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Color shift at end of clip with Alpha Channel
This one really has me thinking. Imported clip from AE, basically motion graphics, with transition at the end, and an Alpha channel revealing the footage below. Exported as RGB + Alpha from AE, and the Alpha channel is clean.
So, that color shift (Roughly 2 IRE’s on blue, a little less on R and even less on G) is happening as the CTI passes the last frame of the clip, and what really stomped me is that it even happens if I leave that clip at 0 opacity, or if I reduce its length. Always at the end of the clip. If the clip is deleted, no shift. I am out of town and don’t have a scope to check if this is happening when I burn a DVD, but I am puzzled, as I am assuming that when the opacity is set to 0, the clip is non existent to the timeline, thus eliminating possibilities of issues with the Alpha channel.
Anybody come across this ?
Cheers,
Vince
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13 Replies
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That IS a weird one…
Is the project interlaced? All I can think of is that (and this is a long shot) maybe the field dominance could be reversed and there is an orphaned field?
If the project isn’t interlaced, then I’ll have to think some more.
Can we have all the pertinent project/clip settings, etc.?
TimK,
Kolb Productions,
Creative Cow Host,
Author/Trainer
http://www.focalpress.com
http://www.classondemand.net -
Tim,
480i DV Project, basically the PP2 default. Lower first on both clips, but again what strikes me is that it happens even when that clip has a 0 opacity all the way. I exported several times, straight or premultiplied, still the same issue. Not happening with any other clips. Again to confirm, that shift happens as the CTI leaves that clip, no matter what I trim it to. Does anybody know if opacity settings in Premiere ignores alpha channels ?
Vince
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Vince –
I have noticed this on QT’s with alpha – try this to see if it fixes your issue – slice off the last frame, select hold on first frame and set speed to zero and retrim the clip – for some reason it gets rid of the shift on the QT’s (although theoretically all it’s doing is showing the same frame it was using in the first place, but it seems to treat it differently).
slainte,
marisu -
Marisu,
Thanks, I’m not sure understood your process. (I won’t ask how you came up with that 😉
I sliced the last frame, deleted it. Put a hold on the in point of the remaining clip, (can only set the speed at a minimum of 0.10). This basically keeps the clip at the same length holding on to the first frame. So I must be missing something.
Thanks again,
Vince
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What happens if you hold the last frame?
If you double click the clip in the project window and look at the last frame in the source window…anything visually peculiar there?
(…and no, the opacity control doesn’y ignore alpha channels.)
TimK,
Kolb Productions,
Creative Cow Host,
Author/Trainer
http://www.focalpress.com
http://www.classondemand.net -
No luck on the hold on out point. The last frame is basically an alpha channel by itself. Happens no matter how I trim the clip, always past the last frame. This clip is actually reducing my color saturation, so unless there is a bad bug in Premiere I don’t see how that could be happening even when the opacity is set to 0.
Vince
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So…please give me the important stuff and I’ll try to duplicate the steps…
DV preset in PPro2…NTSC 48k…file out of AE…DV framesize, lower field, I assume uncompressed to carry the alpha?
What else do I need to know?
TimK,
Kolb Productions,
Creative Cow Host,
Author/Trainer
http://www.focalpress.com
http://www.classondemand.net -
Thanks for looking into that Tim,
So all you listed, out of After Effect 720×480 – 29.97.
Put a piece of footage in AE, end with a card dance transition (Mine’ s pretty customized but it shouldn’t matter)
Put that over another track in Premiere and use the end of the card Dance transition to reveal the footage below.
My export out of AE was RGB+Alpha, million + colors – Straight
Again I really appreciate you taking the time to look into this.
BTW, the shift is much more evident out of firewire through a Canopus Box, but it appears on the Premiere scope as well.
Vince
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One more thing, I don’t see that issue when I export to Quicklime animation.
Now I am on an LCD and without a scope, so I can’t confirm it, but I have a feeling that this maybe a DV issue.
Vince
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This all sounds to me like a RGB to YUV encoding error. If you rendered
the output from AE as a RGB file (QT animation, RGB, etc) then PPro is
having to interpret that as YUV to output in a DV project. It sounds as
if PPro isn’t doing this correctly. Have you tried rendering from AE as
a DV-AVI file? Try it w/o the alpha if you have to just to see if that
makes a difference. I’m just guessing, but that’s what it stinks of to
me…I just re-read the above posts:
But you did say that a QT animation file didn’t have the problem?
Hmmm, now I’m not sure….-Troy Murison
Seattle, WA
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