View Full Version : Compositing Problem: pliz help!

04 April 2004, 10:30 AM
Hi buddies!
I got a sequence to do for a tv-show....
it's a logo that appears..... and then disappear! :p

My big prob is that this animation has to be with alpha as it will be composited with different footages every day; and when I use motion blur and anti-aliasing the blurred parts melt with the background within lightwave.
The result gives strange edges when composited. :cry:

So, my friends, I hope that somebody could help, cause I really don't know how to do......

Thx in advance!

04 April 2004, 10:53 AM
I'm not sure about motion video but couldn't you do a post motion blur effect ???

04 April 2004, 11:03 AM
Originally posted by cyroz2000
when I use motion blur and anti-aliasing the blurred parts melt with the background within lightwave.
The result gives strange edges when composited
When you say the motion blur causes the 3D object to "melt" with the background, maybe the opposite is happening.

From your description, I gather that you created 3D elements in Lightwave with motion blur. But the motion blur on these objects can only blur the object with the black background they were created with. So you get black creaping in.

Then when you composit these 3D elements in your compositing application, you get that black edge creaping in.

I think the answer is to try to add the motion blur in your compositing application (somehow). This way it will blur with the background it is being composited with, rather than black.

What compositing app are you using? There are some plugins around that may help. "Real Smart Motion Blur" is one that comes to mind.
It's a 2D motion blur that tries to calculate the motion vectors.

04 April 2004, 02:38 PM
Just render your logo with black (Or any other solid color) background, then in composite program use Premultiplaed alpha with black (in After effect) - this will eliminate black color from the transparent and semitransparent areas like motion blur and antialiasing. If u use Premier - use Transparency -> Black alpha matte - it's the same. If your composite program doesn't support this feature (hard to believe) or if u use LW to composite - render your logo with SpriteEdger (Scene-> Image Processing -> Add image filter -> SpriteEdger) - it's get u strange result on render but believe me after composting your object will be OK :)
Good luck.

04 April 2004, 02:57 PM
Correct. It's called Remove Color Matting in AFX.
If you're ever stuck with something that doesn't have an Alpha channel, use Knoll's Unmult, still available for free I believe at:

04 April 2004, 10:39 PM
Sure, switching your compositing app to "premultiplied" alpha can reduce some of the black fringing.

But when the 3D elements are rendered with motion blur, I lot more of the background black is combined and blurred with the 3D element, and I don't think using premultiplied alpha settings will remove it.

Mike RB
04 April 2004, 12:06 AM
dont render it with the background, just render the logo against black.

04 April 2004, 12:17 AM
I remember this from the AE forum. Not sure if it will help or not.

04 April 2004, 10:30 AM
Thanks all of you for your help!!! :beer:

Another prob is that I really don't know which app will be used for the compositing, it will a sort of "live-editing", short short time to prepare the show every day...
I'll tell you when I'll have more info about it!

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