JP2005148309A - Exposure controller for white line detection camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress hunting in exposure control even in such a situation that a dark part and a bright part repeatedly appear on a road surface. <P>SOLUTION: When a road surface brightness equivalent value B<SB>IMG</SB>(weighted average brightness V<SB>IMG</SB>) is different from the brightness equivalent value B<SB>TGT</SB>of a target pixel value M<SB>TH</SB>, a target exposure control amount for bringing the road surface brightness equivalent value B<SB>IMG</SB>close to the brightness equivalent value B<SB>TGT</SB>of the target pixel value M<SB>TH</SB>is calculated. Further, it is judged whether the variation C of the target exposure control amount exceeds an increase threshold value T<SB>HI</SB>or a reduction threshold value T<SB>LO</SB>on the basis of the present exposure control amount. When the variation C is beyond the threshold values, the variation C of the target exposure control amount is restricted to the threshold value. Then, even in such the situation that a sunny place and the shade repeatedly appear on the road surface, the degree of hunting is suppressed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an exposure control apparatus that performs exposure control of a camera that captures an image of the front of a vehicle and outputs an image signal in order to detect a white line on a road ahead of the vehicle.

  As a conventional white line detection device, for example, a device described in Patent Document 1 is known. In this conventional white line detection device, exposure control (exposure control) is first performed so that the exposure amount (exposure amount) in the CCD camera is within a predetermined range. Then, the luminance signal for each element of the CCD camera is converted into a digital signal and stored.

Furthermore, a threshold value is calculated based on the maximum value and average value of the luminance signal converted into the digital signal, and the digital signal is binarized using this threshold value. Then, the left and right edge portions of the white line are detected from the change state of the binarized data. At this time, since a plurality of left and right edge portions are usually detected, the current white line position is predicted from the previous change state of the white line position the previous time, the one closest to the predicted position is selected, and the white line position is Output the selected white line coordinates.
Japanese Patent Laid-Open No. 5-289743

  Here, the shooting range of the white line detection camera always moves while the vehicle is traveling. When the vehicle travels on a road where the sun and shade repeatedly occur on the road surface, it is conceivable that the cycle of the sun and shade appearing on the imaging screen of the camera is synchronized with the exposure control cycle of the camera. In this way, when the camera exposure control cycle is synchronized with the cycle of the sun and the shade, the exposure actually increases even if the screen brightness is darkened due to the shade and the exposure is increased. When it is done, the camera will pick up the road surface in the sun. In this way, it is expected that so-called hunting occurs in which the exposure amount of the camera does not adapt to the brightness of the road surface for a long time even if the exposure control is performed.

  The present invention has been made in view of the above-described points, and exposure of a white line detection camera capable of suppressing hunting for exposure control even in a situation where a dark part and a bright part repeatedly occur on the road surface. The object is to provide a control device.

In order to achieve the above object, an exposure control device for a white line detection camera according to claim 1,
An exposure control device that controls the exposure of a camera that is mounted on a vehicle and repeatedly outputs an image signal for detecting a white line that divides a lane on a road on which the vehicle travels,
In the image signal output from the camera, area setting means for setting an area corresponding to a portion excluding the white line on the road;
Exposure control means for controlling the exposure of the camera so that the pixel value of the area in the image signal becomes the target pixel value;
When the pixel value of the area is different from the target pixel value, the exposure control means calculates the next exposure control amount for bringing the area pixel value closer to the target pixel value, and calculates the current exposure control amount and the next calculated If the amount of change from the exposure control amount is larger than a predetermined limit value, the calculated next exposure control amount is corrected to an exposure control amount in which the change amount from the current exposure control amount is limited to the limit value. It is characterized by that.

  Thus, first, an area corresponding to a portion of the image signal excluding the white line on the road is set. The white line is brighter than at least road parts other than the white line. For this reason, if exposure control is performed so that the pixel value of the area corresponding to the portion excluding the white line of the image signal becomes the predetermined target pixel value, the contrast of the white line with respect to the portion excluding the white line can be ensured in the image signal.

