Special Case: Adjustment and Guide Layers
Two special types of layers, adjustment and guide layers, offer extra benefits that might not be immediately apparent.
From a nodal point of view, adjustment layers 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 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 4.8).
Figure 4.8. 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 (basically, “dial back”) any effect; most of them work naturally this way. Many effects do not 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 4.9).
Figure 4.9. Here, the source plate image (a) is shown along with two alternates in which Camera Lens Blur has been applied via an adjustment layer, held out by a mask. With the adjustment layer blending mode set to Normal (b), there is a subtle bloom of the background highlights, but changing it to Add (c) causes the effect to be applied as in (b) and then added over source image (a).
It’s a good idea 99 percent of the time to make sure that an adjustment layer remains 2D, and you will most often also want it to be the size and length of the comp, as when applied. You may not ever choose to move, rotate, or scale an adjustment layer in 2D or 3D, but it is easily possible to do so accidentally. If you enlarge the composition, resize the adjustment layers as well.
Like adjustment layers, guide layers are standard layers with special status. A guide layer’s content 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 a guide layer 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
View LUTs (Figure 4.10)
Figure 4.10. There are many uses for a guide layer; one simple one that is common to most color and compositing applications is a View LUT in which you apply an adjustment layer with a LUT adjustment that is for previewing only. When it comes time to render or nest this clip, the guide layer provides a guarantee that this layer and its effect doesn’t show up.
Any image layer can be converted to a guide layer either by context-clicking it or by choosing Guide Layer from the Layer menu.