JP2519202B2 - Electronic imager - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electronic image pickup apparatus using a CCD solid-state image pickup element as an image pickup element, and sometimes to improvement of a dynamic range expanding means of the CCD solid-state image pickup element.

[Prior art]

When a solid-state image pickup device using a CCD solid-state image pickup element as an image pickup element is applied to an electronic camera, it is necessary to sufficiently widen the dynamic range of the image pickup system. That is, the above CCD
The solid-state imaging device itself has a remarkably narrow dynamic range as compared with the silver salt film. Therefore, the image quality of the captured still image tends to be high contrast unless measures are taken to expand the dynamic range. Moreover, since the CCD solid-state image pickup device has a lower light receiving sensitivity than a silver salt film, a strobe is often used, but if a strobe is used, the dynamic range is further narrowed. As a means for solving such a problem, there has been known a means for controlling the photoelectric conversion characteristics of a CCD solid-state image sensor to expand the dynamic range. That is, P43 to 44 "Knee characteristic control of CCD image sensor" in the Proceedings of the 1978 National Conference of the Television Society of Japan (published by the Institute of Television Engineers of Japan in July 1978) include, for example, the storage electrode φ1, of the frame transfer CCD. φ
There is disclosed a technical means for expanding the dynamic range by controlling the photoelectric conversion characteristics of the CCD solid-state imaging device by changing the level of 2 in multiple values within the storage time. On the other hand, in order to expand the dynamic range by devising the driving method of the CCD image sensor in this way, it is practically necessary to comply with various conditions such as the shutter speed and the use of strobe. A practical device that meets the above requirements has not been proposed yet.

〔Purpose〕

An object of the present invention is to provide a practical electronic image pickup device of this kind having a sufficiently wide dynamic range by controlling the driving mode of the CCD solid-state image pickup device after taking into consideration various conditions such as the shutter speed and the use or non-use of strobe light. To provide.

〔Overview〕

In order to achieve the above object, an electronic image pickup device according to the present invention is characterized by being configured as follows. That is: In an electronic image pickup device capable of adjusting a gamma characteristic of a CCD image pickup device having an overflow control gate by controlling a level of a voltage applied to the overflow control gate and a form of change with time, Shutter speed information (S2) that indicates the shutter speed that should be applied for the shooting using the CCD image sensor
Is received from the outside, information (S8) indicating the ratio of the shutter opening time represented by the shutter speed information (S2) to the vertical scanning time of the image, and the shutter opening / closing timing corresponding to the shutter opening time. The first information processing means (22, 23) for executing the first information processing step for obtaining the prescribed timing information (S7) and the strobe usage information (S4) indicating whether or not the strobe is used for the above-mentioned shooting are provided. Information (S8) received from the outside and representing the ratio of the shutter open time to the vertical scanning time of the image obtained in the first information processing step according to the content of the flash use information (S4), and In order to comply with the timing information (S7) that defines the shutter opening / closing timing corresponding to the shutter opening time, the CCD image sensor overflow control gate Second data processing means for executing a second processing step for generating information which defines the form of changes over time of the voltage to be pressurized (21,2
4) and is included, and the effective dynamic range under the specified conditions is expanded by adjusting the gamma characteristic of the CCD image sensor based on the information obtained in the second information processing step. It is characterized by being configured as follows.

〔Example〕

FIGS. 1 (a), (b) and (c) are views showing a partial configuration of an interline transfer type CCD solid-state imaging device related to the present invention. As shown in FIGS. 2A and 2B, an overflow drain 2 which is a means for discharging excess charges is provided on one side of a light receiving element 1 formed of a photodiode array, and the other side is provided for vertical transfer of signal charges. A vertical shift register 3 composed of CCD is provided. A control gate 4 for controlling the overflow potential is provided between the light receiving element 1 and the overflow drain 2, and the signal charge accumulated in the light receiving element 1 is provided between the light receiving element 1 and the vertical shift register 3. A transfer gate 5 for transferring to the buried channel 3b below the transfer electrode 3a of the vertical shift register 3 is provided. And the above part is interline transfer type CCD
In order to make each unit independent in the vertical direction, a channel stop 6 is provided between the units to prevent the spread of charges in the horizontal direction. Thus, a two-dimensional image sensor is constructed by arranging the above-mentioned independent units in a plurality of rows in the horizontal direction. In the vertical shift register 3 including the vertical transfer electrode 3a and the buried channel 3b, as shown in the potential diagram of FIG. 7C, which is shown in the lower part of FIG. At the time of transfer, the electric potential at the lower part of the transmission electrode 3a fluctuates up and down between the solid line position and the broken line position.

