my code :
    {
        string filename("g:/lib/opencv/samples/data/lena.jpg");
        Mat _I = imread(filename.c_str(), IMREAD_COLOR);

        cv::Mat I = _I;

        if (I.depth())
            cv::normalize(I, I, 0., 255., cv::NORM_MINMAX, CV_8U);

        if (I.channels() == 3)
        {
            cv::Mat Lab, tmp;
            std::vector<cv::Mat> cns;
            cv::cvtColor(I, Lab, cv::COLOR_BGR2Lab);
            cv::decolor(Lab, I, tmp);

        }

        cv::Mat hist;

        cv::calcHist(std::vector<cv::Mat>(1, I), { 0 }, cv::noArray(), hist, { 256 }, { 0.f,256.f });


        cv::Mat hd;

        {
            cv::Mat curr = hist.rowRange(0, hist.rows - 1);
            cv::Mat next = hist.rowRange(1, hist.rows);

            cv::absdiff(next, curr, hd);
        }

        hd.convertTo(hd, CV_32S);

        double thresh = cv::mean(hd)(0);
//        cout << utils::iqr(hd)(0);
        hd = hd > thresh;

        cv::Mat1i idx;

        int i = 0;
        for (auto it_current = hd.begin<uchar>(), it_next = hd.begin<uchar>() + 1; it_next != hd.end<uchar>(); it_current++, it_next++, i++)
        {
            uchar current = *it_current;
            uchar next = *it_next;

            if (current && !next)
                idx.push_back(i);
            if (!current && next)
                idx.push_back(i + 1);
        }

        std::cout << idx << std::endl;
    }
 output in c++
[9;
 9;
 11;
 14;
 16;
 20;
 22;
 24;
 26;
 26;
 28;
 30;
 33;
 34;
 38;
 39;
 44;
 44;
 46;
 46;
 54;
 54;
 56;
 57;
 61;
 63;
 65;
 65;
 67;
 69;
 71;
 71;
 73;
 73;
 75;
 75;
 79;
 81;
 83;
 91;
 94;
 95;
 98;
 98;
 100;
 105;
 112;
 114;
 117;
 118;
 121;
 121;
 123;
 124;
 127;
 127;
 129;
 133;
 135;
 136;
 138;
 143;
 151;
 151;
 158;
 159;
 164;
 164;
 188;
 188;
 193;
 195;
 204;
 204;
 209;
 209;
 211;
 211;
 213;
 213;
 216;
 216]
******************************

my python code :

    imgpath="g:\\lib\\opencv\\samples\\data\\lena.jpg"
    I = cv2.imread(imgpath,cv2.IMREAD_COLOR)
    I, _ = cv2.decolor(cv2.cvtColor(I, cv2.COLOR_BGR2Lab))
    h = cv2.calcHist([I],[0],None,[256],[0,256]).astype(np.int32).reshape((-1,))



    print(h.dtype, I.dtype, I.shape, h.min(), h.max(), I.min(), I.max())

    hd = np.abs(np.diff(h))


    thresh = np.mean(hd)

    print(thresh, np.mean(hd), iqr(hd),flush=True)

    hd = hd > thresh

    print(hd)

    idx = list()

    for i in range(254):
        if hd[i] and not hd[i+1]:
            idx.append(i)
        elif not hd[i] and hd[i+1]:
            idx.append(i+1)
    print(idx)

python output
[9, 9, 11, 14, 16, 20, 22, 24, 26, 26, 28, 30, 33, 34, 38, 39, 44, 44, 46, 46, 54, 54, 56, 57, 61, 63, 65, 65, 67, 69, 71, 71, 73, 73, 75, 75, 79, 81, 83, 91, 94, 95, 98, 98, 100, 105, 112, 114, 117, 118, 121, 121, 123, 124, 127, 127, 129, 133, 135, 136, 138, 143, 151, 151, 158, 159, 164, 164, 188, 188, 193, 195, 204, 204, 209, 209, 211, 211, 213, 213, 216, 216]