Is GI actually used in production environments?

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  04 April 2005
Is GI actually used in production environments?

Heya, I am still new at CG stuff but love lighting/rendering. Of course, at first I got very excited with Max's light tracer, radiosity, mental ray etc, but was stunned by how slow it was. Now, obviously larger production houses have more grunt on hand than I have in my bedroom (ooo-errr!) but is GI/radiosity basically a brute force approach more realistically suited for stills at this point in time?

I have been learning to set up more effective light rigs with the standard lights and of course the results are quicker and often you are allowed more flexibility to make quick changes.

So, my question is: "Is GI used in actual, real production environments or is it just a flashy technique at this point in time".

I am going to focus more on using basic lights as I think that will give me a better grounding in dressing a scene, but would be interested in hearing opinions or experiences.

Cheers, big ears.
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  04 April 2005
It depends on the productions, it's been used even in large ones (i hear Shrek has used its proprietary GI, but don't quote me on that) but usually you also hear "hey we couldn't even afford raytrace, nevermind radiosity!"
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  04 April 2005
GI is being used more and more in feature film vfx. As mentioned Shrek 2 used GI passes rendered on low-res geometry that were then rolled into the final render.

I can't speak for other productions, but here we're using GI for lighting some environments. This is then baked into textures for final rendering. We've also got to do lots of specular reflections (a river) as well that we're raytracing.

Another guy here on a different project is using GI on a character with a clever technique to keep render times low.

I think it'll be a while before TD's regularly just turn GI on and let it render. Since most films are rendered with PRMan, it's taken a while for GI to become a feasible technique to use, since until the latest release, raytracing in PRMan has been pretty much unusable for production.
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  04 April 2005
Sometimes you need to use GI, but it's best if you can limit it. Most productions tend to use ambient occlusion - usually baked into textures. You can also do that with GI if the lighting or objects aren't changing too much. Also for refractive glass etc you do need to use raytracing as there isn't much choice - you can fake one level of refraction with maps, but any more doesn't work.

Simon
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  04 April 2005
With PRMan's ability to bake out lighting data into pointclouds and from there to maps (or brickmaps) I think we'll see more GI turning up in future productions. Brickmaps for SSS are certainly being used in productions now and I see no reason why the same technology can't be leveraged for cheapish one bounce GI.

My 2 pence.

A

PS I see rendermaniac and playmesumch00ns are working on Saturday too. Ah deadlines, how we love 'em... Busy old Soho.
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  04 April 2005
Thanks for the responses. I was just reading about occlusion passes but have not tested it out yet. Good point about baking the lighting into the textures. I assume this would be very useful for backgrounds etc.

So much to learn . . . so few hours in the day!
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  04 April 2005
Originally Posted by mr_wowtrousers: Thanks for the responses. I was just reading about occlusion passes but have not tested it out yet. Good point about baking the lighting into the textures. I assume this would be very useful for backgrounds etc.

So much to learn . . . so few hours in the day!


Well provided your geometry doesn't deform you can bake things like ambient occlusion which is view independent into a map for re-use. Sub surface scattering etc. can't be treated in this way though.

In most instances ambient occlusion is the most useful of the "fancy new techniques" which is I guess why it is now pretty ubiquitous in production.

Andrew
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  04 April 2005
Thanks again Andrew. I checked out your page and tutorials. Certainly some interesting stuff there. It's no wonder I don't have much time to do stuff on weekends when there is so much to take on board!
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  04 April 2005
the writer of PRman came to my school last month (Rob Cook) and we asked him if Pixar would start using GI, and why arent they using it now. And he brought up a good point

GI isnt really directable yet, you press render and the renderer does it thing. If you want the character eyes to be in shadow, or you want his hands to be lit differently you dont really have that option unless you make bouncecards, etc. He said that they're working on making it more controllable and more artist friendly, so it might happen in the future, but he said that the technology isnt that mature yet.
 
  04 April 2005
Hi Andrew

I am posting from home! PS I know what show you are on - I am on the "other" one Anders - is there any more information about Shrek's GI stuff?

I have heard that using GI for things like Shrek makes rendering slightly longer, but makes overall setup shorter as you need simpler lighting setups - the GI does most of the fill lighting for you.

Most vfx houses use prman and it has only been recently that Gi has become useable with brickmaps as Andrew said (and I mean REALLY recently!). Shrek and Robots are different - for a start they are animation houses, not vfx, but mainly because they both have their own prioritory renderers. Blue Sky's CGI Studio seems really nice for all the reflections in Robots (even if the story sucked majorly).

I have used prman raytracing for production work (Sahara - can you guess where ).

Simon
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  04 April 2005
about shrek http://www.tabellion.org/et/paper/s...i_for_films.pdf
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  04 April 2005
Hi all

Good question to ask Matt, thanks to everyone that posted to the questio. I actually wanted to follow up on one thing. Andrew you had mentioned brick maps, are these the equvilant to cache files like ambient occlusion, If I understand correctly that is a form of point cloud? Since you can view cached occlusion (.icf ) files with ptviewer, is that considered a visual representation of a point cloud?

Thanks

Avedis
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  04 April 2005
The short answer is yes. Things like GI and raytracing, which used to be used mainly for people creating stills or low-res output, are now being widely used in feature film productions.

But, in terms of your skills, learning how to light in a "simulated radiosity" style (adding your own bounce lights) will remain a necessity for a long, long time, espectially when lighting elements that will be comped with live-action plates and matte paintings, where there aren't any other surfaces for the renderer to bounce light off.

-jeremy
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Jeremy Birn
Author, Digital Lighting & Rendering, 3rd Edition
 
  04 April 2005
Originally Posted by jeremybirn: But, in terms of your skills, learning how to light in a "simulated radiosity" style (adding your own bounce lights) will remain a necessity for a long, long time, espectially when lighting elements that will be comped with live-action plates and matte paintings, where there aren't any other surfaces for the renderer to bounce light off.

-jeremy


Yes, I am in the process of discovering that. I have been learning how to render passes and layers and having control of your lights is obviously very important (something I learned from your book btw).
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  04 April 2005
Originally Posted by avedis: Andrew you had mentioned brick maps, are these the equvilant to cache files like ambient occlusion, If I understand correctly that is a form of point cloud? Since you can view cached occlusion (.icf ) files with ptviewer, is that considered a visual representation of a point cloud?


Brickmaps are probably best thought of as the 3d equivalent to pixars 2d texture format. In general brickmaps are superior to the old style icf cache files written by prman. Both brickmaps and pointclouds are a way of storing 3d data (any data too, not just GI or ambient occlusion), although because brickmaps are derived from pointclouds, I guess its correct to say that brickmaps are a form of pointcloud.

Brickmaps are better because they can be compressed, are tiled and therefore support load on demand and also can be filtered. prman pointclouds don't have any of these qualities making them less than great for production.

As far as viewing goes, your right that ptviewer provides a visual representation of 3d data in the same way as an image viewer offers a representation for 2d images. You can't view brickmaps with ptviewer though, for that there's an additiaonal program that ships with prman called (wait for it....) brickviewer.

T
 
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