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Thread: Quick GI question

  1. #1
    I'm a Registered User monovich's Avatar
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    Quick GI question

    I don't use LW GI much, but I think I'm going to on this current project.

    I have a car driving through a city. Whats the best/fastest GI to use?
    I've been using Final Gather Interpolated /w the default settings and the renders looked great so I didn't fiddle.
    Then I noticed in some renders that I'm getting flickering.

    The city is static but the buildings flicker a bit. The only thing moving is the cars.

    Is there a setting that'll still render reasonably fast that won't flicker?
    I'm rendering on a small farm. If I pre-compute the GI on a single machine and cache it would that help /w flickering?

    many thx.

  2. #2
    Valiant NewTeKnight Matt's Avatar
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    You wanna Cache it and use the Animation option, it's what it was designed for, finding the right settings is another matter.

    Here's a long thread about the subject:

    http://www.newtek.com/forums/showthread.php?t=99548
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  3. #3
    I'm a Registered User monovich's Avatar
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    ah. thats good news then. caching I can handle, flickering I cannot.

    I have about 8 different cameras to use on the same scene. would I do one cache per camera or does one cache work for every camera?

  4. #4
    Man of many cells. shrox's Avatar
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    Quote Originally Posted by monovich View Post
    ah. thats good news then. caching I can handle, flickering I cannot.

    I have about 8 different cameras to use on the same scene. would I do one cache per camera or does one cache work for every camera?
    Oh, good question.
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  5. #5
    Valiant NewTeKnight Matt's Avatar
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    Quote Originally Posted by monovich View Post
    I have about 8 different cameras to use on the same scene. would I do one cache per camera or does one cache work for every camera?
    Caching adds GI samples where they can be seen.

    So if you cache with one camera, but render from another, any samples that are visible to the second camera will be used, any missing ones it will add to the cache.

    Would be interesting to try, but my gut feeling is that you'd get better results caching per camera.
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  6. #6
    Super Member Captain Obvious's Avatar
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    Cache per camera. The bigger the cache, the slower the rendering. It's very marginal at first, but it adds up.
    Are my spline guides showing?

  7. #7
    I'm a Registered User monovich's Avatar
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    hmm...

    so why cache in the first place? to reduce flickering?

  8. #8
    Valiant NewTeKnight Matt's Avatar
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    Quote Originally Posted by monovich View Post
    hmm...

    so why cache in the first place? to reduce flickering?
    Speed up GI calculation by reusing already calculated areas.
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  9. #9
    I find it much easier and faster rendering to use non-cached, low settings gi (as low as 96 rays) with enough motion blur (classic, 6 to 10 passes) to average the lighting and remove the flicker. I'm sure it depends on the scene, but if getting the caching is difficult (esp. w/8 cameras) or slow rendering it might be worth a try. It works with deformation too, something the cache lacks.

    If you need lots of motion blur for fast motion, the gi settings can go even lower.
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  10. #10
    Quote Originally Posted by monovich View Post
    hmm...

    so why cache in the first place? to reduce flickering?
    You can do an overly high rays initial GI calc, which takes a while but looks fantastic, then not re-calc every render as you change materials, textures, spec etc.

    It's a HUGE time saver for single image setup (and I imagine for animations too).

    With several cameras, you will need to be careful with your directories .. I still don't have a good system for 'storing' my radiosity caches.

    Also be careful of the LW beta - last cycle the way the cache was handled changed often, and you could not use the old cache files.

    Toby: Sounds like a good tip. Cheers.
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  11. #11
    I'm a Registered User monovich's Avatar
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    I ended up caching per-camera. If I didn't I got flickering. caching only took a couple hours per scene, and then the final renders worked great rendering across the network.

    I'm not familiar enough with GI tweaking to play with the settings. (gotta read that great tutorial one of these days). The default settings worked great for me.

    By the way, LW's renderer with outdoor 1 bounce GI, soft shadows, relfections, and photo-real motion blur look fantastic! Its really fast too. I'm constantly suprised by this app.

    thanks again.

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