JPH04117779A - Video camera - Google Patents

Abstract

PURPOSE:To attain a natural change of lightness on a screen and to realize an easy to see picture by receiving a signal varying with an output level of a 1st variable gain amplifier circuit so as to control the 1st variable gain amplifier circuit thereby controlling a 2nd variable gain amplifier circuit. CONSTITUTION:A signal from an the image pickup element 1 is processed by a signal processing circuit 2 and inputted to a 1st variable gain amplifier circuit 3. An output of the 1st variable gain amplifier circuit 3 is also inputted to a detection circuit 16 and its output is inputted to a noninverting input of a 1st operational amplifier 17, in which a voltage in response to an output signal level of the 1st variable gain amplifier circuit 3 and a divided voltage being a reference voltage from a variable resistor 18 are compared and the result of comparison is fed back to the 1st variable gain amplifier circuit 3. Since an output of the 1st operational amplifier 17 being a control signal of the 1st variable gain amplifier circuit 3 is inputted also to an inverting input of a 2nd the operational amplifier 22, the gain of the 1st variable gain amplifier circuit 3 and that of the 2nd variable gain amplifier circuit 11 are changed simultaneously in a same direction with respect to a change in the illuminance of an object. Thus, a change in the lightness of the screen is made natural and an easy to see picture is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION A) Field of Industrial Application The present invention relates to a video camera that is effective for photographing subjects with low illuminance.

(b) Conventional technology Conventionally, as a video camera effective for shooting subjects with low illuminance,
A device in which two stages of variable gain amplifier circuits are connected in series to increase the gain of a video signal is disclosed in Japanese Patent Application Laid-Open No. 119388/1988 (
HO4N 5. /14). In this prior art, 0N10FF of one of the variable gain amplifier circuits is controlled depending on the illuminance of the subject. Therefore, it is possible to give priority to S/N when the subject is bright, and to give priority to gain when it is dark.

(c) Issues to be solved by the invention However, in a conventional video camera in which two stages of variable gain amplifier circuits are connected in series, each variable gain amplifier circuit operates independently, so one variable gain amplifier circuit ON10
FF causes discontinuity in the level change of the output video signal. As a result, the brightness of the screen changes unnaturally, making it very unsightly.

Further, when two variable gain amplifier circuits operate simultaneously, the noise level included in the video signal becomes relatively large due to the high gain. Therefore, when performing so-called hill-climbing autofocus in which the degree of focus accuracy is detected from the high frequency components of the video signal, there is a problem that there is a high possibility of erroneous printing.

(d) Means for resolving tax deferrals.

The present invention provides a video camera including: a first variable gain amplifier circuit; a second variable gain amplifier circuit connected in series with the first variable gain amplifier circuit; , the above 1 so that the output level is constant.
The present invention is characterized by comprising a comparison circuit that receives a first control signal that controls the variable gain amplifier circuit and generates a second control signal that controls the second variable gain amplifier circuit.

Further, inputting a high frequency component of the output video signal of the first variable gain amplifier circuit from a stage before the second variable gain amplifier circuit,
The present invention is characterized by having a focal amount detection circuit that detects focal spotness.

(E) Function The present invention is constructed as described above, so that the gains of the twelve variable gain amplifier circuits are changed in conjunction with each other.

Furthermore, when mountain climbing autofocus is performed, high frequency components of the output video signal with less noise components are input to the focus amount detection circuit.

(f) Example An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit block diagram of a video camera showing an embodiment of the present invention.

In the figure, a signal from an image sensor 1 constituted by a CCD or the like is processed into a luminance signal component and a color signal component by a signal processing circuit 2, and is input to a first variable gain amplifier circuit 3.

Thereafter, only the m-degree signal component is extracted by passing through the low-pass filter 4, and the luminance signal component passes through the gamma correction circuit 5, the IH delay line 6, and the amplifier circuit 7, and is sent to the horizontal contour correction circuit 8. is input. On the other hand, the color signal component is inputted from a branch point 9 to a color signal processing circuit (not shown).

In the horizontal contour correction circuit 8, 0. Horizontal contour correction is performed by creating a contour correction signal using a delay line having a delay time of about 1-0.5 μs. after that,
The first adder 10 adds vertical contour correction signals to perform vertical contour correction. Note that the vertical contour correction signal is created using the original signal, the IH delayed signal, and the 2H delayed signal. Further, since the vertical contour correction signal must be added to the IH-delayed signal, an IH delay line 6 is provided before the adder 10.

After the vertical contour correction signal is added, it passes through the second variable gain amplifier circuit 11, the white clip circuit 12 clips the white signal level to a predetermined value, and the fader circuit 13 adjusts the white signal level as necessary. The fade-in and fade-out are controlled by Thereafter, the set-up circuit 14 clips the pedestal level to a predetermined value, and the second addition 95
At step 15, a synchronizing signal is added and output as a luminance signal of the video camera.

Next, the first variable gain amplifier circuit 3 and the second variable gain amplifier circuit 11 will be explained.

The output of the first variable gain amplifier circuit 3 is also input to the detection circuit 16 and converted into a voltage according to the signal level. The voltage is input to the positive terminal of the first operational amplifier [7]. Also,
A divided voltage from a variable resistor 18 connected between the power supply and the earth line is input to the negative terminal, and the output of the first operational amplifier 7 is input as a control signal to the first variable gain amplifier circuit 3. That is, the first operational amplifier 17 compares the voltage corresponding to the output signal level of the first variable gain amplifier circuit 3 with the divided voltage from the variable resistor 8 which is the reference voltage, and sends the comparison result to the first variable gain amplifier circuit 3. Feedbank. Therefore, the output signal level of the first variable gain amplifier circuit 3 is constant regardless of the illuminance of the subject. Note that resistance 1
9.20 adjusts the gain of the first operational amplifier 17, and the capacitor 21 is provided to prevent the first operational amplifier 17 from oscillating.

