JP2837855B2 - Exposure control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure control device, and more particularly, to an exposure control device that obtains an appropriate amount of light using strobe light.

[Prior Art] In an automatic exposure camera, when the background is brighter than the main subject due to backlight or the like, the main subject is underexposed. In order to prevent this, so-called daylight synchro photography is performed using strobe light. The main subject is given an appropriate exposure amount.

However, if the background is distant, the strobe light does not reach the background portion. Therefore, when performing daylight synchro photography, in this case, on the contrary, only the main subject rises and the background is crushed dark.

The inventor of the present invention has proposed an exposure control method for compensating for insufficient exposure of a background other than the main subject even when a strobe is used to cope with such a problem.
No. 2 (see JP-A-1-214829). In this exposure control method, the exposure amount detection means emits a detection output every time the exposure amount reaches a predetermined value after the start of photometry, and is reset thereafter. An entire exposure time period is set in a time period until the number of times of generation of the detection output signal by the exposure amount detection means reaches a first predetermined value. During the entire exposure time period, normal exposure is performed in a time period until the number of occurrences of the detection output signal reaches a second predetermined value that is smaller than the first predetermined value. In the remaining time section, exposure by the flash light emitting means is performed.

[Problems to be Solved by the Invention] According to the exposure control method already proposed as described above, even when performing daytime synchro-flash photography using the flash light emitting means, the exposure of the entire exposure time Normal exposure is performed for a certain time section starting from the start time, and exposure is performed by the flash light emitting means only for the remaining time section. Therefore, the background is also normally exposed, so that the finished photograph does not have the background darkened.

However, in the above proposed method, in principle, the normal exposure time interval and the exposure time interval by the flash light emitting means are both detected by integrating the exposure amount in real time while performing the actual exposure, and using this detected value. Stipulates the end of exposure,
The so-called direct photometry method is used. Therefore, the ratio of the exposure to the main subject and the exposure to the background are set to a desired value by arbitrarily selecting the ratio of both the normal exposure and the exposure by the flash light emitting unit in the entire exposure time period. It was difficult.

The reason for this difficulty is that, in the above-described exposure control method, a detection output is issued each time the exposure amount reaches a predetermined value, so that the number of times this detection output is generated is changed between normal exposure and flash light emission. Although the ratio of both exposure time sections should be changed, normal flash emission becomes full emission in the order of several hundred μs, and therefore, if flash light adjustment is performed, it is necessary to perform light control at about 10 μs.

The means commonly used to set the dimming time is to charge the integrating capacitor to an initial voltage, and then discharge the charge in the capacitor by the photocurrent flowing through the photodiode in response to the subject light. When the potential at the end drops to the reference potential, this is detected by the comparator, and the dimming time is determined. In order to return, it is necessary to recharge the integrating capacitor to the initial voltage, and this charge / discharge control is performed by turning on / off the analog switch. In general, since the on-resistance of an analog switch is not zero, recharging the integrating capacitor to the initial voltage requires a time constant time determined by the product of the capacitance value of the capacitor and the on-resistance of the analog switch. This time is 10 μs or 20 μs. Therefore, it is quite difficult to perform direct photometry a plurality of times during flash emission, and it is desirable to limit the number of integrations to one if possible.

Next, if the potential level of the above-described reference potential is changed, the discharge time of the integration capacitor can be changed. Therefore, if this reference potential can be reset during exposure, the degree of exposure to the main subject and the degree of exposure to the background portion (Hereinafter referred to as the mixing ratio) should be able to be set quite freely. However, when the main subject is close, the flash emission time is performed on the order of 10 μs to 20 μs, whereas the microcomputer recognizes the end of the first exposure as the processing of the microcomputer. After performing some further processing from, a certain processing time is required to reset the reference potential. Therefore, it is quite difficult as a practical problem to change the mixing ratio by changing the reference potential at the time of strobe light emission from the reference potential at the time of normal exposure and resetting it.