FIG. 2 is a waveform diagram showing a driving method of the CCD solid-state image pickup device according to the present invention. A is a vertical synchronization clock,
B is a pulse applied to the transfer gate 5, and C is a voltage applied to the overflow control gate 4. As shown in FIG. 2, a pulse B is applied to the transfer gate 5 in synchronization with the vertical synchronizing clock A to transfer the accumulated charge of the light receiving element 1 to the vertical shift register 3 and, at that time t1
Since then, light accumulation to the light receiving element 1 is started.
However, the overflow drain 2 is applied with an overflow control voltage of level L1 such that the saturated charge amount of the light receiving element 1 is QK during the period from time t1 to time t2, and the light is received during the period from time t2 to time t3. The overflow control voltage C of level L2 is applied so that the saturated charge amount of the device 1 is QS. It should be noted that the level L0 indicated by the broken line in FIG. 7C indicates the overflow control voltage of the non-accumulation level. When the voltage of the non-accumulation level L0 is applied to the control gate 4, all the photocharges generated by the light receiving element 1 overflow. It is discharged from the drain 2 to the outside. That is, while the voltage of the level L0 is being applied, the same result as that when photoelectric conversion is not substantially performed is exhibited. When the control voltage is controlled like the level L1 or L2, the saturated charge amount in the light receiving element 1 changes.

FIG. 3 (a) is a diagram showing the change over time in the accumulated charge amount when the control voltage is controlled as shown in FIG. As shown in this figure, when the light intensity I1 is such that the accumulated charge amount at time points t1 to t3 is QK or less, the accumulated charge amount is proportional to the accumulation time. However, when the light intensity I2 is such that the accumulated charge amount exceeds QK, the saturated charge amount at time tK
After reaching QK, charge accumulation is prohibited until the contact point t2. From time t2 to time t3, charges are accumulated with an independent slope by the control voltage of the level L2. Therefore, the light receiving element 1 in this case
The photoelectric conversion characteristics of are as shown in FIG. That is, the amount of photoelectric conversion in the range of high light intensity is suppressed, and the dynamic range is substantially expanded.

FIG. 4 shows the control voltage C level of 3 of L3, L4 and L5.
It is a figure which shows the case where it changes into a level. That is, the period from time t1 to time t4 is level L3, and from time t4 to time
The control voltage C of level L4 is applied during the period up to t5, and the level L5 is applied during the period from time t5 to time t6.

FIG. 5 is a diagram showing photoelectric conversion characteristics in the case of FIG. As shown in Fig. 5, the light intensity is IK, IM, IS
While the saturation charge amount changes to QK, QM, QS,
The photoelectric conversion characteristics are smoother than those in the above case.

Next, examples of the present invention will be described. FIG. 6 is a waveform diagram showing an embodiment of the present invention. In this embodiment, the first
This is an example in which a so-called element shutter function is added to the dynamic range expanding means described in the embodiment. That is, as shown in FIG. 6, in this embodiment, time point t1
During the period TA from 1 to time t12, the control voltage C1 is kept at the non-accumulation level L0, and light accumulation in the light receiving element 1 is substantially prohibited during this period. And at time point t1
During the period TB from 2 to the time point t13, the overflow control voltage C1 is changed stepwise in the same manner as described above.

According to this embodiment, the period TB becomes a so-called exposure time, and the dynamic range can be expanded during this exposure period. The control voltage may be continuously changed as indicated by C2 in FIG.

Next, a circuit example of the device of the present invention will be described. Note that the circuit example described below is a horizontal synchronizing signal D as shown in FIG.
Is used as a clock input, the transfer gate pulse B is used as a reset input, and a counter is operated to perform arithmetic processing of the counter output and various information to obtain an overflow control voltage as shown in FIG. .

FIG. 8 is a block diagram showing an example of the circuit. Terminal 11
Is supplied with a horizontal synchronizing signal D. The transfer gate pulse B is applied to the terminal 12. The horizontal synchronizing signal D becomes a clock input of the counter 13, and the transfer gate pulse B becomes a reset input of the counter 13. The counter 13 converts the input serial horizontal synchronizing signal D into an 8-bit parallel signal and outputs it as a timing signal S1.
This output is input to a microcomputer (hereinafter referred to as a microcomputer) 20. The microcomputer 20 is provided with a shutter speed signal S2 from the shutter speed setting device 14, a γ characteristic value signal S3 from the γ characteristic setting device 15, and a strobe use signal S4 from the strobe light emitting device 16 when a strobe is used. Given.

