JP2008206033A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus which clearly photographs required information of an object to be photographed, regardless of ambient illuminance, a state of the object to be photographed, etc. <P>SOLUTION: An imaging apparatus comprises: at least two imaging systems each including an imaging unit which outputs an output signal corresponding to the quantity of light and exposure, an exposure adjusting unit for adjusting the exposure of the imaging unit, and a detection unit which accumulates the output signal to output a photometric value; and an arithmetic unit for controlling the exposure adjusting unit for each imaging system on the basis of the photometric value, wherein the arithmetic unit includes an exposure calculation means for operating a control value controlling the exposure adjusting unit to converge the photometric value to a predetermined value for each imaging system and an illuminance calculation means for operating object illuminance from the photometric value and the control value of the one imaging system, and the exposure of the imaging unit of the other imaging system is controlled in accordance with the object illuminance. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an imaging apparatus having a plurality of imaging units.

In many imaging devices, the photometric value is calculated by accumulating the output signal of an imaging device such as a CCD, and the aperture value of the optical lens or the imaging device is adjusted so that the photometric value becomes an appropriate predetermined value. It has a function to adjust the charge accumulation time, and enables shooting in environments with different daytime and nighttime brightness such as outdoors.
However, the lens that optically adjusts the aperture value of the lens is expensive or the size of the imaging device increases, so that most of the imaging devices have a function of adjusting the charge accumulation time of the imaging element. Yes.

In an imaging apparatus having a function of adjusting the charge accumulation time, in order to cope with the backlight state, the user recognizes that the user is in the backlight state and switches the control method by pressing the backlight correction button. (For example, refer to Patent Document 1).
There has also been proposed an imaging apparatus that divides one screen into a plurality of blocks and determines the backlight state by combining photometric data of the central portion and the peripheral portion (see, for example, Patent Document 2).

JP-A-7-245758 JP-A-6-225205

  However, when shooting in the backlit state at night when mounted on a vehicle, the subject to be photographed does not always move and is not at a specific position on the screen, so the conventional technology does not work well for backlight compensation and is affected by headlights. As a result, the entire image is photographed darkly, and there is a problem that characters on the photographing object, for example, a license plate cannot be identified.

  In addition, in the conventional technology, the charge accumulation time in the imaging device is lengthened to improve sensitivity at night, and when shooting an object moving at high speed, blurring occurs in the captured image, There is a problem that details, such as letters on the license plate, cannot be identified.

  On the other hand, since the LED traffic light whose installation has been recently expanded, full-wave rectification is performed on the commercial power supply and the LED is turned on, because of the characteristics of the LED, it blinks at high speed in half of the cycle of the commercial power supply. Therefore, in the conventional imaging device, since the charge accumulation time is shortened during bright daytime photographing, there is a problem that when the blinking LED traffic light is photographed, the off state is photographed.

  An object of the present invention is to provide an imaging apparatus that clearly captures necessary information of an object to be imaged regardless of the surrounding illuminance and the state of the object to be imaged.

  An imaging apparatus according to the present invention includes: an imaging unit that outputs an output signal corresponding to a light amount and exposure; an exposure adjustment unit that adjusts the exposure of the imaging unit; and a detection unit that accumulates the output signal and outputs a photometric value. An imaging apparatus comprising: at least two imaging systems having an arithmetic unit that controls an exposure adjustment unit for each imaging system based on the photometric value, wherein the arithmetic unit is configured to measure the photometric value for each imaging system. Exposure calculation means for calculating a control value for controlling the exposure adjustment unit so as to converge to a predetermined value, and illuminance calculation means for calculating subject illuminance from the photometric value and the control value of one imaging system. And the exposure of the image pickup unit of the other image pickup system is controlled by the subject illuminance.

  The effect of the imaging apparatus according to the present invention includes a plurality of imaging apparatuses, and the exposure control method can be changed for each imaging unit. Without having to take a picture clearly.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a configuration of an imaging apparatus according to Embodiment 1 of the present invention.
The image pickup apparatus according to the first embodiment of the present invention includes four image pickup systems that pick up different fields of view, and is referred to as a first image pickup system to a fourth image pickup system in order to distinguish the image pickup systems, and is appended with the reference numerals. A, b, c, and d are assigned as alphabets. In the following description, an imaging apparatus including four imaging systems will be described. However, the present invention can be applied to an imaging apparatus including at least two imaging systems.