Therefore, an object of the present invention is to solve the above-described disadvantages, and to compensate for the lack of exposure to the background other than the main subject even when performing daylight synchronized shooting,
An object of the present invention is to provide an exposure control device capable of setting the ratio of exposure between a main subject and a background to a desired value.

[Means and Actions for Solving the Problems] An exposure control apparatus according to the present invention includes an image sensor for photoelectrically converting a subject image, a unit for obtaining contrast information of a subject from the image sensor, and an exposure device formed on the image sensor. A photocharge accumulation period for photoelectrically converting and recording an object image is a first period.
The second exposure time section does not overlap with the first exposure time section.
Means for separately setting an exposure time section; means for performing normal exposure during the first exposure time section; and means for performing exposure using light emission of the light emitting means during the second exposure time section. An exposure control apparatus comprising: means for setting a ratio between the first exposure time section and the second exposure time section to be defined by contrast information of the subject. In the case where the ratio of being recognized as a relatively low luminance in the screen according to the contrast information does not exceed a predetermined value, the light emission unit does not emit light during the second exposure time period.

[Embodiment] FIG. 2 is a block diagram showing a basic system of an electronic still camera to which the exposure control device of the present invention is applied.

Photometric IC 100 including photoelectric conversion element, gate array
200, a photometric microcomputer 300 and a system control microcomputer 400 are connected to each other by a bus or other signal lines so as to exchange signals with each other. The gate array 200 is connected to an in-lens circuit 500 for controlling an aperture and a shutter, and a strobe light emitting circuit 600. The gate array 200 includes a photometric block 210 that performs a predetermined signal processing operation on the strobe light emitting circuit 600 and the like based on transmission and reception of signals to and from the photometric IC 100 and the photometric microcomputer 300, and the photometric block 210 and the photometric microcomputer. Each block (circuit) of the exposure control block 220 that transmits and receives a control signal to and from the circuit 500 in the lens based on transmission and reception of a signal to and from the circuit 300
And a circuit is formed. In this system, the lens has a diaphragm and a shutter and their driving means. The circuit 500 in the lens may also include a microcomputer. Photometric microcomputer 30
0, a switch circuit 310 for externally performing exposure correction and other function settings by an operator's operation, a distance measuring circuit 800 which detects a distance to a main subject in a known manner, and an image sensor The distribution of light and darkness in the screen is identified based on the output of
That is, a contrast detection circuit 900 that outputs a signal of contrast information indicating a ratio of the area of the main subject placed in a backlight state to the entire screen is connected to each other. Similarly, the system control microcomputer 400 is connected to a switch circuit 410 for selecting a photographing mode such as aperture priority or shutter priority or for triggering photographing.

The outline of the operation of the electronic still camera system is as follows.

A description will be given of a case where the present system performs a pre-metering operation in accordance with a command from the system control microcomputer 400. First, a photoelectric conversion output corresponding to the amount of incident light is obtained by the photometric IC 100, which is performed in a so-called open photometric state in which the aperture is fully opened. The counter corresponding to the photoelectric conversion output is performed by a counter in the photometric block 210 in the gate array 200, and the photometric microcomputer 300 calculates the value of the amount of incident light based on the count value of the counter. The shutter speed and aperture value corresponding to the photometric value are also calculated by the photometric microcomputer 300. These values are transferred to the system control microcomputer 400. The system control microcomputer 400 generates a signal for performing a predetermined display operation related to a shutter speed or an aperture value corresponding to the amount of incident light at that time based on the transferred data. In the photometric microcomputer 300, the count output of the counter of the gate array 200 is monitored, and when there is a possibility that the counter overflows, the counting condition is repeatedly changed and reset.

