JPH0723278A - Video camera - Google Patents

Abstract

PURPOSE:To expand a usable photographing illuminance range by expanding the light quantity adjusting range of a photographing without expanding the variable width of shutter speed, by providing a sensitivity control part determining an optimum photosensitivity according to the discrimination result of a photographing illuminance state and supplying a photosensitivity switching signal to the driving circuit of an image pickup element. CONSTITUTION:Based on the present photographing illuminance state discriminated by photographing light quantity and shutter speed, a sensitivity control part 24 determines the optimum photosensitivity of an image pickup element 1, a sensitivity switching signal SW which variably sets to this determined sensitivity is supplied to the driving circuit 2 of the element 1, and the photosensitivity of the element 1 is variably set to the determined sensitivity by the circuit 2. by the variable setting of this sensitivity, a reduction correction is performed for the photosensitivity of the element 1 and white gradation is prevented at a high illuminance time when photographing light quantity becomes excessive though shutter speed is high speed, for instance. Thus, by the combination of the variable of shutter speed and the variable of photosensitivity, a usable photographing illuminance range can be expanded by expanding the light quantity adjusting range of a photographing as cmpared with the case where only conventional shutter speed is varied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera having a variable speed electronic shutter function using a solid-state image pickup device such as a CCD.

[0002]

2. Description of the Related Art Conventionally, in a video camera having a solid-state image pickup device such as a CCD, a limited dynamic range of the image pickup device is effectively used for taking a picture, and an appropriate image is reproduced. Is automatically controlled to an appropriate value. Conventionally, the control of the photographing light amount has been performed by mechanical iris control using an auto iris lens or the like, but nowadays, the electronic iris control is significantly superior to the mechanical iris control in various aspects such as price and reliability. Iris control.

This electronic iris control is performed on pages 63 to 64 of the magazine "Nikkei Microdevice, October 1987" (published by Nikkei BP) and the magazine "TV Technology, November 1988 (Vol. 448)". (Published by Electronic Technology Publishing Co., Ltd.), pages 49 to 54, etc., the signal charge storage time of the image sensor is variably adjusted by the variable speed electronic shutter function.

When the solid-state image pickup device is a CCD of the frame transfer type and unnecessary charges are swept out to the CCD substrate in the same manner as the vertical overflow drain (VOFD) every horizontal blanking period, the variable speed electronic shutter function will be described below. To work.

That is, the photographic output of each field of the CCD is subjected to AGC processing, gamma correction, etc. after the unnecessary components are removed, and then supplied to the recording circuit and the like and also supplied to the iris signal processing circuit. This processing circuit forms an iris signal having a voltage level corresponding to the amount of light (incident light) of the CCD image pickup light by amplifying, inverting, and detecting the luminance component of the image pickup output, and supplies this signal to the electronic iris control circuit.

This control circuit is based on an iris signal and timing pulses such as vertical and horizontal blanking pulses.
The shutter speed for the proper incident light amount is determined based on the result of this determination by detecting the excess or deficiency of the photographing light amount in each field to determine whether the shutter speed is excessive (too fast) or too small (too slow). The unnecessary charge sweeping period of each field is varied based on the determination of, and the electronic shutter control output is formed and output for each horizontal blanking period within this period.

Based on this control output, the shutter drive circuit supplies to the CCD an electronic shutter pulse of about ten and several V necessary for driving the CCD. The electronic shutter pulse, the horizontal and vertical drive pulses of the CCD drive circuit, and the overflow drain (OFD) drive pulse are used to drive the CCD.
Is driven in every field.

At this time, the received electric charge of the CCD is swept in units of horizontal scanning periods in the unnecessary charge sweep period of each field by the electronic shutter pulse, and the remaining period (signal accumulation period) after the sweep period of each field is swept. The received light accumulated charge of the CCD is taken out as a photographing output.

Due to the length of the unnecessary charge sweep period to which the electronic shutter pulse is supplied, for example, in the case of the NTSC system, the shutter speed is 1/60 according to the brightness of the subject.
Seconds (1 field) to 63.5 μs (1 horizontal scanning period)
The iris is automatically controlled by the closed loop control so that the photographing light amount becomes an appropriate amount in the range of (2) in the horizontal scanning period. The lower limit of the shutter speed is 1/60 second,
The upper limit depends on the camera, and 63.5 μsec is the shortest time.

