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View Full Version : Raw FG pass with mental ray


Hasnz
11-10-2005, 01:09 PM
Hi ,
I have been trying to render out a scene in multiple passes and would like to know if u can extract the raw single boune GI pass from final gathering without casting its occlusion . As Im already using occ as a seperate pass .
I have read in the manual that in the final gather calculation the occlusion data is stored in the alpha channel of the fg points . . would it lead a way .
any solutions ???

Hasnz
11-12-2005, 05:23 AM
so that means its not possible :sad:

MoZz
11-12-2005, 06:20 PM
I'm interested on it too! Any idea??

FrizzleFry0
11-13-2005, 08:19 AM
For this pass are you trying to just get the GI information by itself or are you using GI and FG in this pass? I guess I'm not really completely sure as to why you would want to only get the GI single bounce information since it's not very accurate lighting. At that point it would almost defeat the purpose of using GI. But if you would like to get a single bounce, all you have to do is change the max photon depth in your render globals. Either change it to a 1 or 2, depending on if Mental Ray counts the initial hit as a bounce. As for the occlusion being stored in the alpha, I'm not sure. When I do my ambient occlusion passes, I only check on final gather and have the rendering camera's environment color to white. Hope this helps! Good luck.

Hasnz
11-14-2005, 08:42 AM
I am just trying to extract the FG Information . FG is a combination of a single diffuse bouce and ambient occlusion . . and i want these two as seperate passes .

U can get a similar GI photon pass if u have a light with emit specular and diffuse turned off and turning only emit photons . It will just give the the color bleed information which u can comp with ure Key light pass and get similar results .

Basically i have a character lit with HRDI . i want these information as seperate passes
1. FG diffuse light from the HDRI Env . ( through final gather )
2. Ambient Occlusion .
3. Shadow pass . etc

FrizzleFry0
11-15-2005, 03:29 AM
The rays of final gather don't necessarily bounce to another surface for illumination, but do a random bounce on geometry to sort of calculate a smooth gradient of shading. The only secondary rays that would be used would be caused by reflection and specular.

So this is how I would be doing my passes. Definately critique it because I think this stuff is very interesting and I'd like to figure out a good way to divide up the passes. I'd be very interested in how you are setting up your passes also.

Ambient Occlusion - FG only pass and no lights in scene. Either use a white environment background on the rendering camera or use an IBL node with a white texture. The objects in the scene would be using a lambert with white color and a diffuse value of 1. Bump and/or displacement will still be mapped on the lamberts for the scene.

Direct Light - FG only pass with a few lights to simulate direct lighting from the sun or lights. The camera's environment background should be black again and there would not be any IBL. The objects in the scene will use the same lambert with white color and diffuse value of 1, and also with the bump and displacement.

Direct Light GI - GI only pass coming from the lights you used for your direct light pass. Turn down the actual light intensity to 0 so it's not giving off any light, but still let it shoot photons out. The objects in the scene will be using whatever final shaders you created for them (using color, diffuse, bump, spec, etc..). This one will allow for you to pick up on color bleeding as the photons will adapt color from objects depending on their color and diffuse properties.

Ambient GI - GI only pass coming from an IBL node. Setup your shaders similar to how you had them setup for your Direct Light GI pass. This one will give you color bleeding from an ambient light source, so I suppose you could give it a shot. It may be a little overkill for most projects, but who knows.

So those are my lighting passes. Now on to the regular passes!

Diffuse - This information is just rendered out with an ambient light. The ambient light's ambient shade is set down to 0.

Specular - This pass can just be rendered regularly with render layers. I've never had any issues with it.

Shadow - Don't even need it now since you've already got all your lighting and shadow information.

That's what I can come up with. I don't know if this will help at all, but it's actually helped me do some hardcore thinking to just type this up haha. If you have any suggestions, critiques, or ideas let me know. I think this could be a very beneficial thread.

PhillipCrond
11-15-2005, 04:45 AM
In Maya 7.0, it's quite easy to get a FG only render pass. Just make a new render layer containing only the objects and lights that you want to be included in the FG calculation. Click on the "flags" tag in the render layer editor, and select "Global Illumination" as the type, and turn off "Beauty." If you render the layer like this, it still won't work, you have to override something in the above list, it doesn't matter what. So I'll just click on the "motion blur" override, and then the render passes work as expected.

FrizzleFry0
11-15-2005, 08:10 AM
Ah very cool find Brent. Thanks. I'll check that out.

elvis75k
11-15-2005, 08:50 AM
In Maya 7.0, it's quite easy to get a FG only render pass. Just make a new render layer containing only the objects and lights that you want to be included in the FG calculation. Click on the "flags" tag in the render layer editor, and select "Global Illumination" as the type, and turn off "Beauty." If you render the layer like this, it still won't work, you have to override something in the above list, it doesn't matter what. So I'll just click on the "motion blur" override, and then the render passes work as expected.

Then say goodbye to all the bleeding between the different surfaces..

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