Using SSS - help please :)

[atnreg]

Hi!

I try to make a candle but the first problem is how I get the candle body to look realistic with SSS.
I have tried to play with Scatter node settings but couldn't get anything reasonable and settings don't seem to affect

I have checked the dragon SSS demo scene and it of course works but even if I take the dragon object (or copy the surface) to another scene, it changes color (from yellowish to blueish) and if I remove the invert texture nodes the color is closer to the original dragon scene color but again if I try to adjust the colors, I get very little or no change :O
Also the scale and phase settings seem have no effect, I have tried values from 1mm-100m and phase 0.0-1.0.

Manual says: "A specular material is the easiest: by default it is set up properly. Transmission must be nonzero; for the best effect reflection and transmission should be set to 1.0.

On diffuse materials subsurface scattering only works after they are set up with diffuse transmission.

The reflection value needs to be set to a sufficiently low value, as only the part of the spectrum that is not reflected can enter the inside of the object.".

That is confusing as it talks about specular first and says reflection is best as 1, then starts to talk about diffuse use and there it says that reflection(!!) must be low...there is no reflection in diffuse material! Even if it still refers to specular, it is exactly the opposite from one sentence back

But in dragon scene there is nothing connected to Scatter node's Emission pin so obviously that is not needed to get SSS

So, could someone (like Juanjo ) explain the SSS usage thoroughly, preferably with some simple example but carefully explaining all settings and their effect?

And has someone got any reasonable results with SSS other than the dragon demo scene? If so, what I am doing wrong?

Please help, I'm totally lost!

Antti

[juanjgon]

First of all, what kernel are you using? ... SSS only works with Path Tracing or PMC kernels.

-Juanjo

[atnreg]

First of all, what kernel are you using? ... SSS only works with Path Tracing or PMC kernels.

-Juanjo

Oh sorry, forgot to mention that, yes I always use PMC

[juanjgon]

If you want to share your scene perhaps I could build the SSS shader for your object. It is hard to say what could be the problem. The SSS setup is a bit tricky (the lighting setup, the object and scene scale and so on)

-Juanjo

[atnreg]

If you want to share your scene perhaps I could build the SSS shader for your object. It is hard to say what could be the problem. The SSS setup is a bit tricky (the lighting setup, the object and scene scale and so on)

-Juanjo

I actually don't have any scene yet, just wanted to test the SSS so that when I have the candle object, I know how to make it look good

And I would specifically like to UNDERSTAND the SSS settings, not only get working solution
Otherwise Octane is very easy to understand and set up as it works as expected optically and physically but this SSS seems to be very complicated to understand

I thought it was that the scale sets the distance how long the light can go but not from the light source but from the surface, i.e. surface thickness. It seems though that the scale means distance from light source which makes it very difficult if the object moves in scene (even not animated).
Also I don't understand why there is the Emission pin in Scatter node, how and when that is supposed to be used?

So what I need is some example (e.g. cylinder that has light coming close from above like candle so that the light penetrates to the object some distance but then fades.
I simply cannot seem to make that work as I obviously don't understand the different settings.
The manual explains those but it is quite confusing as I told

Main questions are:
-can I use any light source i.e. both real lights and emissive surfaces?
-what effect the colors give to Absorption and other settings that manual only refers to as floats?
-the inverted color seems to work in dragon scene but not in any of my own trials, even with that same object, the colors are always something between?
-how to set up the colors so that the light source, its effect on the surface and the scatter effect are close to same color?
-should the light source be small or large, even larger than the object? I think not but want to be sure
-any 'tricks' needed in light source or rendertarget or other part of scene?

I will continue testing but I would be very happy if you could explain the whole idea of SSS in Octane, best with illustrations of how different settings affect the result but text is fine too

Thank you very much again!

Antti

[atnreg]

Now I slowly start to get it, I loaded the dragon_sss scene and started changing the values, that way I slowly noticed which affects what. And now I even managed to get my candle test to work, some strange things still with colors but it's getting closer
Of course the flame is still missing, now the light source is the candle-snuff which of course is totally wrong but from this angle it is not that bad
The candle object was modeled in ZBrush, then layout made in Lightwave and rendered with this excellent Octane plugin
Scale=80m(!!), Phase=1.0, Scattering=0.23