Exposure control correction device, exposure control correction method, and program

Abstract

To provide an exposure control correction apparatus capable of properly correcting an exposure parameter of a license plate reader.SOLUTION: An exposure control correction apparatus includes: an acquisition unit which acquires exposure parameters in reading a license plate, from each of multiple license plate readers included in one device group; a classification unit which sets a normal range on the basis of exposure parameters of the license plate readers that have read license plates within a predetermined time, and classifies the license plate readers into a normal group for the exposure parameters within the normal range and an out-of-range group for the exposure parameters outside the normal range; and a correction unit which corrects the exposure parameters of the license plate readers classified into the out-of-range group, on the basis of the exposure parameters of the license plate readers classified into the normal group.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to an exposure control correction device, an exposure control correction method, and a program.

Background Art

[0002] In various roads, license plate reading devices that read license plates of vehicles traveling thereon are used. In order to accurately read the characters displayed on the license plate, it is necessary to detect the license plate portion in the image captured by the camera of the license plate reading device and control the exposure so that the luminance thereof becomes an appropriate value.

[0003] For example, Patent Document 1 describes a method of combining average photometry that refers to the luminance of the entire image and spot photometry that refers to the luminance of a specific region within the image to control the background and the subject to appropriate exposure.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the conventional method, for example, when a shadow or light suddenly appears in a specific region used for spot photometry, the exposure parameters may be changed to inappropriate values in accordance with the shadow or light. Then, in the image captured with the changed exposure parameters, the luminance of the license plate does not become appropriate, and it becomes difficult to correctly read the characters on the license plate. Also, when the value of the exposure parameter is inappropriate, it may be difficult to detect the license plate portion from the image. In this case, it takes time until the exposure parameter is correctly adjusted, and there is a possibility that the license plate of the vehicle that has passed during that time cannot be read.

[0006] The purpose of this disclosure is to provide an exposure control correction device, an exposure control correction method, and a program that can appropriately correct the exposure parameters of a license plate reader. [Means for solving the problem]

[0007] According to one aspect of the present disclosure, the exposure control correction device includes: an acquisition unit that acquires exposure parameters at the time of license plate reading from each of a plurality of license plate reading devices included in a group of devices; a classification unit that sets a normal range based on the exposure parameters of license plate reading devices that have not elapsed a predetermined time since reading a license plate, and classifies each of the plurality of license plate reading devices into a normal group in which the exposure parameters are within the normal range and an out-of-range group in which the exposure parameters are outside the normal range; and a correction unit that corrects the exposure parameters of the license plate reading devices classified into the out-of-range group based on the exposure parameters of the license plate reading devices classified into the normal group.

[0008] According to one aspect of the present disclosure, the exposure control correction method includes the steps of: obtaining exposure parameters at the time of license plate reading from each of a plurality of license plate reading devices included in a group of devices; setting a normal range based on the exposure parameters of license plate reading devices for which a predetermined time has not elapsed since reading a license plate, and classifying each of the plurality of license plate reading devices into a normal group in which the exposure parameters are within the normal range and an out-of-range group in which the exposure parameters are outside the normal range; and correcting the exposure parameters of the license plate reading devices classified into the out-of-range group based on the exposure parameters of the license plate reading devices classified into the normal group.

[0009] According to one aspect of the present disclosure, the program causes an exposure control and correction device to perform the following steps: acquire exposure parameters at the time of license plate reading from each of a plurality of license plate readers included in a group of devices; set a normal range based on the exposure parameters of license plate readers that have not elapsed a predetermined time since reading a license plate; classify each of the plurality of license plate readers into a normal group in which the exposure parameters are within the normal range and an out-of-range group in which the exposure parameters are outside the normal range; and correct the exposure parameters of the license plate readers classified into the out-of-range group based on the exposure parameters of the license plate readers classified into the normal group. [Effects of the Invention]

[0010] According to the above embodiment, the exposure parameters of the license plate reader can be appropriately corrected. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows the overall configuration of an exposure control and correction system according to one embodiment. [Figure 2] This block diagram shows the functional configuration of an exposure control and correction system according to one embodiment. [Figure 3] This is a sequence diagram showing an example of the processing of an exposure control and correction system according to one embodiment. [Figure 4] This flowchart shows an example of processing by an exposure control and correction device according to one embodiment. [Figure 5] This is a first diagram illustrating the processing of an exposure control and correction device according to one embodiment. [Figure 6] This is a second figure illustrating the processing of an exposure control and correction device according to one embodiment. [Modes for carrying out the invention]

[0012] (Overall configuration of the exposure control and correction system) Figure 1 shows the overall configuration of an exposure control and correction system according to one embodiment. As shown in Figure 1, the exposure control and correction system 1 comprises a group of license plate readers 2 and an exposure control and correction device 10.

