* NOTICE*
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`JPO and INPIT are not responsible for any damages caused bythe useofthis translation.
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`1. This document has been translated by computer. So the translation may notreflect the original precisely.
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`2.“ shows a word which cannotbetranslated.
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`3.
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`In the drawings, any words are nottranslated.
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`Patent Number
`
`JP2005338941A
`
`Bibliography
`
`(19) [Publication country] JP
`
`(12) [Kind of official gazette] A
`
`(11) [Publication number] 2005338941
`
`(43) [Date of publication of application] 20051208
`
`(54)[Title of the invention] METHOD AND DEVICE FOR DETECTING VISIBILITY
`
`(51) [International Patent Classification 7th Edition]
`GO8G 1/00
`GO8G 1/052
`G08G 1/16
`
`[Fl]
`GO8G
`
`1/00
`
`J
`
`GO8G=1/052
`
`GO8G
`
`1/16
`
`D
`
`(21) [Application number] 2004153471
`
`(22) [Filing date] 20040524
`
`(71) [Applicant]
`
`[Name] FUJITSU LTD
`
`(72) [Inventor]
`
`[Full name] NAGAI KAZUYOSHI
`
`[Full name] OGURA HIROSHI
`
`Abstract
`
`(57) [Overview]
`
`PROBLEM TO BE SOLVED: To provide a method and a device for detecting visibility
`
`capable of detecting deterioration of visibility owing to bad weather, etc. and detecting a
`
`dangerous vehicle that is stopping, running slowly, etc.
`
`SOLUTION: The device for detecting visibility comprises: a vehicle detecting part 131
`
`

`

`that finds the position and the speed of a vehicle from a beat signal of a reflected wave;
`
`a speed judging part 132 that makes judgment of a speed of the vehicle detected by the
`
`vehicle detecting part 131; a region difference extracting part 134 that inputs an image
`
`photographed by a camera 220 and measures the region of the vehicle; a region
`
`reduction ratio calculating and judging part 135 that finds a reduction ratio of the region
`
`of the vehicle in a predetermined time from the region of the vehicle and the region of
`
`the vehicle after the predetermined time; and a visibility distance judging part 136 that
`
`measures a visibility distance from the distance from the vehicle in the respective times
`
`and the reduction ratio of the region of the vehicle. This enables visibility deterioration
`
`and a dangerous vehicle to be detected. A method for detecting visibility using this
`
`visibility detecting device may also be provided.
`
`Claim
`
`[Patent Claims]
`
`[Claim 1]
`
`A radar signal input step of inputting the reflected wave beat signal reflected by the radio
`
`wave ;
`
`A target object detection step of analyzing the reflected wave beat signal and
`
`determining a position and a moving speedof the target object ;
`
`A captured image input step for inputting a captured image obtained by imaging a
`
`predetermined range including the radio waveirradiation position in synchronization with
`
`the irradiation of the radio wave;
`
`A target region measuring step of comparing an image component of an image position
`
`of the target and an image component of another region from the inputted captured
`
`image, and measuring an area in the image occupied by the target;
`
`A moving position measuring step of inputting the reflected wave beat signal after a
`
`predetermined time and determining the position of the target;
`
`A moving target object region measuring step of inputting the captured image after a
`
`predetermined time and measuring an area in the image occupied by the target object
`
`after the predetermined time according to a position after a predetermined time of the
`
`target object ;
`
`A target object region reduction ratio calculating step of determining a reduction ratio of
`
`a region of the target object from an area when the target object is detected and an area
`
`occupied by the target object after the predeterminedtime ;
`
`A visibility distance measuring step of measuring a visibility distance from a distance to
`
`the target at each time and a reduction ratio of an area of the target;
`
`

