#roi-pooling

Question 1: Single choice

R-CNN runs a CNN forward pass separately on each of about 2000 region proposals per image. What is the main change in Fast R-CNN?

It runs the CNN once per image and pools each proposal's features from that map1
It replaces selective search with a learned region proposal network sharing the CNN2
It adds a branch that predicts a pixel mask for each proposal3
It drops region proposals and predicts boxes directly on a fixed grid4