Using output as a lighting source...

#1

I’ve a question regarding the use of “output” as a light source. Applying an output shader to an object such as a box or flat plane (simulating a light card) seems to be a great way to create nice light coverage with soft shading and shadows. My question is

“How do you increase the samples for such a lighting solution?”

I’m using GI and FG and I do have a single omni in my scene that is turned off, needed as a photon emitter even though it is not on. (not real clear on the need for this)

In short I’ve struggled a lot with using Mental Ray, GI and FG. I have a general understanding of the controls but I often find myself starring at a very noisy or blotchy render. The more I reduce the Min and Max sample radii the better the GI solution (sharp shading that is accurate) but the more noise, bringing up the filter size helps but after a setting of 4 I don’t see any real improvement.

A big thanks to Jeff Patton for his help in the past, thank you Jeff and I have to say the sample scenes on your site have been invaluable.

Mental Ray is great, I just have a lot to learn before I truly take advantage of it’s power. I’m at a place now where I’m considering moving over to Vray but hate to do that after gaining such an understanding of Mental Ray.

Does anybody know of any really GOOD books for Mental Ray and Max? I’m desperate.

Thanks

Frank

#2

The problem with using ‘output’ as a sort of geometry light as you have discovered is the sampling problem with high values. The output material can’t generate photon’s unfortunately, so it has to use just Final Gathering… therefore it’s unsurprising that extreme values cause blotchyness as this is outside FG’s normal range, as in it’s not designed for such high values. Hopefully we’ll get proper geometry lights at some stage, but in the meantime there are a few things you can do.

Use larger surfaces, with lower values. The biggest problem is trying to light something really bright which is small, this is a key source of blotchyness from an ‘output’ map.

The most powerful method, although probably not what you are wanting to hear, is to use a small amount of lighting from an ‘output’ map and supplement it with actual area lights using the ‘output’ map lighting as a guide to light placement and intensity.

I know that neither solution is ideal, but I don’t think there is really a proper solution eg, geometry lights yet.

#3

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