Next, the exposure control operation will be described. Switch circuit 410
Is pressed, the system control microcomputer 400 gives a command to the photometric microcomputer 300 to switch the system operation from the pre-photometric operation to the exposure control operation. The exposure control operation of the present system is based on the same photoelectric conversion output from the photometric IC 100 as in the above-mentioned pre-photometry, and is performed by the pre-photometry operation in the first exposure time period starting from the exposure start point. Second from the end of the exposure to the end of the exposure
In the exposure time section, it is performed by a so-called direct photometry method. When the exposure control operation starts, the photometric IC100
At the same time, the operation of accumulating the photoelectric conversion signal is started, and at the same time, the imaging device is instructed to perform the signal integration operation.
The level of the integrated value of the photoelectric conversion signal in the photometric IC 100 (more precisely, the voltage of the capacitor corresponding to the time integral of the current corresponding to the photoelectric conversion) is set for the photometric IC 100 by the photometric microcomputer 300 When the set level is reached, the IC 100 gives an integration end pulse to the photometry block 210 of the gate array 200. Photometry block 210
Resets the photometric IC 100 immediately after each pulse while integrating the number of occurrences of the integration end pulse.
When the integrated count value in the photometry block 210 reaches a value (preset value) set from the system control microcomputer 400 via the photometry microcomputer 300, the photometry block 210 Give control signal to 500. The intra-lens circuit 500 performs an operation to end the exposure based on the control signal. Here, the photometric microcomputer 30
The level of the integral value set for the photometric IC 100 from 0 and the integrated count value set for the photometric block 210 of the gate array 200 from the microcomputer 300 take appropriate values as necessary, such as exposure correction. It can be changed as needed.

The preset value can be set to one or more arbitrary values. For example, if the preset value is set to 2, the exposure ends when the integration end pulse is counted twice. In the photographing mode using a strobe, the strobe light emitting circuit 600 can start and stop emitting light in synchronization with the integration end pulse. For example,
As will be described in detail later, when the preset value is set to 2, when the photometry block 210 receives the first integration end pulse, it resets the photometry IC 100, and again performs the accumulation operation of the photoelectric conversion signal in the same IC100. At the same time, a flash start command is issued to the flash light emitting circuit 600. When the integrated value level of the photoelectric conversion signal in the IC 100 reaches the set level again and receives the next integration end pulse,
The photometry block 210 sends a control signal to the in-lens circuit 500 via the exposure control block 220 to close the shutter and stop the flash emission to end the exposure.

Next, a more detailed configuration and functions of the electronic still camera system will be described with reference to FIG. First
In the figure, parts corresponding to the respective parts in FIG. 2 are denoted by the same reference numerals.

In the photometric IC 100, both ends of the photodiode 101 are connected between both input terminals of the operational amplifier 102, the inverting input terminal and the output terminal of the operational amplifier 102 are connected to one input terminal of the comparator 103, and the other end of the comparator 103 is connected. Are supplied with a reference level signal Er. This reference level signal Er is supplied to a D / A converter provided in the photometric microcomputer 300.
This is the output of 301. Further, an integration capacitor 104 is connected between the cathode of the photodiode 101 and the ground. The connection point between the integrating capacitor 104 and the photodiode 101 is connected to the positive electrode side of a battery 106 that generates a reference voltage Ei via a drain source of a switching FET 105,
The negative electrode side of the battery 106 is grounded.

The gate array 200 has the respective circuits of the photometry block 210 and the exposure control block 220, as described in FIG. The photometric block 210 is provided for the comparator 103 of the photometric IC 100.
A charge / discharge control circuit 211 for receiving a pulse-like reset signal RT to the gate of the FET 105 in response to the integration end pulse IE which is the output of the The frequency divider 212 divides the same pulse by a frequency division ratio according to the frequency division command DV from the photometric microcomputer 300 to produce a count pulse CP, and outputs a photometric / exposure control switching signal MC from the photometric microcomputer 300. In response, the counting pulse CP from the frequency divider 212
And the integration end pulse IE of the comparator 103 of the photometric IC 100
A switching circuit 213 for selectively outputting both or one of them, an 8-bit counter 214 for counting the output pulse SC of the switching circuit 213, and a latch circuit for latching the output of the 8-bit counter 214 and supplying it to the photometric microcomputer 300. 215 respectively. 8-bit counter 214
Receives the integration end pulse IE via the switching circuit 213,
A function of giving a photometric end signal ED to the exposure control block 220 and the photometric microcomputer 300 is added. As will be described later, the preset value from the photometric microcomputer 300 to the 8-bit counter 214 is subtracted and counted by the integration end pulse IE, and the 8-bit counter 21 is counted.
The photometry end signal ED is also output when the count number of 4 becomes 0. Further, the 8-bit counter 214 has a function of receiving a light emission start signal STX and a light emission stop signal STY to the flash light emitting circuit 600 in synchronization with each integration end pulse IE when receiving the integration end pulse IE in the flash tuning mode. . The charge / discharge control circuit 211 and the exposure control block 220 are provided with a photometric start command MS from the photometric microcomputer 300.

