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Final Gather requires altering shaders

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SSGGMM
Final Gather requires altering shaders
on Dec 20, 2006 at 5:55:40 pm

Hello,

I have a room full of shaders (wallpaper, floorboards, whatnot). Final Gather yields nothing. Black. In fact, the only way to get final gather to work is to increase ambiant or incadescent levels on my shaders.

What this means (and somebody please correct me) is that the only way I can take advantage of final gather in my final render is to alter the shaders I spent weeks building. This doesn't seem fair. What if I don't WANT any ambiant levels on my wallpaper?

SGM


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Steve Sayer
Re: Final Gather requires altering shaders
on Dec 20, 2006 at 6:59:56 pm

What are you using for a light source? For an exterior Final Gather scene, the "light source" will be the camera's background colour (usually set to white). You're describing an interior scene, which might mean that the background colour isn't set to white or is not contributing (if the space is fully enclosed). I think you need to look into using some light sources and/or integrating your Final Gather with some GI.

-Steve


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SSGGMM
Re: Final Gather requires altering shaders
on Dec 20, 2006 at 7:45:39 pm

Turns out, I had a one-sided wall right in front of the camera. Couldn't see it in the perspective view. If THAT doesn't get me kicked off the cow, by god, nothing will. I'll start by apologizing for that. There's more.

The setup is a simple one, with a question at the end of it. The room has a single window, with dirty glass. Just outside that window, a point light, not too far, with a mental ray cie node for colour temperature. That's the only source. It casts the shape of the window on the floor: a standard cliche. I'm hoping to make that light bounce off the floor and spill onto the walls, lighting up the room, like it might early in the morning. I'm using both GI and FG, and it's working well. But I still have a few workflow issues.

I started out by setting all my GI parameters and render settings. Pleased with it, I then moved on to include final gather. Having solved that one-sided wall problem (like a genius) I noticed that the light bouncing around the room was much darker then it had been under GI alone. I'd like to solve this, but I'd really like to avoid rebuilding my photon map. Can I brighten up those FG points in the render settings, or do I have to increase ambiant in my shaders?

Here's another question: Is it generally smarter to set final gather BEFORE global illum?

S.




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Steve Sayer
Re: Final Gather requires altering shaders
on Dec 20, 2006 at 8:57:54 pm

Hehe... one sided wall, eh? That's a good story--very festive! Thanks for sharing! ;)

To be honest I'm new to FG myself and haven't even played with GI yet. However, from what I know of the way Final Gather works, I'm not surprised that it darkens your scene. It is basically an occlusion shader, designed to darken surfaces that are obscured by other surfaces. For an enclosed room, it makes sense that the overall effect will be to darken the scene.

There is a 'Final Gather scale' slider in the render globals... try reducing that and see if you can get it to contribute to the scene without making it too dark overall.

Also, if you haven't already tried doing so, try setting your render camera's background colour to white. That's generally what Final Gather expects.

-Steve


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