Qualitative Description of Camera Motion and Scene Depth from Histograms of Normal Flow 1

If we histogram the normal ow vectors in images of a scene viewed by a moving observer, we can use the time-varying histogram to derive qualitative information about the observer's motion|for example, whether it is (primarily) translational or rotational, and whether the direction of translation or axis of rotation is (roughly) parallel or perpendicular to the camera axis. This is illustrated using ow histograms obtained from a variety of real image sequences. If the motion is translational, qualitative information about the scene depth can also be obtained from the ow histograms|for example, whether the scene depth is unimodal or bimodal. This is illustrated for real scenes containing a layer of vegetation seen against a textured background, or two layers of vegetation.