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Home ? Tips & Tricks ? Using Alpha Channel Instead of Chroma Key in Post

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02/06/2016 17:41:47

tim3dwards
tim3dwards
Posts: 5
Hi guys,

I've been having fun the past few weeks playing around with Muvizu. We're intending to use it in a professional context, so I've been seeing what it can do in this regard.

I found something useful today that may be useful to some of the rest of you, and after a quick search I can't find another post that talks about this. A problem with using a key plugin on a video of CG characters is that when anti-aliased, the colour you're using to key with bleeds through onto the character. Therefore, if you're using red for your key, you'll see a slight red halo around the character once the key is working in post. There are various spill suppressors that can be employed to counter this, the problem is that because CG usually involves clean, straight inorganic edges, the result can look a bit messy.

So, what I wanted to do was see if it's possible to export an alpha channel as part of the final exported video. If your scene is set up so that all of the objects exist on a single layer, then the alpha channel included in the exported sequence is pure white, and therefore unusable for keying. This is due to the background being included in the alpha. I then found that it possible to get a usable alpha channel, by moving all of the objects that you want to be keyed into their own new layer. Once this has been done, simply hide the background layer, then export the video as a sequence of stills. Then, load the image sequence into your video editor of choice and voila! You get an instant perfect key layer as part of the sequence.

Apologies if this is already covered in a tutorial / other post somewhere, but it took me a while to figure it out and may well be of use to others who haven't discovered this technique.
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02/06/2016 18:00:17

MrDrWho13Muvizu mogulExperimental user
MrDrWho13
Posts: 2221
Thanks for spending the time to explain this. I've tried to cover this on the Wiki but it's a bit all over the place (Layers separate to the transparency and exporting). Do you mind if I borrow some of this wording for the Wiki?
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02/06/2016 18:42:50

tim3dwards
tim3dwards
Posts: 5
No probs, be my guest!
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Home ? Tips & Tricks ? Using Alpha Channel Instead of Chroma Key in Post