[0013] The license plate reader group 2 is installed at predetermined vehicle detection locations on the road. Alternatively, as shown in the example in Figure 1, multiple license plate reader groups 2A and 2B may be installed at a single vehicle detection location. Although not shown in the illustration, multiple vehicle detection locations are set on the road, and at least one license plate reader group 2 is installed at each location.

[0014] The license plate reading device group 2 (hereinafter also simply referred to as "device group") has multiple license plate reading devices 21. Each license plate reading device 21 belonging to device group 2 is installed in a similar environment. A similar environment is one in which the influence from weather and surrounding structures (sunlight, building shadows, etc.) is roughly the same.

[0015] For example, as shown in Figure 1, device group 2A has a plurality of license plate readers 21A_1 to 21A_6 arranged in the width direction of the road on a gantry provided at the passage detection position. Each of the license plate readers 21A_1 to 21A_6 faces the upstream side of the road and reads the license plate in front of a vehicle traveling on the road. Device group 2B has a plurality of license plate readers 21B_1 to 21B_6 arranged in the width direction of the road on the same gantry as device group 2A. Each of the license plate readers 21B_1 to 21B_6 faces the downstream side of the road and reads the license plate in the rear of a vehicle traveling on the road.

[0016] The license plate reader 21 reads the characters (such as place name, classification number, and serial number) written on the license plate of a vehicle passing through the passage detection location. The information read by the license plate reader 21 is also referred to as license plate information.

[0017] In FIG. 1, an example is shown in which the device group 2 has six license plate reading devices 21, but it is not limited to this. The device group 2 may increase or decrease the number of license plate reading devices 21 according to the number of lanes at the passage detection position or the like. For example, the number of license plate reading devices 21 may be the same as the number of lanes. Further, in order to be able to read the license plate of a vehicle during lane change, the number of license plate reading devices 21 may be made larger than the number of lanes as in the example of FIG. 1, and the shooting ranges of adjacent license plate reading devices 21 may be overlapped.

[0018] Note that all the license plate reading devices 21 included in one device group 2 are of the same model. In the present embodiment, an example in which all the device groups 2A and 2B have license plate reading devices 21 of the same model will be described.

[0019] The exposure control correction device 10 collects the license plate information and exposure parameters of each license plate reading device 21 for each device group 2. Further, the exposure control correction device 10 outputs a correction command signal for adjusting the exposure parameters for each device group 2 based on the exposure parameters collected for each device group 2. The exposure parameters are parameters that contribute to brightness, such as an iris (aperture), exposure time, and gain. For example, the exposure control correction device 10 adjusts the exposure parameters of the license plate reading devices 21A_1 to 21A_6 of the device group 2A based on the exposure parameters collected from the license plate reading devices 21A_1 to 21A_6 of the device group 2A. Similarly, the exposure control correction device 10 adjusts the exposure parameters of the license plate reading devices 21B_1 to 21B_6 of the device group 2B based on the exposure parameters collected from the license plate reading devices 21B_1 to 21B_6 of the device group 2B.

[0020] (Functional configuration of license plate reading device) FIG. 2 is a block diagram showing the functional configuration of an exposure control correction system according to an embodiment. As shown in Figure 2, the license plate reader 21 comprises a camera 200, a lens 201, an illumination 202, an IF (interface) board 203, and an image processing device 204. The illumination 202 is, for example, an LED light, which illuminates the area around the vehicle's license plate, enabling the camera 200 to capture the license plate more clearly. The image processing device 204 reads the license plate information by performing predetermined image processing (license plate detection processing, OCR processing, etc.) on the image captured by the camera 200. The image processing device 204 also outputs signals to the camera 200 and lens 201 to instruct exposure parameters based on the correction command signal received from the exposure control correction device 10. The IF board 203 facilitates the exchange of images and signals between the camera 200, lens 201, illumination 202, and the image processing device 204. The image processing device 204 of the license plate reading device 21 transmits the license plate information D1 (reading result) read from the image and the exposure parameters D2 used when the image was captured to the exposure control and correction device 10. The exposure parameters D2 used when the image was captured are the exposure parameters applied to the camera 200 and lens 201 when the image (frame in the case of video) in which the license plate information D1 was read was captured.

