Neighborhood limit and cluster grouping . (A) A group of clusters with their α-shape boundaries in vermillion. (B–D) Effects of changing the neighborhood limit on the group in A. In each image, the clusters are marked by a convex hull (sky blue). B, 30 nm; C, 50 nm; and D, 80 nm. Increasing the neighborhood limit decreases the number of clusters from four (B) to one (D). Each blink is represented by a 3 × 3 pixel for visibility. Scale bar: 100 nm.