JP2712716B2 - Vehicle distance detection device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle distance detecting device provided in a vehicle to detect a distance between the vehicle and an object, and particularly relates to the brightness of an image including the object. The present invention relates to a technique for satisfactorily capturing an image of a target object regardless of the type.

2. Description of the Related Art The following is already known as one of distance detecting devices for vehicles. This is because, as described in Japanese Utility Model Laid-Open Publication No. 61-19709, (a) each includes a plurality of light receiving elements that generate electric charges according to the intensity of incident light and accumulate the electric charges. (B) pixel signal generating means for generating a pixel signal corresponding to the amount of electric charge accumulated in the plurality of light receiving elements during the light receiving time, respectively. , (C) based on the pixel signals, the two
Distance determining means for determining a shift amount between the two images and determining the distance in accordance with the shift amount.

Problems to be Solved by the Invention The brightness of an object is not always constant, but usually changes. Therefore, in some cases, light that is brighter than the light that can be detected or light that is darker than the light that can be detected may enter the light receiving element. In this case, the target object cannot be accurately imaged. Under such circumstances, to ensure that the light-receiving elements can always perform good imaging regardless of the brightness of the image including the target object, the light-receiving amount, which is the amount of light received by each light-receiving element during the light-receiving time, is appropriate. It is important to control

As the control of the amount of received light, for example, a diaphragm control that is provided in each imaging unit with a variable diaphragm generally used in a camera or the like and controls the effective diameter of the variable diaphragm can be considered. However, since the variable aperture is usually composed mainly of movable parts, if it is mounted on a vehicle and used, there is a possibility that proper operation may not be realized due to vibration of the vehicle body or the like.

Based on the above findings, the present invention has been made to provide a vehicle distance detecting device capable of controlling the amount of received light and suitable for use in a vehicle.

Means for Solving the Problems The gist of the present invention is to provide a vehicular distance detection device including the two image pickup units, the pixel signal generation device, and the distance determination unit based on the pixel signal to determine the length of the light reception time. There is provided a light receiving time adjusting means for adjusting the brightness so that the spatial change amount of the luminance in the image is maximized.

Note that the light receiving time adjusting means obtains, for example, the sum of absolute values of spatial differential values of luminance at each pixel obtained by dividing an image into a plurality of pixels corresponding to each light receiving element,
The length can be adjusted to the length at which the sum becomes the largest. Further, a pixel having the largest absolute value of the spatial differential value is selected as a reference pixel from among the plurality of pixels, and the light receiving time is adjusted to a length at which the absolute value of the spatial differential value of the reference pixel becomes the maximum. You can also.

The light receiving time adjusting means includes: (a) an adjusting direction determining unit that determines a direction in which the length of the light receiving time should be adjusted based on the overall luminance of the pixel; The provisional adjustment is repeated in the direction determined by the determination unit with the set amount, and the luminance spatial change amount is changed based on the direction in which the luminance spatial change amount changes from the previous luminance spatial change amount in accordance with the provisional adjustment each time. And an adjustment amount determining unit that determines an appropriate value of the adjustment amount of the light receiving time.

Function and Effect of the Invention In the device of the present invention configured as described above, the light receiving time is adjusted by the light receiving time adjusting means, so that the light receiving amount of each light receiving element is controlled. Since the light receiving time adjusting means can be realized by adding a simple electronic circuit or changing a control program of a computer, it is not essential to use a movable part for controlling the light receiving amount. Therefore, according to the present invention, the received light amount control is less likely to be affected by the vibration of the vehicle body and the like, and stable received light amount control is realized, and the effect of improving the distance detection accuracy is obtained.

The amount of shift between the two images captured by the two imaging units is obtained, for example, as follows. In the case where each of the image pickup means includes, for example, a light receiving element array in which a plurality of light receiving elements are arranged in a line, the two images are sequentially shifted by one light receiving element and superimposed, and each shift is performed. Is obtained, the degree of inconsistency indicating the degree to which the two images do not coincide with each other is obtained. When the required number of shifts is completed, for example, the shift amount corresponding to the smallest one of the plurality of inconsistencies obtained for each shift amount Is the difference between the two images. Therefore, by implementing the present invention, if the light receiving time is adjusted to a length that allows the change in luminance in the image to be as large as possible, the change in the degree of mismatch between the images with respect to the unit shift amount of the two images is sufficient. As a result, the two images can be compared with high accuracy, and this also has the effect of improving the detection accuracy.

