Tracking of C. reinhardtii. (a) Probability of all tracks ( s). Tracks within the (red, lower right) bordered region (example in top-right inset, 7 s, scale bar = m) are used to measure ; top-left inset: an excluded track with , 30 s, scale bar = m). (b) Normalized from tracks selected in panel a, for two values of τ. Dashed line: from DDM analysis.