JPS6187477A - Image pickup device - Google Patents

Abstract

PURPOSE:To improve the picture sink by providing a waveform shaping means applying waveform shaping to an output of a signal converting means to form a pulse signal, clamping the said pulse signal to a prescribed potential to add it to a control signal of an AGC circuit. CONSTITUTION:An optical signal is fed to an image pickup element 2 via a lens group 1, converted into an electric signal and amplified by an amplifier 3. An output of the amplifier 3 is sliced by a limiter circuit 13 as a waveform shaping means to form a pulse signal. The pulse signal is fed to a clamp circuit 14 and clamped to a prescribed potential, e.g., in the vicinity of '0'V, added to a control signal of an AGC circuit 7 as the control signal and the level of the control signal is decreased for a period of the pulse signal only substantially to improve the gain of the circuit 7. Thus, even when a bright object is given to any part of a pattern, the picture sink is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an imaging device suitable for use in, for example, a video camera.

[Conventional technology]

Generally, in a video camera, an automatic aperture circuit or an AGC circuit may respond to a bright part of the screen, causing the entire screen to become dark, which is a so-called image sink phenomenon. Conventionally, methods called a weighting method and a window method have been used as methods for correcting such a sinking phenomenon.

These methods transmit the signal from the detection circuit of the automatic iris circuit or the AGC circuit to a part of the screen, for example, the weighting method is the shaded area in Figure 4A, and the window method is the area shown in Figure 4B with diagonal lines. It attenuates only the indicated portion (the range of the sheep is always fixed in both cases) and controls the amount of input light and the gain of the AGC circuit.

More specifically, the weighting method is to mix the signal waveform shown in FIG. 5A (V is the vertical scanning period) with a waveform with a fixed weight as shown in FIG. A as shown
The GC detection waveform is generated, rectified, and the gain of the AGC circuit is controlled by the DC signal.

As can be seen from Figure 5, even if a high level signal is input to the part where the weighted waveform is at a low level, the AGC detection waveform will not become a high signal level, so the gain of the AGC circuit will change depending on the weighting. When not in use, the image becomes larger, making the entire screen brighter and correcting the image sinking. Further, in the window method, the principle of weighting is the same as that of the weighting method, except that the waveform is different.

[Problem that the invention seeks to solve]

By the way, as mentioned above, in the case of the conventional method, the part to be corrected is fixed to a specific area as indicated by diagonal lines in FIG. If a bright subject appears in an area other than the shaded area in the figure, correction cannot be made, resulting in the problem of the above-mentioned image sinking phenomenon.

The present invention has been made in view of the above problems, and an object thereof is to provide an imaging device capable of correcting the image sinking phenomenon no matter where on the screen a bright subject falls.

[Means for solving problems]

This invention provides a conversion means (1) for converting an optical signal into an electrical signal.
), (2), (3) and control means (7), (9) for controlling the gain of the output of the conversion means, the output of the conversion means is waveform shaped. A waveform shaping means (to) 4, (8) is provided for forming a pulse signal using the pulse signal, clamping the pulse signal to a predetermined potential, and adding it to the control signal of the control means. The gain of the control means is controlled during the period.

[Effect]

The output of the converter (3) is sliced by a limiter circuit (3) as a waveform shaping means to form a pulse signal, and this pulse signal is set to a predetermined potential by a clamp circuit (3).
AGC circuit (7) as a control means by clamping at L4
The level of the control signal is reduced substantially during the period of the pulse signal to increase the gain of the AGC circuit, thereby correcting the image sinking phenomenon.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail based on FIGS. 1 to 3.

Figure 1 shows the circuit configuration of this embodiment. In the figure, (1) is a lens group 1 consisting of a plurality of lenses, ) is an image sensor that converts optical signals into electrical signals, and (3) is an image sensor. An amplifier that amplifies the output of element (2), (4) is a vertical synchronization signal from terminal (5), weighting is a circuit that forms a waveform, and (6) is feedback from amplifier (3). The signal and the weighting are added to the weighting waveforms from the circuit (4) to form a control signal for automatic aperture, thereby controlling the amount of light passing through the lens group (1). 7) is an f
(3) is an AGC circuit that controls the gain of the output, and this AGC circuit (7) adds the feedback loop signal and the weighting waveform from the weighting circuit (4) in an adder (8). ,
This addition output is rectified by a detector (9) to obtain a DC signal,
The gain is controlled by this DC signal.

ao is a gamma correction circuit, which is a multi-output terminal Ql
) is derived, and the signal obtained at the output terminal α is supplied to a luminance signal processing section (not shown). Further, a multi-output terminal (6) is led out from the output side of the AGC circuit (7), and the signal obtained at this output terminal (2) is supplied to a chroma signal processing section (not shown).

(G) is a limiter circuit to which the clamped signal from the amplifier (3) is supplied, and this limiter circuit α
J has a limiter level L, and when the input signal exceeds this level, a pulse signal corresponding to the time width exceeded is generated. A4 is a clamp circuit that clamps the pulse signal from the limiter circuit <11 to a predetermined potential, for example, near OV, and generates a signal that is an inversion of the supplied pulse signal.

This inverted signal is essentially used as a subtraction signal by the adder (8
), the signal supplied from the AGC circuit (7) and, if necessary, the weighting is also added to the weighting waveform from the circuit (4).

Next, the operation of this circuit will be explained with reference to the signal waveforms shown in FIG.

