Abstract: An automated license plate locator and reader (10) which provides novel methods for 1) correcting for perspective distortion (16), 2) locating the license plate (20), 3) reading the license plate (22) and 4) improving the confidence rating of the output signal (228). The novel method for accommodating a wide range of viewing geometries involves warping the image to eliminate perspective distortion of the plate resulting from roadside camera placement. The novel method for locating plates involves correlating an "idealized" edge template of a license plate with an edge-enhanced version of the image. Edge enhancement and shadow reduction is achieved by applying a Laplacian operator over the input image. Performance is further improved by filtering out distracting edges within the resulting correlation surface and then locating the highest peaks within this filtered correlation surface. The location of the highest peaks provides the location of the plate.

Abstract: A hardware system is disclosed for detecting alignment marks on a substrate in connection with electron beam lithography. The system is considerably faster than prior software approaches. A scanning signal derived from backscattered electrons as the beam scans the substrate is stored and updated in a set of shift registers as scanning proceeds. The signals in the scanning shift registers are compared with a predetermined reference signal, corresponding to the expected scanning signal when the beam traverses an edge of an alignment mark, stored in another set of shift registers. A correlation is obtained between the scanning and reference signals by multiplying the values of the corresponding cells in the scanning and reference registers, and accumulating and weighting the result. The locations of the maximum positive and negative correlations, and hence the locations of the opposed edges of the alignment mark, are obtained by means of a timing mechanism coordinated with the scanning.