`

`The method for detecting the degree of visibility includes :.
`
`[Claim 2]
`
`The visibility detection method according to claim 1, wherein :
`
`A region change rate preparation step of setting a size of a specific region according to
`
`a reference distance at the time of good visibility and preparing a region change rate
`
`value obtained by obtaining a change rate of the size of the specific region according to
`
`a change of the distance;
`
`A visibility reduction determination step of determining a visibility reduction according to
`
`a distance to the target at each time, a reduction ratio of an area of the target, and the
`
`area change rate value ;
`
`A moving speed determining step for determining whether or not the moving speed of
`
`the target satisfies a constant speed ;
`
`A transmission step of transmitting a captured image obtained by imaging within the
`
`predetermined range to a road managerterminal ;
`
`Preparation,
`
`The visibility detection method according to claim 1, wherein when it is determined in the
`
`visibility decrease determination step that the visibility decreases, the transmission step
`
`transmits a captured image in which the target object determined not to satisfy a
`
`constant speed in the movement speed determination step is transmitted.
`
`[Claim 3]
`
`A radar signal
`
`input means for inputting a reflected wave beat signal reflected by
`
`irradiation of radio waves ;
`
`A target object detecting means for analyzing the reflected wave beat signal and
`
`determining a position and a moving speed ofthe target;
`
`A captured image input meansfor inputting a captured image obtained by imaging within
`
`a predetermined range including the radio waveirradiation position in synchronization
`
`with the irradiation of the radio wave ;
`
`A target region measuring means for comparing an image component of an image
`
`position of the target and an image component of another region from the inputted
`
`captured image and measuring an area in the image occupied by the target;
`
`A region reduction ratio calculating means for determining a reduction ratio of a region
`
`at a predetermined time of the target object from an area when the target object is
`
`detected by the target object region measuring means and an area occupied by the
`
`target object after a predetermined time ;
`
`A visibility distance measuring means for measuring a visibility distance from a distance
`
`to the target at each time and a reduction ratio of an area of the target;
`
`

`

`A visual range detection device characterized by preparation ***.
`
`Description
`
`[Detailed description of the invention]
`
`[Technical field]
`
`[0001]
`
`The present invention relates to a visibility detection method and a visibility detection
`
`apparatus which are installed on a road and detects visibility, and more particularly, to a
`
`visibility detection method and a visibility detection apparatus which detect a dangerous
`
`vehicle such as stop and slow, and detect a decreasein visibility due to a weather failure
`
`or the like.
`
`[Background of the Invention]
`
`[0002]
`
`Conventionally, in the case of a road on which a defectin visibility due to a snowstorm
`
`or a dark fog occurs, it is effective to provide information on an obstacle (in particular, a
`
`stopped vehicle or a low-speed vehicle) in front of the driver and a visibility state
`
`indicating a state of the field of view in advance on a display panel or the like for the
`
`purposeof safe traveling, and to urge attention.
`
`[0003]
`
`For this reason, the road manager placesthe visibility meter, the vehicle sensor, and the
`
`like on the side of the road and detects the visibility distance and the dangerous vehicle
`
`(stop / low-speed vehicle).
`
`[0004]
`
`On the other hand, at the time of a dangerous vehicle and a loss ofvisibility, a road
`
`manager sometimes dispatches a patrol car or a management vehicle to a site as
`
`necessary for the purpose of avoiding danger or grasping a state of a field, and acamera
`
`is installed for monitoring only to remotely monitor an image at a site.
`
`[0005]
`
`In order to measure the degreeof visibility, there is a visibility detection device which
`
`measuresvisibility by measuring transmittance using a transmittance meter comprising
`
`a projector and a photodetector which are arranged at a predetermined distance from
`each other.
`
`[0006]
`
`Further, as shown in FIG. 8, there is also a visibility state measuring apparatus (visibility
`
`detecting apparatus) which measuresvisibility using a change rate of chromaticity of an
`
`

