JPH0564087A - Exposure control device for video camera - Google Patents

Abstract

PURPOSE:To reduce the number of parts and to uniformize circuit characteristics by sharing the circuits which can be shared in an iris control system and an AGC system. CONSTITUTION:The light of an object coming through a photographic lens 10 and an iris 12 is converted into an electric signal by an imaging device 14 and then outputted to a video signal processing circuit 22 by way of a preamplifier 18 and an AGC amplifier 20. In the video camera whose signal processings are thus executed as required so as to obtain a desired video signal, the electric signal outputted from the preamplifier 18 is received as the detecting signal for an iris, and an iris control means which controls the iris 12, an AGC means which receives the electric signal outputted from the AGC amplifier 20 as a detecting signal for an AGC so as to control the gain of the AGC amplifier 20, an LPF 24 which can be shared by the iris control means and the AGC means, A/D converter 26. Switches SWI and SW2 which permit a high brightness clipping circuit 42, etc., to be shared in a time divisioning manner and a timing generator 16 are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera exposure control device, and more particularly to a video camera exposure control device adapted to a video camera having two types of sensitivity adjustment functions of iris and AGC.

[0002]

2. Description of the Related Art Generally, video cameras are iris and AG.
It has two types of sensitivity adjustment functions of C. Iris
An electric signal photoelectrically converted by an image sensor such as a CCD and amplified by a preamplifier is input as an iris detection signal, and the iris detection signal is processed to obtain a photometric value. The photometric value is the reference for the iris. It is controlled to be a value.

On the other hand, an AGC (automatic gain control device) inputs an electric signal output from an AGC amplifier in the latter stage of the preamplifier as an AGC detection signal, processes the AGC detection signal, and outputs an image. The integrated value corresponding to the brightness is calculated, and the gain of the AGC amplifier is controlled so that the integrated value becomes the AGC reference value. These two types of sensitivity adjusting devices are different in whether they adjust the light amount or the level of the electric signal, but they are essentially feedback systems that keep the final image brightness constant. The points are equivalent, and the circuits are configured in substantially the same manner.

[0004]

However, in the conventional exposure control device for a video camera, since the dynamic range or the signal level of the detection circuit for iris and the detection circuit for AGC are different, these detection circuits should be shared. I couldn't. A high-intensity clip circuit is generally provided after the detection circuit (Japanese Patent Laid-Open No. 2-2).
No. 68080), a high-contrast scene that is clipped by the high-intensity clip circuit when the clip level of the high-intensity clip circuit on the iris side is different from the clip level of the high-intensity clip circuit on the AGC side. When shooting, the brightness adjusted by the iris and the brightness adjusted by AGC are different, which causes problems such as overexposure and underexposure, whiteout in high-luminance areas, and deterioration of S / N in low-luminance areas. Occur.

The present invention has been made in view of the above circumstances, and a video camera that can share a circuit that can be shared by the iris control system and the AGC system to reduce the number of parts and uniform the circuit characteristics. It is an object of the present invention to provide an exposure control device for use.

[0006]

In order to achieve the above-mentioned object, the present invention converts the subject light incident on an image pickup device through a taking lens and an iris into an electric signal by the image pickup device, and converts the electric signal to an electric signal. In a video camera, which outputs to a video signal processing circuit via a preamplifier and an AGC amplifier and obtains a required video signal by appropriately performing signal processing in the video signal processing circuit, the preamplifier outputs the video signal. An electric signal is inputted as an iris detection signal, an iris control means for controlling the iris based on the iris detection signal, and an electric signal outputted from the AGC amplifier are inputted as an AGC detection signal, and the AGC is inputted. AGC means for controlling the gain of the AGC amplifier based on the detection signal for use with the iris control means and AGC means And means for sharing by time division circuit,
It is characterized by.

[0007]

According to the present invention, the iris control means uses the electric signal output from the image pickup device through the preamplifier as the iris detection signal, and the electric signal output from the preamplifier through the AGC amplifier. Paying attention to the commonality of the configuration with the AGC means that uses as a detection signal for AGC, circuits that can be shared by both, such as a detection circuit and a high-intensity clip circuit, are shared in a time division manner.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of an exposure control device for a video camera according to the present invention will be described in detail below with reference to the accompanying drawings. Figure 1
1 is a block diagram of a video camera including a first embodiment of an exposure control device for a video camera according to the present invention.

