Understanding Volume Absorption/Scattering Colors

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CodeHD
Posts: 96
Joined: Tue Dec 11, 2018 12:38 pm

Understanding Volume Absorption/Scattering Colors

Post by CodeHD » Wed Dec 19, 2018 7:38 pm

I have a bit of a problem with the color settings in the volumes. While playing with it, I have come across some behaviour I find odd.

Question #1:

Simple test setup consisting of:
- a Laser, white
- homogenous world volume
(- and a camera)

Initial setup: absorption and scattering colors white (RGB value (1,1,1)), scattering scale seomthing like 0.001:
I get a white beam, as expected
1.jpg
Next, I change the scattering color to (1,0,0)
I get a red beam, as expected
2.jpg
Next, I change the absorption color to (1,0.99,1)
I get a yellow beam and green atmosphere.
3.jpg
I would expect a red beam as before. Doesn't matter how much green is absorbed, as it should not be scattered.

Is this a bug or am I missing something?

Question #2:

In the wiki, I read that the scattering color can be greater than 1 to account for particle density. What is the difference to the scattering scale exactly? I would have assumed that the scale describes the density, and the scattering color adjust the absorption during each reflection (separate from the "normal" absorption which happens without an accompanying scattering process).

So, what is the difference (if any) from a combination of high color + medium scattering scale to medium color + low scattering scale?
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B.Y.O.B.
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Re: Understanding Volume Absorption/Scattering Colors

Post by B.Y.O.B. » Wed Dec 19, 2018 7:48 pm

CodeHD wrote:
Wed Dec 19, 2018 7:38 pm
In the wiki, I read that the scattering color can be greater than 1 to account for particle density. What is the difference to the scattering scale exactly? I would have assumed that the scale describes the density, and the scattering color adjust the absorption during each reflection (separate from the "normal" absorption which happens without an accompanying scattering process).
The scattering scale is just a helper.
In the background, this is happening:

Code: Select all

final_scattering_color = scattering_color * scattering_scale
So the two are just multiplied, as the name "scale" suggests.

Here's the code where you can see that exactly this is happening: https://github.com/LuxCoreRender/BlendL ... __.py#L238
(the comment contains a copy/paste error, it should read "scale texture" instead of "colordepth texture")
So, what is the difference (if any) from a combination of high color + medium scattering scale to medium color + low scattering scale?
There is no difference.
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