Volumetric Lights behavour -Better than Cinema maybe?:)

[tcastudios]

Since Volumetric Lights are in the work I'd like to point out this problem in Cinema and maybe it could be "corrected" for Vray:)
Pict01.
This is a closed room with a single non volumetric omni light. Its falloff is set
to -barely- reach the surrounding walls. So you should more or less not see
the walls in the rendering.
http://homepage.mac.com/tcastudios/tempfiles/VLights/01_Omni.jpg

Pict02.
In the same room there are two volumetric SpotLights. (The Omni is turned off here). One spot is aimed towards the camera, the other spot comes from the right side. So -none- of them are hitting the wall behind.
http://homepage.mac.com/tcastudios/tempfiles/VLights/02_Spots.jpg

Pict03.
Here comes the problem. When all three lights are turned on, Cinema composit (internally) the result in screen mode and the walls behind are
suddenly visible.
http://homepage.mac.com/tcastudios/tempfiles/VLights/03_OmniSpot.jpg

Pict04.
To get a correct render, I am forced to use multipass for the lights using
the "Atmosphere" pass. It looks like this.
http://homepage.mac.com/tcastudios/tempfiles/VLights/04_Atmosphere.jpg

Pict05.
Comping the Atmosphere pass (in PhotoShop or AfterEffects) over the plain render using "Lighten" mode gives the correct result.
So basically, in Vray, having the option to use "Lighten"instead of "Screen" directly would be a huge timesaver!
http://homepage.mac.com/tcastudios/tempfiles/VLights/05_OmniPlusAtmos.jpg

The scene can be dloaded >here< (http://homepage.mac.com/tcastudios/tempfiles/VLights/VolumLight.c4d.zip)


Cheers
Lennart

[STRAT]

sorry tcastudios, but i dont think it's a problem, maybe your lack of understanding exactly how multiple lights overlap and react with each other. all that faffing you needed to do is nuts.

i downloaded you scene and got the desired results in 3 or 4 test renders. try distance clipping on your omni instead of fall off too. distancing is less harsh than falloff.

[tcastudios]

Hi Strat. Thanks for checking it out.
In the provided scene the omni is not reaching the walls only to show the
added visibility of the wall even if it is not lit.
And yes, using clipping helps in this particular case (the wall should not be visible).
But the use of omni(s) is to add a base light.

Now in the same scene, extend the omni so it is actually reaching the walls.
If you turn off the spots there should be a softly lit room.
Now, turn on the spots again.
The wall becomes -very- visible again(thru the spotlights beams).
Here I don't see how clipping would be of any help.
Also the inverse square falloff is "the only way to go" since it is how light works.

I've been struggling with this for years with no other solution than using multipass.

No one more than me would be happy to get this sorted.
A great deal of my work includes making previews of artificial lit places,
TV shows , awards etc. I often do this together with the Light designer
at my studio sitting besides me.

Cheers
Lennart