Jitter imaging (also known as microscanning) is an efficient method used in astronomical infra-red observations to take care of sky background issues with a minimum loss of observing time. By observing the same spot on the sky with small offsets around a central position for each exposure, it is hopefully possible to deduce the sky background variations directly by filtering the images, and separate astronomical from sky signal.
A typical acquisition in jitter mode consists in a set of 10 to 100 frames. The first frame is assumed centered on the point of interest, the following frames are slightly offseted from the first position with offsets not bigger than a reasonably small proportion of the detector size (15% for SOFI/ISAAC). The data reduction process is doing sky estimation and subtraction, plane recentering, and finally frame co-addition to a single frame. Each processing step is studied here in the context of automatic data reduction in pipeline mode (i.e. without user interaction).