`

`object placed at a predetermined distance.
`
`[0007]
`
`The viewing state measuring device shown in FIG. 8 includes a television camera 1, an
`
`indicator 2, and a processing device 3. The index 2 is provided at a position spaced apart
`
`by a predetermined distance between the television camera 1 and the atmosphere, and
`
`has 2 areas A and B having different chromaticity. On the basis of an image signal from
`
`a television camera 1, a processing device 3 obtains a degree of difference in
`
`chromaticity between the 2 areas A andBof an index 2 at a position separated by the
`
`prescribed distance.
`
`[0008]
`
`In this conventional viewing state measuring apparatus, an index 2 is picked up by a
`
`television camera 1, and a degreeof difference in chromaticity between the 2 regions A
`
`and B of an index 2 at a position separated by the prescribed distance is obtained on the
`
`basis of an image signal from a television camera 1 by a processing device 3. Further,
`
`the processing device 3 obtains the degree ofvisibility from the ratio of the calculated
`
`degreeto the degreeof the difference between the chromaticity of the 2 areas A and B
`
`of the index 2 in a state where the influence of the turbidity of the air is substantially not
`
`affected.
`
`In this way, a visual
`
`recognition state was measured without using a
`
`transmittance meter (see, for example, Patent Document 1).
`
`[Patent document 1]JP 2002-14038A
`
`[Disclosure of invention]
`
`[Problem to be solved by the invention]
`
`[0009]
`
`However, in such a conventional visibility detection device, since an index which serves
`
`as a criterion for the visibility measurement is fixed and is installed, there is a problem
`
`that the visibility cannot be accurately calculated due to the influence of dirt, damage,
`
`snow accretion, and the like.
`
`[0010]
`
`To provide a vehicle sensor for detecting a dangerous vehicle, a visibility meter for
`
`measuring the visibility, and a camera for monitoring the image in order to provide
`
`obstacle information for safe running and visibility state information. To solve the
`
`problems that a system is constructed by configuring an independent device for each
`
`function, a high-order device for integrating and managing these devices is required, a
`
`configuration device is complicated, a cost is increased for introducing and maintaining
`
`a system, and management becomes complicated.
`
`[0011]
`
`

`

`The present invention has been made in order to solve the above problem, and it is an
`
`object of the present invention to provide a method and an apparatus for measuring the
`
`visibility of a vehicle, which can measurethe visibility without being affected by a specific
`
`damage, snow accretion, or the like, by changing the index to be a vehicle passing
`
`through a road without limiting the visibility. To provide a visibility detection method and
`
`a visibility detection device capable of simultaneously detecting a dangerous vehicle.
`
`[Means for solving the problem]
`
`[0012]
`
`The visibility detection method and the visibility detection device of the present invention
`
`receive the reflected wave beat signal, analyze the reflected wave beat signal, determine
`
`the position and the moving speed of the target object, and input the captured image,
`
`and the image component of the image position of the target object and the image
`
`componentof the image position of the target object. The image componentof the other
`
`region is compared with the image componentof the other region, an area in the image
`
`occupied by the target object
`
`is measured, a position of the target object after a
`
`predeterminedtime is determined, and an area in the image occupied by the target object
`
`after the predetermined time is measured. In this constitution, a reduction ratio of a region
`
`of the target object is obtained from an area when the target object is detected and an
`
`area occupied by the target object after the predetermined time, and a visibility distance
`
`is measured from a distance to the target object at each time and a reduction ratio of an
`
`area of the target object.
`
`[0013]
`
`This arrangement detects the position of the object at 2 times and the region within the
`
`image, and depends on the distance of the object and the reduction ratio of the region.
`
`It
`
`is possible to measure the visibility distance and to provide an accurate visibility
`
`measure in the measurement by a change in the time and distance, without limiting the
`
`index as a criterion for the visibility measurement to a specific object.
`
`[0014]
`
`Further, the visibility detection method and the visibility detection apparatus according to
`
`the present invention are characterized in that the target is a moving vehicle passing
`
`through the imaging range.
`
`[0015]
`
`With this configuration, by setting an index which is a criterion of the visibility
`
`measurement as a vehicle passing through a road, the index is not fixed to a specific
`
`object and can be changed sequentially, and it
`
`is possible to perform the visibility
`
`

