Contact array scanners with circulating memory

A plurality of linear image sensors of a contact array scanner are read out at relatively low sensor pixel rates using only a limited number of expensive digital components. For a contact array scanner having sensors with both forward and reverse readouts, outputs are selected and read together in parallel from successive pairs of forward sensor readouts. Individual outputs from each of the forward readout pairs are sequentially sampled and held and the samples from each of the forward readout pairs are digitized. Outputs are also selected and read together in parallel from successive pairs of reverse sensor readouts. Individual outputs from each of the reverse readout pairs are sequentially sampled and held and the samples from each of the reverse readout pairs are digitized. Digitized samples from successive ones of the forward readout pairs are written into alternate ones of two pairs of first in first out digital memories and digitized samples from the reverse readout pairs are written into alternate ones of two pairs of last in first out memories. Finally, the contents of each pair of first in first out memories and the contents of each pair of last in first out memories are read out while the next pairs of digitized samples are being written into the other sets of first in first out and last in first out digital memories.