What parameters would that be? Make it look like Eastman Ektachrome High-Speed Daylight Film 7251 400D? For years, people have taken film negative onto telecines and created content of grain to be used as overlays. For years, colorists have come up with ways of simulating the color of specific film stocks by using reference film with test patterns that's been made available.
If a director/producer wants film grain added to their digital content, that's where it should be done in post. Not by some devs working for a streaming platform. The use of grain or not is a creative decision made by the creators of the work. That's where it should remain
Why? If you're spending a significant chunk of your bits just transmitting data that could be effectively recreated on the client for free, isn't that wasteful? Sure, maybe the grains wouldn't be at the exact same coordinates, but it's not like the director purposefully placed each grain in the first place.
I recognize that the locally-produced grain doesn't look quite right at the moment, but travel down the hypothetical with me for a moment. If you could make this work, why wouldn't you?
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...and yes, I acknowledge that once the grain is being added client side, the next logical step would be "well, we might as well let viewers turn it off." But, once we've established that client-side grain makes sense, what are you going to do about people having preferences? Should we outlaw de-noising video filters too?
I agree that the default setting should always match what the film maker intended—let's not end up with a TV motion smoothing situation, please for the love of god—but if someone actively decides "I want to watch this without the grain for my own viewing experience"... okay? You do you.
...and I will further acknowledge that I would in fact be that person! I hate grain. I modded Cuphead to remove the grain and I can't buy the Switch version because I know it will have grain. I respect the artistic decision but I don't like it and I'm not hurting anyone.
I already normalize audio (modern US produced media is often atrocious), modify gamma and brightness, and probably some other stuff. Oh and it's not as though I'm viewing on a color calibrated monitor in the first place.
The purists can purchase lossless physical copies. The rest of us would benefit from such improvements.