[0021] (Functional configuration of exposure control and correction device) As shown in Figure 2, the exposure control and correction device 10 includes a processor 11, memory 12, storage 13, and communication IF 14.

[0022] The processor 11 performs the functions of an acquisition unit 110, a classification unit 111, and a correction unit 112 by operating according to a predetermined program.

[0023] The acquisition unit 110 acquires the license plate information D1 read from each of the multiple license plate readers 21, as well as the exposure parameters D2 used when reading the license plate.

[0024] The classification unit 111 sets a normal range based on the exposure parameter D2 of the license plate reader 21 that has not elapsed a predetermined time since reading the license plate, and classifies each of the multiple license plate reader 21 into a normal group in which the exposure parameter D2 is within the normal range, and an out-of-range group in which the exposure parameter is outside the normal range.

[0025] The correction unit 112 corrects the exposure parameters of the license plate readers 21 that are classified as being in the out-of-range group based on the exposure parameters D2 of the license plate readers that are classified as being in the normal group.

[0026] The predetermined program executed by the processor 11 is stored on a computer-readable recording medium. A computer-readable recording medium refers to a magnetic disk, magneto-optical disk, CD-ROM, DVD-ROM, semiconductor memory, etc. Alternatively, this computer program may be distributed to a computer via a communication line, and the computer that receives the distribution may execute the program. Furthermore, this program may be intended to implement only a part of the functions described above. Moreover, it may be a program that can implement the above functions in combination with a program already recorded in the computer system, a so-called differential file (differential program).

[0027] Memory 12 has a memory area necessary for the operation of the processor 11.

[0028] Storage 13 is a so-called auxiliary storage device, such as an HDD (Hard Disk Drive) or SSD (Solid State Drive). Data acquired, generated, and referenced by each part of the processor 11 during processing is stored in storage 13.

[0029] Communication IF14 is an interface for sending and receiving various data and control signals with the license plate reader 21.

[0030] (Processing flow of the exposure control and correction system) This section describes an example of adjusting the exposure parameters of device group 2A.

[0031] Figure 3 is a sequence diagram showing an example of the processing of an exposure control and correction system according to one embodiment. As shown in Figure 3, each license plate reader 21A_1 to 21A_6 of the device group 2A photographs and reads the license plate of a vehicle traveling at the vehicle detection position (step S01), and then transmits the read license plate information D1 and exposure parameters D2 to the exposure control correction device 10 (step S02). The license plate information D1 includes the read character information (place name, classification number, serial number, etc.) along with the reading time.

[0032] The acquisition unit 110 of the exposure control correction device 10 records the license plate information D1 and exposure parameters D2 received from each license plate reader 21 in the storage 13 (step S03).

[0033] The processes in steps S01 to S03 are executed repeatedly at all times.

[0034] In parallel with the processing in steps S01 to S03, the exposure control correction device 10 performs a correction process at predetermined intervals (for example, after 1 minute has elapsed) (step S04). The predetermined interval may be changed arbitrarily.

[0035] As described above, the license plate readers 21A_1 to 21A_6 in a single device group 2A are installed under similar environmental conditions. Therefore, even if, for example, license plate reader 21A_1 in this device group 2A has its exposure parameters changed to inappropriate values ​​due to momentary changes in shadow or lighting, making it impossible to read license plates, the exposure parameters of license plate reader 21A_1 can be correctly corrected by referring to the exposure parameters of the most recently successful license plate readers 21A_2 to 21A_6. The details of this correction process will be explained with reference to Figure 4.

[0036] Figure 4 is a flowchart showing an example of the processing of an exposure control and correction device according to one embodiment. First, the classification unit 111 refers to the license plate information D1 recorded in the storage 13 and calculates the elapsed time since the last reading of the license plate information D1 by each of the license plate readers 21A_1 to 21B_6 (step S41).

