Calculating Time-to-Contact Using Real-Time Quantized Optical Flow

Despite many recent advances in optical flow research, many robotic vision researchers are frustrated by an inability to obtain reliable optical flow estimates in real-world conditions to apply for real-world tasks. Recently it has been demonstrated that robust, real-time optical flow is possible using only standard computing hardware [C93]. One limitation of this correlation-based algorithm is that it does not give truly real-valued image velocity measurements. Therefore, it is not obvious that it can be used for a wide range of robotics vision tasks. One particular application for optical flow is time-to-contact: based on the equations for the expansion of the optical flow field it is possible to compute the number of frames remaining before contact with an observed object. Although the individual motion measurements of this algorithm are of limited precision, they can be \em combined in such a manner as to produce remarkably accurate time-to-contact measurements, which can be produced at real-time rates, on the order of 6 frames a second on an 50 MHz Sun Sparcstation 20