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You can perform band math using element-wise operations like this

    vector<Mat> channels;
    split(imageBGR, channels);
    Mat numeratorMat = channels[2] - channels[0]; // red - blue
    Mat denominatorMat = channels[2] + channels[0]; // red + blue
    Mat ratio;
    cv::divide(denominatorMat, numeratorMat, ratio, 1., 5); // here 5 specifies type of ratio (CV_32FC1)

Then you can do something like

   Mat newHue = (ratio.clone() - 0.5 ) * (-360); // float 32
   Mat newLigthness = Mat::ones(imageBGR.rows, imageBGR.cols, CV_32FC1);
   Mat newSaturation = Mat::ones(imageBGR.rows, imageBGR.cols, CV_32FC1);

   vector<Mat> newChannels;
   newChannels.push_back(newHue);
   newChannels.push_back(newSaturation);
   newChannels.push_back(newLigthness);
   Mat newHSL;
   cv::merge(newChannels, newHSL);