License plate reader, license plate reading method, and program

Abstract

The present invention provides a license plate reader, a license plate reading method, and a program that can appropriately set exposure parameters. [Solution] The license plate reader is a vehicle license plate reader and comprises an exposure parameter setting unit that resets the exposure parameters of the imaging device after the vehicle has been imaged by the imaging device, and a reliability calculation unit that calculates the reliability of the exposure parameters based on the elapsed time from the time the exposure parameters were reset. If the calculated reliability falls below a predetermined value, the exposure parameter setting unit resets the exposure parameters using pre-recorded standard exposure parameters.

Description

Technical Field

[0001] The present disclosure relates to a license plate reading device, a license plate reading method, and a program.

Background Art

[0002] In the license plate reading device described in Patent Document 1, after reading the license plate with an image processing device, the brightness of the license plate portion is measured, and if it is too bright, the aperture is adjusted to reduce it, and if it is too dark, the aperture is opened to perform aperture control on the imaging device. By doing so, the brightness of the license plate portion is made the most suitable brightness for reading the license plate for subsequent vehicles.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the license plate reading device described in Patent Document 1, for example, when a long time elapses until a subsequent vehicle arrives after adjusting exposure parameters such as the aperture value with a preceding vehicle, there is a problem that the setting of the exposure parameters may become inappropriate.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to provide a license plate reading device, a license plate reading method, and a program capable of appropriately setting exposure parameters.

Means for Solving the Problems

[0006] To solve the above problems, the license plate reader according to this disclosure is a license plate reader for a vehicle, comprising: an exposure parameter setting unit that resets the exposure parameters of an imaging device after the vehicle has been imaged by the imaging device; and a reliability calculation unit that calculates the reliability of the exposure parameters based on the elapsed time from the time the exposure parameters were reset, wherein if the calculated reliability falls below a predetermined value, the exposure parameter setting unit resets the exposure parameters using pre-recorded standard exposure parameters.

[0007] The license plate reading method relating to this disclosure is a method for reading a vehicle's license plate, comprising the steps of: resetting the exposure parameters of an imaging device after imaging the vehicle with the imaging device; and calculating the reliability of the exposure parameters based on the elapsed time since the time the exposure parameters were reset, wherein if the calculated reliability falls below a predetermined value, the exposure parameters are reset using pre-recorded standard exposure parameters.

[0008] The program relating to this disclosure causes a computer to perform the following steps: resetting the exposure parameters of the imaging device after imaging a vehicle with the imaging device; calculating the reliability of the exposure parameters based on the elapsed time since the time the exposure parameters were reset; and, if the calculated reliability falls below a predetermined value, resetting the exposure parameters using pre-recorded standard exposure parameters. [Effects of the Invention]

[0009] According to the license plate reader, license plate reading method, and program of this disclosure, exposure parameters can be appropriately set. [Brief explanation of the drawing]

[0010] [Figure 1] This is a block diagram illustrating an example configuration of a license plate reader according to an embodiment of the present disclosure. [Figure 2]This is a schematic perspective view showing an example of the configuration of a license plate reader according to an embodiment of the present disclosure. [Figure 3] This figure shows an example configuration of a standard exposure parameter table according to the embodiment of this disclosure. [Figure 4] This figure shows an example of the configuration of data for calculating confidence according to an embodiment of this disclosure. [Figure 5] This figure shows an example of calculating the exposure parameter confidence level according to the embodiment of this disclosure. [Figure 6] This figure shows an example of calculating the exposure parameter confidence level according to the embodiment of this disclosure. [Figure 7] This figure shows another example of calculating exposure parameter confidence according to the embodiment of this disclosure. [Figure 8] This flowchart shows an example of the operation of the license plate reader according to the embodiment of this disclosure. [Figure 9] This flowchart shows an example of the operation of the license plate reader according to the embodiment of this disclosure when the exposure parameter is reset. [Figure 10] This is a schematic block diagram showing the configuration of a computer according to the embodiments of this disclosure. [Modes for carrying out the invention]

[0011] Hereinafter, the license plate reading device, license plate reading method, and program according to the embodiments of this disclosure will be described with reference to Figures 1 to 10. In each figure, the same or corresponding components are referred to by the same reference numerals, and their descriptions are omitted as appropriate.

[0012] Figure 1 is a block diagram illustrating an example configuration of a license plate reader according to the present disclosure. Figure 2 is a schematic perspective view showing an example configuration of a license plate reader according to the present disclosure. As shown in Figures 1 and 2, the license plate (hereinafter also referred to as "NP") reader 1 according to this embodiment comprises an image processing device 11, an imaging device 12, and an illumination device 13.

