Abstract: We present techniques for generating and manipulating vector fields for use in the creation of painterly images and animations. Our aim is to enable casual users to create results evocative of expressionistic art. Rather than defining stroke alignment fields globally, we divide input images into regions using a colorspace clustering algorithm. Users interactively assign characteristic brush stroke alignment fields and stroke rendering parameters to each region. By combining vortex dynamics and semi-Lagrangian fluid simulation we are able to create stable, easily controlled vector fields. In addition to fluid simulations, users can align strokes in a given region using more conventional field models such as smoothed gradient fields and optical flow, or hybrid fields that combine the desirable features of fluid simulations and smoothed gradient information.