PDA

View Full Version : Parti volume lightfog renders complete white alpha?

inkblack
11-16-2006, 08:21 AM
Hi guys,

my first post here after a period of a lot of reading and learning 3d. I must say cgtalk rules! learnt a lot so far by searching this site.
BUT..... i have a question now that i can't figure out by myself or with searching the board.


I want to make multiple overlapping beams of (volumetric)light coming from multiple light sources. The standard lightfog option from maya doenn't render well in mental ray, so after some reading i decided to give the parti volume a shot after reading this tutorial :

http://www.jhavna.net/main.php?page=scatter/

The image looks very good and it's good enough for me to implement this into my own scene, but there is a problem :
The box where the parti volume shader is on, surrounds my whole scene and gives a completely white alpha when rendered. I can't get this different without masking the fog out too.

Anyone now something about this? A solution perhaps :)


Thanks in advance!

Mathijs
mentalboy
02-28-2007, 07:47 PM
hello!

I have the exact same problem myself. Hope to find a solution to this soon.
tfritzsche
02-28-2007, 08:19 PM
welcome inkblack

perhaps you could try rendering only the light fog with a black background and then comp it in, in post, with a screen blend on to your scene, with a little fiddling this should give you what you need.

thomas
ooz
03-02-2007, 09:53 PM
not too good with MR, but try this:
set "mode" to 1
change "ectinction" value, which is density.

worth a try
dsliter
03-05-2007, 03:47 PM
I found that if you go in to the framebuffer options and change the colorclip to RGB that it will create an alpha. I plan on setting it as a render layer over ride because I haven't fully tested how it will effect the rest of my scene.
mentalboy
03-08-2007, 04:01 AM
welcome inkblack

perhaps you could try rendering only the light fog with a black background and then comp it in, in post, with a screen blend on to your scene, with a little fiddling this should give you what you need.

thomas

the volume is not only light. so screen will only do half the job. you need a layer with a white background to multiply first. hate to render two layers to get the full effect.

To fix the Frame Buffer settings from Raw to RGB works fine for the Alpha :)
CGTalk Moderation
03-08-2007, 04:01 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.