WORKING WITH MORE THAN ONE ALPHA CHANNEL

[Mike Clasby]

Why would an image sequence have more than one Alpha Channel? I can’t visuallize the need for this. I also eargerly await an answer to your question.

[Steve Roberts]

Not in AE.

[Aharon Rabinowitz]

I’ve seen some expert photoshop artists who worked with multiple alphas – didnt get what they were doing, but they were doing it.

I would love to hear more about it.

Yeah – AE doesn’t support this.

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Aharon Rabinowitz
arabinowitz(AT)yahoo(DOT)com
http://www.allbetsareoff.com

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[Roland R. kahlenberg]

Working with more than one alpha is analogoue to creating procedural mattes in AE – aka multiple masks.

AE doesn’t support multiple alpha channels – it defaults to picking up the top-most alpha channel in AE. To make things happen, copy and paste the alpha channels into RGB layers and work accordingly in AE.

Once in AE, you’ll have to merge the alphas in a precomp using either the multiple or screen transfer mode. Take note that should there be semi-transparent areas, unexpected results may occur. This will also happen should you manually merge more than one alpha channel within Photoshop.

After merging the alphas. Precomp them and use them as a track matte.

Cheers
Roland Kahlenberg
https://www.broadcastGEMs.com – Adobe After Effects project files
https://www.myspace.com/rorkrgbspace

[Mike Clasby]

Thanks for the explanation.

[Roland R. kahlenberg]

Take note that having multiple clpha channels isn’t really necessary when importing multi-layered PSD files into AE. There was a time when it was impossible to import multi-layered files into AE. At that time, it was imperative to have multiple alpha channels when in Photoshop. And then to manually change the hierarchy of the alpha channels depending on which RGB layer was being saved.

So, the initial poster should rethink his/her workflow. A better workflow would be to create the selections and then perform a copy-paste routine onto a new layer, thereby precluding saving an alpha channel.

Cheers
Roland Kahlenberg
https://www.broadcastGEMs.com – Adobe After Effects project files
https://www.myspace.com/rorkrgbspace

[David Bogie]

Sorry to butt in, I may be totally misunderstanding the thread.

Using advice from Brian Maffitt, I have used RGBA files to hold what are essentially four grayscale images for use with compound effects like Card Dance. Each of the four different grayscale movies carried by the file were extracted to control different aspects of the Card Dance (or Shatter) effects system. I do not know why all four channels could not be pulled for separate alphas but you’d simply use two copies of the file in order to have RGB and multiple alphas.

bogiesan

This is my standard sigfile so do not take it personally: “For crying out loud, read the freakin’ manual.”

[Roland R. kahlenberg]

Hi Dave
It’s fine to have multiple grayscale images within AE for Card Dance and ParticlePlayground, to name a few plugins that utilize grayscale images. In fact, all individual RGB channels are also grayscale. And for CD and PP, one would create distinct grayscale images and then use SetChannels to move these grayscale images, which are essentially RGB AE layers, into a seperate layer’s individual RGB+A channels.

But creating them in PS is not necessary, AFAICS. As AE doesn’t support it. And with video apps being able to support layered PSDs, I don’t see a need for stashing multiple Alpha Channels within PS.

Within PS, as long as a layer’s selection is outlined, AE will create an alpha, automatically, based on the outline – no need for an alpha channel.

Cheers
Roland Kahlenberg
https://www.broadcastGEMs.com – Adobe After Effects project files
https://www.myspace.com/rorkrgbspace