The shutter speed setting device 14 operates a variable resistor or the like by manually operating a dial, for example, and generates an electric signal S2 of a level according to the shutter speed. Note that photometry may be performed by an appropriate measuring means and a shutter speed signal according to the photometric value may be automatically formed.

The γ specific setter 15 operates the dial manually, for example, to set a preset time ratio of T1, T2, and T3 (for example,
The combination of T1: T2: T3 = 3: 2: 1 and 4: 2: 1 is selected), and the γ characteristic value signal S3 is transmitted. In selecting the time ratio, for example, by observing the screen of the subject displayed in the viewfinder in the moving image mode, an appropriate time ratio may be selected from the image quality state.

The strobe light emitter 16 sends a signal S4 indicating that the strobe is being used when the strobe light emitter 16 is used. The strobe light emitting device 16 sends a strobe light emission command signal from the microcomputer 20.
S5 has been given.

The microcomputer 20 will be described later in detail, but
At least, the level of the overflow control voltage and the continuous time are calculated and output based on various information such as at least the given shutter speed, γ characteristic value, and whether or not the strobe is used.

The output of the microcomputer 20 is converted into an analog signal by the D / A converter 17 and then amplified by the amplifier 18 to be a terminal.
It is output from 19.

FIG. 9 is a block diagram showing the internal structure of the microcomputer 20. In FIG. 9, the duration ratio setting means 21 sets the duration ratio of T1, T2, T3 based on the γ characteristic value signal S3 given to the terminal 20a and the strobe use signal S4 given to the terminal 20b. As a result, the γ characteristic value is set. When the strobe is used, the contrast of the entire image is extremely high in many cases. Therefore, the lowest γ characteristic value is set when the strobe is used. Note that a low γ characteristic value means that a period when the control voltage level is high and the light accumulation amount is small (for example, T1) is relatively long, and a control voltage level is low and the light accumulation amount is large (for example, T3). A short state. The signal S6 indicating the time ratio set by the duration ratio setting means 21 is supplied to the OFD level duration setting means 26 of the dynamic range setting means 24 to be operated later.

The shutter opening / closing timing setting means 22 is based on the timing signal S1 from the counter 13 given to the terminal 20c, the strobe use signal S4 given to the terminal 20b, and the shutter speed signal S2 from the shutter speed setting unit 14 given to the terminal 20d. The shutter opening / closing timing signal S7 is generated and supplied to the OFD level setting means 25 of the dynamic range setting means 24 described later. When the strobe light emitter 16 is not used, the strobe use signal S4 does not arrive. Therefore, in this case, the reference value for starting the shutter operation by the shutter speed signal S2 is stored in the setting means 22. When the shutter speed signal S2 is taken in by the means 22, it is compared with the reference value. If it is greater than or equal to the reference value, the shutter open signal is output, and if it is less than the reference value, the shutter close signal is output. On the other hand, when the strobe is used, the strobe use signal S4 arrives. At this time, the strobe light emitter 16
The shutter speed signal S2 determined based on the photometric information obtained by the preliminary light emission is sent. Note that the shutter speed signal S2 in this case is a signal that can be selected as a time signal having a time width that matches the strobe light emission time or exceeds the strobe light emission time. Otherwise, underexposure may occur. Thus, in the setting means 22, when the shutter open signal is input, that is, when the output value from the counter 31 reaches the shutter open value, the strobe light emission command signal S5 is supplied to the strobe light emitter 16 via the terminal 20e. .

The shutter opening time / vertical scanning time / ratio setting means 23, when supplied with the shutter speed signal S2 given to the terminal 20d, is a ratio of the shutter opening time TB included in the shutter speed signal S2 to the vertical scanning time T. Calculate the ratio TB
The signal S8 indicating / T is set to the OFD of the dynamic range setting means 24.
The level duration setting means 26 is supplied.

The dynamic range setting means 24 is the OFD level setting means 2
5 and OFD level duration setting means 26. OFD
The level setting means 25 is supplied with the γ characteristic value signal S3 given to the terminal 20a and the output signal S7 from the shutter opening / closing timing setting means 22, and sets the level of the overflow control voltage. OFD level duration setting method 2
6 is supplied with the output signal S6 of the duration ratio setting means 21 and the output signal S8 from the shutter opening time / vertical scanning time / ratio setting means 23, and becomes the level set by the OFD level setting means 25. Set the duration of each associated. The output signal S6 of the duration ratio setting means 21
The time ratio of time T1, T2, T3 must be realized within a predetermined shutter opening time. Therefore, the time ratio of T1, T2, T3 by the output signal S6 of the duration ratio setting means 21,
From both information of the shutter opening time / vertical scanning time / shutter opening time ratio by the output signal S8 from the ratio setting means 23,
The time ratio of T1, T2, T3 within the shutter open time TB is set. Thus, the dynamic range setting means 24 outputs a signal indicating the level and duration of the overflow control voltage via the terminal 20f.

