JPH04107078A - Imaging device - Google Patents

Abstract

PURPOSE:To eliminate the change of a video signal level due to the change of a zoom rate, and to hold the signal level to be constant by amplifying video signals in order to compensate the change of a lens F value due to the change of the zoom rate according to the change of the zoom rate. CONSTITUTION:Lights incident on an optical system 10 prepare images through a diaphragm 12 and an optical filter 16 on an imaging device 18. The imaging device 18 converts the optical images into electric signals, and applies them to a preamplifier 20. The output signals are inputted through an AGC, gamma correction circuit 22 to an amplifier 24. A diaphragm controlling circuit 30 operates the diapharagm 12 to an open side when the brightness of objects is low, and applies a signal indicating the order to a brightness correcting circuit 38. The circuit 38 responds to both this signal and a zoom position detecting signal from a zoom position detecting circuit 36, and applies a signal indicating the gain to hold the signal level to be constant and to correct the brightness to the amplifier 24. The amplifier 24 amplifies the video signals according to this gain.

Description

[Detailed description of the invention] [Industrial application fields] This invention is a camera-integrated VTR (Video).

The present invention relates to an imaging device such as a tape recorder (Tape Recorder), and particularly relates to a technique for stabilizing a video signal level.

[Prior Art] FIG. 4 is a circuit block diagram of a video camera that is a typical example of a conventional imaging device. Referring to FIG. 4, this video camera includes an optical system 10 having an aperture 12 and a zoom lens 14, an optical filter 16 provided on the optical axis of the optical system 10, and an optical filter 16 provided on the imaging plane of the optical system 10. A CCD (Charge-Coupled Device)
a preamplifier 20 for amplifying the electrical signal output from the imaging device 18; and a preamplifier 20 for amplifying the electrical signal output from the imaging device 18; AGC and γ correction circuit 22 for performing γ correction during conversion, and a sample hold (S/H) L, γ correction circuit 22 for the signal output from the circuit 22
A circuit 26 for performing color separation, white balance processing, etc., and outputting the signal; a signal processing circuit 28 for processing the signal output from the circuit 26 and outputting a luminance signal and a chroma signal; an aperture control circuit 30 for controlling the aperture 12 based on a signal indicating the video signal level; a motor 34 for driving the zoom lens 14;
SSG) circuit 40, and a drive circuit 32 that generates pulses for driving the image sensor 18 and circuits 22 and 26 based on a synchronization signal provided from the SSG circuit 40.

The signal processing circuit 28 processes the electric signal supplied from the circuit 26, adds a synchronization signal, a blanking period, etc. to the luminance signal, and performs white clip processing. The signal processing circuit 28 also synchronizes the line-sequential color signals supplied from the circuit 26, converts them into chroma signals, and outputs the chroma signals.

Referring to FIG. 4, a conventional video camera operates as follows. The optical system 10 collects the incident light and directs it to the image sensor 1.
8. Focus the image of the subject on top. The image sensor 18 converts the incident light into an electrical signal and supplies it to the preamplifier 20. Preamplifier 2
0 amplifies the applied electrical signal and provides it to the AGC and γ correction circuit 22.

The AGC and γ correction circuit 22 amplifies the input signal with a variable gain so that the output level of the video signal remains constant even when the amount of incident light changes. AGC1γ correction circuit 22
provides a signal indicating the amount of incident light to the aperture control circuit 30.

The aperture control circuit 30 controls the amount of aperture of the aperture 12 in response to this signal.

The circuit 26 and the signal processing circuit 28 are AGC.

The signal output from the γ correction circuit 22 is separated into a color signal and a luminance signal, and is converted into a video signal conforming to the broadcasting system and output. The details of the signal processing are not directly related to the present invention and will not be described in detail here.

Strategy 511! J indicates the relationship between the output level of the video signal and the brightness of the subject. Referring to FIG. 5, when the brightness of the subject is above a certain level, the aperture control circuit 30 and the AGC control circuit operate so that the output level of the video signal is constant. In other words, if the subject is dark and the signal level is low,
The AGC control circuit increases the amplification gain of the video signal. Further, the aperture control circuit 30 operates the optical system 10 to the open side when the signal level decreases. As a result, when the subject is bright to some extent, the level of the output video signal is kept constant.

[Problems to be Solved by the Invention] However, conventional video cameras have the following problems. Referring to FIG. 5, in a low illumination region where the amount of light incident on the image sensor is very small, the aperture is almost open and the AGC circuit is also at almost full gain. The signal level is no longer adjusted by the aperture and AGC control circuits. Therefore, the brightness of the video signal also changes in proportion to the amount of incident light.

On the other hand, when using a zoom lens for boat fishing, when the zoom ratio of the lens changes, the F value (brightness of the lens) of the lens changes.

Therefore, even though the brightness of the surrounding area does not change in a low illuminance area, the brightness of the image changes depending on the zoom ratio, resulting in a problem in that the image quality deteriorates.

