Find the median of a single channel using OpenCv

cv_median.cpp

namespace cv {
    // calculates the median value of a single channel
    // based on https://github.com/arnaudgelas/OpenCVExamples/blob/master/cvMat/Statistics/Median/Median.cpp
    double median( cv::Mat channel )
    {
        double m = (channel.rows*channel.cols) / 2;
        int bin = 0;
        double med = -1.0;

        int histSize = 256;
        float range[] = { 0, 256 };
        const float* histRange = { range };
        bool uniform = true;
        bool accumulate = false;
        cv::Mat hist;
        cv::calcHist( &channel, 1, 0, cv::Mat(), hist, 1, &histSize, &histRange, uniform, accumulate );

        for ( int i = 0; i < histSize && med < 0.0; ++i )
        {
            bin += cvRound( hist.at< float >( i ) );
            if ( bin > m && med < 0.0 )
                med = i;
        }

        return med;
    }
}