PDA

View Full Version : Longer falloff with final gathering?


Niber
10-29-2005, 02:26 AM
Hi,
I'm using Final Gathering for the first time in a serious scene, and it's looking really cool,
but problem is that I think the falloff on the lights (ie materials with self-illumination) are way to quick/short.
It's like it's ultra bright near the object, but then the light really fallsoff fast (not extremlt fast but I would prefere slower/longer).

There is a falloff setting but accordantly to a tutorial I've found on the internet that falloff settings can only be used to SHORTEN the falloff range, I wan't to make it longer.

Can I make it longer some way?

ie. I don't think there is a bug in my scene, cuz it's looking normal, I just want a light to lit up a larger area without having to crank the light intensity up so much.

Osaires
10-29-2005, 08:31 AM
Hi, i'm having the same problem, i don't want overexposed areas but thats the only way i get a light source to have a big range.

btw. the falloff stop attribute can longer the range, but only if your light source is bright enof.

if you set the falloff stop too low it takes the color frome the environment, this can brighten your sceen.

I'm also having problem with dark corner with FG, it looks like AO. anyone know why this happens?

http://forums.cgsociety.org/attachment.php?attachmentid=83572&stc=1
check out the corners

Niber
10-29-2005, 11:49 PM
I think corners are supposed to look like that, it's realistic.

But anyway, this falloff thing doesn't seem like an easy thing to fix, man FG really sucks :(

Arcon
10-30-2005, 01:07 AM
if that room is just a sealed box with single window, then the corners will be black, and they would be close to black in real life. you might want photons/GI to bounce light around the room, or increase FG bounces, but interiors that don't allow natural light to get through (or no artificial light to compensate) are obviously harder to get decent lighting.

as a rule i always use decay with unnatural light-sources, usually linear, i know its quadratic in real life but i find in CG sometimes it doesn't go far enough. for something like [direct] sunlight i won't use a decay rate, and just use a low intensity. even though sunlight does decay in theory, over a small field of view the decay shouldn't be noticeable.

Osaires
10-30-2005, 11:39 AM
thanks Arcon thats some usful tips :)

Bernard397
10-30-2005, 01:26 PM
Hello,


where can you set the FG bounces ?


thanks a lot,



bernard

bgawboy
10-31-2005, 03:50 PM
FG bounces are in the Finalgathering section of the mental ray tab of Render Globals.
It is called FG trace depth I believe.
FG diffuse bounce checkbox is also there at the bottom.

Depending on which version of Maya you have, there is also a factor for multiplying just the FG effect, called FG intensity factor or something like that. Check the extra attributes of the mentalrayGlobals or miDefaultOptions nodes. In Maya 7, there is additionally a presample density factor. Maybe this can help with the original post to brighten the effect of the FG.

DJ_
11-01-2005, 08:56 PM
FG bounces are in the Finalgathering section of the mental ray tab of Render Globals.
It is called FG trace depth I believe.
FG diffuse bounce checkbox is also there at the bottom.

Depending on which version of Maya you have, there is also a factor for multiplying just the FG effect, called FG intensity factor or something like that. Check the extra attributes of the mentalrayGlobals or miDefaultOptions nodes. In Maya 7, there is additionally a presample density factor. Maybe this can help with the original post to brighten the effect of the FG.

Sorry man, but FG trace depth is only for mirrors and transparent objects, just like shadows and lights. You can set the number of difuse bounces in the miDefaultOptions. First turn on secondary bounces in your render globals, then set the number of secondary bounces in the miDef (I think the default value is 1).

Niber: I think you should combine photons & FG. Photons are more predictable and they have a decay value. Scale can also be a matter here... try scaling down your scene.

cpan
11-01-2005, 09:18 PM
just to clarify:

* the number of diffuse bounces is controlled by the Final Gather Reflect value (in render globals)
* if you increase the number of bounces you need to increase the Shadow Trace Depth also, otherwise you get overexposed pics. Btw you need to increase this in both render globals and on your lights (in the shadow section)


/p

anthonymcgrath
11-02-2005, 11:06 AM
I'd try playing with the walls shader values too - maybe try setting a negative value in the ambient slot?

Has anyone else noticed that one of the 2 irradiance parameters in each shader are useless - You have irradiance and irradiance colour. the 1st is black and the 2nd white. The first one has never made any difference to any scene with fg in that I've made. Can anyone explain what is for and how it works.

also - the 2nd parameter I've found I had to set to 3.142 (as per earlier mental ray versions in maya) as the supposed 'fixed' default value of 1. just doesn't seem to work :/

Niber
11-05-2005, 11:28 AM
Niber: I think you should combine photons & FG. Photons are more predictable and they have a decay value. Scale can also be a matter here... try scaling down your scene.

Thanks, yes I've switched to GI instead, works better for me.
Hmm I didn't know that scale had anything to do with it, next FG scene I do I'll try scaleing it to get diffrent decay results.

CGTalk Moderation
11-05-2005, 11:28 AM
This thread has been automatically closed as it remained inactive for 12 months. If you wish to continue the discussion, please create a new thread in the appropriate forum.