  Each imaging system captures each field of view and outputs an imaging unit output signal, optical units 2a to 2d that collect light and form images on the imaging units 1a to 1d, and imaging unit 1a. Exposure adjusting units 3a to 3d for adjusting the charge accumulation time of ˜1d, detectors 5a to 5d for accumulating the imaging unit output signals of the imaging units 1a to 1d to obtain photometric values, and photometric values obtained by the detectors 5a to 5d Has exposure calculation means 6a to 6d for obtaining control values of the exposure adjusting units 3a to 3d so that they converge to a predetermined value.

The imaging units 1a to 1d have a plurality of imaging elements arranged two-dimensionally. The imaging elements are arranged in the horizontal direction to form a line, and the lines are arranged in the vertical direction to form a frame. And an imaging part output signal is outputted sequentially from the image sensor in a frame.
Further, the field of view taken by the imaging unit 1a is wider than the field of view taken by the other imaging units 1b to 1d. By adopting the imaging unit 1a having such a wide field of view, the influence of a subject that temporarily enters the field of view, such as a headlight, can be reduced, and as a result, changes between day and night can be captured.
Hereinafter, an example of adjusting the charge accumulation time for the exposure of the imaging units 1a to 1d will be described, but the present invention is not limited to this.

  The imaging unit output signal varies depending on the amount of incident light and the charge accumulation time of the imaging units 1a to 1d, but the charge accumulation time can be changed by the imaging units 1a to 1d. Since the photometric value is obtained by accumulating the imaging unit output signal for one frame, the photometric value can also be changed by changing the charge accumulation time.

  In addition, the imaging apparatus includes a calculation unit 4, and the calculation unit 4 includes exposure calculation units 6 a to 6 d, and a photometric value obtained by the detection unit 5 a of the first imaging system and an exposure calculation unit 6 a of the first imaging system. Illuminance calculation means 7 for calculating subject illuminance from the calculated control value, and determination means 8 for comparing and determining the subject illuminance calculated in the illuminance calculation means 7 and a predetermined threshold value.

The illuminance calculation means 7 calculates the subject illuminance of the subject to be photographed by the imaging section 1a by taking into consideration the photometric value obtained in the detection section 5a and the control value related to the charge accumulation time obtained in the exposure calculation means 6a.
The determination means 8 compares the subject illuminance with the threshold value, and sends a daytime signal to the exposure calculation means 6a to 6d when the subject illuminance exceeds the threshold value and a nighttime signal when the subject illuminance is less than or equal to the threshold value.
The exposure calculation unit 6a of the first imaging system controls the exposure adjustment unit 3a so that the photometric value obtained in the detection unit 5a converges to a predetermined value regardless of the daytime signal or nighttime signal sent from the determination unit 8. A value is obtained and a control value is sent to the exposure adjustment unit 3a. As a result, the photometric value obtained by the detector 5a is converged to a predetermined value. Thus, in the image in which the photometric value is converged to a predetermined value, the overall brightness becomes the predetermined brightness.

  When the daytime signal is sent from the determination unit 8, the exposure calculation units 6b to 6d of the fourth imaging system to the fourth imaging system detect each imaging system in the same manner as the exposure calculation unit 6a of the first imaging system. The control values of the exposure adjustment units 3b to 3d are obtained so that the photometric values obtained in the units 5b to 5d converge to a predetermined value. On the contrary, when the night signal is sent from the determination unit 8, the exposure calculation units 6b to 6d of the second imaging system to the fourth imaging system are fixed to the exposure adjustment units 3b to 3d as predetermined control values. Send value. As a result, since the exposure of the imaging units 1b to 1d, that is, the charge accumulation time is fixed, the brightness of the image changes according to the change in the amount of incident light. For example, since the exposure of an image with a large amount of light such as a headlight is fixed, the image is completely whitened and cannot be determined as a subject. On the other hand, an image with a constant light amount such as a license plate can be recognized as an image with a predetermined brightness because the exposure is fixed. Since the number is displayed on the license plate, the number can be read from the image.

