Linear workflow question

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Badeez
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Linear workflow question

#1

Post by Badeez » Fri May 10, 2019 1:43 pm

Hi everyone,

I have a linear workflow question. I did not find an answer on the web.

I recently jump on fusion try to do all my work in linear space.

So i convert my input file to linear and use the viewer LUT (usualy OCIO) to color correct and transform to sRGB. Just in the viewer.

Great.

But when i use the tracking node, the magnifier (the zoomed pattern) look linear. Extremely dark. It is unusable in dark scene.

So, am i doing something wrong? Or is there something to set in the preference or somewhere else?

Thank in advance

Best

Badi

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Midgardsormr
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Re: Linear workflow question

#2

Post by Midgardsormr » Fri May 10, 2019 2:17 pm

The Tracker node was designed before the industry really understood linear workflows. It therefore assumes a display gamma input. I usually convert to sRGB with a Gamut to do the track, then delete or passthrough the Gamut when I'm done.

You will see similar issues in a couple of other places: The Ranges node and Ranges tab in Color Correct work better in 709 or sRGB, as does LumaKey. For the CC, I usually bracket it between two Gamuts if I need to use the Ranges. For the LumaKey, I seldom use its RGB output anyway, and the Alpha is always linear, so I just leave it in the display gamma most of the time.

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Re: Linear workflow question

#3

Post by SirEdric » Fri May 10, 2019 2:53 pm

In fact, the Tracker (apart from the amazingly cool interface of Fu2.5) was the main reason I bought my own Fu license back in 1996...:-)
So...bear with some non-totally-linear-adopted flaws in this case.
The Tracker itself was always just awesome...:-)

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Re: Linear workflow question

#4

Post by Badeez » Fri May 10, 2019 3:48 pm

Thanks for those quick replies and the further informations.

Brayan, as you explain for the luma key. Can you confirm that the other keyer (Delta,Ultra,...) work without problems or limitation in a linear workspace. Just to clear any doubt in my brain. :-D

Thanks

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Re: Linear workflow question

#5

Post by Midgardsormr » Fri May 10, 2019 3:57 pm

DeltaKeyer definitely works just fine in linear. Ultra Keyer I'm not sure about; I've never really had satisfactory results with it regardless of color space. I would guess that it was designed for rec 601. Primatte is voodoo; there's no telling what it will do. (I'm sure there are plenty of people who use it well; I'm not one of them.)

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Re: Linear workflow question

#6

Post by SecondMan » Fri May 10, 2019 10:06 pm

Midgardsormr wrote:
Fri May 10, 2019 2:17 pm
The Tracker node was designed before the industry really understood linear workflows. It therefore assumes a display gamma input.
Well, not exactly. The Tracker doesn't really assume anything. You feed it whatever and it will work with whatever. The algorithm works with whatever data is coming in, independent of how it is encoded. What you see in the magnifier is the image as it comes in, without any further processing.

What is a little unfortunate is that while an image fed into the viewer can "sit under a LUT", or rather have a LUT applied to it, Fusion's controls can't. It would be better if Fusion would have the ability to apply a truly global LUT that spans the viewers, colour controls, things like the magnifier in the tracker,... Basically anything visual that refers to something in the image should have the same LUT applied as the image itself, if that makes sense.

The User Interface preferences have an option for "Gamma aware color controls" that tries to mitigate the above somewhat, but it can be rather limited in practice. What if for some reason you want to work in log space and have a log->rec709 display LUT? Or more commonly, what about the many totally arbitrary, creative LUTs that a client supplies to be used as a viewing LUT for their project?

Viewer LUTs are rarely simple gamma corrections these days and the "Gamma aware color controls" would be an approximation at best.
Midgardsormr wrote:
Fri May 10, 2019 2:17 pm
The Ranges node and Ranges tab in Color Correct work better in 709 or sRGB, as does LumaKey.
Yes, but that's not because they assume a gamma corrected input. That's just because a gamma corrected input typically maps more evenly into a 0-1 range. To an extent the same applies to a log image. This can be why in some cases a track works better, or a key. But sometimes it won't. The Ranges and any keyers work completely linearly otherwise, and predictably so.

That's not to say they couldn't be improved to be more intuitive. It would be nice if you could set them to use curves that have an adjustable mid gray point for example. I think @GringoFX made a couple of Macros that did some of that, also for a more intuitive Contrast control. I don't think they made it to Reactor yet but I should dig them up one day...

In short, what image processing is concerned, every single tool in Fusion works without issue in a linear space. Its 3D space and rendering are totally linear as well. Whenever and wherever you're choosing to use non-linear images, make sure you know what you're doing and why, because Fusion doesn't care - it's all numbers.

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Re: Linear workflow question

#7

Post by Midgardsormr » Sat May 11, 2019 8:20 am

Maybe I spoke a little imprecisely, but the Tracker's ability to sense contrast does seem to be better near 0.5 than it does near 0.18. Hence, if an image is brought into display gamma, the Tracker may do a better job. That's my experience, at any rate. It might just be confirmation bias at play, though. I should test my assumption more rigorously. For certain the pattern preview is inconvenient.

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Re: Linear workflow question

#8

Post by danell » Sat May 11, 2019 12:11 pm

They should take a look at the code and bring it into 2019 and make it work best with linear workflows. Having to learn what tool needs display luts and so on brings it down a lot :(

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Re: Linear workflow question

#9

Post by SecondMan » Sun May 12, 2019 12:25 pm

danell wrote:
Sat May 11, 2019 12:11 pm
They should take a look at the code and bring it into 2019 and make it work best with linear workflows.
That's a bit of a broad statement - I'm not too sure what you mean?

In terms of "the code" - the code looks fine. The math in Fusion is pretty solid, as far as I can tell. Of course I can point out issues with Fusion's UI in terms of working with images underneath a LUT, as mentioned above, but that's I feel a generic UI wish (which I will try to create a Wish List topic for, if time allows and/or nobody else beats me to it).

(Instead of fiddling with what already worked just fine, I wish BMD had concentrated a bit more on things like that for starters.)

Things to think about - what does linear even mean? Scene linear is linear, but so is AcesCG. If you simply mean material that is not gamma corrected, what gamma are you talking about? 2? 2.2? 2.6? What about LUTS that aren't neutral? Creative? Entirely subjective? What about working in log space? So whatever UI changes are implemented, they would have to go beyond "just linear" workflows - they should be adaptable to any workflows, any custom colour spaces.

Likewise and beyond that, it's more a tooling challenge. Which you can already do just fine in Fusion today. I've dug up Gregory Chalenko's Contrast Around Color Macro which illustrates this beautifully:

Image

ContrastAroundColor_v03-2.setting

EDIT: here's a legible UI so you can see what the tool does:


Image


The tool is great because it doesn't assume anything, really (apart from having gamma compensation on by default, which I personally would advise against). With it, you can dial contrast around any pivot so it works for anything.

A lot of what we are talking about is basically figuring out what it is you need for your workflow, and you can adjust Fusion's tools a little accordingly so they can make your life easier. It's often a case of adding a few nodes, a control or two and some expressions. You don't need to be a TD for this, and there are plenty of people around that can help if you get stuck.

The one thing you need to be able to do is understand and identify what it is that you need.

Nothing beats a solid understanding of your workflow. Whether it's colour, or transformations, or basic compositing theory. Everyone being serious about compositing needs to get their heads around images, from resolution over bit depth and colour space to combining all of them together. It's not called compositing for nothing. Log/lin spaces, gamma correction, gamut and a variety of LUTs and grading processes should be, if not second nature, not too scary :)
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