This paper describes a method for detecting multiple overlapping objects from a real-time video stream. Layered detection is based on two processes: pixel analysis and region analysis. Pixel analysis determines whether a pixel is stationary or transient by observing its intensity over time. Region analysis detects regions consisting of stationary pixels corresponding to stopped objects. These regions are registered as layers on the background image, and thus new moving objects passing through these layers can be detected. An important aspect of this work derives from the observation that legitimately moving objects in a scene tend to cause much faster intensity transitions than changes due to lighting, meteorological, and diurnal effects.

The resulting system robustly detects objects at an outdoor surveillance site. For 8 hours of video evaluation, a detection rate of 92% was measured which is higher than traditional background subtraction methods.