OpenCV - Python's Numpy.transpose by axes equivalent for cv::Mat?

Question

I'm trying to translate the below Python code that uses numpy arrays into C++ and use cv::Mat instead of numpy:

def get_face_mask(im, landmarks):
    im = numpy.zeros(im.shape[:2], dtype=numpy.float64)

    for group in OVERLAY_POINTS:
        draw_convex_hull(im,
                         landmarks[group],
                         color=1)

    im = numpy.array([im, im, im]).transpose((1, 2, 0))

    im = (cv2.GaussianBlur(im, (FEATHER_AMOUNT, FEATHER_AMOUNT), 0) > 0) * 1.0
    im = cv2.GaussianBlur(im, (FEATHER_AMOUNT, FEATHER_AMOUNT), 0)

    return im

(Full source code can be seen here)

I'm finding it a bit difficult to understand what the below lines does:

im = numpy.array([im, im, im]).transpose((1, 2, 0))

I don't seem to be able to find the equivalent of this in OpenCV C++ version.

Any help would be much appreciated.