Now, the optical signal passes through the lens group (1) to the image sensor (2).
The signal is supplied to the amplifier, is converted into an electrical signal, and is amplified by an f(3). If the signal supplied from the amplifier (3) to the limiter circuit O every horizontal scanning period H exceeds the limiter level L as shown in Fig. 2A, the signal supplied to the limiter circuit O from the amplifier (3) exceeds the limiter level L as shown in Fig. 2A, then the signal supplied to the limiter circuit O in Fig. 2B corresponds to the exceeded time width. A pulse signal as shown in is generated at the output side of the limiter circuit α3. This pulse signal is supplied to a clamp circuit a4 and clamped to a predetermined potential, for example, near Ov. As a result, the output side of the clamp circuit α4 is NO'! ? An inverted signal of the pulse signal is obtained, and an adder (8
) is supplied to the − input terminal of

This adder (8) also has a second AGC circuit (7).
A signal equivalent to the signal shown in FIG. A is supplied, and this signal and the inverted signal (subtraction signal) from the α phase of the clamp circuit are added. As a result, a signal whose signal is attenuated by the time width of the Noculus signal is obtained on the output side of the adder (8), as shown in FIG. 2C. This signal is rectified by a wave detector (9) to become a DC signal, which is fed back to the AGC circuit (7) as a control signal, thereby causing the AGC circuit (7) to work to increase the gain. j5 depending on the presence or absence of the limiter circuit (2) as a waveform shaping means and the flange circuit a4.
A difference occurs in the gain of the AGC circuit (7), and the gain is larger when provided as in this embodiment.

Therefore, the image sink phenomenon is corrected.

FIG. 3 shows an example of a specific circuit configuration of the limiter circuit (2), flange circuit α4, and adder (8). In the figure, a pair of transistors (
21) , ■2 is provided, and the pace of the transistor (2'D) is connected to the input terminal @ connected to the output side of Anne 7° (3) (Fig. 1), and the pace of the transistor @ is used for setting the limiter level. Connect to the sliding terminal of the variable resistor (2).

In addition, the emitters of transistors (211 and 23) are commonly connected and grounded via a resistor (manufactured by Co., Ltd.).The collector of transistor (211) is directly connected to the positive power supply terminal B, and the The collector is connected to the positive power terminal B through the resistor C0. One end of the variable resistor (24) is connected to the positive power terminal B, and the other end is grounded. Configure.

In addition, the collector of the transistor is connected to the emitter of the transistor □□□ via a clamping capacitor (2η), and the collector of this transistor is connected to the positive power supply terminal B.
, and its pace is connected to the positive power supply terminal B via a resistor C) 91 and grounded via a diode. Further, the emitter of the transistor (2P!l) is connected to the pace of the transistor C121 via the resistor C31, and its emitter is grounded. These constitute the flange circuit C24J.

In addition, the collector of the transistor C32 is connected to the output terminal (c) connected to the input side of the detector (9) (Fig. 1) via a variable resistor (to), and this output terminal (
) is connected to the AGC circuit (7) through a resistor (
A resistor (b) is provided between the circuit (4) and the weighting circuit. are doing. By varying the variable resistor G3), the setting of the amount of signal attenuation for AGC detection can be freely changed.

Now, when the signal from the amplifier (3) supplied to the input terminal is below the limiter level L determined by the setting of the variable resistor @, no pulse signal is generated on the collector side of the transistor (2), and the transistor The potential on the emitter side of is approximately zero potential, and the transistor C32+ is in an off state.

Next, when the signal from the amplifier f(3) exceeds the limiter level L, a pulse signal corresponding to the time width exceeded is generated, and this pulse signal is supplied to the transistor ω via the capacitor. The transistor 0 is turned on for the duration of the Norse signal.

As a result, a signal whose phase is inverted from the pulse signal supplied to the pace is generated on the collector side of the transistor C3Z. This signal is supplied as a subtraction signal to the output terminal (C) side via the resistor, and the resistor! 361 and (b)
The signal is added to the signal supplied via the .

As a result, the signal fed through resistor (3) and (3) is substantially attenuated by the subtraction signal fed through resistor (3). Detector (
9) (Fig. 1), the signal is rectified into a DC signal, and is fed back to the AGC circuit (7) as a control signal.
The gain of the C circuit (7) is controlled to increase.

〔Effect of the invention〕

Previously, when a bright subject entered an area that had never been taken due to weighting or the window, the image would sink.
By providing a waveform shaping means that distorts the waveform of the output of the signal converting means to form an A' pulse signal as in the present invention, clamps this A' pulse signal to a predetermined potential, and adds it to the control signal of the AGC circuit. It is possible to increase the gain of the AGC circuit even for such a subject, thereby making it possible to improve the image sinking phenomenon no matter where on the screen a bright subject is placed.

Additionally, in the past, weighting was applied regardless of the subject and the window was fixed, but with this invention, when something bright appears in the subject, variable weighting is possible, in which weighting is applied to that part. .

Furthermore, since the limiter level and the signal attenuation amount of AGC detection can be freely changed, there is the advantage that screen production is easier.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention, FIG. 2 is a signal waveform diagram for explaining the operation of FIG. 1, and FIG. 3 is a connection diagram showing an example of the essential parts of the invention. Figures 4 and 5
The figure is a diagram for explaining a conventional method. (1) is the lens group, (2) is the image sensor, (3) is the amplifier, (7) is the AGC circuit, (8) is the adder, (9) is the detector, (to) the first picture of the beam Figure 2 Figure 4 A B Figure 5

Claims (1)

[Claims] In an imaging device comprising a conversion means for converting an optical signal into an electrical signal, and a control means for controlling the gain of the output of the conversion means, the output of the conversion means is waveform-shaped to form a pulse signal, and the pulse signal is An imaging apparatus characterized in that a waveform shaping means is provided for clamping a signal to a predetermined potential and adding it to a control signal of the control means, and the gain of the control means is controlled during a period of the pulse signal.