When last we met, you had established a linear color profile as your project working space.
Why exactly did you do that? Because you wanted to process your pixels in linear-light, for a more photographic look to your basic compositing operations. You want color mixing free of edge artifacts, you want basic color corrections to yield organic results, you want simple blurs to look like smeared light, and you want to be able to speak and work in photographic terms, such as "a stop darker" and "18% gray."
You converted your pixels into your linear color space using Adobe's ICC color engine, which has been expanded to support floating-point for PSCS2 and now AE7.
So now what?
Just like with eLin, you should immediately see that even the most basic compositing operations look better. A simple A over B comp will have better edge blending and more photographic transparency. A layer in Add mode will look exactly like a double-exposure.
A layer in Screen mode will break. Like it says in the eLin docs, stay away from Screen. Add is the new Screen. Lemme just tip a 40 real quick for Screen. You got us through some 8-bit times, homie.
In linear light, basic color corrections become very useful and lovely, as we discussed here. One great example of this is the Exposure effect. It offers a slider for increasing or decreasing the exposure of your image in stops. You don't need to worry about the status of the "Bypass Linear Light Conversion" checkbox at the bottom, since you have a linear Project Working Space.
If you apply Levels to your linear float layers, bear this stuff in mind. Reach for gamma last, not first. Gain is your best friend, and Output White is Gain. And remember to un-check the Clip White checkbox! It defaults on for backwards compatibility, but I wish it didn't.
Since dialing in R, G and B gain is the most lovely way to color correct in linear float, I created a simple Anim Preset that allows you to do it using a color swatch rather than the Levels UI. Apply it to a layer and experiment with different colors in the swatch. Don't touch the Levels effect at all. Just like with our hacked 3-way Color Corrector, you can scrub the swatch in the timeline to adjust its hue and saturation, giving you interactive control over this color correction tool. Cool!
ColorLevels.zip (4kb, unzip to your Presets folder)