As you create mask, you add vertexes.
The vertexes connect the sections of the mask outline. You can change the shape of the mask by adding, moving, or deleting vertexes. To move a vertex one pixel at a time, use the arrow keys.
There are several types of vertexes:
Smooth Vertex: A vertex with Bezier handles. The control points at the end of the Bezier handles are always equidistant from the vertex and 180 degrees from each other.
Straight Vertex: A vertex with Bezier handles. The control points at the end of each Bezier handle are always 180 degrees from each other and may have differing distances from the vertex.
Corner Vertex: A vertex with Bezier handles. The control points at the end of each Bezier handle are freeform.
Sharp Vertex: A vertex with no Bezier handles. This is the traditional vertex used in previous versions of Image Authoring. If a sharp vertex is surrounded by Bezier curves, there are no straight lines on either side of that vertex.
The mask for this seat cushion is in progress. The vertexes are the small, light-blue squares along the edge of the mask.