a definition module configured to define for {TAIL ~ each local region} one or more local black points, wherein each local black point corresponds to {HEAD ~ a single darkest pixel} or local cluster of the darkest pixels in the given local region 
a definition module configured to define for { TAIL ~ each local region } one or more local black points , wherein each local black point corresponds to { HEAD ~ a single darkest pixel } or local cluster of the darkest pixels in the given local region
OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH