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View Full Version : Doesn SSS shaders simulate real transluence effect?


Dreamish
08-29-2004, 09:06 PM
I mean,a SSS shader like the subScatter,diffusion and the "official" one which used to simulate transluence material like milk/skin or marble.But actually for some of these materials,if something is inside the object,you could see/feel something inside(A barely seen blurred black object.)
Like our skin,if you shine your fingers with a very bright torch,you could see veins underneath or even bones....But it seems that those shaders can't do this effect,it just simulate the "glowing" effect of transluence material.
Is it possible to have those effects done?

lazzhar
08-29-2004, 09:15 PM
Real objects are diffrent. But I'm sure if you model all the hidden details, you would get results close to the real transluence. I didnt try it but but I guess you can paint maps for controling the SSS to get better results.

sundialsvc4
08-29-2004, 10:43 PM
Why go to all that trouble just to create translucency? Anything that has an Alpha value less than 1.0 is more-or-less translucent and the effect is effortless to achieve in compositing. (Incidentally, doing translucency directly in rendering takes a lot longer.)

The amount of translucency you actually want is a classic "tweak" and it's nice to be able to adjust it on-the-fly without re-render.

Jozvex
08-29-2004, 11:18 PM
Dreamish look at this image I rendered:

http://www.jozvex.com/temp/translucent.jpg

Is that what you mean? I did that using the Diffusion shader. The cube on the left isn't using any tricks or fake transparency (just SSS), but the cube on the right uses some transparency along with the SSS.

Here is the scene file for Maya 6:

http://www.jozvex.com/temp/translucent.zip

:thumbsup:

lazzhar
08-30-2004, 01:22 PM
Nice rendering Joz :)
Dreamish, I suggest to you to take a look to the PDF SIGGRAPH papers on the renderman.org from the last year(2003) where they explained how Pixar rendered their SSS and faked it many times. It's really interesting to learn how to fake things in 2d like said sundialsvc4, and it's done on the fly too.

ant-
08-30-2004, 01:39 PM
jorvex i have done the stick in the diffusion shader thing a few times, but spent quite a long time tweaking the results, so i thought i would take a look at your scene, but the diffusion shaders don't seem to load correctly. The Shader has no attributes, and doesn't render. I am not sure if this is because we have different versions of diffusion installed or something. I am using maya 6.0.0

I don't suppose you could just give a very quick idea of the settings you used to get the stick in the cube

mrBullseye
08-30-2004, 06:48 PM
Jozvex, how did you achieve that.. I mean, did you use a physically correct sss-shader, or one of the fast ones available?

I'm testing the Mi-sss right now, but I'm nowhere near getting those kind of results yet... maybe I'm doing something wrong, because I cant see the objects I put in my waxy substances at all... :shrug:

lazzhar
08-30-2004, 07:48 PM
I've tested the file posted by Jozvex and it works great. He's just using the Diffusion shader from Daniel (Bigmuh) in nice way.

ant-
08-30-2004, 09:44 PM
So am i. I used diffusion, its all installed and works fine, but when i open jorvexs file it appears blank,

lazzhar
08-30-2004, 09:51 PM
ant
Why not download 6.0.1 from Alias? Maybe it will work.

And for the Diffusion Shader, are you able to use it in other scenes or just the problem comes in this scene from Joz?

Jozvex
08-31-2004, 12:39 AM
Hi, this has happened before where I send a file to someone and my shaders don't show up. :shrug:

There have been two different versions of the same Diffusion shader. An older version which I'm still using (just 'cause I haven't updated it), and a newer one with attributes like IOR and Refractiveness.

I also wonder whether having different Node IDs in our .mi files' would cause the problem?

Anyway, I'll do some testing and try to figure it out. If I can't then I'll just post a screenshot of my settings.

:thumbsup:

_________
UPDATE: I just opened my own scene and the shaders are blank!! :scream: Well actually I suppose that's good because it means I'll get to the bottom of the problem,
-----------

BillSpradlin
08-31-2004, 12:44 AM
The node ID's are only an issue for the local instance of the mental ray Node Factory and wouldn't cause an issue such as that. More than likely it's what you stated, you are running an older version of the .dll file or at least a different one than he is. I had this problem on a couple our systems that were running older .dll's and the Shader would show up in the hypershade, but it would be the old default grey icon and no options in the attr editor.

