Lighting an ambient pass

[lazzhar]

How have you connected the big sphere to the ambient light color?
I guess your just projecting the texture from the light source.

For the ambient lighting why not just using a dome of light instead of this ambient light. I never use this type of lights, I find it annoying. Or just play with your fill light so every part get lit.

[Bonedaddy]

Hey lazzhar, thanks for the response. I am using the Maya "environment ball" texture in the ambient slot, which I suppose just creates a ball around the ambient light. How vexing. Maybe a string of dome lights, GI_Joe style, might be a good idea. No shadows though... hmm... we shall see.

[jeremybirn]

This is all Maya-specific (maybe the thread will get moved to Maya Rendering?), but when its "Ambient Shade" is 0, an Ambient Light will illuminate all sides of all objects equally. A.S. of 1 makes it a point-source light. Between 0 and 1 there are some neat "wrapping light" effects, and you could also blend different color Ambient Lights coming from different directions (if that's really how you want to light your scene?!?)

Maya's Ambient Lights only illuminate objects based on their "Color." They are not linked in any way with the shader parameter called "Ambient Color."

Maya's Ambient Lights can be color mapped (to project a "cookie") just like a point light, but the pattern is just projected out from the position of the light. It sounds like the effect you really want is what's described in
this thread (http://www.cgtalk.com/showthread.php?s=&threadid=122734) - download the scene I link and just map your image onto the big sphere's Incandescence instead of the Ramp that's there.

-jeremy

[Bonedaddy]

Thanks, Jeremy, but I forgot to mention I'm rendering fur, so I can't use Mental Ray (for the fur pass at least). GI_Joe keeps locking my computer up too. I may just try for futzing with ambient lights or a fill light.
Sorry for posting this in the wrong forum; I was hoping to get a more generalized idea of what everyone meant by ambient lighting pass, but I suppose it turned Maya-specific fairly quickly.

[jeremybirn]

To tell the truth, I've been through projects where I render dozens of passes, and never did an "ambient pass." Now, ambient occlusion as a shadow pass, or final gathering from MR, those I can see as useful passes. And sometimes I've done things I called a "color pass" for things like product exterior colors, that other people might have called an ambient pass, so this might just be a semantic argument, but still I don't use ambience much for things that aren't self-illuminating.

If you have access to Maya 5 maybe you'll be able to explore other MR hair rendering options.

-jeremy

[Bonedaddy]

I'm still learning, so I'm giving myself as much leeway as possible come compositing -- thus, the ambient pass. The way that it's ending up, however, is more of a non-shaded color pass, which is fine. I'm not using any environment lighting on it, because I think it'd be a pain to set up.
The way I ended up doing it with Fur (for anyone wanting to do similarly) was to do three passes with three versions of the same light -- one on "shadow map" (for key light), one on "no shading" (for a color/ambient pass), one on "auto shade" (which is self-shading, like an ambient occlusion pass).
If I was more confident in what I was doing, I would just futz with the auto shade parameters until I had an appropriate amount of self-shading, but I feel it's better at this point to give me that sort of leeway in compositing.

Thanks for all your help, though!

[pasghetti]

Bonedaddy - sounds like you're interested in using image-based lighting for your fill light. Is that what you're going for or did you have something else in mind?

don

[Emmortal1]

"If you have access to Maya 5 maybe you'll be able to explore other MR hair rendering options."

Jeremy: Are you referring to Shave and Haircut? Or is there something in MR that allows it to render Fur that I missed somewhere in the docs? I do know that there is a mental ray fur node that you can grow fur with, but I didn't think it was implemented in mental ray for Maya. Any information would greatly be appreciated, thanks!

[Andrew W]

I think a traditional "ambient light" only pass would be pretty redundant. You may as well just add a colour to your texture colour, as that's all it's doing. Maya's light as Jeremy described works differently but there's another option open to you.

An IBL environment light pass could be worth investigating. By this I mean that you could use an environment map of the physical set (or CG set) into which you wish to composite your CG minus the keylight contribution to render a pass which has the fill/ambient/bounce light of the scene in it. i.e. if your character is standing on a red carpet you'd get some nice red bounce on his/her underside. An IBL type fill-light pass would be perfect for this. Even better if you multiply this result by your ambient occlusion.

You can then use CG lights to add the key light, rim light and any other tweaks to the lighting. This is a very powerful lighting technique because it frees you (to a certain extent) from wrangling hundreds of little fill lights whilst maintaining a large degree of creative freedom in your lighting. If you haven't read Hayden Landis's SIGGRAPH paper on "Production Ready Global Illumination" in the RenderMan course from 2002 I urge you to now. Even if you're not using RenderMan renderers it has much of relevence to you. You can download the PDF from The RenderMan Repository (http://www.renderman.org) This PDF also has a great article called "The Lore of the TDs" by Anthony Apodaca of Pixar which is as perfect a distillation of the world of the TD as I've read.

All the best.

Andrew

[Emmortal1]

I read that paper a few weeks ago, great stuff and I highly recommend it as well.

[MooseDog]

may not be helpful in an app-specific way, but ntl may give some insight/background on what needs to be accomplished with such a pass:


http://www.newtek.com/products/lightwave/tutorials/rendering/lw_baker_beethoven/lw_baker_beethoven.html


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