using FG with GI

[carlotristan3d]

Just bought Jaime Cardoso's book 'Realistic Arch'l Visualisation with mental ray'-to plug some holes in my game. the book does not encourage using GI with FG, either you use one or the other but it does not explain why. I've always thought that FG and GI is used together, and thats part of my workflow. what's the other experts take on this?

[thnkr]

I haven't seen the book you mention, but what you cite goes directly against what it says in my copy of "Rendering with mental ray" which I would give more credit for trustworthiness than any other book on mental ray. Final Gather is designed to work with GI; it solves the problem of sparse photon distribution.

[odouble]

There's no real "correct" way to use gi & fg in mental Ray. That being said, there are definitely times to use both.

 

Photons greatly speed up interior renderings as they do a better job at bouncing light on the first bounce when used with FG; albeit at a cost to your memory. GI+FG is definitely more effecient for interiors assuming you optimize your GI photons. In general photons tend to work better than FG in low light situations, hence interiors. You will also notice a little more saturation in your images with GI photons.

 

For exterior scenes I have not seen a use for GI photons in production as FG with a couple of bounces does the job admirably. Shooting photons in an exterior scene can be extremely expensive but they can be optimized. Setup will take some more time; but why do that when you can use FG with extra bounces with a couple if clicks.

 

It all boils down to how much time you have on your hands and the amount of rendering horsepower at your disposal.

 

You can try a test with both interior and exterior scenes and come to your own conclusions.

[Crazy Homeless Guy]

Did it give a reason why? .....that goes against everything I have read.

[TheAllusionisst]

If you use both, you can use lower settings in both to make up for the double computations. mr even has a check box for optimizing your GI for use with FG. As mentioned already, in a big open outdoor scene (Statue in a Park) FG does the trick. If it was a house in a canyon floor, GI would help out. Basically if light rays are un-obstructed in their path to the object you are lighting, FG does the trick.

 

I was recently setting up a interior studio scene for rendering out cars and entourage and with the amount of light I was shooting at the focus area, GI wasn't necessary. So there are situations that you just adapt to, even if it is contrary to standard conventions.

[odouble]

http://www.scribd.com/doc/3076415/3ds-Max-9-Tutorial-Lighting-and-Rendering

Scroll to p52 and check out the GI+FG explanations.

 

Both Cardoso and Joep van der Steen's books have their merits.

Joep delves into a lot of Mental Ray shaders and setting up FG and GI; in a more universal environment. Cardoso concentrates more on Arch VIZ production situations and his own techniques at that.

 

They use different methods to achieve their goals as you would expect from two different creative minds. Their books actually complement each other.