[0037] Next, the classification unit 111 terminates the correction process if the elapsed time for all license plate readers 21A_1 to 21A_6 is longer than a predetermined time T (for example, 30 minutes) (step S42; YES). The length of the predetermined time T may be arbitrarily changed depending on the traffic volume on the road where the group of devices 2A is installed.

[0038] Furthermore, if the elapsed time for all license plate readers 21A_1 to 21A_6 is less than a predetermined time T (step S42: NO, and step S43: YES), the classification unit 111 determines that all license plate readers 21A_1 to 21A_6 have successfully read the license plates and terminates the process.

[0039] Next, we will explain the case where there is a mix of license plate readers 21 whose elapsed time is longer than a predetermined time T and license plate readers 21 whose elapsed time is less than a predetermined time T (step S42; NO, and step S43; NO). Possible reasons why license plates have not been read for longer than a predetermined time T include the case where no vehicles are passing and the case where the exposure parameters of the license plate readers 21 are inappropriate. For this reason, the classification unit 111 groups the license plate readers 21A_1 to 21A_6 based on their exposure parameters in order to determine whether the reason for the lack of reading is that no vehicles are passing or that the exposure parameters are inappropriate.

[0040] First, the classification unit 111 calculates the brightness magnification for each license plate reader 21A_1 to 21A_6 (step S44). The brightness magnification is obtained by multiplying each parameter (iris, exposure time, gain) included in the exposure parameter D2. The brightness magnifications for the license plate readers 21A_1 to 21A_6 are denoted as L1 to L6, respectively.

[0041] Next, the classification unit 111 classifies each license plate reader 21 into a normal group and an out-of-range group based on the brightness magnification L1 to L6 of the license plate readers 21A_1 to 21A_6 (step S45). That is, the classification unit 111 classifies and identifies license plate readers 21 whose brightness magnification L (exposure parameter D2) deviates from that of other devices into the out-of-range group.

[0042] Figure 5 is a first diagram illustrating the processing of an exposure control and correction device according to one embodiment. Figure 6 is a second diagram illustrating the processing of an exposure control and correction device according to one embodiment. In Figure 5, the vertical axis represents the brightness magnification L, and the horizontal axis represents the elapsed time t from the last reading time. Figure 5 shows an example of mapping each license plate reader 21A_1 to 21A_6 based on the brightness magnification L1 to L6, which is determined by the exposure parameters, and the elapsed time t1 to t6.

[0043] First, the classification unit 111 extracts the license plate reading devices 21 where the elapsed time t is less than the predetermined time T. In the example of FIG. 5, three license plate reading devices 21A_1, 21A_3, and 21A_5 are extracted. Since these three license plate reading devices 21A_1, 21A_3, and 21A_5 have recently succeeded in reading, it is determined that the exposure parameters are appropriate.

[0044] Also, the classification unit 111 sets the normal range based on the brightness magnification factors L1, L3, and L5 of the three extracted license plate reading devices 21A_1, 21A_3, and 21A_5. Specifically, the classification unit 111 obtains the median value Lmed from these three brightness magnification factors L1, L3, and L5. In the example of FIG. 5, the median value Lmed = L1. The classification unit 111 sets the normal range based on the median value Lmed and a predetermined classification coefficient x. The classification coefficient x is a value for determining the normal range of the brightness magnification factor. In this embodiment, the classification unit 111 sets the value obtained by multiplying the median value Lmed by the classification coefficient x (Lmed * x) as the upper limit value Lmax of the normal range. The classification unit 111 sets the value obtained by dividing the median value Lmed by the classification coefficient x (Lmed / x) as the lower limit value Lmin of the normal range.

[0045] When the brightness magnification factor L of the license plate reading device 21 is within the normal range (Lmin ≤ L ≤ Lmax), the classification unit 111 classifies them into the normal group G1. On the other hand, when the brightness magnification factor L of the license plate reading device 21 is outside the normal range (L > Lmax or L < Lmin), the classification unit 111 classifies them into the out-of-range group. In this embodiment, the out-of-range group is divided into two groups: the first out-of-range group G2 where the brightness magnification factor L exceeds the upper limit value Lmax of the normal range and the second out-of-range group G3 where the brightness magnification factor L is less than the lower limit value Lmin.

