Shading objects differently inside a volume.

[davision]

I don't know if this is going to make any sense, but here goes:

I want to highlight certain objects (or portions of objects) as they pass through a volume. It's sort of a pyramidal shape (although more irregular). I don't want the edges of the volume to visible in the renderings, so I can't just use a regular refractive object. I just want anything inside the volume to become very dark or preferably turn dark red or some other color.

I'm trying to figure out if I can do this using some type of render element or some function of Vray (or maybe even using some function of Max. If there was a way to apply an ambient light (or negative ambient light) and limit it to within the volume, that would work I think. But I doubt that's possible.

Maybe there is a simple answer but it's not coming to me at the moment.

Any suggestions?

[vlado]

There is the VRayDistanceTex texture - you can put it in a VRayAmbientLight to make it affect only a certain volume (or maybe affect only the outside of the volume to brighten things up).

Best regards,
Vlado

[joconnell]

I don't know if this is going to make any sense, but here goes:

I want to highlight certain objects (or portions of objects) as they pass through a volume. It's sort of a pyramidal shape (although more irregular). I don't want the edges of the volume to visible in the renderings, so I can't just use a regular refractive object. I just want anything inside the volume to become very dark or preferably turn dark red or some other color.

I'm trying to figure out if I can do this using some type of render element or some function of Vray (or maybe even using some function of Max. If there was a way to apply an ambient light (or negative ambient light) and limit it to within the volume, that would work I think. But I doubt that's possible.

Maybe there is a simple answer but it's not coming to me at the moment.

Any suggestions?

Sounds like a job for comping anyway - for your region why not do something like render an extra tex pass of a circle gradient projected from a camera looking down on your scene so you get a pass of a white matte on all your objects in a certain region that you can then drive colour correction with?

[davision]

Thanks for the idea Vlado. That works perfectly. That VrayDistanceTex sure is handy.

Joconnell -- not sure I understood your method. How would a circular gradient help me if the volume that needs to be affected is irregular?

[joconnell]

Could you pop up a wee diagram showing what you want? I wonder is there any kind of projection that could fake the rough shape of the volume you're talking about?