Horizontal tilt correction method for license plate image
A license plate image and correction method technology, which is applied in the direction of instruments, character and pattern recognition, computer components, etc., can solve the problems of low correction rate, borders, and large image background interference, and achieve the effect of improving robustness
Active Publication Date: 2018-01-26
WENZHOU UNIV
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Problems solved by technology
However, the license plate has its complexity. On the one hand, the frame of the license plate may not be a standard straight line; on the other hand, the image obtained by the positioning algorithm does not have a frame.
In addition, there are some correction algorithms, either the calculation is time-consuming and the correction rate is low, or they are greatly disturbed by the image background
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[0072] There are two situations for the tilt direction of the license plate area: horizontal tilt, such as figure 1 (a) and 1(b); vertically inclined, such as figure 2 (a) and 2(b). figure 1 In (a) and 1(b), only the angle α between the axis X’ of the inclined area and the horizontal axis X is unknown. Once the angle α is obtained, the entire license plate image can be corrected by only rotating -α. figure 2 In (a) and 2(b), only the angle θ in the vertical direction is unknown. In practical applications, there are two kinds of inclinations in most license plates at the same time. Therefore, the inclination in the horizontal direction is corrected first, and then the inclination in the vertical direction is corrected. The algorithm in the present invention only involves corrections in the horizontal direction.
[0073] The colors of the characters in the license plate are the same or close, so in the binary image of the license plate, a complete independent character wil...
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The invention discloses a method for correcting the horizontal inclination of a license plate image. Due to the shooting angle and other reasons of the license plate image, the license plate will be tilted, which is not conducive to character segmentation, so the license plate needs to be corrected. After a series of image enhancement operations, the edge image quality of the obtained license plate is better. Based on the edge image, the present invention uses the rules of characters to find the legal character connected domain of the edge image, and performs linear fitting on the upper and lower endpoints of the connected domain to find the characters. The upper and lower boundaries of the area are calculated to obtain the slope, and then the rotation angle of the tilt correction is calculated to rotate the license plate. The invention improves the removal method of the pseudo-connected domain and the search method of the connected domain, and greatly improves the robustness of the tilt correction algorithm.
Description
technical field [0001] The invention relates to a method realized based on character connected domains in a license plate image, in particular to a method for correcting the horizontal inclination of the license plate image. Background technique [0002] In intelligent transportation system (ITS, Intelligent transportation system), automatic license plate recognition (LPR, License Plate Recognition) plays an important role. Generally, LPR consists of the following steps: image acquisition, license plate location, license plate character segmentation, and recognition. However, due to the shooting angle and other reasons, the license plate in the image will appear tilted, such as figure 1 . This will cause problems such as connection and destruction between license plate characters, which is not conducive to character segmentation and recognition. Therefore, the importance of license plate image tilt correction is obvious. [0003] Some existing correction methods generall...
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IPC IPC(8): G06K9/32
CPCG06V30/1478G06V30/158
Inventor 叶修梓洪振杰盛佳相徐斌张三元
Owner WENZHOU UNIV