License Plate Recognition System, License Plate Recognition Method, and Program

Abstract

To recognize license plate information with a simple configuration.SOLUTION: A license plate recognition system for recognizing license plates N arranged in the front and rear parts of a vehicle A traveling on a lane L includes: a camera 2 which is arranged to photograph one of the license plates N arranged in the front and rear parts of the vehicle A; a mirror 3 which is arranged to be photographed by the camera 2 and on which the other one of the license plates of the vehicle A is reflected; and a recognition processing section which recognizes license plate information from the image photographed by the camera 2.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] At toll gates on toll roads, in order to collect appropriate tolls according to the vehicle type classification of vehicles in motion, etc., technologies are used to read the license plates of moving vehicles and perform vehicle type discrimination, individual identification, etc. of the moving vehicles.

[0003] In addition to the desire to improve the recognition accuracy of license plates for a single moving vehicle, there is a demand for toll collection facilities that can recognize license plates on both the front and rear sides of a moving vehicle, due to the desire to be able to recognize motorcycles that only have license plates on the rear side.

[0004] In order to photograph and recognize both license plates provided on the front and rear of a moving vehicle, it is conceivable to arrange two cameras: a camera for recognizing the front license plate and a camera for recognizing the rear license plate.

[0005] Also, as a method of performing front and rear two-directional photography with a single camera, a method using two plane mirrors is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In a toll collection system capable of recognizing license plates in the front and rear of a moving vehicle, simplification of the configuration is required.

[0008] The present disclosure has been made in view of the above-described problems, and an object thereof is to provide a license plate recognition system, a license plate recognition method, and a program that can recognize license plates in the front and rear of a moving vehicle with a simpler configuration.

Means for Solving the Problems

[0009] To achieve the above object, a license plate recognition system according to an aspect of the present disclosure is a license plate recognition system for recognizing license plates provided in the front and rear of a vehicle traveling in a lane, and is disposed so as to be able to photograph one of the license plates provided in the front or rear of the vehicle. A camera, a mirror disposed so as to be photographable by the camera and reflecting the other license plate of the vehicle, a recognition processing unit that recognizes license plate information from an image captured by the camera, and a roadside at a detection position in the lane direction. A vehicle detector that detects entry into and exit from a predetermined traveling position of the vehicle traveling in the lane, wherein the camera is disposed downstream of the vehicle detector in the vehicle traveling direction and is provided so as to be able to photograph from the downstream side toward the upstream side, and the mirror is disposed upstream of the vehicle detector in the vehicle traveling direction, of the vehicle Upstream side in the vehicle traveling direction surface Is provided so as to reflect.

[0010] In the above license plate recognition system, the recognition processing unit may recognize the license plate information by performing a horizontal flip process on the image reflected in the mirror included in the image captured by the camera.

[0011] In the above license plate recognition system, the recognition processing unit may store characters that have been horizontally flipped in advance as inverted character information in a database, and based on the inverted character information in the database, the license plate included in the image captured by the camera. License plate information in the image reflected in the mirror may be recognized.

[0012] In addition, in the above license plate recognition system, the mirror surface of the mirror has a curved surface, and the recognition processing unit may perform a distortion correction process for correcting the distortion of the image generated according to the curved surface shape of the mirror.

[0013] In addition, in the above license plate recognition system, the recognition processing unit stores, in a database, characters distorted with a curvature corresponding to the curved surface shape of the mirror in advance as distorted character information, and based on the distorted character information in the database, recognizes license plate information in the image reflected by the mirror included in the image captured by the camera.

[0014] In addition, in the above license plate recognition system, the recognition processing unit associates the first license plate information obtained from the first image capturing the one license plate with the second license plate information obtained from the second image capturing the other license plate reflected in the mirror, and compares the one license plate with the other license plate to recognize identity.

[0015] In addition, the above license plate recognition system the vehicle detector further includes an image acquisition unit that acquires an image in which the one license plate is reflected at the timing when the entry of the vehicle is detected, and acquires an image in which the other license plate N2 is reflected through the mirror at the timing when the exit of the vehicle is detected.

[0016] In addition, in the above license plate recognition system, the camera may be provided so as to be able to continuously capture images in time series.

