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Hiding transmissible materials from emitters

Posted: Wed May 11, 2011 1:26 am
by el.mustafa
Hi again.

If a scene has more than one light source can you hide an object from one emitter and reveal it to the other?

For example a tinted glass object in a scene with Physical Sky and a light emitter.
It looks much better when lit by HDRI or Sky.

Now add a small emitter to the scene e.g a Camera Light and the object reflects
terrible noise from the surface.

I know you can solve this with compositing two versions of the image one lit by one emitter and
one lit by the sky. But then that removes the nice light reflections..etc

So is there a way to be selective about which emitters/light sources your object will respond to?

El

Re: Hiding transmissible materials from emitters

Posted: Wed May 11, 2011 2:35 am
by el.mustafa
I haven't found a way to answer the question I poster earlier but
somehow solved the problem with transmittance and small emitters that
prompted me to ask the question in the first place.

Here is a sample scene to explain what I mean.
A wire frame shows a sphere (assigned a tinted glass material)
A camera with a small polygon assigned an emitter to act as a Camera light

Image


Render the scene out with a sky dome, no probs:

Image


Now dim the sky and strengthen the emitter,
notice the reflected light speckles at the top half
of the sphere. The higher the sampling rate the
worse it gets:

Image


If I scale up my emitter to become a large polygon object the problem
disappears but I don't see my emitter reflecting on the surface of the sphere.

To get the best of both worlds, getting rid of the reflective noise and making
sure the emitter shows on the shiny object's surface I simply hid the emitter polygon
from GI.

Image

Not sure why it works but it does.

El