JP4901651B2 - License plate imaging system for vehicles - Google Patents

Description

  The present invention relates to a vehicle license plate imaging system that captures and recognizes a vehicle number (number plate) when a vehicle enters and exits a parking lot or the like.

Regarding a system for imaging a license plate of a vehicle, Patent Literature 1 describes a character recognition method and apparatus capable of realizing imaging of an appropriate character area under various environments. Further, Patent Document 2 describes an apparatus that captures an image of a license plate with sufficient contrast even in places where the brightness changes greatly, such as outdoors. Patent Document 3 describes a method of measuring the amount of light in the surrounding environment using a conventional optical sensor.
JP 2003-242440 A Japanese Patent No. 2706314 Japanese Patent Publication No. 1-145800

  However, the method described in Patent Document 1 is a method in which a plurality of images with different brightness are captured with respect to a recognition target object, and an image with the best character recognition result is extracted from the images. The condition is that the object stays in the image capturing area for a relatively long time. If the object to be recognized is a vehicle, it is necessary to divide the stopped state several times.

  On the other hand, in a parking lot or entrance / exit lane of a toll road where it is necessary to recognize the license plate by detecting that the vehicle has entered the lane and capturing images instantaneously, In order to capture an image, it is difficult to image a vehicle under a plurality of conditions at a time. Therefore, the technique of Patent Document 1 is not suitable for use in such a parking lot or a toll road.

  In addition, when the vehicle is completely stopped, the gate bar that restricts the vehicle's travel is usually in the way, and the license plate at the front of the vehicle may not be properly imaged. The image capturing position at a position such as a few meters before the gate bar is necessary to image while the vehicle is still moving, which is also the reason why the technique of Patent Document 1 cannot be used in a parking lot.

  Furthermore, the technique described in Patent Document 2 captures the front part of the vehicle entering the vehicle approach path, processes the captured image to read the license plate, and measures the brightness of the license plate image. Based on the result, a corrected aperture control signal is output to the imaging device to set the conditions for the next imaging, but it is sufficient that the vehicle always enters continuously. It is conceivable that the entrance of the image is interrupted, the surrounding environmental conditions change during that time, and the aperture value as an appropriate imaging condition becomes meaningless.

  The technique disclosed in Patent Document 2 uses an expensive lens with an automatic iris adjustment (auto iris) mechanism to appropriately adjust the iris and take an image before the imaging. The problem is that the number of characters on the license plate is adjusted to the brightness including the surrounding images, such as color differences, and as a result, the image of the license plate is too bright or too dark to read the license plate characters properly. It was invented as a method of eliminating the point.

  In any case, the invention of Patent Document 2 is based on the premise that the vehicle keeps entering at a constant interval in an ideal posture in a parking lot or a toll road. Was a difficult technology.

  As another means, a light amount sensor for measuring the light amount of the surrounding environment in the vicinity of the vehicle approach path described in Patent Document 3 (in the document, it is described as an optical sensor, but in other documents, an optical sensor for detecting a vehicle imaging position) In order to avoid confusion, a light quantity sensor is installed, and the measurement value of the light quantity sensor is always reflected in the imaging conditions. However, this also requires an expensive light quantity sensor. There is also a problem that the system configuration is complicated and expensive, such as communication connection between the camera and the imaging device.

  In addition, the installation position of the light quantity sensor is not necessarily close to the number plate imaging position, so if there is a difference between the light quantity measured by the light quantity sensor and the light quantity at the license plate, the license plate will have the appropriate brightness. There was also a problem that the image could not be taken.

  The present invention has been made to solve the above-described problems, and its technical problem is suitable for use in a parking lot installed outdoors, and an expensive light quantity sensor or To provide a license plate imaging system that can capture a license plate image with a stable brightness and contrast without using a lens with an auto iris mechanism or the like at a low cost.

(1) In order to solve the above technical problem, in the vehicle license plate imaging system according to claim 1 of the present invention, when the vehicle enters the imaging position, the camera receives from the image processing apparatus in advance. A license plate imaging system for a vehicle that images a license plate of a vehicle according to imaging setting conditions, recognizes the captured image in a plate image processing unit, and reads number information when the vehicle has not entered, Camera imaging setting condition updating means for providing an interval imaging mode for checking camera imaging setting conditions and deriving camera imaging setting conditions for the next and subsequent times from an image captured by the camera in the interval imaging mode, and updated And storage means for transmitting and storing camera imaging setting conditions to the camera.

