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CS4 Alpha Interpretation Changes

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alex wells
CS4 Alpha Interpretation Changes
on Aug 14, 2009 at 1:28:03 am

I'm having a hard time figuring out the changes that have been made to alpha interpretation in after effects cs4. Previously (cs3) I was able to output an flv with a perfectly clean alpha (no halo). This is no longer the case. I've tried every possible combination of alpha interpretation on import and video output color and haven't been able to get the desired result. The magical combination in cs3 was Premultiplied against black on import and straight unmatted output. In cs4 it seems I'm only able to come close to that result with a straight unmatted import and output, and even then there's still a slight (but noticable) white halo around the image. I've linked to example images below. Any help is greatly appreciated.thnx.


CS3: Premul In, Straight Out

CS4: Straight In, Straight Out


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Todd Kopriva
Re: CS4 Alpha Interpretation Changes
on Aug 14, 2009 at 3:54:11 am

Does this page help?

"Flash, FLV, and alpha channels: straight or premultiplied?"

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Todd Kopriva, Adobe Systems Incorporated
putting the 'T' back in 'RTFM' : After Effects Help on the Web
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alex wells
Re: CS4 Alpha Interpretation Changes
on Aug 14, 2009 at 4:15:26 am

Thanks for the link, Todd. I had actually checked that out before posting and wasn't able to come up with a solution. I've tried every possible combination of alpha interpretation and video output color to no avail. At this point, I'd usually assume the issue was with my source footage, but ae cs3 is able to handle the exact same footage just fine.


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Matt Lamothe
Re: CS4 Alpha Interpretation Changes
on Jan 20, 2010 at 6:51:50 pm

I'm having the same issue Alex. Alpha video exported from the CS3 media encoder has little to no white halo. The CS4 media encoder, set to the same settings, produced a very noticeable white halo. I have yet to try Squeeze, but it is annoying that Adobe makes these seemingly undocumented changes. The problem is that the CS3 encoder lacks a lot of the advanced settings that CS4 has.


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