The element shutter control signal output from the exposure control block 220 is supplied to a synchronization signal generation circuit 910.
Then, the generation circuit 910 sends a synchronization signal for regulating the operation timing of each of these circuits to the image sensor 920, the contrast detection circuit 900, and the imaging system circuit 930. Image sensor 920
Is the discharge of unnecessary charges before the start of the exposure operation and the start of the operation of accumulating signal charges by closing the transfer gate in the image sensor, that is, the start of exposure, the signal charge by opening the transfer gate and transferring the signal charges to the shift register End of accumulation operation,
That is, the image sensor is operated by itself with an exposure control function, such as the end of exposure, and the signal charge transferred to the shift register is sequentially transferred at a predetermined timing and output as an image signal. A series of driving operations for reading out a video signal are performed by this.

The video signal read from the image pickup device 920 is supplied to an image pickup system circuit 930, where the signal is converted into a signal that conforms to the standard of an electronic still camera, and is recorded on a medium.

The output of the image sensor 920 is output to the contrast detection circuit 900.
Is also supplied. In this contrast detection circuit 900,
In synchronization with the synchronization signal supplied from the synchronization signal generation circuit 910, for example, one horizontal line passing through the center of the screen, one horizontal line located between the center horizontal line and the upper end of the screen, and For a luminance signal sampled at an appropriate rate from three representative horizontal lines of one horizontal line positioned between the horizontal line and the lower end of the screen, the luminance signal is set to high luminance, medium luminance, and Digital information is obtained by ternarization according to which of the low-luminance level ranges belongs to, and this information is stored in its own memory circuit unit. That is, this digital information becomes contrast information indicating the distribution state of light and dark in the screen.

Next, the operation of the present system having the configuration shown in FIG. 1 will be described. First, the pre-metering operation of the present system will be described. The aperture provided in a lens (barrel) not shown is controlled by a circuit 500 in the lens during the pre-metering operation according to a command from the photometric microcomputer 300. Maintains open state. Microcomputer 30
When a photometry start command MS is given to the charge / discharge control circuit 211 from 0, the charge / discharge control circuit 211 outputs a reset signal RT to the photometry IC 1.
00 to the gate of the FET 105. The FET conducts during the high-level section of the reset signal RT having a relatively small duty, during which the integrating capacitor 104 is charged to the reference voltage Ei by the current from the battery 106, that is, integrated. Immediately after the reset signal RT changes to low level, the switch by the FET 105 is cut off, and the charge accumulated in the integration capacitor 104 is discharged through the photodiode 101 with a current value corresponding to the amount of light incident on the photodiode 101. You. The voltage on the positive electrode side of the integrating capacitor 104, which was Ei at the beginning of charging, decreases at a rate of change corresponding to the discharge current at this time. Accordingly, the output voltage of the operational amplifier 102 also decreases, and when this voltage becomes equal to the level of the reference level signal Er set for the comparator 103, the comparator 10
3 outputs an integration end pulse IE.

