{TAIL ~ a storage capacity} required to store one page of {HEAD ~ the second read data output} from the second image reading unit; and 
{ TAIL ~ a storage capacity } required to store one page of { HEAD ~ the second read data output } from the second image reading unit ; and
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH