An error measure is generated as {HEAD ~ a function} of {TAIL ~ the decoded pixels} of the decoded region and the previous pixels of a previous region 
An error measure is generated as { HEAD ~ a function } of { TAIL ~ the decoded pixels } of the decoded region and the previous pixels of a previous region
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 OTH OTH OTH OTH OTH OTH OTH