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Method for horizontal tilt correction of number plate image

A correction method and license plate image technology, which is applied in the direction of instruments, character and pattern recognition, computer components, etc., can solve the problems of low correction rate, large image background interference, and borders, and achieve the effect of improving robustness

Active Publication Date: 2015-01-28
WENZHOU UNIVERSITY
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AI Technical Summary

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

Method used

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  • Method for horizontal tilt correction of number plate image
  • Method for horizontal tilt correction of number plate image
  • Method for horizontal tilt correction of number plate image

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Embodiment Construction

[0072] There are two situations for the tilt direction of the license plate area: horizontal tilt, such as figure 1 ;vertical tilt, such as figure 2 . figure 1 Among them, 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 , 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 will become a connected domain. On the other hand, du...

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Abstract

The invention discloses a method for horizontal tilt correction of a number plate image. Due to the reasons of a shooting angle and the like of the number plate image, a number plate is tilted so that character segmentation is not facilitated, and the number plate needs to be corrected. After a series of image enhancement operations, obtained number plate edge images are good in quality; based on the edge images, the character law is utilized to search a legal character connected domain of the edge images, linear fitting is performed on an upper endpoint and a lower endpoint of the connected domain so as to find out the upper boundary and the lower boundary of a character zone, the slope is obtained, the tilt correction rotation angle is calculated, and the number plate is rotated. A removing method of a pseudo connected domain and a connected domain searching method are improved, and the robustness of the tilt correction method is greatly improved.

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...

Claims

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Application Information

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IPC IPC(8): G06K9/32
CPCG06V30/1478G06V30/158
Inventor 盛佳相徐斌叶修梓洪振杰张三元
Owner WENZHOU UNIVERSITY
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