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Alpha Channels in Synthetik Studio Artist 2.0

Using alphas in stills, video and animation By Dave Nagel
We've examined Synthetik Studio Artist in quite a bit of detail over the years, particularly the creative aspects. But we seldom get into production techniques, particularly the points that can help Studio Artist fit better into your pipeline, such as dealing with alpha channels. It's not difficult at all to get a little confused about alpha channels in general, especially when working with video in multiple applications that all output alphas differently. Throw on top of this the various ways different applications interpret alphas and the limitations of some video codecs, and you can wind up with quite a mess. So let's take a look at how these things work in Studio Artist.

One of the very first tutorials I ever wrote for Synthetik Studio Artist--way back when I drove to work in a covered wagon and dinosaurs still roamed the earth--involved outputting alpha channels for still images. That was back in version 1.0, and the process has changed a little bit. So we'll take another look at alphas for still images and also talk about alphas in video as well.

The setup
In Studio Artist, the most critical starting point for outputting alpha channels is the initial setup of your canvas and your output options. After you launch Studio Artist and set your source image and canvas options, you need to make a few changes to the default preferences. First, if you plan to use transparency a lot in your work, you'll want to go into File > Preferences > Layer and set your default composite mode to Alpha Layer Overlay, which is the mode that provides you with basic layer transparency. This step isn't necessary, but it will provide you with an accurate view of your output as it will appear in any program into which you import your file, such as Adobe After Effects or Photoshop.

You can also change these layer modes in the Layer window (Command-1) by selecting the mode for each individual layer through the pull-down menu.

If you're using Studio Artist for rotoscoping, animation or other video work, you'll also need to set the "out alpha" preference. Go to File > Preferences > Movie Stream, and choose the "Layer Alpha" option.

Finally, Studio Artist also provides encoding options for your output in a standard QuickTime dialog, and it's critical that you select a codec that actually supports alpha channels--and that the codec's settings are defined for alpha output. So go to File > Preferences > Movie Compression, and choose a codec that supports alpha channels, and make sure that you switch the settings to "Millions of Colors+." (The "+" means that the file will be output with an alpha channel, i.e. 8 bits per channel "+" an 8-bit alpha.)

So how do you know which codec supports alpha channels? I'm not going to get into every single one of the codecs, but all of the codecs available to QuickTime that include the "Millions of Colors+" option will support alpha output, as long as this option is selected.

OK, and if you're doing automatic rotoscoping in Studio Artist through a Paint Action Sequence (PASeq), there's an additional setting you need to choose. Go to Action > Process File Settings, and then choose the alpha output for your rotoscoped video. The reason this is a separate option is that there are times when you will want to use your source footage's alpha channel as your output alpha, and these settings allow for that. Or you can simply choose to use the Layer Alpha, as with other video creation techniques we're discussing.

Finally, in terms of setup, keep in mind that for both video and stills, there are limitations on how the current version of Studio Artist handles alphas on multiple layers. If you're outputting video, it's best to work with just a single layer in Studio Artist. The standard "Layer Alpha" output will track your layers and switch back and forth between the alpha channels on each layer as you switch, which can cause you problems. (We'll get to a potential workaround for this below.) If you're working with stills, there is no problem with alpha channels on multiple layers. However, at present, you have to save each layer individually and then recomposite them in a program like Photoshop. You do this by going to the Layer window and selecting the View: Current Layer Only option and then selecting the layer you want to save. Repeat this for each individual layer.

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