NAryMatIterator Class Reference
[Basic structures]

    void computeNormalizedColorHist(const Mat& image, Mat& hist, int N, double minProb)
    {
        const int histSize[] = {N, N, N};

        // make sure that the histogram has a proper size and type
        hist.create(3, histSize, CV_32F);

        // and clear it
        hist = Scalar(0);

        // the loop below assumes that the image
        // is a 8-bit 3-channel. check it.
        CV_Assert(image.type() == CV_8UC3);
        MatConstIterator_<Vec3b> it = image.begin<Vec3b>(),
                                 it_end = image.end<Vec3b>();
        for( ; it != it_end; ++it )
        {
            const Vec3b& pix = *it;
            hist.at<float>(pix[0]*N/256, pix[1]*N/256, pix[2]*N/256) += 1.f;
        }

        minProb *= image.rows*image.cols;

        // initialize iterator (the style is different from STL).
        // after initialization the iterator will contain
        // the number of slices or planes the iterator will go through.
        // it simultaneously increments iterators for several matrices
        // supplied as a null terminated list of pointers
        const Mat* arrays[] = {&hist, 0};
        Mat planes[1];
        NAryMatIterator itNAry(arrays, planes, 1);
        double s = 0;
        // iterate through the matrix. on each iteration
        // itNAry.planes[i] (of type Mat) will be set to the current plane
        // of the i-th n-dim matrix passed to the iterator constructor.
        for(int p = 0; p < itNAry.nplanes; p++, ++itNAry)
        {
            threshold(itNAry.planes[0], itNAry.planes[0], minProb, 0, THRESH_TOZERO );
            s += sum(itNAry.planes[0])[0];
        }

        s = 1./s;
        itNAry = NAryMatIterator(arrays, planes, 1);
        for(int p = 0; p < itNAry.nplanes; p++, ++itNAry)
            itNAry.planes[0] *= s;
    }