[0017] Also, a license plate recognition method according to an aspect of the present disclosure is a license plate recognition method for recognizing license plates provided in front of and behind a vehicle traveling in a lane, and uses a camera arranged to be able to photograph one of the license plates provided in front of or behind the vehicle to photograph the one license plate, a step of photographing a mirror reflecting the other license plate of the vehicle with the camera, a step of recognizing license plate information from the image photographed by the camera, and a step of detecting entry into and exit from a predetermined traveling position of the vehicle traveling in the lane using a vehicle detector installed on the roadside at a detection position in the lane direction, wherein the camera is arranged downstream of the vehicle detector in the vehicle traveling direction and photographs from the downstream side toward the upstream side, and the mirror is arranged upstream of the vehicle detector in the vehicle traveling direction, of the vehicle the upstream side in the vehicle traveling direction surface reflects.

[0018] Also, a program according to an aspect of the present disclosure causes a computer of a license plate recognition system for recognizing license plates provided in front of and behind a vehicle traveling in a lane to use a camera arranged to be able to photograph one of the license plates provided in front of or behind the vehicle to photograph the one license plate, a step of photographing a mirror reflecting the other license plate of the vehicle with the camera, a step of recognizing license plate information from the image photographed by the camera, and a step of detecting entry into and exit from a predetermined traveling position of the vehicle traveling in the lane using a vehicle detector installed on the roadside at a detection position in the lane direction, and execute the steps, wherein the camera is arranged downstream of the vehicle detector in the vehicle traveling direction, and in the step of photographing the one license plate with the camera, the camera photographs from the downstream side toward the upstream side, and the mirror is arranged upstream of the vehicle detector in the vehicle traveling direction, and in the step of photographing the mirror with the camera, the mirror of the vehicle the upstream side in the vehicle traveling direction surface reflects. [Effect of the Invention]

[0019] According to the license plate recognition system, license plate recognition method, and program of the present invention, it is possible to recognize license plates in front of and behind a moving vehicle with a simpler configuration.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Modes for Carrying Out the Invention

[0021] Hereinafter, a license plate recognition system, a license plate recognition method, and a program according to an embodiment of the present disclosure will be described. Such an embodiment shows one aspect of the present invention, does not limit the present invention, and can be arbitrarily changed within the scope of the technical idea of the present invention.

[0022] <First Embodiment> With reference to FIGS. 1 to 7, the license plate recognition system according to the first embodiment will be described in detail.

[0023] (Overall Configuration of License Plate Recognition System) FIG. 1 is a first plan view showing the overall configuration of the license plate recognition system according to the first embodiment.

[0024] The license plate recognition system 1 shown in FIG. 1 is used as one of the configurations of a toll collection system that collects tolls from a traveling vehicle A at a tollgate on a toll road.

[0025] As shown in FIG. 1, a vehicle A using a toll road travels on a lane L at a tollgate. In the following description, the direction in which the lane L extends (±X direction) is also referred to as the "lane direction", and the direction (±Y direction) that is horizontally orthogonal to the lane direction (±X direction) is also referred to as the "lane width direction". Also, the front side (-X direction side) of the traveling direction of the vehicle A is also referred to as the "upstream side", and the rear side (+X direction side) of the traveling direction of the vehicle A is also referred to as the "downstream side". Also, the -Y direction side in the lane width direction (±Y direction) is the "right side in the traveling direction" of the vehicle A, and the +Y direction side in the lane width direction (±Y direction) is the "left side in the traveling direction" of the vehicle A. Also, the direction (±Z direction) orthogonal to the plane including the lane direction (±X direction) and the lane width direction (±Y direction) is also referred to as the "vertical direction".

[0026] The license plate recognition system 1 is a system that recognizes license plates N (N1, N2) provided in front of and behind a vehicle A traveling in a lane L. Here, the license plate provided on the front side of the vehicle A is also referred to as "license plate N1", and the license plate provided on the rear side of the vehicle A is also referred to as "license plate N2".

[0027] As shown in FIG. 1, the license plate recognition system 1 includes a camera 2, a mirror 3, and a vehicle detector 5. The camera 2, the mirror 3, and the vehicle detector 5 are installed on the roadside of the lane L.

[0028] The camera 2 is provided so as to be able to photograph the license plate N1 on the front side of the vehicle A traveling in the lane L. Specifically, as shown in FIG. 1, the camera 2 is on one side in the lane width direction (±Y direction) of the lane L (the right side (-Y direction side) in the vehicle traveling direction), and is arranged to photograph from the downstream side (+X direction side) to the upstream side (-X direction side) of the lane L. Also, the camera 2 has a viewing angle 20R that can photograph both the license plate N1 on the front side of the vehicle A and the mirror 3 in which the license plate N2 on the rear side of the vehicle A is reflected.

