CN106503707B - Licence plate recognition method and device under a kind of infrared lighting condition - Google Patents
Licence plate recognition method and device under a kind of infrared lighting condition Download PDFInfo
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- CN106503707B CN106503707B CN201610920708.8A CN201610920708A CN106503707B CN 106503707 B CN106503707 B CN 106503707B CN 201610920708 A CN201610920708 A CN 201610920708A CN 106503707 B CN106503707 B CN 106503707B
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
- G06V20/00—Scenes; Scene-specific elements
- G06V20/60—Type of objects
- G06V20/62—Text, e.g. of license plates, overlay texts or captions on TV images
- G06V20/63—Scene text, e.g. street names
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06V—IMAGE OR VIDEO RECOGNITION OR UNDERSTANDING
- G06V20/00—Scenes; Scene-specific elements
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Abstract
The invention discloses the licence plate recognition methods and device under a kind of infrared lighting condition, belong to technical field of image processing, the method obtains license plate image to be processed cross in vehicle image first, divides license plate image by character bumps line, obtains license plate background area therein；Then the color of license plate background area image is adjusted to preset color；Character recognition, output identification license plate finally are carried out to the license plate image after adjustment color.Accordingly, the inventive system comprises background segment module, color adjustment module and character recognition modules.Method and device of the invention is adjusted by the color to license plate background area in license plate image, is retrieved the higher license plate image for meeting character recognition requirement of a contrast in license plate position, is improved license plate recognition rate.
Description
Technical field
The invention belongs under technical field of image processing more particularly to a kind of infrared lighting condition licence plate recognition method and
Device.
Background technique
In traffic administration, by capturing the video image of vehicle, identifies license plate, have become presently the most common
A kind of traffic administration means.However as the propulsion of urban modernization, city light pollution phenomenon is controlled it is more and more stringent,
In the scheme application of intelligent transportation, the stroboscopic lamp of high brightness, flashing light is used in down town section by gradually limitation.And
The infrared bayonet camera of ball-type can reduce light pollution to the limit, and human eye is almost nil to the excitement of infrared light, while ball
Compared to gun shaped camera, the advantage in terms of project installation, security monitoring becomes apparent from the structure of type camera, such as reduces a large amount of external
Equipment flexibly changes monitoring visual angle etc..Therefore in intelligent traffic administration system, start more and more using the infrared bayonet phase of ball-type
Machine.
The infrared bayonet camera of current ball-type possesses and captured the functions such as vehicle, identification license plate number, its integrated colored one
Change camera, holder, decoder, shield etc. it is multi-functional with it is integrated, it is easy for installation, use simple but powerful, extensive use
In the monitoring of open area, different occasions can be used.The infrared bayonet camera of ball-type is a kind of quite high production of integrated level
Product, are integrated with clouds terrace system, communication system and camera system, and clouds terrace system refers to motor-driven rotating part, communication system
Refer to the control to motor and the processing part to image and signal, camera system refers to the all-in-one machine machine core of use.
But there is also the problems on image procossing simultaneously for the infrared bayonet camera of ball-type, and the engineering of normal intelligent transportation is answered
With scheme, bar is six meters high, and level captures 20 meters or so of position.This leads to the light filling effect for being always on infrared light compensating lamp for license plate
It is not good enough, there are problems that contrast wretched insufficiency.And current licence plate recognition method, including license plate image positioning, Character segmentation,
And character recognition, due to contrast wretched insufficiency, font cannot be extracted accurately in license plate, lead to car data Car license recognition
The relatively low phenomenon of rate.
Summary of the invention
The invention proposes the licence plate recognition methods and device under a kind of infrared lighting condition, exist for solving the prior art
Infrared light compensating lamp is not good enough for the light filling effect of license plate, and it is relatively low that car data license plate recognition rate is crossed caused by contrast wretched insufficiency
The problem of.
To achieve the goals above, technical solution of the present invention is as follows:
A kind of licence plate recognition method under infrared lighting condition, the licence plate recognition method include:
License plate image is obtained to be processed cross in vehicle image, license plate image is divided by character bumps line, is obtained therein
License plate background area；
The color of license plate background area image is adjusted to preset color；
Character recognition, output identification license plate are carried out to the license plate image after adjustment color.
Further, described after obtaining license plate image in vehicle image excessively to be processed, pass through character bumps line partition cart
Board image, before obtaining license plate background area therein, the method also includes:
Calculate the contrast of the license plate image；
It when threshold value of the contrast lower than setting, executes and license plate image is divided by character bumps line, obtain wherein
License plate background area.
