I haven't read the paper in full detail, but reading between the lines I'm guessing that there's a significant portion of manual processing and hand waving involved. From the abstract, emphasis mine:
> the second stage uses a pixel-wise nearest neighbor method to map the smoothed output to multiple high-quality, high-frequency outputs in a controllable manner.
My interpretation is that they select training data by hand and generate a bunch of outputs. Repeating the process until they like the final result. From the paper:
> we allow a user to have an
arbitrarily-fine level of control through on-the-fly editing of
the exemplar set (E.g., “resynthesize an image using the eye from this image and the nose from that one”).
> the second stage uses a pixel-wise nearest neighbor method to map the smoothed output to multiple high-quality, high-frequency outputs in a controllable manner.
My interpretation is that they select training data by hand and generate a bunch of outputs. Repeating the process until they like the final result. From the paper:
> we allow a user to have an arbitrarily-fine level of control through on-the-fly editing of the exemplar set (E.g., “resynthesize an image using the eye from this image and the nose from that one”).