Patent US 4,843,631

A process for analyzing a two-dimensional image, wherein the structural identity of stored reference patterns with image contents or portions is determined, irrespective of the position of said image content or portion in the image to be analyzed. The image is subjected to a two-dimensional Fourier transformation operation and the separated amplitude distribution or power distribution is compared to amplitude or power distributions in respect of the reference patterns in the Fourier range, while determining the respective probability of identity, the twist angle and the enlargement factor as between the reference pattern and the image content or portion. Storage and processing of the image and the reference patterns or the Fourier transforms thereof are effected in digital form. In order to locate an image content or portion in the original image, which is identical with a reference pattern, the respective reference pattern or the Fourier transform thereof is assimilated to said image content or portion, in respect of size and orientation, by inverse rotary extension, with the ascertained twist angle and enlargement factor, and finally the position or positions at which the reference pattern when converted in that way has maximum identity with a section of the image is established.