`

`measurementwithout being affected by a specific failure, snow accretion, or the like.
`
`[0016]
`
`Further, the visibility detection method according to the present invention is characterized
`
`in that the measurement of an area within the image occupied by the target object is
`
`measured by comparing a luminance of an image position of the target object with a
`luminance of another area.
`
`[0017]
`
`With this configuration, it is possible to more favorably determine the area reduction of
`
`the target object due to the disturbance of the image such as bad weather.
`
`[0018]
`
`In addition, according to the present invention, there is provided a method for detecting
`
`a degree of visibility, comprising : preparing a region change rate value obtained by
`
`determining a rate of change of a size of a specific region based on a referencedistance;
`
`and determining a decreasein visibility according to a distance from the target object at
`
`each time period, a reduction rate of an area of the target object, and the region change
`rate value.
`
`[0019]
`
`By this arrangement, it is possible to determine a decreasein visibility accurately, since
`
`it can be determined by comparing the visibility drop with the value of the reference area.
`
`[0020]
`
`In addition,
`
`the visibility detection method according to the present
`
`invention is
`
`characterized in that, at the time of occurrence of the degreeofvisibility reduction, it is
`
`judged whether or not the moving speed of the target object satisfies a constant speed,
`
`and a captured image in which the target object which does not satisfy the constant
`
`speed is imaged is transmitted to the road manager terminal.
`
`[0021]
`
`With this configuration, since the image of the dangerous vehicle is transmitted to the
`
`road manager terminal at the time of lowering the visibility,
`
`it is possible to accurately
`
`check the situation of the detection area even if the road manager does not perform the
`
`patrol or the like at
`
`the site, and it
`
`is possible to quickly perform appropriate
`
`correspondence.
`
`[0022]
`
`In addition, the visibility detection device of the present invention is characterized in that
`
`the imaging range after a predetermined time has elapsed in accordancewith a position
`
`and a moving speed at whichthe target is detected.
`
`

`

`[0023]
`
`According to this configuration, since the imaging range is changed according to the
`
`position and the moving speed when thetarget object is detected, it is possible to capture
`
`the target vehicle and capture an image, and thusit is possible to expand the visibility
`
`determination range.
`
`[Effect of the Invention]
`
`[0024]
`
`The object detection step of determining the position and speed of the target object from
`
`the reflected wave beat signal and the target object region measuring step of measuring
`
`the region of the target object from the input captured image are performed. An object
`
`region reduction ratio calculating step of determining a reduction ratio of a region at a
`
`predetermined time of the target object from a region of the target object and a region of
`
`a target object after a predetermined time, and a visibility distance measuring step of
`
`measuring a visibility distance from a distance to the target object at each time and a
`
`reduction ratio of an area of the target object are provided. To provide a visibility detection
`
`method and a visibility detection device capable of measuring visibility without being
`
`affected by a specific breakage or snow accretion, etc., by changing an index as a vehicle
`
`passing a road, etc., without
`
`limiting an index serving as a reference of visibility
`
`measurementto a specific object.
`
`[Best modefor carrying out the invention]
`
`[0025]
`
`Hereinafter, embodiments of the present invention will be described with reference to the
`
`drawings.
`
`[0026]
`
`(First embodiment)
`
`FIG.
`
`1
`
`is a block diagram showing a configuration of the visibility detection apparatus
`
`according to the 1 embodiment of the present invention. FIG. 2 is a system configuration
`
`diagram including a visibility detection device.
`
`[0027]
`
`As shownin FIG. 1, the visibility detection device 100 includes a radar signal processing
`
`unit 110, an image signal processing unit 120, and a detection processing unit 130, and
`is connected to the millimeter wave radar 210 and the camera 220.
`
`[0028]
`
`As shown in FIG. 2, the visibility detection device 100 may include a communication
`
`control unit 150, and is connectedto the display guide 300 and the management server
`400 via a communication line.
`
`

