Explanation of Sub Surface Scattering?

[DaForce]

Mmm the leaf texture is there. Its a red leaf.
the texture is just not shown on the inside, and after having abit of a tinker now, i cant seem to get it to show up. any ideas?

Well the sphere just had the leaf texture wrapped around it and then the shape of the leaf was cut out using displace and water level. So the texture is still there but it just doesnt show up on the inside curl of the leaf, what you see is the bloodredness.

[TishoChaos]

@ngrava: Is this what you are after?



The leaves material has simple refraction with glossiness 0.1 on it. You don't need translucency for leaves because they are just planes. Translucency is more useful when the objects have volume.

We are working on the upcoming translucency tutorial.

[dieciduej]

"You can have the max file for it if you want."

Yes, I would be interested in getting the file. By playing with it I may get a better understanding of SSS. So if you could post it that would be great. Thanks in advance.

JoeD

[DaForce]

Tisho:
That seems like a pretty good alternative!! Didnt even think about that.. haha
It seems my way doesnt work to well (at all) on planes or think meshes, maybe i am just missing something but on a very think box no light comes thru at all.
Ahh well.

Side by side comparison of Mine and Tisho's way.


Its weird how the texture shows up on the inside when using glossy refraction but not when using Translucency...odd

And the max file with both materials.
http://www.apex.net.au/~daforce/vray/leaftest.rar

[ngrava]

Well, I still need to mess around a bit more but I think I have a much better handle on it. Basically, The three main parameters that affect translucency are IOR, IOR glossiness and Thickness. If you need a light boost you can always use the light mult. Scatter and fwd/bck coefficients just don't seem to be as effective as they used to. That was the big brain block for me. That's OK though. The parameters that effect the surface the most are actually closer to how things work in the real world. Really, when you think about it; Sub Surface Scattering is really just refraction glossiness (scattering really) that transmits light through a surface and can be absorbed within the object. So, in this case, Refraction glossiness is the scattering of the light, IOR is the amount of light that is aloud the pass through the surface and thickness is the absorption depth.

Tisho, Yes that's closer to what I'm trying to do except that my petals actually have depth so this doesn't work as well.

DaForce, Thanks for that strange optical illusion there. It is odd that the texture isn't transmitted though the object... Maybe it's because the IOR would need to be mapped in this case.

[TishoChaos]

Hi Daforce!

This oddness is actually the expected behavior from the material. You don't see the texture on the back side of the sphere, because it is leave texture and has no thickness. If you want to see it, drag-copy the diffuse map into the translucency map slot.



And still you can't see a lot of the texture because the translucency doesn't affect much the surface with a little thickness.

Another thing - the image that you have renders for 39s. You can cut that down to 10-15s by Using Interpolation with Subdivs 24 and min/max rate on the refraction interpolation -4/-2.
Here is the same result for 15s.



There was also a discussion with RErender about the leaf texture - I was also kind of confused from all that so here it is. As you said, the leaf texture was wrapped around the sphere, leaving an area under the water displacement level - this area that is left out looks like a leaf, but in fact it is the surface under water which happened to be looking like a leaf

Here is the sphere from a bit different angle:


I hope I left nobody scratching his head.

[DaForce]

Yeah it is a bit weird.

Well I reckon a combination of both techniques is what your after... good luck hehehe

Tisho:
Ahh that explains the mising inside texture.
As for the speed, I had tested it with interpolation and it was much faster, but the version i saved and uploaded was before I had done that.

Yeah it did look rather odd without the texture on the inside so that was confusing, although i hoped the 360 rotation AVI would help resolve this. But having the texture on the inside makes things alot easier to explain

Thanks for you input on this Tisho

[TishoChaos]

No Problem DaForce.

Just a quick explanation - the translucency color as I said is the color just underneath the object's surface, the Refraction color is the color just above this surface, and the Fog Color is the color inside the object that fills it. There will be also Examples in the Help about translucency.

[DaForce]

Ahhhh HA.....got it... Never really though of it that way. But now its blindingly obvious. Thanks heaps

Ohhh and just to squash any more doubt about the leaf, a few more renders without any displacement and with the texture. Only the white part was removed out of the mesh using displacement, the leaf (red) part was left there as there is no point in removing it is there now

[RErender]

heheh, I see now. Thanks for your examples and explanations guys.

[flipside]

No Problem DaForce.

Just a quick explanation - the translucency color as I said is the color just underneath the object's surface, the Refraction color is the color just above this surface, and the Fog Color is the color inside the object that fills it. There will be also Examples in the Help about translucency.

Hu? The color above the surface? I don't understand that one, above the surface is air no?

[CCS]

Yes. He's talking about refracted light, which does occur just outside the object.

[RErender]

He didn't say "above the surface" he said "above this surface" "this" surface being the "color just underneath the object's surface" which would make it THE surface

[CCS]

Don't we always use "surface" (whether 'the' or 'this') to refer to the outer extents of an object's mass?

[RErender]

hmmm, how many surfaces does an onion have?

*note: all opinions and translations are mine and mine alone, not intending to put words in the mouth of the author. :P