Further, the contrast for calculating the license plate image, comprising:
Setting ratio is pressed to the length and width of license plate image to reduce, and is obtained the central area of license plate image, is calculated the center
The contrast in domain, using the contrast of the central area as the contrast of the license plate image.
Method proposed by the invention, further includes:
When threshold value of the contrast not less than setting, directly executes and character recognition is carried out to the license plate image, it is defeated
License plate is identified out.
Further, in the method for the invention, the width pixel quantity of the license plate image is greater than the width of setting
Threshold value.
The invention also provides the license plate recognition device under a kind of infrared lighting condition, the license plate recognition device includes:
Background segment module passes through character bumps line partition cart for obtaining license plate image to be processed cross in vehicle image
Board image obtains license plate background area therein；
Color adjustment module, for adjusting the color of license plate background area image to preset color；
Character recognition module, for carrying out character recognition, output identification license plate to the license plate image after adjustment color.
Further, the background segment module passes through character after obtaining license plate image in vehicle image excessively to be processed
Concave-convex line segmentation license plate image also performs the following operations before obtaining license plate background area therein:
Calculate the contrast of the license plate image；
It when threshold value of the contrast lower than setting, executes and license plate image is divided by character bumps line, obtain wherein
License plate background area.
Further, the background segment module calculates the contrast of the license plate image, performs the following operations:
Setting ratio is pressed to the length and width of license plate image to reduce, and is obtained the central area of license plate image, is calculated the center
The contrast in domain, using the contrast of the central area as the contrast of the license plate image.
Background segment module of the present invention is in threshold value of the contrast not less than setting, directly by the license plate figure
Character recognition, output identification license plate are carried out as being sent to the character recognition module.
Licence plate recognition method and device under a kind of infrared lighting condition proposed by the present invention, by vehicle in license plate image
The color of board background area adjusts, and retrieves the higher license plate for meeting character recognition requirement of a contrast in license plate position
Image improves license plate recognition rate.
Detailed description of the invention
Fig. 1 is the licence plate recognition method flow chart under the infrared lighting condition of the present invention；
Fig. 2 is that license plate of embodiment of the present invention background color adjusts schematic diagram；
Fig. 3 is the license plate recognition device structural schematic diagram under the infrared lighting condition of the present invention.
Specific embodiment
Technical solution of the present invention is described in further details with reference to the accompanying drawings and examples, following embodiment is not constituted
Limitation of the invention.
Prior art lower part dividend outer bayonet camera (is such as always on the ball-type bayonet camera of light filling using low-light or other is infrared
The bayonet camera of light filling) acquisition night picture when, often exist license plate contrast it is too low caused by license plate sign character can not
The case where extracting identification, is not able to satisfy normal use.
The infrared bayonet camera of ball-type is always on light filling using integrated low-light, after vehicle reaches predetermined position, ball-type phase chance
Acquired vehicle picture immediately, first choice positions license plate by texture, color, length-width ratio etc., then by the license plate of positioning into
Line character extracts, and finally identifies to the character extracted.For same style equipment in white light light filling and infrared light filling
Under video image, the license plate difference on effect that two kinds of light filling modes are presented is very big, in the case where infrared light filling contrast compared with
It is low, and contrast is higher in the case where white light light filling.
Due to the sharply decline of night-environment light, it is always in the bayonet camera picture collected of light filling by infrared low-light
Characters on license plate and license plate background color contrast difference are unobvious, can not accomplish that normal character separates and identifies.Although but infrared
License plate and character contrast are extremely low in the video image obtained under light filling, but still have significantly among character and license plate background
The profile for generating light refraction because of concave-convex exists, the present embodiment according to contours segmentation video image, to license plate background color into
After row processing, then Car license recognition is carried out, to achieve the effect that improve license plate recognition rate.
As shown in Figure 1, the licence plate recognition method under a kind of infrared lighting condition, comprising:
Step S1, license plate image is obtained to be processed cross in vehicle image, calculates the contrast of license plate image.
Bayonet camera can shoot the video image of vehicle, in the present embodiment when there is vehicle to pass through according to trigger condition
Referred to as cross vehicle image.For crossing vehicle image, further progress Car license recognition exports the license plate number of vehicle, is used for intelligent transportation
Management.
