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