JPH11237665A - Electronic image photographic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decide a correct exposure level through a photographing lens and to decide exposure at the time of flashing with good operability without sacrificing size or cost, etc., in an electronic image photographic device for photographing an image by using an image pickup element. SOLUTION: This device is equipped with a flashlight emitting means 12 which performs light pre-emission before the main light emission at the time of photographing. In the device, the image is picked up by using the image pickup element 1 outputting a signal in accordance with light quantity made incident through the photographing lens. In such a case, the device is provided with light pre-emission control means 9, 10 and 11 monitoring the output level of the element 1 at the time of the light pre-emission by the means 12 and stopping the light pre-emission when a monitored value attains a specified level, and emitted light quantity setting means 21, 22 and 11 monitoring and integrating the emitted light quantity in the light pre-emission by the means 12 and setting the emitted light quantity in the main light emission by the means 12 based on the integrated monitored value at the time of stopping the light pre-emission.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an electronic image photographing apparatus such as a digital camera using an image sensor for inputting an image.

[0002]

2. Description of the Related Art Conventionally, a camera using a silver halide film employs a photoelectric conversion element in which a pre-emission is performed to determine an exposure at the time of accurate flash photography, and a light emission amount is set at a position equivalent to the film surface. And the amount of exposure to the film is determined from the results.

[0003] However, in flash photography by a so-called digital camera in which photography is performed using an image sensor,
In order to determine the light emission level, more accurate exposure is required because the dynamic range of the image sensor is narrower than that of the silver halide film.

[0004] Further, in a digital camera, it is difficult to adopt a TTL metering method similar to that of a silver halide film camera due to constraints such as a small image size. For this reason, for example, Pre-emission is performed with a predetermined amount of light. At that time, the amount of exposure is measured by the image sensor, and the exposure level of main emission during photographing is determined from the result.

[0005] 2. Without performing pre-emission, the amount of exposure at the time of photographing is monitored by a separately provided photoelectric conversion means, and it is estimated that an appropriate amount of exposure has been reached, and emission is stopped.

Various methods have been adopted.

[0007]

However, the above-mentioned 1.
In, because the dynamic range of the image sensor is narrow, the output of the image sensor is likely to be saturated when shooting a short distance or a white subject. Also, when photographing a subject having a long-distance low reflectance, a situation arises in which the signal is buried in noise and the main light emission level cannot be accurately determined. For this reason, it often occurs that the pre-emission is re-executed again by changing the amount of light emission of the flash, or the main emission amount is determined based on inaccurate information.

[0008] In addition, although some contrivances have been made to use the autofocus signal together with the autofocus signal or the like, the reliability of the autofocus may be low at a brightness that requires flash photography. If not, the exposure amount could not be determined accurately, and the operability was significantly impaired.

On the other hand, as described in 2. In particular, when a zoom lens or the like is equipped, a significant difference occurs between a subject to be photographed and a subject that is metering due to a difference in angle of view,
There have been problems such as an inability to determine an accurate exposure amount.

[0010] In general, the light receiving portion of the image sensor is very small compared to a silver halide camera, the distance from the rear end of the lens to the surface of the image sensor is short, and an optical low-pass filter, an infrared cut filter, and the like are provided. Therefore, it is very difficult to provide photometric means equivalent to a silver halide film camera in the photographing optical path.

In view of the above, the present invention provides an electronic image photographing apparatus for photographing an image using an image pickup device.
An object of the present invention is to make it possible to determine an exposure amount at the time of flash with good operability without sacrificing cost or the like.

[0012]

In order to achieve the above object, the first invention of the present application has a flash light emitting means for performing a pre-light emission prior to a main light emission at the time of photographing. 2. Description of the Related Art In an electronic image photographing apparatus that performs image photographing using an image pickup device that outputs a corresponding signal, the output level of the image pickup device is monitored at the time of pre-emission of a flash light emitting unit, and when the monitor value reaches a predetermined level, the pre-emission is performed. And a light emission amount setting means for integrating the pre-light emission amount of the flash light emission means and setting the main light emission amount of the flash light emission means based on the integration monitor value at the time of the pre-emission stop. I have.

That is, a CMO that is being put into practical use in recent years
Using an S-type image sensor or the like, while monitoring the output level at the time of pre-emission from the image sensor that actually shoots an image through the imaging lens in real time, the pre-emission amount saturates the image sensor or the signal becomes noise. They are determined not to be buried in. Then, a main light emission amount (exposure amount) is determined from the pre-light emission amount, thereby realizing an electronic image photographing apparatus capable of quickly and accurately performing flash exposure.

