Questions

1. Why is a replay buffer used in a DQN?
2. Why do we use target networks?
3. Why do we stack four frames into one state? Will one frame alone suffice to represent one state?
4. Why is the Huber loss sometimes preferred over L2 loss?
5. We converted the RGB input image into grayscale. Can we instead use the RGB image as input to the network? What are the pros and cons of using RGB images instead of grayscale?