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So there you have some broad applications for expressions in visual effects work. Maybe you still want morea more thorough understanding of the basics, if you're a beginner, or more advice on developing your own expressions, if you're an expert.

Unfortunately, expressions is one area where the official After Effects documentation falls short. Plenty of information is there, but it's organized in such a way that you already need to know quite a bit about expressions before you can understand it.

Happily, a couple of Web sites take up the slack.

• www.motionscript.com This site is the work of Dan Ebberts, a prolific contributor of expressions information in various online forums. One section of the site, Mastering Expressions, thoroughly explains how JavaScript works as is implemented in After Effects. The Expressions Lab contains more hands-on examples for you to dissect.
• www.aenhancers.com This is a forum-based site filled with sample expressions and scripts created for specific purposes, as well as areas for discussion about how they work.These sites also contain information on scripting, automation, and UI customization, a feature set in After Effects that, alas, makes creating expressions look like child's play (and I should know, having documented this feature on Adobe's behalf for version 6.0 and 6.5). Someday, perhaps the development team will be able to add recordable Actions as are found in Photoshop, and scripting will be unlocked for the masses. For now, however, the scripting controls are double-black-diamond expert features for most After Effects artists, typically requiring full-fledged programming skills to accomplish anything truly significant.

The book's disc also includes a couple of scripts (located in the Redefinery folder) that were created just for this book by Jeff Almasol, whose site, www.redefinery.com, contains many useful After Effects scripts. These are

• rd_MergeProjects.jsx: Suppose that you followed the advice given back in Chapters 1 and 4 and created a comp template with a custom file hierarchy for your project. The problem is that if you need to combine two such projects (by importing one into the other), you end up with two hierarchies, one nested inside the other. This script automatically merges the contents of folders in the imported project into folders with the same names in the master project (Figure 10.21).

  Figure 10.21. Scripts can launch floating palettes such as this one, for rd_MergeProjects.jsx, which allows you to specify whether to consolidate redundant folders and footage, remove them, or both. (Script courtesy Jeff Almasol.)

• rd_Duplink.jsx: One very cool feature that competing programs such as Fusion 5 contain is instance objects, whereby you can duplicate an object and all properties of the duplicates (sometimes known as slave objects) update when the master is updated. This script recreates some of this functionality; when you use it to create duplicates of a layer, it adds expressions to the types of properties that you specify (including masks, material options, and effects) linking them to the source layer, so that as you edit it, the instanced layers change (Figure 10.22).

  Figure 10.22. The palette, for rd_Duplink.jsx, contains options to create instances of the selected layer that remain linked to it via expressions. (Script courtesy Jeff Almasol.)

And hold on to your hats, because the complicated stuff isn't over with yet. The next chapter deals with issues specific not only to film but to a high dynamic range pipeline, which is now part of After Effects thanks to the addition of 32-bit-per-channel compositing.