[0046] In the examples shown in Figures 5 and 6, the classification unit 111 classifies license plate readers 21A_1 and 21A_3 into the normal group G1 because their brightness magnifications L1 and L3 are within the normal range. The classification unit 111 classifies license plate readers 21A_5 and 21A_6 into the first out-of-range group G2 because their brightness magnifications L5 and L6 exceed Lmax. The classification unit 111 classifies license plate readers 21A_2 and 21A_4 into the second out-of-range group G3 because their brightness magnifications L2 and L4 exceed Lmin.

[0047] Next, the correction unit 112 determines whether correction is necessary for the license plate readers 21 that are classified into out-of-range groups G2 and G3.

[0048] First, the correction unit 112 calculates the time score for each group G1, G2, and G3 (step S46). Specifically, for each license plate reader 21 classified into a group, the correction unit 112 adds (+1) to the score if the elapsed time t is less than a predetermined time T.

[0049] In the example in Figure 5, the elapsed times t1 and t3 of license plate readers 21A_1 and 21A_3, which are classified as normal group G1, are both less than the predetermined time T, so a score of +1 is added to each. Therefore, the score for normal group G1 is "2".

[0050] For the first group outside the range G2, the elapsed time t5 for license plate reader 21A_5 is less than the predetermined time T, so the score is +1, and the elapsed time t6 for license plate reader 21A_6 is equal to or greater than the predetermined time T, so the score is +0. Therefore, the score for the first group outside the range G2 is "1".

[0051] For the second group outside the range, G3, the elapsed times t2 and t4 for license plate readers 21A_2 and 21A_4 are both equal to or greater than the predetermined time T, so no score is added for them. Therefore, the score for the second group outside the range, G3, is "0".

[0052] Next, the correction unit 112 corrects the exposure parameters of the license plate reader 21 that have not recently been successfully read (elapsed time t≧T) and are classified into the group with a score of "0" (step S47).

[0053] In other words, even if the brightness magnification L is outside the normal range, the correction unit 112 determines that there is no problem with the exposure parameters if there is a license plate reader 21 that has recently succeeded in reading at a similar brightness magnification L. On the other hand, if the brightness magnification L is outside the normal range and only license plate readers 21 that have not succeeded in reading are included, the unit determines that correction is necessary, as it is possible that the reading has failed due to inappropriate exposure parameters.

[0054] For example, in the examples in Figures 5 and 6, the license plate reader 21A_5 successfully reads the first out-of-range group G2 (it is included in the region G21, which is less than the predetermined time T). Therefore, the correction unit 112 determines that there is no problem with the exposure parameters for the license plate reader 21A_6, which did not successfully read the first out-of-range group G2 (it is included in the region G22, which is longer than the predetermined time T), and does not perform any correction.

[0055] On the other hand, in the second group outside the range G3, there are no license plate readers 21 that have successfully read the license plate (included in the region G31 with a time of less than a predetermined time T), and only license plate readers 21A_2 and 21A_4 that have not successfully read the license plate (included in the region G32 with a time of time T or longer). In this case, the correction unit 112 corrects the exposure parameters of these license plate readers 21A_2 and 21A_4.

[0056] The method for correcting the exposure parameters of the correction unit 112 will now be described. The correction unit 112 corrects the exposure parameters of the license plate readers 21A_2 and 21A_4 based on the exposure parameters of the license plate reader 21 classified as normal group G1. Specifically, the correction unit 112 corrects the exposure parameters of the license plate readers 21A_2 and 21A_4 to the same value as the exposure parameters of the license plate reader 21A_1, which is the median brightness magnification value Lmed.

[0057] Furthermore, the correction unit 112 outputs a correction command signal D3, which includes the corrected exposure parameters, to the license plate reading devices 21A_2 and 21A_4 (step S48). Then, the license plate reading devices 21A_2 and 21A_4 (image processing device 204) control the camera 200 and lens 201 based on the corrected exposure parameters included in the correction command signal D3.

[0058] This allows the exposure parameters of license plate readers 21A_2 and 21A_4 to be corrected to match those of devices that have successfully read license plates under similar conditions, even if the exposure parameters are inappropriately changed. This helps to prevent license plate reading failures due to inappropriate exposure parameters.