[0029] The mirror 3 is a plane mirror and is arranged on the right side (-Y direction side) in the vehicle traveling direction of the lane L, that is, on the same side as the camera 2 in the lane width direction. The mirror 3 is arranged on the upstream side (-X direction side) of the camera 2 as shown in FIG. 1. And the mirror 3 is arranged at a position included in the viewing angle 20R of the camera 2 on the downstream side (+X direction side) of the lane L. The posture (the direction of the mirror surface) of the mirror 3 is adjusted so that the license plate N2 on the rear side of the vehicle A can be reflected through the mirror 3 from the camera 2.

[0030] The vehicle detector 5 is installed on the roadside at the detection position in the lane direction and detects the entry and exit of the vehicle A. The vehicle detector 5 is, for example, a transmissive vehicle detector and has a pair of a light projector 51 and a light receiver 52 that are installed opposite each other across the lane L. The vehicle detector 5 outputs a vehicle detection signal that can distinguish the presence or absence of a vehicle at the detection position based on whether the light receiver 52 receives the light projected from the light projector 51. While the light receiver 52 is receiving light, the vehicle detector 5 outputs a vehicle detection signal (OFF) indicating that there is no vehicle at the detection position. On the other hand, while the light receiver 52 is not receiving light, the vehicle detector 5 outputs a vehicle detection signal (ON) indicating that there is a vehicle at the detection position.

[0031] (Functional Configuration of License Plate Recognition System) FIG. 2 is a diagram showing the functional configuration of the license plate recognition system according to the first embodiment.

[0032] As shown in FIG. 2, the license plate recognition system 1 includes a lane control device 4. The lane control device 4 is a processing device installed for each lane L of the toll gate and is a computer that performs all charging processes for vehicles traveling on the lane L. The lane control device 4 includes a CPU 40, a memory 41, a connection interface 42, and a recording medium 43.

[0033] The CPU 40 is a processor that operates according to a pre-prepared program. In the present embodiment, the CPU 40 functions as an image acquisition unit 400 and a recognition processing unit 401 by operating according to the program. The memory 41 is a so-called main storage device and is a storage area necessary for the operation of the CPU 40. The connection interface 42 is a connection interface for signal exchange with roadside devices (camera 2, vehicle detector 5). The recording medium 43 is a so-called auxiliary storage device, and information necessary for the charging process for the vehicle traveling in the lane L is recorded. In particular, in the present embodiment, character information and the like that are referred to during the recognition process (matching process) by the recognition processing unit 401 are recorded on the recording medium 43.

[0034] The image acquisition unit 400 operates the camera 2 to take a picture according to the vehicle detection signal received from the vehicle detector 5, and acquires a captured image. The recognition processing unit 401 recognizes the front license plate N1 and the rear license plate N2 from each of the first image D1 (see FIG. 4) and the second image D2 (see FIG. 5) taken by the camera 2, and acquires each license plate information. Specific processes of the image acquisition unit 400 and the recognition processing unit 401 will be described with reference to the following flowcharts (FIGS. 6 and 7).

[0035] (Processing Flow of License Plate Recognition System) FIG. 3 is a second plan view showing the overall configuration of the license plate recognition system according to the first embodiment. Also, FIGS. 4 and 5 are diagrams showing the first image showing the front license plate of the vehicle according to the first embodiment and the second image showing the rear license plate of the vehicle, respectively. Also, FIGS. 6 and 7 are diagrams showing the processing flows of the license plate recognition system according to the first embodiment, respectively. Hereinafter, the operation procedure for the license plate recognition system 1 to recognize the license plate N of the vehicle A traveling in the lane L will be described in detail with reference to FIGS. 1 to 6.

[0036] First, based on the processing flow shown in FIG. 6, the flow of the process for recognizing the front license plate N1 of the vehicle A will be described.

[0037] First, when vehicle A arrives at the toll gate and travels on lane L, the front end of the vehicle body of vehicle A enters (reaches) the detection position in lane L. At this time, the vehicle detection signal output by the vehicle detector 5 switches from OFF to ON (step S11). At this point, the front license plate N1 of vehicle A is located near the detection position of the vehicle detector 5 as shown in FIG. 1.

[0038] The image acquisition unit 400 of the lane control device 4 activates the camera 2 at the timing when the vehicle detection signal switches from OFF to ON to acquire a captured image (step S12). The image thus acquired is an image (first image D1) in which the front license plate N1 of vehicle A is directly reflected (without passing through the mirror 3) as shown in FIG. 4.

