Chema Guerra (Author of Fryrender) says,
This post is just a small tip with a visual explanation attached to it.
As you know, fryrender vBeta1.9 will bring a new BRDF which produces better materials. This new BRDF blends mirror-like materials with lambertian materials seamlessly, producing more believable rough materials (such as metals and plastics).
Needless to say, this improvement in the material system will bring more life-like materials in general, but, as always, a good understanding of it will be crucial in order to being able to get the most out of it.
For example, one IMPORTANT thing to know is what is the exact difference between a 'quasi-lambertian' material (Roughness close to 100), and a lambertian material (Roughness = 100).
Lambertian materials (R=100) have *NO FRESNEL* effect at all. They diffuse light in all directions. They're the most rough materials possible. In fact, they're so rough that there's no such thing as a 'lambertian material' in nature. The good thing about lambertians is that they have a very simple BRDF and their lack of directionality makes them render pretty fast.
Quasi-lambertian materials (R almost 100) are slightly specular. They have a small scent of Fresnel, and are slightly reflective at grazing angles. They look pretty much like lambertians, but they're capable of reflecting the environment slightly at grazing angles. <= THIS behavior looks MUCH MORE natural to the eye than that of a lambertian material.
Basically, you could say that a lambertian material looks exactly the same no matter from what angle you're looking at it, while a quasi-lambertian becomes slightly more reflective at grazing angles.
Here's a very powerful example. Please, watch it carefully, because the highlighted differences are IMPORTANT in order to learning how to create better materials.
The first frame contains lambertian materials (R=100) only.
The second frame contains quasi-lambertian materials (R=85) only.
The third frame adds some text comments to the second frame.
As you can see, the front of the red element looks more or less the same in both cases, *BUT* the right side looks TOTALLY unnatural in the first frame while it exhibits a very realistic behavior in the second one.
-- CONCLUSIONS --
1- Lambertian materials do -not- exist in nature. In the real world, the most rough materials are closer to roughness 85..95, but never 100.
2- Lambertian materials render faster, though.
3- The use of quasi-lambertians is --STRONGLY RECOMMENDED-- over lambertians. Use quasi-lambertians whenever that scent of specularity is crucial. For example, -never- make lambertian walls for a building. Never make lambertian floors for a street, etc...
I hope that this tip will be useful, and also that the new BRDF will help you encore the realism of your scenes without any extra effort on your side.
Thanks for watching!
Last edited by chema on Thu Oct 25, 2007 1:00 pm; edited 1 time in total
What would be an equivalent setting in luxrender to replicate this phenomenon in Fryrender?
thankyou for your time in helping me with this issue