[0010]

In the case of the conventional video camera having the variable speed electronic shutter function, as compared with a video camera which performs mechanical iris control as will be described below, the light amount adjustment range for photographing ( There is a problem that the dynamic range) is extremely narrow.

That is, in the conventional mechanical iris control, the control range of the exposure amount (incident light amount) of the auto iris lens is generally F1.4 to F125 (widespread type) or F1.2 to F300 in F number notation. (High grade type), and the light amount adjustment range is (125 / 1.4) ² ≈ 79
72 (times) or (300 / 1.2) ² ≒ 62500
It will be wide (double).

On the other hand, in the case of electronic iris control by the variable speed electronic shutter function, the light amount adjustment range is determined by the variable range of the shutter speed. For example, in the case of the NTSC system, the variable range of the shutter speed is 1/60 as described above. Second to 63.5
μ seconds. When the variable range of the shutter speed is set to 1/60 to 1/10000 seconds for easy calculation, the light amount adjustment range is (1/10000) / (1/60) ≈167.
Calculated as (times).

Therefore, in the case of electronic iris control, the light amount adjustment range for photographing is remarkably narrower than in the case of mechanical iris control. And because the light amount adjustment range is narrow,
Conventionally, a video camera having such a variable speed electronic shutter function has a limited usable illuminance range.

In the case of a video camera having such a variable speed electronic shutter function, the variable range of the shutter speed is further expanded on the basis of the phenomenon (smear) in which light bands appear above and below the high brightness portion in the screen. Is difficult. That is, when the shutter speed is increased, the amount of smear during shooting output does not depend on the shutter speed, but the amount of the original signal component decreases according to the shutter speed, so the relative amount of smear depends on the shutter speed. Increase and smear becomes noticeable.

In order to widen the variable range of the shutter speed, for example, a CCD with a smear amount of 4% is 1/10000.
If the shutter is operated at a high shutter speed of 0 second, the relative smear amount is 0.04 × {(1/60) / (1/100
000)} ≈67%, and at this time, the false signal due to the smear and the original signal become almost at the same level, and the reproduction screen becomes extremely unsightly.

Therefore, in practice, the variable range of the shutter speed cannot be expanded to dark fog in terms of the amount of smear. It is an object of the present invention to expand the light quantity adjustment range for shooting without expanding the variable range of shutter speed, thereby expanding the usable shooting illuminance range.

[0017]

In order to achieve the above object, in the video camera of the present invention, the solid-state image pickup device is formed by a sensitivity variable element whose light sensitivity is variably set,
A sensitivity control unit is provided that determines the photographing illuminance state based on the amount of incident light based on the iris signal and the determined shutter speed, determines the optimum light sensitivity according to the determination result, and supplies a light sensitivity switching signal to the drive circuit of the image sensor. .

[0018]

In the case of the video camera of the present invention configured as described above, the sensitivity control section determines the optimum light sensitivity of the image pickup device based on the current photographing illuminance state determined by the photographing light amount (incident light amount) and the shutter speed. Then, a sensitivity switching signal for variably setting the determination sensitivity is supplied to the drive circuit of the image sensor, and the optical sensitivity of the image sensor is variably set to the determination sensitivity by this drive circuit.

By the variable setting of the sensitivity, for example, the light sensitivity of the image pickup device is reduced and corrected at the time of high illuminance in which the amount of photographing light is excessively high even though the shutter speed is high, and white crushing is prevented.

Therefore, the combination of the variable shutter speed and the variable photosensitivity expands the light quantity adjustment range for shooting and the usable shooting illuminance range as compared with the conventional case where only the shutter speed is changed.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment will be described with reference to FIGS. In FIG. 1, reference numeral 1 is a CCD of a frame transfer type which is a solid-state image pickup device, and is described in, for example, a document “Technical Report of the Television Society,“ High sensitivity of a frame transfer type CCD image sensor ”, ITEJ.
Technical Report Vol. 10, N
O. 52. pp. 25-30, TEBS'87-5, '
ED87-10 (Feb, 1987) ”and the like, which is composed of a variable sensitivity element having a cross-gate (CG) structure frame transfer CCD configuration.