`

`[0029]
`
`The display guide 300 is installed in front of the road than the detection area of the
`
`visibility detection device 100, and the detection result of the visibility detection device
`
`100 is displayed. The management server 400 is installed in a remote management
`
`office remote from the visibility detection device.
`
`[0030]
`
`Further, the management server 400 includes a server communication control unit 420
`
`which communicates with the visibility detection device 100, a server control unit 420
`
`which controls the entire management server 400, and a server display unit 430 which
`
`displays information under the control of the server control unit 410.
`
`[0031]
`
`The millimeter wave radar 210 and the camera 220 areinstalled at high positions on the
`
`side of the road and are mounted at an angle for detecting the vehicle A moving in the
`
`detection area. Further, the millimeter wave radar 210 irradiates the detection area with
`
`an electric wave, receives the reflected wave beat signal, and outputs the reflected wave
`
`beat signal to the visibility detection device 100. The camera 220 captures an image of
`
`a predetermined range within the detection area and outputs the captured image signal
`
`to the visibility detection device 100.
`
`[0032]
`
`Here, the millimeter wave irradiation range of the millimeter wave radar 210 is within an
`
`imaging range of the camera 220, and the camera 220 performs an imaging processin
`
`synchronization with the millimeter wave irradiation of the millimeter wave radar 210.
`
`Conversely, it is if it says.
`
`A camera 220 captures an image of a range including the millimeter wave irradiation
`
`position of the millimeter wave radar 210. In addition, although a millimeter wave radar
`
`which is superior in detection performance to other sensors than other sensorsis used
`
`for detecting the distance and the speed of the vehicle, the present invention is not limited
`thereto.
`
`[0033]
`
`Further,
`
`the radar signal processing unit 110 of the visibility detection device 100
`
`receives the reflected wave beat signal from the millimeter wave radar 210, performs
`
`signal processing, and outputs the signal processing to the detection processing unit 130.
`
`The image signal processing unit 120 inputs an image signal in which the predetermined
`
`range is captured by the camera 220, performs signal processing, and outputs the signal
`
`processing to the detection processing unit 130.
`
`

`

`[0034]
`
`The detection processing unit 130 includes a vehicle detection unit 131, a speed
`
`determination unit 132, a vehicle identification unit 133, an area difference extraction unit
`
`134, an area reduction ratio calculation / determination unit 135, and a visibility distance
`
`determination unit 136.
`
`[0035]
`
`The vehicle detection unit 131 receives a signal from the radar signal processing unit
`
`110, performs signal analysis, obtains position information and speed information
`
`(hereinafter, referred to as target information) of the target, and detects a vehicle as a
`
`target. The speed determination unit 132 determines the speed of the vehicle detected
`
`by the vehicle detection unit 131 and, when the speed is equal to or lower than a constant
`
`speed (the dangerous vehicle determination speed Ve),
`
`regards the vehicle as a
`
`dangerous vehicle (low-speed and stopped vehicle).
`
`[0036]
`
`The vehicle identification unit 133 identifies whether the vehicle detected by the vehicle
`detection unit 131 and the vehicle detected this time are the same vehicle or not. If the
`
`vehicle is not a detected vehicle, the vehicle is identified as a new vehicle. For example,
`
`in this identification, the position of the vehicle is predicted from the detected original
`
`position and speed of the vehicle, and the position of the vehicle is predicted by
`
`comparing the predicted position with the actually detected position of the vehicle,
`
`thereby determining whether the vehicle is the same vehicle or not.
`
`[0037]
`
`The region difference extracting unit 134 compares the luminance of the image position
`
`of the vehicle with the luminance of another region from the captured image input from
`
`the image signal processing unit 120, obtains an area in which the luminance of the
`
`vehicle detection position and the luminance difference of the surrounding area are within
`
`a constant luminancedifference, and extracts this area as an area (hereinafter referred
`
`to as a target vehicle area) occupied by the target vehicle.
`
`[0038]
`
`FIG. 3 is an image diagram of image processing of the target vehicle area. As shown in
`
`FIG. 3, a luminance of an image position of a vehicle is obtained, a position having a
`
`luminance within a predetermined difference from the luminance is searched around the
`
`position, and an area having the luminance within the constant luminance difference is
`
`extracted as the target vehicle area.
`
`[0039]
`
`The area reduction ratio calculation / determination unit 135 compares the number of
`
`

