Fill in the blanks.$($a$)(2$ pts$)$ The motion field $($is$/$ isn$$t$)$ equivalent to the optical flow field.$($b$)(2$ pts$)$ MPEG is the abbreviation of $.($c$)(4$ pts$)$ Motion estimation is needed in video coding because it helps remove$$redundancies$,$ and we call this process coding.$($d$)(6$ pts$)$ compression is widely used when dealing with television signals$$because a certain amount of information loss $($is$/$ isn$$t$)$ allowed. In medical$$diagnosis$,$ we usually use compression.