means for reading said second memory means containing compressed video data from a first document image while writing data from {HEAD ~ a second document image} into said {TAIL ~ first memory} means 
means for reading said second memory means containing compressed video data from a first document image while writing data from { HEAD ~ a second document image } into said { TAIL ~ first memory } means
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH