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Alpha channel: objects borders problem

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Alberto Bedin
Alpha channel: objects borders problem
on Aug 20, 2010 at 3:03:39 pm

I have exported some frame with test objects from 3d studio max to AE in .tga format.

So there's an alpha channel for the background enviroment.

In AE I tried to change the background according to the alpha channel.

Here you can see the result: http://f1.creativecow.net/1011/alpha-channel-objects-borders-artifacts

How can I remove that white-border artifact problem?

Please note that frames from MAX are taken using a moving camera and motion blur on (mental ray render engine).

Thank you


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Dave LaRonde
Re: Alpha channel: objects borders problem
on Aug 20, 2010 at 4:13:16 pm

It looks like it's a premultiplied alpha channel, but AE is interpreting it as a straight alpha channel. Go to the interpret footage settings and change the interpretation to premultiplied, and see what happens.

AE is usually VERY good about interpreting alpha channels properly. This is puzzling.

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


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Chris Wright
Re: Alpha channel: objects borders problem
on Aug 20, 2010 at 7:52:53 pm

There's two things I'd watch out for...

1. Partial transparency in the image premultiplied with the wrong color which means you'll need to use the AE effect remove color matting.

2. Instead of tga,arg! use Tiff 16 bit trillions lzw off.

http://technicolorsoftware.hostzi.com/


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Alberto Bedin
Re: Alpha channel: objects borders problem
on Aug 21, 2010 at 11:53:28 am

Fixed changing interpret footage to straight (it was premultiplied).

What about output format? Is it better exporting in .tiff then in .tga? What about .rpf? Does they all support alpha channels?

Thank you a lot!


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Walter Soyka
Re: Alpha channel: objects borders problem
on Aug 21, 2010 at 2:26:21 pm

[Alberto Bedin] "What about output format? Is it better exporting in .tiff then in .tga? What about .rpf? Does they all support alpha channels?"

TIFF and TGA can both carry uncompressed RGBA, but as Chris mentioned, TGA can be touchy and TIFF supports higher bit-depths.

RPF is an option, and it can carry a lot more information from a 3D scene. See Import RLA or RPF data into a camera layer in the help.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Alberto Bedin
Re: Alpha channel: objects borders problem
on Aug 21, 2010 at 2:47:23 pm

I have just tried RPF instead of TGA and it's really faster in AE preview. Also, as you said, I can control obj IDs from MAX and other things.

I will definetly use it in the future.

Thank you


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