[0013] In the NP reading device 1 according to this embodiment, the image processing device 11 receives a shutter trigger signal output by two vehicle detection devices 2 installed on the roadside of the vehicle access road 100 via the input / output device 3 when a vehicle 101 passes between them. The image processing device 11 then controls the imaging device 12 to capture, for example, a forward image of the vehicle 101. The image processing device 11 also performs image recognition processing based on the image captured by the imaging device 12 to recognize (read and convert into data) the information represented by the NP 102 of the vehicle 101 (hereinafter also referred to as NP information) (codes, characters, symbols, colors, NP size, etc.). The image processing device 11 then transmits the captured image and the NP recognition result to the higher-level image server 4. The higher-level image server 4 stores the received image and recognition result in a database. The illumination device 13 illuminates the area in front of the vehicle 101, for example, in synchronization with the shutter trigger signal or continuously.

[0014] The image processing device 11 can be configured using a computer such as a server. The image processing device 11 comprises an imaging control unit 111, an NP recognition unit 112, an exposure parameter setting unit 113, a reliability calculation unit 114, and a storage unit 115 as functional blocks composed of a combination of hardware and software. The storage unit 115 stores a standard exposure parameter table 116 and reliability calculation data 117.

[0015] The image capture control unit 111 controls the imaging timing of the imaging device 12 in response to the shutter trigger signal. The image capture control unit 111 also sets the exposure parameters instructed by the exposure parameter setting unit 113 to the imaging device 12. The exposure parameters are parameters that set the exposure of the imaging device 12 and include parameters that specify the shutter speed, aperture value, and gain (or ISO sensitivity). The image capture control unit 111 stores the image captured by the imaging device 12 in, for example, the storage unit 115.

[0016] The NP recognition unit 112 recognizes NP information from the image captured by the imaging device 12. There are no limitations on the method of recognition used by the NP recognition unit 112. For example, a machine learning model may be used, or pattern recognition may be used.

[0017] The exposure parameter setting unit 113 re - sets the exposure parameters of the imaging device 12 after the vehicle 101 is imaged by the imaging device 12. The exposure parameter setting unit 113 re - sets the exposure parameters so that, for example, the contrast of the NP image (an image obtained by cutting out NP) included in the captured image is improved. Alternatively, the exposure parameter setting unit 113 re - sets the exposure parameters based on, for example, the recognition success rate or evaluation value by the NP recognition unit 112. Also, when the exposure parameter reliability (also referred to as reliability) calculated by the reliability calculation unit 114 is below a predetermined value (also referred to as the exposure parameter reliability threshold), the exposure parameter setting unit 113 re - sets the exposure parameters using the pre - recorded standard exposure parameters.

[0018] FIG. 3 shows a configuration example of the standard exposure parameter table 116. The standard exposure parameter table 116 is a table that defines standard exposure parameters by date and time. In the example shown in FIG. 3, it includes exposure parameters every 10 minutes for one year. However, the time interval is an example and may be equally spaced or non - equally spaced. The exposure parameter setting unit 113 can obtain the standard exposure parameters by referring to the standard exposure parameter table 116 and specifying the date and time for re - setting the exposure parameters. The standard exposure parameter table 116 can be determined based on the installation position (latitude and longitude) and imaging direction of the imaging device 12. For example, if the imaging directions of a plurality of imaging devices 12 with the installation position (latitude and longitude) within a certain range are within a certain range, the same standard exposure parameter table 116 can be used to set the exposure parameters for the plurality of imaging devices 12. Each standard exposure parameter defined by the standard exposure parameter table 116 can be set, for example, experimentally or based on the results of simulations based on experimental results or experimental verification results of simulation results.

[0019] Furthermore, the reliability calculation unit 114 calculates the reliability of the exposure parameter based on the elapsed time since the exposure parameter was reset. In this embodiment, the exposure parameter reliability indicates the degree to which the currently set exposure parameter is appropriate. For example, the longer the elapsed time since the exposure parameter was last set, the lower the reliability generally becomes, although this may vary depending on the circumstances. In this embodiment, the reliability calculation unit 114 calculates the reliability, for example, as shown in Figure 5, using the reliability calculation data 117 shown in Figure 4. In the example shown in Figure 4, the reliability calculation data 117 includes the slope k value every 10 minutes for one year.

