Light colours don’t match swatches in VRay 5.2.1 with ACES

[AOCreative]

Hi all,

We’ve recently switched to Maya/ VRay and want to use ACES in our workflow. We have 12 brand colours that we need to match in our renders but I’m struggling to get any of the colours with RGB values over 207 looking correct in VRay.

Following Chris’s method in this ACES Central thread (https://community.acescentral.com/t/...-question/3769) I’ve got the colours to match in Arnold but it doesn’t carry over to VRay.

Both scenes are lit with a dome light set to ‘Colour’ with RGB values 0.81, 0.81, 0.81 at an intensity of 1.

OCIO config is Maya Default 2.0
Rendering Space is ACEScg
Display is sRGB
View is ACES 1.0 SDR-video
Mixing Colour Space in colour picker is set to Display Space

I added the square swatches in Photoshop to compare.



VRay Colour Settings



Arnold Colour Settings



I tried using the OCIO 1.2 config file and an edited version of it with colour_picking set to ACES – ACEScg recommended in this thread (https://forums.chaos.com/forum/v-ray...ur-match-issue) but no luck.



I also tried using the method to match a logo’s colour detailed in this thread, converting the RGB values to non-Linear sRGB and going through an OCIO node (https://forums.chaos.com/forum/v-ray...e2#post1064394) but still no match.
If I’m understanding the Maya video on Colour Management/ Colour picking correctly (https://www.youtube.com/watch?v=mgKH...MUhE8z0oD99MMY xJq2s2goa&index=2), RGB values over 207 are reserved for highlights, so is Vray not converting the RGB values to ACES correctly (like Arnold?) or am I entering the values incorrectly?
The video mentions switching from ACES 1.0 SDR-video to Un-tone-mapped in the Colour Preferences before picking colours you do not want the ACES transform to be applied to, this gets the Light Blue looking closer but still too grey.



Is it possible to get these light colours in VRay with ACES or are we better going back to rendering in sRGB?

Thank you all, in advance,

Alex!

[Muhammed_Hamed]

Hello AOCreative

Here is the color you used for the Sphere on the right,



If you turn off Color Management, you will be able to see the actual RGB values used by V-Ray/Arnold internally



In this case Arnold will use these values for Diffuse, this is quite bad. It breaks PBR, causes unresolvable noise and you get unexpected behavior(Arnold result above doesn't look correct for HDR values, you shouldn't get dark shadows on the sphere)

V-Ray on the other hand will clamp the values to 1, this happens for Diffuse, SSS and Reflection color channels. This is mostly to avoid issues, you really don't want to break PBR on your materials

There are 2 ways you go around this, depending on what you wanna achieve..
-You can load this colors in Self-illumination of the V-Ray material which doesn't get clamped and should represent HDR color in a more physical way.

-Change Color Picking in your Config file to Utility-sRGB-Texture
In this case the ACES RRT tonemapping will affect your colors, so they will not look the same
To disable the ACES tonemapping you can swap Display correction to sRGB, this way it applies an OETF transfer function + Gamut conversion to Linear sRGB color space
It is fine to use ACES without the tonemapping, you can build your own tonemapping using our Filmic Tonemap layer, make sure to set it to ACEScg

I hope this solves your issue, let me know what exactly the swatches are going to be used for, I will think about this and find more solutions.

Like what Chris said, this issue is not easy by any means. I think this is one downside to the ACES workflow and the ACES ODTs in particular

If you have more questions let me know.

Best,
Muhammed

[AOCreative]

Hi Muhammed_Hamed ,

Thanks for explaining how Arnold is getting those values!

We render images like this with a backdrop, assorted shapes and some hero products. We want the backdrop and shape materials to match our brand colours as closely as possible.



I had tried using Self-illum before in the material but didn’t like the results, things looked too flat.
Switching to Utility-sRGB-Texture in the OCIO config, setting Display Correction to sRGB and adding our own Filmic Tonemap layer is giving promising results, thank you!
Going into the Filmic Tonemap layer should we be using a specific Type? The colours are looking much better using Power curve, just want to check I’ve got it set up correctly.



Thanks for all the help,

Alex

[Muhammed_Hamed]

Hey AOCreative

I'm glad you had success with the Filmic Tonemap approach. This is totally fine in the ACES system and you still get all the benefits of Wide Gamut Rendering, it is just that you skipped the ACES default tonemapping and created your own.

Going into the Filmic Tonemap layer should we be using a specific Type? The colours are looking much better using Power curve, just want to check I’ve got it set up correctly.

As long as you set Tone Mapping Space to ACEScg, you should be all good. This way the layer expects ACEScg values
This process is mostly artistic, feel free to pick the curve type that you like

Here is a video of what I usually do in the frame buffer

https://www.youtube.com/watch?v=1mcE5cJ198U

We render images like this with a backdrop, assorted shapes and some hero products. We want the backdrop and shape materials to match our brand colours as closely as possible.

Thanks for explaining, you can create a mask for the brand colors and have a perfect match in Post/Frame buffer if needs be.
If it is possible to upload me the scene above, I can give this a try and upload you my setup

Best,
Muhammed

[AOCreative]

Hi Muhammed_Hamed ,

Thanks for all the help. Here are the scene files:

https://we.tl/t-gjMlKEoVAN

One last question, when using the 1.2 Utility – sRGB – Texture config the Colour Picker doesn’t choose the correct values. For example, the MidBlue RGB values are 74, 109, 206 but the Colour Picker gives values of 96, 132, 252.



This isn’t a major inconvenience as we can just enter the values but is there a way to get the Colour Picker to select the correct values?

Thanks,

Alex

[sebbiej]

I seem to be getting a similar issue with V-Ray 5 update 2.2. Maya 2023 with ACES 1.2.

I need brand colours to be spot on correct in the render. If I manually put in the RGB values from Affinity Designer the colours seem massively washed out in the render, it's like the gamma is off. I've tried putting the colours through a gamma node set to 0.454 and they are closer but not 100% correct. I need them to be correct throughout the workflow in to my Photoshop comp.

Example attached. Might the devs know how I can fix this?