(2) In the vehicle license plate imaging system according to claim 2 of the present invention, a target for determining imaging setting conditions in the interval imaging mode is installed in the imaging field of view of the camera, and the installation position is imaged in advance. The camera imaging setting condition is derived from the brightness of the image at the target installation position of the image stored in the processing unit and captured in the interval imaging mode.

(3) In addition, in the vehicle license plate imaging system according to claim 3 of the present invention, printing on the external casing of the trigger sensor in which the target to be imaged in the interval imaging mode is installed on both sides of the lane or one of the islands. It is configured by a mark or an external shape of the housing, and has at least a light color part and a dark color part.

(4) Further, in the vehicle license plate imaging system according to claim 4 of the present invention, when the vehicle detection means detects the vehicle entering the lane during the interval imaging mode operation, the normal mode is immediately started by interruption. It is characterized by returning to.

(5) In the vehicle license plate imaging system according to claim 5 of the present invention, the interval imaging mode is a time when a preset time has elapsed after imaging in the previous normal imaging or the previous interval imaging mode. It is characterized by starting every time.

(6) Further, in the vehicle license plate imaging system according to claim 6 of the present invention, the interval imaging mode is also performed when it is detected that the vehicle has passed during the previous normal imaging, and then a preset time is set. It is characterized by starting every time it has passed.

(7) In addition, the vehicle license plate imaging system according to claim 7 of the present invention is configured to capture the camera imaging setting condition set from the brightness obtained by measuring the target mark image captured in the interval imaging mode, and the conditions. The lightness measured by the license plate image is compared, and the lightness measurement parameters of the target mark image are updated and changed so that the average of a plurality of data nearest to the lightness of the license plate image is optimized.

(8) In the vehicle license plate imaging system according to claim 8 of the present invention, the condition to be changed in the camera imaging setting condition is only the camera electronic shutter speed, or the camera electronic shutter speed and the camera gain, When the brightness of the target mark imaged in the interval imaging mode is darker than the preset brightness, or when the brightness of the license plate image is preset, under the condition that the image at the slowest electronic shutter speed and the maximum camera gain value is dark When it is darker than the set brightness, the process shifts to the flash emission setting, and other camera imaging setting conditions in the flash emission setting state are constant conditions.

(9) Further, the vehicle license plate imaging system according to claim 9 of the present invention performs imaging under the condition of the maximum camera gain value in the interval imaging mode after the condition shifts to the flash emission setting. If the brightness of the image is appropriate under that condition, that is, if the brightness is darker than the preset brightness, the flash emission setting is maintained. If the brightness is brighter than the appropriate brightness, the flash emission mode is terminated and the flash is not emitted. It is characterized by shifting to the interval imaging mode at a slow electronic shutter speed.

  According to the means described in (1) above, since the interval imaging mode is provided, the brightness of the lane can be obtained by imaging in the interval imaging mode even when the surrounding environment changes while the vehicle passes for a while. Therefore, it is possible to take an image under appropriate conditions every time and maintain the license plate recognition rate with high accuracy even in an outdoor parking lot.

  Further, according to the means described in (2) above, since the position for judging the brightness from the image captured in the interval imaging mode is fixed, the environmental condition of the lane can be stably confirmed every time. Enable imaging under appropriate conditions.

  Further, according to the means described in the above (3), since the target is performed by the trigger sensor, it is not necessary to newly provide a special target member, and a seal is provided on the external housing of the trigger sensor indicating the license plate imaging position. Since it is possible to measure the environmental conditions at a position very close to the actual license plate position, and it is not necessary to enlarge the field of view in particular. While following the configuration and layout of the apparatus, stable environmental conditions can be measured and imaged without increasing costs.

  Further, according to the means described in (4) above, when the next vehicle enters during imaging or measurement processing in the interval imaging mode, a loop coil or a special one is introduced before the trigger sensor. Because the installed ingress sensor can detect it and immediately return to the original normal mode state by interruption, it can capture the number plate of the vehicle properly, so that the vehicle came during the interval imaging mode There is no problem that the vehicle cannot be imaged until the processing is completed.

