View Full Version : Nasty rendering glitch

05-25-2010, 05:17 PM
Anybody get this annoying line in their renders?

I captured my adventure with this glitch in a YouTube video: Part 1 (http://www.youtube.com/watch?v=9JKn6xo_6PM) - Part 2 (http://www.youtube.com/watch?v=WmhnpIBwHo8)

05-26-2010, 01:22 PM
hey carm,
I cant say Ive run into this problem, but then again I havent used the spherical lights too much. What I was going to ask you though is that you said it only shows up in the alpha in the first video: dont you just make the shadow pass 24 bit (no alpha channel) when you composite your shots, thus eliminating the problem and letting you still take advantage of the light setup you liked?

05-26-2010, 02:04 PM
I didn't know that was possible. I thought the only way to extract the shadow density from the surface was to save out the render's alpha channel.

05-26-2010, 11:47 PM
You could get the same shadow with area lights, I've done it many times with far fewer lights. Or do you get the same artifact? Looks like a real bug.

Mr Rid
05-27-2010, 04:11 AM
Yeah, am wondering why not simply use one big area light.

05-27-2010, 04:37 AM
I've ran into that exact problem many times. Always when I use an UNPREMULTIPLY alpha as the Alpha Format. and the "flare to alpha" effect turned on. Flare to Alpha works fine with premultiply alpha.

I do a lot of broadcast news animations, lots of light effects that need to be composited and posted, so rendering with the background disabled give me a truer colors. Except I get that line.

It seems that LW has a problem rendering the matte of light/shadow effects. Such as a lens flares or using shadow density as you're alpha channel. I have yet to figure out how to fix it. Changing my lights have not had any effect.

If you have any luck squashing that bug, I would love to know the trick.

05-27-2010, 08:17 AM
Thanks for the insight, gschrick. I posted the project and video links to FogBugz. Hopefully they can do something about it.