FIG. 3 is a diagram showing the timing of each signal described above.
3A shows the reset signal RT, FIG. 3B shows the positive terminal voltage of the integration capacitor 104, and FIG. 3C shows the integration end pulse IE. As shown in the figure, charging and discharging of the integration capacitor 104 are repeated in synchronization with a reset signal RT from the charging / discharging control circuit 211.
RT is formed and emitted each time the integration end pulse IE arrives. As described above, the change in the positive electrode voltage of the integrating capacitor 104 as shown in FIG. 3 (b) is due to the discharge of the charge of the capacitor through the photodiode 101. , Ie, the current value is proportional to the amount of light incident on the photodiode 101 having a proportional relationship. The time integration value of the discharge current is equal to the amount of discharge charge in the integration capacitor 104 in the same section.

That is, when the capacitance of the integrating capacitor 104 is C, and the voltage of the capacitor is reduced from the voltage Ei of the battery 106 to the reference level Er, the discharge current is t, and the time required for the _isc voltage to change from Ei to Er is t. From the above equation (1) Although the discharge current _isc in the above equation (2) corresponds to the incident light amount, since the capacitance C of the integrating capacitor 104 is fixed, the incident light amount is determined by measuring the time t. Can be. When the amount of incident light fluctuates, the value t of the above-mentioned t in each discharge is t ₀ , t ₁ , t _2.
Will be different. Also, even if the amount of incident light is constant, Er
Is changed, the value of t changes. In this system, the oscillation circuit 700 is used in the 8-bit counter 214.
, Counting pulses CP of a predetermined frequency supplied through the frequency divider 212 and the switching circuit 213 (accordingly, the output pulses SC of the switching circuit 213), and calculating the time t based on the counted value. .

In the above description, the 8-bit counter 214 is provided with a photometric / exposure control switching signal MC from the photometric microcomputer 300.
, The counting pulse CP from the frequency divider 212 or the integration end pulse IE from the comparator 103 can be selectively counted. When the system operates in the pre-photometering mode in accordance with a command from the system control microcomputer 400 (see FIG. 2), the switching circuit 213 supplies the count pulse CP to the 8-bit counter 214 and counts by the signal MC. It has become.

When the photometric operation starts, the photometric microcomputer 300 supplies a reference level signal Er to the comparator 103 via the D / A converter 301. Further, a frequency dividing instruction DV is issued to the frequency divider 212.
To set a predetermined frequency division ratio, the frequency divider 21
Initialize the frequency F of the count pulse CP which is the output of 2.
The photometry start command MS is issued from the photometry microcomputer 300, and based on this, the charge / discharge control circuit 211 resets the integration capacitor 104 by the reset signal RT (that is, charges the integration capacitor 104 to the voltage Ei). Microcomputer 300 at the same time
Resets the 8-bit counter 214 by the counter clear instruction CC. Immediately after this reset, the integration capacitor 10
The voltage of 4 starts dropping at a rate of change corresponding to the amount of light incident on the photodiode 101 due to discharge. In the time period in which the voltage of the integration capacitor 104 continues to drop, the 8-bit counter 214 simultaneously counts the count pulse CP supplied as the switching circuit output pulse SC of the switching circuit 213. The voltage of the integrating capacitor 104 drops and the operational amplifier 102
When the output of the comparator reaches the level of the reference level signal Er, the comparator
103 outputs an integration end pulse IE. Based on the integration end pulse IE, the charge / discharge control circuit 211 issues a reset signal RT again, whereby the charge / discharge operation of the integration capacitor 104 is repeated as described above. The integration end pulse IE passes through the switching circuit 213 and the 8-bit counter 214 (a circuit provided separately from the 8-bit counter unit) in the above-described order.
Photometry microcomputer 300 as photometry end signal ED
Given to. Upon receiving the photometry end signal ED, the microcomputer 300 reads the count number D of the 8-bit counter 214 via the latch 215. In the above operation, when the amount of light incident on the photodiode 101 is large, the integration capacitor 104 is discharged quickly, and the voltage of the integration capacitor 104 is set to the reference level Er within a relatively short time.
, But when the amount of incident light is small,
It takes a relatively long time for the voltage of 104 to reach Er. Therefore, when the amount of incident light is extremely small, the discharge time is extended, and the 8-bit counter 214 that counts this time may overflow. In particular, in the present system, so-called open photometry is performed in the pre-photometry mode, so that the required dynamic range of photometry is extremely wide, about 100 dB. In order to secure a discrimination accuracy of about ± 10% in this wide dynamic range, a counter of about 20 digits is usually required. However, in this system, the value of the count number D is monitored by the photometric microcomputer 300, and the reference level Er and the frequency F of the count pulse CP are changed so that the value of D is within a predetermined range. .
As a result, a wide dynamic range which cannot be covered unless a counter of about 20 bits is normally used can be covered with sufficient accuracy by a counter of only 8 bits. That is, the photometric microcomputer 300 reads the data as described above and changes the count number D of the 8-bit counter 214 from "11" to "25" in decimal.
It is discriminated whether or not the value is within the range up to 5 ". If the value of D is out of the above range, the comparator 103 is output via the D / A converter 301.
And / or the count pulse CP by the frequency divider 212 controlled by the frequency division command DV.
Is also changed and reset. If the counter number D does not fall within the above range even after this resetting, the reference signal
The level of Er and / or the frequency F of the counting pulse CP is further changed and set again. The above-described counting operation of the 8-bit counter 214 accompanying charging and discharging of the integrating capacitor 104 is configured to be repeated about 10 times per second. When discriminating that the count number D is within the above range, the photometric microcomputer 300 determines the count number D,
Based on the reference level Er and the frequency F of the count pulse CP, the amount of incident light during the pre-photometry control operation is calculated.