According to a second aspect of the present invention, there is provided an electronic image photographing apparatus which has a flash light emitting means capable of emitting light at the time of photographing, and performs image photographing using an image sensor which outputs a signal corresponding to the amount of light incident through a photographing lens. And a light emission stopping means for stopping light emission of the flash light emitting means when the output level of the image sensor reaches a predetermined level during photographing with light emission of the flash light emitting means.

That is, while using an image sensor called a CMOS type or the like and monitoring the output level at the time of flash shooting from an image sensor that actually shoots an image through a shooting lens, the image sensor saturates the flash emission amount. An electronic image photographing apparatus capable of quick and accurate flash exposure without the need for separately providing a pre-emission amount monitoring means as in the first aspect of the present invention as described above so that the signal is determined not to be buried in noise. Has been realized.

[0016]

(First Embodiment) FIG. 1 shows the configuration of a digital camera (electronic image photographing apparatus) according to a first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes an image sensor, which is a kind of so-called CMOS sensor. In addition,
Although only one image pickup device for one pixel is shown in the figure, in actuality, a plurality of such devices are formed vertically and horizontally to recognize an image.

The imaging device 1 includes a photodiode (photoelectric conversion device) 2, a field effect switching device 3 for resetting the charge generated by the photodiode 2 in accordance with a command of an imaging device controller, and a photodiode 2.
A field effect element 4 which is a source follower for converting the electric charge accumulated in the photodiode, a read control element 5 for reading an output of the photodiode 2 to an output circuit and other output units, and a circuit for converting the output of the photodiode 2 into impedance. It has a constant current source 7 to be used.

Reference numeral 6 denotes a controller for controlling the operation of the image pickup device 1. Reference numeral 8 denotes an image output circuit for outputting an image signal formed based on an output signal from the image pickup device 1 to an image display panel or a memory (not shown). .

Reference numeral 9 denotes a comparator (comparing means) which compares the reference voltage output from the reference voltage generating circuit 10 with the output voltage from each photodiode 2, and outputs a signal when the output voltage reaches the reference voltage. To the control circuit 11.

The control circuit 11 controls the operation of the flash unit 12 that emits flash light. In addition,
The reference voltage generation circuit 10, the comparator 9, and the control circuit 11 constitute a pre-emission control unit described in claims.

The flash unit 12 includes a xenon lamp 15 that emits flash light by discharge, and a power supply voltage (3).
-6V) to 300V required for discharging the xenon lamp 15.
A booster circuit 13 for boosting the voltage to the vicinity, and a xenon lamp 15
A main condenser 14 for storing the discharge energy of
A trigger coil 16 for generating a high-voltage pulse for starting emission of the xenon lamp 15, a trigger capacitor 17 for generating a pulse current on the primary side of the trigger coil 16, and a resistor 18 for limiting a current charged in the trigger capacitor 17. A switching transistor 19 for supplying a trigger current in response to a light emission signal from the control circuit 11, and a switching device called an IGBT for stopping discharge by a signal from the control circuit 11 when a predetermined amount of discharge current flows to the xenon lamp 15. Element 2
0, a monitoring photodiode 21 for monitoring the amount of light generated by the xenon lamp 15, and an integrating circuit 22 for integrating the photocurrent generated by the photodiode 21.

The monitor photodiode 21, the integration circuit 22, and the control circuit 11 constitute a light emission amount setting means described in claims.

Next, the operation of the digital camera will be described in order. First, when the photographer enters the photographing preparation operation, a shutter (not shown) is opened, and the setting of the aperture and the determination as to whether or not the light emission of a flash is necessary are performed by a photometric circuit or the like.

When it is determined that the flash needs to be emitted,
The operation of the booster circuit 13 is started by the control circuit 11, and the charging of the main capacitor 14 is started.

When the charged voltage of the main condenser 14 becomes equal to or higher than a predetermined value, photographing becomes possible. When the photographer presses the shutter button, a command for pre-emission is issued from the control circuit 11, and the switching transistor 19 is turned on. As a result, a trigger voltage is applied to the xenon lamp 15 from the trigger coil 16 and the xenon lamp 15
Discharge light emission (pre-light emission) is started.

At the same time as the pre-emission is started, the charge generated in the monitoring photodiode 21 is integrated by the integration circuit 22.

