

* OCL Luv2RGB_b: XYZ are limited to [0, 2]; docs updated

* Luv2RGB_b rewritten to universal intrinsics

* test_lab.cpp moved to luv_tetra branch

* Imgproc_ColorLab_Full.accuracy test fixed

* Lab and Luv tests: rewritten, constants explained

* CV_ColorCvtBaseTest: added methods for 8u implementations

* Lab2RGB_b: bit-exactness enabled for all modes; non-vectorized code fixed to comply with vectorized

* srgb support added

* XYZ constants made softdouble

* bit-exact tests written for Lab

* ColorLab_full test fixed

* reverted: no 8u convertors for CV_ColorCvtBaseTest

* added checksum-based test for Lab bit-exactness

* extra declarations removed

* Lab test fix: stop at first mismatch

* test info output improved

* error message fixed

* lab_tetra squashed

* initial version is almost written

* unfinished work

* compilation fixed, to be debugged

* Lab test removed

* more fixes

* Luv2RGBinteger: channels order fixed

* Lab structs removed

* good trilinear interpolation added

* several fixes

* removed Luv2RGB interpolations, XYZ tables; 8-cell LUT added

* no_interpolate made 8-cell

* interpolations rewritten to 8-cell, minor fixes

* packed interpolation added for RGB2Luv

* tetra implemented

* removing unnecessary code

* LUT building merged

* changes ported to color.cpp

* minor fixes; try to suppress warnings

* fixed v range of Luv

* fixed incorrect src channel number

* minor fixes

* preliminary version of Luv2RGBinteger is done

* Luv2RGB_b is in progress

* XYZ color constants converted to softfloat

* Luv test: precision fixed

* Luv bit-exactness test added

* warnings fixed

* compilation fixed, error message fixed

* test_lab.cpp removed

- Optimizations set change. Now IPP integrations will provide code for SSE42, AVX2 and AVX512 (SKX) CPUs only. For HW below SSE42 IPP code is disabled.
- Performance regressions fixes for IPP code paths;
- cv::boxFilter integration improvement;
- cv::filter2D integration improvement;

RGB2Lab_f and trilinear interpolation code are in separate branch; cubeRoot(x) instead of std::pow(x, 1.f/3.f)

file with internal accuracy&speed tests moved to lab_tetra branch

RGB2Lab_f added, bugs fixed, moved to float

several bugs fixed

LUT fixed, no switch in tetraInterpolate()

temporary code; to be removed and rewritten

before refactoring

extra interpolations removed, some things to do left

added Lab2RGB_b +XYZ version, etc.

basic version is done, to be sped up

tetra refactored

interpolations: LUT for weights, refactor., etc.

address arithm optimized

initial version of vectorized code added (not compiling now)

compilation fixed, now segfaults

a lot of fixes, vectorization temp. disabled

fixed trilinear shift size, max error dropped from 19 to 10

fixed several bugs (255 vs 256, signed vs unsigned, bIdx)

minor changes

packed: address arithmetics fixed

shorter code

experiments with pure integer calculations

Lab2RGB max error decreased to 2; need to clean the code

ready for vectorization; need cleaning

vectorized, to be debugged

precision fixed, max error is 2

Lab->XYZ shortened

minor fixes

Lab2RGB_f version fixed, to be completely rewritten using _b code

RGB2Lab_f vectorized

minors

moved to separate file

refactored Lab2RGB to float and int versions

minor fix

Lab2RGB_f vectorized

minor refactoring

Lab2RGBint refactored: process methods, vectorize by 4 pix

Lab2RGB_f int version is done

cleanup extra code

code copied to color.cpp

fixed blue idx bug

optimizations enabled when testing; mulFracConst introduced

divConst -> mulFracConst

calc min time in perf instead of avg

minors

process() slightly sped up

Lab2RGB_f: disabled int version

reinterpret added, minor fixes in names

some warnings fixed

changes transferred to color.cpp

RGB2Lab_f code (and trilinear interpolation code) moved to rgb2lab_faster

whitespace

shift negative fixed

more warnings fixed

"constant condition" warnings fixed, little speed up

minor changes

test_photo decolor fixed

changes copied to test_lab.cpp

idx bounds checking in LUT init

several fixes

WIP: softfloat almost integrated

test_lab partially rewritten to SoftFloat

color.cpp rewritten to SoftFloat

test_lab.cpp: accuracy code added

several fixes

RGB2Lab_b testing fixed

splineBuild() rewritten to SoftFloat

accuracy control improved

rounding fixed

Luv <=> RGB: rewritten to SoftFloat

OCL cvtColor Lab and Lut rewritten to SoftFloat

minor fixes

refactored to new SoftFloat interface

round() -> cvRound, etc.

fixed OCL tests

softfloat.cpp: internal functions made static, unused ones removed

meaningful constants

extra lines removed

unused function removed

unfinished work

it works, need to fix TODOs

refactoring; more calls rewritten

mulFracConst removed

constants made bit exact; minors

changes moved to color.cpp

fixed 1 bug and 4 warnings

OCL: fixed constants

pow(x, _1_3f) replaced by cubeRoot(x)

fixed compilation on MSVC32

magic constants explained

file with internal accuracy&speed tests moved to lab_tetra branch

 - let it possible to reach Bayer2BGRA conversion

* fixed wrong equivalence in YUV conversion

* fixed channel order from YVU to YUV

--perf_instrument parameter now has int type and 0, 1, 2 modes (1 - simple trees, 2 - expanded trees for functions with same name but different calling address);

Maximum depth limit var was added to the instrumentation structure;

Trace names output console output fix: improper tree formatting could happen;
Output in case of error was added;

Custom regions improvements;

Improved timing and weight calculation for parallel regions; New TC (threads counter) value to indicate how many different threads accessed particular node;

parallel_for, warnings fixes and ReturnAddress code from Alexander Alekhin;