Properties of different materials?

[loserem]

Hi everyone,

 

I'd like to know if there's any list, tut or something wich explain the difference between some materials like wood, metal, crystal, etc... in A:M terms like refraction, reflection, transparency, etc... My first steps in differencing materials have been applying decals, but, of course, wood does not reflect light the same as a metal does and a generic comparison list would help a lot.

 

Thanks for helping me.

[ypoissant]

This is a much more complex question than it seems.

 

The main visual characteristic of material the color of course. The second most important characteristic is rough vs shiny. When you try to reproduce real world material, try to analyse them from those two characteristics.

 

Through the years in which computer graphics have developped, researchers have come up with a whole set of cheap tricks to help simulate in CG what we perceive in real life. Thus the plethora of surface properties available such as diffuse falloff, specularity size, intensity and color, reflectivity, etc.

 

In reality, material appearance is very much more simpler than that. It all boils down to reflectance or more to the point to "Bidirectional Reflectance Distribution Function", commonly known as BRDF. That's all. A BRDF represents how light is reflected off a material surface.

 

The catch, though is that a BRDF itself is a very complex 5D function. It is very expensive to acquire a BRDF of a material because it requires very expensive equipment and thus only large studios can acquire them and they keep the data for themselve. So there are a very small set of low quality BRDF data available on the net. The other catch is that, as the name implies, a BRDF is, by its very nature "distributed", which, in the computer simulation world, signify that it takes large CPU resource to correctly use a BRDF once you have one which means very long render times.

 

For this reason, most 3D application users still prefer to use the old efficient tricks like specularity, reflectivity, etc. to simulate material appearance. Unfortunately, there are no scientific rules that will translate a BRDF into a set of those trick properties. You need to experiment and tweak until you get the look you want for the given scene you are building.

 

A:M comes with a good set of "materials". Those are preset material properties that gives believable characteristic appearances. I recomment you start by using those materials and examine how they were setup to give their appearances. This will help you understand how to use A:M surface properties and come up with your own materials.

 

There are a very few number of material masters in the 3D universe. Those who have become masters have been working with material setup for a long time. And, unfortunately, there are very few tutorials on the subject too. This is a vast and complex subject and mastering it requires both a strong technical basis as well as a keen artistic eye.

[loserem]

Thanks for your comments Yves,

 

Essay and error. That's what I'll do. I have only a little experience with A:M and with 3D software in general and I've noticed that recreate ambients, realistic or not, is a very complex work.

 

Thanks again.