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Thread: Off-Camera Radiosity/Bounced Light

  1. #1
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    Off-Camera Radiosity/Bounced Light

    I'm having a lighting issue with a scene that I had planned on having lit by radiosity from subsurfacescattering-infused wax candles and the luminosity-infused hypervoxel flames (luminosity requires radiosity to illuminate any other objects). To my chagrin, radiosity appears to be entirely dependent upon the camera. Whenever the candles drop out the camera's view, the scene is pitch black.

    The first workaround I can think of is to ditch radiosity, only use the smaller candles where the flame isn't obscured, and drop in point lights instead. This is much less pretty and I'm trying to avoid it.

    The second, for a weird option to simulate bounced light I could use a higher ambient light value in the scene and somehow fake things with occlusion/occlusion-mapping? Subtractive lighting if you will. I haven't a clue how I'd do such a thing, much less do it without a hard-bake (it is an animated scene after all.)

    In these uploaded images the hand and floor have no illumination properties and thus are the test-objects.
    Click image for larger version. 

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    Suggestions?

  2. #2
    Super Member spherical's Avatar
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    How many bounces? How many second bounces? Might be good to post a screen grab of your GI settings panel.

    One way around it would be to widen the field of view, so that the candles are in the shot and then crop in on it to the final frame dimension.
    Blown Glass · Carbon Fiber + Imagination

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  3. #3
    Registered User ArtGoblin's Avatar
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    What do you mean radiosity seems to be dependant on the camera? As in when the self-illuminate object isn't in frame it doesn't add to the radiosity solution? If I'm understanding the problem correctly I couldn't manage to replicate this problem, radiosity works like a charm on self-illuminate objects and hypervoxels alike (allthough you have to have "Volumetric Radiosity" turned on from within the GlobalIllumination panel if you are using self-illuminate hypervoxels)

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    So I'm realizing that it's not the radiosity per se that's causing the problem, but rather it's the subsurface scatting. I don't think that SSS calculates those objects when they're offscreen, The preprocess time that SSS objects incur on the render decreases as there are fewer SSS objects on screen, no time at all when the shot is empty of such objects. The hypervoxels are illuminating the scene but were in fact very dim, however I was cheating by inflating the values on the SSS so most of the light was from the wax. I might be able to do a workaround with translucency on a vertical gradient. With a high radiosity value without the artificial SSS pump, I can't really keep the color range of the flame inside the gamut, but oh well.

    By the way, the crop-frame solution would be awkward to plan for but it is rather inventive.

    Here's the scene packaged if you wanted to peek at it. https://dl.dropboxusercontent.com/u/...iosityTest.zip

  5. #5
    Super Member spherical's Avatar
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    Quote Originally Posted by shangramus View Post
    By the way, the crop-frame solution would be awkward to plan for but it is rather inventive.
    Glad you like it. What could be done to better preview the shot is to make a thin picture frame object that represents the final crop and parent it to the camera. It would become a custom Limited Region that would allow you to frame the final shot.
    Blown Glass · Carbon Fiber + Imagination

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  6. #6
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    Hey it worked!

    So I wound up working seriously off of your proposal and just doing a full 360, equirectangular render, then sending it back to LightWave as a textured environment. I'd already been animating in photoshop and exporting to backgrounds but sourcing from 3D hadn't occurred to me for a while til I remembered this thread.

    It worked beautifully!

    I wrote a tutorial for class on it.
    http://art-design.missouristate.edu/.../Tutorial.html

    I may or may not have rendered the image sequence slightly off of equirectangular, there's a minute perspective weirdness to the top of the candles in the scene, but maybe I'm imagining it.

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