  Further, according to the means described in the above (5), if the setting time (N minutes) of the interval imaging mode is set short, it is possible to immediately respond to a sudden environmental change.

  Further, according to the means described in (6) above, since the target is imaged and confirmed once every time the vehicle passes, it is possible to follow changes in the environment more finely.

Furthermore, according to the means described in the above (7), the dirt around the target mark is learned, and the brightness can be appropriately measured even with a mark that has gradually become dirty with the passage of time. Maintenance is not required, and as a result, operation at a low running cost is possible.

  In addition, according to the means described in (8) above, since the iris (aperture) is not included in the camera imaging setting condition, the camera setting is reflected instantaneously, and the change of the setting condition at a fine cycle is reliably reflected. In addition, an iris driving mechanism or the like is unnecessary, and the cost is reduced. That is, since the iris is mechanically opened and closed by the drive motor, a time delay occurs in the operation. When the vehicle enters immediately after the interval imaging mode, there is a possibility that the iris cannot follow. In addition, since the camera imaging conditions in the flash emission mode are fixed, it is possible to operate with a simple algorithm such as flash emission when dark and adjustment with electronic shutter and gain when bright.

  In addition, according to the means described in (9) above, flash emission in a state where the vehicle has not entered the lane may be misunderstood as a malfunction of the device. Therefore, the interval imaging mode can be implemented with a fine cycle without giving such a misunderstanding to the user or the parking lot administrator, and without worrying about the life of the flash bulb or the storage battery of light emission power, A system with high number recognition accuracy can be realized at low running costs while keeping costs down overall.

  As described above, according to the vehicle license plate imaging system of the present invention, a license plate image that can be appropriately recognized even in various environments such as outdoors or at night is installed in an outdoor parking lot. In addition to exhibiting the advantages that can be achieved, the cost of the apparatus can be kept low, and the economy that can be realized at a low running cost can be exhibited.

  In the following, an embodiment in which the vehicle license plate imaging system according to the present invention is used in a parking lot management apparatus will be described in detail with reference to the drawings. The embodiment described here is a preferred specific example of the present invention. Although various technically preferable limitations may be given, the technical scope of the present invention is not limited to these embodiments unless specifically described to limit the present invention.

  FIG. 1 is a block diagram showing the configuration of a vehicle license plate imaging system according to the present invention. As an example, a camera unit 1 installed in one exit lane of a parking lot, a trigger sensor 20, a checkout machine 30, an exit The connection state with the image processing apparatus 10 installed in a place different from the lane is shown, and although not shown, a similar camera unit, trigger sensor, and ticketing machine are installed in a separate entrance lane, and a similar entrance / exit One or two other lane configurations are installed, and one image processing apparatus 10 manages the states of a plurality of lanes.

  In addition, the plate image processing unit 11 constituting the image processing apparatus 10 has a character dictionary server in which a license plate character font and the like are registered, and is registered as being present when the vehicle enters and deletes data when entering (or An entry / exit server (moved to the history server as having already entered) and an image server for storing captured images of the entrance vehicle and the regularly registered vehicle are connected.

  The configuration shown in FIG. 1 will be described in more detail. 2 is a camera constituting the camera unit 1, 3 and 3E are flash control units and flashes, and 31 and 32 are loop coils and gate switches connected to the checkout machine 30. . The plate image processing unit 11 includes a plate cutout unit 14, a character recognition unit 15, a number matching unit 16, a matching determination unit 17, and a camera imaging setting unit 18. The camera imaging setting unit 18 is a camera. The matching determination unit 17 is connected to the above-described settlement machine 30 and each terminal via the external communication unit 13 via the control unit 12, and the settlement machine 30 further includes the trigger sensor 20 described above. Are also connected to the camera 2 of the camera unit 1.

  FIGS. 2A and 2B are a plan view and a side view illustrating the configuration of an exit lane OT showing an embodiment of a license plate imaging system according to the present invention, where the vehicle CR emits and receives light. The state located on the detection line TL (trigger line) of 20A, 20B is shown. In the figure, AL and AR are left and right islands constituting the exit lane OT, NP is a license plate of the vehicle CR, and 32 is a gate opening / closing device that opens and closes the gate bar 32T.

