A fully automated upscaler with automatic black bar cropping.

There is only one thing you need to do: adjust the degrade_sigma parameter in the PiD Conditioning node to your liking (I personally set it to 0.10). You can always compare the result with the original image using the Image Comparer (rgthree) node. A perfect 1536x1536 square yields a 4096x4096 output. It doesn't matter what your input resolution is; this upscaler is smart enough to automatically determine the necessary settings and crop out any black bars from the final image.