Further, at the same time, the field effect element 3 is turned off from on, and the reflected light of the image is incident on the photodiode 2 of the image pickup element 1 via a photographic lens (not shown).
The charge generated in the photodiode 2 starts to be integrated into the capacitance of the diode itself.

At the same time, the read control element 5
Both the field effect element 4 and the field effect element 4 are turned on, and a voltage corresponding to the integrated charge amount of the photodiode 2 is applied to the comparator 9.

Here, the reference voltage generating circuit 10 is set to a reference voltage level higher than the noise level and lower than the image signal level required for normal photographing (image signal level for photographing). Therefore, if the pre-emission is controlled so that the output signal of the photodiode 2 reaches the reference voltage level, the pre-emission does not saturate the image pickup device 1 (photodiode 2) or prevent the signal from being buried in noise. Exposure information can be obtained.

The reference voltage level is used to prevent the flash light emission energy from being wasted due to the pre-emission, so that it takes a long time to charge the flash light during the actual photographing and the operability is deteriorated. It is desirable to set as low as possible.

When the input signal of the comparator 9 (the output signal of the photodiode 2) reaches the reference voltage level, the output of the comparator 9 is inverted, and the inverted signal is input to the control circuit 11. As a result, the control circuit 11 stops the pre-emission.

The figure shows a set of photodiodes 2
Although only the comparator 9 is shown, a plurality of sets are provided corresponding to the plurality of photodiodes 2 as described above. The pre-emission is stopped when the output of any one of the comparators 9 is inverted.

Some of the plurality of comparators 9 (for example, comparators corresponding to the photodiodes 2 disposed within a predetermined range whose center is emphasized as in the case of evaluation photometry of a normal silver halide camera) It is also possible to stop pre-emission when it is detected that 9) is reversed.

When the pre-emission is stopped, the control circuit 11 stores the integrated voltage (integrated monitor value) of the integrating circuit 22. Then, by using a coefficient or the like set in advance based on the stored voltage level, an integrating circuit 2 suitable for photographing is used.
In step 2, the main light emission integrated voltage level is set to prepare for shooting.

As soon as the above operation is completed and other photographing preparation operations (such as auto-focusing) are completed, the field effect element 3 is turned on and off once to reset the charge of the photodiode 2 and the charge of the photodiode 2 is released. Clear and start shooting.

In photographing, the main light emission operation of the flash unit 12 is started, and at the same time, the integration of the charge of the photodiode 21 is started by the integration circuit 22.

When the integrated voltage of the integration circuit 22 reaches the previously set integration voltage level for main light emission, the control circuit 11 generates a signal for stopping main light emission.

Thereafter, the shutter (not shown) is closed, and the photodiode 2 is kept in a state where no light is irradiated thereon, and the charge of the photodiode 2 is kept as it is. Then, after the exposure is completed, the readout element 5 is sequentially turned on, the electric charge generated in the photodiode 2 is output to the image output circuit 8, and the photographing is completed.

(Second Embodiment) FIG. 2 shows a second embodiment of the present invention.
1 illustrates a configuration of a digital camera (electronic image capturing apparatus) according to an embodiment. Note that, in the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In the present embodiment, two sets of the photodiodes 2 and 2 'are shown.

In this embodiment, the comparator 9 adds the outputs of the plurality of photodiodes 2, 2 ',..., And compares the sum with the reference voltage level generated by the reference voltage generation circuit 10, and feeds back the flash emission amount. The difference from the first embodiment is that there is no monitor circuit.

In FIG. 2, reference numerals 23, 24, and 25 denote resistors, which are connected to the outputs of the photodiodes 2, 2 ', respectively. Reference numeral 26 denotes a feedback resistor of the operational amplifier 27. As a result, the outputs of the photodiodes 2, 2 '... Are added and input to the comparator 9.

Reference numeral 28 denotes a flash unit.
The configuration is the same as that of the flash unit 12 of the first embodiment, except that there is no monitor photodiode and no integration circuit for its output.

In the present embodiment, the reference voltage generating circuit 10, the comparator 9, and the control circuit 11 constitute a light emission stopping means according to the claims.

Next, the operation of the digital camera of this embodiment will be described in order. In the first embodiment, the flash unit is pre-emitted before photographing to determine the exposure level (main light emission amount) at the time of photographing. In the present embodiment, however, the field effect element 4 is used to read the output of the photodiode 2. Since the image signal is used in principle, the image signal is not affected by the reading, so that the exposure is performed without performing the pre-emission operation by using the image signal.

