does indirect illumination cast shadows?

[kuui]

afaik there'll be shadowed areas where light is just reflected through GI and not directly falling on the surfaces. this is the way real shadows work, too, but you ain't got really control over that darker shaded areas compared to usual CG shadows

[jeremybirn]

Got a question here.

Does indirect illumination (fill or bounce) cast shadows? Does a bright sunny day indirect light cast darker, subtle or no shadows?
Yes, of course. Opaque objects block light, no matter if it is direct or indirect.

On a bright, sunny day the indirect light would likely come from a range of directions, so it could be very soft shadows, but still fading off towards black as you head under a car or into an area where most sky and bounce light gets blocked. In other cases, shadows caused by indirect light can be focused, with clearly defined shapes. Sharp shadows in indirect light happens most often if the indirect light is concentrated in one area, such as a sunbeam hitting one wall of a room. The shadows you see in caustics are often still sharp, even on a sunny day.

When using GI, people sometimes avoid using the word "shadow" when the indirect light is blocked, and call it "occlusion" - but that's a technicality; a shadow by any other name is still a shadow.

-jeremy

[TerryHan]

thanks for the help.

by the way, is there any technique to remove lighting from a picture? I mean making the lighting flat so that the picture can be used as a texture.

thanks alot.

[jeremybirn]

is there any technique to remove lighting from a picture? I mean making the lighting flat so that the picture can be used as a texture.
For overall shifts and variation, you can try this tutorial (http://www.3drender.com/light/EqTutorial/tiling.htm). If it's specific shadows and highlights, you can sometimes clone them out. But there's no perfect single solution for that - people usually shoot texture map pictures on cloudy days, to start with flat lighting.

-jeremy

[cgJD]

The colour dodge and colour burn tools in photoshop (or equivalent) can be used to paint out subtle variations. Make sure the 'amount' is set low when painting using these tools to only make small changes to the image.

JD

[Rastermon]

Caveat - I didn't go to Siggraph this year, but I read about Paul Debevec's Parthanon.
They used their light probe to "unlight" their textures. Don't remember the details.
So there is a way, but you may need to be programming guru.
Rob

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