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Video with Alpha Channels

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Greg Ball
Video with Alpha Channels
on Mar 10, 2017 at 8:47:27 pm

My graphic artist gave me several animations of an iPhone and iPad He gave them to me with alpha channels. I'm trying to key these over a matte background, and no matter what composite mode I try, I can't seem to get it to work. I still get a black background, and never get to the matte colored background I want.

Is there a suggestion on how to do this? What combo do I use in composite mode and alpha channel?

Thanks so much.

Greg Ball, President
Ball Media Innovations, Inc.
https://www.ballmediainnovations.com


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Shane Ross
Re: Video with Alpha Channels
on Mar 11, 2017 at 1:00:28 am

No mode...you KEY it. Luma key most likely. Actually, if this is a file with a built in alpha, it should just DO it. What codec is this? ProRes 4444 allows embedded alphas

Shane
Little Frog Post
Read my blog, Little Frog in High Def


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Greg Ball
Re: Video with Alpha Channels
on Mar 11, 2017 at 3:27:47 am

Hi Shane,

The video as given to me keys perfectly. But it's an .h264 with an animation codec. I'm editing this on a 720p prores sequence.

I tried converting the videos to prores444 but it didn't key. Thoughts?

Greg Ball, President
Ball Media Innovations, Inc.
https://www.ballmediainnovations.com


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Shane Ross
Re: Video with Alpha Channels
on Mar 11, 2017 at 5:16:54 am

[Greg Ball] "But it's an .h264 with an animation codec. "

Sorry, that makes no sense. H.264 is a codec...Animation is a codec. It can be a MOV with the Animation codec.

[Greg Ball] "The video as given to me keys perfectly."

Wait....but I thought you said it doesn't key. You said:

[Greg Ball] "I'm trying to key these over a matte background, and no matter what composite mode I try, I can't seem to get it to work. I still get a black background, and never get to the matte colored background I want."

Shane
Little Frog Post
Read my blog, Little Frog in High Def


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Dave LaRonde
Re: Video with Alpha Channels
on Mar 11, 2017 at 10:42:03 pm

Sounds like it's time for Alpha Channel School.
A still or a movie can have an alpha channel. It's an unseen channel that determines transparency. If you could see this channel, the iPhone would look white, and the background would be black.

Not every video codec supports alpha channels. In Quicktime you're limited to the Animation, JPEG 200, PNG and ProRes 4444 codecs. Anything else won't have an alpha channel.

To summarize -- Quicktime movies. Straight alpha channel. Animation, JPEG 2000, PNG or ProRes 4444 codecs. It's that simple. Accept no substitutes.

To use footage with an alpha channel, put it on the track above some video. Poof! There's the subject and NOTHING else. If you're not getting that, your footage does not have an alpha channel. Talk to the animator. Demand the animations as Quicktime movies in one of the codecs mentioned above.

A final note: there two variants of alpha channels, Straight and Premultiplied. FCP defaults to using straight alpha channels. If you see footage with a funny-looking border around the subject, it's a premultiplied alpha channel.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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Roger Poole
Re: Video with Alpha Channels
on Mar 12, 2017 at 12:50:45 pm

Sometimes fcp doesn't interpret the alpha channel correctly. If you right click on the clip in the browser then click on "Item properties" you will see all the info about that clip. If you go down to Alpha it will most likely display as "none/ignore. If you click on none you should get a drop down to "straight" , choose that. If it doesn't show that then the clip has no alpha channel. As already pointed out, the only codecs which support transparency are the animation and/or ProRes 4444 for video, and tiff or PNG in the case of still images.


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