JP2007295093A - Exposure control method of on-vehicle monitoring camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exposure control method of an on-vehicle monitoring camera with which an image with a proper exposure can quickly be obtained even when a rapid change takes place in luminance in front of a vehicle in spite of a simple configuration. <P>SOLUTION: When the power switch of the in-vehicle monitoring camera is closed, a photometry sensor executes photometry. The exposure time of an electronic shutter of a CCD is determined on the basis of a photometry signal and the camera carries out automatic bracketing photographing on the basis of the exposure time. An image signal output from the CCD is subjected to various processes and the processed signal is given to a memory. Image data with a proper exposure or image data closest to the proper exposure are selected from three image data received by the memory, the selected image data are given to an image processing section, and a new reference exposure time is established, and the camera executes succeeding automatic bracketing photographing. The image processing section applies image processing to the received image data, outputs the processing result to a drive control unit, and the drive control unit executes travel control to make the vehicle travel along a white line. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exposure control method for controlling the exposure of an in-vehicle monitoring camera that captures an image in front of a vehicle.

  Conventionally, as an automatic traveling control device for a vehicle, an image in front of the vehicle imaged by an in-vehicle monitoring camera is processed to recognize a white line drawn on the road, and based on the recognition result, an engine, a brake, a steering, etc. By controlling the vehicle to automatically run along the white line on the road and the image in front of the vehicle imaged by the in-vehicle monitoring camera, recognize the distance from the preceding vehicle, based on the recognition result, 2. Description of the Related Art A vehicle that automatically drives a vehicle so as to keep a distance from a preceding vehicle constant by controlling an engine, a brake, and the like is known (for example, Patent Documents 1 and 2).

  The vehicle-mounted surveillance camera used in such an automatic travel control device has a so-called auto exposure function that detects ambient illuminance with a built-in optical sensor and automatically controls the camera exposure according to the illuminance. There is something to do.

  However, if the illuminance around the vehicle suddenly changes while entering or exiting a tunnel while the vehicle is running, in-vehicle surveillance cameras with an exposure auto function can only perform exposure control after the ambient illuminance changes. In-vehicle surveillance camera's exposure cannot follow the sudden change in illuminance in the surrounding area, and the clear image required for image processing cannot be acquired for a certain period of time. Image processing for automatic driving control is temporarily inaccurate. There is a problem of becoming.

In order to improve such a problem, an exposure control device for an in-vehicle monitoring camera as described in Patent Document 3 is known. This exposure control device uses the exposure control unit to determine the illuminance in the vehicle traveling direction from the vehicle ambient illuminance detected by the upward light sensor with a wide light reception angle and the vehicle front illuminance detected by the front light sensor with a narrow light reception angle during traveling of the vehicle. When the ambient illuminance changes abruptly, such as at the entrance and exit of a tunnel, by changing the exposure of the imaging unit for vehicle monitoring immediately before that, the imaging unit immediately changes the ambient illuminance (for example, , Immediately after entering the tunnel).
JP 2000-242769 A Japanese Patent No. 2715442 JP 2005-167842 A

  The exposure control device described in Patent Document 3 requires two sensors, an upper light sensor with a wide light reception angle and a front light sensor with a narrow light reception angle, in addition to the light sensor provided in the vehicle-mounted monitoring camera. However, there is a problem in that the number of parts increases, the associated cost increases and control becomes complicated.

  The present invention has been made to solve the above-described problems, and it has a very simple configuration without adding any parts to a conventional in-vehicle surveillance camera, and is used as a tunnel entrance / exit. An object of the present invention is to provide an exposure control method for an in-vehicle monitoring camera that can quickly obtain an image with an appropriate exposure even when there is a sudden change in luminance in front of the vehicle.

  The exposure control method for an in-vehicle monitoring camera according to the present invention is an exposure for an in-vehicle monitoring camera having a function of auto-bracketing shooting that continuously shoots a plurality of frames while changing the exposure stepwise with a predetermined exposure value as a reference exposure value. In the control method, a first step of selecting the appropriate exposure or the image data closest to the appropriate exposure from the image data of the plurality of frames obtained by the auto bracketing photographing, and the exposure value of the image data selected in the first step And a second step of performing auto bracketing shooting with the new reference exposure value, and hereinafter, the first step and the second step are alternately repeated.

  In addition, the reference exposure value when performing the first auto bracketing shooting after the vehicle-mounted monitoring camera is turned on is an exposure time determined based on the photometric value measured by the photometric sensor provided in the vehicle-mounted monitoring camera It is characterized by being. Further, the proper exposure selected in the first step or the image data closest to the proper exposure is input to an image processing unit for recognizing a specific object in the photographing screen based on the image data. To do.

