Indirect illumination/light bouncing

[Chris MacDonald]

Hi folks, got a bit of a problem here. relatively simple scene with light coming through a (physically modelled, double glazed) window into a room - but for some reason the light doesn't appear to be scattering much at all when it hits the floor.

 

I've got the render on fairly decent settings too - Final gather (500 rays/1.0 density) and GI enabled with 60,000 photons.

 

Any ideas why i'm not getting any light bouncing around that room?

[ramy]

A couple things to check:

-Have you tried increasing your FG bounces from 1 to something like 3 or 4?

-Are you using a mr sky portal at your window?

-using GI with FG can help brighten things up.

[Chris MacDonald]

Yeah it's already on 3 bounces, i'm not using light portals because I want to also take outside shots (perhaps video flythrough) and GI is already on - which is why this is confusing me =/

[raziel]

Yeah it's already on 3 bounces, i'm not using light portals because I want to also take outside shots (perhaps video flythrough) and GI is already on - which is why this is confusing me =/

 

Try using portals, but set the transparency level so you can see the outside more clearer.

[Matt McDonald]

and if you are using GI the additional Final Gather bounces will do nothing for you.

 

turn on the the diagnostic mode for photons and see how many are actually coming into your room...not many I'd bet.

[pixelperfectg]

turn on the the diagnostic mode for photons and see how many are actually coming into your room...not many I'd bet.

Especially true if the original poster hasn't properly focused the photons emitting from the mrSun via the photon target settings on the mrSun.

 

i'm not using light portals because I want to also take outside shots (perhaps video flythrough) and GI is already on

Why would that prevent you from using portal lights at the windows?

[Chris MacDonald]

Why would that prevent you from using portal lights at the windows?

 

I'm completely new to mental ray/3DS max, but my understanding was that they focus ALL of the photons through the window? Therefore leaving none to go elsewhere. Perhaps I've gotten things all confused!

[RevitGary]

Sky Portals do not use all the Photons. They just shot more into the space. I to am fairly new to mental ray also, although I feel I have a pretty good handle on it now. Read every thing you can in this forum there is lots of good info. It all seems very confusing at first.

 

If you turn off FG and leave GI on you can see where the photons are hitting.

This will help you decide on your settings

 

Pattons tutorials are great.

Edited January 30, 2010 by RevitGary

[pixelperfectg]

my understanding was that they focus ALL of the photons through the window? Therefore leaving none to go elsewhere.

That's incorrect. As Gary explained each light generates it's own unique amount of photons. Of course there's always an exception to the rule and in this case it's the skylight/mrSky which doesn't generate photons at all.