ABSTRACT
The Roto Brush is a new tool introduced in After Effects CS5 that helps automate creating a matte to separate a foreground from a background, such as isolating an actor from the room around him. After Effects uses the information in conjunction with edge detection, motion tracking, and optical flow technologies to follow the changes in foreground and background over time. This chapter guides the user through a preferred workflow for achieving good results with Roto Brush. Roto Brush starts with the strokes the user define on their Base frame, then attempts to propagate the resulting criteria backward and forward through adjacent frames. It attempts to detect movement from frame to frame, and uses that information to determine where the Segmentation Boundary should be on those adjacent frames. Roto Brush is capable of creating an antialiased matte with feathering and motion blur; it can even color correct the areas around the edges.
