JP3155830B2 - Imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging device such as a video camera.

[0002]

2. Description of the Related Art In recent years, the development of video equipment such as video cameras has been remarkable, and various functions have been automated and operability has been improved. For example, automation of zoom lens equipment, automatic focus control, automatic exposure control, etc. Is essential, for example, when it comes to automatic exposure control, it is an important factor in determining the quality of a captured image, and in any shooting environment, stable and good automatic exposure control must always be possible. The importance of the automatic exposure control function is extremely high.

FIG. 11 is a block diagram showing a configuration of an exposure control device applied to a video camera device before the present invention was made.

In FIG. 1, reference numeral 1 denotes a photographic lens, 2 denotes an iris for adjusting the amount of incident light passing through the photographic lens, and 3 denotes an image formed on the image pickup surface of the photographic lens 1 and the amount of light is adjusted by the iris 2. An image pickup device such as a CCD for photoelectrically converting an image into an image pickup signal, a double correlation sampling circuit (CDS circuit) 4 for reducing noise of the electric charge stored in the image pickup device 3, and a gain adjustment for the image pickup signal. An AGC circuit 6 is a camera signal processing circuit that performs predetermined signal processing on the image signal output from the AGC circuit 5 to convert the image signal into a standardized video signal. A gate circuit for applying a gate to the signal output from the AGC circuit 5 in order to extract an image signal corresponding to the region of the image pickup device; The integrator 9 integrates the respective imaging signals corresponding to the designated area to obtain the average light amount. The integrator 9 converts the signal output from the integrator 8 into a digital signal that can be processed by a system control circuit described later. A D converter 10, a CCD drive circuit for controlling the accumulation operation, the read operation, and the reset operation of the image sensor 3;
Reference numeral 11 denotes an iris motor that drives the iris 2;
Denotes an iris drive circuit for driving the iris motor 11, 13 denotes a D / A converter for converting a digital iris control signal output from a system control circuit described later into an analog signal, and 14 denotes an iris opening amount, that is, an aperture value. An iris encoder composed of a Hall element or the like for detection, 15 is an A / D converter for converting the output of the iris encoder 14 into a digital signal that can be processed by a system control circuit described later, and 16 is an output from a system control circuit described later Digital A
Converting the GC control signal into an analog control signal,
A D / A converter 17 to be supplied to the C circuit 5 is a system control circuit constituted by a microcomputer for comprehensively controlling the entire video camera system.

In the above arrangement, the means for controlling exposure is controlled by the iris 2, the AGC circuit 5, and two types of exposure control means, and the shutter speed is controlled by the vertical synchronizing signal of the standard television signal. It is set to be the same as the time (field period) for one cycle of the cycle (field cycle) (NTSC is 1/60 (second), PAL is 1
/ 50 (sec)).

The exposure control device in the video camera apparatus prior to the present invention has the above-described configuration, and the specific operation will be described below.

The amount of incident light that has passed through the taking lens 1 is controlled by an iris 2, an optical image is formed on an imaging surface of the imaging device 3, and is photoelectrically converted by the imaging device 3. The imaging signal output from the imaging element is subjected to gain control via the AGC circuit 5 after noise is removed by the CDS circuit, supplied to the camera signal processing circuit 6, and output as a standardized television signal. .

Referring to an exposure control system for controlling the exposure, a luminance signal in the video signal output from the AGC circuit 5 is gated by the gate circuit 7 to control the exposure on the screen. The luminance signal corresponding to the light intensity within the photometric frame is extracted, integrated by the integrator 8 to obtain an average value, and supplied to the system control circuit 17 via the A / D converter 9. System control circuit 17
Controls the iris drive circuit 12 to control the drive current supplied to the iris motor 11 so that the luminance level taken from the A / D converter 9 falls within a predetermined range, and Variable opening amount.

That is, in the exposure control system based on the iris control, the iris 2 is opened and closed so that the luminance level of the video signal obtained by photoelectrically converting the incident light passing through the iris 2 by the image pickup device always falls within a predetermined range. A closed loop of iris control for controlling is formed.

[0010] Looking at the exposure control system by the AGC circuit 5, similar to the exposure control system by the iris 2,
The AGC circuit 5 is controlled so that the brightness level captured by the system control circuit 17 falls within a predetermined range.
A closed loop of gain control is configured such that the gain is controlled by the system control circuit 17.

Next, the actual control characteristics will be described in more detail. FIG. 12 is a program for explaining how the two types of exposure control systems of the iris 2 and the AGC circuit 5 are controlled in accordance with the illuminance. FIG.