  As a basic operation, the operation is performed in the order of the processing units 14 to 18 shown in the plate image processing unit 11 of FIG. 1, but first, immediately before the vehicle CR reaches the trigger line TL as shown in FIG. When the vehicle CR arrives on the first loop coil 31A (same as in the state of FIG. 4), the settlement machine 30 detects that the first loop coil 31A is ON, and simultaneously with the image processing apparatus 10, the column 1K A loop coil ON signal is also output to the attached camera unit 1. At that time, if the camera unit 1 is performing an interval imaging mode described later, the camera unit 1 immediately stops.

  After that, the vehicle CR has reached the position shown in FIG. 2 and the trigger sensor light receiving side 20B detects that the infrared rays from the trigger sensor light emitting side 20A (a plurality of beams form a wall-like line on the trigger line) are shielded. Then, the trigger ON signal is transmitted to the checkout machine 30, and further the trigger ON is transmitted to the camera 2 of the camera unit 1, and the camera 2 at that time indicates whether flash 3F emission is necessary, the electronic shutter speed, and the camera gain. Imaging setting conditions such as the above are stored in advance in an internal memory (not shown), and the state of the lane OT is imaged with the latest imaging setting conditions.

  FIG. 3 is a state diagram of the exit lane OT showing an embodiment of the license plate imaging system according to the present invention. The imaging field when the trigger is ON, that is, the camera field 2H is viewed from the camera 2 side. It is indicated by a dotted line. At this time, the visual field and focus are adjusted at the time of installation of the camera 2 so that both the light emitting side 20A and the light receiving side 20B of the trigger sensor are within the camera visual field 2H.

  FIG. 6 is an operation flow of the image processing apparatus 10 according to the embodiment of the present invention. This will be described together with FIG. 1. An image captured by the camera 2 that has received the trigger ON in step S1 is the image processing apparatus 10 in step S2. And then immediately transferred to the plate cutout unit 14 of the plate image processing unit 11 in step S3 to cut out the portion of the license plate NP from the image of the camera field of view 2H, and further to step S4 Then, the character recognition unit 15 extracts characters from the clipped image and compares the characters with the data of the character dictionary server to recognize individual characters. In step S5, the vehicle CR corresponding to the recognized character data is loaded / unloaded. The number matching unit 16 searches for a specific number from the search candidates. The vehicle data is compared in detail to narrow down the best matching, and then the process proceeds to step S6, where the matching determination unit 17 determines the data number and admission time of the vehicle CR based on the matching determination result, and external communication is performed in step S7. The information is transmitted to the settlement machine 30 via the unit 13.

  The settlement machine 30 calculates a parking fee from the entry time of the approaching vehicle CR included in the matching determination data, and when the fee settlement is completed, a gate opening signal is transmitted to the gate opening / closing device 32, and then the vehicle enters. When the second loop coil 31B is passed, a gate closing signal is transmitted, and the participation of the vehicle CR is notified again to the image processing apparatus 10 in step S8. The entry / exit server performs processing such as deleting on-vehicle data by moving the vehicle CR or moving to another participation history server, and ends the entire processing. The above is an example of the operation when a normal vehicle participates.

  When such a lane OT is installed outdoors, the optimum imaging condition of the lane OT changes every moment due to changes in weather, daytime and night differences, and the influence of shadows from surrounding buildings. Conventionally, in order to follow this, a lens equipped with an auto iris mechanism is adopted to control the light amount of the entire camera field of view 2H to be constant, or a light amount sensor is separately provided in a part of the lane OT, and the detection value by the light amount sensor is obtained. Although it always transmitted to the camera 2 and the imaging conditions of the camera 2 were changed, these devices are expensive including elements that detect the amount of light delicately, leading to an increase in the cost of the entire system. It was.

  Further, in these methods, the image of the license plate NP is only adjusted from another part or the entire image. As a result, the image of the license plate NP is not captured at an appropriate brightness and is too bright. For this reason, the image itself of the license plate NP cannot be cut out properly, or a part of characters cannot be recognized.

  Therefore, in the present invention, in order to properly maintain the brightness of the image of the number plate NP portion of the captured image, the trigger input has elapsed for N minutes in the determination flow formed by steps S13 and S1 in the flow of FIG. Enter it at home? When not shifting to YES, it is supposed to shift to the imaging flow of the interval imaging mode indicated by the circle A. Next, FIG. 7 shows an imaging setting processing flow in the interval imaging mode in the embodiment of the present invention.

