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We describe an effi cient GPU algorithm which extracts multiple contours from an image. The algorithm uses crack codes to generate contours which sit logically between adjacent image values; it works scan line by scan line and it can generate multiple contours in parallel with an image streamed directly from a camera. Whilst specifi cally targeted at detecting object contours in stereo disparity maps, it can also be used for general segmentation with a trivial change to the code generating the crack code masks. Using a 480 ALU 1.4 GHz nVidia GPU, it can generate ~ 25000 contours from a real 2048 × 768 resolution 128 level disparity map image in ~ 29 ms if the contours are further processed in the GPU or ~ 39 ms if contours are transferred to the host - typically ~ 40 times faster than an OpenCV CPU implementation.
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