Another frame grab from Act I.
We'll take her in tow
I’m really pleased with how this sequence turned out, but at the moment I’m very annoyed with LightWave 9.6 (the modeling and rendering software I’m using for this project). You don’t see them in this still (because I picked a frame where they didn’t manifest themselves!), but about a third of the 108 frames of the Enterprise in this sequence have little luminous “spots” roughly the size of one of the round portholes that randomly appear and disappear all over the saucer hull surface.
After a lot of digging around and consulting with professionals at some of the visual F/X forums I haunt, I’ve concluded that the spots are caused by a bug in LightWave’s rendering engine that has to do with the global lighting method I’m using on this project. When it works correctly, LightWave’s renderer is one of the best in the industry, but when it f***s up, it’s a pain to deal with. After almost a week of trying to debug what was going on, I gave up and rendered the scene as is, and am now hand-correcting the frames that have the spot artifacts.
One the theories about what is causing the bug to manifest itself is that I have a lot of small luminous objects on my model (e.g., the bussard collector volumetric lights, the little red lights on the bridge dome, etc.) which have been known to cause problems with LightWave’s “Monte Carlo” global lighting type. I think when I finish Act I I’m going to take a small project detour and investigate multi-pass rendering–this is a technique where you render parts of your scene in separate passes.
I already render each of the scene elements in their own passes (e.g., the Enterprise is rendered in one sequence, the Constellation in another sequence, the asteroids in yet another, etc.), but with multi-pass rendering you render aspects of your scenes in separate passes: the diffused color of objects in one pass, the lighting on those objects in another pass, the specular highlights in yet another pass, etc. What I’m hoping I’ll see is that the spotting artifacts will disappear (or at least be easier to isolate). But right now I have a deadline to hit and no time to experiement further, so mush!
#1 by Metryq at July 18th, 2009
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Does Lightwave have the ability to eliminate certain light sources or luminous materials from Global Illumination — like whether or not a light source generates shadows, or an object casts and receives them? The whirling nature of the Bussard collectors might cause them to act like a mirrored disco ball.
#2 by Scott Gammans at July 18th, 2009
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Yes it does, and those two elements (the port and starboard blade assemblies) are both excluded from radiosity. It’s very strange!