An automatic scanning densitometer and its application to x-ray crystallography

A digital scanning-densitometer system has been assembled in this laboratory for the purpose of processing x-ray diffraction films. The system consists of a scanning densitometer of the rotating-drum type, linked to a small computer equipped with a magnetic disk memory. In 5 min, it is able to scan a 5 in × 5 in film on a raster 200 μm × 200 μm and store the entire digitized image (about 400 000 optical density measurements) on a disk. The optical density measurements range from 0·0 to 2·2 with 256 grey levels. Because of the rapid-access capabilities of the disk memory, the film image can be processed efficiently and automatically by a computer program to evaluate the intensity of the desired reflections. This instrument is capable of making an integrated intensity measurement in about 0·6 s with an accuracy to about 3%.