1. An image processing system, comprising: a processor; and optical flow determination logic to quantify relative motion of a feature present in a first frame of video and a second frame of video with respect to the two frames of video, the optical flow determination logic configures the processor to: convert each of the frames of video into a hierarchical image pyramid, wherein the image pyramid comprises a plurality of image levels, with image resolution reduced at each higher one of the image levels; and for each image level: for each pixel in the first frame: establish an initial estimate of a location of the pixel in the second frame; and apply a plurality of sequential searches, starting from the initial estimate, that establish refined estimates of the location of the pixel in the second frame; wherein a first of the sequential searches identifies a pixel at the initial estimate or at a first distance from the initial estimate that most closely matches the pixel in the first frame as a first refined estimate of the location of the pixel in the second frame, and a second of the sequential searches identifies a pixel at the first refined estimate or at a second distance from the first refined estimate that most closely matches the pixel in the first frame; wherein the first distance is not less than the second distance.