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, found by convolution with a two‐dimensional Gaussian function. These methods were implemented using the IDL programing language. They were tested on diffraction patterns from systems containing oriented molecules of the protein collagen: collagen tape, elastoidin spicules and annulus fibrosus of intervertebral disc. Specimens were dusted with quartz to calibrate the diffraction patterns. These patterns were recorded on film, using a semi‐transparent beam stop to obtain an image of the undeflected beam, and digitized at a resolution of 105 µm. Intermolecular spacings, calculated from the distance between a peak and the centre of a pattern, were in good agreement with those determined previously.