title: Blob-detection in multiple ROI's in a single image / frame, using OpenCV - is it possible?
body: <p>Is it possible to perform blog-detection where there are multiple Regions-of-Interest in a frame, using OpenCV ?</p>
  
  <p>I have been reading the 'Learning OpenCV' book, which is based on 1.x 'C' API, and I realized that the ROI information in IplImage accommodates as single ROI, thus all operations would assume a single ROI. Does it mean that I cannot work with multiple ROI's ?</p>
  
  <p>My requirement of multiple ROI stems from a desire to reduce processing while I know for sure that the blobs of interest for me, happen to be in about only 30-40% of the total image area, split into 3-4 regions. Operating on entire image means an overhead of 60-70% in terms of processing power / time. Or, am I missing something very basic here ?</p>
  
  <p><strong><em>Edited:</em></strong></p>
  
  <p>Found <a href="https://stackoverflow.com/questions/7946383/using-roi-in-opencv">this</a> question on SA, and looks like this could be one approach. If I understood it correctly, I could use a mask over the entire frame, unmasking the multiple ROI's, but not use a ROI per-se, in IplImage. Is that right ? Also, does this serve my purpose of reducing processing requirement, which was my main objective behind using ROI ?</p>