MATLAB: Imshow and plot not displaying when using opticalFlow

Computer Vision ToolboxMATLABoptical flowplot

Hi, Following the optical flow examples, the code below is behaving in an odd way. If I only use imshow on the image it will refresh in real-time (i.e comment out the plot command), however if I try to plot the optical flow vectors, I will only get the very last frame displayed once the loop has completed. Could anyone shed any light on this?
vidDevice = imaq.VideoDevice('winvideo', 1);
optical = opticalFlowHS;
nFrames = 0;
while (nFrames<100)
    nFrames = nFrames + 1;
    rgbData = step(vidDevice);
    grey = rgb2gray(rgbData);
    optFlow = estimateFlow(optical,grey);
      imshow(rgbData);
      hold on
      plot(optFlow, 'DecimationFactor',[5 5],'ScaleFactor',25);
      hold off
  end
  release(vidDevice);
Many thanks

Best Answer

Try to insert a drawnow command to allow Matlab to update the display.
It will be faster to create the axes and image objects once before the loop and update the 'CData' property inside the loop only.
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