The process of Car license recognition first has to position license plate, identifies the corresponding license plate image in license plate position, so as to
In subsequent carry out image procossing, character therein is identified.About License Plate, current method includes the license plate based on edge
Positioning, the License Plate based on color, the License Plate based on machine learning etc., which is not described herein again.
This step is handled the license plate image obtained by License Plate, and the contrast of license plate image is calculated.
Contrast refer to it is most bright to light and shade region in piece image it is white and most dark it is black between different brightness levels measurement, this reality
Apply contrast in example be for entire license plate image, such as a license plate in full white screen state brightness be 500cd/m2,
Completely black screen state luminance is 0.5cd/m2, and the contrast of such license plate is exactly 1000:1.
Influence of the contrast to visual effect is very crucial, and in general contrast is bigger, and the image the clear eye-catching, color
Also more distinct gorgeous；And contrast is small, then entire picture can be allowed all dusky.Pass through the comparison of calculated license plate image
Degree, it can be determined that cross whether vehicle image is shooting at night, for the specific formula for calculation of contrast, which is not described herein again.
It is worth noting that, a threshold value can be set generally according to empirical value, when contrast is not less than the threshold value,
When thinking that license plate image is easier to carry out character recognition, and being lower than the threshold value for contrast, it is believed that license plate image is at night
Between shoot, it is not easy to carry out character recognition, the method subsequent step for needing through this embodiment identifies after being handled.
Step S2, the license plate image for contrast lower than the threshold value of setting divides license plate image by character bumps line,
Obtain license plate background area therein.
By the calculating of preceding step contrast, pass through simple threshold decision, so that it may judge license plate image whether be
Nighttime image, the i.e. license plate image for contrast lower than the threshold value of setting, it is believed that it is nighttime image, is handled, it is no
Then think that license plate image meets the correct contrast for carrying out character recognition, directly progress character recognition.I.e. for contrast
Not less than the license plate image of the threshold value of setting, the processing of step S2 and step S3 are needed not move through, is directly executed to license plate image
Carry out character recognition, output identification license plate.
Although license plate and character contrast are extremely low in the video image obtained under infrared light filling, in character and license plate background
Centre is still with the presence of the apparent profile for generating light refraction because of concave-convex.And the identification for profile, it can pass through
The grey scale change of pixel is identified in binary image, can also be identified by other common methods.
Such as by the concave-convex line of character and license plate background color because the profile that refraction generates carries out the segmentation of lasso trick algorithm, segmentation
Process uses widely used Live Wire algorithm, which is a kind of interactive edge extracting and image partition method, work
Making mechanism is that the optimal path that point-to-point transmission is given in image is generated using Dynamic Programming scheme, reasonably constructs cost function and choosing
Starting point and target point are selected, to extract the edge of object.Divided by using license plate of the Live Wire algorithm to acquisition
It cuts, obtains the image of license plate background parts.
The present embodiment can also carry out Image outline identification using OpenCV method, be not discussed here.
After identifying the profile among character and license plate background, so that it may divide license plate figure by character bumps line
Picture obtains license plate background area therein, i.e., character and license plate background area is separated, so as to subsequent to license plate background area
Domain carries out color filling.
Step S3, the color of license plate background area image is adjusted to preset color.
License plate background color includes blue, yellow and black, and in the majority with blue, the present embodiment is default to fill out by taking blue as an example
The color of license plate background area is filled for blue.
To be adjusted to the color of the image of license plate background area, i.e., to this after obtaining license plate background area
Area filling blue.
Assuming that required license plate background background color A represents design parameter tone a, saturation degree b, brightness c, red x, green y, it is blue
Color z, then the license plate background parts other than character outline that finally background color A is added to.One pair is retrieved in license plate position
The license plate image for meeting character recognition requirement more higher than degree.
As shown in Fig. 2, the left side is the license plate image that contrast is lower than given threshold, the right is to pass through license plate background color tune
License plate image after whole, it is seen that by adjusting the color of license plate background area image to preset color, license plate can be made
The becoming to be more easier of image identifies.
Step S4, character recognition, output identification license plate are carried out to the license plate image after adjustment color.
The license plate image of color is filled with for license plate background area, improves the contrast of license plate image, already close to
License plate image under daytime or white light lighting condition, to can correctly identify license plate according to normal character identifying method
Character in image substantially increases the accuracy rate of Car license recognition.
