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alpha channel background issue
Hello, i posted about this and got an answer awhile back, but no luck getting it to work.
I am using a jumpbacks .mov file as a background with an interview on top.
everything looks fine in the preview window, but when i render, the motion background comes up black.I’ve tried it with the interviewer on track 1 with a mask cut out (basically an oval) and also tried it with the motion menu on track 1 with the mask in that, and set to negative to only show the outer portion of the oval.
I’ve right clicked and changed the alpha properties to straight unmatted (as suggested on the DJ forums and FAQ), but then the jumpback file background only shows up on the timeline as an empty alpha channel with the gray boxes.
I also tried the same thing, only using the motion background as a lower third instead, with the same result.
I’ve messed with the compositing settings as well, with no luck.
Can anybody help??
Thanks!Below is the old thread–
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Name: DV Memories Video
Date: Mar 5, 2007 at 8:27:49 am
Subject: Adding Motion Lower Thirds/Backgrounds-problem with alpha??I tried to add a lower third from digital juice the other day and it renders out black.
The file is a motion .mov background which I pan/cropped down to a rectangle with feathered edges.
I placed it over my video track, then placed text over it.All was transparent and looked excellent in the preview window.
When I rendered it, it comes out gray/black. I tried playing with different alpha channel settings, but cannot figure out what is going on.
Can anybody help??Eric.
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Name: Mike Piontek
Date: Mar 5, 2007 at 10:00:17 am
Subject: Re: Adding Motion Lower Thirds/Backgrounds-problem with alpha??The bit below is from the DJ website. There is another tutorial type thing on using DJ poducts with Vegas but I couldn’t find it.
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Vegas doesn’t automatically detect the alpha channel, so the background behind overlays, lower thirds, transitions and motion design elements are not transparent and appear black.To get Vegas to detect the alpha:
1. Drop the overlay into a track above your video.
2. Right-click the overlay and select Properties.
3. From the Alpha channel drop down (or on the Media tab), select Straight (unmatted).
****************************Hope this helps.
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Name: Terry Esslinger
Date: Mar 5, 2007 at 8:23:26 pm
Subject: Re: Straight or dirty?Mike, Your answer has raised another question that I have wondered about. What is the difference between ‘straight’ and ‘dirty’??
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Name: Mike Piontek
Date: Mar 6, 2007 at 12:07:52 pm
Subject: Re: Straight or dirty?I’m not an expert on this one but the differences are basically between ‘straight’ and ‘premultiplied’ alpha channels. Premultiplied applies the alpha information to each color individually as opposed to using the straight alpha channel value for each pixel. If you google ‘premultiplied alpha’ you can find lots of explanations on it’s effects and use.
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Name: DV Memories Video
Date: Mar 29, 2007 at 2:21:07 pm
Subject: Re: alpha channel.I am using a jumbacks .mov file and tried all options for alpha channel, and they all render out black. Prior to rendering, it shows up fine in the preview window with straight-unmatted, but as soon as i go to avi, it comes up black.
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4 Replies
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This is just a guess, but do you have QuickTime on that computer?
Charlie
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yes.
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GOOD guess, Charles, you’re a genius.
I remembered that i was having problems with quicktime and gave up on it awhile ago. I couldnt install itunes, and was stuck in quicktime version 7.1 beta or something to that effect, and it just wasn’t working right. I could not update it, nor could i delete it or uninstall it.
I just went and did a quicktime update, rather than uninstall/reinstall and it did some updating, i changed my .mov file properties to always open with quicktime, and voila.
My overlay rendered beautifully as an .avi file. Not sure if i should mask the video footage or the background file, guess it doesnt matter. I ended up masking the video footage. I did not need to change the alpha properties, it is set on undefined. Since it worked, i didnt bother changing it.
Thanks again.
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Your welcome.
Charlie
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