  In FIG. 7, in the first step S <b> 14, the camera control unit 12 of the image processing apparatus 10 transmits an instruction to shoot the camera (capture an image without trigger input) to the camera unit 1. The memory of the camera unit 1 (the memory of the camera 2) stores the imaging conditions at that time, performs color shooting under the conditions, and transmits the image to the image processing apparatus 10. When the camera control unit 12 of the image processing apparatus 10 receives the image in the next step S15, the process proceeds to step S16 and the plate image processing unit 11 cuts out the target mark TM at a preset position instead of normal number cutout.

  FIG. 5 shows a state diagram of the exit lane OT showing an embodiment of the target mark TM used in the present invention. In this example, the white and black or dark green target mark TM is used as a seal and the outer casing of the trigger sensors 20A and 20B. Affixed to the side facing the camera.

  Returning to the flow of FIG. 7, when the image of the target mark TM is cut out in step S <b> 16 (two in the example), the process proceeds to step S <b> 17 to measure the brightness of each target mark TM. FIG. 8 is an explanatory diagram of the lightness determination method of the target mark TM according to the embodiment of the present invention. The shade state is extracted as the lightness from the image of the target mark TM as in the embodiment, and the horizontal length is also shown. Measure and measure the amount of each part w, b, c, d, e. That is, the duty of the waveform indicating the light and dark levels, the maximum value, the minimum value, the difference between the maximum and minimum, and the like of the level are measured to determine whether or not the brightness is appropriate.

  According to the determination in step S18, <mark image brightness OK? If> is NO (too bright or too dark), the camera imaging setting is changed in step S19 and the changed imaging setting is transmitted to camera 2 in step S20. Rewrite the memory. The image processing apparatus 10 transmits a color shooting instruction again and repeats the above-described flow. In step S18, <the brightness of the mark image is OK? If YES (appropriate image) is obtained for>, the process proceeds to step S21 where the camera imaging setting is also stored on the image processing apparatus 10 side, and imaging in the interval imaging mode is terminated.

  When the vehicle CR enters the first loop 31A as shown in FIG. 4 during the processing of the interval imaging mode, the flow of the interval imaging mode immediately jumps to the end in step S22. In other words, the program is programmed so that the forcible termination of the interval imaging mode is performed by an interrupt process depending on the state of the first loop coil 31A. (Point of claim 4)

  In this way, the mode is shifted to the interval imaging mode, and the last best imaging setting condition when shooting with the camera 2 is stored in the memory of the camera 2, so that the license plate has the appropriate brightness at the next imaging. NP can be imaged (point of claim 1). Further, by setting the target mark TM for measuring the brightness within the camera field of view 2H, a system for shooting a color can be made in the same flow as in normal imaging (point of claim 2). Furthermore, the target mark TM at the time of shooting is set to the trigger sensor 20A. Since it is performed with a sticker affixed to the exterior of the case of 20B, brightness measurement and determination can be performed appropriately (point of claim 3). In addition, the frequency of shooting in the interval imaging mode is determined to be N minutes in advance, and the N minutes may be set quite frequently depending on the degree of environmental change, and it is possible to cope with sudden environmental changes. (Point of claim 5).

  In step S9 in the latter half of the flow shown in FIG. 6, after the image processing apparatus 10 receives the completion of participation in the lane OT and updates the entry / exit data, it is used for image processing at this time in step S10. The brightness of the image of the license plate NP is measured by the same method as shown in FIG. 8, and if the measurement result is not optimal, the brightness of the license plate NP is adjusted to the optimal brightness in step S11. In step S12, the camera imaging setting is transmitted from the camera control unit. However, this is not only the result of the plate image brightness measurement at that time, but also the same tendency (brighter or darker) multiple times in succession. (Tendency) A method may be used in which the camera imaging setting is determined from the plate image and transmitted only when the shifted state continues.

  Next, FIG. 9 shows the relationship between the illuminance of the surrounding environment of the lane OT and the electronic shutter speed in the embodiment of the present invention. In this example, the electronic shutter speed is assumed to be a camera 2 that can be set in a plurality of steps. At the same time, as the camera gain, for example, the amplifier gain for amplifying the input light at the time of imaging to the CCD element is also changed. In order to simplify the description, the case where the brightness of the image is adjusted only by the electronic shutter speed will be described, and the camera gain and the iris (iris) are fixed.

