W4S: A real-time system detecting and tracking people in 2 1/2D

W 4 S is a real time visual surveillance system for detecting and tracking people and monitoring their activities in an outdoor environment by integrating realtime stereo computation into an intensitybased detection and tracking system. Unlike many systems for tracking people, W 4 S makes no use of color cues. Instead, W 4 S employs a combination of stereo, shape analysis and tracking to locate people and their parts (head, hands, feet, torso) and create models of people's appearance so that they can be tracked through interactions such as occlusions. W 4 S is capable of simultaneously tracking multiple people even with occlusion. It runs at 5–20 Hz for 320120 resolution images on a dual-pentium 200 PC.