Why no complete material?

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  06 June 2012
Why no complete material?

Why is there no material neither for mental ray nor vray? The A&D materials has everything except fast SSS and physical SSS. What could possibly be the point of having these attributes in their own separate materials? Its like the developers intended to make it impossible for users to have a material with all the needed attributes. Having the feature of SSS in separate material with little more but diffuse is almost as bad as like having a separate material for reflections. PSSS can be combined with AD material using the material to shader thing but it does not allow the use for refraction. A questionable option is to mix AD and PSSS in a shellac material to be allowed to use PSSS. Fast SSS however can not be combined in any proper way it seems with AD.

In short why is there no material with all the needed features that are available in the renderers?
 
  06 June 2012
For the same reason that there's no single pill cure all diseases Diverging requirements ask for different solutions.
 
  06 June 2012
Incorrect analogy. These attributes I mentioned are not mutually exclusive, they are all needed for the same thing. A better analogy would be a car without breaks. It can drive, has lights, good seats all stuff that a car needs... except breaks which is a vital part.

There is no reason to split attributes that are useless alone and only useful when combined and then not even make a proper way to combine them. Like forcing someone to either use fork or knife to eat, not both.

Diffuse, reflection, refraction and SSS are all needed for a complete material.

Last edited by TheHagfish : 06 June 2012 at 06:12 PM.
 
  06 June 2012
I'm not arguing, I'm explaining Blending all the components correctly is far from trivial, requires extra work that it looks like nobody has done yet.

Last edited by Glacierise : 06 June 2012 at 06:42 PM.
 
  06 June 2012
Originally Posted by TheHagfish: A better analogy would be a car without breaks. It can drive, has lights, good seats all stuff that a car needs... except breaks which is a vital part.
That is an incorrect analogy as well. The proper would be a mode of road transportation that can complete the main objective of all modes of road transportation. As described by Glacerise that is a difficult task to achieve, and could result in having to remove optimizations that can be made by removing certain items from the equation. So what is more important speed and optimized code or a do-it-all material?
Quote: Diffuse, reflection, refraction and SSS are all needed for a complete material.
Personally I think you need to go read up on the materials. Translucency (which both VrayMtl and A&D support) is a form of SSS. So your assumption is wrong as support does exist, but to provide speed enhancements it is typically on single bounce in translucency and multi-bounce in the SSS materials.

You should go read up on the BRDF and BSSRDF models to know more about the technology that the Base material and SSS materials are typically based off of.

-Eric
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"The Evil Monkey hiding in your closet."
 
  06 June 2012
Originally Posted by PiXeL_MoNKeY: That is an incorrect analogy as well. The proper would be a mode of road transportation that can complete the main objective of all modes of road transportation. As described by Glacerise that is a difficult task to achieve, and could result in having to remove optimizations that can be made by removing certain items from the equation. So what is more important speed and optimized code or a do-it-all material?

So what you're saying it's simply too difficult to achieve for programmers? No one has succeeded? Sounds very strange when thinking about all the other graphical features programmers have been able to achieve. You ask if it's better to a) have the materials but not be able to use them properly, so they are almost redundant waste of time or b) not having them at all. Like having access to both nails and hammer even though they can not be used together (for some magic reason), or have neither. What is the use of them then? Just to play around with?

Originally Posted by PiXeL_MoNKeY: Personally I think you need to go read up on the materials. Translucency (which both VrayMtl and A&D support) is a form of SSS. So your assumption is wrong as support does exist, but to provide speed enhancements it is typically on single bounce in translucency and multi-bounce in the SSS materials.

Translucency is one part of SSS. Could you make juice, skin, gemstones, ketchup materials etc with only translucency? Like the real deal is only necessary if you need puuurrrfect stuff?

[
Originally Posted by PiXeL_MoNKeY: You should go read up on the BRDF and BSSRDF models to know more about the technology that the Base material and SSS materials are typically based off of.
-Eric

I really don't see what use I would have of reading lots of complicated text and math equations that is used by programmers or whatever to achieve these features. You mean I should try to write my own materials or something?

Please explain to me then how these materials are used by people. All I find about fast SSS is people talking about making human skin and the only reflection they care about is specular, meaning reflection of light sources and not environment. Yes there is a custom shader by some famous guy here that adds reflection to fast sss skin material but it does not include refraction making it incomplete. It can not be used for stuff that require refraction, reflection and sss. I wonder how did people use fast sss before this guy came and wrote this material? I find little to no info about how to use physical sss material. Only a few about opaque materials and I find them not covering enough about how to use psss with all it's parameters and the seemingly crazy photon amount required.

The explanations also does not seem to match with the results I get. Scatter coefficient reducing "grainyness" and "splotchy effect"? My results are rather about changing the color of the photons.

Last edited by TheHagfish : 06 June 2012 at 10:03 PM.
 
  06 June 2012
The way people are practically using it is work multiple renders and materials that get comped together, that gives both soured and control.
 
  06 June 2012
Originally Posted by Glacierise: The way people are practically using it is work multiple renders and materials that get comped together, that gives both soured and control.

Impressive that people have patience to learn and do that. How does it work for animated videos? They compose every frame?
 
