A pre processor stores {HEAD ~ digital voltage values} of {TAIL ~ respective pixels} of an image received from a pre processor in a memory, performs a pre process for the digital voltage values of respective pixels sequentially received from the memory, thereby producing a pre processed current image, and extracts a pre processed current central image from the pre processed current image 
A pre processor stores { HEAD ~ digital voltage values } of { TAIL ~ respective pixels } of an image received from a pre processor in a memory , performs a pre process for the digital voltage values of respective pixels sequentially received from the memory , thereby producing a pre processed current image , and extracts a pre processed current central image from the pre processed current image
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH