JPH057334A - Electronic still camera - Google Patents

Abstract

(57) [Summary] [Purpose] To reduce the release time lag due to photometry in electronic still cameras. [Structure] When the charge accumulation time is set to (2) and photometry is started, and when the average value of the output of the solid-state image sensor in the photometry exceeds the upper limit value, the charge accumulation time is set to (1) and photometry is performed. If the lower limit is exceeded, the charge accumulation time is set to (3) and photometry is performed. In this way, the average value is controlled so as to fall within the range between the upper limit value and the lower limit value, and the required exposure amount is calculated based on the average value when it falls within the range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic still camera (also called a still video camera), and more particularly to photometry thereof.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram of a conventional electronic still camera. In the figure, 1 is a lens unit, 2 is a lens drive motor, 22 is a shutter, 3 is an aperture, and 4
Is a shutter diaphragm drive circuit. Reference numeral 5 denotes a solid-state image sensor that converts an image into an electric signal, and has a function of changing the charge storage time in 1H (horizontal scanning period) units according to an instruction from the system control circuit 9. Reference numeral 23 is a γ correction circuit. Reference numeral 6 denotes A for performing analog-digital conversion on the output of the solid-state image sensor
It is a / D conversion circuit. Currently, most of the A / D conversion circuits that can be obtained at low cost have about 8-bit resolution, so the γ correction circuit 2
Generation of quantization noise is suppressed by performing A / D conversion after performing .gamma. A frame memory 7 stores the output of the A / D conversion circuit 6. A system control circuit 9 controls the entire system. 10
Is an imaging signal processing circuit that performs processing such as band limitation on the output of the memory 7. Reference numeral 11 is a D / A conversion circuit that performs digital-analog conversion on the output of the imaging signal processing circuit 10. Reference numeral 12 denotes an F that FM-modulates the output of the D / A conversion circuit 11.
It is an M modulation circuit. Reference numeral 13 is a REC (recording) amplifier that current-amplifies the output of the FM modulation circuit 12. Reference numeral 14 is a magnetic head, 15 is a magnetic sheet as a recording medium, 16 is a motor for rotating the magnetic sheet 15, and 17 is a motor servo circuit for stabilizing the rotation of the motor. Reference numeral 20 denotes a release switch. When the switch is turned on, a series of photographing operations is started. Reference numeral 21 is an average value calculation circuit for calculating the average value of the signals of the A / D conversion circuit 6.

FIG. 6 is a conceptual diagram of an interline CCD as an example of a solid-state image pickup element that is often used. In the figure, reference numeral 102 denotes a photodiode that converts light into electric charges and stores the electric charges, and reference numeral 103 denotes a vertical CCD that vertically transfers the electric charges transferred from the photodiode 102 to 1H step by step. V1 to V4 are transfer electrodes of the vertical CCD, and V1 also serves as a transfer gate for transferring the charges in the odd rows of the photodiode 102 to the vertical CCD. Similarly, V3 is a transfer gate corresponding to the photodiodes 102 in even rows. The vertical CCD is driven by four-phase transfer pulses. Reference numeral 104 denotes a horizontal CCD that horizontally transfers the charges transferred from the vertical CCD 103 one stage to 1H. H
Reference numerals 1 and H2 denote horizontal CCD transfer electrodes, which are driven by two-phase pulses. Reference numeral 105 denotes an output amplifier that converts charges into a voltage and outputs the voltage. Vout is an output terminal. Reference numeral 106 is a top drain for sweeping away unnecessary charges. V
Sub is a substrate bias terminal.

FIG. 7 is an interline CCD shown in FIG.
It is a figure which shows the drive timing of. In FIG. 7, the vertical blanking period of the odd field starts from time t1. At time t2, the transfer gate V1 is set to the high level to transfer the charges in the odd rows to the vertical CCD 103. Time t3
By applying four-phase drive pulses from V1 to V4, the charges are shifted line by line to 1H to the horizontal CCD 104, and are transferred at high speed in the horizontal direction for reading. At time t5, the charge reading of the odd field is completed and the vertical blanking period of the even field starts. Transfer gate V3 at time t6
Is set to a high level, the charges of even rows are vertically C
The data is transferred to the CD 103 and the reading is started from time t7. V
By applying a pulse of about 30 V to the sub, it is possible to sweep away the charges accumulated in the photodiode 102 up to that time toward the substrate. This can be used to control the charge storage time. Figure 7
At time t4 is the horizontal blanking period, and when a pulse is applied to Vsub as shown at time t4,
The charge accumulation time of the photodiode 102 is from 4 to t6.

