The appearance variation cue for obstacle avoidance

A visual cue is introduced that exploits the visual appearance of a single image to estimate the proximity to an obstacle. In particular, the appearance variation cue captures the variation in texture and / or color in the image, and is based on the assumption that there is less such variation when the camera is close to an obstacle. Random sampling is applied in order to evaluate the appearance variation fast enough for use in robotics. It is demonstrated that the randomly sampled appearance variation cue can be complementary to optic flow for obstacle detection; combining the two visual cues leads to better obstacle detection performance. Random sampling leads to sufficient computational efficiency for the cue´s utilization in autonomous flight: a speed-up of a factor ~100 is attained, which allows the successful control of the 16-gram flapping wing MAV DelFly II.