Color Grading question

I work for/with/teach pro colorists, mostly based in Resolve. I work in Resolve daily, and still have a computer with Adobe's former SpeedGrade app loaded ... yea, been doing this awhile. I've got a full Tangent Elements panel too, which I can map for Hades in Premiere. Even use it for audio track mixing, moving screen elements around/rotation/resizing ... so yea, it's a thing for me.

The first thing I'll note.  LUTs are ... well, useful but problematic? Colorists call them "the dumbest math out there" ... and they are prone to clip or crush or do weird things to shadows or cause artifacting. All they are is a simple look-up table, X value becomes Y. A "3d" LUT has a couple more tricks, but it's just a slightly fancier version of X becomes Y.

So most colorists take a manufacturer's LUT, through it on a test clip/chart and ramp, to put it through a "stress test", and see what it does ... and may or may not use it. Often, they'll "roll their own" versions.

A 33 point LUT has more "inflections" than a 17 point cube, but ... not as many as a 64. So it's kinda in-between, better than a 17, not as spiffy as a 64. And that's what you're starting with.

Next ... how you apply that LUT to the media is CRUCIAL!

Remember, that LUT was built on "ideal" media. A totally controlled, accurate setup between camera, exposure, scene lighting, scene contrast, scene saturation. And therefore works best when used with media that was all exposed under identical situations. 

Which ... ain't likely, to be polite. And the scenes your clips capture will have varying scene contrast, brightness, and saturation from each other. Let alone from "the Ideal".

How do you control for that? Semi-easy.

You apply the LUT in the processing chain of effects. Then, in a step that will be applied in the processing chain before the LUT, you "trim" the exposure, contrast, shadow, white/highlight, and saturation such that the image after the LUT is both correct in the Scopes (Waveform, Parade, and Vectorscope) and on your reference monitor.

The above is absolute mandatory for reliable use of any LUT for normalization work ... log to linear (display space) correction. It's as taught by all colorists I know, including the guy what wrote most of the best colorist teaching books ... Alexis Van Hurkaman. Who used to do the massive and awesome Resolve manuals, and now ... is an Adobe staffer. (Maybe this will change ... ?)

Ergo ... by definition, you cannot correctly apply a log-to-linear normalization LUT in the Lumetri Basic tab Input LUT slot unless you have a prior instance of Lumetri applied to do your trim work in!

I've discussed this with the chief color scientist, he understands my viewpoint ... but things ain't changed. Ah well.

If in Resolve, you apply a LUT in a node, and do other corrections in that node, the corrections are correctly applied prior to processing the LUT. Which is CORRECT processing order.

HOW DO WE CORRECTLY APPLY NORMALIZATION (LOG-TO-LINEAR) LUTS IN PREMIERE?

• Apply the LUT in the Creative Tab's "Look" dropdown slot.
• Use the Basic tab controls to trim.
• Understand that the Contrast control always, ONLY pushes out from the 50 IRE center point.
• So you must adjust the Exposure control to lift or drop clip values, so when the Contrast control pushes out the signal data, it does so from the right point of the clip data.
• Set Saturation so the scene is 'natural' in appearance.

This will get you part of the way forward. And may take care of a lot of the problems you're getting currently.

I've found that working with a control surface is nice in Resolve, but an absolute MUST in Premiere. As it's the only way to get targeted changes done accurately and quickly.

I've got my Elements panel mapped so the Color Wheels are 'live' on my wheels controls, and most of the Basic tab and some of the Creative tab controls are in my 12 knobs.

So I can push the Basic tab shadows down while lifting the Wheels shadow "luma" ring control, keeping the black point steady but pulling shadows down, without much change in Mids.

I've another setting where the Basic and Creative tab controls are mapped to my three wheels. And can work WB/Tint against each other while also working exposure/contrast against each other with a different ball. Hit a button, and be working some of the Basic tab controls against each other on the wheels/balls, but with the Creative tab's Highlight and Shadow wheels on two of the balls of the Elements panel. Another slick use of multiple tools against each other.

Such things are incredibly useful.

Chip Charts Are Your Friend!

Oh ... if they did any chip charts of the cameras ... put the clip on on a sequence, and use Hue v Hue then Hue v Sat to get the six hues set correctly, and with sat, to about a halfway point from Vectorscope center to the outside Sat Max boxes. Fixes a lot of color hue issues, doesn't induce artifacting.

Now save this, with only  those two changes to Lumetri, as a named Preset. Then apply this preset to all shots from the same camera in the bin.

Applied like that as a Source effect, it corrects any use of any part of those clips anywhere in the project. And as Pr isn't great at shotmatching hue differences, this is a massive boost to both what you can achieve, and how long it takes to get there.