In the figure, the subject light is the taking lens 10
Also, an image is formed on the light receiving surface of the image sensor (CCD) 14 via the iris 12. The CCD 14 accumulates incident light as a charge,
The accumulated charge is read in synchronization with the timing pulse applied from the timing generator 16. The electric signal thus read out from the CCD 14 is amplified by the preamplifier 18 and then added to the AGC amplifier 20 and the amplifier 21.

An AGC gain control signal, which will be described later, is added to the AGC amplifier 20, and the AGC amplifier 20 amplifies the electric signal with a gain controlled by the AGC gain control signal, and the amplified signal is supplied to a video signal processing circuit 22. To the switch SW1 as an AGC detection signal.
To the input terminal SW1a. Video signal processing circuit 22
Includes a white balance circuit, a γ correction circuit, a matrix circuit, an encoder circuit, etc., and after performing predetermined signal processing by these circuits, outputs an NTSC video signal to the recording device 23, for example.

The recording device 23 includes a recording circuit, and after converting the video signal into a recording signal suitable for magnetic recording, the recording signal is magnetically recorded on a video tape via a magnetic head. On the other hand, the amplifier 21 amplifies the electric signal input from the preamplifier 18 to the same level as the signal level after passing through the AGC amplifier 20, and outputs this as an iris detection signal to the input terminal SW1b of the switch SW1.

The switch SW1 has its movable contacts alternately switched between the input terminals SW1a and SW1b by a timing pulse applied from the timing generator 16, and switches the AGC detection signal and the iris detection signal to, for example, one horizontal scanning line ( It is alternately output to the LPF (low pass filter) 24 every 1H. The signal that has passed through the LPF 24 is detected as a signal indicating the luminance signal,
It is converted into a digital signal by the converter 26 and output to the switch SW2.

The switch SW2 is synchronized with the switch SW1 by a timing pulse applied from the timing generator 16, and its movable contact piece has output terminals SW2a and S2.
Alternately switched between W2b. This gives A
The data of the GC detection signal is input to the AGC integration circuit 28, and the data of the iris detection signal is input to the iris integration circuit 30.

Each of the integrating circuits 28 and 30 integrates the respective input data for one field and outputs the integrated data as an MP.
It is output to U (microprocessor unit) 32. M
The PU 32 processes these integrated data based on a program stored in a ROM (Read Only Memory) 34, AGC reference data, and iris reference data, and D
The AGC gain control signal and the iris control signal are output via the / A converters 36 and 38, respectively. That is, MP
U32 compares the integrated data input from the AGC integration circuit 28 with the AGC reference data, and the integrated data is AG
If it is larger than the reference data for C, it is judged to be too bright, and the gain of the AGC amplifier 20 is lowered so that D /
The AGC gain control signal is output to the AGC amplifier 20 via the A converter 36. On the other hand, when the integrated data is smaller than the AGC reference data, it is judged to be too dark, and the AG
D / A converter 3 to increase the gain of C amplifier 20
The AGC gain control signal is sent to the AGC amplifier 20 via
Output to.

Similarly, the MPU 32 compares the integrated data input from the iris integrating circuit 30 with the iris reference data, and when the integrated data is larger than the iris reference data, it is judged to be too bright and the iris 12 To output the iris control signal to the iris drive circuit 40 via the D / A converter 36 so that the iris 12 is closed, and when the integrated data is smaller than the iris reference data. Determines that is too dark, and outputs an iris control signal to the iris drive circuit 40 via the D / A converter 36 so as to open the iris 12.
This drives the iris 12 in the opening direction.

According to the exposure control device for a video camera having the above-described structure, the iris control circuit and the AGC circuit have LP
The F24 and the A / D converter 26 can be shared.
Although the switches SW1 and SW2 are switched every 1H in the above embodiment, the integrating circuits 28 and 30 can be shared by switching each field, for example.

FIG. 2 is a block diagram of a video camera including a second embodiment of the exposure control device for a video camera according to the present invention. The same parts as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. When the first embodiment of FIG. 1 and the second embodiment of FIG. 2 are compared, in the first embodiment the LP
The F24 and the A / D converter 26 are shared, but the second embodiment is different in that the high-luminance clip circuit 42 is mainly shared.