Furthermore, it is an object of the present invention to provide an imaging device in which the video signal level does not change much even when the zoom ratio changes.

[Means for Solving the Problems] An imaging device according to the present invention includes an optical system having a zoom mechanism and converting an optical image of a subject formed by the optical system into a video signal having a level corresponding to the illuminance thereof. the brightness of the optical system by amplifying the video signal with a gain based on the zoom ratio signal; and compensation means for compensating for changes in height.

[Operation] When the zoom ratio changes, the zoom signal output from the zoom ratio detection means changes. The compensation means responds to changes in the zoom ratio signal and amplifies the video signal with a gain that compensates for changes in brightness of the optical system due to changes in the zoom ratio.

[Example 1] FIG. 1 is a block diagram of a video camera that is an example of an image sensor according to the present invention. Referring to FIG. 1, this video camera is different from the conventional video camera shown in FIG. and for determining the amplification factor of the video signal in order to compensate for the level change of the video signal in the low illuminance region in response to the output of the zoom position detection means 36 and the signal indicating the aperture opening given from the aperture control circuit 30. It includes a brightness correction circuit 38 and an amplifier 24 for amplifying the video signal according to an amplification factor determined by the brightness correction circuit 38. The zoom position detection means 36 is for detecting the zoom ratio of the optical system 10, and includes the brightness correction circuit 38 and the amplifier 1.
4 is a compensation means for compensating for changes in brightness of the optical system 10.

Identical parts have been given the same reference numbers and names in FIGS. 1 and 4. Their functionality and operation are also the same. Therefore, detailed explanations about them will not be repeated here.

FIG. 2 shows the first part of the zoom lens 14 near the motor 34.
It is a schematic diagram which shows the drive mechanism which is not shown in a figure. Second
Referring to the figure, this drive mechanism includes a motor 34, a pulley 58 that is rotated by the motor 34 via a reduction gear 54, and a pair of two-wheel gears 48 that are driven by the pulley 58 via an electric belt 56. .50. Worm gear 48
．． 50 drives the zoom lens 14.

The zoom position detection circuit 36 is provided with a resistor 46 provided so as to be in contact with one end of the worm gear 48, and an end of the worm gear 48 that is in contact with the resistor 46. It includes a slider 44 that contacts and moves on the end surface of the resistor 46 as the worm gear 48 rotates, and a terminal 45 that is fixed to the end surface of the resistor 46. Slider 44
and terminal 45 are connected to brightness correction circuit 38 (FIG. 1).

Referring to FIG. 3, the brightness correction circuit 38 has a terminal A to which a signal from the zoom position detection circuit 36 is input, and a terminal B to which a signal indicating the aperture opening from the aperture control circuit 30 is applied. . The brightness correction circuit 38 has a base connected to terminal B.
, a transistor Tr2 whose emitter is connected to the ground potential, resistors R2 and R3 connected in series between the collector of Tr2 and the power supply potential Vcc, a negative input terminal connected to terminal A, and a positive input terminal connected to terminal A. It includes an operational amplifier 60 connected to the contacts of resistors R2 and R3, respectively, and a resistor R4 connected between the negative input terminal and output terminal of the operational amplifier 60.

The amplifier 24 is an FET (Field Effect) whose gate electrode is connected to the output of the operational amplifier 60 via a resistor R5, and whose drain electrode is connected to the ground potential via a capacitor C1 and a resistor R7 connected in parallel.
Transistor) 62, the base is AGC, the output of the γ correction circuit 22, the emitter is connected in series to the ground potential via resistors R9 and R8, the collector is connected to the resistor RIO
transistors T each connected to the power supply potential via
ri, a resistor R6, and a capacitor C2 connected in series between the source electrode of the FET 62 and the contacts of the resistors R9 and R8.
including. The collector of the transistor Tri is connected to the signal processing circuit 28.

The zoom position detection circuit 36 includes a resistor 46 and a slider 44 connected to the terminal A of the brightness correction circuit 38 as described above.
including. The zoom position detection circuit 36 further includes the slider 4
4 and the ground potential.

Referring to FIGS. 1 to 3, the video camera according to the present invention operates as follows. The light incident on the optical system 10 is
An image is focused on an image sensor 18 through an aperture 12 and an optical filter 16. The image sensor 18 converts the optical image into an electrical signal and provides it to the preamplifier 20. The preamplifier 20 amplifies the input electrical signal and supplies it to the AGC and γ correction circuit 22. The circuit 22 electrically corrects the level of the input signal to a constant level, performs γ correction processing, etc.
Give to 4.

The AGC and γ correction circuit 22 also provides a signal indicating the video signal level to the aperture control circuit 30. The diaphragm control circuit 30 controls the diaphragm 12 so that the image G and the bell become constant. As a result, the video signal level is normally controlled to a certain level depending on the brightness of the subject.

