Thank you again for your quick reply.
- - -
I am not quite done experimenting with this but everything points me to the one question:Would it in theory be possible to have Octane combine the "black shadow" and "reflection passes" in one pass (layer mode normal)?
¨At least that is the combination I would be most interested in.
For some cases it might as well be interesting to have
"Shadows and reflection"
"Colored Shadows and reflection"
each combination in one pass.
- - -Update/Edit:
The underlying question I have is:
Are the choosen layer blend modes set in stone or can OctaneRender calculate combinations of those passes with a resulting layer blend mode of "normal"?
Black shadows (normal)
Reflections (linear dodge - add)
Colored shadows (multiply)
Would it be possible to render out
Beauty + Black Shadows + Reflections
in one pass with layer mode normal?
- - -Just to be clear for some cases you definitely want to have shadows and reflections on separate layers.
But the longer I test with this the more I get the impression that for compositing it might actually be easier for some cases to have black shadows, reflections and maybe even beauty combined in one pass with the layer mode normal (IF that would be possible).How do others think about this?
No, Octane cannot combine those passes in one single pass. I don't fully understand the original question but let me try to answer the underlying question
The blend modes are fixed but we didn't choose them arbitrarily. For example, consider a black shadow cast on a plane. You can think of this shadow as a ratio defining how much of the underlying plane is actually visible (Or the other way around, how much light is actually falling on the plane). More formally:
shadow(at point x) = light(reaching point x) / total_light(send towards point x)
, a ratio of 0 means fully shadowed, a ratio of 1 means fully lit. For black shadows (and matte material), we write this value directly in the alpha channel, alpha 1 means shadowed and alpha 0 means not shadowed. If you then do alpha blending (normal mode) you get
alpha * foreground + (1 - alpha) * background
. Since the black shadows is only an alpha channel foreground is 0 and the formula reduces to
(1 - alpha) * background
. And that is why normal mode is used. Does it make any sense?
Some render engines (Mental ray for example
), render shadows as the differences between
render without shadows - normal render
. In that case, the shadows need to be subtracted. We choose not to do this because it requires to render the scene twice (with and without shadows). I also don't know if this works good in compositing on a backplate for anything but black shadows.