View Full Version : Combining GI and FG

04-17-2005, 01:32 PM
Edit: Fixed prob - results at bottom of page. thanks all. C&C welcome ;)

Hi, I've been having real problems with this scene.

Its from Dagon's tutorial.

OK first of - I'm running Maya 6.0

The first thumb is where I got to with GI only... (about 5min on a dual 2.8 Xeon) Lots of photons not a bad result but still a bit blochy

The second thumb is with FG turned on (only 4min). I'm using 1000 rays - (have gone way above and below with very similar results) - In this render the filter is turned off and I'm using the default radii (0,0)
When rendering the FG preview tiles are monotone gray then the render comes out like this. boo.

Has anyone seen this before?

I'm really struggling here and I need to get this hit on the head as I have gone down the route of GI FG mix with my MPhil project and I am rapidly running out of time.

I'm using labmerts rather than DGS but I tried DGS and all I got was huge render times and similar results.

the third image is part of the geometry that I am goin to light with this technique....

Any help would be welcome.

04-17-2005, 01:40 PM
Do you have some parti_volume shaders in your scene? Looks like it to me..
Select the camera you're using for rendering, goto the mentalray tab and look if there's any volume shader attached. If it's the case, simply break the connection or delete the shader.
If there isnt any volume shader on your cam, there has to be a big surrounding object containing it. If this is the case, simply hide or delete the object.

04-17-2005, 02:47 PM
Hi floze.

No parti_volume...

I had the same thought - Originallt there was a big sphere with a surface shader around the scene. I deleted that but then i lost all the GI effect (black apart from the direct light). So I made the camera environment bright. Then the image went back to looking like the one in my first post. grrr.

Maybe its a buggy thing. I'll try deleting prefs and see if a clean boot makes any diff.

04-17-2005, 04:35 PM
I cant find dagon's tut anymore, and I dont feel like registering at the italian forum.. maybe you want to share the scene?

04-17-2005, 05:59 PM
The obj and mb files are on this translation... http://www.bem.com.tr/images/mentalray_about_inner_lighting.htm

my scene is 6meg - I could mail you it.

04-17-2005, 06:32 PM
I had a look at the scene but couldnt find anything unusual (except hundreds of empty transforms without any connections.. what are they good for?).
I did a little testrender and it renders as expected. Try to upload your file (zipped if possible)to http://www.rapidshare.de/

04-17-2005, 06:53 PM
I sent dagon the english translation of his tutorial a few days ago and then talked to him today. He said should be posted later this week, so that'll probally help you out..just keep an eye open for that.

04-17-2005, 10:59 PM
The link in my second post is to a mediocre translation.

I am having issues in other scences aswell (thought it might just be the geometry).

Here. in this scenwe again Gi works fine and as expected. - when I rendered with a low setting FG (250 rays) it looked as expected - better but noisy - upping the rays and the scene goes black.


04-18-2005, 07:52 AM
Ok - I figured it out.

It was actually the camera, I upped the near clip value so that I could get more of the room in without having to use a distorting 15mm lens or anything. If the camera clip plane cuts the walls or anything that is being used to generate the fg map (so pretty much everything) then the fg build goes crazy. I just had to put the Primary viz of for the walls that I needed to get close to.

Anyway - thanks for the help.

Here is a quick test with 200fg rays - about 20min @800x600 on a dual 2.8 xeon (down to about 12min reusing the fgmap and the pmap)




04-18-2005, 08:02 AM
the floor looks really nice - just wanted to add this ;)

04-18-2005, 07:37 PM
The floor is amazing!

How'd you make it?

04-18-2005, 09:30 PM
floor is just a blinn with a col map, a bump and quite low reflectivity...

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