Weird lut behavior in Lumetri (with conversion luts). Seems to be counter-intuitive

Sorry to say, but this is a "like, duh ... " thing. Though as many people as possible pushing on this would be appreciated!

It's the processing order ... pure and simple. And I and others have been harping on this since Lumetri was first rolled out. The processing order in the Basic tab is wrong. Has always been so. Why?

LUTs are the pure dumbest, stupidest math out there. Useful, yes, but SO darn dumb you need to apply them correctly or they break your media.

First thing to know, is LUTs will hard-clip data outside their through-put range. Which is exactly what you spent a good deal of time discovering in that video. It's something Alexis Van Hurkman and every flipping other teaching colorist teaches ... you apply a conversion/tech LUT, ANY such LUT ... and then "trim" the media through the LUT from tonal/color controls processed/applied before the LUT.

Take Resolve ... you apply a LUT to a node, by design the LUT is the last thing processed in that node. All other corrections are processed before the LUT. You get the exact same effect if you apply a LUT in a node and in the same node do some trimming, or create two nodes, apply LUT in the second and trim in the first. Either way, you get correct behavior.

Premiere's processing order is pretty much top-down. Within any clip, the effects applied (as viewed in the ECP) are processed top-down. Within Lumetri, it's top down with the exception of the Hue/Sat curves, which are all processed after the RGB Curve tool but taking their inputs directly from the RGB Curves tool. Essentially, the Hue/Sat curves are the only equivalent of a parallel processing node in Premiere.

And in the Basic tab, it's top->down with the exception of the White Balance tool, which is actually processed last.

So back to this issue ... note where the LUT slot is on the Basic tab? Up top, right? It's the very first thing processed ... so it is applied before the trims you make below it in the Basic tab.

WRONG.

It's very frustrating. The WB tool according to most of the foks I know should be processed up top ... but instead, you trim through it with the Basic tab's tonal tools.

The Input LUT slot is also up top, but ... processed up top! ... when it SHOULD be processed after all other Basic tab tools.

You are most correct, and as numerous of us have hollered since forever, APPLY CORRECTIVE/TECH LUTS in the CREATIVE tab slot ... then 'trim' using the Basic tab controls. Otherwise you will have clipped and crushed values depending on the clip and the tech LUT applied. Which you cannot restore with any tool in Lumetri ... unless you correct before the LUT.

I hammer the engineers and supers on this at NAB/Vegas every flipping year. Francis Crossman, who was a color engineer and now promoted to co-Product Manager for Premiere, took a good look at this over the summer and read up on the things I sent him to study. And ... essentially agrees that it should be changed, it's just a matter of when the "extra" time is available to do so.

In truth ... I'd rather they fixed the utterly broken and stupid "Blacks" control in the Basic tab first. Take a full ramp image, work with the Blacks control, and watch the scopes. It's essentially a swinging door hinged about 20IRE. And ... if you drop it much ... gives you this most amazing J figure, complete with the bottom curl. Which means you can't really adjust black point efficiently in the Basic tab. Which ... when using a LUT in the Creative tab to trim through ... can be an issue.

Of course, throwing a simple RGB Curves effect before Lumetri allows you to change the black point same as a Lift operation would do. But the Black tool in the Basic tab should simply work correctly.

I've got an explanation of the functioning of the Lumetri controls on my blog ... been there for some time now. Including examples of this. In looking through this old post, I do need to redo this look at things as a couple things have changed behavior slightly.

http://rneilphotog.com/2017/06/lumetri-basic-tab-what-do-the-tonal-controls-really-do/

Neil