Establishing correct BRDF settings?

#1

How do you guys decide which amounts to use for different materials? I find it difficult to look at an object and decide how reflective it is based on an angle. Any tips?

Also, I read that this is a multiplier for the regular reflection value in mr Arch Design material. Does that mean that I should leave the regular reflection value set to 1, and make my adjustments here?

#2

I’m guessing your talking about the mental ray arch shader?

Look up complex index of refraction, that will give you some settings for common materials.

More here:
http://forums.cgsociety.org/archive/index.php/t-1025256.html

#3

Trust it to be complex. I was hoping someone would say along the lines of look at the surface, close one eye and point the hour hand of your watch at the sun and you’ll be enlightened!

#4

Where would the fun in that be :wink:

#5

Yep good point. I just thought there might be a simple observation technique to adjust this. Not quite up to the mathematics behind this!

#6

results are what matters, and Art Direction really doesnt care if its mathematically correct. So yeah, you have to do by eye.

#7

So how do you select the right settings? I was sat at home trying to work out how reflective surfaces were and what settings I would use. My curvy speakers for example looks more reflective face on than on the edges which I think had more to do with the lighting position in the room. I may be wrong but I don’t think I’d use a higher reflectancy when looking straight at it.

#8

Well keep in mind that BRDF settings are simply a workaround for simulating the Fresnel effect. They don’t actually “exist” in real life - the Fresnel effect applies to any material, but with most CG shaders it doesn’t “look right”, so BRDF curves were used to tweak the effects.

But with the mia_mat_x shader, you can just use the Fresnel effect and then the IOR to achieve 99% of the materials you need. The trick is to push your IOR beyond diamond (2.5), especially with metals. For Brushed Nickel, for example, I generally use an IOR of 30.

What you see in metals that tends to appear to defy the Fresnel effect is simply microsurface scattering. Take some photos from a few, you’ll see what I mean. There’s a few excellent posts illustrating this topic around here somewhere, I’ll try to dig 'em up and link you to them.

#9

This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.