Clustering steps. A positive subimage (a), its segmented (b), and clustered with DBSCAN (c) corresponding. A close look at (c) reveals small green regions that are represent noisy groups of pixels of (b). For example, the endothelium region around the center of image has many small red regions in (b). However, they are too small to be counted as pericytes or other structures since they are so small and far from other same kind of structure. Hence, they are removed and only significant structures are kept in subimage (c).