Chaos Corona Forum
Chaos Corona for 3ds Max => [Max] I need help! => Topic started by: Kum on 2020-08-25, 14:29:27
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Hello everyone,
I have a question that is keeping my mind quite busy for a long time. I have been searching through forums, asking around. Yet, I couldn't find an answer to this. It's possible that I'm totally missing something in the theory, so I would be happy if we can discuss this to figure out. My question is all about color usage and color ranges, in not only Corona Renderer but also all PBR theory. Corona Renderer makes it a bit more complicated on my side. Please correct me if I'm wrong at any point.
Anyways, here are some information that I've been trying to make sense:
PBR diffuse/albedo range is either 30-240 sRGB or 50-249 sRGB. Let's keep 30-240 for now. So this means, blackest natural dielectric material should not go below 30 sRGB value and whitest should not go above 240 sRGB. I imagine these materials in a 3D scene as Charcoal and Fresh Snow. Although there are sources defining Fresh Snow as 232 sRGB. (Not considering Vantablack, etc).
Let's say, I want to use RAL Classic color chart in my scene. I will take the darkest and brightest colors, RAL 9005 Jet Black and RAL 9016 Traffic White, in that order. RAL 9005 has the value of 16 sRGB and RAL 9016 has the value of 241 sRGB. We are already out of PBR range so I take it as RAL 9016 should be brighter than fresh snow, for example. This is not just for RAL Color but also other color books.
On the other hand, Corona Renderer CShading_Albedo pass has warning value of 0.0 to 0.85 (although I don't know how to convert the range to 0-255). So for whites, If I use a value above 240 sRGB, pass is set show red and has no limit for blacks, by default.
And the more interesting part, Helpdesk says we should keep our Albedo under 180 RGB (218 sRGB).
The way I see it, from darkest to brightest, PBR standarts has a different value range, Corona Renderer has a different value range and color books have a different value range.
So the questions are:
- How do we keep using color books as their defaults in our scenes with values higher than 218 sRGB?
- If we can't, how do we translate these colors to 0-218 range? (Below 180 RGB)
- If we can manage to translate all the colors accurately to Corona, when exporting to a real time engine (or Substance Designer etc.), how do we translate those colors to keep them in between 30-240 range, without manually adjusting all the nodes.
P.S. I totally understand that these color values, books, scans, materials, render engines or shading models might not be or can not be %100 accurate, but still, the difference is obvious to me by numbers. It is possible to adjust everything by eye, use color pickers, post production etc. But my main goal is to understand and translate this ranges in between each other as accurate as possible. Just to sleep better, that's it.
If you made it until the end, thanks a lot. I would really appreciate your opinions.
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Hi, sorry for no responses for such a long time. I will try to fix that. Stay tuned...
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Hello! I was wondering if there is anything new about this? In the meantime I also keep searching and asking around but I guess it's not that easy to find a clear answer regarding this topic. Looking forward to any kind of update on this.
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Sorry again, but nothing so far. I will try asking around in the team again.
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Here is some of the feedback I got from the team:
There is no consensus about what the correct albedo values are.
Some real-life color can be more white due to fluorescence, where the material converts ultraviolet light to visible color and thus seems to glow (for example, washing powder for white laundry contains some fluorescent particles).
As for trying to imitate RAL colors, their RGB values are dependent on the used illuminant (they look different when looking at them in room lit by a bulb and different in direct sun light).
Sorry that it's rather vague, but it seems that the topic is very complicated.
If you have some more specific questions, I guess that would help provide more specific answers. For example: "I am trying to do X, but Y is happening - why?"