Velocity vector (optical flow etc.) to RGB color conversion

Question

I have computed an optical flow and I wish to convert this to images.

Following the tutorials of opencv2:

    mag, ang = cv2.cartToPolar(flow[...,0], flow[...,1])
    hsv = np.zeros_like(cv2.imread(img_path))
    hsv[...,1] = 255
    hsv[...,0] = ang*180/np.pi/2
    hsv[...,2] = cv2.normalize(mag,None,0,255,cv2.NORM_MINMAX)
    bgr = cv2.cvtColor(hsv,cv2.COLOR_HSV2BGR)

    cv2.imshow('optical flow',bgr)

I am able to do this, however the RGB image is not as smooth and continuous as the one that comes with more recent papers: such as T. Brox's High Accuracy Optical Flow Estimation Based on a Theory for Warping or FlowNet which looks like smooth, continuous regions as seen here: https://www.youtube.com/watch?v=JSzUdVBmQP4

Any recommendations how I can achieve this conversion instead of what I am doing (opencv tutorial)?

I have found a piece of Matlab script that might be achieving the latter one, but I do not understand how the conversion is made. Can someone explain?

    flow = mex_OF(double(im1),double(im2));

    scale = 16;
    mag = sqrt(flow(:,:,1).^2+flow(:,:,2).^2)*scale+128;
    mag = min(mag, 255); 
    flow = flow*scale+128;
    flow = min(flow,255);
    flow = max(flow,0);

    [x,y,z] = size(flow);
    flow_image = zeros(x,y,3);
    flow_image(:,:,1:2) = flow;
    flow_image(:,:,3) = mag;

    imwrite(flow_image./255,sprintf('%s/%s/flow_image_%s',save_base,video,frames{k}))

Thank you.