[0020] In the example shown in Figure 5, the horizontal axis represents the elapsed time since the exposure parameter reset time, and the vertical axis represents the confidence level calculated by the confidence level calculation unit 114. This example shows a state where the vehicle 101 has not arrived since at least the reset time (0 hours). The exposure parameter is reset at 3:00 AM on Month Day (where "〇" is an arbitrary number), and with 3:00 AM as 100%, the confidence level decreases over time at a slope k set in the confidence level calculation data 117 for Month Day at 3:00 AM. In this case, the confidence level can be calculated as (confidence level = 100 - k × elapsed time). In the example shown in Figure 5, after time T11 has elapsed, the confidence level has fallen below the threshold, and the exposure parameter is reset again using the standard exposure parameter.

[0021] Furthermore, the example shown in Figure 6 illustrates the relationship between elapsed time and reliability, represented by the solid line, with examples of cases where the slope k is small and cases where the slope k is large. For example, when the set time is 10am and 7pm, the change in ambient illuminance is small, so the slope k can be small. On the other hand, when the reset time is 5am and 5pm, the change in ambient illuminance is large, so it is desirable to increase the slope k. In addition, the example shown in Figure 7 represents a nonlinear characteristic of the relationship between elapsed time and reliability.

[0022] Next, an example of the operation of the license plate reader 1 (image processing device 11) will be described with reference to Figures 8 and 9. The process shown in Figure 8 is started when a vehicle is detected to be entering the system. When the process shown in Figure 8 is started, the imaging control unit 111 controls the imaging device 12 to capture an image of the vehicle (step S1). Next, the NP recognition unit 112 performs NP recognition processing (step S2). Next, for example, the NP recognition unit 112 transmits the NP recognition result (to a higher level) (step S3). Next, the exposure parameter setting unit 113 calculates the exposure parameters (step S4).

[0023] In step S4, the exposure parameter setting unit 113 reads the NP part coordinate data (step S41), reads the NP part and character part coordinates (step S42), calculates the respective luminance values ​​for the NP background part and the NP character part (step S43), and calculates the optimal exposure parameter from the difference in luminance values ​​(step S44).

[0024] Then, the exposure parameter setting unit 113 updates the exposure parameters (step S5) and terminates the process shown in Figure 8.

[0025] Furthermore, the process shown in Figure 9 is executed at predetermined intervals. When the process shown in Figure 9 begins, the exposure parameter setting unit 113 calculates the elapsed time since the last reset time (step S21). Next, the reliability calculation unit 114 calculates the exposure parameter reliability based on the reset time and elapsed time (step S22). Next, the exposure parameter setting unit 113 determines whether the exposure parameter reliability has fallen below the exposure parameter threshold (step S23). If the exposure parameter reliability has fallen below the exposure parameter threshold (step S23: YES), the exposure parameter setting unit 113 resets the exposure parameters based on the standard exposure parameters (step S24) and terminates the process shown in Figure 9.

[0026] (Effects and Benefits) The license plate reader 1 with the above configuration is a reader for the license plate 102 of a vehicle 101, and comprises an exposure parameter setting unit 113 and a reliability calculation unit 114. The exposure parameter setting unit 113 resets the exposure parameters of the imaging device 12 after the vehicle 101 has been imaged by the imaging device 12 (step S1) (step S5). The reliability calculation unit 114 calculates the reliability of the exposure parameters based on the elapsed time since the exposure parameters were reset. If the calculated reliability falls below a predetermined value (exposure parameter reliability threshold), the exposure parameter setting unit 113 resets the exposure parameters using pre-recorded standard exposure parameters. According to the license plate reader 1, license plate reading method, and program of this embodiment, the exposure parameters can be set appropriately.

[0027] The confidence level is calculated based on the relationship between the elapsed time and the confidence level, which varies depending on the reset date and time. With this configuration, for example, the slope k can be appropriately varied depending on the reset date and time.

[0028] Furthermore, standard exposure parameters are defined separately for each date and time. This configuration allows for the appropriate determination of standard exposure parameters.

[0029] Furthermore, the standard exposure parameters are determined based on the imaging direction and installation position of the imaging device 12.

[0030] (Other embodiments) Although embodiments of this disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and may include design changes and the like that do not depart from the gist of this disclosure. For example, the exposure parameter setting unit 113 may correct the exposure parameters based on weather data obtained from a higher-level device, for example. The exposure parameter setting unit 113 may also set at least one of the exposure parameters: shutter speed, aperture value, and gain. Furthermore, some of the configurations of the image processing device 11 may be provided by, for example, the imaging device 12.

