Understanding Splines in After Effects

The Use of Splines

Splines are various types of mathematical curves used within post production. Splines can be used in many different ways including:

    • To create a mask in After Effects
    • Tracking a path in Mocha AE
    • Interpolate keyframes in Maya
    • Build a shape in Photoshop.

Types of Splines

  • In many cases, a curved spline is more desirable than a straight one (e.g. following the contour of a subject’s head).
  • There are several types of curves that can be used.
  • Bezier curves are the most common, as they give the most precise control over the shape of a spline.
  • Other types include Cubic, Akima, and B-splines. These mathematical functions each automatically calculate the curve between two vertices in different ways.

Bezier Curves

Bezier curves function with the use of handles.  These are essentially control points that define the shape of a curve. The farther a point is drawn from its associated vertex, the more the handle pulls the curve in that direction. Bezier curves, along with their handles, can be animated over time to closely follow a desired path.

How Splines Are Made

Regardless of the application, splines are generally manipulated with a pen tool. A spline is drawn by marking a series of connected vertices. In most applications, you will find tools to add and subtract vertices, as well as a tool that can convert these vertices between a straight line and a curve.

Splines in After Effects

The most common use of splines in After Effects is to create a mask. Masks tell After Effects which portion of a layer you would like to see, and can be used for a variety of tasks such as removing unwanted elements or adjusting specific areas in your footage.

Splines can also be used to create custom shape layers in After Effects.

  • To begin, select the layer you want to make a mask for in your timeline.
  • Now I’ll head to the toolbar at the top of the page and select either the “rectangle tool” or the “pen tool.”
  • Left clicking and holding down the mouse button over the rectangle tool will provide me with a variety of basic shapes to choose from, but just in case we have something more complex to trace let’s click on the pen.

After selecting the desired layer, one can click anywhere to create points for a mask.

If one holds down the left mouse button and continues dragging it will create a bezier curve.

For more info and practice with bezier curves, check out the site:  http://bezier.method.ac/

It’s a fun game that teaches you how to trace shapes using a standard spline tool.