A sensor was designed to compute speed at the image focal plane for robotic navigation. It employs an array of parallel sensing and computing blocks, and outputs a signal that varies linearly with image speed.
Vivek Pant and Charles M. Higgins, "A Biomimetic Focal Plane Speed Computation Architecture", in Proceedings of the Computational Optical Sensing and Imaging (COSI) conference, Vancouver, BC, Canada, June 18-20, 2007.