In this case, as shown in FIG. 2A, the image pickup portion of the CCD 1 is a P-channel silicon substrate 1a.
An N (-) N well layer 1b and a N (+) lateral OFD layer 1c are formed as transfer channels, and a gate electrode 1e is further formed on the substrate 1a via an insulating film layer 1d of Sio _2. ing.

Then, the N well layer 1b accumulates the electric charge e (-1) formed by photoelectric conversion during the light accumulation period of the CCD 1 in which a pulse of a constant voltage is applied from the gate electrode terminal 1f to the gate electrode 1e, During the transfer period of the CCD 1 in which the clock pulse is applied from the gate electrode terminal 1f to the gate electrode 1e, the accumulated charge is transferred to the subsequent circuit section.

The OFD layer 1c is an OFD electrode terminal 1g.
When a voltage is applied from, the depletion layer is formed according to the applied voltage and the excess charge is discharged.
Suppress the blooming phenomenon that overflows.

That is, the applied voltage V _{OFD of the} OFD layer 1c
= Va and the applied voltage V _G = Vb to the gate electrode 1e, the well state of FIG.
The applied voltage to the D layer 1c is increased by α (α> 0), and V _OFD = V
When a + α and V _G = Vb, the depletion layer based on the applied voltage of the OFD layer 1c expands by an amount corresponding to α, and (c) in FIG.
As shown in FIG. 5, the photosensitive area D of the transfer channel CH becomes narrower than that in (b) of the figure, and the blooming phenomenon is suppressed.

This suppression equivalently leads to a photosensitivity reducing effect, which is generally 20 to 30%.
2 (b) and 2 (c) are potential diagrams in the cross section of FIG. 2 (a), and the negative symbols surrounded by circles in the figure indicate charges.

Further, even if only the applied voltage V _OFD is changed, the range of light quantity adjustment for photographing based on this change is not sufficient. The CCD 1 is the horizontal of the CCD drive circuit 2,
The operation is controlled by the horizontal and vertical drive pulses of the vertical drive unit 3, the OFD drive pulse of the OFD drive unit 4, and the shutter pulse of the electronic shutter drive circuit 5, and the shooting output (image signal) of each field is output.

The photographing output of each field of the CCD 1 is supplied to the video signal processing circuit 9 through the AGC amplifier 7 and the gamma correction circuit 8 after the unnecessary components are removed by the sample / hold circuit 6, and this processing circuit A video signal is processed by 9 and supplied from a video output terminal 10 to a subsequent circuit such as a recording circuit.

Further, the output of the sample / hold circuit 6 is also supplied to the iris signal processing circuit 11, and the processing circuit 11 performs signal amplification, inversion, detection, etc., to obtain a voltage level corresponding to the photographing light amount (incident light amount) of the CCD 1. Iris signal IR
S, and outputs this signal IRS to the iris output terminal 12 and the electronic iris control circuit 1 of the microcomputer configuration.
Supply to 3.

Then, the control circuit 13 causes the iris level determining section 14 to detect the iris signal IRS and the reference terminals 15 and 1.
6 is compared with the reference signals Vr ₁ and Vr ₂ for judging whether the current is excessive or small, and it is judged whether the present incident light amount is excessive, proper or insufficient.

Further, the pulse generator 17 of the control circuit 13 uses the horizontal and vertical blanking pulses HD and VD of the timing generator 18 and the exposure timing pulse XSG to latch the data hold 19 and to increase the shutter speed. / Timing pulses for operation control are supplied to the down counter 20 and the shutter control output down counter 21.

The determination output of each field of the determination unit 14 is supplied as up / down data to the counter 20 via the latch 19, and the counter 20 increments the current shutter speed data according to the supplied data. /
The shutter speed of the optimum light amount is determined according to the determination output, and the data of the accumulation time of the CCD 1 corresponding to this speed is determined by the down counter 21, the digital comparator 22 for abnormality reset, and the decoder 23 for shutter speed data output.
Supply to.

