system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can the quality of films and tv shows be 'upgraded' to HD without reshooting the whole thing?

Basically what the title says. Recently I watched the tv show friends in HD and wonderded this. How is this possible?
gpt
They originally shot it on 70mm film which has a ridiculously high resolution.  Then they reduced those to 35mm film with a resolution of about 4000x2000 then compressed it for VHS.

They're not taking the VHS to make the new BlueRays, they're taking the 35 mm or 70mm film.