Next, the exposure control operation will be described with reference to the time chart shown in FIG. This exposure control operation is performed between the normal exposure in the first exposure time section τ ₀ and the second exposure time section τ
_{1 with} direct photometry.

First, when the system control microcomputer 400 switches the present system to the exposure control mode upon detecting that the trigger button has been pressed, the photometry microcomputer 300 receives this and receives a photometry / exposure control switching signal M.
The switching circuit 213 is switched by C. That is, the frequency divider 212
In place of the counting pulse CP, the integration end pulse IE from the comparator 103 is supplied to the 8-bit counter 214 as a counted pulse. Further, the exposure control operation is performed in a normal state, or how many exposure corrections are performed, and furthermore, a value corresponding to a strobe use state or the like is preset in the 8-bit counter 214 as a preset value PS from the photometric microcomputer 300. , The level of the reference level signal Er provided from the D / A converter 301 to the comparator 103 is set.

However, in the normal exposure in the first exposure time section τ ₀ , as shown in FIG. 4, since the reset pulse RT keeps maintaining the high level, the FET 105 also keeps the ON state,
As a result, the integration capacitor 104 becomes the first exposure time section τ
_{During 0} , the current from the battery 106 keeps maintaining the reference voltage Ei. Therefore, even if the subject light is incident on the photodiode 101, the comparator 103 does not output the integration pulse IE, so that the 8-bit counter 214 does not perform the counting operation.
Since the light emission start signal STX and the light emission stop signal STY, which are to be output from the bit counter 214 to the flash light emitting circuit 600, are not output, the flash light remains off.

Further, in the exposure control mode, the control signal of the element shutter supplied from the photometric microcomputer 300 via the exposure control block 220 becomes active, so that the imaging element 920 closes its transfer gate to accumulate signal charges. The operation, that is, exposure is started. Furthermore, the photometric microcomputer 300 sends a contrast information read signal to the contrast detection circuit 900. Then, the contrast detection circuit 900 supplies the contrast information held in the memory circuit unit to the photometric microcomputer 300. Photometric microcomputer 3
00 determines whether or not the ratio of the main subject, which is recognized as a dark area under a backlight, to the entire screen exceeds a predetermined value based on the contrast information. Only the normal exposure in the first exposure time section is performed, and direct strobe light control in the second exposure time section described later is not performed.

