Robust character segmentation for license plate images
First Claim
1. A license plate character segmentation method, said method comprising:
- determining an initial character boundary of a vehicle image utilizing a midpoint of a segment along a vertical projection histogram in order to partition said initial character boundary from said vehicle image;
classifying said initial character boundary as a valid character boundary or a suspect character boundary;
analyzing said suspect character boundary and enabling robust performance over a plurality of state logos, fonts, and character spacing;
receiving a character image and a label and identifying said character image utilizing said label as a likely character or not;
creating a copy of an input character label array as outlabel and initializing all values of said outlabel to zero;
setting each element in said outlabel to one for a character identified as a non-character that is touching a boundary until a valid character is encountered;
assigning said outlabel element to two for each non-character surrounded by said valid character;
setting said outlabel element to three for each set of at least two non-characters surrounded by said valid character and combining at least two images and copying to a first location for each set of element in said outlabel set to three and also set outlabel for second location back to one; and
normalizing and passing said suspect character boundary to an optical character recognition subsystem for decoding and generating a confidence quote for each suspect character boundary of said vehicle image analyzed and thereafter modifying each suspect character boundary decoded based on a set of confidence thresholds.
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Accused Products
Abstract
A method and system for achieving accurate segmentation of characters with respect to a license plate image within a tight bounding box image. A vehicle image can be captured by an image capturing unit and processed utilizing an ALPR unit. A vertical projection histogram can be calculated to produce an initial character boundary (cuts) and local statistical information can be employed to split a large cut and insert a missing character. The cut can be classified as a valid and/or a suspect character and the suspect character can be analyzed. The suspect character can be normalized and passed to an OCR module for decoding and generating a confidence quote with every conclusion. The non-character images can be rejected at the OCR level by enforcing a confidence threshold. An adjoining suspect narrow character can be combined and the OCR confidence of the combined character can be assessed.
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Citations
15 Claims
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1. A license plate character segmentation method, said method comprising:
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determining an initial character boundary of a vehicle image utilizing a midpoint of a segment along a vertical projection histogram in order to partition said initial character boundary from said vehicle image; classifying said initial character boundary as a valid character boundary or a suspect character boundary; analyzing said suspect character boundary and enabling robust performance over a plurality of state logos, fonts, and character spacing; receiving a character image and a label and identifying said character image utilizing said label as a likely character or not; creating a copy of an input character label array as outlabel and initializing all values of said outlabel to zero; setting each element in said outlabel to one for a character identified as a non-character that is touching a boundary until a valid character is encountered; assigning said outlabel element to two for each non-character surrounded by said valid character; setting said outlabel element to three for each set of at least two non-characters surrounded by said valid character and combining at least two images and copying to a first location for each set of element in said outlabel set to three and also set outlabel for second location back to one; and normalizing and passing said suspect character boundary to an optical character recognition subsystem for decoding and generating a confidence quote for each suspect character boundary of said vehicle image analyzed and thereafter modifying each suspect character boundary decoded based on a set of confidence thresholds. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A license plate character segmentation system, said system comprising:
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a processor; a data bus coupled to said processor; and a computer-usable medium embodying computer code, said computer-usable medium being coupled to said data bus, said computer code comprising instructions executable by said processor and configured for; determining an initial character boundary of a vehicle image utilizing a midpoint of a segment along a vertical projection histogram in order to partition said initial character boundary from said vehicle image; classifying said initial character boundary cut as a valid character boundary or a suspect character boundary; analyzing said suspect character boundary and enabling robust performance over a plurality of state logos, fonts, and character spacing; receiving a character image and a label and identifying said character image utilizing said label as a likely character or not; creating a copy of an input character label array as outlabel and initializing all values of said outlabel to zero; setting each element in said outlabel to one for a character identified as a non-character that is touching a boundary until a valid character is encountered; assigning said outlabel element to two for each non-character surrounded by said valid character; setting said outlabel element to three for each set of at least two non-characters surrounded by said valid character and combining at least two images and copying to a first location for each set of element in said outlabel set to three and also set outlabel for second location back to one; and normalizing and passing said suspect character boundary to an optical character recognition subsystem for decoding and generating a confidence quote for each suspect character boundary of said vehicle image analyzed and thereafter modifying each suspect character boundary decoded based on a set of confidence thresholds. - View Dependent Claims (12, 13, 14)
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15. A non-transitory processor-readable medium storing code representing instructions to cause a process to perform a process of license plate character segmentation, said code comprising code to:
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determine an initial character boundary of a vehicle image utilizing a midpoint of a segment along a vertical projection histogram in order to partition said initial character boundary from said vehicle image; classify said initial character boundary as a valid character boundary or a suspect character boundary; analyze said suspect character and enable robust performance over a plurality of state logos, fonts, and character spacing; receive a character image and a label and identifying said character image utilizing said label as a likely character or not; create a copy of an input character label array as outlabel and initializing all values of said outlabel to zero; set each element in said outlabel to one for a character identified as a non-character that is touching a boundary until a valid character is encountered; assign said outlabel element to two for each non-character surrounded by said valid character; set said outlabel element to three for each set of at least two non-characters surrounded by said valid character and combining at least two images and copying to a first location for each set of element in said outlabel set to three and also set outlabel for second location back to one; and normalize and pass said suspect character boundary to an optical character recognition subsystem for decoding and generating a confidence quote for each suspect character boundary of said vehicle image analyzed and thereafter modifying each suspect character boundary decoded based on a set of confidence thresholds.
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Specification