When the photographer enters the photographing preparation operation, a shutter (not shown) is opened, and it is determined by a photometric circuit or the like whether or not flash emission is necessary.

When it is determined that flash emission is necessary,
The operation of the booster circuit 13 is started by the control circuit 11, and the charging of the main capacitor 14 is started. When the charged voltage of the main condenser becomes equal to or higher than a predetermined value, photographing becomes possible. When the photographer presses a shutter button (not shown), auto focus, aperture, and the like are set.
Command of flash emission is issued from 1. This allows
The switching transistor 19 is turned on, a trigger voltage is applied from the trigger coil 16 to the xenon lamp 15, and the xenon lamp 15 starts discharging and emitting light.

At the same time, the field effect element 4 is turned on from off, and the charge integration of the photodiode 2 is started. At the same time, the operational amplifier 27 is connected via the read control element 5 and the field effect element 4 which are both turned on.
A current flows so that the input terminal of the input terminal becomes equal to the reference potential.
The operational amplifier 27 includes a plurality of photodiodes 2, 2 '.
Are added, and the added output is applied to the comparator 9.

In the reference voltage generation circuit 10, an addition output level at which a preset appropriate exposure amount is expected is set as a reference voltage level.

When the input of the comparator 9 reaches this reference voltage level, the output of the comparator 9 is inverted,
This inverted output is input to the control circuit 11. As a result, the control circuit 11 instructs the flash emission to stop, the IGBT 20 is turned off, and the flash emission stops.

Thereafter, the shutter is closed, and the exposure is completed. At this time, the charges of the photodiodes 2, 2 '... Are maintained as they are, and the read control element 5 is driven in accordance with the subsequent normal image signal reading process, and the normal image signal reading order is sent to the image output circuit 8. The image signal is output according to.

As described above, in the first embodiment, the outputs of the plurality of photodiodes 2 are input to the comparator 9, and the control circuit 11 controls the amount of flash light emission based on the results, and in the second embodiment, After integrating the outputs of the plurality of photodiodes 2, 2 ',..., They are input to the comparator 9, and the flash emission amount is controlled based on the average exposure amount of a certain portion. Each of these has advantages and disadvantages, and in some cases, these may be used in combination.

In the first embodiment, pre-emission is performed prior to actual exposure, and the output level of the photodiode 2 at that time is read out in real time, and the pre-emission amount monitor value at the time when the output level reaches a predetermined level is actually used as a basis. In the second embodiment, the image signal is read out in real time at the time of actual exposure, and when a predetermined exposure level is reached, the flash emission is stopped to determine the exposure amount. The difference is that the configuration of the second embodiment is simpler, but in implementing this, the image signal after reading the amount of light received by the photodiode in real time is kept in a state free from noise and the like. Must be. It is said that a general CMOS sensor can read out the amount of received light in real time without affecting the amount of charge stored in the sensor.

However, in this CMOS sensor, there is a configuration in which it is impossible to monitor the amount of light received by the photodiode in real time in order to cancel various noises. In this case,
As in the first embodiment, it is necessary to consider separately when monitoring the light emission amount and when actually exposing. Here, an embodiment has been described that can cope with any of these.

Further, there is no relation between the method of determining the exposure amount, whether the peak of the image pickup device or the integration of a plurality of devices, and the real-time monitoring of the photodiode, and the combination thereof is completely free.

Further, by combining the above embodiments with the photometric value when the flash is not fired, a digital camera requiring a more accurate exposure level than a conventional silver halide camera, It is also possible to perform accurate exposure in a state where sunlight and a fluorescent light and a flash light are mixed, which were extremely difficult, and it is possible to realize a camera that is easier to use.

[0057]

As described above, according to the first aspect of the present invention, a CMOS type image sensor, which has recently been put into practical use, is used. While monitoring the output level at the time of the pre-emission in real time, the pre-emission amount can be determined so as not to saturate the image pickup device or bury the signal in noise. Then, since the main light emission amount (exposure amount) is determined from the pre-emission amount, the factors contributing to the error of the exposure amount are greatly reduced, and the overwhelmingly accurate determination of the exposure amount is compared with the conventional method. An electronic image photographing apparatus that can be quickly performed can be realized with a simple configuration.

