I don't know exactly what was used to upscale here, but Progressive Growing of GANs[0] was a breakthrough last year that proved at least 1024x1024 was viably pr

I don't know exactly what was used to upscale here, but Progressive Growing of GANs[0] was a breakthrough last year that proved at least 1024x1024 was viably producable. The short explanation is: Train and freeze the most basic layer of the model progressively to "let the network" understand higher resolution concepts one piece at the time, and avoid mode-collapse. The network architecture illustrating this a bit better is shown on page 3 of the paper [1] [0]: https://github.com/tkarras/progressive_growing_of_gans https://github.com/tkarras/progressive_growing_of_gans [1]: https://arxiv.org/pdf/1710.10196.pdf https://arxiv.org/pdf/1710.10196.pdf