FIG. 8 is a diagram showing an operation sequence of the electronic still camera shown in FIG. In the figure, when the release switch 20 (see FIG. 5) is turned on at time T0, the shutter 22 is opened and a series of photographing sequences is started. From time T0 to T1, scanning is performed M times, that is, photometric scanning while changing the charge storage time at a certain aperture value, and the optimal aperture value Av and the optimal shutter speed Tv are calculated from the average value of the output of the solid-state image sensor 5. .. The photometric operation will be described. First, the diaphragm 22 is opened and K times of scanning are performed while changing the charge accumulation time, and at the same time, the average value detection circuit 21 detects the average value of each output of the solid-state image sensor 5 for each scan. The charge storage time is the maximum value (eg 1/30) in the first scan.
Every second scan, the charge storage time is changed to 1/2 of the previous scan. If the average value which is the output of the average value calculation circuit 21 falls within a range of a certain value, the system control circuit 9 calculates the shutter speed and the aperture values Tv and Av for obtaining an appropriate exposure amount from the value. Can be done. If the average value is too large, it is considered that most of the area of the solid-state image sensor 5 is saturated. If the average value is too small, the S / N is too bad and the calculation error when obtaining the appropriate exposure amount becomes too large. Therefore, scanning is performed while changing the charge accumulation time until the average value of the image falls within the appropriate range. .. If the optimum exposure amount is not obtained even with the minimum charge storage time, the aperture is stopped by one step and the scanning is performed M times while changing the charge storage time again. This operation is repeated until the optimum exposure amount is obtained. From time T1 to T2, set the aperture to Av
Then, a reset pulse is applied to Vsub of the solid-state image sensor 5 to sweep away all the accumulated charges to the substrate and start the main exposure. At time T3, the shutter 22 is closed and the main exposure is finished. Next, from time T4 to T5, read scanning is performed and a processing signal is recorded on the magnetic sheet 15.

[0006]

Generally, the metering range required for a metering system in a general-purpose camera is EV value EV.
A minimum of 8 to EV17 is required. However, in the above-mentioned conventional example, it takes a maximum of 1 to determine the optimum exposure amount.
Scanning is required 0 times, and even if the switching time of the diaphragm is neglected only by photometric scanning, it takes 160 milliseconds or more, which causes a release time lag.

The present invention has been made to solve such a problem, and an object of the present invention is to provide an electronic still camera capable of reducing the release time lag due to photometry.

[0008]

According to the present invention, in order to achieve the above object, an electronic still camera is constructed as shown in the following (1). (1) A solid-state image sensor capable of changing a charge storage time, an average value calculating means for inputting an output of the solid-state image sensor with a linear characteristic and calculating an average value or an integrated value thereof, and the charge storage time in N stages. When the charge accumulation time setting means to be set and photometry is started from a stage in the middle of the N steps, and when the output value of the average value calculation means in the photometry exceeds the upper limit value, the charge accumulation time is reduced by one step to perform further photometry. When the value exceeds the lower limit value, the charge accumulation time is increased by one step, and further photometry is performed to control the photometric state so that the output value of the average value calculation means falls within the range between the upper limit value and the lower limit value. An electronic still camera comprising: an exposure amount calculation unit that calculates a required exposure amount based on the output value when the output value of the average value calculation unit falls within a range of an upper limit value or a lower limit value.

[0009]

Since the output of the solid-state image pickup device is inputted as a linear characteristic and the average value or integrated value thereof is calculated, photometry in a range of a plurality of EV values can be performed by setting the charge accumulation time in one step, and the step in the middle of N steps can be performed. Since photometry is started from, the time required for photometry is short after all.

[0010]

EXAMPLES The present invention will be described in detail below with reference to examples.
FIG. 2 is a block diagram of an "electronic still camera" which is an embodiment of the present invention. In the figure, blocks having the same numbers as those in FIG. 5 have the same functions, and are different in that the variable gain amplifier 24 for switching the gain with respect to the output of the solid-state image sensor 5 and the output of the variable gain amplifier 24 are different. On the other hand, the variable γ correction circuit 25 is configured to turn γ correction on and off. FIG. 1 is a table showing an example of an average output value of the solid-state image pickup device in each charge storage time setting when a uniform light amount is given to the solid-state image pickup device. In this table, the output value of the solid-state image sensor is shown as a relative value when the saturated output value guaranteed by the standard of the solid-state image sensor is 3. Here, as an example, it is assumed that the gain is set so that the level of the signal to be recorded becomes 100% at an output of about 1/3 of the saturation of the solid-state image sensor. In that case, if the average value of the output levels of the image signals is 60% with respect to 100% of the recording signal level, it is determined that the exposure amount is appropriate. When the coefficient of γ correction is 0.45, the average value of the output of the solid-state image pickup element that gives an appropriate level is 0.32 when the saturation is 3. In the example shown in FIG. 1, when the charge storage time is 6H, EV17 has 2.56, and EV14 has 0.32. Similarly, when the charge storage time is set to 48H, E
A value of 2.56 is obtained with V14 and a value of 0.32 is obtained with EV11. Similarly, when the charge storage time is set to 384H, E
A value of 2.56 is obtained with V11 and a value of 0.32 is obtained with EV8.
If the resolution of the A / D conversion circuit 6 in FIG.
Since it has a resolution of 56 steps, if a gain of 2.56 is set to a full scale, values up to about 0.32 can be expressed accurately. Therefore, it is possible to obtain the photometric data in the range corresponding to 4 EV from the average value of the output of the solid-state image sensor 5 accumulated in one step of charge accumulation time. FIG. 3 is a flowchart showing an algorithm for obtaining the optimum exposure amount in a short time based on such a concept. In this embodiment, the number N of stages of charge storage time is 3. If N = 3, the normally required range of EV8 to 17 can be measured sufficiently.