Examples Hereinafter, examples of the present invention will be described in detail with reference to the drawings.

An inter-vehicle distance detecting apparatus according to an embodiment of the present invention includes a main unit 10 shown in FIG. 2 and a signal processing unit 12 shown in FIG. The main body 10 is attached to the center of the front end of the vehicle. A reference plane is assumed for the main body 10, and is attached so that the reference plane is parallel to the horizontal plane of the vehicle.

A pair of mirrors 14, 16 and a prism 18,
A pair of lenses 20 and 22, a pair of diaphragms 24 and 26, a first CCD line sensor 30, a second CCD line sensor 32 (hereinafter simply referred to as a sensor 3).
0, 32) along the reference plane and symmetrically with respect to a reference axis extending in the front-rear direction of the vehicle. The prism 18 has two reflecting surfaces 36 and 38 each sandwiching the apex angle thereof, and the reflecting surfaces 36 and 38 are disposed along the reference plane and symmetrically with respect to the reference axis. ing. In addition, mirrors 14 and 16 facing each other
And the respective reflecting surfaces 36 and 38 of the prism 18 are parallel to each other.

Each of the sensors 30 and 32 includes a light receiving element array 42 in which n _MAX light receiving elements 40 are arranged in a line. The light receiving element arrays 42 are perpendicular to the reference axis and parallel to the left and right direction of the vehicle. They are arranged along a plane. Each light receiving element 40 generates a larger amount of electric charge and accumulates it as the light incident thereon becomes brighter. The plurality of light receiving elements 40 are assigned element numbers n of 1 to n _{MAX for the} sensors 30 and 32, respectively.

In the main body 10 configured as described above, light traveling toward the main body 10 from the vehicle in front of the host vehicle enters the sensor 30 through the mirror 14, the reflecting surface 36 of the prism 18, the lens 20, and the aperture 24 in that order. At the same time, the light enters the sensor 32 through the mirror 16, the reflecting surface 38 of the prism 18, the lens 22, and the stop 26 in that order. Each of the sensors 30, 32 represents an image of the preceding vehicle, and each of the sensors 30, 32
The imaging is performed in an imaging region corresponding to the n _MAX light receiving elements 40 belonging to, that is, an imaging region extending in the horizontal direction in a band shape.

As is clear from the above description, the mirror 14, the prism 1
The eight reflecting surfaces 36, the lens 20, the aperture 24, and the light receiving element array 42 of the sensor 30 constitute the first imaging means 50, and include the mirror 16, the prism 1
The eight reflecting surfaces 38, the lens 22, the stop 26, and the light receiving element array 42 of the sensor 32 constitute a second imaging means 52.

Sensor 30 further includes, as shown in FIG. 3, the switching element array 64 of the switching element 62 is set equal to the number n _MAX of the light receiving element 40, CCD shift, equal set and the number n _MAX of the light receiving element 40 with a capacitor 66 And a register (hereinafter, simply referred to as a register) 68. The switching element row 64
When one transfer pulse is input thereto, the plurality of switching elements 62 are simultaneously switched from the OFF state to the ON state, and the electric charges respectively accumulated in the n _MAX light receiving elements 40 are simultaneously transmitted to the corresponding capacitors. Forward to 66. When one shift pulse is input to the register 68, the charge stored in each capacitor 66 is shifted to the immediately adjacent capacitor 66 (the capacitor 66 immediately below in the figure). The input of the shift pulse is performed the same number of times as the number n _MAX of the light receiving elements 40 each time the transfer pulse is input, and the charges accumulated in the n _MAX capacitors 66 are the most downstream (most in the figure). It is sequentially taken out from the lower one) to the most upstream one (the uppermost one in the figure). Although not shown,
The sensor 32 also includes a switching element array 64 and a register 68.

The signal processing unit 12 includes a computer 70 as shown in FIG.
It has. The computer 70 is a CPU, ROM, RA (not shown)
Includes M, bus, input interface and output interface. As shown in the figure, the input interface is connected to the analog signal output terminal of the register 68 of each sensor 30, 32 via each A / D converter 72. On the other hand, the output interface is connected to a shift pulse input terminal of each register 68 via each shift pulse generator 74, a transfer pulse input terminal of each switching element array 64 via each transfer pulse generator 76, and a warning device 88 via a driver 86. It is connected. The warning device 88 is activated when the current distance between the own vehicle and the preceding vehicle is insufficient in relation to the current vehicle speed of the own vehicle, and notifies the driver of the fact.