  According to the exposure control method for the in-vehicle monitoring camera of the present invention, after performing auto bracketing shooting with a predetermined exposure value as a reference exposure value, an image closest to the appropriate exposure or the appropriate exposure is obtained from a plurality of obtained image data. The data is selected as a new reference exposure value, and the auto bracketing shooting is repeated, so there is no need to add any parts to the conventional in-vehicle surveillance camera. Even when there is a sudden change in the brightness in front of the vehicle, an image with proper exposure can be obtained quickly.

  Moreover, it is preferable that the predetermined exposure value initially set as a reference is an exposure time determined based on a photometric value measured by a photometric sensor provided in the in-vehicle monitoring camera. Further, the appropriate exposure or the image data closest to the appropriate exposure is input to an image processing unit that recognizes a specific object in the shooting screen based on the image data. For example, a white line on a road, a preceding vehicle, etc. The specific object can be reliably recognized.

  In FIG. 1 showing the electrical configuration of the in-vehicle monitoring camera 10 to which the exposure control method of the present invention is applied, a well-known CCD 14 is provided behind the taking lens 12 facing the front of the vehicle. The photographing lens 12 is a pan-focus type wide-angle lens, and a subject image is always formed on the photoelectric surface of the CCD 14.

  In the CCD 14, micro red color filters of red (R), green (G), and blue (B) are arranged in a matrix on the photocathode, and MOS diodes (MOS capacitors) are respectively arranged behind them. Yes. The signal charge accumulated in each MOS diode is sequentially read out as a voltage signal (image signal) having luminance information of each color of RGB corresponding to the signal charge based on a pulse supplied from the CCD driver 15.

  The CCD 14 has a so-called electronic shutter function that controls the charge accumulation time (exposure time) of each MOS diode according to the timing of the shutter gate pulse. In the present invention, as shown in FIG. As a reference, auto bracketing shooting is performed in which three frames are continuously shot while changing the exposure stepwise so that the exposure time is shifted by, for example, ± 1 EV.

  The predetermined exposure time serving as the reference is determined based on the brightness in front of the vehicle measured by the photometric sensor 16 immediately after the power is turned on. Thereafter, of the three image data obtained by the immediately preceding auto bracketing shooting, the exposure time at which the appropriate exposure is obtained or the exposure time closest to the appropriate exposure is set as the reference exposure time in the next auto bracketing shooting. . The determination as to whether or not the exposure is appropriate will be described later.

  The image signal output from the CCD 14 is sent to the analog signal processing circuit 17. The analog signal processing circuit 17 includes signal processing circuits such as a sampling hold circuit, a color separation circuit, and a gain adjustment circuit. In the analog signal processing circuit 17, correlated double sampling (CDS) processing and R, G, and B colors are included. The signal is subjected to color separation processing, and the signal level adjustment (pre-white balance processing) of each color signal is performed.

  The signal output from the analog signal processing circuit 17 is converted into a digital signal by the A / D converter 18 and then stored in the memory 20. The timing generator (TG) 22 provides timing signals to the CCD driver 15, the analog signal processing circuit 17 and the A / D converter 18 in accordance with instructions from the system controller 24, and the synchronization of each circuit is achieved by this timing signal. It has been.

  The system controller 24 is a control unit that performs overall control of each circuit of the in-vehicle monitoring camera 10 as a whole. When the power switch 26 is turned on, the system controller 24 controls the operation of each unit in accordance with a program stored in the ROM 27. Further, immediately after the power switch 26 is turned on, the photometric sensor 16 measures the luminance in front of the vehicle and inputs the photometric data to the system controller 24.

  The system controller 24 compares the three pieces of image data shot by the auto bracketing shooting and stored in the memory 20, and selects image data for proper exposure from among the three pieces of image data. To determine whether or not the image data has proper exposure, the average density of the image is compared with the density of 18% gray, and if both match, the proper exposure is determined. In addition, when there is no image data with proper exposure, image data closest to the proper exposure is selected. Here, “close to proper exposure” is, for example, within ± 2 EV from proper exposure.

  Then, the system controller 24 uses the exposure time (shutter speed) when the selected image data is captured as a reference exposure time for the next auto bracketing imaging (see FIG. 2), and the selected image data is converted into the CCD. Send to driver 15. At the same time, the same image data is sent to the image processing unit 30.

  Based on the input image data, the image processing unit 30 performs image processing such as recognition of a white line of a road that is a specific target object and recognition of a distance from a preceding vehicle, and the processing result is sent to the travel control device 31. Output. The travel control device 31 is an engine control signal, a brake control signal, and a steering control signal that are necessary for automatic travel control such that the vehicle travels along the white line or keeps the distance from the preceding vehicle constant. Are output to each control unit 32.

  Next, the operation of the above embodiment will be described with reference to the flowchart of FIG. When the power switch of the in-vehicle monitoring camera 10 is turned on (st1), a predetermined control program is read from the ROM 27 into the system controller 24, and control of the in-vehicle monitoring camera 10 is started. First, photometry is performed by the photometry sensor 16 (st2), and this photometry signal is input to the system controller 24.

