The distribution of object and clutter points in the 2D SRFS is
shown in Figs. 3 and 4, respectively. As it can be observed, the object
points form a more compact distribution than the clutter points
irrespective of the size and the relative distance of the rectangles
constituting the Haar-like feature. Compact distribution of object
points results from making similar rectangle mean measurements.
This can be understood from the fact that the images within the
object class are strongly correlated to each other. The clutter points,
however, are spread-out as the clutter images are very different from
each other