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Old 24-02-2003, 08:26 PM   #1
Zytrex
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Exclamation GLOBAL ILLUMINATION DISCUSSION

Am I the only person getting fed up with GI because of how difficult it can be to get even barely acceptable results without ending up with horrible rendering times? The movie and game industry has been getting along without GI for a very long time because it is so slow. I have some scenes that take more time to render than it took to design. That, to me, is quite disgusting.

There are some situations where GI can help the design process. For instance, if one is modeling a complicated character or vehicle, a well set up skylight-style GI can help identify problems in the mesh. But for a final render, no pun intended, I like to see some depth and shadow, not just some dark areas where the faces are close to each other and at an angle facing each other, or close to it. In other words, skylight-style GI is out for final renders as far as I'm concerned.

So how about full blown radiosity or something in-between? Well, if it's of any quality, the render times will blow you away, even if you are only doing a still. Animation? Out of the question! I read an article about Final Fantasy: The Spirits Within. In it, people working on the project said that the average render time for a final frame in the movie was 90 minutes. And when I say final frame, I mean all frames that were rendered separately and then composted together into one frame. So that's 90 minutes, on their PIII Linux machines, for several different frames that are turned into one frame in the movie. I have a P4 2.53 with 512MB DDR and I have a scene where, after about 40 minutes of calculating radiosity, takes about 150 minutes to render. That's a total of 190 minutes for a single frame. Sure, if nothing in the scene changes, I don't have to recalculate the radiosity, but what kind of animation has no movement? And my room is very simple compared to the scenes in Final Fantasy. I just have six walls, three windows, and two tables! And what's more, this is just my scene. I've read things on here where people spend 4 to 8 hours rendering a single frame.

I remember back to before I had access to global illumination. I would render an animation while I slept. There would be 8 or so lights for well rounded lighting and about 400 frames. When I got up in the morning, it would be all done. Remember that scene of mine that would take 190 minutes to render? Before I added GI, I had a whole bunch of lights in there to get it looking good and the whole thing would render in about 15 minutes!

There are many ways to make light appear to bounce around a scene. I wish I knew some of the tricks to faking GI. Sure, you can put lights of colors corresponding to colors in the scene near geometry that should be receiving that color through bounces of light from other geometry, but that isn’t nearly as easy as it sounds. At least, it isn’t for me. If anybody wants to comment on why they like or don't like GI, please post. Hey, if you think GI is great, tell me! I know it sounds like I hate GI, but I really just hate that it’s slow. Having used it a lot, I am aware of how great the results can be. So now I address those of you out there who have been setting up good lighting in a scene without wasting time with global illumination. Please, tell us how you do it. Even better, show us. Thank you!

If this thread works out and people start posting, perhaps the admins will consider making this a sticky thread? I'm sure the many people out there who have GI but are sick of the render times and the many more people out there who don't have GI at all would love a thread about making realistic lighting for a scene!
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Last edited by Zytrex; 26-02-2003 at 05:31 PM..
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