  However, if exposure control is performed so that the pixel value of the area set in the image signal matches the target pixel value at once, the responsiveness to changes in the brightness of the road surface is improved. There are concerns about the occurrence.

  Therefore, in the exposure control apparatus according to claim 1, the exposure control means calculates the exposure control amount when the change amount between the current exposure control amount and the calculated next exposure control amount is larger than a predetermined limit value. Is corrected to an exposure control amount in which the amount of change from the current exposure control amount is limited to the limit value. As a result, even in situations where the sun and shade are repeatedly generated on the road surface, the amount of change in the exposure control amount is limited based on the current exposure control amount, thereby suppressing the effects of hunting. Can do.

  As described in claim 2, when a predetermined dead zone is set with reference to the target pixel value and the area pixel value belongs to this dead zone, the exposure control means considers that the area pixel value is equal to the target pixel value, The exposure control amount is preferably unchanged. This is because if the area pixel value approximates the target pixel value, an image in which contrast with the white line is secured is obtained, and no further exposure control is necessary. Also, by executing exposure control, there is a possibility that the area pixel value may be separated from the target pixel value.

  According to a third aspect of the present invention, as the limit value, an increase limit value when the exposure control amount increases and a decrease limit value when the exposure control amount decreases are provided, and a large value when the exposure control amount increases. It is preferable to set the increase limit value and the decrease limit value so that the magnitude at the time of decrease differs. Exposure control hunting occurs when the same amount of increase / decrease in exposure control amount is repeated. For this reason, the influence of hunting can be more effectively suppressed by making the magnitude at the time of increase of the exposure control amount different from the magnitude at the time of reduction.

  For example, in the case where the magnitude at the time of increase of the exposure control amount is different from the magnitude at the time of decrease, it is preferable that the magnitude at the time of increase is larger than the magnitude at the time of decrease as described in claim 4. In this case, the influence of hunting can be effectively suppressed while corresponding to the brightness change characteristics of the entrance and exit of the tunnel.

  As described in claim 5, the amount of change between the current exposure control amount and the calculated exposure control amount can be obtained by using the ratio between the current road surface luminance and the road surface luminance corresponding to the target pixel value. Of course, it is possible to obtain the amount of change by taking the difference between the current road surface luminance and the road surface luminance corresponding to the target pixel value, but the amount of change may be obtained using the ratio of the two.

  Preferably, the area setting means sets a plurality of areas in the image signal. In an actual road environment, the brightness of the road surface in the imaging range of the camera changes in various ways as a whole and in part. Therefore, in the image signal output from the camera, if a plurality of areas corresponding to the portion excluding the white line on the road is set, and the exposure control of the camera is performed based on the road surface brightness of the plurality of areas, Even if the brightness of the road surface in the imaging range of the camera changes in various ways, exposure control can be performed by comprehensively considering the change from the road surface brightness of a plurality of areas.

  As described in claim 7, the area setting means sets, as a plurality of areas, a center area corresponding to a road surface portion of the lane in which the host vehicle travels, and white lines that divide the lane in which the host vehicle travels. It is preferable to set the left and right side areas respectively on both side portions beyond the above. Thus, by setting areas for measuring brightness on both sides of the white line across the white line, it is possible to set the road surface brightness as a reference for securing the contrast of the white line based on a wide range of brightness. it can. For this reason, even if the brightness in the imaging range of the camera changes in various ways, the influence of the change on the exposure control can be reduced.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a lane departure warning device including a white line detection camera exposure control device will be described.

  FIG. 1 is a block diagram illustrating a configuration of a lane departure warning device according to an embodiment. As shown in FIG. 1, the lane departure warning device includes a camera 1, a control unit 2, a lane departure warning ECU 7, and a warning unit 8.

  The camera 1 is installed at a predetermined position in the vehicle interior, for example, on the back side of a room mirror, and images a road ahead in the traveling direction of the vehicle. In addition, when the camera 1 is installed at a predetermined position in the vehicle interior, the direction and the like of the camera 1 are adjusted so that the imaging range is a predetermined imaging range with respect to the traveling direction of the vehicle. Further, the camera 1 includes an amplifying unit and an A / D conversion unit, and when an image is captured, the pixel value indicating the brightness of each pixel of the image is amplified with a predetermined gain, and the amplified pixel Convert the value to a digital value and hold it. Then, the camera 1 outputs the held pixel value as an image signal for each line of the image.

