In the words of the late Bob Ross, I've had a "happy little accident".
The other day I finally settled on a proper method of color correcting the blacks: I ended up making a white-balance curve for each of the grades in Photoshop with the black point being on the colored black bar that I forgot to crop out last time, and then export a LUT to use specifically on the shots that used that aforementioned grade. However, it was during this that I discovered something kind of interesting...
There was one still I made a grade off of in particular. It was particularly faded looking one and in the end, I decided not to use it even after post-black correction (replaced it with a slightly less faded looking compilation Attic LUT). However, what I did end up using was the resultant correction LUT.
It was a LUT that not only ended up fixing the faded, colored black look for the movie, but it kept in some of the colored blacks where it looked intended as well as giving a colder, bluer tint that pushed the blues in the direction I've been trying to get it to go without the need of any adjustments to the color wheel. It also helped unify the entire movie kept things looking consistent throughout. On top of that, all of the other specific LUTs I made ended up making some characters look inflicted with jaundice as well as sapping some of the wanted colors away. So with that, I ended up nixing the inferior LUTs I made and just applied it to the entire movie which, again, reinforced the blues beautifully in my opinion. It may not be perfect, and there are still hints of colored blacks, but I think it's darkened to the point of it being passable.
So with that, I present to all of you...
Project: Celluloid Regrade (V2)
Now one thing you may notice is that everything looks a fair bit darker, but I am quite happy with that change since it gives the movie a bit of a spookier mood as well as giving the blues a deeper look as mentioned prior.
I'm reconsidering my statements on DNRing the movie since it kind of came to me how this project at heart is merely a regrade, not a full-blown restoration. If someone wants to fix the grain issue then that's fine by me, but I'd rather not screw up a perfectly good regrade with sub-par DNR.
I'm thinking of leaving this project as it is right now. Unless any real glaring issues come to my attention or some more scans (or hell, a telecine even) come out that are less faded and more comprehensive than JohnCarpenterFan's, I don't see any real way of going forward with this project. So with that, I am currently working on exporting this from Da Vinci and cramming it into an MKV as soon as I can.
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Minor update: After talking with TomArrow, I've agreed to look into the crushed blacks issue. We've worked out a rough method where the darkest areas will be isolated and then composited over the crushed areas but I'll have to do some experimenting with the nodes system in Da Vinci later to get the desired effect.