초록 ▼

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 accommodati

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. The novel method for reading the license plates involves performing a modified binary correlation of an image of the plate with reference characters to provide output signals indicative of the symbols on the plate. This output is correlated with valid license plate signals to improve the confidence rating thereof.

대표청구항 ▼

A method for reading symbols including characters and numerals on a license plate mounted on a vehicle comprising the steps of: providing an input image of said license plate using a camera positioned to a side of the license plate, said input image containing lateral perspective distortion resultin

A method for reading symbols including characters and numerals on a license plate mounted on a vehicle comprising the steps of: providing an input image of said license plate using a camera positioned to a side of the license plate, said input image containing lateral perspective distortion resulting from a first side of the license plate being closer to the camera than a second side of the license plate; mitigating said lateral perspective distortion in said input image to provide a corrected image by warping same; applying a Laplacian operator to said corrected image to enhance edges and reduce the effects of shadows therein; locating the license plate on the vehicle further including the steps of: providing an idealized edge template of the license plate; providing an edge-enhanced version of the input image; and correlating the idealized edge template of the license plate with the edge-enhanced version of the input image and locating the license plate on the vehicle; and reading the license plate, further including the steps of: storing said input image in memory; storing images of reference symbols in memory; and correlating said input image with said images of symbols to provide output signals indicative of the symbols on said license plate.