View Full Version : Alpha channel from volometric light?

03-18-2003, 05:32 AM
Does anybody know if u can render with an alpha channel when using volometric lighting? If not is there any other trick in getting this result stright from lightwave?

03-18-2003, 05:45 AM
There is a plugin called Post Alpha that will do exactly what you need. Look it up at http://www.flay.com


Arnie Cachelin
03-18-2003, 08:14 AM
Volumetric light effects like lens flares are generally additive effects, so compositing with an alpha channel will give 'wrong' results. This is why the lens flares and default volumetric lights do not change the alpha channel. For volumetric lights, the Opacity setting directly determines how much of the volume effect blocks the background, or the res of the volume. This setting thus also controls how much of the volumetric light appears in the alpha channel.
Plugins like Flare2Alpha are handy for putting values in the alpha channel where things like flares appear, but users should be aware that using them in a naive compositing process will generally yield incorrect results.

03-18-2003, 12:31 PM
Hi Arnie,

Thanks for your words. However the bad thing about tweaking opacity is that it will affect how the light is distributed within the volume. Especially with textures and strongly colored lights this is not an real option. It gets even worse with multiple intersecting lights. From my point of view it should not be to difficult to have an extra option for writing a (normalized) alpha value - some plugins already do it and most other 3D progs as well. While you're at it, please do the same for glow ;) . Thanks in advance.