Now, referring to FIG. 2, an AGC amplifier 20 is provided.
The AGC detection signal output from the preamplifier 18 and the iris detection signal output from the preamplifier 18 are different from each other.
Input terminals SW1a and SW1b of the switch SW1 via the PFs 24A and 24B and A / D converters 26A and 26B.
Added to. The movable contact piece of the switch SW1 is alternately switched between the input terminals SW1a and SW1b by a timing pulse applied from the timing generator 16, and the brightness data and A / A of the AGC detection signal input from the A / D converter 26A. The brightness data of the iris detection signal input from the D converter 26B is alternately output to the high brightness clip circuit 42 for each horizontal scanning line (1H), for example.

A clip level control signal, which will be described later, is added to the high-intensity clip circuit 42. The high-intensity clip circuit 42 clips the intensity data input from the switch SW1 at the clip level controlled by the clip level control signal. To do. That is, when the brightness data of the clip level or higher is input, the brightness data is output with the clip level as the upper limit.

The brightness data that has passed through the high brightness clipping circuit 42 or has been clipped is output to the switch SW2. The switch SW2 is the timing generator 1
Switch S by a timing pulse applied from 6
In synchronization with W1, its movable contact piece has output terminals SW2a and SW.
Alternately switched between 2b. This allows AG
The brightness data corresponding to the C detection signal is input to the AGC total area integration circuit 28, and the brightness data corresponding to the iris detection signal is input to the iris screen center integration circuit 30A and the screen total area integration circuit 30B.

The AGC total area integrating circuit 28 integrates the input luminance data for one field, outputs the integrated data to the MPU 46, and similarly the screen entire surface integrating circuit 30B.
Integrates the input brightness data for one field and outputs the integrated data I ₂ to the MPU 46. On the other hand, the window signal generation circuit 44
A screen center selection signal indicating the timing at which the brightness data of the screen center in one field is output is added, and the screen center integration circuit 30A receives the brightness data of the input brightness data from the screen center selection signal. Only the brightness data in the center of the screen in one field is integrated and the integrated data I ₁ is output to the MPU 46.

The MPU 46 stores these integrated data in the ROM.
A program and reference data for AGC stored in 48,
Processing is performed based on the iris reference data, and the AGC gain control signal and the iris control signal are output via the D / A converters 36 and 38, respectively. That is, the MPU 46 is
Integrated data and A input from the AGC total integration circuit 28
If the integrated data is larger than the AGC reference data, it is judged to be too bright,
An AGC gain control signal is output to the AGC amplifier 20 via the D / A converter 36 so as to reduce the gain of the AGC amplifier 20, and if the integrated data is smaller than the AGC reference data, it is too dark. A determination is made to output an AGC gain control signal to the AGC amplifier 20 via the D / A converter 36 so as to increase the gain of the AGC amplifier 20.

Further, the MPU 46 is provided with an integrating circuit 3 at the center of the screen.
0A and the photometric data are calculated from the integrated data I ₁ and I ₂ input from the screen entire surface integration circuit 30B. For example, backlight state or spot light from the accumulated data I ₁ and I ₂ will determine the state of hitting the object, calculates the photometric data by weighting based on the integrated data I ₁ or the integrated data I ₁ when these conditions .. The photometric data calculated in this way is compared with the iris reference data, and when the photometric data is larger than the iris reference data, it is judged to be too bright, and the iris 12 is closed.
The iris control signal is output to the iris drive circuit 40 via the A / A converter 36 to drive the iris 12 in the closing direction. On the other hand, if the photometric data is smaller than the iris reference data, it is determined that it is too dark. Then, an iris control signal is output to the iris drive circuit 40 via the D / A converter 36 so as to open the iris 12, thereby driving the iris 12 in the opening direction.

Further, the MPU 46 is provided with a screen central portion integrating circuit 3
0A and the integration data I ₁ and I ₂ input from the screen whole surface integration circuit 30B are used to determine the state in which the spot light hits the subject, and the clip level control signal is output via the D / A converter 39. That is, the MPU 46 is
As shown in FIG. 3, the absolute value of the difference between the integrated data I ₁ and I ₂ ,
| I ₁ −I ₂ | is larger than the threshold Th (| I ₁ −I ₂ |
> Th) is determined (step 102), and if larger, it is determined that the backlight or spot light is shining on the subject, and the process proceeds to step 102.

