As astonomical CCD image sensors have incorporated more pixels the total readout time of the arrays has increased to the point where it can significatly reduce overall available observing time. The incorporation of multiple readout circuits on CCDs and multiple readout capability in their associated controllers allow several pixels to be read out simultaneously, reducing the overall readout time of the array. A controller is used to operate a single CCD containing four readout circuits that operate simultaneously, giving a factor of three reduction in readout time, and a small increase in readout noise. Another tactic for reducing readout time is described, that is easily implemented with programmable CCD controllers that reads out only selected regions of interest and discards the uninteresting portions of the image, giving a considerable decrease in readout time and no readout noise penalty.
Robert W. Leach,
"Noise and readout performance of a multiple-readout CCD controller", Proc. SPIE 2198, Instrumentation in Astronomy VIII, (1 June 1994); doi: 10.1117/12.176781; https://doi.org/10.1117/12.176781