If the ratio of the main subject to the entire screen exceeds a predetermined value set in advance, direct strobe light control is performed in the second exposure time period following the normal exposure in the first exposure time period. In this case, in order to set the exposure ratio between the main subject and the background portion to a desired value, the time width of the first exposure time section in which the normal exposure is performed can be changed. That is, the time width variable adjustment of the first exposure time section τ ₀ is performed by performing arithmetic processing on the following four types of information in the photometric microcomputer 300.

(B) the above-mentioned contrast information, (b) the distance information to the main subject supplied from the distance measuring circuit 800, (c) the information on the light amount of mainly the background obtained by the above-mentioned pre-photometry operation, (d) the system control Microcomputer 40
Information that selects the exposure ratio between the main subject and the background portion given from 0. Therefore, the amount of incident light mainly from the background portion, which is irradiated on the image sensor 920 in the normal exposure mode in the first exposure time section τ ₀ , is varied. Will be.

The photometric microcomputer 300 performs a real-time clocking operation in the first exposure time interval τ ₀ by its own clock signal, and supplies an end signal TS to the gate array 200 at the end of the clocking operation. In the apparatus according to the present embodiment, the termination signal TS is converted into a strobe light emission signal STX via the 8-bit counter 214 of the gate array 200, and is supplied to the strobe light emission circuit 600. Further, the microcomputer 300 sends the direct light metering start command MS to the charge / discharge control circuit 211 at the same time as emitting the terminal signal TS. Generation timing of the signal TS and MS is counted time of the second exposure time period tau _1.

The second exposure time section τ ₁ is reached and the microcomputer
Direct photometry start command MS from 300 charge / discharge control circuit 211
, The charge / discharge control circuit 211 outputs the reset signal RT
To a low level as shown in FIG.
This is applied to the gate of the FET 105 of the IC 100 to start the direct photometry operation.

As soon as the reset signal RT goes low, FET1
05, the switch is turned off, the integration operation is started, and the charge accumulated in the integration capacitor 104 is charged to the photodiode 101 exposed under the same conditions as the exposure intensity for the image sensor.
The light is discharged through the photodiode 101 with a current value corresponding to the amount of incident light. The voltage on the positive electrode side of the integrating capacitor 104, which was Ei at the beginning of the completion of charging, starts to drop at a rate of change corresponding to the discharge current at this time. Accordingly, the output voltage of the operational amplifier 102 also decreases, and when this voltage becomes equal to the level of the reference level signal Er set for the comparator 103, the integration end pulse IE output from the comparator 103 becomes low level. Become. When the low-level output IE of the comparator 103 is input to the charge / discharge control circuit 211,
The charge / discharge control circuit 211 sets the reset signal RT to high level. That is, charging and discharging of the integration capacitor 104 are performed in synchronization with the reset signal RT from the charging and discharging control circuit 211,
This reset signal RT is issued in synchronization with the integration end pulse IE output from the comparator 103.

Since the integration end pulse IE is input to the 8-bit counter 214 through the switching circuit 213, the 8-bit counter 214 sends the strobe signal to the strobe generating circuit 600 in synchronization with the falling edge of the integration end pulse IE. Flash stop signal
Output STY. As a result, the flash stops flashing, and the second exposure time section τ ₁ has now reached the end. At the same time, the 8-bit counter 214 sends a photometry end signal ED to the exposure control block 220 to close the element shutter and end the exposure operation.

Since the above operation is performed, for example, when photographing a subject in backlight, during the normal exposure period of the first exposure time section, exposure to natural light is mainly performed on the background portion, and direct photometry in the second exposure time section is performed. In the integration period, the main subject at a short distance to which the strobe light can reach is exposed by the strobe light. At first glance, it seems that double exposure control is performed,
In the above-mentioned daytime synchro photography, exposure is performed by light from different subjects, so that neither the main subject nor the background portion flies or crushes, and furthermore, the main subject and the background portion are separated according to the shooting situation. The exposure ratio is automatically controlled, which allows you to take crisp images of every detail.

