A new algorithm for the determination of crystal lattices [by electron microscopy]

A novel algorithm for the automatic determination of crystal lattices is described. This task has to be performed before computer filtering of an image of a crystal can take place, and its accuracy is critical for the rest of the processing. The novel method explores the Fourier transform of the image, looking for bright spots in the vicinities of their expected positions. Weak spots are automatically discarded. When the whole transform has been explored, a least-squares fit of the experimental data to a theoretical lattice is performed. The procedure is iterated twice in order to detect as many crystal reflections as possible. This method has been found to provide very good estimates of the true lattice vectors, while requiring minimal human intervention. The proposed method is being used in a routine way to process images of crystals in molecular biology and in inorganic chemistry, leading to satisfactory results