In Chapter 1, Getting Started, we discussed max pooling. Max pooling is a sampling strategy that picks the maximum value from a window. This could be reversed for upsampling. Each value can be surrounded with zeros to upsample the layer, as shown here:
The zeros are added at the same locations which are the numbers that are upsampled. Un-pooling can be improved by remembering the locations of downsampling and using it for upsampling, as shown here:
Index-wise, upsampling yields better results than appending ...
