Figure 10
From: Lesion detection in demoscopy images with novel density-based and active contour approaches
A primitive cluster as convex hull. In the forming of a larger cluster, the first step is to initiate the cluster with a polygon, which is a convex hull. This is also defines boundary of an R-neighborhood region. The dashed circled is search space for the query. However, to represent those points, a region of actual points (pixels in an image) is given by convex hull around all points in the dashed circles.