title: What is the purpose of the ROI layer in a Fast R-CNN?
body: <p>In <a href="https://leonardoaraujosantos.gitbooks.io/artificial-inteligence/content/object_localization_and_detection.html" rel="noreferrer">this</a> tutorial about object detection, the fast R-CNN is mentioned. The ROI (region of interest) layer is also mentioned.</p>
  
  <p>What is happening, mathematically, when region proposals get resized according to final convolution layer activation functions (in each cell)?</p>