Hi, guys, A quick question for the GI pros. When doing indirect lighting I assume GI will use off screen objects when computing the photon map. Is this correct? For instance, if I put a ceiling that is not visible in the scene, GI will still bounce light off the ceiling, won't it? Thanks, Marc

That should be the case. In the attached image, I built a room with a floor, 4 walls, a ceiling and a window. The only part of the structure you can see is the back wall. I built the full room just so GI could bounce the light off multiple surfaces and also for the reflective surfaces in the scene (spoon and vase). I am no GI pro but that was the thinking behind building this scene.

And a very effective scene it is! Very nice! I have a similar concept in mind although in my case, I was considering interior lights (essentially a pair of candles both off scene). Just wanted to make sure I was on the right track before venturing down the path. GI renders are slooow. Thanks! Marc

Slow is right. I rendered this one on my PC at work. Started it Friday night when I left and I think it finished early Monday morning before I got in. But it did come out nice.

The answer to your question is yes. The above scene is, as the insert shows, only illuminated by a single spotlight that's aimed at a cube above the frame. The ambient light is set at zero. Antialiasing is fast, object accuracy is 2 pixels, shadow at 4, and indirect lighting is enabled, lighting quality at fast and accuracy at 16 pixels. Even with these default, fairly low quality settings, this simple sphere took about 6 minutes to render.

But, damn, GI looks good!

It dose, tkane18 that is one beautiful rendering. I have been messing around with GI, but it is way to slow for me to experiment. I just became a Dad so my time is very limited. I hear that it is much faster on Carrara 3.0. Can anyone with the beta confirm this?

I saw someone do some C2 / C3 comparisons in the Yahoo group. The times were faster. Then someone else posted that depending on the scene and settings C3 will be much faster in some cases and only a little bit faster in others. Overall, it should be faster.

GI is much faster in C3 - provided that you don't crank up quality settings unnecessarily. Transparencies also can kill render times, that's nothing new to any 3D app. But if you throw in GI, Indirect Lighting and Caustics, and a helping of reflections...well, I'll leave the light on for you.

Thanks, guys. Useful stuff. Hey, sfdex, I noticed your spot light was very bright. I take it you really need to crank it up for a good bounced light? My plan was to have two bulb light sources but since they are also illuminating the scene, I can't crank them up. Looks like I need separate lighting on the reflected surfaces. Or was the light really 200% (I didn't know it could go to 2000% but never tried...)? While I'm on the topic, is it possible to do negative light in CS2? Thanks, Marc

Hey, Marc --

Yep, the light was really up to 2,000%. That's its max value, and I tried a couple area renders at lower levels; I decided to go with this much intensity to get some light really bouncing around in there.... I suspect the same effect might have been possible by using several lights pointing at the bounceboard at a normal intensity. I certainly could have used less intensity, but then the scene would have been much darker. (Would have rendered faster, though.)

I come at 3D from a traditional production background, so my setups often reflect what I might do if I were working in the real world. This kind of bounceboard effect (which wasn't available in Carrara or RDS until CS2 -- thank you Eovia!) is a standard kind of thing to do in film or video production. It results in some beautiful soft lighting effects.

As for negative light, I just tried it out and it doesn't seem to be available. Now, negative light; that's something I'd LOVE to have in the real world.... Until then, just use flags, cookies and gels!

• Dex

I've never saw much need for negative light until reading Birn's book. There are some tricks where it looks of use (and a gel or cookie won't do the same thing). Not really a big deal, just curious. Thanks for the info on the light brightness. It is one of those things I'd've have (hopefully) uncovered on my own but with the slow GI render speeds, it might have taken a few days. Definitely worth experimenting, too, of course. Marc

Could you guys give me a quick definition of negative light? I never heard of this term before.

I did a simple set-up when checking out GI...spotlight and bounce-board behind the test object. It looked as if objects in shadow were still casting light back into the scene. Has anyone run a physics lab to check this out?

I'm not an expert on negative light but I recall Bruce had it. Anyway, it removes illumination rather than adds it. Birn showed an example of using it to fake a shadow (so as to speed render time). Say you had a ball. You could light it from the front with a normal light. You could then setup an anti-light that doesn't cast shadows (so it shines through the ball) and also have the anti-light not illimunate (or in this case darken) the ball (apparently some apps allow that?). When I saw it added to Bryce 4 or 5, I didn't really know what to use it for. Birn has a few examples but it still doesn't seem absolutely necessary. Marc (Digital Lighting & Rendering by Jeremy Birn, George Maestri (Editor) )

That's Bryce, not Bruce ;-)

Hi all, I have been using Bryce5 for a few years and i have just got a copy of ray dream5. Is this program similar to carrara? And can it be used for bryce aswell? Ben

Hi, Ben, You probably want to post this as a new post rather than a followup to this thread; you will get more answers that way. I switched from Bryce5 to Carrara in April. Not familiar with RD5, though, so can't answer abuot RD. Carrara can be used to create objects for Bryce. But unless you do landscapes, you'll probably switch to Carrara, it is much more capable. marc

Amazing the info you get from 6 year old posts =B