Re: blackbody and daylight functions


Brecht Van Lommel
 

From what I understand, high blackbody temperatures giving similar colors to a blue sky is coincidental.

Still, I think that with correct color space conversions and a neutral view transform the result should look blue rather than red/purple. And I do get blue with OSL blackbody() in Blender/Cycles. So I suspect a color space conversion issue.


On Mon, Jan 11, 2021 at 1:28 PM <chrisbrejon@...> wrote:
Hi everyone,
thanks a lot for your answers ! They are definitely helpful.

I was not speaking specifically about skylight here even if topics are definitely connected. ;-)
I have been looking at some papers myself for the past few months and there are indeed different approaches/datasets :

wiki_sky_comparison_02
Sebastien Hilaire has done a great presentation, comparing different approaches (with LUTs, without...).
So we could say that skylights are indeed a complex topic which include many factors/parameters.

In my original question, I was actually more talking about light's temperatures, like an area light.
If we look at Arnold, Guerilla or Renderman,you may find in the lights some temperature options.
If we look at the Renderman documentation :


We can read that at 15000 to 27000 kelvin temperature would be a clear blue poleward sky. Except that it looks very red/purple...
I wish there would be a mention : blackbody values are not recommended for temperatures above 5500 for example. But if there is
no general agreement/consensus on a daylight data set, that would indeed make things hard to implement. ;-)

I don't know if any of this makes sense,
Chris

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