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Rendering Mov with Alpha and Kepping Add Mode

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Heath Alseike
Rendering Mov with Alpha and Kepping Add Mode
on Jan 22, 2010 at 12:00:51 am

I have been having a problem rendering Movs with Alpha's and having it keep the add mode the same. I am not sure if it is even possible but if someone can, please help. Basically what I am trying to do is render out some lower thirds I made with an alpha Chanel so they can be used as overlays by others with no effort (Blah blah you know that park if you can help). Where I am having a problem is I have some of those stock footage of fire clips with a black background. I add mode them so they appear to be overlaid just fine. When I render the black backgrounds are still there. Its like it lost the add mode when it rendered. How do I render and keep the add mode and the alpha? Any one Please help?


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scott novasic
Re: Rendering Mov with Alpha and Kepping Add Mode
on Jan 22, 2010 at 12:08:34 am

what i do with fire is precomp the fire, make it black and white and tweak the curves or levels to "taste" then apply that layer over the top of your fire as a luminance matte. It can take a little tweaking but ive always gotten pretty good results doing this..

SuperNova
Animation & Visual Effects
Scott Novasic
Los Angeles Ca
web:http://web.mac.com/finaleffects


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Dave LaRonde
Re: Rendering Mov with Alpha and Keeping Add Mode
on Jan 22, 2010 at 12:11:07 am

Sorry, it's not possible.

Think about it: AE's Blend Modes influence the layers below the layer. But when you make an alpha-channeled movie, there's no layer beneath the layers with the blend modes... so there's nothing more to affect.

I don't know how Artbeats gets the alpha channels on their explosions and fires without rotoscoping, but I do know that they look really fake until you start using the blend modes.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Heath Alseike
Re: Rendering Mov with Alpha and Keeping Add Mode
on Jan 22, 2010 at 12:27:32 am

Yeah it made sense that it wouldn't work. However, once I render I get there is nothing under to add mode over but once I overlay the new mov over a new film there is no way to keep the add mode info in the mov? But then again the same thing happens in photoshop when I merge layers. Do you have any recommendations on how to pull this off with out roto. Do you think keying the black would be a bad Idea?


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Michael Szalapski
Re: Rendering Mov with Alpha and Keeping Add Mode
on Jan 22, 2010 at 12:39:11 am

Do what Scott said and use the fire footage as its own luma matte. Duplicate the fire layer, desaturate it, and use levels or curves to crush the contrast and use that duplicate as a luma matte. You may need to play with the levels or curves to get it right, a bit of rotoscoping may be needed to clean some parts up or to make sure the middle doesn't get matted out.

Or you could create two separate pieces of your lower thirds, one part to be normal, and the fire part. Some NLE's (like Premiere) have blending mode capabilities so your lower thirds could be on two layers; one normal, one with a blending mode.

- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')

No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.


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Gary Hazen
Re: Rendering Mov with Alpha and Keeping Add Mode
on Jan 22, 2010 at 7:22:12 am

Unmult and Xmult are free plugins that will generate an alpha from footage on a black background.



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Heath Alseike
Re: Rendering Mov with Alpha and Keeping Add Mode
on Jan 22, 2010 at 4:32:42 pm

Awesome Thank You!


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