US 9,177,211 B2Granted

Method and apparatus for identifying motor vehicles for monitoring traffic

AssigneeJENOPTIK Robot GmbH

InventorMichael Lehning

Life of this patent

Estimating the term…

Loading patent…

Abstract

A method and an apparatus for identifying motor vehicles for monitoring traffic. The identification is carried out by image-evaluation and includes determining the size ratios of a license-plate contour in a perspectively distorted image on the basis of stored standardized license-plate formats, determining the size of the perspective distortion of the license-plate contour on the basis of the associated standardized license-plate format, establishing a calculation rule for the perspective rectification on the basis of the ascertained distortion of the license-plate contour with respect to the associated license-plate format, rectifying the extracted license-plate-containing motor-vehicle view, and comparing the rectified image with reference images of front views of motor vehicles stored in a database in order to assign the image with greatest correspondence to a group of classified motor vehicles.

Claims16

Dependent claims

A method for identifying motor vehicles for monitoring traffic, comprising the following steps:

a) recording a perspective image of a motor vehicle under an acute angle with respect to the road, wherein the recorded image contains at least a motor-vehicle view that has a license plate,
b) recognizing the license plate in the recorded image and capturing a license-plate contour,
c) ascertaining the format of the license-plate contour from the comparison of the corner points of the license-plate contour with stored standardized license-plate formats from a memory,
d) ascertaining a calculation rule for perspective rectification of the license-plate contour on the basis of the associated standardized license-plate format,
e) producing an image region which is perspectively distorted in a matching manner with respect to the license-plate contour, with a prespecified magnification in dependence on the ascertained format of the license-plate contour,
f) extracting the content of the distorted image region surrounding the license-plate contour, and discarding the remaining recorded image of the motor vehicle,
g) adapting a license-plate-containing motor-vehicle view, which is extracted from the distorted surrounding image region, to the format of reference images stored in a database,
h) rectifying the motor-vehicle view using the calculation rule ascertained from the license-plate contour,
i) comparing similarities of the captured contours and their position with those of reference images from the database, and recognizing the greatest correspondence of the captured contours with one of the reference images, and
j) categorizing the recorded motor vehicle into a reference-image class, with which the reference image with the greatest correspondence was associated, and outputting a motor-vehicle class derived from the reference-image class.

7 more elements

An apparatus for identifying motor vehicles for monitoring traffic, comprising

an image-capture device being aligned for recording an image of the motor vehicle with at least one motor-vehicle view, which contains a license plate,
a database with reference images,
a computer based image-evaluation unit with memory containing,
computer software configured to recognize said license plate,
computer software configured to separate image background and to extract a relevant motor-vehicle view from the recorded image,
computer software configured to capture characteristic features within the extracted motor-vehicle view,
computer software configured to determine the size ratios of a license-plate contour in the perspectively distorted image on the basis of stored standardized license-plate formats,
computer software configured to determine the size of the perspective distortion of the license-plate contour on the basis of the associated standardized license-plate format,
computer software configured to establish a calculation rule for the perspective rectification on the basis of the ascertained distortion of the license-plate contour with respect to the associated license-plate format, and
computer software configured to rectify the extracted license-plate-containing motor-vehicle view, wherein the calculation rule for rectification of the license-plate contour is intended for the rectification of the entire extracted license-plate-containing motor-vehicle view such that the perspective rectification is achieved from the exact knowledge of the angle of the image recording with respect to the road of the motor vehicle;
an image comparison unit having
computer software configured to compare characteristic features of the extracted motor-vehicle view with those of reference images from a database,
computer software configured to recognize the greatest correspondence of the motor-vehicle view with one of the reference images and
computer software configured to associate the ascertained reference image with the greatest correspondence to a motor-vehicle class, and
an output unit.

12 more elements

Dependencies are inferred from the claim text.