In FIG. 1, the horizontal axis represents the illuminance of the subject, and the vertical axis represents the set value of each exposure control system. Each exposure control system is divided into two control areas A and B according to the illuminance of the subject. That is, exposure control is performed by combining two exposure control systems of iris and AGC according to the illuminance of the subject.

In the area A, the shutter speed is reduced to 1/6.
The gain is fixed to 0 (second) (PAL is 1/50 (second)), the gain of the AGC circuit 5 is also fixed to OdB, and exposure control is performed only by the iris 2.

In the area B, the shutter speed is 1/60
(PAL is fixed at 1/50 (second)), and the iris 2 is also fixed at the open state, and exposure control is performed only by the AGC circuit 5.

[0015]

However, in the above-described exposure control device, the shutter speed is fixed to the field frequency of the standard television signal. If the exposure cannot be compensated for by opening the AGC,
Since the gain of the circuit 5 is inevitably increased, the S / N ratio is deteriorated, and there is a problem that the image quality is deteriorated.

Focusing only on the shutter speed, it is possible to realize a low-speed shutter of substantially 1/30 second by performing the readout cycle of the image sensor every two fields and doubling the accumulation time. However, even if the shutter speed is simply changed, if it is fixed in a certain shooting mode, fine exposure control cannot be performed in response to subtle changes in the shooting environment. Is
It cannot be improved.

[0017]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is characterized by photoelectric conversion means for photoelectrically converting incident light, and light incident on the photoelectric conversion means. Light amount control means for controlling the light amount, storage means for storing the signal photoelectrically converted by the photoelectric conversion means, storage time control means for controlling the storage time of the signal stored in the storage means, and predetermined read timing Reading means for reading stored information from the storage means, gain control means for controlling the gain of an output signal read from the storage means, and changes in each of the light quantity adjusting means, the gain control means, and the storage time control means. A mode storage means for storing a possible operation range according to the shooting mode; and a mode selected from the shooting modes stored by the mode storage means. Control means for continuously variably controlling the light quantity adjusting means, the gain control means, and the accumulation time control means within respective operation ranges in accordance with the photographing mode, wherein the control means comprises: The exposure control mode can be set by fixing the set value of the gain control means and continuously changing the accumulation time by the accumulation time control means within the operation range of the photographing mode selected according to the illuminance. The imaging device is characterized in that:

[0018]

According to the present invention, the iris and the AGC gain are controlled in accordance with the illuminance of the subject, and the shutter speed can be continuously varied by continuously controlling the accumulation time of the image sensor. It is possible to realize an exposure control program capable of coping with a change in the photographing environment in small steps, instead of coarse control that immediately degrades the image quality by increasing the gain.

[0019]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of an image pickup apparatus according to the present invention.

FIG. 1 is a block diagram showing the configuration of an image pickup apparatus according to the present invention. In FIG. 1, the components denoted by reference numerals 1 to 17 are the same as those in FIG. 11, and a description thereof will be omitted. In the figure, reference numeral 18 denotes an A / D converter for A / D converting an output signal from the camera signal processing circuit 6;
Reference numeral 9 denotes an image memory device for storing and outputting an output signal from the A / D converter 18 in accordance with a signal from the system control circuit 17, and 20 denotes the memory device 1.
A D / A converter for D / A conversion of the output from 9, a shooting mode selection switch 21 for the operator to select a shooting mode, and 22 various control characteristics in each shooting mode selectable by the shooting mode selection switch A data table memory 23 stores information in advance, and a recorder 23 such as a video tape recorder records the image information output from the D / A converter 19 on a recording medium such as a video tape (not shown).

The luminance signal (Y) and the color difference signals (RY) and (BY) output from the camera signal processing circuit 6 are A /
Each digital signal is converted into a digital signal by the D converter 18 and supplied to the image memory device 19.
Stores and outputs image information input based on a command from the system control circuit 17. The image information output from the image memory device 19 is converted into an analog signal by the D / A converter 20, and the luminance signal (Y ') is again output.
The color difference signals (RY) ′ and (BY) ′ are output to the recorder device 23 and recorded on a recording medium.

In the above configuration, the means for controlling the exposure includes the iris 2, the AGC circuit 5, and the shutter speed (slow shutter) by increasing the light accumulation time of the image sensor 3. Exposure is controlled by three types of exposure control means.

The imaging apparatus according to the present invention has the above-described configuration, and the specific operation will be described in order.