Next, the down counter 21 is preset with storage time data, and this data is stored in the pulse generator 1.
Down-counting is performed by the timing pulse 7 and a shutter control signal SHT is generated as an electronic shutter control output at each accumulation start timing in each horizontal scanning period. The control signal SHT is supplied to the drive circuit 5, and the drive circuit 5 forms an electronic shutter pulse for a charge accumulation start command at the timing of the control signal SHT, and supplies this pulse to the CCD 1 to control the shutter speed of each field. To do.

The comparator 22 compares the given accumulation time data with the set reference time data to determine whether there is an abnormality in the accumulation time, and resets the counter 20 when an abnormality occurs to prevent malfunction. To do. Further, the decoder 23 converts the data of the given storage time into the data of the shutter speed, and supplies this data to the sensitivity control section 24 of the control circuit 13.

Based on the determination result of the determination unit 17 and the shutter speed data determined by the decoder 23, the control unit 24 identifies the current photographing light amount and shutter speed for each field and switches the sensitivity for varying the light sensitivity. Forming the signal SW,
This signal SW is supplied to the OFD drive unit 4.

That is, in this embodiment, the photosensitivity of the CCD 1 is switched between standard (high sensitivity) and low sensitivity, so that the control unit 24 changes the current photographing illuminance state depending on the photographing light amount and the shutter speed. Determine whether i) or (ii) is applicable. (I) Even though the shutter speed is set to the maximum speed, the light quantity for photography is too large, and the bright part may be whitened. (Ii) Illumination conditions other than the above (i).

Further, the sensitivity switching signal SW is set to a high level when the above (i) is determined, and the sensitivity switching signal SW is set to a low level when the above (ii) is determined.

The OFD drive unit 4 to which the sensitivity switching signal SW having the binary level change is supplied is formed as shown in FIG.

During a normal time when the sensitivity switching signal SW is at a low level, the output of the NAND gate 4a is always held at a high level, and the output at this high level is the capacitor 4
It is supplied to the base of a transistor 4e for input buffer via b and resistors 4c and 4d, and this transistor 4e is turned on.

At this time, the voltage of + 16V at the power supply terminal 4f is applied to the resistor 4g and the collector and emitter of the transistor 4e, and the collector voltage of the transistor 4e becomes low level of OV.

Further, the collector voltage of the transistor 4e is output through the resistor 4h to the transistors 4i, 4 for controlling the output.
When applied in parallel to the base of j and the collector voltage of the transistor 4e is at a low level, the transistor 4i turns off and the transistor 4j turns on.

When the transistor 4j is turned on, the voltage at the power supply terminal 4f causes the backflow prevention diode 4 to operate.
k, the charging / discharging capacitor 4l, and the emitter / collector of the transistor 4j, so that the capacitor 4l is charged to the polarity shown in the figure.

Further, the capacitor 4l and the transistor 4j
When the transistor 4j is turned on, the output resistance 4m is provided in parallel with the series circuit of the above, and a voltage of + 16V of the power supply terminal 4f is generated between the terminals of the output resistance 4m. This voltage is equal to the applied voltage V _OFD = Va. CCD as OFD drive pulse
1 is supplied.

At this time, the standard applied voltage V _OFD of + 16V causes the photosensitive area D of the CCD 1 in the light accumulation period to become the wide area shown in FIG.

Next, when the sensitivity switching signal SW is at high level and the sensitivity is low, the output of the NAND gate 4a is low during the light accumulation period in which the high-level timing pulse is supplied from the timing generation circuit 18 to the driving units 3 and 4. Become a level.

This low level turns off the transistor 4e to bring the collector voltage of the transistor 4e to a high level of + 16V. This high level turns on the transistor 4i and turns off the transistor 4j.

At this time, + 16V of the power supply terminal 4f is serially connected to the charging voltage of + 16V of the capacitor 4l via the transistor 4i, and the output resistance 4m is connected by this series connection.
The voltage between the terminals of the terminal rises about + 15V from the standard time,
Applied voltage V _OFD supplied as an OFD drive pulse
Rises from Va to Va + α.

Then, as the applied voltage V _OFD rises, C
In CD1, the photosensitive area D during the light accumulation period is a narrow area in FIG. 2C, and the light sensitivity is variably set to a lower sensitivity than in the normal case. Due to this decrease in sensitivity, the excessive amount of photographing light is eliminated, and the incident light amount becomes appropriate within the variable range of the shutter speed.