  The control unit 2 recognizes the position of the white line by processing the image signal output from the camera 1, and outputs the recognized white line position to the lane departure warning ECU 7. Further, the control unit 2 controls the exposure of the camera 1 so that the contrast between the white line and the road surface portion excluding the white line is appropriate. That is, the control unit 2 outputs camera control values including these adjustment instruction values to the camera 1 in order to adjust the shutter speed and frame rate of the camera 1 and the gain of the amplification unit.

  The control unit 2 includes an image interface (I / F) 3, a CPU 4, a memory 5, and a communication I / F 6. The image I / F 3 receives position information of pixel values output from the camera 1 and transmits the position information to the CPU 4. The CPU 4 recognizes which pixel position the pixel value output for each line of the image corresponds to based on the position information transmitted by the image I / F 3. Then, the pixel value output from the camera 1 is stored in the memory 5 so as to correspond to the recognized pixel position. In this way, the image signal output from the camera 1 is stored in the memory 5.

  Communication I / F6 adjusts communication between CPU4 and lane departure warning ECU7. In the present embodiment, the CPU 4 recognizes the position of the white line in the image signal and transmits the recognized white line position to the lane departure warning ECU 7. On the other hand, the lane departure warning ECU 7 detects the position of the preceding vehicle or the like by a radar device (not shown), and indicates the distance between the own vehicle and the preceding vehicle and the direction of the preceding vehicle based on the own vehicle, indicating the position of the preceding vehicle. As shown in FIG.

  The lane departure warning ECU 7 determines whether or not the vehicle has deviated from the inside of the lane based on the white line position transmitted from the CPU 4. Is instructed to issue an alarm.

  The lane departure warning ECU 7 also has a follow-up running control function, and is illustrated so that the own vehicle follows the preceding vehicle based on the position and relative speed of the preceding vehicle detected by the radar device described above. The traveling speed of the host vehicle is controlled by adjusting the throttle valve opening and the braking state of the braking device.

  However, the lane departure warning device does not necessarily have the lane departure warning ECU 7. For example, the CPU 4 can determine whether or not the vehicle has deviated from the lane, and can be configured to issue an alarm when necessary. In addition, when the vehicle deviates from the lane (not likely), it not only issues an alarm, but also adjusts the amount of assist in the steering device to make it easier to return to the center of the lane, or automatically May be driven to return the vehicle to the center of the lane.

  FIG. 2 is a flowchart showing processing executed in the control unit 2. In FIG. 2, first, in step S110, the image signal output from the camera 1 is captured. That is, as described above, each pixel value constituting the image signal is stored in the memory 5 so as to correspond to the position information output from the camera 1.

  In step S120, calculation processing is performed on the image signal stored in the memory 5, and the position of the white line is recognized. In this calculation process, first, a threshold value for extracting a pixel value corresponding to the white line portion is set based on the pixel value of each pixel constituting the image signal. Then, the threshold value is compared with the pixel value of each pixel to extract a pixel having a pixel value equal to or greater than the threshold value. Furthermore, when these extracted pixels are combined, an extracted pixel set having a shape corresponding to a white line is specified, and this extracted pixel set position is recognized as a white line position.

  Some cameras output pixel values that are not simply proportional to the brightness level of the imaging range. In other words, there is a camera having a pixel value characteristic in which the resolution on the dark side becomes fine and the resolution on the bright side becomes coarse. When a camera having such a pixel value characteristic is used, each pixel value is converted into a mutually comparable luminance according to the pixel value characteristic of the camera 1 in the initial stage of the above-described processing. Based on the converted luminance, threshold value setting, size comparison, and luminance extraction processing from each pixel are performed.

  In subsequent step S130, the white line position recognized in step S120 is output in order to transmit the white line position to the lane departure warning ECU 7.