In step 102, it is judged whether or not the integrated data I ₁ is larger than the integrated value I ₂ (I ₁ > I ₂ ). If it is larger, it is judged that the spot light is shining on the object, Proceed to 104. Step 10
4 sets the clip target value to level 2 (for example, IRE20
0), and the clip level control signal is output so that this becomes the next clip level. IRE is N
Indicates the brightness level of the TSC system video signal.
E100 is the brightest white.

On the other hand, in step 100, | I ₁ −I ₂ |>
If it is not Th and if I ₁ > I ₂ in step 102, the process proceeds to step 106, in which the clip target value is set to the normal level 1 (for example, IRE100), and the clip level is set to the next clip level. Output a control signal. According to the exposure control device for a video camera having the above configuration, the high brightness clip circuit 42 can be shared by the iris control circuit and the AGC circuit, and the high brightness clip circuit 42 shared by a single clip level control signal can be used. You can control the clip level.

FIG. 4 is a block diagram of a video camera including a third embodiment of the exposure control device for a video camera according to the present invention. The same parts as those in FIGS. 1 and 2 are designated by the same reference numerals, and detailed description thereof will be omitted. That is, FIG.
In the third embodiment shown in FIG. 1, the iris control circuit and the AGC circuit are similar to the first embodiment in FIG.
The converter 26 is shared, and the high-intensity clip circuit 42 is shared as in the second embodiment of FIG.

The exposure control device for a video camera according to the present invention is applicable not only to a video movie camera but also to an electronic still video camera.

[0029]

As described above, according to the exposure control device for a video camera of the present invention, the iris control system and the AG
Since the circuit that can be shared in the C system, that is, the detection circuit, the high-intensity clip circuit, and the like are shared in a time-division manner, it is possible to reduce the number of components and uniform the circuit characteristics.

[Brief description of drawings]

FIG. 1 is a block diagram of a video camera including a first embodiment of an exposure control device for a video camera according to the present invention.

FIG. 2 is a block diagram of a video camera including a second embodiment of an exposure control device for a video camera according to the present invention.

FIG. 3 is a flowchart used to explain a clip level determined by the MPU of FIG.

FIG. 4 is a block diagram of a video camera including a third embodiment of an exposure control device for a video camera according to the present invention.

[Explanation of symbols]

 10 ... Photographing lens 12 ... Iris 14 ... Imaging element 16 ... Timing generator 18 ... Preamplifier 20 ... AGC amplifier 21 ... Amplifier 22 ... Video signal processing circuit 24, 24A, 24B ... LPF 26, 26A, 26B ... A / D Converter 28 ... AGC integrating circuit 30 ... Iris integrating circuit 30A ... Screen central part integrating circuit 30B ... Screen entire surface integrating circuit 32, 46 ... MPU 34, 48 ... ROM 40 ... Iris drive circuit SW1, SW2 ... Switch

Claims (3)

[Claims] 1. A subject light incident on an image pickup device through a taking lens and an iris is converted into an electric signal by the image pickup device, and the electric signal is output to a video signal processing circuit through a preamplifier and an AGC amplifier. Then, in a video camera in which a required video signal is obtained by appropriately performing signal processing in the video signal processing circuit, an electric signal output from the preamplifier is input as an iris detection signal, and the iris detection is performed. Iris control means for controlling the iris based on a signal, and an electric signal output from the AGC amplifier are input as an AGC detection signal, and the gain of the AGC amplifier is controlled based on the AGC detection signal. AGC means, and means for sharing a sharable circuit in the iris control means and the AGC means in a time-sharing manner Exposure control device for a video camera according to claim. 2. The sharable circuit is a detection circuit,
The iris control means outputs the detection signal for iris to AG
The exposure control device for a video camera according to claim 1, further comprising an amplifier that amplifies the signal to the same level as the C detection signal. 3. The exposure control device for a video camera according to claim 1, wherein the sharable circuit is a high-intensity clipping circuit.