The ROM of the computer 70 stores various control programs, including a transfer pulse supply routine, an image data capture routine, an inter-vehicle distance detection routine, and a light reception time correction routine, which are respectively represented by flowcharts in FIGS. 4 to 7. Also, as shown in FIG. 3, a first image memory for storing first image data representing a first image captured by the sensor 30 and a second image captured by the sensor 32 are stored in the RAM. A second image memory for storing the second image data, and a current light receiving time memory and a next light receiving time memory for respectively storing a current light receiving time and a next light receiving time, which will be described later, are provided.

Next, the operation will be described. First, a schematic description will be given based on FIG.

The electric charges respectively accumulated in the n _MAX light receiving elements 40 belonging to each light receiving element row 42 are simultaneously transferred to the register 68 via the switching element row 64 every time the transfer pulse is extinguished, that is, every time the transfer pulse falls. Will be transferred. Also,
Between the disappearance of one transfer pulse and the disappearance of the next transfer pulse, the same number of shift pulses as the number n _MAX of the light receiving elements 40 are supplied to the registers 68 of the sensors 30 and 32 at predetermined time intervals. Accordingly, n _MAX light receiving elements 40
The analog signals representing the electric charges respectively stored in the register 68 are sequentially taken out from the register 68 one by one. Analog signal is A /
The digital signal is converted into a digital signal by the D converter 72, and the digital signal is stored in the first and second image memories of the RAM.
1, stored as second image data. If the same number of shift pulses as the number n _MAX of the light receiving elements 40 are generated, n _MAX first and second image data relating to the sensors 30 and 32 are stored in the first and second image memories, respectively. And their first
A set of second pixel data is first and second image data, respectively.

Since transfer pulse is adapted to be generated each time elapses receiving time T _R is, in each light receiving element 40 a charge corresponding to the amount of light incident between the light receiving time it T _R is accumulated. The photodetection time T _R is changeable between the upper and lower limit values, and so that the imaging of the image regardless of the brightness of the image containing the vehicle in front is adjusted to a length that performed well I have.

The method of adjusting the light receiving time T _R will be described in brief.

First, the sum of the voltages output by the light receiving elements 40 belonging to the sensor 30 is obtained as the overall luminance of the first image. afterwards,
The overall brightness is compared with a predetermined appropriate range. For example, the appropriate range is set to a range sufficiently close to and including the sum of the appropriate voltages output by the respective light receiving elements 40 in a state where all the light receiving elements 40 belonging to the sensor 30 can perform the best imaging. The time of the first image for example, when the entire luminance as shown in FIG. 9 is intended to be proper range, but the brightness is determined just as good light receiving time T _R of the first image is not changed, For example, as shown in FIG.
If the overall luminance is lower than the lower limit of the appropriate range, it is determined that the first image is too dark, and the current light receiving time T _R
The next light receiving time T _R is calculated by adding the positive correction amount ΔT _R to, and, for example, as shown in FIG.
If the overall luminance is higher than the upper limit of the appropriate range, it is determined that the first image is too bright, and the current light receiving time
By negative correction amount [Delta] T _R is added to T _R, i.e., the next light receiving time T _R by the current receiving time T _R is positive correction amount [Delta] T _R is subtracted is calculated. In addition,
9 to 11, the maximum voltage of the light receiving element 40 is 5V and the appropriate voltage is 2.5V.

The upper limit value of the light receiving time T _R is, for example, the light receiving element 40 even if the nighttime preceding vehicle image is formed only by the headlight of the vehicle is determined to a size capable of satisfactorily capturing the preceding vehicle, On the other hand, the lower limit value is determined to be longer than the time required for converting all analog signals of the plurality of light receiving elements 40 belonging to the sensors 30 and 32 into digital signals by the A / D converter 72, for example.

Hereinafter, the operation of this embodiment will be described in detail with reference to FIGS.

When the power of the computer 70 is turned on, first, a predetermined initial light receiving time is stored in a current light receiving time memory, the initial light receiving time is also stored in a next light receiving time memory, and the value of the elapsed time t is stored. Initial setting to zero is performed. Note that the first light receiving time is, for example, a length that allows good imaging when the brightness of an image including the preceding vehicle is assumed to be a statistical average value. Thereafter, FIGS. 4 to 7
Each routine in the figure is executed.