[0039] Next, the recognition processing unit 401 of the lane control device 4 recognizes the front license plate N1 from the first image D1 acquired in step S12 (step S13). Here, the recognition processing unit 401 identifies the image captured at the time of entry of vehicle A (the timing when the vehicle detection signal switches from OFF to ON) as the "first image D1". According to the angular field of view 20R of the camera 2, the positional relationship between the front license plate N1 of vehicle A and the mirror 3 as shown in FIG. 1, the image of the front license plate N1 of vehicle A is included in the region on the upper right side of the center (the region where the image of the mirror 3 is not reflected) within the first image D1 (see FIG. 4). Therefore, the recognition processing unit 401 performs the recognition processing of the license plate information with the region on the upper right side of the center (the region where the image of the mirror 3 is not reflected) within this first image D1 as the recognition target.

[0040] As described above, the recognition processing unit 401 reads the license plate information related to the front license plate N1 of vehicle A.

[0041] Next, based on the processing flow shown in FIG. 7, the processing flow for recognizing the rear license plate N2 of vehicle A will be described.

[0042] When the rear end of the vehicle body of vehicle A moves away from the detection position of the vehicle detector 5 in the lane L, the vehicle detection signal output by the vehicle detector 5 switches from ON to OFF (step S21). At this time, the rear license plate N2 of vehicle A is located near the detection position of the vehicle detector 5 as shown in FIG. 3.

[0043] The image acquisition unit 400 of the lane control device 4 activates the camera 2 at the timing when the vehicle detection signal switches from ON to OFF to acquire a captured image (step S22). The image thus acquired is, as shown in FIG. 5, the second image D2 in which the rear license plate N2 of vehicle A is reflected through the mirror 3 (through the mirror). However, in the second image D2, the character string printed on the license plate N2 is in a state where left and right are reversed.

[0044] Next, the recognition processing unit 401 of the lane control device 4 performs image processing to reverse left and right on the second image D2 acquired in step S22 (step S23). Here, the recognition processing unit 401 identifies the image captured at the time of the exit of vehicle A (the timing when the vehicle detection signal switches from ON to OFF) as the "second image D2". According to the angle of view 20R of the camera 2 as shown in FIG. 3, the area photographed through the mirror 3 (hereinafter also referred to as the "area photographed through the mirror 30R"), and the positional relationship of the rear license plate N2 of vehicle A, the rear license plate N2 of vehicle A is included in the area in the second image D2 where the image of the mirror 3 is reflected (see FIG. 5). Therefore, the recognition processing unit 401 performs image processing to reverse left and right on the area in this second image D2 where the image of the mirror 3 is reflected as the recognition target. Since the positional relationship between the camera 2 and the mirror 3 does not change from the initial installation time, by grasping and storing in advance the "area where the image of the mirror 3 is reflected" in the image acquired through the camera 2 at the initial installation of the camera 2 and the mirror 3, the recognition processing unit 401 can, in step S23, target only the area where the image of the mirror 3 is reflected in the image as the recognition target (the target of the inversion processing).

[0045] Subsequently, the recognition processing unit 401 performs recognition processing of license plate information on the inverted image obtained by the inversion processing in step S23 (step S24).

[0046] As described above, the recognition processing unit 401 reads license plate information related to the license plate N2 on the rear side of the vehicle A.

[0047] (Function and effect) According to the license plate recognition system 1 described above, the first image D1 in which the license plate N1 on the front side of the vehicle A is reflected without passing through the mirror 3, and the second image D2 in which the license plate N2 on the rear side of the vehicle A is reflected through the mirror, can be captured by one camera 2 and one mirror 3. Then, in the lane control device 4, license plate information can be recognized from the first image D1 and the second image D2 captured by one camera 2. In this way, according to the license plate recognition system 1 according to the present embodiment, with a simple configuration using only one camera (camera 2) and one mirror (mirror 3), the license plates before and after the traveling vehicle can be recognized.

[0048] Further, according to the license plate recognition system 1 according to the present embodiment, for the second image D2 captured by the camera 2 of the rear license plate N2 reflected in the mirror 3 in a horizontally inverted state, the lane control device 4 (recognition processing unit 401) performs a horizontal inversion process (step S23 in FIG. 7). Thereby, license plate information can be correctly recognized from the image of the license plate captured through the mirror.