  As shown in FIG. 9, the flash 3F in FIG. 1 is set to adjust the brightness of the image by changing the electronic shutter speed without emitting light if the illuminance is more than a certain illuminance f. It is possible to slow down from the approach speed of the vehicle CR to the lane OT to an electronic shutter speed that does not blur the image. When the illuminance becomes darker than that, the electronic shutter speed is fixed and the flash 3F is controlled to emit light while being synchronized with the electronic shutter.

  Here, there is a method of changing the electronic shutter speed while the flash 3F is in the light emission state. However, the amount of light of the flash 3F is strong to some extent, and the position of the license plate NP is normally expected to be gathered almost in the center of the camera field of view 2H. Therefore, if the flash light always illuminates the license plate NP, the license plate NP can be used regardless of whether the surrounding environment is dark or dark. Can properly capture an image.

  Therefore, in the embodiment of the present invention, imaging is performed under the same conditions with the electronic shutter speed set to a fixed value when the flash 3F emits light from a somewhat dark environment to a completely dark state. Accordingly, the above-described color shooting in the interval imaging mode does not emit the flash 3F even in a somewhat dark environment, and if the result is too dark as shown in FIG. 8, the camera imaging setting condition is the flash emission condition. Therefore, since the flash 3F is not fired in the color shooting in the interval imaging mode, the life of the flash 3F is not reduced, and the period of the color shooting in the interval imaging mode (N-minute interval). ) Can be made frequently, and follow-up to surrounding environmental changes can be secured. (Points of Claims 8 and 9) In FIG. 8, the horizontal axis indicates the illuminance (Lux). In the embodiment of the present invention, the correlation between the brightness of the license plate (Brightness) and the illuminance of the surroundings is shown in advance. In this table, illuminance is explained because lightness changes in proportion to illuminance. Further, the electronic shutter speed is the exposure time, and in terms of exposure time, the vertical axis of the table of FIG. 8 indicates that the exposure time is shorter as it goes up and the exposure time is longer as it goes down.

  FIG. 10 shows an operation flow of the image processing apparatus in the second embodiment of the present invention. In FIG. 10, steps S31 to S42 in the first half are the same as steps S1 to S12 shown in FIG. 6 described above. However, after the camera imaging setting transmission by the camera control unit 12 in step S42, the circle A in FIG. The target mark TM is immediately captured and the best brightness of the target mark image at that time is measured, and then the actual appearance before that in step S44. The image of the target mark TM may become dirty due to aging, based on the brightness of the image of the license plate NP of the vehicle CR and the statistics and transition of the best brightness of the target mark image in the multiple interval imaging modes. It is possible to detect fading and to update the condition of the determination parameter at the time of brightness measurement in step S45 To become.

  That is, the optimum condition of the ratio of w and b in FIG. 8 was initially w = b, but since the white part gradually became dirty, w was measured to be small, and as a result, the license plate NP In the case where the frequency at which the brightness of the image is captured brighter is increased, for example, w × 1.1 = b can be updated to the optimum condition. Similarly, it is also effective to update the absolute value of the maximum / minimum difference c at the optimum contrast or the maximum value e of the white portion to be small. (Point of claim 7)

  In this embodiment, the target for imaging in the interval mode is the target mark TM provided on the exterior body of the trigger sensors 20A and 20B on both sides of the lane OT, but these two target marks TM and TM are used. If the optimum conditions are inconsistent with each other, the average value may be taken, or the data of either target mark TM may be basically adopted, and the surrounding environment What is necessary is just to set suitably according to a state.

  Moreover, although the layout which images the license plate TM of the front part of the vehicle CR is shown in the embodiment, even in the case of the layout which images the license plate of the rear part of the vehicle CR, the shielding state of the trigger sensors 20A and 20B is shown. In the system that captures an image from the rear of the vehicle CR at the timing when the release is made, the technology of the present invention can be used as it is.