[0059] (Effect, Action) As described above, the exposure control correction device 10 according to this embodiment includes: an acquisition unit 110 that acquires exposure parameters D2 at the time of license plate reading from each of the multiple license plate reading devices 21 included in one device group 2; a classification unit 111 that sets a normal range based on the exposure parameters D2 of the license plate reading device 21 that has not elapsed a predetermined time T since reading the license plate, and classifies each of the multiple license plate reading devices 21 into a normal group G1 in which the exposure parameters D2 are within the normal range, and out-of-range groups G2 and G3 in which the exposure parameters D2 are outside the normal range; and a correction unit 112 that corrects the exposure parameters of the license plate reading devices 21 classified into out-of-range groups G2 and G3 based on the exposure parameters of the license plate reading device 21 classified into normal group G1.

[0060] In this way, even if the exposure parameters of some of the license plate readers 21 included in a group of 2 are changed to inappropriate values, the exposure control and correction device 10 can appropriately correct them based on the exposure parameters of other license plate readers 21 that are reading normally.

[0061] Furthermore, the classification unit 111 calculates the brightness magnification L for each of the multiple license plate readers 21 based on the exposure parameter D2, and sets a normal range based on the median value Lmed of the brightness magnification L of the license plate readers 21 that have not elapsed a predetermined time T since reading a license plate.

[0062] In this way, the exposure control and correction device 10 can set an appropriate normal range for classification without being affected by the exposure parameter D2, which has been set to an extreme value, even though it has successfully read the license plate. Furthermore, the exposure control and correction device 10 can appropriately adjust the normal range to match the exposure parameter D2 of each license plate reader 21, which changes moment by moment.

[0063] Furthermore, the correction unit 112 corrects the exposure parameters of the license plate readers 21 classified as out-of-range groups G2 and G3 if the out-of-range groups G2 and G3 include only license plate readers 21 that have elapsed a predetermined time T since reading a license plate.

[0064] In this way, if no license plate reader 21 has successfully read a number plate with similar exposure parameters, the exposure control and correction device 10 can determine that the exposure parameters may have been inappropriately changed and correct them. On the other hand, if a license plate reader 21 has successfully read a number plate with similar exposure parameters, the exposure control and correction device 10 determines that there is no problem with the exposure parameters. Unnecessary corrections to exposure parameters can be suppressed.

[0065] Furthermore, the classification unit 111 further classifies the license plate readers 21 classified as being in the out-of-range group into a first out-of-range group G2 in which the brightness magnification L exceeds the upper limit Lmax of the normal range, and a second out-of-range group G3 in which the brightness magnification L falls below the lower limit Lmin of the normal range.

[0066] In this way, the exposure control correction device 10 can process cases where the brightness magnification L is too large and cases where it is too small separately, allowing it to more accurately determine whether correction is necessary for each license plate reader device 21.

[0067] Furthermore, the correction unit 112 corrects the exposure parameters of the license plate readers 21 classified as out-of-range groups G2 and G3 so that they become the same value as the exposure parameter D2 of the license plate readers 21 whose brightness magnification L is the median value Lmed, among the license plate readers 21 that have not elapsed a predetermined time T since reading the license plate.

[0068] In this way, the exposure control correction device 10 can appropriately correct the exposure parameters of the license plate reader 21, which may have failed to read the license plate even though it has successfully read it, without being affected by the exposure parameter D2 which has been set to an extreme value.

[0069] As described above, embodiments relating to this disclosure have been explained, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

[0070] <Note> The exposure control and correction device, exposure control and correction method, and program described in the above-described embodiment can be understood, for example, as follows.

[0071] (1) According to the first embodiment, the exposure control correction device 10 includes an acquisition unit 110 that acquires exposure parameters D2 at the time of reading a license plate from each of the plurality of license plate readers 21 included in the device group 2, a classification unit 111 that sets a normal range based on the exposure parameters D2 of the license plate readers 21 that have not elapsed a predetermined time T since reading a license plate, and classifies each of the plurality of license plate readers 21 into a normal group G1 in which the exposure parameters D2 are within the normal range and out-of-range groups G2, G3 in which the exposure parameters D2 are outside the normal range, and a correction unit 112 that corrects the exposure parameters of the license plate readers 21 classified into out-of-range groups G2, G3 based on the exposure parameters D2 of the license plate readers 21 classified into normal group G1.