  In step S140, exposure control of the camera 1 is performed. In the exposure control of the camera, the brightness of the road surface portion excluding the white line is calculated, and the exposure of the camera 1 is controlled so that the road surface brightness can be photographed as the target pixel value. Thereby, since at least the white line is brighter than the road surface portion, an image signal in which the contrast between the road surface portion and the white line is ensured can be obtained. Details of the exposure control process will be described with reference to the flowchart of FIG.

  In FIG. 3, first, in step S210, a plurality of areas are set in the image signal output from the camera 1 so as to correspond to portions excluding white lines on the road. A method for setting this area will be described with reference to FIGS. 4 and 5A and 5B.

  As shown in FIG. 4, in the present embodiment, there are three areas, that is, a center area B corresponding to the road surface portion of the lane in which the vehicle travels, and both side portions beyond the white line that divides the lane in which the vehicle travels. Left side area C_LFT and right side area C_RGT, respectively. These three areas are preset at fixed positions in the image signal.

  Since the camera 1 is fixed at a predetermined position such as the rear side of the rearview mirror, the imaging range of the camera 1 is constant when the vehicle is used as a reference. Since the vehicle normally travels substantially in the center of the lane, the position where the white line appears in the image signal can be specified in advance. However, when the vehicle travels on a curve, the white line in the image signal is inclined according to the degree of the curve, as shown in FIG. Therefore, even if the white line is inclined, the area not including the white line is specified on the own lane and on both sides beyond the white line defining the own lane, and the center area B and the left and right side areas in the area are specified. By setting C_LFT and C_RGT, the positions of these areas can be fixed. Thus, by setting the area according to the position fixed in advance, the processing load for setting the area can be reduced.

  However, the area shapes of the center area B and the left and right side areas C_LFT and C_RGT are corrected depending on the presence or absence of a preceding vehicle. That is, the CPU 4 determines whether or not the preceding vehicle belongs to the center area B and the left and right side areas C_LFT and C_RGT based on the information indicating the position of the preceding vehicle output from the inter-vehicle distance ECU 7. And when it determines with the preceding vehicle which belongs in each area not existing, as shown to Fig.5 (a), the shape of the area set beforehand is maintained as it is.

  On the other hand, when it is determined that the preceding vehicle belongs to the center area B and / or the left and right side areas C_LFT and C_RGT, the shape of the area is corrected so as not to include the preceding vehicle. FIG. 5B shows the center area B whose shape has been corrected so as not to include the preceding vehicle when the preceding vehicle exists on the traveling lane of the host vehicle and belongs to the center area B. That is, based on the distance from the preceding vehicle, the front end position of the center area B is set to be equal to or less than the distance from the preceding vehicle. Thereby, the shape of the center area B can be corrected so as not to include the preceding vehicle. In addition, when the own vehicle travels on a road composed of a plurality of lanes, there may be other vehicles in the lane adjacent to the traveling lane of the own vehicle, and the other vehicles may belong to the left and right side areas C_LFT and C_RGT. Therefore, when it is determined that another vehicle belongs to the left and right side areas C_LFT and C_RGT based on the information related to the position of the preceding vehicle transmitted from the inter-vehicle distance ECU 7, the shapes of the left and right side areas C_LFT and C_RGT are included. Correct so that there is no.

When the center area B and the left and right side areas C_LFT and C_RGT are set and corrected in this manner, the road surface brightness of each area is calculated in step S220. That is, as shown in FIG. 6, calculates the road surface brightness _{V IMG_B} center area B, the right side area road surface brightness _{V IMG_C_RGT,} and road surface brightness _{V IMG_C_LFT} the left area. Note that the road surface brightness of each area is calculated by averaging the pixel values of the pixels in the capture line included in each area. In this way, the road surface brightness of each area that is a basis for calculating the brightness of the road surface portion is calculated. However, as described above, when using a camera that outputs a pixel value that is not simply proportional to the brightness level of the imaging range, the pixel value of each pixel is converted to luminance according to the pixel value characteristics of the camera, and Above, the luminance after conversion is averaged, and the road surface luminance of each area is calculated.