Therefore, the combination of the variable shutter speed and the variable photosensitivity of the CCD 1 greatly expands the light quantity adjustment range for shooting and expands the usable shooting illuminance range as compared with the case where only the shutter speed is changed.

The applied voltage V _OFD is changed to change the CCD 1
It is needless to say that the range of light quantity adjustment for photographing is greatly expanded by changing the shutter speed, as compared with the case of only switching the light sensitivity.

The configuration of FIG. 1 is different from the conventional configuration in that a sensitivity control section 24 is added to the control circuit 13 and the OFD drive pulse of the CCD 1 is changed by the sensitivity switching signal of the control section 24 which changes the binary level. The OFD drive unit 4 for varying the voltage is provided in the CCD drive circuit 2. Therefore, with a cheap and simple configuration, the light amount adjustment range for shooting is expanded without inconvenience such as an increase in the amount of smear, the usable shooting illuminance range is expanded, and the performance is greatly improved.

In the above embodiment, the photosensitivity of the CCD 1 is variably set in two steps, but it may be variably set in three or more steps. Further, the configuration and the like of each unit are not limited to the embodiment, and it goes without saying that the solid-state image sensor may be a sensitivity variable element having a transfer method and structure different from those of the embodiment.

[0053]

Since the present invention is configured as described above, it has the following effects. The sensitivity control unit 24 determines the optimum light sensitivity of the image pickup device 1 based on the current image pickup illuminance state determined by the image pickup light amount (incident light amount) and the shutter speed, and a sensitivity switching signal variably set to this decided sensitivity is used as the image pickup device 1. To the driving circuit 2, and the driving circuit 2 variably sets the light sensitivity of the image pickup device 1 to the determination sensitivity. By this variability setting of the sensitivity, for example, even if the shutter speed is high, the photographing light amount becomes excessive. At high illuminance, the light sensitivity of the image sensor 1 is reduced and corrected, and white crushing is prevented.

Therefore, by combining the variable shutter speed and the variable photosensitivity, it is possible to expand the light quantity adjustment range for shooting and the usable shooting illuminance range as compared with the conventional case where only the shutter speed is changed.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a video camera of the present invention.

2 (a), (b) and (c) are a sectional view of a part of the CCD of FIG. 1, a standard potential diagram, and a potential diagram when sensitivity is lowered.

FIG. 3 is a detailed block diagram of an overflow drain driving unit provided in the CCD driving circuit of FIG.

[Explanation of symbols]

 1 CCD as a solid-state image pickup device 2 CCD drive circuit 5 overflow drain drive unit 24 sensitivity control unit

[Procedure amendment]

[Submission date] August 31, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

Due to the length of the unnecessary charge sweep period to which the electronic shutter pulse is supplied, for example, in the case of the NTSC system, the shutter speed is 1/60 according to the brightness of the subject.
The iris is automatically controlled by the closed loop control so that the photographing light amount becomes an appropriate amount in the range of seconds (1 field) to the maximum shutter speed in units of horizontal scanning period. In addition,
The lower limit of the shutter speed is 1/60 second, upper limit differ by the camera.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

On the other hand, in the case of electronic iris control by the variable speed electronic shutter function, the light amount adjustment range is determined by the variable range of the shutter speed. For example, in the case of the NTSC system, the variable range of the shutter speed is 1/60 as described above. Second to its highest
The shutter speed . When the variable range of the shutter speed is set to 1/60 to 1/10000 seconds for easy calculation, the light amount adjustment range is (1/10000) / (1/6).
0) ≈167 (times).

Claims (1)

[Claims] 1. An iris signal corresponding to the amount of incident light is formed by the image pickup output of a solid-state image sensor, a shutter speed of an appropriate amount of incident light is determined by the iris signal, and shutter control timing of the image sensor is determined according to the determined speed. In a video camera having a variable speed electronic shutter function that is variable, the image sensor is formed by a sensitivity variable element whose light sensitivity is variably set, and a shooting illuminance state is set by an incident light amount based on the iris signal and a determined shutter speed. A video camera, comprising: a sensitivity control section for performing a determination, determining an optimum light sensitivity according to the determination result, and supplying a light sensitivity switching signal to a drive circuit of the image sensor.