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Alpha channel bug

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Maxime Marquis
Alpha channel bug
on Sep 21, 2010 at 5:52:07 pm

Hi,

I'm trying to export a TGA image sequence (with alpha) using quicktime conversion. I learned that the sequence needs to be unrendered so the alpha channel shows up. The problem arises when there's a fade in or fade out in the sequence.

Let's say there's a fade in at the beginning of the video:

1st frame: tga is white, so complete transparency
2nd frame: the bg becomes a little greyer
last frame of the fade in: bg is now completly black (no transparency)
1st frame after the fade in and for the rest of the clip: bg is white, complete transparency

Seems like a bug to me. Any ways to correct it?

Thanks!


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Jeremy Garchow
Re: Alpha channel bug
on Sep 21, 2010 at 6:17:31 pm

[Maxime Marquis] "Seems like a bug to me. Any ways to correct it?"

What kind of fade are you using? You just want it to fade to nothing, instead of black, right?

Don't use the cross dissolve as the transparency won't keep.

Try an opacity fade instead.

Jeremy


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Maxime Marquis
Re: Alpha channel bug
on Sep 21, 2010 at 6:33:46 pm

Hi Jeremy,

I received a TGA sequence of a dancer (originally, he was in front of a green screen but the footage was keyed) with a transparent bg. I made an animation sequence in QT and imported it in FCP. What I want is the dancer to slowly appear/disappear. Originally, I used a cross dissolve. After your comments, I used the pen tool and keyframed opacity, with the same results. I also used the fade in-out effects, with no luck.

Any other suggestions?


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Maxime Marquis
Re: Alpha channel bug
on Sep 21, 2010 at 6:37:04 pm

Another thing,

I have many sequences in which I need to do the same thing. this morning, I did it with success, with the same settings. i just tried another sequence and it works fine. Weird.


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Jeremy Garchow
Re: Alpha channel bug
on Sep 21, 2010 at 7:21:48 pm

So it's only the one sequence now?


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