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