Strange magenta tint on Vray Sky under ACEScg color space

[alessandro_consonni]

Dear community, I've noticed that Vray sky with clouds does have a strange behavior under ACEScg color space, it seems to cast a strange magenta tint on the sky, much more noticeable on clouds as you can see in the attached images.
I know that ACEScg has a wider gamut that is translated in more colors, but seems to me to be completely off from the cast light from the sky.

I already tried to add an OCIO conversion on the sky map but doesn't seem to work, maybe the sunlight color is not converted properly?

Any advice?

Thanks

AC

[vladimir_krastev]

Hi, thanks for posting. The slight magenta tint is not only over the clouds but also over the whole scene. This is expected.

[alessandro_consonni]

vladimir_krastev thank you for your clarification. I don't want to be offensive and I hope you will take my POV as a constructive idea sharing. I found really strange such a significant colour shift during the conversion from ACEScg to sRGB. I'm saying that because I found perfectly realistic the sky and clouds colour under sRGB internal colour space, not realistic when working in ACEScg colour space. I mean, I'm not expecting red clouds in a midday shot. I'm used to shooting real pictures and videos and doing post-production in ACES and never experienced such strange behaviour in the sky. Hope you can take it into consideration

AC

[vladimir_krastev]

Hi, could you share a bit more details about your set-up? Please include screengrabs of your VFB Display correction tab as well. What version of aces configuration are you using? Please read this docs page.

[^Lele^]

vladimir_krastev thank you for your clarification. I don't want to be offensive and I hope you will take my POV as a constructive idea sharing. I found really strange such a significant colour shift during the conversion from ACEScg to sRGB. I'm saying that because I found perfectly realistic the sky and clouds colour under sRGB internal colour space, not realistic when working in ACEScg colour space. I mean, I'm not expecting red clouds in a midday shot. I'm used to shooting real pictures and videos and doing post-production in ACES and never experienced such strange behaviour in the sky. Hope you can take it into consideration
AC

EDIT: it's seemingly a bug with the clouds.
To confirm it, turn them off and the cast should disappear.

[alessandro_consonni]

^Lele^ Thank you for your feedback, I perfectly understand your point and I perfectly agree with that, my point when I started this topic was why the sky under sRGB color space looks much more natural than under ACEScg. I'm now picking up more informations from my scene as asked by vladimir_krastev

[alessandro_consonni]

vladimir_krastev I've uploaded 2 images with the scene settings. What I did was open a brand new scene, change the RGB primaries in the Vray Settings, and set up the OCIO file inside the VFB as you can see in the pictures. That's it. The ACES version is the one included with 3dsmax2024

Just to clarify, I don't want to dig into technical stuff, which I'm not qualified for, I just want to understand why sRGB looks more natural than ACEScg which technically has more colors to make the image look more rich and natural.

[^Lele^]

vladimir_krastev I've uploaded 2 images with the scene settings. What I did was open a brand new scene, change the RGB primaries in the Vray Settings, and set up the OCIO file inside the VFB as you can see in the pictures. That's it. The ACES version is the one included with 3dsmax2024

Just to clarify, I don't want to dig into technical stuff, which I'm not qualified for, I just want to understand why sRGB looks more natural than ACEScg which technically has more colors to make the image look more rich and natural.

I edited the post, so it may have slipped: it's highly likely it's a bug with the cloud part of the sky system.
That's what gets the purple cast (as it's possibly not inverted for ACEScg.), and then in turn it influences the cast on the scene.
The relevant Dev has been notified, i'll post here for reference if it's indeed a bug.