Adjustment and Guide Layers
Two special types of layers, adjustment and guide layers, offer extra benefits that might not be immediately apparent, and are thus underused by less-experienced After Effects artists.
Adjustment layers are the most natural thing in the world to anyone working with nodal compositing; they are a way of saying "at this point in the compositing process, I want these effects applied to everything that has already rendered." Because render order is not readily apparent in After Effects until you learn how it works, adjustment layers can seem trickier than they are.
The adjustment layer is itself invisible, but its effects are applied to all layers below it. It is a fundamentally simple feature with many uses. To create one, context-click in an empty area of the Timeline panel, and choose New > Adjustment Layer (Ctrl+Alt+Y/Cmd+Opt+Y) (Figure 4.10).
Figure 4.10 The highlighted column includes toggle switches, indicating an adjustment layer. Any layer can be toggled but the typical way to set it is to create a unique layer. An adjustment layer created under Layer > New > Adjustment Layer (or via the shortcuts) is a white, comp-sized solid.
Adjustment layers allow you to apply effects to an entire composition without precomping it. That by itself is pretty cool, but there's more:
- Move the adjustment layer down the stack and any layers above it are unaffected, because the render order in After Effects goes from the lowest layer upward.
- Shorten the layer and the effects appear only on frames within the adjustment layer's In/Out points.
- Use Opacity to attenuate any effect; most of them work naturally this way. Many effects do not themselves include such a direct control, even when it makes perfect sense to "dial it back 50%," which you can do by setting Opacity to 50%.
- Apply a matte to an adjustment layer to hold out the effects to a specific area of the underlying image.
- Add a blending mode and the adjustment layer is first applied and then blended back into the result (Figure 4.11).
Figure 4.11 The basic setup in these two examples is identical: An adjustment layer uses the image itself as a luma matte so that it works only with the highlights, to which it applies a Box Blur (for a defocused look) and a Levels adjustment (to bring a glow to the highlights), as seen in the top figure. But applying Add mode to the adjustment layer (bottom) causes the adjusted image to be added to the original, giving it a subtle extra pop (that can be seen in the brighter highlights) in one simple step.
It's a good idea 99% of the time to make sure that an adjustment layer remains 2D and at the size and length of the comp, as when applied. It's rare that you would ever want to transform an adjustment layer in 2D or 3D, but it is possible, so don't let it happen by accident. If you enlarge the composition, you must resize the adjustment layers as well.
Like adjustment layers, guide layers are standard layers with special status. A guide layer appears in the current composition but not in any subsequent compositions or the final render (unless it is specifically overridden in Render Settings.) You can use this for
- foreground reference clips (picture-in-picture timing reference, aspect ratio crop reference)
- temporary backgrounds to check edges when creating a matte
- text notes to yourself
- adjustment layers that are used only to check images (described further in the next chapter); a layer can be both an adjustment and a guide layer
Any image layer can be converted to a guide layer either by context-clicking it or by choosing Guide Layer from the Layer menu. (Figure 4.12).
Figure 4.12 Check out all the guide layers that won't render but help you work: One pushes up gamma to check blacks, and two provide crops for different aspects (1.85:1 and 2.35:1, the common cinematic formats). A picture-in-picture layer shows timing reference from the plate, along with a text reminder that does not render, either. None of this is visible in another composition, or in the render.