More details about lab

1. prepro_images.py: pre-process the images in COCO dataset (val2014.zip and train2014.zip). The dates are in /homework/datasets

2. The weights of pre-trained ResNet101 is in ./data/imagenet_weights

3. x(t) uses the previous ground truth t(t-1) in training but x(t-1) in testing

4. The V bar in topdown model is taking average pooling on each feature map (7x7x2048→1x2048)