Method and Apparatus for Identifying Motor Vehicles for Monitoring Traffic
First Claim
1. 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) similarity comparison 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, andj) 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.
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Abstract
The invention relates to a method and an apparatus for identifying motor vehicles for monitoring traffic. The object of permitting capture of features suitable for identification of a motor vehicle (13) with the least material-related outlay and motor-vehicle identification independently of the exact alignment of the apparatus is achieved according to the invention by the image-evaluation unit (BA) having means for determining the size ratios of a license-plate contour (21) in the perspectively distorted image (20) on the basis of stored standardized license-plate formats, means for determining the size of the perspective distortion of the license-plate contour (21) on the basis of the associated standardized license-plate format, means for establishing a calculation rule for the perspective rectification on the basis of the ascertained distortion of the license-plate contour (21) with respect to the associated license-plate format, and means for rectifying the extracted license-plate-containing motor-vehicle view (14).
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Citations
16 Claims
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1. A method for identifying motor vehicles for monitoring traffic, comprising the following steps:
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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) similarity comparison 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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. 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, an image-evaluation unit with memory containing, means for recognizing the license plate, means for separating image background and extracting a relevant motor-vehicle view from the recorded image, means for capturing characteristic features within the extracted motor-vehicle view, means for determining the size ratios of a license-plate contour in the perspectively distorted image on the basis of stored standardized license-plate formats, means for determining the size of the perspective distortion of the license-plate contour on the basis of the associated standardized license-plate format, means for 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, and means for rectifying 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 means for the similarity comparison of the characteristic features of the extracted motor-vehicle view with those of reference images from a database, means for recognizing the greatest correspondence of the motor-vehicle view with one of the reference images and means for associating the ascertained reference image with the greatest correspondence to a motor-vehicle class, and an output unit. - View Dependent Claims (14, 15, 16)
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Specification