Similarity Measurement between color image using OpenCv library

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C++

I'm working with a CBIR(Content-based Image Retrieval) project which will draw RGB histogram of images and also calculate the distance between other images with query image.

I';m using VS 2008 - MFC and OpenCV Library. The method i wanted to use for calculating the distance is Euclidean Distance(ED), but somehow i failed to find a method in OpenCV to help me to this calculation.

There is a cvCompareHist function in OpenCV where help us to compare 2 histogram with one of the following method:
1) Correlation : cv_COMP_CORREL
2) Chi-Square : cv_COMP_CHISOR
3) Intersection : cv_COMP_INTERSECT
4) Bahttacharyya Distance : cv_COMP_BAHTTACHARYYA

My Question:

Is there any function can help me do the comparison in OpenCV?
If yes, which function?
If no, how do i code it myself for this formula?