tf.depth_to_space is an alternative approach to increasing the height and width of a tensor for decoders. http://www.inference.vc/holiday-special-deriving-the-subpixel-cnn-from-first-principles/
It is sometimes referred to as SubPixel method, and it reduces artifacts that would otherwise come from strided deconvolution.
tf.space_to_depth instead of strided convolutions in the encoder in order to ensure symmetry in the network.
Hope that explains things!