[0072] In this way, even if the exposure parameters of some of the license plate readers 21 included in a group of 2 are changed to inappropriate values, the exposure control and correction device 10 can appropriately correct them based on the exposure parameters of other license plate readers 21 that are reading normally.

[0073] (2) According to the second embodiment, in the exposure control correction device 10 according to the first embodiment, the classification unit 111 calculates the brightness magnification L for each of the multiple license plate readers 21 based on the exposure parameter D2, and sets a normal range based on the median value Lmed of the brightness magnification L of the license plate readers 21 that have not elapsed a predetermined time T since reading a license plate.

[0074] In this way, the exposure control and correction device 10 can set an appropriate normal range for classification without being affected by the exposure parameter D2, which has been set to an extreme value, even though it has successfully read the license plate. Furthermore, the exposure control and correction device 10 can appropriately adjust the normal range to match the exposure parameter D2 of each license plate reader 21, which changes moment by moment.

[0075] (3) According to the third embodiment, in the exposure control correction device 10 according to the first or second embodiment, the correction unit 112 corrects the exposure parameters of the license plate readers 21 classified as out of range groups G2 and G3 when the out of range groups G2 and G3 include only license plate readers 21 that have elapsed a predetermined time T since reading a license plate.

[0076] In this way, if no license plate reader 21 has successfully read a number plate with similar exposure parameters, the exposure control and correction device 10 can determine that the exposure parameters may have been inappropriately changed and correct them. On the other hand, if a license plate reader 21 has successfully read a number plate with similar exposure parameters, the exposure control and correction device 10 determines that there is no problem with the exposure parameters. Unnecessary corrections to exposure parameters can be suppressed.

[0077] (4) According to the fourth embodiment, in the exposure control correction device 10 according to the second or third embodiment, the classification unit 111 further classifies the license plate reader 21 classified into the out-of-range group into a first out-of-range group G2 in which the brightness magnification L exceeds the upper limit Lmax of the normal range, and a second out-of-range group G3 in which the brightness magnification L falls below the lower limit Lmin of the normal range.

[0078] In this way, the exposure control correction device 10 can process cases where the brightness magnification L is too large and cases where it is too small separately, allowing it to more accurately determine whether correction is necessary for each license plate reader device 21.

[0079] (5) According to the fifth embodiment, in the exposure control correction device 10 according to any one of the second to fourth embodiments, the correction unit 112 corrects the exposure parameters of the license plate readers 21 classified into out-of-range groups G2 and G3 to the same value as the exposure parameter D2 of the license plate readers 21 whose brightness magnification L is the median value Lmed, among the license plate readers 21 that have not elapsed a predetermined time T since reading the license plate.

[0080] In this way, the exposure control correction device 10 can appropriately correct the exposure parameters of the license plate reader 21, which may have failed to read the license plate even though it has successfully read it, without being affected by the exposure parameter D2 which has been set to an extreme value.

[0081] (6) According to the sixth embodiment, the exposure control correction method includes the steps of: obtaining exposure parameters D2 at the time of license plate reading from each of the plurality of license plate reading devices 21 included in the group of devices 2; setting a normal range based on the exposure parameters D2 of the license plate reading device 21 that has not elapsed a predetermined time T since reading the license plate, and classifying each of the plurality of license plate reading devices 21 into a normal group G1 in which the exposure parameters D2 are within the normal range, and out-of-range groups G2 and G3 in which the exposure parameters D2 are outside the normal range; and correcting the exposure parameters of the license plate reading devices 21 classified into out-of-range groups G2 and G3 based on the exposure parameters D2 of the license plate reading device 21 classified into normal group G1.