`

`pixels of the target vehicle area previously extracted by the area difference extraction
`
`unit 134 (hereinafter referred to as "target vehicle area") and the target vehicle area
`
`extracted this time (after the predetermined time), and calculates the area reduction ratio
`
`(due to the movementof the vehicle) at a predetermined time. Further, a theoretical area
`
`reduction rate is also obtained from the distance to the detected vehicle and the distance
`
`to the vehicle to be detected (after a predetermined time).
`
`[0040]
`
`The visibility distance determination unit 136 measures the visibility distance from the
`
`distance to the vehicle at each time and the actual area reduction ratio of the vehicle. In
`
`addition, the theoretical area reduction ratio and the actual area reduction ratio are
`
`compared, and it is determined whether or not the difference between the theoretical
`
`area reduction ratio and the actual area reduction ratio is reduced only by the movement
`
`of the vehicle, thereby determining the degree ofvisibility reduction.
`
`[0041]
`
`Inthe example of FIG. 3, the position of the vehicle detected by the first vehicle detection
`
`is a distance of 20 m, and the luminance of the detected vehicle position and the number
`
`of pixels within the predetermined luminancedifference (target vehicle area) are 1300.
`
`Next, when the vehicle is detected,
`
`if the target vehicle area is 700 at a position of a
`
`distance of 50 m, the reduction ratio in this case is 700/1300=53.8%. This reduction ratio
`
`is compared with a theoretical reduction ratio, and it is judged whether or not the range
`
`is reduced only by the distance. Place
`
`After a fixed time, when the vehicle was detected, the vehicle area was 100 at a position
`
`of a distance of 400 m. In this case, the reduction ratio is 400/1300=30.8%. Further, as
`
`described above, this reduction ratio and the theoretical reduction ratio are compared,
`
`andit is determined whether or not the range is reduced by only the distance. Thus, it is
`
`possible to determine a decreasein visibility.
`
`[0042]
`
`Next, a flow chart of the radar signal processing unit 110, the image signal processing
`
`unit 120, and the detection processing unit 130 in the visibility detection device 100 will
`
`be described with reference to FIGS. 4 5, and 6. Since the millimeter wave radar 210,
`
`the radar signal processing unit 110, and the camera 220 and the image signal
`
`processing unit 120 are closely related to each other, they will be described in the same
`flowchart.
`
`[0043]
`
`As shownin FIG. 4, in the millimeter wave radar 210 and the radar signal processing unit
`
`

`

`110, first, the millimeter wave radar 210 irradiates a wavein the detection area, and the
`
`millimeter wave radar scan operation is performed (s 11), and the radarsignal processing
`
`unit 110 performs signal processing of the beat signal (s 12). Here, the distance (target
`
`distance = R) to the target object (vehicle A) is calculated (s 13), and further, the speed
`
`of the target object (target speed = V) is calculated (s 14), and the processing result
`
`(target information) is output to the detection processing unit 130.
`
`[0044]
`
`Also, as shown in FIG. 5, the camera 220 and the image signal processing unit 120
`
`capture an image of a predetermined range within the detection area of the camera 220
`
`(S 21) and output the image signal to the visibility detection device 100.
`
`In the image
`
`signal processing unit 120 of the visibility detection device 100, an image signal output
`
`from the camera 220 is input (s 22). When an image signal is input, a luminance of an
`
`image is calculated (S 23), and a processing result is output to the detection processing
`unit 130.
`
`[0045]
`
`A millimeter wave radar 210 and a camera 220 synchronously perform a millimeter wave
`
`radar scanning operation and a video imaging at predetermined time intervals, and a
`
`radar signal processing part 110 and an image signal processing part 120 perform
`
`processing accordingly, and outputs a processing result to a detection processing part
`
`130. Although this interval is actually a very short time, in the example of FIG. 3, a case
`in which the distance to the vehicle is 20 m and a case in which the distance to the
`
`vehicle is 50 m in the example of FIG. 100 is taken.
`
`[0046]
`
`Next, as shown in FIG. 6,
`
`the detection processing unit 130 receives the target
`
`information output from the radar signal processing unit 110 from the vehicle detection
`
`unit 131 and detects the vehicle as the target object
`
`(S 31). Here,
`
`the speed
`
`determination unit 132 determines whether or not the target speed Vn of the vehicle that
`
`has been input this time is equal to or less than a predetermined dangerous vehicle
`
`determination speed Ve (s 32), and detects that the vehicle is a dangerous vehicle (a
`
`stop / low-speed vehicle) when the vehicle speed is lower than or equal to the dangerous
`
`vehicle determination speed Ve (s 33).
`
`[0047]
`
`Further, the vehicle identification unit 133 assigns vehicle identification information to the
`
`vehicle detected this time (s 41), and determines whether the vehicle detected this time
`
`is a new vehicle or a vehicle already detected (s 42).
`
`[0048]
`
`