[0049] Note that in the present embodiment, as the horizontal inversion process by the lane control device 4, the area of the mirror 3 that reflects the image of the license plate N2 in the second image D2 is horizontally inverted. However, in other embodiments, it is not limited to this mode. For example, the lane control device 4 according to another embodiment stores characters that are inverted left and right in advance in a database (recording medium 43) as inverted character information, and recognizes the license plate information of the license plate N2 reflected in the mirror 3 included in the second image D2 by performing matching processing with the inverted character information in the database. By doing so, the recognition processing unit 401 can correctly recognize the license plate information based on the pre-stored inverted character information without inverting the target area of the second image D2 left and right.

[0050] Further, the license plate recognition system 1 of the present embodiment further includes a vehicle detector 5 that detects the entry into and exit from a predetermined driving position (detection position) of the vehicle A traveling in the lane L. Then, the license plate recognition system 1 acquires an image (first image D1) in which the front license plate N1 is reflected at the timing when the vehicle detector 5 detects the entry of the vehicle A, and acquires an image (second image D2) in which the rear license plate N2 is reflected through the mirror at the timing when the vehicle detector 5 detects the exit of the vehicle A. By doing so, the timing when the front license plate N1 exists within the angle of view 20R of the camera 2 (see FIG. 1), and the timing when the rear license plate N2 exists within the range of the shooting area 30R through the mirror (see FIG. 3) are used for shooting. Therefore, regardless of the type of vehicle (ordinary vehicle, large vehicle, etc.) that arrives, it is possible to surely acquire both the image (first image D1) in which the front license plate N1 is reflected and the image (second image D2) in which the rear license plate N2 is reflected.

[0051] <Second Embodiment> Next, a license plate recognition system according to the second embodiment will be described with reference to FIGS. 8 to 10. Components having the same functions as those of the first embodiment described above are denoted by the same reference numerals, and detailed descriptions thereof are omitted since the descriptions would be redundant.

[0052] (Overall Configuration of License Plate Recognition System) Figs. 8 and 9 are plan views showing a license plate recognition system according to the second embodiment.

[0053] As shown in Fig. 8, in the license plate recognition system 1A according to the second embodiment, the mirror 3 of the first embodiment is a convex mirror 3A. Also, as shown in Fig. 9, in the license plate recognition system 1B according to the second embodiment, the mirror 3 of the first embodiment is a concave mirror 3B. According to the license plate recognition system 1A provided with the convex mirror 3A, the viewing angle θ1 is wider than that of the plane mirror 3 of the first embodiment described above. Also, according to the license plate recognition system 1B provided with the concave mirror 3B, the viewing angle θ2 is narrow, and the image through the mirror can be enlarged.

[0054] (Processing flow of license plate recognition system) Fig. 10 is a third flowchart showing the processing of the license plate recognition system according to the second embodiment.

[0055] Next, the operation procedure for recognizing the license plate N using the license plate recognition systems 1A and 1B according to the second embodiment will be described in detail with reference to the third flowchart shown in Fig. 10. Note that the flow of the process for recognizing the license plate N1 on the front side of the vehicle A is the same as the operation flow shown in Fig. 6 of the first embodiment described above, and thus a detailed description thereof will be omitted here.

[0056] The flow of the process for recognizing the license plate N2 on the rear side of the vehicle A by the license plate recognition systems 1A and 1B will be described.

[0057] When the rear end of the vehicle body of the vehicle A moves away from the detection position of the vehicle detector 5 in the lane L, the vehicle detection signal output by the vehicle detector 5 switches from the ON state to the OFF state (step S31). At this time, the license plate N2 on the rear side of the vehicle A is located near the detection position of the vehicle detector 5 as shown in Figs. 8 and 9.

[0058] The image acquisition unit 400 of the lane control device 4 activates the camera 2 at the timing when the vehicle detection signal switches from ON to OFF to acquire a captured image (step S32). The image thus acquired is a second image D2 in which the rear license plate N2 of the vehicle A is reflected through (behind) the mirror 3. In the second image D2, the character string printed on the license plate N2 is in a state where left and right are reversed.

[0059] Furthermore, in the present embodiment, the images reflected on the mirrors 3A and 3B having a curved surface shape are distorted according to the curved surface shape.

