LUT on a separate layer produces different results than on the same clip

[goguvarra]

Hello,

I have the following problem.

For this project I'm working with proxy files with the official sony slog3 to rec 709-type A lut applied.

The issue appears when I apply a lumetri color effect on a clip and I start to modify the colors a bit.

If I have the LUT applied on an adjustment layer above the current clip and the clip only containts the lumetri efect with my color grade it will be different than having the grade in the same clip (with the LUT applied on the proxy file or the LUT applied in the lumetri effect in the Basic Correction tab, it makes no difference).

Is this normal operation or a bug?

The reason it bothers me is that I would prefer to grade with the proxy files because it is easier on my system but I can t do this because if I apply the rec709 LUT when I export the results are not the same in the final clip, as I explained above. 

I've also attached 3 screenshots to illustrate the issue.

first - is the proxy + the grade applied with a lumetri effect inside the clip

second - is the lut + the grade applied inside a lumetri effect on an adjusment layer above the clip

third - is the lut applied on a separate adjustment layer + the grade applied with a lumetri effect inside the clip

Thanks.

[basil1891]

if I apply the rec709 LUT when I export the results are not the same in the final clip, as I explained above. 

That's expected. Order of effects matters to final result.

[goguvarra]

well, maybe...but i m not sure this is the case

When applying the LUT at export it is the same as applying the LUT in the timeline on the layer above, the 3rd picture in my example.

And why would this different results than applying everything, the LUT AND the grade inside the same lumetri effect instance.

Isn't Lumetri configured like this from the start? Each tab inside it, Basic correction, creative, curves, etc. is supposed to add to the effects from the tab above it. So the input LUT field in the Basic correction tab should take precedence over the other effects with are lower in the "pipeline", thus it should apply the LUT first.

that is the same as applying the LUT separately on a layer above, right? 

Why then should there be a difference in the color and contrast of the image?

[basil1891 · Accepted solution]

It depends. 

- for Effects panel and Lumetri panel the order is "top - to - bottom"
- for video tracks/adj layers on a timeline the order is reversed, "bottom- to- top"

[goguvarra]

It depends. 

- for Effects panel and Lumetri panel the order is "top - to - bottom"

By @basil1891

Wow. I've now realised this is working exactly opposite to what I'm used to. After all these years.  I thought you were wrong. But Neil says the same thing below.

This is so strange and hard to comprehend. And Adobe doesn't warn you about this. 

Why on earth would you design it this way when all the others layer based apps, work the other way around. 

Even in the timeline things are working as they should.

[R Neil Haugen]

Funsies, right? It'd buried in several places in their help files.

So ... effects applied directly on a clip, are top to bottom as shown in the Effects Control panel.

Applied across tracks ... V1 is first, then V2, then V3, and on up adding things to the lower tracks as you get up the track listing.

Neil

[R Neil Haugen]

Processing order in Premiere is strictly followed, but not always obvious. I'll start with track processing order.

First, within one video or audio track, expect "top down" behavior. As in the ECP, effects are processed top to bottom. An effect above another is processed first.

Second, when Adjustment Layers are involved, they stack like this: V2 is applied after all effects in V1; V3 is applied after all effects in V2 ... and on. The upper layers are 'added' to the work done on the clip, after the work done on the clip.

Within Lumetri, it's also top-down with one exception that just popped out of my head, but it's only one control. This means that the Input LUT slot in the Basic tab is unfortunately applied before the trim controls of the Basic tab, which is backwards from what any colorist teaches. You should always apply a Tech/corrective LUT, then trim the clip 'through' the LUT with controls applied to the clip before the LUT.

Which means in Lumetri, you really should apply tech/corrective LUTs in the Creative tab so you can trim the clip exposure/contrast/saturation prior to the LUT. Remember, LUTs are created from clips made in perfect studio situations. That ain't where any clips you work with are being made, even if made in a studio. It isn't the same studio with the exact same lighting as went into creation of that LUT.

The one oddball in Lumetri, is that in the Curves tab, the RGB curve is processed first, BUT the HSL curves are processed in parallel after the RGB curve. Meaning each of the HSL curves ... Hue/Hue, Hue/Sat etal, get their data from right after the RGB curve. That is the only parallel processing in Lumetri.

The above also means that the HSL Secondary tab gets the data for making a key after all Lumetri controls above it are processed ... not always optimal. Once you've set a key, IF you go above and change anything, you may have just mangled your key. Which is why often a Track Matte stack is a better way to apply HSL secondary corrections.

The track matte stack is a useful trick. Dupe the clip twice above the original; on V3, set an HSL key in Lumetri with mask on set to black/color; on V2, apply Track Matte Effect set to V3, Luma, then apply Lumetri ... and you can use any control in Lumetri to modify the keyed material. This takes original clip data, and applies the correction to the original clip data on V1.

Neil

[goguvarra]

Wow. Really useful information. Thanks a lot.

Although is just goes to show that lumetri is really not yet made for easy and fast colour grading. 😩 Speedgrade was so much better.

One question though. In Speedgrade for example if I played with the colour wheels and changed the distribution of Shadows mids and highs in an image, the next layer would affect the "new" lows mids and highs that were modified by the first layer. I mean if I lifted the shadows way up into the mids, the shadows wheel on the next layer would pretty much do nothing. 

This is very useful in grading as you get fine control and tone separation to work with.

Is lumetri the same if I put it on 2 separate adjustment layers to simulate the 2 instances? Or is it just dumb? 🙂

Thanks