License Plate Tilt Detection and Correction for Accurate Recognition

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Solution Overview

Problem

Existing license plate recognition systems struggle to accurately identify and correct for the tilt angle of license plates due to deformation caused by the vehicle's orientation in images, which affects the recognition process.

Innovation Solution

A system and method that determines an approximate angle range for the tilt of a license plate using feature points from the vehicle, identifies a tilt angle within this range, and performs tilt correction based on these angles, potentially reconstructing the license plate to facilitate accurate recognition.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional license plate recognition methods are used without tilt correction, then the recognition process is simpler and faster, but the recognition accuracy decreases due to deformation from vehicle orientation

Engineering Contradiction:
Improvelicense plate recognition accuracyVSAvoidsystem complexity
Core Design Contradiction:
Measurement precisionVSDevice complexity

Solution Approach 1:

The patent performs tilt angle detection and correction as preliminary steps before license plate recognition. By detecting the tilt angle using feature points and correcting the license plate image beforehand, the system ensures accurate recognition while maintaining a structured workflow that separates preprocessing from recognition tasks.

Inventive Principle:
Principle #10Preliminary action

Solution Approach 2:

The patent replaces complex mechanical or manual tilt correction mechanisms with computational methods. Instead of physical adjustments, the system uses image processing algorithms to detect tilt angles and perform digital correction, simplifying the overall system while improving accuracy.

Inventive Principle:
Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If tilt correction is performed using detailed feature point analysis, then the tilt angle detection accuracy improves, but the processing time increases

Engineering Contradiction:
Improvetilt angle detection accuracyVSAvoidprocessing time
Core Design Contradiction:
Measurement precisionVSLoss of time

Solution Approach 1:

The patent segments the tilt detection process into distinct stages: detecting feature points on the license plate, calculating tilt angle from these points, and then performing correction. This segmentation allows the system to focus computational resources on critical measurement steps while streamlining less critical operations.

Inventive Principle:
Principle #1Segmentation

Solution Approach 2:

The system uses the license plate's own feature points (corners, edges, or character patterns) to detect and correct its own tilt, eliminating the need for external reference objects or manual intervention. This self-service approach reduces processing overhead while maintaining accuracy.

Inventive Principle:
Principle #25Self-service

Data Source

PatentEP3874401B1Systems and methods for license plate recognition
Publication Date: 2025.08.13 ZHEJIANG DAHUA TECH CO LTD
  • EP3874401B1 patent drawingFigure 1
  • EP3874401B1 patent drawingFigure 2
  • EP3874401B1 patent drawingFigure 3

AI summary

A system and method for license plate recognition may be provided, the method may include obtaining an image including a license plate mounted on a vehicle, and identifying at least one feature point associated with the vehicle. The method may also include determining an approximate angle range within which a tilt angle of the license plate is located based on the at least one feature point, and determining the tilt angle of the license plate within the approximate angle range. The method may further include performing a tilt correction on the license plate based on the tilt angle of the license plate.