a method for recognizing the presence of a particular target in a field of view which is target position , rotation , and intensity invariant includes the preparing of a target - specific invariant filter from a combination of all eigen - modes of a pattern of the particular target . coherent radiation from the field of view is then imaged into an optical correlator in which the invariant filter is located . the invariant filter is rotated in the frequency plane of the optical correlator in order to produce a constant - amplitude rotational response in a correlation output plane when the particular target is present in the field of view . any constant response is thus detected in the output the u . s . government has rights in this invention pursuant to contract no . de - ac04 - 76dp00789 between the u . s . department of energy and at & amp ; t technologies , inc .