Automatic determination of diffuse-peak positions and the centre of a diffraction pattern

Correlation with a two-dimensional Gaussian function was used to locate the positions of diffuse peaks in X-ray diffraction patterns. The centre of a pattern was defined as the centroid of the image of the undeflected beam, f ound by convolution with a two-dimensional Gaussian function. These methods were implemented using the IDL programing language. They were tested on di ffraction patterns from systems containing oriented molecules of the protei n collagen: collagen tape, elastoidin spicules and annulus fibrosus of inte rvertebral disc. Specimens were dusted with quartz to calibrate the diffrac tion patterns. These patterns were recorded on film, using a semi-transpare nt beam stop to obtain an image of the undeflected beam, and digitized at a resolution of 105 mu m. Intermolecular spacings, calculated from the dista nce between a peak and the centre of a pattern, were in good agreement with those determined previously.