Adaptive color palette?

Back in the '50s/'60s, film had a very specific look about colors. It'd be saturated, but it would have a limited range of colors. What I mean by that is that if the actor would wear, let's say, a yellow pullover, the type of yellow color shown would be very similar throughout the pullover. Same about the sky: the blue-ness of the sky had the same color throughout the image, without gradients/variations.

With modern cameras, that are more sensitive to light, they capture all the color variations on faces, clothes, sky, sea etc. This gives it a more realistic look, but it's losing its filmic, almost painted-like look.

Is there a way in Resolve to make the colors of similar ranges "collapse" on fewer possible values?

Please understand that I'm not looking into reducing the bit depth (e.g. like Photoshop can reduce to 256 colors). Instead, I'm looking into collapsing the similar colors into fewer values (with a bias towards the most saturated ones), but remaining 10 or 12 bit overall.

How one goes about it?

I'm sure you could make a LUT that compresses colors into a single "step", but I'm not sure how to go about creating this. Maybe could use a very small matrix and compress using absolute colorimetric.

I'm sure you could make a LUT that compresses colors into a single "step", but I'm not sure how to go about creating this. Maybe could use a very small matrix and compress using absolute colorimetric.

Films were designed to do this in order to make pleasant images.

And our brains tend to do this when viewing "real life" as well.

You might try using a film emulation LUT in your grade to mimic this effect. You might find the effect too strong, but you can lower the opacity of the LUT to achieve a partial effect. You will also notice that the film emulation LUT shows cyan shadows and reddish highlights. You can use some correction RGB curves to minimize this.

No, Luts won't work for that I think, because luts bake an image using predefined values. I think it needs an actual smart algorithm, possibly in the form of a plugin instead. Filmconvert does have some of these properties, but it doesn't go far enough.

Back in the '50s/'60s, film had a very specific look about colors. It'd be saturated, but it would have a limited range of colors. What I mean by that is that if the actor would wear, let's say, a yellow pullover, the type of yellow color shown would be very similar throughout the pullover. Same about the sky: the blue-ness of the sky had the same color throughout the image, without gradients/variations.

With modern cameras, that are more sensitive to light, they capture all the color variations on faces, clothes, sky, sea etc. This gives it a more realistic look, but it's losing its filmic, almost painted-like look.

What gives you the idea that printed film has such a limited colorspace?

I don't think what you say is true at all.

It was not a matter of limited colorspace, it was a matter of how it would print similar colors. Here's an example: on Amazon Prime check "Age of Consent", here are some screenshots of it too. Look at the color of the sky, look at the color of her handbag: https://imgur.com/a/7FKSr7o Such overall look you can't have with digital cameras. They capture way too much detail, detail that I want to throw away. Both in terms of actual visual detail, and in terms of color. The colors should remain saturated, but kind of teamed together, rather than having too much gradientation.

Digital behaves like slides (i.e. positive / reversal) where it can't deal with overexposure but has plenty of room for underexposure. Negative film has room for overexposure but gets muddy in underexposed areas. I'm after the negative film look. The exact opposite of what digital cameras offer. So I'm trying to find software ways to reverse the look.

So far, the best way to deal with it has been to work in ACEScct. It does make a difference in color reproduction when it transforms from whatever format to Aces and then back to RGB. Basically, I expand the colors, and then I reduce them again. By doing it that way, I kind of trick the software to do that "color reduction" I want. Here's the film-like quality I get from the original BMPCC by doing it that way: https://imgur.com/a/3KENmnZ

You could try using the Color Compressor plugin along with some masking/qualifiers. On a recent project I did set in the 60's I found Color Boost to give me a better look than saturation, I do have to give credit to the set because it was pretty 60's already.

When I was about done with that project I stumbled upon this 3 Strip Technicolor technique that may prove useful, I haven't played with it much so can't say for sure but I wish I found it earlier in my project.
http://www.ditspot.net/3-strip-technico ... i-resolve/

Edit to add: Also can try using the Soft Clip under curves and Mist control under blur. If I had time I'd try matching your references but maybe some of these will help you out.

