What pixel count is required for a near perfect digital copy of an old movie? I stupidly posted this on Photography SE yesterday evening. I'm posting now in a more appropriate place.

I've been trying to get my hands on some of the very best digital versions of some classic movies recently. (As well as some which aren't classics; they're just old!) The question I'm trying to answer at the moment is: How high does the pixel count need to be to make sure that, within reason, the most faithful possible digitisation has been achieved?

To pick a concrete example: What pixel count would be required for a near perfect digitisation of Casablanca (1942)? Would it be different for Total Recall (1990)? What about a TV movie from the 70s?

I've read that, in principle, an image of 70mm film is capable of holding about the same level of detail as a 8640p digital image. (I'm very happy to be corrected on that point.) After few hours of looking through different digitisations of various old movies, it seems that, in practice, film often gives a level of resolution well short of 8640p. With some old movies digitised to 1080p, if you gradually blow up a still, you can see the image start to become "hazy" long before you can see any pixellation. With some movies, you can even observe that effect at 720p.

A select few movies - these are always more obscure titles - look like all possible detail has been squeezed out of them even at 480p, and they're so obscure that I'd struggle to get hold of a 720p version to check. Is it wishful thinking to imagine that, in some cases, a 480p digitisation could be very faithful?
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.