deltaCIEDE2000_ fix into the MCC module

[kevineor]

DeltaE CIEDE2000 function fix into MCC module

This function did not pass the test case 17 and 19 of Gaurav Sharma's test data.

This was due to a mistake into the "RT" value, it was computed with the value instead of .

Sources :

• Wikipedia ;
• The CIEDE2000 Color-Difference Formula : Implementation Notes, Supplementary Test Data, and Mathematical Observations.

And now i have a little question about this module, why color conversion and color distances classes are not exposed to the API ?
They are really useful because, at the moment, OpenCV can't convert sRGB D65 2° to CIELAB D50 2° or perform any CIE color comparison.

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• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or other license that is incompatible with OpenCV
• The PR is proposed to proper branch
• There is reference to original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
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[alalek]

/cc @riskiest Could you please take a look?

[kevineor]

Where does the test data come from? Should i change it?

[alalek]

Thank you!