This paper considers coherence scanning interferometry as a linear filtering operation that is characterised by a point
spread function in the space domain or equivalently a transfer function in the frequency domain. The applicability of the
theory is discussed and the effects of these functions on the measured interferograms, and their influence on the resulting
surface measurements, are described. The practical characterisation of coherence scanning interferometers using a
spherical reference artefact is then considered and a new method to compensate measurement errors, based on a modified
inverse filter, is demonstrated.