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