9. The views  The buttons left of the timeline let us choose to see the Alpha channel, the Selection Boundary or with a Rubylith overlay. They also toggle on or off the selection’s visibility. You can paint on the mask in any of the views to refine your selection, as well as select the brush size from the Brushes palette.

10. Propagation  When the Roto Brush is applied, its controls appear in the Effect Controls palette. The Propagation controls regulate how the program selects the boundary. Reducing the Search Boundary from the default 30 tightens overspill. Check View Search Region to see it represented on screen as a yellow border.

11. Motion  Motion Threshold and Dampening define how the search area responds to motion. The default of 50 per cent is good but a well-defined figure running across a scene may need an increased Threshold and lower Dampening. For a relatively still figure you could increase Dampening to sharpen the edges of the mask.