JP3395188B2 - Video camera - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera, and more particularly to exposure control of a video camera. 2. Description of the Related Art In a conventional video camera, exposure control is performed by an auto iris circuit and an AGC circuit. That is, FIG. 3 shows a configuration of an exposure control circuit of a conventional video camera. In FIG. 3, the lens 5
1. The optical information transmitted through the iris 52 is
An image is formed on the light receiving surface 3. The output of the CCD image sensor 53 is supplied to an AGC amplifier 54 and also to a detection circuit 55. A detection circuit 55 detects an output level V ₁ of the CCD image sensor 53. Output V ₁ of the detection circuit 55 is supplied to the comparator 56. The comparator 56 is supplied with a predetermined reference level V _r1 . The output level V ₁ of the CCD image sensor 53 is calculated by the comparator 56.
And the reference level V _r1 are compared. The comparison output is supplied to the iris drive circuit 57, and the iris 52 is opened and closed according to the comparison output. The output of the AGC amplifier 54 is supplied to a video signal processing circuit 58 and to a detection circuit 59. In the detection circuit 59, the output level V of the AGC amplifier 54
₂ is detected. Output V ₂ of the detection circuit 59 is supplied to the comparator 60. The comparator 60 is supplied with the reference level _Vr2 . Comparator 56
In the output level V ₂ and the reference level V _r2 of the AGC amplifier 54 are compared. The comparison output is supplied to the AGC amplifier 54, and the gain of the AGC amplifier 54 is controlled according to the comparison output. [0005] For example, immediately after the power of the video camera is turned on, the opening of the iris 52 and the AGC
The gain of the amplifier 54 is greatly deviated from the target position,
As the auto iris control and the AGC control progress, the opening of the iris 52 and the gain of the AGC amplifier 54 are drawn to the target positions. In order to quickly bring the opening of the iris 52 and the gain of the AGC amplifier 54 to target values, it is desirable to increase the loop gain. However, if the loop gain is increased, stable control cannot be performed. Therefore, in order to shorten the control time and perform stable control, it is necessary to perform loop control when the opening of the iris 52 or the gain of the AGC amplifier 54 is greatly deviated from the target position, such as when power is turned on. It is desirable to perform control such that the gain is increased and the loop gain is reduced when the gain approaches the target value. However, in a conventional video camera, FIG.
As shown in (1), the auto iris circuit and the AGC circuit are each constituted by separate analog hardware. Therefore, the loop gain of the auto iris circuit and the AGC circuit cannot be easily changed. When the configuration is such that the loop gain is variable, the hardware scale increases, which hinders miniaturization and increases the cost. For this reason, in the conventional video camera, the auto iris circuit and the A
The loop gain of the GC circuit is fixed. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a video camera in which the exposure control time can be shortened and the exposure control can be performed stably without increasing the hardware scale. [0008] The present invention relates to a lens
And iris for limiting the light amount of information through, the more the iris
An image sensor that converts optical information into an electric signal and an output of the image sensor.
An AGC circuit for adjusting the level of the force signal ;
An A / D conversion circuit for digitally converting an output signal, A / D
Digital signal for detecting the exposure state from the output signal of the conversion circuit
Signal processing and a detection circuit that detects whether the power is turned on.
Immediately after the power is turned on by the detection circuit.
The gain of the optical control loop is
This is a video camera characterized by being all larger . [0010] For example, a plurality of tables of characteristics of the iris opening, shutter speed, and gain of the AGC amplifier with respect to incident light amounts having different gains are prepared, and by switching these tables, the gain of the exposure control loop is adjusted. Can be easily switched. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In FIG. 1, light information transmitted through a lens 1 is imaged on a light receiving surface of a CCD image sensor 3 via an iris 2. The iris 2 is opened and closed by an iris drive motor 4. The shutter speed of the CCD imaging device 3 can be changed by a shutter speed setting circuit 5. The output of the CCD image pickup device 3 is
Supplied to The gain of the AGC amplifier 6 is set according to the output of the D / A converter 7. The output of the AGC amplifier 6 is supplied to the A / D converter 8. The A / D converter 8 digitizes a video signal from the CCD image sensor 1. The output of the A / D converter 8 is supplied to a digital signal processing circuit 9 for performing video signal processing.
It is supplied to the detection circuit 10. The detection circuit 10 is, for example, a digital circuit for detecting the exposure state of two exposure detection areas. The detection circuit 10 includes a center area setting circuit 11A and a peripheral area setting circuit 11B, and average value detection circuits 12A and 12B.
And peak value detection circuits 13A and 13B and distribution detection circuits 14A and 14B. Among the digital video signals output from the A / D converter 8, a signal in the center area of the screen is extracted by the center area setting circuit 11A. The video signal in the center area of the screen is supplied to the average value detection circuit 12A, the peak value detection circuit 13A, and the distribution detection circuit 14A. The average value of the video signal in the center area of the screen is detected by the average value detection circuit 12A. The peak value of the video signal in the center area of the screen is detected by the peak detection circuit 13A. Distribution detection circuit 1
In 4B, the number of samples of a predetermined level or more in the video signal in the central area of the screen is obtained. Average value detection circuit 12A,
Outputs of the peak value detection circuit 13A and the distribution detection circuit 14A are supplied to the system controller 15. Among the digital video signals output from the A / D converter 8, signals in the peripheral area of the screen are extracted by the peripheral area setting circuit 11B. The video signal in the peripheral area of the screen is supplied to the average value detection circuit 12B, the peak value detection circuit 13B, and the distribution detection circuit 14B. The average value detection circuit 12B detects the average value of the video signal in the peripheral area of the screen. The peak value of the video signal in the peripheral area of the screen is detected by the peak detection circuit 13B. Distribution detection circuit 1