`

`If the detected vehicle is a newly detected vehicle, the area difference extracting unit 134
`
`extracts the luminance of the position Rn at which the current vehicle is present and the
`luminance difference around the current vehicle from the luminance information of the
`
`image input from the image signal processing unit 120 (S 43). Then, from the luminance
`
`difference around the vehicle position Rn, an area within a predetermined luminance
`
`differenceis identified, and this area is generated as the first area (reference area) XYn
`
`of the vehicle (S 44).
`
`[0049]
`
`In the new vehicle determination process (S 42), if the detected vehicle is a vehicle that
`
`has already been detected,
`
`the region difference extraction unit 134 extracts the
`
`luminance of the current vehicle position Rn 1 and the luminance difference of the
`
`periphery from the luminance information of the image input from the image signal
`
`processing unit 120 (S 51). Then, an area within a predetermined luminance difference
`
`is identified from the luminance difference around the vehicle position Rn 1, and the
`
`current vehicle area XYn 1
`
`is generated (S 52).
`
`[0050]
`
`Next, the area reduction ratio calculation / determination unit 135 compares the number
`
`of pixels of the first detected reference area XYn (reference vehicle area) and the number
`
`of pixels of the current vehicle area XYn 1 (target vehicle area), and calculates the area
`
`reduction ratio of the vehicle (step S 53). Further, based on the initial distance Rn of the
`
`vehicle and the current distance Rn 1, the area reduction ratio on the image of the vehicle
`
`only based on the distance theoretically determined is extracted and compared with the
`
`actual area reduction ratio of the vehicle (S 54).
`
`[0051]
`
`Next,
`
`it is determined whether or not the difference between the theoretical reduction
`
`ratio and the actual reduction ratio is within a predetermined value (s 55), and if the
`
`difference is within a predetermined value, the visibility distance determination unit 136
`
`determines that the distance Rn 1 with the vehicle detected this time is valid (S 56) and
`
`further calculates the effective visibility distance (S 57).
`
`[0052]
`
`In the difference determination of the area reduction ratio (s 55), if the value exceeds the
`
`predetermined value, the visibility distance determination unit 136 determines that the
`
`distance Rn 1 from the vehicle detected this time is invalid (s 61), and calculates the
`
`effective visibility distance (s 57).
`
`[0053]
`
`

`

`[ for not limiting the index used as the standard of visual range measurementto a specific
`
`object by the above processing ]
`
`[ by considering it as the vehicles which pass through
`
`a road ] An index can be changed one after another, and while being able to perform
`
`visual range measurement, without being affected to specific damage, snow-stucking,
`
`etc., detection of a dangerous vehicle can also be performed simultaneously.
`
`[0054]
`
`Also, the visibility detection device 100 transmits the information on the visibility distance
`
`obtained by the detection processing unit 130 and the information on the dangerous
`
`vehicle and the like to the managementserver 400installed in the managementoffice at
`
`the remote location and the display guide portion 300 located in front of the detection
`
`area of the visibility detection device 100 by the communication control unit 150.
`
`[0055]
`
`The display guide 300 receives the information transmitted from the visibility detection
`
`device 100 and displays the attention information for the dangerous vehicle and the
`
`visibility information.
`
`[0056]
`
`In the server communication control unit 410, the management server 400 receives the
`
`information transmitted from the visibility detection device 100 and, under the control of
`
`the server control unit 420, displays the vehicle detection information and the visibility
`
`measurement information received from the visibility detection device 100 on the server
`
`display unit 430.
`
`[0057]
`
`Through the above processing, information on the detection area can be notified to the
`
`driver of the vehicle entering the area detected by the visibility detection device 100 by
`
`the display guide portion 300.
`
`In addition,
`
`information on the detection area can be
`
`notified by the management server 400 to the road managerat the managementoffice.
`
`[0058]
`
`Further, a control unit for controlling an imaging range of the camera 220 is provided in
`
`the visibility detection device 100, and by changing the imaging range of the camera 220
`
`according to the position and the moving speed when the vehicle is detected, it is also
`
`possible to capture the target vehicle and capture an image, thereby enlarging the
`
`visibility determination range.
`
`[0059]
`
`(Second embodiment)
`
`Next, a visibility detection apparatus according to a 2 embodiment of the present
`
`invention will be described. FIG. 7 is a block diagram ofthe visibility detection device 102
`
`

`

`according to the present embod