JP2785526B2 - Exposure control device for video camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Generally, video cameras are iris and AG.
C has two kinds of sensitivity adjustment functions. Iris,
An electrical 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. Controlled to be a value.

On the other hand, an AGC (automatic gain control device) receives an electric signal output from an AGC amplifier subsequent to the preamplifier as an AGC detection signal, and processes the AGC detection signal to perform image processing. , And the gain of the AGC amplifier is controlled so that the integrated value becomes the AGC reference value. Although these two types of sensitivity adjustment devices differ in whether to adjust the light amount or the level of the electric signal, they are essentially a feedback system that keeps the brightness of the final image constant. In this respect, they are the same, and the circuit is configured almost in the same way.

[0004]

However, in the conventional video camera exposure control device, the dynamic range or the signal level of the iris detection circuit and the AGC detection circuit are different, so that these detection circuits must be shared. Could not. In general, a high-brightness clip circuit is provided at a stage subsequent to the detection circuit (see Japanese Patent Laid-Open No. 2-2 / 1990).
68080), a high-contrast scene that is clipped by the high-brightness clipping circuit when the clip level of the high-brightness clipping circuit on the iris side is different from the clip level of the high-brightness clipping circuit on the AGC side. When the image is taken, the brightness adjusted by the iris and the brightness adjusted by the AGC are different, which causes problems such as overexposure and underexposure, overexposure of high-luminance areas, and deterioration of S / N in low-luminance areas. Occur.

The present invention has been made in view of such circumstances, and a video camera that can share a circuit that can be shared between an iris control system and an AGC system to reduce the number of parts and make the circuit characteristics uniform. The purpose of the present invention is to provide an exposure control device.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention converts subject light incident on an image pickup device via a photographic lens and an iris into an electric signal by the image pickup device, and converts the electric signal to a previous signal. A video camera which outputs to a video signal processing circuit via a preamplifier and an AGC amplifier and performs appropriate signal processing by the video signal processing circuit to obtain a required video signal is output from the preamplifier. An iris control means for inputting an electric signal as an iris detection signal, controlling the iris based on the iris detection signal, and an electric signal output from the AGC amplifier as an AGC detection signal; AGC means for controlling the gain of the AGC amplifier based on a detection signal for use with the iris control means and the AGC means. And means for sharing by time division circuit,
It is characterized by having.

[0007]

According to the present invention, there is provided an iris control means for using an electric signal output from an image sensor via a preamplifier as an iris detection signal, and an electric signal output from the preamplifier via an AGC amplifier. Focusing on the commonality of the configuration with the AGC means that uses AGC as a detection signal for AGC, a circuit that can be shared by both, such as a detection circuit and a high-brightness clipping circuit, is shared in a time-division manner.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an exposure control apparatus for a video camera according to the present invention will be described below in detail with reference to the accompanying 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.

Referring to FIG.
Then, an image is formed on a light receiving surface of an image sensor (CCD) 14 via the iris 12. The CCD 14 accumulates the incident light,
The stored charge is read out in synchronization with a timing pulse applied from the timing generator 16. The electric signal read from the CCD 14 in this manner is amplified by the preamplifier 18 and then applied 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. 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, and the like, performs predetermined signal processing by these circuits, and outputs, for example, an NTSC video signal to the recording device 23.

The recording device 23 includes a recording circuit, which converts the video signal into a recording signal suitable for magnetic recording, and magnetically records the recording signal 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 to the input terminal SW1b of the switch SW1 as an iris detection signal.

The switch SW1 has its movable contact 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 ( 1H) and output to an LPF (low pass filter) 24 alternately. The signal that has passed through the LPF 24 is detected as a signal indicating a luminance signal, and the A / D signal at the subsequent stage is detected.
The signal 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 is connected to the output terminals SW2a and S2.
W2b. Thus, 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 input data for one field, and outputs the integrated data to the MP.
Output to U (microprocessor unit) 32. M
The PU 32 processes the integrated data based on the program stored in the ROM (Read Only Memory) 34, the AGC reference data, and the iris reference data,
An AGC gain control signal and an 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 integrating circuit 28 with the AGC reference data,
If it is larger than the reference data for C, it is determined that the image is too bright, and D / D
An AGC gain control signal is output to the AGC amplifier 20 via the A converter 36. On the other hand, if the integrated data is smaller than the AGC reference data, it is determined that the integrated data is too dark.
The D / A converter 3 increases the gain of the C amplifier 20.
6 through the AGC gain control signal to the AGC amplifier 20.
Output to

Similarly, the MPU 32 compares the integrated data input from the iris integrating circuit 30 with the iris reference data, and judges that the integrated data is too bright when the integrated data is larger than the iris reference data. Is output to the iris driving circuit 40 via the D / A converter 36 so as to close the iris, thereby driving the iris 12 in the closing direction. On the other hand, when the integrated data is smaller than the iris reference data, Is determined to be 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 video camera exposure control device having the above-described configuration, the iris control circuit and the AGC circuit use the LP control circuit.
The F24 and the A / D converter 26 can be shared.
In the above embodiment, the switches SW1 and SW2 are switched every 1H. However, if the switches are switched every field, for example, the integration circuits 28 and 30 can be shared.

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 denoted by the same reference numerals, and detailed description thereof will be omitted. Comparing the first embodiment of FIG. 1 with the second embodiment of FIG.
Although the F24 and the A / D converter 26 are shared, the second embodiment is different mainly in that the high brightness clip circuit 42 is shared.