It is easily understood that infrared light filling can usually be opened when ambient brightness is less than certain value, therefore the present embodiment
The step of contrast calculates and judges can also be omitted, directly handles after infrared light filling is opened and crosses vehicle image, i.e., default is opened infrared
Vehicle image of crossing after light filling is only image to be processed, needs to divide license plate image by character bumps line, obtains license plate therein
Background area, the adjustment of Lai Jinhang color.Therefore for the present embodiment step S1 and step S2, also can simplify for directly to
License plate image is obtained in processed vehicle image, license plate image is divided by character bumps line, obtains license plate background area therein,
Be equivalent to default treatment is the vehicle image excessively after opening infrared light filling, i.e. the vehicle image excessively at night.It is preferable that this implementation
Example executes step S1 and step S2, after being judged by contrast, weeds out the license plate that contrast meets character recognition requirement
Image can adapt to any occasion, reduce the vehicle image excessively that carry out subsequent processing.
The present embodiment step S1 calculates contrast with entire license plate image, increases a kind of preferred scheme below:
It is had an impact to exclude license plate frame and anti-theft screw to contrast judgement, the present embodiment is identifying license plate position
After corresponding license plate image, it is also subject to the license plate position navigated to, setting ratio is pressed to the length and width of license plate image and is reduced
50% obtains the central area of license plate image, the contrast of central area is calculated, using the contrast of the central area as license plate
The contrast of image is compared with preset contrast threshold.It is easily understood that specific reduced scale is adjustable,
Adjusting range relative to license plate original size 40%~70%, relatively good effect can be obtained.Can also rule of thumb,
Centered on the central point of license plate image, rectangle or the square area of setting range is taken to calculate contrast, as license plate
The contrast of image, which is not described herein again.If the contrast of license plate image is greater than the threshold value of setting, directly carries out character and mention
It takes and identifies, because even for yellow card vehicle with person who is not a member of any political party's vehicle because of its black font, contrast still meets knowledge under infrared light filling
Not, the color for not needing to carry out license plate background adjusts.If license plate image contrast is less than the threshold value of setting, need to license plate
It is post-processed, the profile generated by the concave-convex phenomenon of character and license plate background divides license plate, the license plate of font periphery is carried on the back
Scape resets color.
It should be noted that in order to which the vehicle image of crossing guaranteed meets subsequent processing condition, certain in light exposure parameter
In the case of, it is necessary to assure license plate width pixel reaches certain requirement, is greater than the width threshold value of setting.The embodiment of the present invention is
It is calculated with the sample of license plate width pixel 120, it is therefore desirable to pay attention to capturing position in practical applications, capture position
Lane width should coincide with picture width unanimously, so that suitable license plate width pixel quantity is obtained, as pixel is unsatisfactory for
It is easy to cause license plate character contour not clear enough, influences to handle in next step.
Accordingly with the above method, as shown in figure 3, license plate recognition device under a kind of infrared lighting condition of the present embodiment,
Include:
Background segment module passes through character bumps line partition cart for obtaining license plate image to be processed cross in vehicle image
Board image obtains license plate background area therein；
Color adjustment module, for adjusting the color of license plate background area image to preset color；
Character recognition module, for carrying out character recognition, output identification license plate to the license plate image after adjustment color.
The present embodiment background segment module passes through character bumps line after obtaining license plate image in vehicle image excessively to be processed
Segmentation license plate image also performs the following operations before obtaining license plate background area therein:
Calculate the contrast of the license plate image；
It when threshold value of the contrast lower than setting, executes and license plate image is divided by character bumps line, obtain wherein
License plate background area.
It is easily understood that if the vehicle image of crossing after the infrared light filling of default opening is only image to be processed, it is unified all to need
Color adjustment is carried out, then is not needed to calculate contrast, i.e. default contrast is below the threshold value set.
The present embodiment background segment module calculates the contrast of the license plate image, performs the following operations:
Setting ratio is pressed to the length and width of license plate image to reduce, and is obtained the central area of license plate image, is calculated the center
The contrast in domain, using the contrast of the central area as the contrast of the license plate image.
It is easily understood that contrast can also be calculated with whole picture license plate image, zoning is reduced, advantageously reduces
Calculation amount.
Accordingly with the above method, background segment module is in threshold value of the contrast not less than setting, directly by institute
It states license plate image and is sent to the character recognition module progress character recognition, output identification license plate.
The above embodiments are merely illustrative of the technical solutions of the present invention rather than is limited, without departing substantially from essence of the invention
In the case where mind and its essence, those skilled in the art make various corresponding changes and change in accordance with the present invention
Shape, but these corresponding changes and modifications all should fall within the scope of protection of the appended claims of the present invention.