Next, the operation of the imaging apparatus according to Embodiment 1 will be described. Since the operation of the first imaging system does not differ between day and night, the first imaging system will be described first.
The imaging unit 1a accumulates the charge induced by the light collected by the optical unit 2a over the charge accumulation time controlled by the exposure adjustment unit 3a, and outputs the accumulated signal as an imaging unit output signal.
The detection unit 5a accumulates the imaging unit output signal output from the imaging unit 1a in units of one frame and outputs it as a photometric value.
The exposure calculation means 6a calculates the control value of the exposure adjustment unit 3a so that the photometric value calculated in the detection unit 5a converges to a predetermined value.
The exposure adjustment unit 3a controls the charge accumulation time of the imaging unit 1a according to the control value input from the exposure calculation unit 6a. As a result, the magnitude of the imaging unit output signal output from the imaging unit 1a changes.
With this series of feedback control, the photometric value obtained in the detector 5a converges to a predetermined value.

The illuminance calculation means 7 calculates subject illuminance using the photometric value obtained by the detector 5a and the control value obtained by the exposure calculation means 6a.
The determination unit 8 compares the subject illuminance with a predetermined threshold, and sends a daytime signal to the exposure calculation units 6a to 6d when the subject illuminance exceeds the threshold and a nighttime signal when the subject illuminance is less than the threshold.
Thus, the daytime signal or nighttime signal is sent from the determination means 8 to the exposure calculation means 6b-6d of the fourth imaging system from the second imaging system. For this reason, the operations of the second imaging system to the fourth imaging system are different when a daytime signal is sent and when a nighttime signal is sent. However, since the operation when the daytime signal is sent is the same as the operation in the first imaging system, the description is omitted.

Next, the operation in the second imaging system in which a night signal is sent will be described. Note that the operations in the third imaging system and the fourth imaging system are the same as the operations in the second imaging system, and a description thereof will be omitted.
Since the night signal has been sent, the exposure calculation means 6b sends a predetermined fixed value to the exposure adjustment unit 3b as a control value regardless of the photometric value obtained by the detection unit 5b.
The exposure adjustment unit 3b controls the exposure of the imaging unit 1b according to a fixed value.

  The image pickup apparatus according to Embodiment 1 controls the charge accumulation times of the image pickup units 1a to 1d and controls the photometric value in the daytime so that the brightness of the picked-up image becomes a predetermined brightness as a whole. Is controlled. Also, by fixing the charge accumulation time of the imaging units 1b to 1d at night regardless of the incident light, the brightness of other subjects in the image is maintained even when a subject with a large amount of light enters the field of view. The brightness of the image of the subject whose light amount does not change is kept constant.

If the photometric value is feedback-controlled at daytime at night, when a very large amount of light is incident like a vehicle headlight, the photometric value increases and the charge accumulation time is shortened in an attempt to reduce the photometric value. Therefore, the image of the subject excluding the headlight becomes dark and the subject cannot be identified.
However, since the illuminance around the license plate of the vehicle running at night is within a certain range, the license plate can be identified by fixing the charge accumulation time corresponding to this illuminance. However, at this time, the headlight part is completely crushed and information is lost.

In addition, since the field of view of the imaging unit 1a is set to a relatively wide range and the headlight part is configured to capture a small image with respect to the field of view, no significant change occurs in the photometric value calculated in the detection unit 5a. In addition, the illuminance of the subject calculated by the illuminance calculation means 7 is stabilized, and the influence on the day / night determination can be reduced.
In particular, when a strong light such as a headlight of a vehicle is photographed, the photometric value calculated by the detectors 5a to 5d changes greatly, and the calculation result of the subject illuminance calculated by the illuminance calculation means 7 changes greatly.
Moreover, it is possible to suppress a change in the photometric value calculated by the detection unit 5a by reducing the ratio of the area occupied by the headlight unit with respect to the viewing angle to be photographed.

  Note that the determination unit 8 compares the subject illuminance with a threshold value, and immediately determines that the subject illuminance exceeds the threshold value, but immediately determines that it is night time. It may be judged at night. As a result, it is possible to prevent frequent switching of processing during a twilight period from day to night.