Back in the '50s/'60s, film had a very specific look about colors. It'd be saturated, but it would have a limited range of colors. What I mean by that is that if the actor would wear, let's say, a yellow pullover, the type of yellow color shown would be very similar throughout the pullover. Same about the sky: the blue-ness of the sky had the same color throughout the image, without gradients/variations.

I think this was just good art direction, good costume design, and a concerted effort by the filmmakers to get everything to fit in a specific color pallet. Many years ago, when Technicolor started, Natalie Kalmus (the wife of Dr. Herb Kalmus, the lead inventor of Technicolor), served as "color consultant," specifically choosing paints and fabrics and makeup to make sure the pictures would reproduce correctly on film. If a character was associated with yellow, they would work diligently with the costume and prop department to make sure it was all exactly the same shade, and it would reproduce with the same intensity in most of the film.

I think you can limit the visual color range just through careful use of curves and keeping an eye on the vectorscope. For example, if you want a scene that leans away from green, then pull green overall and push it in the opposite direction: grab the green hue-vs-sat curve and reduce it so it's greatly reduced in the image. An argument can be made that custom LUTs can do this and provide a pretty specific look in that no matter what, a specific color will be diminished and other colors will be increased. I can recall a case where we'd have one node that would boost overall saturation, the next node used curves to reduce a couple of specific colors the director didn't want to see, and the final node would pull saturation back to normal. This is kind of a cheat, and it doesn't always work, but in some cases it can do the job. (You do have to be cautious not to clip anything on the way in and out.)

I know of the tricks of technicolor, but that's not the case with the movie screenshots I linked above, which was a 1969 low budget australian movie. The film color and contrast is just perfect, on its own. That's what I want, I want that exact look.

I know of the tricks of technicolor, but that's not the case with the movie screenshots I linked above, which was a 1969 low budget Australian movie. The film color and contrast is just perfect, on its own. That's what I want, I want that exact look.

Then I'd say shoot it on 1969 film stock, light it the same way, and you'll get that look.

I color-corrected plenty (hundreds) of movies from the 1960s and 1970s, and trust me, they go all over the place in terms of looks, mainly because the film stocks, labs, and techniques were so different. I've even done a few Australian films (including Breaker Morant back in the 1980s), and very recently, a restoration of the 1982 Australian film Darkroom. But those looks were more about the period -- 1902 in the case of the former, 1982 in the case of the latter. Radically different, yet both shot around the same time on similar stock.

If you want that look, it's more about the lighting style, the exposure, the lenses, and the art direction. Do all that and you'll have a fighting chance of winding up in that same direction. Many cinematographers start with a "look book" and conferences with the director to determine what a new film should look like, but it's more about inspiration and possibilities than it is rigidly recreating or "borrowing" the look of an existing film.

maybe the color compressor OFX within some (very) soft keys for the color ranges you're targeting

maybe the color compressor OFX within some (very) soft keys for the color ranges you're targeting

If you're making a radical change, you're going to get some "chewing" on the key, artifacts that show where the processing is breaking the image. I think a window would be a better approach than a key.

There are very definitely cases where tracking masks are better than keys, where keys are better than tracking masks, and sometimes where you have to use both. I had a situation very recently where I had a film restoration with very bright yellow titles over an existing background. I didn't have the separate elements, so I had to process them carefully. I would up qualifying the title in an earlier node and then bringing it down to a level that didn't overwhelm the rest of the image behind it. But it was tricky, because in some case, the actors wore yellow sweater that were a little too close to the title color. I wound up using masks and keyframes, puls very careful sat qualification plus de-noising the key, and all of that made it work. I never could've predicted that it would take that much work (maybe an hour) just for a 2-minute title sequence, but in the end, it all looked great, and that's all I care about. Color compressor alone could not have done it.