In 4B, the number of samples equal to or higher than a predetermined level in the video signal in the peripheral area of the screen is obtained. Average value detection circuit 12A,
Outputs of the peak value detection circuit 13A and the distribution detection circuit 14A are supplied to the system controller 15. The system controller 15 detects the video signal level in the center area of the screen using the output of the average detection circuit 12A and the output of the peak detection circuit 13A. The video signal level in the peripheral area of the screen is detected using the output of the average value detection circuit 12B and the output of the peak detection circuit 13B. From the video signal level at the center of the screen and the video signal level at the periphery of the screen, the video signal level of the entire screen is obtained. The video signal level of the entire screen, the opening of the iris 2 at that time, the shutter speed,
The amount of incident light is obtained from the gain of the AGC amplifier 6.
An exposure control value is determined according to the amount of incident light. This exposure control value is supplied to the iris drive circuit 18, the shutter speed setting circuit 5, and the D / A converter 7. When the amount of incident light is small, the iris 2 is opened, the shutter speed is set long, and the gain of the AGC amplifier 6 is increased.
When the amount of incident light is large, the iris 2 is closed, the shutter speed is set short, and the gain of the AGC amplifier 6 is reduced. Thereby, the video signal level supplied to the digital signal processing circuit 9 is controlled to be a predetermined level. FIG. 2 shows an example of setting characteristics of the opening of the iris 2, the shutter speed, and the gain of the AGC amplifier 6 with respect to the amount of incident light. 2, the horizontal axis indicates the amount of incident light, and the vertical axis indicates the gain. A ₁ indicates the gain of the AGC, A ₂ indicates the gain by opening and closing the iris, and A ₃ indicates the gain by changing the shutter speed. Brightness in until B _1, by changing the gain of the AGC amplifier 6, the exposure control is performed.
When the brightness is between B _{1 and} B ₂ , exposure control is performed by controlling the opening and closing of the iris 2. When the brightness is greater than B _2, the exposure control is performed by changing the shutter speed of the CCD image pickup device 3. The gain of the exposure control loop is determined by the opening degree of the iris 2, the shutter speed, and the gain of the AGC amplifier 6 with respect to the amount of incident light. This characteristic is prepared as a table in the system controller 15, for example. In one embodiment of the present invention, the opening degree of the iris 2, the shutter speed, and A
Tables 17A and 17B of gain characteristics of GC amplifier 6
Are prepared at least two types. One table 17A
Is a characteristic having a high loop gain, and the other table 17B is a characteristic having a low loop gain. A power-on detection circuit 16 is provided, and the two tables 17 are provided in accordance with the output of the power-on detection circuit 16.
A and 17B are switched. That is, immediately after the power is turned on, the table 17A having the characteristic of high loop gain is used. When a predetermined time elapses immediately after the power is turned on, a table 17B having a low loop gain characteristic is used. As described above, in the embodiment of the present invention, the power-on detecting circuit 16 detects whether or not the power is immediately turned on. Immediately after the power is turned on, the opening of the iris 2 with respect to the incident light amount, the shutter speed, and the AGC amplifier 6 are turned on. Table of gain characteristics of Table 17 is a table of characteristics of large loop gain.
A, and after a lapse of a predetermined time after the power is turned on, the table is switched to the table 17B having a small loop gain. Therefore, the exposure control loop can be quickly pulled in immediately after the power is turned on, and the control can be stabilized. It should be noted that the table of the characteristics of the opening of the iris 2, the shutter speed, and the gain of the AGC amplifier 6 with respect to the amount of incident light may be switched according to whether or not the error amount of the exposure control loop is large. That is, when the error amount is large, the loop gain is increased, and when the error amount is small, the error amount is decreased. The characteristics of the opening degree of the iris 2, the shutter speed, and the gain of the AGC amplifier 6 with respect to the amount of incident light are changed according to a sport mode for photographing a moving subject and a portrait mode for photographing a stationary subject. The table may be switched. That is, in the sports mode, the loop gain is increased so as to follow a quick movement. In the portrait mode, the loop gain is reduced so that the exposure state does not change due to the movement of another object. According to the present invention, for example, a plurality of tables of the characteristics of the iris opening, the shutter speed, and the gain of the AGC amplifier with respect to the incident light amounts having different gains are prepared, and the tables are switched. The gain of the exposure control loop can be easily switched. Therefore, it is easy to increase the loop gain immediately after turning on the power and decrease the loop gain after a predetermined time has elapsed, or to increase the loop gain when the error amount is large and decrease the loop gain when the error amount is small. The exposure control time can be shortened and the control state can be stabilized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of one embodiment of the present invention. FIG. 2 is a graph used to explain one embodiment of the present invention. FIG. 3 is a block diagram used for explaining a conventional exposure control circuit. [Description of Signs] 16 Power-on detection circuit 17A, 17B Cable

────────────────────────────────────────────────── (5) References JP-A-63-126371 (JP, A) JP-A-63-299462 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 5/222-5/257

Claims (1)

(57) [Claims] [Claim 1] An eye for limiting the amount of optical information through a lens
Squirrel and image sensor for converting optical information from the iris into an electric signal
And an AGC circuit for adjusting the level of an output signal of the image sensor
When, A / D converter for digitally converting an output signal of the AGC circuit
De detecting the circuit, the exposure condition from the output signal of the A / D converter circuit
Digital signal processing and a detection circuit for detecting whether or not the power is turned on. The exposure control is performed immediately after the power is turned on by the detection circuit.
The gain of the loop is large compared to a predetermined time after power-on.
A video camera characterized by the fact that it is sharp .