The detectors 5a to 5d calculate the photometric value using the image pickup unit output signal of the entire frame, but set the detection range in the frame and set the image pickup unit output signal within the detection range to the photometric value. You may use for a calculation.
When it rains, the road surface gets wet and becomes a reflective surface, so the headlights of the oncoming vehicle are reflected by the road surface and the reflected light reflected by the road surface is photographed in addition to the direct light from the headlights. Since the reflected light reflected on the road surface spreads more widely than the direct light from the headlight, the subject illuminance calculated by the illuminance calculating means 7 is calculated brightly and may be erroneously determined as daytime.
Therefore, if the vicinity of the road surface reflected by the headlight is excluded from the detection range, the reflected light does not affect the photometric value, so that accurate subject illuminance can be calculated.

Further, when the determination unit 8 determines that it is nighttime, it sends a night signal to the exposure calculation units 6b to 6d, and the exposure calculation units 6b to 6d set fixed values as control values in the exposure adjustment units 3b to 3d. Based on the subject included in the field of view of the parts 1b to 1d, the determination means 8 may select a night signal or a daytime signal and determine to send it to the exposure calculation means 6b to 6d when it is determined that it is night.
For example, when the subject included in the field of view of the imaging unit 1b is not a license plate but a person walking on a sidewalk, it may be better to perform feedback control. In this case, the determination unit 8 sends a daytime signal to the exposure calculation unit 6b so that the photometric value of the imaging unit 1b converges to a predetermined value and becomes appropriate. In this way, necessary information corresponding to the subject included in the field of view can be captured.

Embodiment 2. FIG.
The imaging apparatus according to the second embodiment of the present invention is different from the imaging apparatus according to the first embodiment of the present invention in the exposure calculation means, and is otherwise the same. .
The exposure calculation means 6b of the second imaging system according to Embodiment 2 of the present invention controls a fixed value other than an integral multiple of one cycle of the commercial power supply when the daytime signal is input. The value is sent to the exposure adjustment unit 3b. The exposure adjustment unit 3b adjusts the charge accumulation period of the imaging unit 1b according to this fixed value. For example, one cycle of the commercial power supply in the 60 Hz region is 1/60 seconds, and a fixed value is set in advance so that the charge accumulation period is 1/120 seconds or more.

FIG. 2 is a waveform for explaining the blinking operation of the LED traffic light.
In the imaging apparatus according to Embodiment 2 of the present invention, one imaging unit 1b includes an LED traffic light in the field of view, and photographs the lighting state of the LED traffic light.
The LED traffic light is lit by full-wave rectification of the commercial power supply. When full-wave rectification is performed on a commercial power source indicated by a current waveform as shown in FIG. 2A, full-wave rectification indicated by a current waveform as shown in FIG. When the LED traffic light is turned on by this full-wave rectification, the LED repeats lighting and extinguishing in an LED blinking waveform as shown in FIG. That is, the lighting is repeatedly turned on / off in 1/100 seconds in the 50 Hz region (East Japan) and 1/120 seconds in the 60 Hz region (West Japan).

FIG. 3 is a timing chart showing the photographing timing in the imaging apparatus according to Embodiment 2 of the present invention.
Here, a case will be described as an example where an LED traffic light is imaged with an imaging device that repeats charge accumulation every 1/60 seconds in a 60 Hz region. As shown in FIG. 3A, the LED of the LED traffic light is turned on for 0.7 / 60 seconds at a 1/60 second period and turned off for 0.3 / 60 seconds.
At the time of bright daytime shooting, as shown in FIG. 3B, the charge accumulation period is shortened, and when the LED is turned off and the charge accumulation period is aligned, the turn-off state is photographed. At this time, the lighting state of the LED traffic light is not photographed.

Therefore, as shown in FIG. 3 (c), when the LED traffic light is photographed by the imaging unit 1b adjusted to 0.8 / 60 seconds, the state of 0.8 / 60 seconds is accumulated. The LED traffic light is photographed in a lighting state.
By the way, when the control value of the exposure adjustment unit 3b of the image pickup unit 1b is set to a fixed value during the daytime for shooting with the LED traffic light, there is a problem that subjects other than the LED traffic light cannot be shot with appropriate brightness.
However, since the imaging apparatus according to the second embodiment of the present invention includes the other imaging units 1c and 1d, one imaging unit 1b is used exclusively for LED traffic light imaging, and the other imaging units 1c and 1d are in front.・ This problem can be solved by using the camera for side photography.