[0060] Next, the recognition processing unit 401 of the lane control device 4 performs distortion correction processing for correcting the distortion of the image generated according to the curved surface shape of the convex mirror 3A or the concave mirror 3B, in addition to the image processing for reversing left and right, on the second image D2 acquired in step S33 (step S33). Here, since the curved surface shape (curvature) of the convex mirror 3A or the concave mirror 3B is known in advance, by performing distortion correction processing according to this curved surface shape on the target area of the second image D2, the distorted image reflected on the convex mirror 3A or the concave mirror 3B can be converted into an undistorted image as if it were reflected on a plane mirror.

[0061] Subsequently, the recognition processing unit 401 performs recognition processing of license plate information using the inverted and corrected image obtained by the inversion processing and distortion correction processing in step S33 as the recognition target (step S34).

[0062] As described above, the license plate recognition systems 1A and 1B according to the second embodiment read the license plate information related to the rear license plate N2 of the vehicle A.

[0063] (Function and effect) As described above, according to the license plate recognition systems 1A and 1B according to the second embodiment, for the second image D2 obtained by the camera 2 photographing the rear license plate N2 reflected in a distorted state with a curvature corresponding to the curved surface shape of the convex mirror 3A or the concave mirror 3B, the lane control device 4 performs distortion correction processing, so that the license plate information can be correctly recognized.

[0064] In addition, in the license plate recognition system 1A, since the area reflected through the mirror 3 is widened, it is effective, for example, when the lane width of the lane L is wide.

[0065] On the other hand, in the license plate recognition system 1B, since the area reflected through the mirror 3 becomes narrower, it is possible to photograph the license plate N2 by enlarging it. Therefore, it is effective when higher license plate recognition accuracy is required.

[0066] Note that the recognition processing for an image distorted by the curved surface of the mirror 3 is not limited to the above-described aspect, and for example, in other embodiments, it may be as follows. That is, the lane control device 4 according to another embodiment stores, in advance, characters distorted with a curvature corresponding to the curved surface shape of the convex mirror 3A or the concave mirror 3B as distortion character information in a database (recording medium 43), and by performing matching processing with the distortion character information in this database, recognizes the license plate information of the license plate N2 reflected in the convex mirror 3A or the concave mirror 3B included in the second image D2. By doing so, the recognition processing unit 401 can correctly recognize the license plate information based on the pre-stored distortion character information without performing distortion correction processing on the target area of the second image D2.

[0067] As described above, in the second embodiment, for the second image D2 obtained by the camera 2 photographing the rear license plate N2 reflected in a distorted state with a curvature corresponding to the curved surface shape of the convex mirror 3A or the concave mirror 3B, the lane control device 4 performs distortion correction processing, so that the license plate information can be recognized.

[0068] The above has described each embodiment of the license plate recognition system, the license plate recognition method, and the program. However, the present disclosure is not limited to the above embodiments and can be appropriately modified without departing from the gist thereof.

[0069] For example, the positions of the camera 2 and the mirror 3 in the lane direction X may be arranged on either the upstream side (+X direction side) or the downstream side (-X direction side). That is, in the above embodiment, the front license plate N1 is imaged without passing through the mirror 3, and the camera 2 and the mirror 3 are arranged such that the rear license plate N2 is photographed through the mirror 3. However, in other embodiments, the positions of the camera 2 and the mirror 3 in the lane direction may be arranged in reverse. That is, the mirror 3 may be arranged on the downstream side (+X direction side) in the lane direction, and the camera 2 may be arranged on the upstream side (-X direction side), and the camera 2 and the mirror 3 may be arranged such that the front license plate N1 is photographed through the mirror 3 and the rear license plate N2 is imaged without passing through the mirror 3.

[0070] Also, in the above-described embodiment, the camera 2 is configured to take a picture based on the detection information of the vehicle detector 5, but it is not limited thereto. For example, in other embodiments, it is also possible to omit the vehicle detector 5. In this case, for example, the camera 2 is configured to continuously acquire still images at a predetermined time interval (for example, 30 frames per second, etc.) (that is, take a moving image). In such a case, as the vehicle A travels, the still images acquired by the camera 2 also change every moment. Therefore, the image acquisition unit 400 can acquire an image (first image D1) in which the front license plate N1 is directly photographed at any timing during the travel of the vehicle A, and can further acquire an image (second image D2) in which the rear license plate N2 is photographed through the mirror at another timing. Also, the recognition processing unit 401 performs recognition processing for each still image continuously photographed by the camera 2. Thereby, the recognition processing unit 401 can acquire license plate information through the recognition processing for the first image D1 and the second image D2 acquired at any timing during the travel of the vehicle A.

