What pixel count is required for a near perfect digital copy of an old movie?
In reality, I think the other forum was a good place to ask. But people there tend to vote to close the moment they see the word "video" :o)



It is a bit complex to answer. And old movie could probably not have a sharp focus because of the lens, or the grain of the film. Probably there are inconsistencies in the filming across all the movie.

Even today some scenes in some movies are filmed using normal digital film and some other action scenes could be filmed in Imax.

And because you did not have pixel-peeping mania like some times we have.



You could find some papers, like the ones Xiota pointed in the other forum, stating that film can hold information on XXX Mpx. I have not seen a real-life comparison making large prints using both media in equal conditions, probably using the same lens.

There is a difference between the theoretical limit vs the real-life limit. You can argue that the size of the silver crystals is the real limit, but in reality, it is "only" grain.



To answer this you would probably need to know


The size of the frame.
The grain of the film, probably based on the ISO.
Lens used.


Not only the year of production, but that would give you some hints.

But there is more to it, mainly if the scanning has a post-process.

Here is a restoration, reescalation and re-fps-action of the "arrival of the train" The Lumière Brothers, 1896.