Layer PropertiesLast week we learned how to place footage in a composition...but placing footage is just the beginning of working with After Effects. The majority of your work in AE will involve animating that footage, and most animation in After Effects starts with properties . Properties are simply aspects of a layer which can be changed over time. Each layer has a wide variety of properties which you can work with, but to get started there are a few important ones which you will use almost all the time. These properties are called Transform Properties and the ones we want to start off with are:
- Position (P) is the current position of the layer's center within the current composition. Position always has two values - X and Y - which are expressed in pixels. Position is relative to the upper left-hand corner of the composition, which corresponds to the X and Y values of 0,0.
- Rotation (R) is the layer's rotation relative to it's original orientation in the composition (so however it looked when you first dragged it into the comp, that's 0 degrees of rotation). Rotation is expressed as revolutions+degrees, so 2 and a half rotations would be 2 revolutions+180 degrees.
- Scale (S) is the width and height of a layer expressed in pixels or percentages.
- Opacity (T) is how visible a layer is expressed as a percentage. 100% opacity means you can't see through the layer at all, and it obscures any layers below it. 0% opacity means the layer is completely transparent and is not visible at all in the composition. Any percentage in between will make the layer semi-transparent so that it blends with the layers below.
- Anchor Point (A) is the point that the other transform properties are performed around - the layer rotates around it, scales up or down from it, and it is the point you are moving when you change position. It is represented in the comp window as a small circle with an X in the middle, and by default it is placed in the center of the layer. You probably won't be animating the anchor point very often, but you often will find you want to change it to some point other than the absolute center of a layer - it's usually best to do this before changing any other properties because they are all based on the position of the anchor point.
Changing A Layer's PropertiesOnce you have made a property visible on the timeline you can usually change it's current value in several different ways:
- First you can change the layer in the composition. For instance, dragging a layer in the composition will change it's current position value.
- To change a property value numerically you can click on the value once and it will highlight. Type in a new value, hit enter/return, and the new value will be applied to the layer
- You can also click and drag on the current value. With scale, for example, if the current scale is 75% and you click on the value, dragging the mouse to the right will raise the value while dragging to the left will lower it. As you drag, the numerical values will change and the comp will update continuously to reflect the current value.
- Finally, if you control-click(right click with a two-button mouse) on the numerical value of a property a contextual menu will appear with the command "edit value...". If you select this a new dialogue box will open up which lets you enter a new value numerically. Thus if you control-click on the current opacity value you will get a dialog box where you can type in 50%, and as soon as you hit 'ok' the current opacity value will become 50%. Often the dialogue box which opens using this method will give you additional options - for instance, with scale you can choose to set the scale in pixels rather than as a percentage of the original scale.
Once you know how to change these four properties for a layer you are almost set to begin animating things in your compositions...however, you are missing one crucial thing: A way to record your property changes over time. For that, we use Keyframes