[0071] In addition, within the scope not departing from the gist of the present invention, it is possible to appropriately replace the components in the above-described embodiments with well-known components, and the above-described embodiments may also be appropriately combined.

[0072] <Appendix> The license plate recognition system, license plate recognition method, and program described in the above embodiments can be understood as follows, for example.

[0073] (1) According to the first aspect, a license plate recognition system 1 is a license plate recognition system for recognizing a license plate N provided in front of and behind a vehicle A traveling in a lane L, and includes a camera 2 arranged to be able to photograph one of the license plates N provided in front of or behind the vehicle A, a mirror 3 arranged to be able to be photographed by the camera 2 and reflecting the other license plate N of the vehicle A, and a recognition processing unit 401 for recognizing license plate information from the image photographed by the camera 2.

[0074] By doing so, a first image D1 in which the license plate N1 on the front side of the vehicle A is reflected without passing through the mirror 3, and a second image D2 in which the license plate N2 on the rear side of the vehicle A is reflected through the mirror 3 can be photographed with one camera 2 and one mirror 3. Then, the recognition processing unit 401 can recognize each license plate information from the images (D1, D2) photographed by one camera 2.

[0075] (2) According to the second aspect, the recognition processing unit 401 recognizes license plate information by performing a left-right inversion process on the second image D2 reflected in the mirror 3 included in the image photographed by the camera 2.

[0076] By doing so, for the second image D2 photographed by the camera 2 of the license plate N2 reflected in the mirror 3 in a left-right inverted state, by performing a left-right inversion process with the lane control device 4, the license plate information can be correctly recognized.

[0077] (3) According to the third aspect, the recognition processing unit 401 stores characters that have been reversed left and right in advance in a database as reversed character information, and recognizes license plate information in the image reflected in the mirror 3 included in the image captured by the camera 2 based on the reversed character information in the database.

[0078] By doing so, for the second image D2 captured by the camera 2 of the license plate N2 reflected in the mirror 3 in a left-right reversed state, without performing the left-right reversal process by the lane control device 4, the license plate information can be recognized by the matching process with the pre-stored reversed character information.

[0079] (4) According to the fourth aspect, the mirror surface of the mirror 3 has a curved surface.

[0080] By doing so, a desired range corresponding to the curved surface can be photographed through the mirror 3.

[0081] (5) According to the fifth aspect, the recognition processing unit 401 performs a distortion correction process for correcting the distortion of the image generated according to the curved surface shape of the mirror 3.

[0082] By doing so, for the second image D2 captured by the camera 2 of the license plate N2 reflected in a state where distortion occurs according to the curved surface shape of the convex mirror 3A or the concave mirror 3B, by performing the distortion correction process of correcting the distortion of the image according to the curved surface shape of the mirror 3 by the lane control device 4, the license plate information can be correctly recognized.

[0083] (6) According to the sixth aspect, the recognition processing unit 401 stores characters distorted with a curvature corresponding to the curved surface shape of the mirror (convex mirror 3A, concave mirror 3B) in advance in a database as distorted character information, and recognizes license plate information in the image reflected in the mirror (convex mirror 3A, concave mirror 3B) included in the image captured by the camera 2 based on the distorted character information in the database.

[0084] By doing so, it is possible to recognize the license plate information by performing a matching process with the pre-stored distortion character information on the second image D2 obtained by photographing the license plate N2 reflected in a distorted state on the convex mirror 3A or the concave mirror 3B with the camera 2 without performing a distortion correction process.

[0085] (7) According to the seventh aspect, the license plate recognition system 1 includes a vehicle detector 5 that detects entry into and exit from a predetermined driving position (detection position) of the vehicle A traveling in the lane L, and an image (first image D1) in which one (front side) license plate is reflected at the timing when the vehicle detector 5 detects the entry of the vehicle A, and an image acquisition unit 400 that acquires an image (second image D2) in which the other (rear side) license plate N2 is reflected through the mirror at the timing when the vehicle detector 5 detects the exit of the vehicle A.

[0086] By doing so, shooting is performed at the timing when the front license plate N1 exists within the angle of view 20R of the camera 2, and at the timing when the rear license plate N2 exists within the shooting area 30R through the mirror. Therefore, regardless of the type of vehicle that arrives, it is possible to surely acquire both the image (first image D1) in which the front license plate N1 is reflected and the image (second image D2) in which the rear license plate N2 is reflected.

[0087] (8) According to the eighth aspect, the camera 2 is provided so as to be able to continuously shoot in time series.

