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