title: How to split a video frame into 9 pieces?
body: <p>I am using Opencv2 in Python3.<br/>
  I'm writing "shot boundary detection" program for news videos.<br/> 
  I've just need to split a video frame into 9 pieces for the beginning. But, i'm not sure how to do that cus i'm new in this field. I did it with cropping but it seems to me that it is not right thing to do to split a frame into pieces. <br/></p>
  
  <p>Note: When i search with "my title", i couldn't reach the ROI answer. But it now seems that this is ROI.</p>