Adjustment and Guide Layers
Two special types of layers that don’t render, adjustment and guide layers, offer extra benefits that might not be immediately apparent.
An 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, and choose New > Adjustment Layer (Ctrl+Alt+Y/Command+Option+Y) (Figure 4.10).
Figure 4.10 Any pixel layer becomes an adjustment layer by toggling this switch. An adjustment layer created by After Effects is a white, comp-sized solid with this switch toggled on.
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 layers above it are unaffected.
- Change its timing and the effects appear only on frames within the adjustment layer’s In/Out points.
- Time any effect in an adjustment layer by setting layer In/Out points.
- Use Opacity to attenuate the amount effects are applied. Many effects do not themselves include so direct a 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 apply an effect to one area of the 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 ball on the top left was created with a Shape layer. To the right is the ball with a Glow effect applied (default settings), and with the Blending mode set to Normal. The bottom image shows what occurs when the Blending mode is changed to Add: The result of the second ball has been added to the first.
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 normal layers with special status. A guide layer appears in the current composition but not in any subsequent compositions or the final render (unless you specifically override this functionality in Render Settings, which kind of defeats the purpose). Common uses include
- Foreground reference clips
- Temporary backgrounds to check edge transparency
- Text reminders (Specific render instructions? Add a text layer with a bullet-pointed list in the render comp and set it as a guide layer.)
- 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 made a guide layer either by context-clicking it or by choosing Guide Layer from the Layer menu. Within the current comp, you’ll notice no difference (Figure 4.12). You can still apply effects to this layer or have other layers refer to it, and it is fully visible. Nest this composition in another composition, however, and the guide layer disappears.
Figure 4.12 A gradient can clarify matte problems; to ensure that it doesn’t render, make the background a guide layer.