We saw in the earlier section that Fast R-CNN brought down the time required for scoring (testing) images drastically, but the reduction ignored the time required for generating Region Proposals, which use a separate mechanism (though pulling from the convolution map from CNN) and continue proving a bottleneck. Also, we observed that though all three challenges were resolved using the common features from convolution-map in Fast R-CNN, they were using different mechanisms/models.
Faster R-CNN improves upon these drawbacks and proposes the concept of Region Proposal Networks (RPNs), bringing down the scoring (testing) time to 0.2 seconds per image, even including time for Region Proposals. ...