By the way, in the above embodiment, the normal exposure is mainly performed on the background portion during the first exposure time section starting from the exposure start time, and the flash on the main subject is mainly performed during the second exposure time section from the end of the first exposure time section to the end of the exposure. Although the exposure using the light emission of the light emitting means is configured to be performed, the invention is not necessarily limited to this, and the exposure is performed by the light emission of the flash light emitting means during the first exposure time interval by reversing the order. The normal exposure may be performed in the second exposure time section, or the exposure by the flash light emitting means may be performed before and after the normal exposure period. Each of these methods has advantages and disadvantages, and can be used depending on the purpose.

That is, if the present embodiment, in which the normal exposure is performed first, and then the exposure using the light emission of the flash light emitting means is applied to, for example, an electronic still camera having a shutter function such as an element shutter, so-called sharp emission of light is reduced. Even when a bad strobe is fired, the adverse effect of the surplus light emission can be neglected, so it can be said that this is a very advantageous exposure control method for close-up photography.

In addition, in the electronic still camera, when the strobe is fired when shooting with the strobe light, a large current flows at that moment and pulse noise is generated. In order to avoid the pulse noise and stably perform strobe shooting with an electronic still camera, exposure using flash light emission is performed during the first exposure time period, in reverse to the exposure sequence in the above embodiment. If the normal exposure is performed during two exposure time intervals, and if the strobe is started to be emitted before opening the element shutter of the electronic still camera, the strobe light prior to the opening operation of the element shutter is wasted. Instead, since the element shutter has not been opened at the time of the peak of the pulse noise, the video signal is stored in the CCD image pickup element without being affected by the noise.

Furthermore, in the method of performing direct flash light control during normal exposure, the total exposure time from the start of exposure to the end of exposure is counted by a microcomputer counter, for example, regardless of the direct flash light control time. can do. During that time, direct strobe light control can be performed to adjust the exposure level for the main subject.

[Effects of the Invention] As described above, according to the present invention, when a main subject under backlight is flashed during the day by the flash light emitting means,
It is possible to set the exposure ratio between the background portion and the main subject to a desired value, thereby obtaining a clear image photograph even for background portions other than the main subject while maintaining an appropriate amount of light for the main subject. A remarkable effect is exhibited.

In addition, since it is possible to perform synchro imaging by obtaining contrast information from a subject that is actually photographed by the imaging device, it is possible to obtain a good image signal according to a photographing scene.

[Brief description of the drawings]

FIG. 1 is a block diagram of a main part of an exposure control device according to an embodiment of the present invention. FIG. 2 is a block diagram showing a schematic configuration of an electronic still camera to which the exposure control device of the present invention is applied. FIGS. 3 and 4 are time charts showing the operation of each section in FIG. 1, wherein FIG. 3 shows the pre-photometry mode and FIG. 4 shows the exposure control operation. 101 photometric photodiode 920 image pickup device (means for performing normal exposure and means for performing exposure using light emission of light emitting means) τ ₀ … time (first exposure time section) τ ₁ … time (first 2 exposure time section)

Claims (2)

(57) [Claims] An imaging device for photoelectrically converting a subject image; a unit for obtaining contrast information of the subject from the imaging device; and a photoelectric charge storage for photoelectrically converting and recording the subject image formed on the imaging device. Means for setting a period separately from a first exposure time section and a second exposure time section that does not overlap with the first exposure time section; means for performing normal exposure during the first exposure time section; An exposure control device comprising: means for performing exposure using light emission of a light emitting unit in the second exposure time section, wherein a ratio between the first exposure time section and the second exposure time section is
An exposure control apparatus, comprising: means for being defined by the contrast information of the subject. 2. The method according to claim 1, wherein the light emission means does not emit light during the second exposure time interval when the ratio of the relatively low brightness within the screen does not exceed a predetermined value according to the contrast information. The exposure control device according to claim 1, wherein