Render specific color in ACES/OCIO workflow

[thophile_riviere]

Hi chaos members,

Been using proper ACES workflow recently, which is great but I have a question regarding colors output.

Is there a way in ACES worflow with OCIO display corection to have a specific rgb value output ?
Often our clients ask to have a very specific color in the render to match their color guideline.


Rendering in ACES color management with sRGB display correction, I get exactly the colors wanted (diffuse chanel) :


Rendering in ACES color management with OCIO display correction, all the colors are toned down (diffuse chanel) :


I searched a lot to find a way to have exaclty the colors wanted and being with OCIO display correction that is much more easy to work with.

Nothing seems to work, even getting pure white in the diffuse chanel seems to be impossible. I can only get to 0.811 RGB values but not to 1.

There's probably something I don't understand clearly working with ACES, but I hope there's a way to get some spefic color values other than tweaking it in post .



Cheers,

[^Lele^]

It's unfortunately a well known issue that has to do with the sRGB display ODT, as that's non-linear, and applies both tonal compression and contrast to the input.
Even the sRGB-displayed colors may look about right, but will prove strange (negative values and so on) when picked (don't pick the raw, toggle the picker to RGB.).
There is currently no solution I am aware of (i tried also the newest configs available), but maybe some user with more knowledge of the subject matter may be of more help.

[thophile_riviere]

Thx for your quick response.
I'm currently working with the latest released config, that is aces_1.2. Older config like 1.0.0 seems to have the same result.

I stumbled upon this great thread that explained this a bit : https://community.acescentral.com/t/...rrt-odt/1779/2

But now I truly don't know how I should work. Am I supposed to choose between : "exact" color output (sRGB from Vray) or the S-shape curve that compresses highlights to allow headroom for “over-brights” (sRGB from OCIO config) ?

It is much easier to light a scene with the OCIO config but if I can't have specific colors the problem will just be moved to compositing...

[thophile_riviere]

From what I've read I need to use the "output sRGB" to "ACEScg" before the display correction "ACEScg" to "sRGB" -> nullifying any transform and getting my exact values.



Unfortunatly the raw values seems to be clamped to 1 so I can't do that.

[piotrus3333]

this should be the correct setup. how does your VRayBitmap setup look?

[^Lele^]

There's been a fairly recent thread with some great posts that give us a general idea of who's who, both in terms of standards, and in terms of who's working on them (meaning their inclinations.).
I think the key is patience: the standard will mature, what can be fixed will be fixed.
For now, i know of now way to have an LWF workflow analogous to the one we used with sRGB while using ACES.

[thophile_riviere]

this should be the correct setup. how does your VRayBitmap setup look?

here is my bitmap setup :

[^Lele^]

EDIT: Nevermind, i looked at the wrong dropdown. -.-'

[piotrus3333]

EDIT: Nevermind, i looked at the wrong dropdown. -.-'

exactly. auto should default to srgb for 8 bit textures. 16 bit psd?

[^Lele^]

For PSDs it'll depend on the encoding.
If it's higher than 8, though, hte likelyhood is that it's not for viewing, so perhaps raw?

[piotrus3333]

ok - there is a few things happening here.

Since quite some time VRayOCIO is no longer needed. You just set the correct primaries via VRayBitmap or VRayColor.

VRayDiffuse filter is for some reason affected by Display Correction in VFB.

sRGB Display Correction in VFB is not the same as OCIO ACEScg > sRGB. It is missing the tone curve.

edit:

[thophile_riviere]

Thanks for all your feedback, sorry for the late responce (got sick).

Now I think I undesrtand how this work. I though my render with OCIO workflow was busted cause it displayed my passes with the ACEScg curve.
The goal to work with ACES OCIO workflow is to get realistic results thanks to the curve applied. So it is normal that very bright color are toned down since it is how we percieve it in real life.
And I still have the good values stored in my exr pass so I guess it's okay. I'll just need to talk with the compositor to get a clear workflow.

We just need to be carefull and build around a specific color if a client want to have exactly that color in the final render ^^.

Thanks for all the clarification !