Adobe has officially launched Creative Suite 5, which includes major updates to virtually all of their applications. Adobe has seeded us with preliminary versions, and hired us to help create some documentation on the new release; we wanted to share with you our own impressions plus insights into the new features in After Effects CS5.
The largest fundamental change in After Effect CS5 is rewriting it to be a 64-bit native application. This brings several pros and a few provisional cons: Pros + After Effects can take advatange of all of the available memory in your computer, instead of being restricted to 2-4 GB per instance of the application (depending on OS). The most obvious advantages are longer RAM Previews, the ability to handle larger media and create larger comps without out-of-memory errors, and the option to work at higher bit depths than you normally would for improved color fidelity. The chart below provides some typical scenarios for the types of improvements you should see with varying configurations; note that the more RAM you have, the bigger the difference: + Performance is improved. Michael Coleman (After Effects product manager) recently posted some benchmarks; a 30% improvement is typical. + Linked in with this rewrite, multiprocessing is greatly improved. For one, there is now almost no time lag to launch a multiprocessor preview or render; this lag used to negate the advantage of enabling Render Multiple Frames Simultaneously for shorter comps and previews. There have also been other refinements to multiprocessor rendering, including better RAM utilization and the ability to access virtual cores. Cons - You must be running a 64-bit OS, or AE CS5 won’t even install. (If you install Adobe CS5 Master Collection on a computer with a 32-bit OS, After Effects and Premiere Pro CS4 will be installed instead.) On the Mac, OS 10.5.7 or later is suggested. On Windows, you need to be running a 64-bit flavor of either Vista 64 with Service Pack 1 or Windows 7, and at least the Home Premium version or higher. We recommend at least Business/Professional, as Home Premium is restricted in the maximum amount of RAM it can access. - All plug-ins must be updated to 64-bit versions (also previously reported by Michael Coleman). Fortunately, many third-party developers have already announced plans to release 64-bit versions around the time AE CS5 ships. However, if you have any mission-critical plug-ins that you rely on, check with the vendor before upgrading to CS5. Adobe has created a video as well as a web page with more information on upgrading your computer to get the most out of Production Premium CS5 (which includes After Effects).
Roto Brush
Aside from the 64-bit issue, the other major new feature in After Effects CS5 is the introduction of the Roto Brush tool. This tool allows you to create broad strokes defining where the foreground is (the green stroke below) and where the background is (the red stroke below). From these, it automatically determines where the transition between the two is, creating an alpha channel in the process:
In contrast to traditional rotoscoping methods which required the creation of very precise brush strokes or mask shapes, the new Roto Brush tool allows you to make general strokes defining foreground (green) and background (red), from which it creates an alpha channel. Smaller strokes are used to clean up areas missed by the automatic edge detection routines. Footage courtesy Artbeats/Business Executives.
Roto Brush then uses motion estimation to auto-track and animate the boundry between foreground and background from frame to frame. You can use smaller corrective strokes to fix any places where it got the boundary wrong, including holes that open up as a person moves their arm away from their body and so forth. These corrective strokes are also used by Roto Brush to predict edge movement in subsequent frames. Although it is heavily automated, Roto Brush does give you access to parameters and diagnostic displays that help you refine how the boundary is calculated and propagated across frames. In addition to edge detection, Roto Brush also features a Matte section which processes and refines the output of the edge detection engine. This includes the ability to smooth, feature, and choke the matte, dampen “edge chatter” for areas that are not actually moving, calculate motion blur for edges that are moving, and to remove background color contamination from around the edges - particularly useful for partially transparent or motion blurred edges.
What is particularly nice is this section is also available as a 32-bpc stand-alone effect in CS5 called Refine Matte, which can be applied to any matte including those generated by keying, masking, painting, mocha shape, etc. (application note: you may need to precomp the matte so that Refine Matte can properly detect the motion).
Above left shows the output of the edge detection portion of Roto Brush. Above right shows the result of enabling the Matte section, which detects motion and generates a corresponding amount of motion blur (and edge color decontamination) for the moving edges.
Roto Brush is hardly perfect; it particularly has trouble if there is low contrast between foreground and background (such as an actor emerging from the shadows), if there is a lot of dust or other atmospheric effects, if there is excessive motion blur, etc. However, even if you need to create a lot of corrective Roto Brush strokes - or augment the results with AE’s paint and masking tools - you can often achieve a good result much more quickly than by using traditional rotoscoping methods. Its ease of use may also encourage you to create traveling mattes more often for less-critical applications, such as focused color correction and other image enhancements.
Below is a tutorial from Adobe on using Roto Brush; we also have a much more extensive tutorial as part of our After Effects CS5 New Creative Techniques course for lynda.com, plus a new chapter dedicated to Roto Brush in CMG5.
next page: mocha & mocha shape; Digieffects FreeForm; Adobe Repoussé
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In addition to edge detection, Roto Brush also features a Matte section which processes and refines the output of the edge detection engine. This includes the ability to smooth, feature, and choke the matte, dampen “edge chatter” for areas that are not actually moving, calculate motion blur for edges that are moving, and to remove background color contamination from around the edges - particularly useful for partially transparent or motion blurred edges. 