  In subsequent step S230, a weighted average luminance of the road surface luminance of each area is calculated. Hereinafter, an arithmetic expression for calculating the weighted average luminance will be described.

When calculating the luminance of the road surface excluding the white line, basically, it is preferable to mainly use the road surface luminance V _{IMG_B} of the center area B. This is because the image signal may include a white line, a roadside band, a separation band, a parallel vehicle, an oncoming vehicle, and the like in addition to the road surface portion. This is because these effects mainly appear in the left and right side area luminances V _{IMG_C_LFT} and V _{IMG_C_RGT} . Therefore, if the center area road surface brightness V _{IMG_B} is used as a basis for calculating the road surface brightness, the influence thereof can be avoided.

However, in an actual road environment, the brightness in the imaging range of the camera 1 is disturbed by sound insulation walls, roadside trees, side-by-side vehicles, oncoming vehicles, and the like, and changes in various manners in whole or in part. For this reason, if the road surface brightness is _obtained only from the center area road surface brightness V _{IMG_B,} it may not be an appropriate road surface brightness that should be the basis for securing contrast with the white line due to the influence of the disturbance. For this reason, when the influence of a shadow or an oncoming vehicle is suspected, it is desirable to appropriately consider the influence of disturbance by weighted averaging of the road surface luminance of a plurality of areas.

Therefore, for the three areas, the magnitude of the luminance variation is determined, and the road surface luminance of the three areas is weighted and averaged according to the magnitude of the luminance variation to obtain the final road luminance. The indicated weighted average luminance V _IMG is determined. An example of an arithmetic expression for calculating the weighted average luminance V _IMG is shown in Expression 1 below.
(Formula 1)
V _{IMG_C} = (V _{IMG_C_LFT} + V _{IMG_C_RGT} ) / 2
(1 + W _BC ) ・ V _IMG = V _{IMG_B} + W _BC・ V _{IMG_C}
That is, first, the side area average luminance V _{IMG_C} obtained by averaging the left and right side area luminances V _{IMG_C_LFT} and V _{IMG_C_RGT} is obtained, and a value obtained by multiplying the side area average luminance V _{IMG_C} by the weight value W _BC and the center area luminance V _{IMG_B} are added. The weighted average luminance V _{IMG_BRIGHT} is _obtained from the obtained value.

Here, as shown in FIG. 7, the weight value W _BC includes the maximum value (MAX [V _{IMG_B} , V _{IMG_C_RGT} , V _{IMG_C_LFT} ]) and the minimum value (MIN [V _{IMG_B} , V _{IMG_C_RGT) of the three areas.} , V _{IMG_C_LFT} ]), it is determined in the range of 0-2. When the weight value W _BC is set according to the characteristics shown in FIG. 7, the weight value W _BC becomes zero when the difference between the maximum value and the minimum value is smaller than X1, and the difference is large in the range from X1 to X2. It increases in proportion to the length and becomes 2 when it is larger than X2.

Therefore, when the difference in road surface brightness in the three areas is small, the weight value W _BC multiplied by the side area average brightness V _{IMG_C} is small, so the weight of the center area road surface brightness V _{IMG_B} is relatively large. _Thus , the weighted average luminance V _IMG is obtained mainly based on the center area road surface luminance V _{IMG_B} . As the difference in road surface brightness in the three areas increases, the value of the weight value W _BC increases. Therefore, the weight of the left and right side area road surface brightness is relatively increased, and the left and right side area road surface brightness V _{IMG_C_LFT} , V _The weighted average luminance V _IMG can be obtained in consideration of _{IMG_C_RGT} .

After _obtaining the weighted average luminance V _IMG in this way, in step S240, the value F _{B → V} (V _IMG ) obtained by converting the weighted average luminance V _IMG into a pixel value and the target pixel value M _TH are used as references. The dead zone upper limit value H _TH and the dead zone lower limit value L _TH for defining the dead zone are compared. When the value F _{B → V} (V _IMG ) obtained by converting the weighted average luminance V _IMG into a pixel value is determined to belong to the dead zone (L _TH <F _{B → V} (V _IMG ) <H _TH ), The value F _{B → V} (V _IMG ) obtained by converting the weighted average luminance V _IMG into a pixel value is regarded as corresponding to the target pixel value M _TH , and the exposure control amount is maintained as the current exposure control amount.