[0088] By doing so, it is possible to recognize the license plate information from each of the first image D1 and the second image D2 included in the still images continuously shot at a predetermined time interval.

Explanation of Reference Numerals

[0089] 1, 1A, 1B License plate recognition system 2 Camera 3 Mirror 4 Lane control device 5 Vehicle detector 401 Recognition Processing Unit D1 First Image D2 Second Image L Lane N, N1, N2 License Plate X Lane Direction Y Lane Width Direction Z Vertical Direction

Claims

1. A license plate recognition system for recognizing license plates provided before and after a vehicle traveling in a lane, comprising: A camera arranged to be able to photograph one of the license plates provided in front of or behind the vehicle; A mirror arranged to be able to be photographed by the camera and reflecting the other license plate of the vehicle; A recognition processing unit for recognizing license plate information from an image photographed by the camera; A vehicle detector installed on the roadside at a detection position in the lane direction for detecting entry into and exit from a predetermined traveling position of the vehicle traveling in the lane; characterized in that: The camera is arranged on the downstream side of the vehicle detector in the vehicle traveling direction and is provided so as to be able to photograph from the downstream side toward the upstream side; The mirror is arranged on the upstream side of the vehicle detector in the vehicle traveling direction and is provided so as to reflect the upstream side surface of the vehicle in the vehicle traveling direction, a license plate recognition system.

2. The recognition processing unit recognizes the license plate information by performing a left-right inversion process on the image reflected in the mirror included in the image photographed by the camera. The license plate recognition system according to Claim 1.

3. The recognition processing unit stores characters that have been left-right inverted in advance in a database as inverted character information, and recognizes license plate information in the image reflected in the mirror included in the image photographed by the camera based on the inverted character information in the database. The license plate recognition system according to Claim 1.

4. The mirror surface of the mirror has a curved surface. The license plate recognition system according to any one of Claims 1 to 3.

5. The recognition processing unit performs a distortion correction process for correcting the distortion of the image generated according to the curved surface shape of the mirror. The license plate recognition system according to Claim 4.

6. The recognition processing unit stores characters distorted with a curvature corresponding to the curved surface shape of the mirror in advance in a database as distorted character information, and recognizes license plate information in the image reflected in the mirror included in the image photographed by the camera based on the distorted character information in the database. The license plate recognition system according to Claim 4.

7. An image acquisition unit that acquires an image in which one of the license plates is reflected at the timing when the vehicle detector detects the entry of the vehicle, and acquires an image in which the other license plate is reflected through the mirror at the timing when the vehicle detector detects the exit of the vehicle. The license plate recognition system according to any one of claims 1 to 6, further comprising

8. The camera is provided to be able to continuously photograph in time series. The license plate recognition system according to any one of claims 1 to 6.

9. A license plate recognition method for recognizing license plates provided in front of and behind a vehicle traveling in a lane, comprising: Using a camera arranged to be able to photograph one of the license plates provided in front of or behind the vehicle, and photographing the one license plate; Photographing, by the camera, a mirror reflecting the other license plate of the vehicle; Recognizing license plate information from the image photographed by the camera; Using a vehicle detector installed on the roadside at the detection position in the lane direction, and detecting entry into and exit from a predetermined traveling position of the vehicle traveling in the lane; having The camera is arranged downstream of the vehicle detector in the vehicle traveling direction, and photographs from the downstream side toward the upstream side. The mirror is arranged upstream of the vehicle detector in the vehicle traveling direction, and reflects the surface on the upstream side of the vehicle in the vehicle traveling direction. A license plate recognition method.

10. In a computer of a license plate recognition system for recognizing license plates provided in front of and behind a vehicle traveling in a lane, Using a camera arranged to be able to photograph one of the license plates provided in front of or behind the vehicle, and photographing the one license plate; Photographing, by the camera, a mirror reflecting the other license plate of the vehicle; Recognizing license plate information from the image photographed by the camera; Using a vehicle detector installed on the roadside at the detection position in the lane direction, and detecting entry into and exit from a predetermined traveling position of the vehicle traveling in the lane; causing to execute The camera is arranged downstream of the vehicle detector in the vehicle traveling direction. In the step of photographing the one license plate with the camera, the camera photographs from the downstream side toward the upstream side. The mirror is arranged upstream of the vehicle detector in the vehicle traveling direction. In the step of photographing the mirror with the camera, a program for reflecting the surface on the upstream side of the vehicle in the vehicle traveling direction by the mirror.

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