Microsoft Research Cambridge, UK
Wednesday 18 April 2007, 16:00
Seminar Room B10 (Basement)
Alexandra House, 17 Queen Square, London, WC1N 3AR
Video segmentation by fusion of colour, contrast and stereo
Technology advances mean that a stereo webcam could be manufactured and sold for essentially the same price as a monocular one. There are two outstanding advantages for teleconferencing in using stereo vision (http://research.microsoft.com/vision/cambridge/i2i). First, automatic control of pan/tilt/zoom, which is possible monocularly, is particularly robust in stereo. Second privacy can be protected by obscuring background elements and replacing them with safer ones. These capabilities and others are being developed at Microsoft research in a prototype system for two-way collaboration -- see http://research.microsoft.com/vision/cambridge/C-Slate .
At a more detailed level: a new algorithm will be described that is capable of real-time segmentation of foreground from background layers in stereo video sequences. Automatic separation of layers from colour/contrast or from stereo alone is known to be error-prone. Here, colour,contrast and stereo matching information are fused to infer layers accurately and efficiently. The "Layered Graph Cut" algorithm does not directly solve stereo. Instead it marginalises the stereo match likelihood over foreground and background hypotheses, and fuses it with a contrast-sensitive colour model that is learned on the fly. Segmentation is then solved efficiently and exactly by binary graph cut. Further recent advances in active stereo will be mentioned as time permits.