If the value F _{B → V} (V _IMG ) obtained by converting the weighted average luminance V _IMG into a pixel value approximates the target pixel value M _TH , an image in which the contrast between the road surface excluding the white line and the white line is secured can be obtained. This is because there is no need to change the exposure control amount. Further, although the value F _{B → V} (V _IMG ) obtained by converting the weighted average luminance V _IMG into the pixel value is approximate to the target pixel value M _TH , the weighted average luminance V _IMG is further converted into the pixel value. When exposure control is executed so that the value F _{B → V} (V _IMG ) approaches the target pixel value M _TH , the value F _{B → V} (V _IMG ) obtained by converting the weighted average luminance V _IMG into a pixel value is the target pixel value. This is because there is a possibility of moving away from _MTH . The above FB _{→ V} is a function for converting a luminance equivalent value into a pixel value. Further, the exposure control amount includes the shutter speed of the camera 1, the frame rate, and the gain of the amplification unit.

On the other hand, in step S240, it is determined that the value F _{B → V} (V _IMG ) obtained by converting the weighted average luminance V _IMG into a pixel value is equal to or greater than the dead band upper limit value H _TH or equal to or smaller than the dead band lower limit value L _TH. In this case, since the difference between the value F _{B → V} (V _IMG ) obtained by converting the weighted average luminance V _IMG into a pixel value and the target pixel value M _TH is large, in step S250, the difference is reduced. A target exposure control amount is calculated. At the same time, the amount of change between the calculated target exposure control amount and the current exposure control amount is also calculated. Hereinafter, an example of a method for calculating the target exposure control amount will be described.

When the above-described weighted average luminance V _IMG is the current road surface luminance equivalent value B _IMGk and the value obtained by converting the target pixel value M _TH into the luminance equivalent value is B _TGT (= F _{V → B} (M _TH )), the frame Assuming that the rate is constant, the following Equation 2 is established.
(Formula 2)
B _TGT / B _{IMG K} = (ShutSpd _TGT · 10 ^{GAINTGT / 20} ) / (ShutSpd _{IMG k} · 10 ^{GAINIMG k / 20} )
FV _{→ B} is a function for converting the pixel value into a luminance equivalent value, ShutSpd _TGT is the control target shutter speed, GAIN _TGT is the control target gain, ShutSpd _{IMG k} is the current shutter speed, and GAIN _{IMG k} is the current control gain. .

That is, in step S250, ShutSpd _TGT · 10 ^{GAINTTG / 20} of the above equation 2 is calculated as the next target exposure control amount.

Further, according to Equation 2, the change amount C between the current exposure control amount and the next target exposure control amount is expressed by the current road surface luminance equivalent value B _{IMG k} and the luminance equivalent value B _TGT corresponding to the target pixel value M _TH. The ratio can be obtained.

Then, in step S270, it determines whether the magnitude of the change amount C of the current amount of exposure control and the next target exposure control amount is smaller than the decrease side threshold T _LO. If “Yes” is determined at this time, the change amount C of the target exposure control amount is limited to the decrease limit value T _LO in step S280. That is, the ratio (magnification) between the road surface luminance equivalent value B _{IMG k} for calculating the target exposure control amount and the luminance equivalent value B _TGT corresponding to the target pixel value M _TH is replaced with the reduction limit value T _LO , Calculate the exposure control amount.

On the contrary, in step S290, the ratio (magnification) between the road surface luminance equivalent value B _{IMG k} indicating the magnitude of the change amount C and the luminance equivalent value B _TGT corresponding to the target pixel value M _TH is increased side limit value T _HI. It is judged whether it is larger than. At this time if it is determined that "Yes" at step S300, the limits of variation C of the target amount of exposure control to increase the limit value T _HI. That is, the ratio (magnification) between the road surface luminance equivalent value B _{IMG k} indicating the change amount C of the target exposure control amount and the luminance equivalent value B _TGT corresponding to the target pixel value M _TH is replaced with the increase limit value T _HI . A target exposure control amount is calculated.