First, an electronic shutter for controlling the accumulation time of the image sensor constituting the shutter speed control means will be described.

FIG. 2 is a conceptual diagram of the CCD, showing a schematic structure of a so-called interline transfer type CCD, and FIG. 3 is a sectional view taken along line AA 'in FIG. 2 and a potential diagram. In the figure, 110 is a sensor unit for performing photoelectric conversion, 111 is a vertical transfer register, 112 is a horizontal transfer register, and 113 is an output amplifier.

Reference numeral 114 denotes a channel stop (CS) for separating pixels, 115 denotes a readout gate (ROG) for transferring electric charges accumulated in the sensor unit 110 to the vertical transfer register 111, 116 denotes a substrate, 117
Is an oxide film.

FIG. 4 is a diagram of one field of a standard television signal. φROG is a pulse applied to the readout gate 115 and has a logic level “H”.
At the time, the potential of the readout gate 115 decreases, and the electric charge of the sensor unit 110 is transferred to the vertical transfer register 111.
Transfer to The removal pulse φSUB is a pulse applied to the substrate 116.
It operates to sweep out (remove) the electric charge accumulated in 0 to the outside through the φSUB terminal.

Next, the electronic shutter operation will be described.

FIG. 5 is a timing chart for frame reading and a schematic diagram of signals of various parts, in which the shutter speed is 1/30 (second). In frame reading, the exposure time is twice as long as one field period. In the figure, the vertical synchronizing signal V _D from the sensor unit 110, a timing for moving the charges to the vertical transfer register.
ΦROG is a read pulse for transferring the electric charge accumulated in the sensor unit 110 to the vertical transfer register 111.

As shown in the figure, by applying a φROG pulse only once in two fields,
Are accumulated for about two fields, starting at time t0, and then at time t1, the vertical transfer register 111
Moved to Thereafter, at a predetermined timing, the electric charges are transferred to the horizontal transfer register 112, and are output to the signal processing circuit 5 through the output amplifier 113.

Here, in the figure, in one field period (B1 period) immediately after the φROG pulse is applied, at time t0
From the time t1 to the time t1, that is, the charge accumulated for about two fields is output as a signal through the output amplifier 113 (SB1).
However, in the next one field period (B2 period), φROG
Since no pulse is applied, an empty signal will be output.

Therefore, the CCD driving circuit 10 shown in FIG.
Immediately after the φROG pulse is generated, the A / D conversion device 18 is driven, and the charge output from the signal processing circuit 6 and accumulated for about two fields is stored in the image memory device 1.
9 and output to the D / A converter 20 (B1 period). Then, in the next one field (B2 period), the signal stored in the image memory device 19 during the B1 period is output to the D / A converter 20 (B2 period). Therefore, the output of the D / A converter 20 is as shown in FIG.
The same signal continues for two consecutive fields.

As described above, when the illuminance of the subject is insufficient, etc.
When the exposure time longer than the field period is required, for example, when the state where φROG is added every field is changed to the state where every two fields are added, the exposure time of the sensor unit 10 is twice as long as one field period. And the shutter speed is 1/30 (second).

Next, in a long-time exposure of one field period or more required when the illuminance of the subject is insufficient, the exposure time is not changed to 1/30 (seconds) but is changed continuously. Exposure correction that can respond finely according to the brightness of the subject
This will be described with reference to FIG.

In FIG. 4, φROG is during the vertical retrace interval, and φSUB is during the horizontal retrace interval. Time t1
After the charge of the sensor unit 110 is read to 0, the next period starts, but during the horizontal retrace period until time t11, φSU
Since B = “H”, the charge from t10 to t11 does not remain in the sensor unit 110. From time t11 to t1
Since φSUB = “L” until the time t2, the charge during this period is accumulated in the sensor unit 1 and φROG =
The signal is transferred to the vertical transfer register 111 by the “H” pulse.
After all, the exposure time in this case is (t12-t11).

FIG. 6 is a schematic diagram showing the operation.
FIG. 5 shows signals of various parts when the removal pulse φSUB is applied to the CCD 1 from the charge accumulation start time t0 to the time t0 ′ of the sensor unit 110 when the shutter speed shown in FIG. 5 is 1/30 (second). It is a thing.