[0031] <Computer Configuration> Figure 10 is a schematic block diagram showing the configuration of a computer according to at least one embodiment. The computer 90 includes a processor 91, main memory 92, storage 93, and an interface 94. The image processing device 11 described above is implemented in the computer 90. The operation of each processing unit described above is stored in storage 93 in the form of a program. The processor 91 reads the program from storage 93, loads it into main memory 92, and executes the above processing according to the program. The processor 91 also allocates memory areas in main memory 92 corresponding to each of the storage units described above, according to the program.

[0032] The program may be for implementing some of the functions that the computer 90 is to perform. For example, the program may perform functions in combination with other programs already stored in storage, or in combination with other programs implemented in other devices. In other embodiments, the computer may include a custom LSI (Large Scale Integrated Circuit) such as a PLD (Programmable Logic Device) in addition to, or instead of, the above configuration. Examples of PLDs include PAL (Programmable Array Logic), GAL (Generic Array Logic), CPLD (Complex Programmable Logic Device), FPGA (Field Programmable Gate Array), etc. In this case, some or all of the functions implemented by the processor may be implemented by the integrated circuit.

[0033] Examples of storage 93 include HDDs (Hard Disk Drives), SSDs (Solid State Drives), magnetic disks, magneto-optical disks, CD-ROMs (Compact Disc Read Only Memory), DVD-ROMs (Digital Versatile Disc Read Only Memory), and semiconductor memory. Storage 93 may be an internal medium directly connected to the bus of the computer 90, or an external medium connected to the computer 90 via an interface 94 or a communication line. Furthermore, if this program is distributed to the computer 90 via a communication line, the computer 90 that receives the program may expand it into main memory 92 and execute the above processing. In at least one embodiment, storage 93 is a tangible storage medium that is not temporary.

[0034] <Note> The license plate reading device 1 described in each embodiment is understood, for example, as follows:

[0035] (1) The license plate reader according to the first embodiment is a vehicle license plate reader comprising: an exposure parameter setting unit that resets the exposure parameters of the imaging device after the vehicle has been imaged by the imaging device; and a reliability calculation unit that calculates the reliability of the exposure parameters based on the elapsed time from the time the exposure parameters were reset. If the calculated reliability falls below a predetermined value, the exposure parameter setting unit resets the exposure parameters using pre-recorded standard exposure parameters. According to this embodiment and the following embodiments, the exposure parameters can be set appropriately.

[0036] (2) The license plate reading device according to the second embodiment is the license plate reading device of (1), wherein the reliability is calculated based on the relationship between the elapsed time and the reliability, which differs depending on the reset date and time.

[0037] (3) The license plate reader according to the third embodiment is the license plate reader according to (1) or (2), wherein the standard exposure parameters are determined separately for the date and time.

[0038] (4) The license plate reading device according to the fourth embodiment is the license plate reading device of (1) to (3), wherein the standard exposure parameter is determined based on the imaging direction and installation position of the imaging device. [Explanation of Symbols]

[0039] 1… License plate reader 11…Image processing device 12…Imaging device 111...Imaging Control Unit 112...NP recognition section 113... Exposure parameter setting section 114...Reliability calculation unit 116…Standard Exposure Parameter Table 117...Data used for calculating confidence level

Claims

1. A vehicle license plate reader, An exposure parameter setting unit that resets the exposure parameters of the imaging device after the vehicle has been imaged by the imaging device, A reliability calculation unit calculates the reliability of the exposure parameter based on the elapsed time since the time the exposure parameter was reset, Equipped with, If the calculated reliability falls below a predetermined value, the exposure parameter setting unit resets the exposure parameters using pre-recorded standard exposure parameters. License plate reader.

2. The confidence level is calculated based on the relationship between the elapsed time and the confidence level, which varies depending on the reset date and time. The license plate reading device according to claim 1.

3. The aforementioned standard exposure parameters are determined separately for each date and time. The license plate reading device according to claim 2.

4. The standard exposure parameters are determined based on the imaging direction and installation position of the imaging device. The license plate reading device according to claim 3.

5. A method for reading vehicle license plates, The steps include: resetting the exposure parameters of the imaging device after imaging the vehicle with the imaging device; A step of calculating the reliability of the exposure parameter based on the elapsed time since the time the exposure parameter was reset. Includes, If the calculated reliability falls below a predetermined value, the exposure parameters are reset using the pre-recorded standard exposure parameters. How to read license plates.

6. The steps include: resetting the exposure parameters of the imaging device after imaging the vehicle with the imaging device; A step of calculating the reliability of the exposure parameter based on the elapsed time since the time the exposure parameter was reset, If the calculated reliability falls below a predetermined value, the exposure parameters are reset using pre-recorded standard exposure parameters. A program that causes a computer to execute something.

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