Jozvex
08-31-2004, 01:03 AM
Hmmmmm. Well I just tried what I believe to be both the old version and the new version (of both the DLL and mi files) but I get blank shaders using either!!

I'm going on the files properties as to which are the old and new versions:

OLD:

Diffussion.dll = Modified: Monday, 24 May 2004, 4:04:14 AM
Diffussion.mi = Francesca spelt "author" wrong on the first line.

NEW:

Diffussion.dll = Modified: Wednesday, 9 June 2004, 2:45:30 AM
Diffussion.mi = Typo fixed and 3 new lines added.

What version are you using Lazzhar? You can see the shaders.

Jozvex
08-31-2004, 02:08 AM
Well, some good news is that I found out you can use the 'getAttr' command on the non-shaders to find out their attributes. So for the stick-cube the setttings are:

* First two colours are only slightly brighter than default.
* Diffusion set on 1
* Intensity set on 5
* Samples on 16
* Direct Scattering on 0
* Indirect Scattering on 0.65

And then because I used FG, I had Use_irradiance turned on, and the Radiance set to a HSV value of 0.4.

And hey I just thought of something. Now that in Maya 6 we have blurry reflections and refractions on normal phong shaders etc, you could probably use blurry refractions combined with fake transparency and the Diffusion shader.

Just meaning that I could probably give my 'green-sphere-cube' some more coolness by blurring the sphere with blurry refraction at an IOR of 1.

:thumbsup:

Jozvex
08-31-2004, 05:05 AM
Yay! My idea worked pretty well I think:

http://www.jozvex.com/temp/InsideSSS.jpg

I used a Diffusion shader with a Phong E applied to the Surface Shader attribute. It uses 0.2 Surface Shading. The Phong E is totally transparent, no diffuse, just pure refraction with an IOR of 1 so that no light bending occurs. Refraction blur set to 10 with 10 rays.

This is cool because you have complete control over the blurriness and visibility of the 'inside objects'.

A slight trick to remember though is that you need to set the IOR of the Diffusion shader to 1 also, even if the Refractiveness is set to 0. It still bends the rays.

In my image I should have actually turned off the 'Visible in Refractions' for the floor, because you can see some white being added.

What do you guys think?

:)

ant-
08-31-2004, 12:26 PM
Yup thats how i have achieved these results before when i tried the popsicle. Thanks for your settings, I am using the latest version of muh and francesca's code, seemed tobe speed up slightly and no longer needed lights to be linked.


btw the reason i didn't get the 6.0.1 update is, there seems to be nothing new and i havn't hit any of the bugs. I hear of people having trouble with 6.0.1 and there seems no reason to wreck my workflow now :shrug:

Getting back to the orriginal problem i think this is the best (if not the fastest) way. I did play with the facing ratio >> ramp >> transparency as a way to do a really quick and dirty way to fake the popsicle transparency. But i dont think it would work on everything

Jozvex
09-01-2004, 03:06 AM
This effect can be achieved with the new Misss_Physical shader too:

http://www.jozvex.com/temp/SSSPhysical.jpg

Maya's rendering power has basically exploded since Maya 4.5!

protproto
09-04-2004, 02:00 AM
Maya's rendering power has basically exploded since Maya 4.5!

Thank you Jozvex for your sharing! Your shader looks great!
As beginner, it was nice for me to try with your scene, even your misss shader didn't work for me, it was empty as it was telled before. But I liked to use your lightsituation, as I often have with SSSshaders lightproblems. (I am on OS X with Maya 6.0.1)
http://maiahnny.home.solnet.ch/physicalmisss.jpg
After I noticed with the red physical misss, that it covers only one side. Do you know why?
http://maiahnny.home.solnet.ch/einseitig.jpg

maia

Jozvex
09-04-2004, 02:59 AM
Well SSS shaders are simulating light penetrating into a solid object that has volume. A flat plane object has no volume, so I guess that's why it doesn't work.

protproto
09-04-2004, 09:56 AM
Well SSS shaders are simulating light penetrating into a solid object that has volume. A flat plane object has no volume, so I guess that's why it doesn't work.

Thanks Jozvex. Of course, that sounds logical.

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