The Structure of the Optic Flow Field

The optic ow eld is deened as preserving the intensity along ow-lines. Due to singularities in the image at xed time, poles are created in the optic ow eld. In this paper we describe the generic types of ow singularities and their generic interaction over time. In a general analytic ow eld, normally the topology is characterised by the points where the ow vanish again subdivided into repellers, attractors, whirls, and combinations hereof. We point out the resemblance, but also the important diierences in the structure of a general analytic ow eld, and the structure of the optic ow eld expressed through its normal ow. Finally, we show examples of detection of these singularities and events detected from non-linear combinations of linear lter outputs.