Image Based Lighting

Zocky

Hey all!

I'm doing a map for UDK, and i just came across something that people call "image based lighting"....Seems like a really neat feature, so i'm wondering if anyone has any info how to achieve this with UDK (and dx9 or 10)....

tnx!

Visceral

Do you mean image based reflection? Beacuse imagebased lighting is kinda the default lighting option when you bake shadows.

Zocky

Well, this is still new to me, so pard me if i looks noobish in this, but as i understand, IBL means, you grabs a cube map or domemap of your environment, and then use that as a source for light color. So if the sky is blue, not just shadows will be blue-tinted, but the lighting (meaning, on object that moves) will also get blue light color (Besides other colors on the image).

WIth GI and stuff, i understand it just applies to shadow, while as i understand, this control actual light color (instead of just being one color, you use this cube map texture to bring wider range of (light) color.

That's how i understand it atleast.

Also, tnx for your reply!

Xendance

You could probably make your sky dome emissive and override the influence distances to get a hacky solution. I once tried it:

http://i211.photobucket.com/albums/bb309/Xendance/emissivedomemat-1.jpg

http://i211.photobucket.com/albums/bb309/Xendance/emissivedomemat.jpg

The lighting only view was built with preview lightmass setting.

Vailias

IBL in the purest sense doesn't really exist in UDK.

The light environments and lightmass data are similar, but not quite the same thing.

Image Based Lighting.. ya know I'll just link the seminal paper that brought this stuff to CG back in 2000 or so...
Paul Debevec's research page

Which was spectacular for both highly reflective and diffuse objects, except that the calculations ran offline due to being a global illumination solver.

Eventually there were advances which led to creating a separate cubemap for the diffuse contribution based on one or another method, a typical one being spherical harmonics.
http://http.developer.nvidia.com/GPUGems2/gpugems2_chapter10.html

Zocky

@Vailias,
Tnx, will take a look at that document!

@Xendance,
Hm, haven't played a lot with emmissive materials, but that sounds like an intresting idea. I'll try to play around with it and see if i can get any result.

Tnx both!

Could this also be somehow hacked by using multiple directional light from different angles, with differnt colors? none of those would cast shadows or anything, they would just contribute to the actual lighting, not the shadows?

Vailias

The "array of lights" will work.
Before global illumination/ radiosity solvers became available that was the way to do it.
But then it's not IBl it's just a lot of light calculations.. Which totally loses the advantage of IBl bring a quick texture fetch.
However in a totally differed lighting renderer, that could be a more viable option.

Zocky

Tnx!

Yeah, i'm aware this isn't exactly as good solution as IBL, but i was just wondering if i could use that as backup plan if nothing else works.