  We describe a system that lets a designer interactively draw patterns of
strokes in the picture plane, then guide the synthesis of similar patterns over
new picture regions. Synthesis is based on an initial user-assisted analysis
phase in which the system recognizes distinct types of strokes (hatching and
stippling) and organizes them according to perceptual grouping criteria. The
synthesized strokes are produced by combining properties (eg. length,
orientation, parallelism, proximity) of the stroke groups extracted from the
input examples. We illustrate our technique with a drawing application that
allows the control of attributes and scale-dependent reproduction of the
synthesized patterns.