[0082] (7) According to the seventh aspect, the program causes the exposure control correction device 10 to perform the following steps: acquire exposure parameters D2 at the time of reading a license plate from each of the multiple license plate readers 21 included in the group of devices 2; set a normal range based on the exposure parameters D2 of the license plate readers 21 that have not elapsed a predetermined time T since reading a license plate; classify each of the multiple license plate readers 21 into a normal group G1 in which the exposure parameters D2 are within the normal range, and out-of-range groups G2 and G3 in which the exposure parameters D2 are outside the normal range; and correct the exposure parameters of the license plate readers 21 classified into out-of-range groups G2 and G3 based on the exposure parameters D2 of the license plate readers 21 classified into normal group G1. [Explanation of Symbols]

[0083] 1. Exposure control and correction system 10. Exposure control and correction device 11 processors 110 Acquisition Department 111 Classification Department 112 Correction Unit 12 memory 13 Storage 2,2A,2B License plate reading device group (device group) 21. License plate reader 200 Cameras 201 Lens 202 Lighting 203 IF board 204 Image Processing Device D1 License Plate Information D2 Exposure Parameters D3 Correction Command Signal

Claims

1. A group of license plate readers is included in a set of devices, and each license plate reader automatically changes the exposure parameters of the camera so that the brightness of the license plate portion in the image captured by the camera becomes a preset value. An acquisition unit acquires the exposure parameters during license plate reading from each of these license plate readers. A classification unit calculates the elapsed time since each of the license plate readers last read a license plate, sets a normal range based on the exposure parameters of license plate readers whose elapsed time is less than a predetermined time, and classifies each of the multiple license plate readers into a normal group in which the exposure parameters when the last license plate was read were within the normal range, and an out-of-range group in which the exposure parameters when the last license plate was read were outside the normal range. If the elapsed time for all license plate readers classified as outside the range group is equal to or greater than the predetermined time, a correction unit corrects the exposure parameters of the license plate readers classified as outside the range group based on the exposure parameters of the license plate readers classified as normal group. An exposure control and correction device equipped with the following features.

2. The aforementioned classification unit is Based on the exposure parameters, the brightness magnification of each of the multiple license plate readers is calculated. The normal range is set based on the median brightness magnification of the license plate reader for which the elapsed time since the last license plate reading is less than a predetermined time. The exposure control and correction device according to claim 1.

3. The classification unit further classifies the license plate readers classified into the out-of-range group into a first out-of-range group whose brightness magnification exceeds the upper limit of the normal range, and a second out-of-range group whose brightness magnification falls below the lower limit of the normal range. The exposure control and correction device according to claim 2.

4. The correction unit corrects the exposure parameters of the license plate readers classified as being in the out-of-range group so that they become the same value as the exposure parameters of the license plate readers whose brightness magnification is the median value among the license plate readers whose elapsed time since the last license plate was read is less than a predetermined time. The exposure control and correction device according to claim 2 or 3.

5. The process involves obtaining the exposure parameters during license plate reading from each of the license plate reading devices, which are a group of license plate reading devices that automatically change the exposure parameters of the camera so that the brightness of the license plate portion in the image captured by the camera becomes a preset value. The steps include: calculating the elapsed time since each of the license plate readers last read a license plate; setting a normal range based on the exposure parameters of license plate readers whose elapsed time is less than a predetermined time; and classifying each of the multiple license plate readers into a normal group, where the exposure parameters at the time of the last license plate reading were within the normal range, and an out-of-range group, where the exposure parameters at the time of the last license plate reading were outside the normal range. If the elapsed time for all license plate readers classified as belonging to the out-of-range group is equal to or greater than the predetermined time, the exposure parameters of the license plate readers classified as belonging to the out-of-range group are corrected based on the exposure parameters of the license plate readers classified as belonging to the normal group. An exposure control and correction method having the following characteristics.

6. The process involves obtaining the exposure parameters during license plate reading from each of the license plate reading devices, which are a group of license plate reading devices that automatically change the exposure parameters of the camera so that the brightness of the license plate portion in the image captured by the camera becomes a preset value. The steps include: calculating the elapsed time since each of the license plate readers last read a license plate; setting a normal range based on the exposure parameters of license plate readers whose elapsed time is less than a predetermined time; and classifying each of the multiple license plate readers into a normal group, where the exposure parameters at the time of the last license plate reading were within the normal range, and an out-of-range group, where the exposure parameters at the time of the last license plate reading were outside the normal range. If the elapsed time for all license plate readers classified as belonging to the out-of-range group is equal to or greater than the predetermined time, the exposure parameters of the license plate readers classified as belonging to the out-of-range group are corrected based on the exposure parameters of the license plate readers classified as belonging to the normal group. A program that causes the exposure control and correction device to execute.

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