FIG. 10 is a flow chart showing the operation sequence of the circuit having the above configuration. In the figure, Y indicates the flow when the determination content is YES, and N indicates the flow when the determination content is NO.

〔The invention's effect〕

The present invention first recognizes the shutter speed information (S2) that is regulated (set) from the outside in the first information processing step as the preceding step, and under the condition regulated by this recognition, the second step as the next step. In step 2 of the information processing, the voltage applied to the overflow control gate of the CCD image pickup device is changed according to the content of the strobe use information (S4), which also indicates whether or not the strobe is used as information that is regulated (set) from the outside. Since it is configured to adjust the gamma characteristics of the CCD image sensor by defining the form of change over time, conditions such as the shutter speed that is externally regulated (set) and the use of strobe are taken into consideration. Since the gamma characteristics of the CCD image sensor can be adjusted above, the effective dynamic range can be maximized even under such various specified conditions. This type of electronic imaging, which can be magnified, can be realized.

[Brief description of drawings]

1 (a) (b) (c) to FIG. 5 are explanatory views of a technique related to the present invention, and FIGS. 1 (a) (b) (c) are interlines related to the present invention. FIG. 2 is a diagram showing a partial configuration of a transfer CCD solid-state image sensor, FIG. 2 is a waveform diagram showing a driving method of the CCD solid-state image sensor, and FIG. 3 (a) is a control voltage control shown in FIG. FIG. 3 (b) shows the photoelectric conversion characteristics of FIG. 3 (a), and FIG. 4 shows the levels of the control voltage C as L3, L4, L5. 5 is a diagram showing the case of changing to three levels, FIG. 5 is a diagram showing the photoelectric conversion characteristics of FIG. 4, and FIG. 6 is a diagram showing a second embodiment of the present invention. FIG. 6 is a diagram showing an embodiment of the present invention, which is a waveform diagram showing a driving method, and FIGS.
FIG. 10 is a diagram for explaining a circuit example for realizing the driving method of the present invention, FIG. 7 is a diagram showing operation waveforms, FIG. 8 is a block diagram showing the entire configuration, and FIG. 9 is a microcomputer. FIG. 10 is a block diagram showing the internal configuration of FIG. 10, and FIG. 10 is a flow chart showing the operation sequence. 1 ... Light receiving element, 2 ... Overflow drain, 3 ...
Vertical shift register, 4 ... Overflow control gate, 5 ... Transfer gate, 6 ... Channel stop,
A: Vertical sync clock, B: Transfer gate pulse, C,
E: Overflow control voltage, D: Horizontal sync signal, TA: Light accumulation inhibition period, TB: Light accumulation period (exposure time).

Claims (1)

(57) [Claims] 1. An electronic image pickup device capable of adjusting a gamma characteristic of a CCD image pickup device having an overflow control gate by controlling a level of a voltage applied to the overflow control gate and a form of change with time. In the above, the shutter opening information represented by the shutter speed information (S2) is received from the outside, and the shutter opening time represented by the shutter speed information (S2) is externally received by the CCDT image sensor. The first information processing step is executed to obtain information (S8) that represents the ratio of the image to the vertical scanning time and timing information (S7) that defines the shutter opening / closing timing corresponding to the opening time of the shutter. First information processing means (22, 23) and strobe use information indicating whether or not the strobe is used for the above-mentioned shooting (S) is received from the outside and, in accordance with the content of the flash use information (S4), information indicating the ratio of the shutter open time to the vertical scanning time of the image obtained in the first information processing step ( S8) and information defining the form of the change over time of the voltage applied to the overflow control gate of the CCD image sensor so as to conform to the timing information (S7) that defines the shutter opening / closing timing corresponding to the shutter opening time. Second information processing means (21,2) for executing a second information processing step for generating
4) and is included, and the effective dynamic range under the specified conditions is expanded by adjusting the gamma characteristic of the CCD image sensor based on the information obtained in the second information processing step. An electronic imaging device having the above-described configuration.