However, if the subject is very dark or in a low-light area, the AG
The C control circuit has almost full gain. Further, the aperture 12 is also almost opened.

On the other hand, due to the optical design of a zoom lens, the smaller and lighter the zoom lens is, the larger the change in lens F value becomes.

In some cases, the amount of light that passes through the lens and enters the image sensor at the wide-angle end and at the telephoto end changes by nearly twice.

In such a situation, if the zoom ratio is changed during low illuminance, the change in the amount of incident light due to the change in zoom will be directly reflected in the level of the video signal. In other words, even if you take a picture of the same subject in a dark place, it will appear darker if you take it at telephoto than if you take it at wide-angle. A video in which the video signal level changes in this way becomes extremely unsightly.

In order to prevent such problems, the video camera according to the present invention includes a zoom position detection circuit 36 and a brightness correction circuit 3.
8 and an amplifier 24.

Referring to FIG. 2, when motor 34 rotates to move the zoom lens, worm gear 48 also rotates.

Since the resistor 46 is fixed, the positional relationship between the slider 44 and the terminal 45 changes as the resistor 44 rotates on the end face of the resistor 46. By detecting the resistance value between the slider 44 and the terminal 45, the zoom lens 14
In other words, the zoom ratio of the optical system 10 can be known. The resistance value between the slider 44 and the terminal 45 is the resistance R
1 (FIG. 3), the voltage is changed into a voltage and applied to the brightness correction circuit 38. This signal will be referred to as a zoom position detection signal.

The aperture control circuit 30 operates the aperture 12 to the open side when the brightness of the subject becomes low. When the aperture 12 is in the open state, the circuit 30 provides a signal indicating this to the brightness correction circuit 38. In response to this signal and the aforementioned zoom position detection signal, the brightness correction circuit 38 provides the amplifier 24 with a signal indicating a gain for brightness correction while keeping the signal level constant. The amplifier 24 amplifies the video signal according to this gain. This makes it possible to correct the brightness of the subject in a low illuminance area that cannot be compensated for even by AGC or aperture control.

Referring to FIG. 3, an analog voltage formed by a resistor 46 and a slider 44 for zoom position detection is applied to terminal A as a zoom position detection signal. Terminal B is supplied with a voltage from the aperture control circuit 30 when the aperture is opened. As a result, the operational amplifier 60 operates and F
A voltage is applied to the gate electrode of ET62. In response to a change in gate voltage, the resistance value between the drain and source of the FET 62 changes. This changes the resistance on the emitter side of the transistor Trl. An AGC output is applied to the base of the transistor Tr1.

The collector of the transistor Tri is connected to the input of the signal processing circuit. As a result, the gain of the amplifier 24 can be changed, and a signal whose output level has been corrected due to changes in the brightness of the zoom lens is provided to the circuits 26 and 28.

As described above, according to the present invention, when the aperture is opened in a low-light region and the AGC is at full gain, a good video signal is generated whose output level does not change even when the zoom ratio of the zoom lens changes. can be obtained.

The invention has been described above by way of one embodiment.

However, the present invention is not limited to the above-described embodiments, and can be implemented in various other ways.

[Effects of the Invention] As described above, according to the present invention, a change in the zoom rate is detected, and the video signal is amplified according to the change in the zoom rate so as to compensate for the change in the lens F value due to the change in the zoom rate. be done. Therefore, even when it is not possible to automatically adjust the video signal level using the AGC circuit or aperture, for example when the subject is very dark and under low illumination, it is possible to eliminate changes in the video signal level due to changes in the zoom ratio and keep the signal level constant. can be kept.

That is, even if the zoom ratio changes, it is possible to provide an imaging device that can compensate for changes in the lens F value of the optical system and reduce changes in the video signal level.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a video camera that is an example of an imaging device according to the present invention, FIG. 2 is a schematic diagram of an example of a zoom position detection circuit, and FIG. 3 is a schematic diagram of a video camera according to the present invention. FIG. 4 is a block diagram of a conventional video camera, and FIG. 5 is a diagram showing the relationship between the brightness of a subject and the level of an output signal. In the figure, 10 is an optical system, 12 is an aperture, 18 is an image sensor, 2
2 is an AGC and γ correction circuit, 24 is an amplifier, 30 is an aperture control circuit, 36 is a zoom position detection circuit, 38 is a brightness correction circuit, 44 is a slider, and 46 is a resistor. Note that the same reference numerals in the figures indicate the same or equivalent parts. Figure 81 Figure 2

Claims (1)

[Claims] (1) an optical system having a zoom mechanism; an imaging means for converting an optical image of a subject formed by the optical system into a video signal; and detecting a zoom ratio of the optical system and generating a zoom ratio signal. An imaging device comprising: a zoom ratio detection means for outputting the output; and a brightness compensation means for compensating for a change in brightness of the optical system by amplifying the video signal with a gain based on the zoom ratio signal. .