  Thus, the reason why the target exposure control amount is limited when the change amount C of the target exposure control amount with respect to the current exposure control amount is large will be described below.

  As shown in FIG. 8, for example, when buildings and roadside trees that block sunlight are arranged at equal intervals, a bright portion that is sunny and a dark portion that is shaded appear repeatedly on the road surface. In this way, when the vehicle travels on a road where road surface luminance is low and high, the repetition cycle of the low luminance portion and the high luminance portion appearing on the imaging screen of the camera 1 is the exposure control cycle of the camera 1. In other words, so-called hunting occurs in which the weighted average luminance of the area diverges because the exposure amount of the camera 1 by the exposure control cannot be adapted to the brightness of the road surface.

  More specifically, when the camera 1 captures the first low-luminance portion, the area pixel value calculated as the road surface luminance is low, so the control unit 2 outputs a camera control value for increasing the exposure to the camera 1. . When the exposure amount of the camera 1 is increased according to this camera control value, the road surface in the area for calculating the luminance is a high luminance portion, and the area pixel value becomes too high with the increased exposure amount. ing. Therefore, the control unit 2 outputs a camera control value for reducing the exposure amount to the camera 1. Thus, the area pixel value diverges by repeating the state in which the control of the exposure amount of the camera and the brightness of the road surface conflict.

Therefore, in this embodiment, the magnitude C is determined by comparing the change amount C of the next target exposure control amount with respect to the current exposure control amount with the increase limit value T _HI and the decrease limit value T _LO. It was decided to limit the large change amount C exceeding the limit value. As a result, even in a situation where a low-luminance portion and a high-luminance portion occur repeatedly on the road surface, such as in the shade and in the sun, the amount C of change in the target exposure control amount is limited. Can be suppressed.

Note that the decrease limit value T _LO and the increase limit value T _HI described above are the change amount C, which is the ratio (magnification) between the luminance equivalent value B _TGT of the target pixel value M _TH and the current road luminance equivalent value B _{IMG k.} Since they are to be compared, the decrease limit value T _LO is set to a value in a range greater than 0 and less than 1, and the increase limit value T _HI is set to a value greater than 1.

However, it is preferable to set the increase limit value _THI and the decrease limit value _TLO so that the magnitudes thereof differ between when the target exposure control amount increases and when it decreases. For example, when the target exposure control amount is decreased, if the target exposure control amount is limited to 50% of the current exposure control amount, the target exposure control amount is increased more than 150% of the current exposure control amount. It is set to allow a large change, for example, up to about 250 percent. Exposure control hunting occurs when the same amount of increase / decrease in exposure control amount is repeated. Therefore, by size and decreased when the magnitude of the time increase of the amount of exposure control is set to a different increase limit value T _HI and reduced limit value T _LO, suppressing the degree of more effectively hunting Can do.

In particular, when the increase limit value _THI and the decrease limit value _TLO are set so that the magnitude when the exposure control amount increases is different from the magnitude when the exposure control amount decreases, as described above, the magnitude when the exposure control amount increases. Is preferably larger than the size at the time of decrease. In this case, it is possible to effectively suppress the degree of hunting while corresponding to the brightness change characteristics at the entrance and exit of the tunnel.

Finally, in step S310, a camera control value corresponding to the exposure control amount calculated in step S250 or the exposure control amount corrected in steps S280 and S290 is output. That is, a combination of a gain and a shutter speed for achieving the target exposure control amount ShutSpd _TGT · 10 ^{GAINTTG / 20} is determined, and the determined gain and shutter speed are output as camera control values. If the target exposure control amount exceeds the gain or shutter speed adjustment range, a camera control value corresponding to the target exposure control amount is generated by changing the frame rate.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

For example, in the above-described embodiment, the amount of change C between the target exposure control amount and the current exposure control amount is _{calculated by} multiplying the luminance equivalent value B _TGT of the target pixel value M _TH with the current road luminance equivalent value B _{IMG k} (magnification ). However, the amount of change between the target exposure control amount and the current exposure control amount can be calculated from the difference between the target exposure control amount and the current exposure control amount.

