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Multiple lights (Read 3004 times)
Andy
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Multiple lights
01/12/07 at 23:33:29
 
I imagine I'm probably not the first person to think of this, but the other thing that struck me when looking over the format is that it might be useful to allow multiple lights.  In fact, it was also the first thing that occured to my colleague, Brad.  I was originally thinking about HDR images with interior lights baked into them, but Brad also pointed out that you might have planetary arrangements with multiple suns, or moons.

Seems like this would be a pretty simple thing to allow for in the plugins and the syntax, no?  The standalone tool is a little trickier obviously, but from a development standpoint, it seems like it would be acceptable for a syntax change to preceed a change to the standalone tool in this case, since you could just add the additional lights manually.

While I'm on the topic of lighting, I should mention that a technique I've used in the past for recreating outdoor lighting is to "block" the sun from the HDR image before I create the pre-blurred image, so that the enormous directional light of the sun does not get blurred out the way the rest of the environment does.  I've found that this is helpful for both reducing the amount of samples needed to get consistent image based lighting, and maintaining the directional integrity of directional light.  Something to consider down the road, anyway.  The idea occurred to me listening to Paul Debevec talk about the Parthenon project, where the sun was too bright to be captured in the environment image, and they used a black ball to isolate it as a separate lighting phenomenon.  Aside from "blocking" the sun, you could also allow the user to specify a max value for the HDR image, such that anything beyond a certain brightness has to be represented by lights in the scene or other techniques.  Not quite as nice, but maybe a little easier to implement...  Let me know if this doesn't make sense and you want further clarification.

-Andy
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Blochi
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Re: Multiple lights
Reply #1 - 01/15/07 at 05:21:11
 
Yes, the multiple light thing is what everybody has thought about. Mee too. Opening that up certainly makes the whole thing more versatile.

But consider the purpose of this Sunlight! Multiple lights should not be as extensively used to make that into whole LightGen setup - the ambient is what we got the ENV for. I see a lot of use for them in a situation where there are multiple  streetlamps, like in the one vienna SDR.

So yeah, I'm in for it.

-Blochi

PS. Yes, ideally the sun should be blocked from the ENV image. Or painted out before the blurring. However, in my experience I found a general directional in the ambient light quite pleasing, because it wraps around into the harsh sunlight shadow a bit... I guess in the end it boils down to the preference of the author of the SDR set.
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Dschaga
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Re: Multiple lights
Reply #2 - 01/23/07 at 23:24:27
 
The basic idea behind the SDR format was to "cheat" the 3d enviroment by placing a 3d light as virtual Sun where the real sun - captured by the HDR-  can't give the full range.

The hdri acts ..for lighing the scene... as skymap only and our sdr-light overlays the hdr and acts as sun.

Having more then one *very* strong light ..and we are talking about 80000+ lux... seems to be odd.
Indoor or night hdri's can be done with cheap cameras too.
About Lightgen ..here some new papers:  http://graphics.uni-ulm.de/EIbHDRI.pdf

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The idea of blocking the sun is nice!
Why not cheating again by "painting" a cropped sun from a very high range hdri onto the blurred SDR?
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