In this chapter we describe the algorithm used to process ENFS and SNFS data, acquired by a CCD, in order to evaluate of the scattered intensity. From a set of images, taken at different times, we are able to subtract the stray light, point by point: this is a noteworthy feature of the heterodyne techniques. The algorithm we describe is similar to the one which has been applied to shadowgraph, and should work for every heterodyne technique.
The algorithm has been applied to SNFS, and the results are shown in Chapter 9; in this chapter, all examples refers to colloid measurements made with ENFS.