According to the second aspect of the present invention, the CMOS
Using an image sensor called a type, the output level during flash shooting from the image sensor that actually shoots an image through the shooting lens is monitored in real time, and the amount of flash emission becomes saturated or the signal becomes noise. You can decide not to be buried. Therefore, there is no need to separately provide a pre-emission amount monitoring means as in the first aspect of the invention, and an electronic image photographing apparatus capable of quick and accurate flash exposure can be realized with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a digital camera according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a digital camera according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Image sensor 2 ... Photodiode 3, 4, 5 ... Field effect element 6 ... Image sensor controller 7 ... Constant current source 8 ... Image signal output circuit 9 ... Comparator 10 ... Reference voltage generation circuit 11 ... Flash control circuit 12 ... Flash unit 13 Boost circuit 14 Main capacitor 15 Xenon lamp 16 Trigger coil 17 Trigger capacitor 18 Resistor 19 Transistor 20 IGBT 21 Monitor photodiode 22 Integration circuit 23, 24, 25 Resistor 26 Resistance 27 ... Op amp 28 ... Flash unit

Claims (14)

[Claims] 1. An electronic image photographing apparatus, comprising: a flash light emitting means for performing a pre-emission before a main light emission at the time of photographing; and photographing an image by using an image sensor which outputs a signal corresponding to the amount of light incident through a photographing lens. A pre-emission control unit that monitors an output level of the image sensor at the time of pre-emission of the flash emission unit and stops the pre-emission when the monitored value reaches a predetermined level; Monitor the integration,
An electronic image photographing apparatus, comprising: a light emission amount setting unit that sets a main light emission amount of the flash light emission unit based on an integral monitor value at the time of stopping the pre-emission. 2. The electronic image photographing apparatus according to claim 1, wherein the predetermined level is set higher than a noise level and lower than a photographing image signal level. 3. The pre-emission control unit includes a comparison unit that compares an output level of the image sensor with the predetermined level, wherein the image sensor includes the comparison unit and a control unit for forming an image. 3. The electronic image photographing apparatus according to claim 1, wherein a signal is output to an image output unit that outputs a signal. 4. An image pickup device comprising: a plurality of light receiving elements; wherein the image pickup element outputs all output signals of the plurality of light receiving elements to the image output means; 4. The electronic image photographing apparatus according to claim 3, wherein an output signal of the section is output to the comparison unit. 5. The electronic image photographing apparatus according to claim 3, wherein the comparing unit is built in the image sensor. 6. An image pickup device comprising a plurality of light receiving elements, wherein said image pickup element adds an element output means for outputting an output signal for each light receiving element and an output signal of the light receiving element for each image pickup area. The electronic image photographing apparatus according to any one of claims 1 to 5, further comprising a plurality of area output means for outputting the image data. 7. The electronic image photographing apparatus according to claim 1, wherein the image pickup device is a CMOS type image pickup device. 8. An electronic image photographing apparatus which has a flash light emitting means capable of emitting light at the time of photographing, and performs image photographing using an image pickup device which outputs a signal corresponding to the amount of light incident through a photographing lens. When the output level of the image sensor reaches a predetermined level during shooting with light emission,
An electronic image photographing apparatus, comprising: a light emission stopping means for stopping light emission of the flash light emitting means. 9. The electronic image photographing apparatus according to claim 8, wherein the predetermined level is an image signal level corresponding to an appropriate exposure amount. 10. The light emission stopping means has a comparing means for comparing an output level of the image sensor with the predetermined level, and the image sensor has the comparing means and a signal for forming an image. The electronic image photographing apparatus according to claim 8, wherein a signal is output to an image output unit that outputs the image data. 11. The image pickup device is formed of a plurality of light receiving devices, wherein the image pickup device outputs all output signals of the plurality of light receiving devices to the image output means, and outputs one of the plurality of light receiving devices. The electronic image photographing apparatus according to claim 10, wherein an output signal of the section is output to the comparison unit. 12. The electronic image photographing apparatus according to claim 10, wherein the comparing unit is built in the image sensor. 13. The image pickup element is formed of a plurality of light receiving elements, wherein the image pickup element adds an output signal for outputting an output signal for each light receiving element and an output signal of the light receiving element for each image pickup area. 13. The electronic image photographing apparatus according to claim 8, further comprising a plurality of area output means for outputting the image data. 14. The electronic image photographing apparatus according to claim 8, wherein said image sensor is a CMOS type image sensor.