Claims (8)
1. the licence plate recognition method under a kind of infrared lighting condition, which is characterized in that the licence plate recognition method includes:
License plate image is obtained to be processed cross in vehicle image, license plate image is divided by character bumps line, obtains license plate therein
Background area；
The color of license plate background area image is adjusted to preset color；
Character recognition, output identification license plate are carried out to the license plate image after adjustment color；
It is crossed in vehicle image after acquisition license plate image to be processed, license plate image is divided by character bumps line, is obtained therein
Before license plate background area, the method also includes:
Calculate the contrast of the license plate image；
When threshold value of the contrast lower than setting, executes and license plate image is divided by character bumps line, obtain vehicle therein
Board background area.
2. the licence plate recognition method under infrared lighting condition according to claim 1, which is characterized in that described in the calculating
The contrast of license plate image, comprising:
Setting ratio is pressed to the length and width of license plate image to reduce, and is obtained the central area of license plate image, is calculated the central area
Contrast, using the contrast of the central area as the contrast of the license plate image.
3. the licence plate recognition method under infrared lighting condition according to claim 1, which is characterized in that the method is also wrapped
It includes:
It when threshold value of the contrast not less than setting, directly executes and character recognition is carried out to the license plate image, output is known
Other license plate.
4. the licence plate recognition method under infrared lighting condition according to claim 1, which is characterized in that the license plate image
Width pixel quantity be greater than setting width threshold value.
5. the license plate recognition device under a kind of infrared lighting condition, which is characterized in that the license plate recognition device includes:
Background segment module divides license plate figure by character bumps line for obtaining license plate image to be processed cross in vehicle image
Picture obtains license plate background area therein；
Color adjustment module, for adjusting the color of license plate background area image to preset color；
Character recognition module, for carrying out character recognition, output identification license plate to the license plate image after adjustment color；
The background segment module passes through character bumps line and divides license plate after obtaining license plate image in vehicle image excessively to be processed
Image also performs the following operations before obtaining license plate background area therein:
Calculate the contrast of the license plate image；
When threshold value of the contrast lower than setting, executes and license plate image is divided by character bumps line, obtain vehicle therein
Board background area.
6. the license plate recognition device under infrared lighting condition according to claim 5, which is characterized in that the background segment
Module calculates the contrast of the license plate image, performs the following operations:
Setting ratio is pressed to the length and width of license plate image to reduce, and is obtained the central area of license plate image, is calculated the central area
Contrast, using the contrast of the central area as the contrast of the license plate image.
7. the license plate recognition device under infrared lighting condition according to claim 5, which is characterized in that the background segment
Module the contrast not less than setting threshold value when, directly by the license plate image be sent to the character recognition module into
Line character identification, output identification license plate.
8. the license plate recognition device under infrared lighting condition according to claim 5, which is characterized in that the license plate image
Width pixel quantity be greater than setting width threshold value.
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Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN108108746B (en) * | 2017-09-13 | 2021-04-09 | 湖南理工学院 | License plate character recognition method based on Caffe deep learning framework |
| CN108710857B (en) * | 2018-05-22 | 2022-05-17 | 深圳前海华夏智信数据科技有限公司 | Method and device for identifying people and vehicles based on infrared supplementary lighting |
| CN109785251B (en) * | 2018-12-25 | 2021-02-12 | 北京中科慧眼科技有限公司 | Image quality improving method and device and automatic driving system |
| CN111563402B (en) * | 2019-02-14 | 2023-05-09 | 杭州海康威视数字技术股份有限公司 | License plate recognition method, license plate recognition device, terminal and storage medium |
| CN111666788B (en) * | 2019-03-07 | 2024-01-26 | 杭州海康威视数字技术股份有限公司 | Image processing method, device and equipment and storage medium |
| CN111582268B (en) * | 2020-04-13 | 2023-05-12 | 浙江大华技术股份有限公司 | License plate image processing method and device and computer storage medium |
| CN115050082B (en) * | 2022-08-12 | 2022-12-09 | 深圳市三千米光电科技有限公司 | Light filling monitoring system based on infrared laser lamp |
| CN116129157B (en) * | 2023-04-13 | 2023-06-16 | 深圳市夜行人科技有限公司 | Intelligent image processing method and system for warning camera based on extreme low light level |
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