Section 11.3.1. Introduction

Key steps in the processing of diffraction data from single crystals involve: (a) accurate modelling of the positions of all the reflections recorded in the images; (b) integration of diffraction intensities; (c) data correction, scaling and post refinement; and (d) space-group assignment. Much of the theory and many of the methods for carrying out these steps were developed about two decades ago for processing rotation data recorded on film and were later extended to exploit fully the capabilities of a variety of electronic area detectors; some CCD (charge-coupled device) and multiwire detectors allow the recording of finely sliced rotation data because of their fast data read-out. In this chapter, the principles of the methods are described as they are employed by the program XDS (Section 25.2.9 ). These apply equally well to rotation images covering small or large oscillation ranges. A large number of other systems have been developed which differ in the details of the implementations. Some of these packages are described in Chapter 25.2 . The theory and practice of processing fine-sliced data have recently been discussed by Pflugrath (1997).