A pre processor stores digital voltage values of respective pixels of an image received from a pre processor in a memory, performs a pre process for {HEAD ~ the digital voltage values} of {TAIL ~ 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 
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A pre processor stores digital voltage values of respective pixels of an image received from a pre processor in a memory , performs a pre process for { HEAD ~ the digital voltage values } of { TAIL ~ 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
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