Your scan looks a lot worse than mine at 4K, you can’t really see the pattern at 4K on your scan.
That appears to be the very beat-up IB print that was scanned of a DFT scanity, which is a terrible scanner for prints, and struggles a bit with smearing due to its line scanner, unlike the area scanner of the Arri or the Director.
I don’t want to come across as a dick, its just that all we do is scan and restore film, that is literally our job, and we regularly get detail that is one pixel high on a 4K scan from a print, and at 5K on negs.
The 10K scanner is really only that high for oversampling reasons, but up to 5K there is detail on a good negative that cannot be resolved properly if you resize to a lower resolution.
We often get referred to reports or tests done that ‘prove’ that film cannot resolve this level of detail, yet we see it resolved in our daily work. The tests are often very specific, or done by people with not a lot of film experience, or by companies that make sensors in digital cameras, and test specific film stocks at specific labs and specific lens combinations, which is all great, but it leads to conclusions that are often off-base, or are correct for a specific setup, and they then generalise out.
Yes, generally films resolving power on any given shoot isn’t pixel perfect at 4K, often there is around 3K of detail (full aperture) , it is a lot more complex than that due to grain structures and channel issues, processing and light, but generally if you look at a single frame, often 2K would be enough to represent what you can see on the film as a final delivery (if you scanned at 4K or 6K and down sampled properly).
Not particularly rare though, especially on original negatives, are single frame images that cannot be accurately represented at 2K, or even at UHD resolution, especially cinemascope or full frame images that end up at less than 1500 lines on a 4K UHD Blu-ray. This is not theory, this happens in the restoration process that we do.
When you get something like that door-frame, and the alternating lines of the pattern are about 1 pixel high when scanning at 3500 lines of resolution, no processing will keep that pattern at Blu-ray resolutions.
I know I’m banging on, but it drives me nuts sometimes to be told, repeatedly over the years, that film is not capable of doing something we see it do regularly in our work.
Anyway, my gut feel is that for the SE, if it didn’t come from the neg, which I’m not sure a lot of it did, I think we will not need more than 2K as the final delivery to make it indistinguishable from the film, but to do that we would need to scan at 4K anyway, even if it was mastered at 2K.
So to answer the oringal question, we would want to scan it at least at 4K either way.
I’m really hoping we will get better resolution than the IB scans we have of the OUT, we will know soon.