  06 June 2012
Oh yeah. Many dozens of elements, depending on the complexity of the shot. It's not done per frame, but per shot - connected sequence of frames between cuts.
 
  06 June 2012
So that's the way to do it. Just annoying that there are no tutorials how to compose stuff properly. All I hear is the screen dodge filter in photoshop as if that would be enough. No layer mode seems to work properly with any type of reflection element render and sss of any kind can not be rendered as element.
 
  06 June 2012
Originally Posted by TheHagfish: So what you're saying it's simply too difficult to achieve for programmers? No one has succeeded? Sounds very strange when thinking about all the other graphical features programmers have been able to achieve. You ask if it's better to a) have the materials but not be able to use them properly, so they are almost redundant waste of time or b) not having them at all. Like having access to both nails and hammer even though they can not be used together (for some magic reason), or have neither. What is the use of them then? Just to play around with?
It is the same reason there a special applications dedicated to animation, modeling, etc. The code and workflow is optimized for those specific tasks.

Quote: It can not be used for stuff that require refraction, reflection and sss. I wonder how did people use fast sss before this guy came and wrote this material?
You should really go read up on the material models. SSS is a sub function of refraction. So any SSS is already using refraction. For reflection/refraction/SSS you would use translucency, fog, or glossy refractions to get the SSS effect you want. You won't get refraction plus multi-bounce SSS. Refraction bends the intersecting ray by the IOR at the entrance and exit of the surface, after that it is going to be effected by the SSS. So I have no idea why you want everything at once.

Quote: I find little to no info about how to use physical sss material. Only a few about opaque materials and I find them not covering enough about how to use psss with all it's parameters and the seemingly crazy photon amount required.
Again it comes down to speed and optimization. Physical SSS is like brute force GI, where fast SSS is like FG or light caching. Therefore people use the Fast SSS version with the limitations, because of the optimization/feature tradeoff.

-Eric
__________________
"The Evil Monkey hiding in your closet."
 
  06 June 2012
I think what you need is a course on shading for production. I'm not places like Gnomon should have these.
 
  06 June 2012
Originally Posted by PiXeL_MoNKeY: You should really go read up on the material models. SSS is a sub function of refraction. So any SSS is already using refraction. For reflection/refraction/SSS you would use translucency, fog, or glossy refractions to get the SSS effect you want. You won't get refraction plus multi-bounce SSS. Refraction bends the intersecting ray by the IOR at the entrance and exit of the surface, after that it is going to be effected by the SSS. So I have no idea why you want everything at once.

So transparent materials in real life (semi transparent plastics, various organic substances etc) never have complete sss? Only the translucent effect?

Originally Posted by PiXeL_MoNKeY: Again it comes down to speed and optimization. Physical SSS is like brute force GI, where fast SSS is like FG or light caching. Therefore people use the Fast SSS version with the limitations, because of the optimization/feature tradeoff.

-Eric

I guess psss is not for the average user then, only the most high end stuff. :(
 
  06 June 2012
Originally Posted by TheHagfish: So transparent materials in real life (semi transparent plastics, various organic substances etc) never have complete sss? Only the translucent effect?
3d is about mimicking real life. I personally don't care about how accurate the calculation is, I care about how close it looks to what the client expects (see look development below).
Quote: I guess psss is not for the average user then, only the most high end stuff. :(
Not really. The high end guys would use what gives them the proper look for the shot. Whether it is Fast SSS, Physical SSS, or some internal tool/shader all depends on the production, resources available, and shot requirements.

In reality if you want Physical Correct you need to use an unbiased renderer with unlimited bounces. That is the best way to ensure that all light/materials/shading/etc is physically accurate. Using Final Gather + Physical SSS is kind of an oxymoron. Your light caching isn't Physically Correct (it can be, but requires a user that knows what they are doing to get there), but you care that the SSS material is? There is a lot more that goes into "Physically Correct" beyond the materials. If any of the lights, materials, gi, shadows, camera, scale, model density, etc, etc, etc aren't physically accurate then what is the specific need for the SSS to be?

The best process really is to start with look development (see Scott Kirvan's article on it here), and then make sure your scene gets as close to that as possible. How you get there shouldn't depend on the name or technology behind a technique. It should depend on the tools you have available and what you can do with those tools to get to the end result.

-Eric
__________________
"The Evil Monkey hiding in your closet."
 
  06 June 2012
Originally Posted by PiXeL_MoNKeY: 3d is about mimicking real life. I personally don't care about how accurate the calculation is, I care about how close it looks to what the client expects (see look development below).Not really. The high end guys would use what gives them the proper look for the shot.
...
In reality if you want Physical Correct you need to use an unbiased renderer with unlimited bounces. That is the best way to ensure that all light/materials/shading/etc is physically accurate.

I never meant that it's the math behind that is of importance, but just the result. I assume that certain materials requires SSS and features that are not available in the SSS materials. To make for example fruit juice you need both SSS (I doubt translucency alone from AD is enough to make it look good) and reflection. I red that psss is the proper thing for making gemstones like emeralds but emeralds have both reflection and refraction.
 
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