It is a block diagram which shows the structure of the lane departure warning apparatus in embodiment. It is a flowchart which shows the process for recognizing and outputting a white line position in the process part. 4 is a flowchart showing details of exposure control processing of the camera 1. Three areas set corresponding to the road surface portion excluding the white line, that is, the center area B set corresponding to the road surface portion of the lane in which the vehicle travels, and the white line that divides the lane in which the vehicle travels It is explanatory drawing which shows the left side area C_LFT and the right side area C_RGT which are each set in the both-sides part exceeding this. It is explanatory drawing for demonstrating that the center area B and right-and-left side area C_LFT, C_RGT are corrected by the presence or absence of a preceding vehicle, (a) is the center area B and left-right side area C_LFT, C_RGT when there is no preceding vehicle. (B) shows the shape of the center area B and the left and right side areas C_LFT and C_RGT when there is a preceding vehicle. It is explanatory drawing for _{demonstrating} the calculation method of the brightness _| luminance _{VIMG_B} of the center area B, the brightness _| luminance _{VIMG_C_RGT of} the right side area, and the brightness _| luminance _{VIMG_C_LFT of} the left side area. It is a characteristic view which shows the change characteristic of weight value _WBC . It is explanatory drawing for demonstrating the principle which hunting generate | occur | produces in exposure control.

Explanation of symbols

1 Camera 2 Control unit 3 Image I / F
4 CPU
5 Memory 6 Communication I / F
7 Lane departure warning ECU
8 Alarm section

Claims (7)

An exposure control device that controls the exposure of a camera that is mounted on a vehicle and repeatedly outputs an image signal for detecting a white line that divides a lane on a road on which the vehicle travels,
In the image signal output from the camera, area setting means for setting an area corresponding to a portion excluding the white line on the road;
Exposure control means for performing exposure control of the camera so that the pixel value of the area in the image signal becomes a target pixel value;
When the pixel value of the area is different from the target pixel value, the exposure control means calculates a next exposure control amount for making the area pixel value close to the target pixel value, and calculates the current exposure control amount and the next time If the amount of change from the exposure control amount is greater than a predetermined limit value, the calculated next exposure control amount is changed to an exposure control amount in which the change amount from the current exposure control amount is limited to the limit value. An exposure control device for a white line detection camera, wherein correction is performed.   When a predetermined dead zone is set on the basis of the target pixel value and the area pixel value belongs to the dead zone, the exposure control means considers that the area pixel value is equal to the target pixel value, and sets an exposure control amount. 2. The white line detection camera exposure control device according to claim 1, wherein the exposure control device is invariable.   As the limit value, an increase limit value when the exposure control amount increases and a decrease limit value when the exposure control amount decreases are provided, and the magnitude when the exposure control amount increases and the magnitude when the exposure control amount decreases 3. The exposure control device for a white line detection camera according to claim 1, wherein the increase limit value and the decrease limit value are set so as to be different from each other.   The white line detection camera according to claim 3, wherein the increase limit value and the decrease limit value are set so that a magnitude when the exposure control amount increases is larger than a magnitude when the exposure control amount decreases. Exposure control device.   5. The amount of change between the current exposure control amount and the next exposure control amount is obtained using a ratio between the current road surface luminance and the road surface luminance corresponding to the target pixel value. An exposure control device for a white line detection camera according to any one of the above.   6. The white line detection camera exposure control device according to claim 1, wherein the area setting means sets a plurality of areas in the image signal.   The area setting means sets, as the plurality of areas, a center area corresponding to a road surface portion of a lane in which the vehicle travels, and on both side portions beyond a white line that divides the lane in which the vehicle travels. The white line detection camera exposure control device according to claim 6, wherein left and right side areas are set.

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