An image processing system to process interference patterns has been developed. Basic image processing tools are used and specific software has been developed to perform a quantitative analysis of interferometric data. In the case of a single interferogram the analysis consists of the following steps: linear and non-linear filtering to suppress noise and to correct shading, masking of areas without fringes, detection of fringe extrema, interactive fringe ordering and computation of the phase surface or the fringe density by interpolating between the fringe extrema. This paper discusses the problems involved in interferogram analysis and several image processing techniques to solve those problems. Some of these techniques will be illustrated using an interferogram of a vibrating diskl.