The transfer pulse supply routine of FIG. 4 is executed at regular intervals. When executing this routine each time, first
At S1 (hereinafter simply referred to as S1; the same applies to other steps), an increment Δt (equal to the execution cycle of this routine) is added to the current value of the elapsed time t. over time T _R is read, the current value of the elapsed time t is whether or not the current receiving time T _R or not is determined. Otherwise, the result of the determination is NO, and one execution of this routine ends. Then, a result of execution of the present routine is repeated many times, if the current value of the elapsed time t reaches the current receiving time T _R, S2 of the determination result is YES, at S3, each transfer pulse generator At 76, a transfer pulse supply signal is supplied which supplies a transfer pulse to the switching element array 64 of each of the sensors 30, 32. Thereafter, in S4, is stored as the next receiving time the next receiving time from the memory T _R is read it new current receiving time to the current receiving time memory T _R of RAM, S5
The value of the elapsed time t is restored to 0 at.

The image data fetching routine of FIG. 5 is also executed at regular intervals. First, it is determined in S11 whether or not the transfer pulse has disappeared. If not, the result of the determination is NO, and one cycle of this routine ends. On the other hand, when the transfer pulse has disappeared, the determination result in S11 is YES, and in S12, the value of the element number n of the light receiving element 40 belonging to each of the sensors 30, 32 is set to 1. Thereafter, in S13, each shift pulse generator 74 outputs a shift pulse supply signal for supplying a shift pulse to the register 68 of each sensor 30, 32.
An A / D conversion signal for converting an analog signal extracted from each register 68 into a digital signal is output to the / D converter 72. Subsequently, in S15, the digital signal from each A / D converter 72 is stored in the first and second image memories as the first and second image data, respectively.
Is increased by one. Then, in S17,
It is determined whether the value of the element number n is greater than the number n _MAX of the light receiving elements 40. If so, the result of the determination is NO and S1
Return to 3, but if not, the result of the determination is YES,
One execution of this routine ends.

The inter-vehicle distance detection routine of FIG. 6 is also executed at regular intervals. First, it is waited that the A / D conversion is not being performed in S20. If the A / D conversion is not being performed, the first and second image data are read from the first and second image memories in S21.
In S22, from the first and second image data, the sensor 30,
The shift amount between the two images captured by the respective 32 is obtained. Then, in S23, the current inter-vehicle distance corresponding to the deviation amount is obtained according to the correspondence relationship between the deviation amount and the inter-vehicle distance (not shown) .In S24, the current inter-vehicle distance is calculated from the safe inter-vehicle distance corresponding to the current vehicle speed of the own vehicle. It is determined whether it is short. If so, the result of the determination is YES, the fact is notified to the driver via the warning device 88 in S25, otherwise the result of the determination is NO, and the warning device 88 is stopped in S26. This completes one execution of this routine.

The light receiving time correction routine of FIG. 7 is executed, for example, every one minute. The routine is not executed as frequently as in the inter-vehicle distance detection routine of FIG. At the time of each execution of this routine, first, it is waited that the A / D conversion is not being performed in S100. If the A / D conversion is not being performed, the first image data is read from the first image memory in S101. In S102, the sum of the voltages represented by the pixel data belonging to the first image data is calculated as the overall luminance. Subsequently, in S103, the overall luminance and the appropriate range are compared with each other. Assuming that this time the entire brightness is in the proper range, one cycle of execution of the present routine is terminated without correcting the light receiving time T _R.

On the contrary, when the entire luminance is higher than the upper limit of the proper range, then the sign of the correction amount [Delta] T _R is negative in S104, in S105, the luminance for each of a plurality of pixels constituting the first image A differential value is calculated. The luminance differential value of each pixel is a difference in luminance between the pixel and one pixel adjacent thereto. Thereafter, in S106, the sum of the absolute values of the luminance differential values (hereinafter, simply referred to as the sum of the luminance differential values, the same applies in the drawing) is calculated. Then, S107
In, is read out next receiving time T _R the next time the light receiving time memory, receiving time T _R is calculated new next by a positive or negative correction amount [Delta] T _R is added to the next receiving time T _R together, the next receiving time T _R is stored in the next receiving time memory.

