3) Non-Maximum SupressionBolt: Since the Viola &
Jones algorithm is invariant to minor position and scale
changes, there will often be a set of overlapping faces
being detected around the vicinity of an actual face.
These overlapping results should be processed in order to
determine the final valid face locations. This process is
usually called Non-Maximum Supression (NMS), which
is a a key post-processing step in many computer vision
applications. In the context of object detection, it is used
to transform a smooth response map, which triggers many
imprecise object window hypotheses in, ideally, a single
bounding-box for each detected object. Therefore, two
key points on NMS include: