Accurately Determining GI Influence

[jujubee]

Is there a method to do this? It seems like strong colors in a room can overpower white-ish materials.

[RErender]

One rule of thumb is to consider the surface of the object, Carpet for instance is often mapped to a flat surface that does not diffuse the GI but in reality it is guite rough and does not actually bounce much light so reducing the send GI is in order for carpet .25 to .30 seems about right and so on.

[priad]

It will be cool if we had a list of GI influence by materials, it will be very usefull.
Carpet wood metal concrete etc...
It depend also of the finishing or not?

[jujubee]

Using Vratmtl Wrappers right to reduce the send?

A comprehensive list for GI (almost like an IOR) would be nice... This should be in the wishlists.

[n6]

Lightscape works like that : it use different coefs depending on the material surfaces for the reflected radiosity energy.

[priad]

I don't know if there is a real difference between Vratmtl Wrappers and an old right clic (vray property) I think that they are the same.
Color bleeding in Vray is strong perhaps a little too.

[flipside]

It's impossible to make a general list of how much a certain material will absorb/reflect light.

The rule is pretty simple, a light color (or texture map) will bounce more light than a dark color. A reflective material will bounce more light than a non reflective one (if you have reflective GI caustics turned on!!). But the more reflective, the less impact the diffuse color has. So a very reflective red surface will not send much red into the scene, it will leave the light ray that bounces on it almost the same color as before the bounce.

But note that by default reflective GI caustics is turned off, so reflection doesn't influence GI in that case, only diffuse does.

As rerender said, not only the material is important, also it's surface roughness.

In real life there is as much colour bleed as in vray, but your eye compensates for this. It's like an automatic white balance device

Cameras always apply a white balance correction to compensate for the colour bleed. You can easily post process your images to get rid of excessive colour bleed.

The send GI can reduce it too, using lower second bounce multiplier or using the sturation controls in GI rollout. A bit of all three will greatly reduce the colour bleed.

[plastic_]

it would be really important to control color bleeding on material basis.
otherwise using flat mapped planes for grass etc. is really a problem.
the GI send value isn't really the right tool to deal with it.

[jujubee]

It's impossible to make a general list of how much a certain material will absorb/reflect light.

I don't think a 'general' list for common objects/mats would be impossible. On the other hand, to be completely accurate is something entirely different.

[Da_elf]

isnt it at all possible to have a check box that says "Disable Diffuse for GI Color" and under that have a color swatch.

[RErender]

I do think that some correlation between surface brdf's and gi output would be feasable.