For example, the first time the computer 70 reads the first time
If the first image represented by the image data is as shown in FIG. 11, since the first image is determined to be too bright, as shown in FIG. 1, the next light receiving time T _R is time It is shorter than the receiving time T _R by a positive correction amount [Delta] T _R. Light receiving time
Correction to the initial value of T _R is the added once. The effect of the correction is as shown in FIG.
Does not appear in the first image represented by the first image data read out the second time, but appears in the first image represented by the first image data read out the third time.

After that, it is waited in S108 that the next A / D conversion ends. When the processing is completed, in S109, a new first image is read from the first image memory only once from the previous time, and the sum of the luminance differential values is calculated for the first image. In S110, the sum of the luminance differential values is calculated. Is determined to be less than or equal to the previous value. Otherwise, the result of the determination is NO and the process returns to S107.

For example, the first time the computer 70 reads the second time
If the first image represented by the image data is shown in FIG. 11 and the first image represented by the first image data read out for the third time is shown in FIG. 12,
The primary differential image of the preceding first image is as shown in FIG. 13, and the primary differential image of the subsequent first image is as shown in FIG. Comparing the pixels circled in FIGS. 13 and 14 with each other, the luminance differential value is larger in the first image than in the first image.
Assuming that the same sum of differential luminance values, the determination result of S110 is NO, and the determination time T _R is further only positive correction amount [Delta] T _R shorter.

If repeated increase or decrease of the light receiving time T _R, or the sum of the differential luminance values hardly changed between the previous and current, or leads to this is smaller than the previous. In a state where the receiving time T _R becomes too short, the light receiving over time T _R to shorten, among e.g. darkest portion detected not become the voltage of the light receiving element 40 is the minimum voltage by the light receiving element 40 of the first image (e.g., 0V ), The voltage of the light receiving element 40 in the other portions decreases, so that the sum of the luminance differential values changes from increasing to maintaining or decreasing. In a state where the light receiving time T _R is too long, as a longer receiving time T _R, for example, the brightest part voltage of the light receiving element 40 is not detected by the light receiving element 40 of the first image is the maximum voltage ( For example, while the voltage is maintained at 5 V), the voltage of the light receiving element 40 in the other portion increases, so that the sum of the luminance differential values changes from increasing to maintaining or decreasing. Thus, while the execution of S107~S110 is repeated, if the YES determination result of S110, the next receiving time memory, it next time that has been stored before twice than the next receiving time T _R which is currently stored receiving time T _R is determined to a desired length. Subsequently, in S111, is read out next receiving time T _R the next time the light receiving time memory, a positive or negative correction amount from the next receiving time T _R delta
Minus twice the T _R is stored in the next receiving time memory. This completes one execution of this routine.

For example, as shown in FIG.
When the sum of the luminance differential values of the first image represented by the first image data read out at the time is smaller than the previous time, the first image represented by the first image data read out by the computer 70 at the fifth time since the sum of the differential luminance value is estimated to be proper, the first light receiving time T _R of the image used to obtain, i.e., light reception plus 3 times the correction to the initial value of the light receiving time T _R the appropriate value of the time T _R. Under such circumstances, the next light receiving time read by the computer 70 for the sixth time
T _R, i.e., in order to disable the double dose correction from plus 5 times the correction to the initial value of the light receiving time T _R, the current read received time T _R is only twice the positive correction amount [Delta] T _R It will be lengthened.

As is apparent from the above description, in the present embodiment, a portion of the computer 70 for executing the routines of FIGS. 4 and 5, a switching element array 64, a register 68, and a shift pulse generator 74 And the transfer pulse generator 76
These constitute the pixel signal generating means, and the part of the computer 70 executing the routine of FIG. 7 constitutes the light receiving time adjusting means. In addition, S100 to S1 in FIG.
04, S107 and S112 constitute an adjustment direction determining unit, and S105 and S1
06 and S108 to S111 constitute an adjustment amount determining unit.

The above-described embodiment is an example of the inter-vehicle distance detection device used to warn the driver of the fact that the inter-vehicle distance between the own vehicle and the preceding vehicle is insufficient for safe driving. The device can be used for other purposes.
For example, it is also possible to use the present invention in a following travel control device that causes the own vehicle to follow the preceding vehicle based on the inter-vehicle distance between the subject vehicle and the preceding vehicle.