Embodiment 3 FIG.
FIG. 4 is a block diagram showing a configuration of an imaging apparatus according to Embodiment 3 of the present invention.
The imaging apparatus according to the third embodiment of the present invention is the same as the imaging apparatus according to the first embodiment except that the vertical synchronization adjusting unit 9 is added. Is omitted.
As shown in FIG. 4, the vertical synchronization adjusting unit 9 receives a vertical synchronization signal from the imaging unit 1a, and inputs a vertical synchronization signal obtained by delaying the vertical synchronization signal by a quarter cycle of the commercial power supply to the imaging unit 1b. . The imaging unit 1b starts the charge accumulation period with the vertical synchronization signal as a trigger.

FIG. 5 is a waveform chart showing the charge accumulation timing of the image pickup apparatus according to Embodiment 3 of the present invention.
Even when the charge accumulation period of the imaging unit 1a of the first imaging system coincides with the OFF state of the LED signal, the charge accumulation period of the imaging unit 1b of the second imaging system is set to the OFF state of the LED signal by the vertical synchronization adjusting means 9. Accordingly, the lighting state of the LED traffic light can be photographed by the imaging unit 1b.
The image pickup apparatus according to the third embodiment includes a plurality of image pickup units 1a to 1d, and the vertical synchronization adjusting unit 9 can shift the start point of the charge accumulation period of the image pickup unit 1a and the image pickup unit 1b. It is possible to prevent shooting in the off state.

It is a block diagram which shows the structure of the imaging device by Embodiment 1 of this invention. It is a waveform for demonstrating blinking operation | movement of a LED traffic light. It is a timing chart which shows the imaging timing in the imaging device by Embodiment 2 of this invention. It is a block diagram which shows the structure of the imaging device by Embodiment 3 of this invention. It is the figure which showed the electric charge accumulation timing of the imaging device by Embodiment 3 of this invention with the waveform.

Explanation of symbols

  1a to 1d imaging unit, 2a to 2d optical unit, 3a to 3d exposure adjustment unit, 4 arithmetic unit, 5a to 5d detection unit, 6a to 6d exposure calculation unit, 7 illuminance calculation unit, 8 determination unit, 9 vertical synchronization adjustment unit .

Claims (4)

An imaging unit that outputs an output signal corresponding to the amount of light and exposure; an exposure adjustment unit that adjusts the exposure of the imaging unit; and a detection unit that accumulates the output signal and outputs a photometric value; and An arithmetic unit that controls an exposure adjustment unit for each imaging system based on the photometric value,
The arithmetic unit is
Exposure calculation means for calculating a control value for controlling the exposure adjustment unit so as to converge the photometric value to a predetermined value for each imaging system;
Illuminance calculating means for calculating subject illuminance from the photometric value and the control value of one of the imaging systems;
Have
An image pickup apparatus that controls exposure of an image pickup unit of another image pickup system based on the subject illuminance. The calculation unit includes a determination unit that compares the subject illuminance with a predetermined threshold value.
The exposure calculation means calculates a control value so that a photometric value converges to a predetermined value for each imaging system when the subject illuminance exceeds a threshold, and when the subject illuminance is equal to or less than the threshold, A control value is calculated so that a photometric value of the imaging system converges to a predetermined value, and a predetermined control value is output so that the exposure of the imaging unit of at least one other imaging system is fixed. The imaging device according to claim 1. The calculation unit includes a determination unit that compares the subject illuminance with a predetermined threshold value.
The exposure calculation means calculates a control value so that a photometric value of the one imaging system converges to a predetermined value when the subject illuminance is equal to or greater than a threshold, and at least one of the imaging units of the other imaging systems. The imaging apparatus according to claim 1, wherein a predetermined control value is output so that the exposure is fixed.   The imaging apparatus according to any one of claims 1 to 3, wherein the imaging unit of the one imaging system has a field of view in which a surrounding illuminance can be detected.

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