In the figure, the period from time t0 to time t0 '
Since the charge of the sensor unit 110 is removed by the removal pulse φSUB, the substantial exposure time is from time t0 ′ to time t1. Thereafter, the output of the D / A converter is as shown in FIG. 1 by the same operation as the above-mentioned conventional example. Therefore, by appropriately changing the time t0 ′ at which the operation of the removing means ends according to the brightness of the subject, 1
Exposure time (t1-t) having a length equal to or longer than the field period
0 ′) can be changed continuously.

In this way, the exposure time can be continuously changed even in the long-time exposure of one field period or more, so that even if the illuminance of the subject is insufficient, fine exposure correction is performed according to the brightness of the subject. be able to.

Although the case where a CCD is used has been described, other solid-state imaging devices may be used.

Next, the overall exposure control of the image pickup apparatus according to the present invention will be described.

The optical image from the photographing lens 1 is photoelectrically converted by the image pickup device 3 through the iris 2, passes through the CDS circuit 4, passes through the AGC circuit 5, becomes a video consonant, and becomes a video consonant. It is sent to the processing circuit 6. A signal for exposure control is obtained by gating the luminance signal output from the AGC circuit 5 by the gate circuit 7, integrating the luminance signal by the integration circuit 8, and passing through the A / D converter 9.
The iris 2 is controlled by the system control circuit 17 to control the iris drive circuit 12 so that its level falls within a predetermined range, and the drive current output to the iris motor 11 is controlled. The exposure control system is configured by a closed loop of iris control that varies the exposure control system.

The exposure control system by the AGC circuit 5 is similar to the exposure control system by the iris 2 so that the output level of the A / D converter 9 taken into the system control circuit 17 falls within a predetermined range. The AGC circuit 5
The gain level of the system control circuit 1
The exposure control system is constituted by a closed loop controlled by the control unit 7.

The exposure control system based on the shutter speed, like the exposure control system based on the iris 2, controls the driving circuit 10 of the image sensor so that the level captured by the system control circuit 17 falls within a predetermined range. The exposure control system is configured by a closed loop by controlling the image memory device 19 by the system control circuit 17.

When the operator selects various photographing modes with the photographing mode selection switch 21, each set value of the exposure control means corresponding to the selected photographing mode is read from the data table memory 22, and these are set. The information sets the characteristics of the exposure control system.

A photographing mode described below (for example, a full auto mode adaptable to the most photographing conditions)
When is selected, it is possible to shoot a high-quality image even with a low-illuminance subject. Therefore, the actual exposure control for a low-illuminance subject in the shooting mode will be described.

First, the shutter speed, the iris 2 and the AGC circuit 5 will be described with reference to the program diagram of FIG.
How the three types of exposure control means are controlled according to the illuminance will be described. This program diagram is stored in the information table memory 22, and its data table will be described later with reference to FIG.

In FIG. 7, the horizontal axis represents the illuminance of the subject, and the vertical axis represents the set values of the iris, shutter speed, and gain of each exposure control means. As is clear from the figure, each exposure control means is divided into three areas A, B and C according to the illuminance of the subject.

That is, exposure operation control is performed by combining three types of exposure control means according to the illuminance of the subject.

In the area A, the shutter speed is 1
/ 60 (second) is fixed (PAL is 1/50 (second)),
The gain of the AGC circuit 5 is also fixed at OdB, and the exposure is controlled only by the opening amount of the iris 2.

In the area B, the iris 2 is fixed open and fixed at the gain OdB of the AGC circuit 5. As described above, the removal pulse φSUB between the read clocks of the image sensor is controlled to store the accumulated charge. By controlling the amount, the shutter speed is reduced from 1/60 (second) to 1
The shutter speed can be continuously changed according to the illuminance up to / 8 (seconds), and the exposure is controlled by the shutter.

In the area C, the iris 2 is fixed open and the shutter speed is fixed at 1/8 (second), and the exposure is controlled only by the AGC circuit 5.

The data table of the photographing mode for executing the exposure control mode is as shown in FIG. 10, and the characteristics of the program diagram for each of the iris, shutter, and AGC gain are attributed (function or fixed value) for each parameter. ), Data format (threshold value, map format, definition by numerical value, definition by code, etc.), and actual data are stored, and by reading them into the system control circuit 17, The program diagram is set.

In the information table, other setting information is also stored. In the AE weighting shown in the figure, weighting data of each photometry area when the imaging screen is divided into a plurality of photometry areas is stored in a map format. As shown in the figure, the screen is divided into 16, the weight at the center is set to 1, and the weight at the periphery is halved to 0.5, which is a so-called center-weighted metering. ing.

