How to make Translucency (SSS) effect obvious ?

[modoneer]

I'd like to make syrup materials like chocolate and jam. And no matter how I set the parameters in Translucency (SSS) section, it seems no obvious response except when I switched the type to Hard(wax) model. But the look of Hard model is too much for me.

I think the appearance is related to actual mesh size, so what's the unit of those parameters like Thickness? mm,cm or meter? In my situation after choosing the Hybrid model, the mesh just shows the Refraction color.

What is the relationship among Refraction color, Fog color and Translucency color?

Here is my test scene file:
2014_11_Nov_Vray_learning_6_SSS.zip

Thanks,
Kent

[kubbek]

I have also trouble to control translucent effect in VrayMaterial. It would be also great to have presets in fastSSS2 material for a starting point. Default settings give no translucent effect at all.

[vladimir.nedev]

I'd like to make syrup materials like chocolate and jam. And no matter how I set the parameters in Translucency (SSS) section, it seems no obvious response except when I switched the type to Hard(wax) model. But the look of Hard model is too much for me.

I think the appearance is related to actual mesh size, so what's the unit of those parameters like Thickness? mm,cm or meter? In my situation after choosing the Hybrid model, the mesh just shows the Refraction color.

What is the relationship among Refraction color, Fog color and Translucency color?

Here is my test scene file:
[ATTACH]21638[/ATTACH]

Thanks,
Kent

Generally all distances in the V-Ray materials/settings are in meters, unless otherwise stated in their name. At some point I will mark them as "distance" type MODO channels so you can specify cm, mm, etc. when entering the
values (and this will also clear-up the confusion what the actual units are).

So, the "thickness" is in meters. When "fog units system scaling" is checked, the "fog multiplier" is also in meters (or some unit derived from meters, it is a bit complex). If it is unchecked the "fog multiplier" is in centimeters.
The thickness is actually the maximum distance inside the object to trace, so it is an optimization parameter, you can just increase it to some huge value and leave it there.

If you are going to use just the fog, with no translucency, it is best to set the "fog color" to whatever color you want in the final image and then play with the "fog multiplier" to increase/decrease the absorption.

If you are going to use the translucency (SSS), it is best to just leave fog color at some grey value. There is a caveat here though, if you set ANY of the color components of the "fog color" to 1.0, it will
disable the translucency effect completely. I am not sure whether that's a bug or intended behavior, Vlado can tell more probably.
After that you set the actual color you want in the "translucency color".

Bear in mind that the SSS in the V-Ray material uses only 1 bounce for scattering. It is also sampled with the image sampler (there is no separate subdivs parameter).
This means it will be very hard to clear up the noise.
Which means it is probably best not to use it, and instead use the V-Ray Fast SSS2 material instead. More on that in a separate reply.

V-Ray for MODO supports the "thickness" input of the gradient texture, so you can also use that to achieve translucent effects. I think there are some
examples of this in the MODO forums.

Greetings,
Vladimir Nedev

[vladimir.nedev]

I have also trouble to control translucent effect in VrayMaterial. It would be also great to have presets in fastSSS2 material for a starting point. Default settings give no translucent effect at all.

For the Fast SSS2 material, it is probably my fault the default values have no translucent effect. I obviously didn't think them through completely.

I set the multiple scattering mode to "object-based illumination map". In that mode the number of samples depends on the surface area of the object.
If the surface area is large enough, you will have enough irradiance samples, but the object will be to big to have any noticeable translucency.
If it is small enough to have noticeable translucency, the number of irradiance samples is too little, and the illumination computations are wrong and the SSS effect is lost.
I will talk to Vlado and probably change the default values for a future beta release.

So, the best way to work with the SSS2 material (and for that matter the Skin material as well), is to make sure your object is the correct scale.
Then switch to "Prepass-based illumination map" or "Raytraced" for the multiple scattering. Or you can leave it at the default "object-based illumination map"
and play with "samples per unit area" parameter.

If you want to increase/decrease the SSS effect without scaling your object in the scene, increase/decrease the "Scale" or "Scatter radius" parameters.

Greetings,
Vladimir Nedev

[kubbek]

I set the multiple scattering mode to "object-based illumination map". In that mode the number of samples depends on the surface area of the object.
If the surface area is large enough, you will have enough irradiance samples, but the object will be to big to have any noticeable translucency.
If it is small enough to have noticeable translucency, the number of irradiance samples is too little, and the illumination computations are wrong and the SSS effect is lost.
I will talk to Vlado and probably change the default values for a future beta release.

So, the best way to work with the SSS2 material (and for that matter the Skin material as well), is to make sure your object is the correct scale.
Then switch to "Prepass-based illumination map" or "Raytraced" for the multiple scattering. Or you can leave it at the default "object-based illumination map"
and play with "samples per unit area" parameter.

If you want to increase/decrease the SSS effect without scaling your object in the scene, increase/decrease the "Scale" or "Scatter radius" parameters.

Greetings,
Vladimir Nedev

Thank you for your explanation. I experimented with the fast sss2 material and it works well.

[modoneer]

At some point I will mark them as "distance" type MODO channels so you can specify cm, mm, etc. when entering the values (and this will also clear-up the confusion what the actual units are).

Thanks Vladimir!
It's great to have unit clarified for parameters.

Which means it is probably best not to use it, and instead use the V-Ray Fast SSS2 material instead. More on that in a separate reply.

After giving V-Ray Fast SSS2 a try, it did let me reach what I'd want to achieve much faster.



Regards,
Kent