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Preserving black while exporting Alpha Channel

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Prema Ball
Preserving black while exporting Alpha Channel
on May 4, 2010 at 8:40:42 pm

I am creating some lower thirds and I need to export them for use in Avid.

I have done this before many times, but never using black as one of the colors of the graphic, because I've never been able to export the alpha channel and still preserve black as an opaque color within the graphic.

How can I export my lower third graphic, and maintain the opacity of the black in the graphic and export the alpha channel so everything but my lower third graphic is transparent?

thanks


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Dave LaRonde
Re: Preserving black while exporting Alpha Channel
on May 4, 2010 at 10:07:11 pm

First thing: don't export from AE, Render using AE's Render Queue.

Second thing: if you create an alpha channel movie, the background color of the comp is absolutely irrelevant. It could be purple, green, black, yellow... what have you. What IS important is whether your edit system works with a Straight or a Premultiplied alpha channel.

Here's how you do it:

If it's a still, do a Save Frame As command. It puts the comp in the Render Queue, using the frame where the comp's timeline cursor is located. Once in the queue, you can click on the Output Modeule to select from one of the many kinds of stills that support alpha channels -- Tiff, Targa, Pict, PNG -- then set it for Millions of Colors +, RGB + Alpha... and then you have to choose Premultiplied or Straight.

If it's a MOVIE, do a Make Movie command to put it in the Render Queue. In the Output Module, choose a codec that supports alpha channel; the two most universal are the Animation and PNG codecs, but there may be a preferred Avid Codec for that, too. Then set it for Millions of Colors +, RGB + Alpha... and again, you have to choose Premultiplied or Straight.

Hey, you can run a test first to see which kind of alpha channel your Avid likes.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Prema Ball
Re: Preserving black while exporting Alpha Channel
on May 5, 2010 at 6:58:34 am

Sorry I misspoke on the export/render. Go back and forth between so many programs that sometimes I use the wrong terminology.

It would be a movie. A quicktime animation codec. Millions of colors + (rgb+alpha) at best (100) quality.

but the problem I run into, is that if I have black as part of the graphic I've made, it comes out translucent, treats the black as part of the alpha. do I have to make the background something toher than black for it to differentiate it from the BG?

thanks for the response.


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John Cuevas
Re: Preserving black while exporting Alpha Channel
on May 5, 2010 at 1:28:13 pm

It sounds to me that you used the "BKG color" as part of your graphic, rather than a solid. Test this out by hitting "shift+cntl+b" and change the color to red. If the black part of your graphic that you need changes to red, you don't have anything there, there's nothing to create an alpha channel.

Fixing this is as simple as creating a solid"shift+y" and modifying it so it fits your graphic correctly...ie masking it to fit into the lower third, track matte.

Also there is a turn background off button under the comp window--little checkboard icon. If you press that, you'll see exactly what will be transparent or not. Push the green-red-blue circle pulldown and you can also switch to the alpha channel to see what you're exporting.

Good luck

Johnny Cuevas, Editor
http://www.ckandco.net


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Dave LaRonde
Re: Preserving black while exporting Alpha Channel
on May 5, 2010 at 4:26:34 pm

...and in case John's suggestion doesn't work...

Did you have to key any layer in this comp? It could be a bad key, and you'll need to duplicate some layers and do some masking to preserve opacity in certain spots.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Prema Ball
Re: Preserving black while exporting Alpha Channel
on May 5, 2010 at 4:36:45 pm

I didn't have to key any part of it, but that is definitely something that I will keep in mind on other projects I'm working on.

Both John's and your suggestions have been very helpful.

Thank you.


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