The AE reference value indicates a target reference value when performing exposure control so that the level of the imaging signal becomes constant. In addition, image quality adjustment such as changing the gamma characteristic according to the shooting state, applying a fade effect, and the presence / absence of image effect processing are set. In this embodiment, “NORMAL” indicates that no special image quality and image effect processing is performed.

In controlling the above three types of exposure control systems, in this embodiment, the exposure is controlled in the order of iris, slow shutter, and AGC circuit in the order of increasing the illuminance of the subject, as shown in FIG. The order can be changed in the order of iris → AGC → slow shutter. The operation is as shown in FIG. 8, and the description is omitted.

In the above-described embodiment, the photographing mode in which the exposure is continuously controlled in the region of the slow shutter from 1/60 (second) to 1/8 (second) has been described.
A shooting mode in which the operation area of the slow shutter is changed from (second) to 1/30 (second) is also included in the plurality of shooting modes, and can be selected by the shooting mode selection switch 21 (FIG. 9). ).

[0057]

As described above, according to the imaging apparatus of the present invention, before increasing the gain of the AGC circuit 5, which is a cause of S / N deterioration that occurs when the illuminance is insufficient, the shutter in the region below the field frequency is required. By selecting a shooting mode having an area where exposure is controlled by speed, it is possible to prevent S / N degradation, which has been considered a problem.

Further, the shutter speed of the electronic shutter forming one of the exposure control means can be continuously varied even in a slow shutter region longer than one field cycle, and the program control is performed together with other exposure control parameters. Because it was done, compared to the conventional,
Finer exposure control can be performed following changes in the shooting environment.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an imaging device according to the present invention.

FIG. 2 is a diagram showing a structure of an interline transfer type CCD used for the imaging apparatus according to the present invention.

FIG. 3 is a diagram showing an internal structure of an interline transfer type CCD used in the imaging apparatus according to the present invention;
FIG. 2 is a cross-sectional view and a potential diagram of AA ′ in FIG. 1.

FIG. 4 is a diagram of one field of a standard television signal.

FIG. 5 shows a frame readout (shutter speed 1/30)
(Second)) and a schematic diagram of a signal of each part.

FIG. 6 is a timing chart showing an operation in the case where the shutter speed is continuously changed in a region of 1/60 (second) or less, and a schematic diagram of a signal of each unit.

FIG. 7 is a first embodiment of a program diagram showing an exposure control operation in the present invention.

FIG. 8 is a second embodiment of a program diagram showing an exposure control operation according to the present invention.

FIG. 9 is a third embodiment of a program diagram showing an exposure control operation according to the present invention.

FIG. 10 is a diagram for explaining an internal structure of a data table in which set values of a program chart showing an exposure control operation according to the present invention are stored.

FIG. 11 is a block diagram showing a configuration of a general video camera.

12 is a program diagram showing an exposure control operation of the video camera in FIG.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Koji Takahashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-2-60378 (JP, A) JP-A 1-236779 (JP, A) JP-A-4-170175 (JP, A) JP-A-1-314225 (JP, A) JP-A 1-260424 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 5/222-5/257

Claims (3)

(57) [Claims] A photoelectric conversion unit configured to photoelectrically convert incident light; a light amount adjustment unit configured to control a light amount incident on the photoelectric conversion unit; a storage unit configured to accumulate a signal photoelectrically converted by the photoelectric conversion unit; Accumulation time control means for controlling the accumulation time of the signal stored in the storage means; read means for reading the stored information from the storage means at a predetermined read timing; gain for controlling the gain of the output signal read from the storage means Control means; mode storage means for storing changeable operation ranges of the light amount adjustment means, the gain control means, and the accumulation time control means in accordance with a shooting mode; and a shooting mode stored by the mode storage means The light amount adjusting means, the gain control means, and the accumulation time control means are arranged in accordance with the photographing mode selected from the above. Control means for continuously variably controlling within each operation range, wherein the control means fixes the set values of the light amount adjusting means and the gain control means, and sets the photographing mode selected according to the illuminance. An imaging apparatus characterized in that a mode for performing exposure control can be set by continuously varying the accumulation time by the accumulation time control means within an operation range. 2. The imaging apparatus according to claim 1, wherein the accumulation time control unit includes a removal unit that removes information stored in the storage unit during a read timing of the read unit. . 3. The control unit according to claim 1, wherein the control unit controls an order in which the light amount adjustment unit, the gain control unit, and the accumulation time control unit are changed according to the illuminance in accordance with the selected photographing mode. An imaging device characterized by the above-mentioned.