The operation of this embodiment will be described below with reference to FIG. When the photometry operation is started, the system control circuit 9 releases the diaphragm, sets the γ correction value of the variable γ correction circuit 25 to 1, and the gain of the variable gain amplifier 24 to the saturation of the solid-state image sensor 5 at the input of the A / D conversion circuit 6. Output is A / D conversion circuit 6
The gain is set so as to be the full scale (see S1). Next, the data is accumulated and scanned for the accumulation time shown in (2) of FIG. 1 (S2). When the average value is calculated by the average value calculation circuit 21 and is larger than the preset upper limit value (S3
If "YES", the charge is accumulated for 1/8, and scanning is performed with the accumulation time (1) of FIG. 1 set (S4). On the contrary, when it is smaller than the preset lower limit value (S3 N
O, S8 YES) means that the charge storage time is eight times as long as in FIG.
The data is accumulated and scanned in the accumulation time (3) (S9). If it is between the upper limit and the lower limit (S3 NO, S8 N
O), the optimum exposure amount (required exposure amount) from the data accumulated for the initially set accumulation time (2), that is, the average value of the output of the solid-state image sensor 5 is 0.32 when the saturation is set to 3. Calculate the aperture and shutter speed values (S
13). If the average value is larger than the upper limit value even after scanning (S4) in the accumulation time (1) (YES in S5), it is determined that the amount of light that the camera can follow exceeds (S7).
If it is less than or equal to the upper limit value (S5 NO), the optimum exposure amount is calculated from the average value of the data of the accumulation time (1). If the value is below the lower limit even if the data is accumulated for the accumulation time (3) (S10
(YES) It is determined that the amount of light is below the range that the camera can follow (S12). If the lower limit value or more (S10
(NO) The optimum exposure amount is calculated from the average value of the accumulation time (3). During recording, the gain of the variable gain amplifier 24 is set so that the saturated output of the solid-state image sensor 5 gives a 100% level of the recording signal, and the γ correction value of the variable γ correction circuit 25 is 0.4.
Set to 5.

As described above, according to the present embodiment, it is possible to obtain 4 times with one photometry.
Since the photometry in the EV range can be performed and the photometry is started from the middle stage, the time required for the photometry can be short and the release time lag due to the photometry can be shortened.

FIG. 4 is a block diagram of the second embodiment of the present invention. In the figure, reference numeral 26 is an amplifier having a gain setting such that the saturated output of the solid-state image sensor 5 gives the maximum value in the output of the A / D conversion circuit 6. 27 and 28 are switches controlled by the system control circuit 9. As is clear from the first embodiment, the γ correction value may be two kinds of 1 and 0.45, and it suffices that the amplifier gain can be changed in two ways during the normal shooting and the photometry. Therefore, in the present embodiment, the variable gain is variable. The operation of the amplifier 24 and the variable γ correction circuit 25 is switched to the switch 2
The configuration is realized by 7, 28 and the amplifier 26. During photometry, switches 27 and 28 are switched to the amplifier side,
During recording, 27 and 28 are switched to the γ correction circuit 23 side.

The solid-state image pickup device has an interline CCD if the charge storage time can be changed in minute units.
Alternatively, the present invention can be implemented. It is also possible to carry out by calculating an integral value instead of calculating the average value.

[0015]

As described above, according to the present invention,
The release time lag due to photometry can be shortened.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a first embodiment.

FIG. 2 is a block diagram of the first embodiment.

FIG. 3 is a flowchart showing the operation of the first embodiment.

FIG. 4 is a block diagram of a second embodiment.

FIG. 5 is a block diagram of a conventional example.

FIG. 6 is a conceptual diagram of an interline CCD.

FIG. 7 is a drive timing chart of an interline CCD.

FIG. 8 is a diagram showing an operation sequence of a conventional example.

[Explanation of symbols]

 5 solid-state image sensor 9 system control circuit 21 average value calculation circuit 25 variable γ correction circuit

Claims (1)

Claim: What is claimed is: 1. A solid-state image sensor capable of changing a charge storage time, and an average value calculating means for inputting an output of the solid-state image sensor with a linear characteristic and calculating an average value or an integrated value thereof. Charge accumulation time setting means for setting the charge accumulation time to N stages, and photometry is started from a stage in the middle of the N stages, and charge accumulation is performed when the output value of the average value calculation means in the photometry exceeds the upper limit value. When the time is reduced by one step and the photometric value is further exceeded and the lower limit value is exceeded, the charge accumulation time is increased by one step and the photometric value is further measured so that the output value of the average value calculating means falls within the range between the upper limit value and the lower limit value. And an exposure amount calculation unit for calculating a required exposure amount based on the output value when the output value of the average value calculation unit falls within the range of the upper limit value and the lower limit value. Electronic still characterized by Mera.