optical flow

The per-pixel apparent-motion field estimated between two consecutive video frames.

Optical flow is the per-pixel apparent-motion field estimated between two consecutive video frames -- a vector at every pixel describing how far and in what direction that point appears to have moved. Background subtraction is a cheaper, related technique that separates a moving foreground from a mostly static scene by comparing each frame against a running model of the background, without estimating a full per-pixel motion field.

Examples

A car moving left to right across two consecutive frames produces a rightward-pointing flow vector at every pixel on its body.