  The system controller 24 determines the exposure time (shutter speed) of the electronic shutter of the CCD 14 based on the photometric signal and sends it to the CCD driver 15. The CCD driver 15 controls the CCD 14 and performs auto-bracketing shooting for three frames based on the exposure time (st3).

  The image signal output from the CCD 14 is input to the memory 20 through the analog signal processing circuit 17 and the A / D conversion circuit 18. The system controller 24 selects image data with appropriate exposure from the three pieces of image data input to the memory 20 (st4), and sends it to the image processing unit 30.

  If there is no image data for proper exposure, the image data closest to the proper exposure is selected (st5) and sent to the image processing unit 30. Although the possibility is extremely low, if there is no image data close to the appropriate exposure, for example, if the image is too dark and the image is crushed black or too bright and white, the photometric sensor 16 again Re-measure the light (st2).

  The image processing unit 30 performs predetermined image processing on the input image data (st6), and outputs the processing result to the travel control device 31. The travel control device 31 sends an engine control signal, a brake control signal, a steering control signal, and the like to each control unit 32 so that the vehicle travels along a white line, recognizes a sign / signal, changes a travel speed, Further, automatic traveling control such as keeping the distance from the preceding vehicle constant is performed (st7).

  As long as the power of the in-vehicle monitoring camera 10 is not turned off (st8), the system controller 24 uses the exposure time of the image data with the appropriate exposure or the image data close to the appropriate exposure as a new reference exposure time via the CCD driver 15. Then, the CCD 14 is driven to perform auto bracketing photographing (st9). Then, returning to step 4 (st4), the same sequence is repeated until the power of the in-vehicle monitoring camera 10 is turned off.

  Since auto bracketing photography is performed around the standard exposure time in this way, even if there is a sudden change in the brightness in front of the vehicle, such as at the entrance and exit of a tunnel, it is easy to obtain appropriate exposure image data. Even if the image data cannot be obtained, the auto bracketing shooting is continued based on the exposure time of the image data close to the proper exposure, so that the image with the proper exposure can be obtained more quickly than the photometry using the conventional photometric sensor alone. Data can be obtained. Accordingly, an image with proper exposure can be obtained quickly, the speed of white line recognition and sign / signal recognition can be improved, and automatic traveling control with higher accuracy can be performed.

  In the embodiment described above, the photometry by the photometry sensor is performed again even when there is no image data close to the appropriate exposure. However, the present invention is not limited to this, for example, by a gain adjustment circuit of an analog signal processing circuit. The gain may be changed.

  In the above embodiment, the auto bracketing shooting is performed three times of ± 1 EV centering on the reference exposure time. However, the present invention is not limited to this, and for example, the total of five times of ± 1 EV and ± 2 EV may be used. Good. Further, although the swing width (exposure difference) in auto bracketing shooting is set to ± 1 EV, the present invention is not limited to this, and may be set to ± 1/2 EV, for example.

  In the above embodiment, the power source of the in-vehicle monitoring camera is provided independently. However, the present invention is not limited to this. For example, the in-vehicle monitoring camera is operated immediately after the engine is started in conjunction with the engine key of the automobile. It is also possible to turn on the power, stop the engine, and turn off the power of the in-vehicle monitoring camera.

It is a block diagram which shows the electrical structure of a vehicle-mounted monitoring camera. It is a time chart which shows auto bracketing imaging | photography. It is a flowchart which shows the sequence of exposure control.

Explanation of symbols

10 On-board surveillance camera 14 CCD
16 Photometric sensor 20 Memory 24 System controller 30 Image processor 31 Travel controller

Claims (3)

In an in-vehicle surveillance camera exposure control method having an auto bracketing shooting function that continuously shoots a plurality of frames while changing the exposure stepwise with a predetermined exposure value as a reference exposure value,
A first step of selecting appropriate exposure or image data closest to proper exposure from a plurality of frames of image data obtained by the auto bracketing photographing;
The second step is to perform auto bracketing shooting using the exposure value of the image data selected in the first step as a new reference exposure value. Hereinafter, the first step and the second step are alternately repeated. An on-vehicle surveillance camera exposure control method as a feature.   The reference exposure value at the time of performing the first auto bracketing shooting after the vehicle-mounted monitoring camera is turned on is an exposure time determined based on the photometric value measured by the photometric sensor provided in the vehicle-mounted monitoring camera. The exposure control method for a vehicle-mounted surveillance camera according to claim 1.   The proper exposure selected in the first step or the image data closest to the proper exposure is input to an image processing unit for recognizing a specific object in the shooting screen based on the image data. Item 3. An exposure control method for an in-vehicle monitoring camera according to Item 1 or 2.

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