The block diagram which showed the structure of the whole license plate imaging system which concerns on this invention. (1) is the top view which showed the structure of the exit lane which shows the Example of the license plate imaging system which concerns on this invention, (2) is the side view. The state figure of the exit lane which shows the Example of the number plate imaging system which concerns on this invention. (1) is the top view which showed the structure of the exit lane which shows the Example of the interruption operation | movement in this invention, (2) is the side view. The perspective view of the exit lane part which shows the Example of the target mark of this invention. FIG. 3 is an operation flowchart of the image processing apparatus according to the embodiment of the present invention. The flowchart of the imaging setting process in the Example of this invention. Explanatory drawing of the lightness determination method of the target mark in the Example of this invention. The figure showing the relationship between the illumination intensity and the electronic shutter speed in the Example of this invention. The operation | movement flowchart of the image processing apparatus in 2nd Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Camera unit 2 Camera 2H Camera visual field 3F Flash 10 Image processing part 11 Plate image processing part 12 Camera control part 14 Plate clipping part 15 Character recognition part 16 Number matching part 17 Matching determination part 18 Camera imaging setting part 20A, 20B Trigger sensor 30 Settlement machine 31A, 31B Loop coil CR Vehicle NP License plate AL, AR Island OT Exit lane TM Target mark

Claims (9)

When the vehicle enters the imaging position, the camera images the vehicle license plate in accordance with the imaging setting conditions received from the image processing apparatus in advance, and the captured image is character-recognized by the plate image processing unit to obtain the number information. A vehicle license plate imaging system for reading
Camera imaging setting that provides an interval imaging mode for checking camera imaging setting conditions when the vehicle is not approaching, and derives the camera imaging setting conditions for the next and subsequent times from images captured by the camera in the interval imaging mode A vehicle license plate imaging system comprising: condition updating means; and storage means for transmitting and storing the updated camera imaging setting conditions to the camera.   A target for determining imaging setting conditions in the interval imaging mode is installed in the imaging field of view of the camera, the installation position is stored in advance in the image processing unit, and the image of the target installation position of the image captured in the interval imaging mode is stored. The vehicle license plate imaging system according to claim 1, wherein camera imaging setting conditions are derived from the brightness of the vehicle.   The target to be imaged in the interval imaging mode is configured with a print mark on the external housing of the trigger sensor installed on both sides of the lane or one of the islands, or the external shape of the housing, and at least a light color portion and a dark color portion The vehicle license plate imaging system according to claim 2, further comprising:   4. The vehicle license plate according to claim 1, wherein when the vehicle detection means detects vehicle entry into the lane during the interval imaging mode operation, the vehicle license plate immediately returns to the normal mode upon interruption. Imaging system.   5. The interval imaging mode is activated every time when a preset time has elapsed after imaging in the previous normal imaging or the previous interval imaging mode. 6. License plate imaging system for vehicles.   The interval imaging mode is also performed when it is detected that the vehicle has passed during the previous normal imaging, and is activated every time a preset time has elapsed thereafter. Or the license plate imaging system for vehicles of 5.   Compare the camera imaging setting conditions set from the brightness measured from the target mark image captured in the interval imaging mode with the brightness measured from the license plate image captured under those conditions, and multiple data closest to the brightness of the license plate image The number plate imaging system for a vehicle according to claim 1, 2, 3, 4, 5 or 6, wherein the parameter of brightness measurement of the target mark image is updated and changed so that the average of .   The conditions to be changed in the camera imaging setting conditions are only the camera electronic shutter speed, or the camera electronic shutter speed and the camera gain, the slowest electronic shutter speed, and the dark image at the maximum camera gain. When the brightness of the target mark imaged in the interval imaging mode is darker than the preset brightness, or when the license plate image is darker than the preset brightness, the process proceeds to the flash emission setting, and other flash emission settings are displayed. 8. The vehicle license plate imaging system according to claim 1, wherein the camera imaging setting condition is a constant condition.   In the interval imaging mode after the condition has shifted to the flash emission setting, imaging is performed under the condition of the maximum camera gain value, and when the brightness of the image is appropriate under that condition, that is, when the brightness is darker than the preset brightness 9. When the flash emission setting is maintained and the brightness is brighter than an appropriate brightness, the flash emission mode is terminated and the interval imaging mode at the slowest electronic shutter speed without flash emission is entered. License plate imaging system for vehicles as described in 4.

Images