A method of processing image data from a multi-chip array with a plurality of photosensitive chips aligned substantially in a transverse direction, including: generating, using a processor for at least one specially programmed computer, a Δy or Δx optical error value equal to a difference in process and transverse directions, respectively, between actual and apparent locations for a first photosensor, the apparent location due to optical error; and storing, in a memory element for the specially programmed computer, respective outputs from the photosensors in the array for first and second scan lines. The actual location is included in the first scan line. The processor retrieves, for use as at least part of useful image data for the first photosensor, the stored output of: the first photosensor for the second scan line for a Δy optical error, or a second photosensor for the first line for a Δx optical error.