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Alpha Channel color shift (also posted in AE forums)
I might as well throw it all in those 2 posts.
I mentioned a while back an issue with clips imported from AE with an Alpha Channel, and layed over video footage. This was a lower third animation in that case. There was a noticeable color shift in the waveform monitor, as well as in the external DV broadcast monitor, as the CTI exited that lower third clip, and showed only the original video footage, even if the lower thirds clip opacity was set to 0%. This issue was not noticeable on my LCD monitors or in NON DV exports. Now I am starting to wonder if this had to do with the fact that AE is working in RGB and that this shift was simply a conversion artifact from RGB to Premiere’s YUV colorspace, but why would it happen even if the clip was set at 0% opacity? Any ideas ?
Thanks,
Vince
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10 Replies
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Cant seem to duplicate your concern;
1. Create a lower 3rd in AE, export as QT Animation with alpha
2. insert it into V2 in Premiere
3. Create a color matte and position in V1, extending beyond the end of the lower 3rd.
4. toggling between the last frame of the lower 3rd and the next frame (color matte only), waveform and monitor show no change.
Do you have a 3rd party card? -
Hi Mike,
Good weekend to you sir. I was rendering a lossless AVI (RGB + Alpha, Straight), but I tried QT animation, same problem 🙁
That issue does not happen with a color matte (YUV matte ?), but if you have a DV file handy, you might see what I mean. There is a slight Luma shift, but the Chroma shift is the most striking, (about 20 IRE’s). Again, I was thinking about a YUV color space compression, but it shouldn’t affect the luma part of the file, so I am at a loss… Dynamic link isn’t really an option here since we work in different locations.
Vince
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I forgot to mention that the Chroma in that particular footage peaks at around 117, so my scope might show a more drastic shift.
Vince
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Tried several DV clips without any shift in luma or chroma. I toggle between the last frame with the AE title and the next frame, all OK
Do you have a 3rd party capture card? -
Mike, thanks for looking at this.
I have to say, it happens on two machines with both ATI Radeon cards (a 9200 and a 9800)
This is happening through firewire as well however…
Now, tell me I’m not crazy, here’s a 3 frame sample I exported using QT animation RGB + Alpha.
https://www.kaptis.com/media/web/Lower 3rd.zip
Set its opacity to 0 and look at frames 2 and 3.
It ONLY happens on DV footage, not on images, mattes, etc…
Let me know what you think..
Thanks,
Vince
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Here the before / after scope pics.
BEFORE
AFTER
Vince
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Vince,
This is just a wild guess, but is your project 32 bpc by any chance?– Aanarav
Aanarav Sareen
premiere@asvideoproductions.com
https://www.asvideoproductions.com/techtalk -
Hi Aanarav,
No, just in the default 8 bit. I actually noticed the same type of shift when using simple AE transitions such as page turn in Premiere.
Vince
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I don’t know did I get right the thing here, but have you tried to export 32 bit TGA image sequence from AE?
If I have something to do with an alpha channel I never export any avi or qt.I always export image sequence, because I believe that avi or qt on PC has not correct alpha channel, I guess that’s why you have color and/or luma shift. And did you use “remove mate” filter in PPRO? Its necessary to use it when your mate is black or white otherwise you can expect or dirty edges, or some color shift depending on color of your mate. -
I have weened this problem out of my workflow by using 100% avi. I used to get it in instances that you mentioned but also when I had a QTDV clip on V1 and a avi with alpha on V2.
The QT clip on V1 was the culprit.
Brian
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