Now, referring to FIG.
The AGC detection signal output from the iris and the iris detection signal output from the preamplifier 18 are separate L
Input terminals SW1a and SW1b of the switch SW1 via the PFs 24A and 24B and the A / D converters 26A and 26B.
Is added to The switch SW1 has its movable contact 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 / D of the AGC detection signal input from the A / D converter 26A. The luminance data of the iris detection signal input from the D converter 26B is alternately output to the high luminance clip circuit 42, for example, for each horizontal scanning line (1H).

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

The luminance data that has passed through or clipped the high luminance clip circuit 42 is output to the switch SW2. The switch SW2 is the timing generator 1
Switch S by the timing pulse applied from
In synchronization with W1, the movable contact is connected to the output terminals SW2a and SW2.
2b. Thereby, AG
The luminance data corresponding to the C detection signal is input to the AGC full area integration circuit 28, and the luminance data corresponding to the iris detection signal is input to the iris screen center integration circuit 30A and the screen full area integration circuit 30B.

The AGC full-area integrating circuit 28 integrates the input luminance data for one field, outputs the integrated data to the MPU 46, and similarly performs the entire screen integrating circuit 30B.
Integrates the input luminance 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, and the screen center integration circuit 30A uses the screen center selection signal to output Only the luminance data at 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 a ROM
48 and the reference data for AGC,
Processing is performed based on the iris reference data, and an AGC gain control signal and an iris control signal are output via D / A converters 36 and 38, respectively. That is, the MPU 46
Integrated data and A input from the AGC full integration circuit 28
By comparing with the GC reference data, if the integrated data is larger than the AGC reference data, it is determined that it is too bright,
An AGC gain control signal is output to the AGC amplifier 20 via the D / A converter 36 so as to lower the gain of the AGC amplifier 20. On the other hand, if the integrated data is smaller than the AGC reference data, it is too dark. Judgment is made, and an AGC gain control signal is output 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 a screen central portion integrating circuit 3.
From the integrated data I ₁ and I ₂ entering from 0A and the entire screen integration circuit 30B calculates the photometric data. 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 thus calculated is compared with the iris reference data. If the photometric data is larger than the iris reference data, it is determined that the image is too bright, and D is set so that the iris 12 is closed.
An iris control signal is output to the iris drive circuit 40 via the / A converter 36, thereby driving 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 the image 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 an integrating circuit 3 at the center of the screen.
Based on the integrated data I ₁ and I ₂ entering from 0A and the entire screen integration circuit 30B to determine the state like the spot light is striking the object, and outputs a clipping level control signal through the D / A converter 39. That is, the MPU 46
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 greater than the threshold Th (| I ₁ −I ₂ |
> Th) is determined (step 102), and if it is larger, it is determined that the subject is in a backlight state or a state in which a spotlight is hitting the subject, and the process proceeds to step 102.

In step 102, it is determined 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 determined that the spot light is hitting the subject. Proceed to 104. Step 10
In step 4, the clip target value is set to level 2 (for example, IRE20).
0), and outputs a clip level control signal so that this becomes the next clip level. IRE is N
Indicates the luminance level of the video signal of the TSC system.
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, where the clip target value is set to a normal level 1 (for example, IRE100), and the clip level is set so that it becomes the next clip level. Outputs control signal. According to the exposure control apparatus for a video camera having the above configuration, the iris control circuit and the AGC circuit can share the high-brightness clip circuit 42, and the single high-brightness clip circuit 42 Clip level can be controlled.

FIG. 4 is a block diagram of a video camera including a third embodiment of the video camera exposure control apparatus according to the present invention. 1 and 2 are denoted by the same reference numerals, and detailed description thereof will be omitted. That is, FIG.
In the third embodiment shown in FIG. 2, the LPF 24, the A / D
The converter 26 is shared, and the high luminance clip circuit 42 is shared similarly to the second embodiment of FIG.

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

[0029]

As described above, according to the exposure control apparatus for a video camera according to the present invention, the iris control system and the AG are controlled.
Circuits that can be shared in the C system, that is, the detection circuit and the high-brightness clipping circuit are shared in a time-sharing manner, so that the number of components can be reduced and the circuit characteristics can be made uniform.

[Brief description of the drawings]

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

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.

FIG. 3 is a flowchart used to explain a clip level determined by the MPU of FIG. 2;

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.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Photography lens 12 ... Iris 14 ... Image sensor 16 ... Timing generator 18 ... Preamplifier 20 ... Amplifier for AGC 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 integrating circuit 30B: Full screen integrating circuit 32, 46: MPU 34, 48 ROM 40: Iris drive circuit SW1, SW2: Switch

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-6973 (JP, A) JP-A-63-141458 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04N 5/222-5/243 H04N 5/30-5/335

Claims (3)

(57) [Claims] 1. An image pickup device converts object light incident on an image pickup device via a photographing lens and an iris into an electric signal, and outputs the electric signal to a video signal processing circuit via a preamplifier and an AGC amplifier. The video signal processing circuit appropriately performs signal processing to obtain a required video signal. An electric signal output from the preamplifier is input as a detection signal for iris, and the detection for iris is performed. An iris control unit for controlling the iris based on a signal; an electric signal output from the AGC amplifier being input as an AGC detection signal; and controlling a gain of the AGC amplifier based on the AGC detection signal. AGC means; and means for sharing a circuit sharable 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 iris detection signal to AG
2. 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-brightness clip circuit.