Further, in the above-described embodiment, the supply of the transfer pulse and the shift pulse is controlled by the computer 70, but may be controlled by an electronic circuit such as a clock. Omitting the supply control of these pulses from the execution contents of the computer 70 is effective for enabling the detection of the inter-vehicle distance to be performed at higher speed.

Further, in the above embodiment, as with the overall brightness of the first image is determined using the sensor 30, the necessity determination for the whole luminance and appropriate range and the comparison result from the light receiving time T _R correction is performed had become, the provided illuminance sensor for detecting a vehicle ahead of the illumination may be performed necessity determination of the correction of the light receiving time T _R by using the illuminance sensor.

Further, in the above embodiment, (not mean the execution of the light receiving time correcting routine, means changing the receiving time T _R to reality) correction of the light receiving time T _R is the overall brightness of the first image It was supposed to be performed only when it is determined that out of the proper range, may be performed to correct the photodetection time T _R without determining whether the overall brightness is out of the proper range. For example, as shown in the flowchart in FIG. 15, first, in S200, regardless of whether it is real need of the reducing and increasing decided not to change the receiving time T _R is either ,
Increasing the light receiving time T _R by a positive correction amount [Delta] T _R, then, S2
In 01, it is determined whether or not the amount of change in luminance (for example, the sum of the luminance differential values) is greater in the image after the increase than in the image before the increase, or whether both are equal. judgment increases again receiving time T _R returns to S200 and if so, to reduce the light receiving time T _R in S202 otherwise only positive correction amount [Delta] T _R, then, S203
In, it is determined whether the amount of change in luminance is greater in the image after the reduction is performed than in the image before the reduction is performed or whether the two are equal, and if so, the process returns to S202. reducing the light-receiving time T _R again Te is the process may return to S200 otherwise. That is,
It is also possible to determine whether or not it is out of the appropriate range by obtaining the overall luminance, to determine whether the deviated direction is a direction that is too bright or a direction that is too dark, and to implement the present invention. It is not essential.

Although the embodiments of the present invention have been described in detail with reference to the drawings, the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of control of a light receiving time in an inter-vehicle distance detecting apparatus according to an embodiment of the present invention. FIG. 2 is a plan view showing a main body of the inter-vehicle distance detecting device.
FIG. 3 is a block diagram showing a signal processing unit of the inter-vehicle distance detecting device. 4 to 7 are flowcharts showing a transfer pulse supply routine, an image data acquisition routine, an inter-vehicle distance detection routine, and a light reception time correction routine stored in the ROM of the computer in FIG. 3, respectively. FIG. 8 is a timing chart for explaining the operation of the inter-vehicle distance detecting device. Figures 9 to 14
Each of the figures is a graph showing an image used to explain how the light receiving time correction routine of FIG. 7 is executed. No.
FIG. 15 is a flowchart for explaining how the light receiving time is controlled in another embodiment. 30, 32: first and second CCD line sensors 40: light receiving element, 42: light receiving element row 50, 52: first and second imaging means 64: switching element row 68: CCD shift register 70: computer 74: shift pulse Generator 76: Transfer pulse generator

Claims (2)

(57) [Claims] 1. A vehicle distance detecting device provided in a vehicle for detecting a distance between the vehicle and an object, wherein each of the light receiving devices generates an electric charge according to the intensity of incident light and accumulates the electric charge. A pixel including a plurality of elements, each of which captures an image including the object, and a pixel which generates a plurality of pixel signals corresponding to the amount of electric charge accumulated in the plurality of light receiving elements during a light receiving time. A signal generating unit; a distance determining unit that obtains a shift amount between the two images captured by the two image capturing units based on the pixel signals, and determines the distance according to the shift amount; And a light-receiving time adjusting unit that adjusts the length of the light-receiving time so that the spatial variation of luminance in the image is maximized based on the following formula: 2. The light receiving time adjusting means: (a) an adjusting direction determining unit for determining a direction in which the length of the light receiving time is to be adjusted based on the overall luminance of the image; The length is repeatedly provisionally adjusted by the set amount in the direction determined by the adjustment direction determining unit, and the luminance spatial change amount is changed by the previous luminance spatial change in accordance with each provisional adjustment. The vehicle distance detection device according to claim 1, further comprising: an adjustment amount determining unit that determines an appropriate value of the adjustment amount of the light receiving time based on a direction changing from the change amount.