Strange behavior of Houdini's light color

[marcosimonvfx]

Hi

I'm experimenting with (rendering) colorspaces and found something I can't explain. Hopefully someone here can:

#the setup:
My OCIO is set to ACEScg as working space. I create a lightbox with a green wall and shine a red light on it. Rendering on Mantra, preview LUT is turned off (raw)

Scenario #1:
The wall is made green via a color node (0/1/0) and a principled shader that uses point colors. All other things are set to 0.
--> the wall is completely black.

Scenario #2:
The wall uses now a principled shader with a green texture (saved as "raw" with (0/1/0) color values)
--> without anything else the wall still is completely black (no matter whether "source color space" is set to automatic or linear)
--> if I use an ocio transform and transform from sRGB to ACEScg the wall lights up a little!
This makes sense, because when I do the same transformation in Nuke I can see that sRGB 0/1/0 becomes (0.29/5.11/+0.00) - so a pure red light now would pick up some of the color.

Scenario #3:
The wall uses again a color node (0/1/0) with a principled shader. The light now gets a red texture ("raw" 1/0/0)
--> The wall is black again (so I assume no transformation of the texture was done)
--> However: Changing the RGB color settings from (1/1/1) on the light to something else in addition to the texture changes the image.

The last point confuses me. So far everything pointed towards Houdini just reading the RGB values of textures as "data" without changing them unless an ocio node is used. But that way with a purely red texture (1/0/0) there should always be a 0 in green and blue, no matter if I set the light color to (1/1000/1000).
The render also changes whether I use a principled shader or a classic shader and becomes very noisy and error-y when a light color of for example (0.001/1000/1000) is used - so it might be a bug.

 

Wondering if anybody else has any thoughts on that.