On the other hand, the output of the first operational amplifier 17 is
It is also input to the negative terminal of. The second operational amplifier 22 is a comparator circuit that creates a control signal for the second variable gain amplifier circuit 11, and its positive terminal receives a divided voltage from resistors 23 and 24 connected between the power supply and the earth line, and outputs is input to the diode 25. Note that the resistance is 26.27
adjusts the gain of the second operational amplifier 22 and connects the capacitor 28
is provided to prevent the second operational amplifier 22 from oscillating. In addition, a resistor 29 and a second variable gain amplifier circuit]1
There is a resistor 30. connected between the power supply and the ground line.
It is biased by a divided voltage by 31.

Next, the operations of the first variable gain amplifier circuit 3 and the second variable gain amplifier circuit 11 will be explained.

If the illuminance of the subject increases, the output level of the first variable gain amplifier circuit 3 will increase, and the output voltage of the detection circuit 16 will increase. Therefore, the output of the first amplifier 7 becomes large and the gain of the first variable gain amplifier circuit 3 is controlled to be small. Conversely, when the illuminance of the object becomes lower, the gain becomes thicker. Therefore, the output level of the first variable gain amplifier circuit 3 becomes a constant level according to the setting value of the variable resistor 18.

On the other hand, since the output of the first operational amplifier 17, which is the control signal for the first variable gain intensifier circuit 3, is also input to the negative terminal of the second operational amplifier 22, when the illuminance of the subject becomes high, the output of the second operational amplifier 22 is becomes smaller. Therefore, a forward current flows through the diode 25, the potential between the resistor 30 and the resistor 31 decreases, and the gain of the second variable gain amplifier circuit 1 is controlled to be reduced. That is, the first variable gain amplification circuit 3 and the second variable gain amplification circuit 11 change their gains simultaneously in the same direction in response to changes in the illuminance of the subject. Furthermore, since the variable gain amplifier circuit is configured in two stages in series, the camera becomes a highly sensitive video camera that can be used even when the illuminance of the subject is low.

FIG. 2 is a graph showing the output luminance level with respect to the control voltage of the first variable gain amplifier circuit 3, which is a combination of the first variable gain amplifier circuit 3 and the second variable gain amplifier circuit 11. @1 The maximum gain is larger than the characteristic A of only the variable gain width circuit 3. Furthermore, even though two stages of variable gain amplifier circuits are connected in series, there is no discontinuity in the special changes.

In this embodiment, the second variable gain amplifier circuit 11 uses a circuit in which the control voltage vs. gain characteristic is not linear, but the gain of the second operational amplifier 22 is set small by the resistors 26 and 27. 2. Mainly uses the portion where the control voltage vs. gain characteristic in the variable gain intensifier circuit 11 is linear. Note that this characteristic becomes steep as the gain approaches its maximum value. Further, unless the output voltage of the second operational amplifier 22 becomes lower than the voltage on the anode side of the diode 25 set by the resistors 29, 30, and 31, the gain of the second variable gain amplifier circuit 11 does not change. Therefore, the range of illuminance of the object in which the gain of the second variable gain amplifier circuit 1 is changed can be adjusted by the set voltage on the anode side.

Furthermore, in this embodiment, a branch point 3 is provided at the front stage of the second variable gain amplifier circuit 11 and at the output stage of the first variable gain amplifier circuit 3.
2, the high frequency component of the video signal is input to the focus amount detection circuit 34 via the bypass function 33. The focus amount detection circuit 34 is a circuit that detects the focus amount by utilizing the fact that when the optical system of the video camera is in focus, the level of the high frequency component of the video signal is at its maximum. When the illuminance of the subject is low, the output luminance signal contains many noise components because it is amplified with a high gain by the two variable gain amplifier circuits. If the high frequency component of the output luminance signal is input to the focus amount detection circuit 34, there is a high possibility that the circuit will malfunction due to the noise component. However, if the input of the focal amount detection circuit 34 is obtained from the output stage of the first variable gain amplifier circuit 3 as in this embodiment, compared to the output luminance signal, the input of the focal amount detection circuit 34 is not passed through the second variable gain amplifier circuit 11. Since there are few noise components, the possibility of malfunction is reduced.

Note that the frames 35, 36, 37, and 38 in FIG. 1 indicate that the amplifier circuits and the like included therein are constructed of integrated circuits.

Further, in this embodiment, only the luminance signal is passed through two variable gain amplifier circuits, but it goes without saying that the color signal may be similarly passed through two variable gain amplifier circuits.

(G) Effects of the Invention As described above, according to the present invention, since the gains of the two variable gain amplifier circuits change together, there is no discontinuity in the output video signal, and therefore changes in screen brightness are prevented. It becomes natural and easier to see.

In addition, although the video camera has a high gain that can handle low illuminance, the focus amount detection circuit that inputs the high frequency component of the video signal and detects the focus accuracy has the effect of reducing malfunctions due to noise. The effect is great.

[Brief explanation of the drawing]

1 and 2 relate to one embodiment of the present invention, with FIG. 1 being a circuit block diagram and FIG. 2 being a control voltage-output luminance level characteristic diagram. 31. 1st variable gain amplifier circuit, 11... 2nd variable gain amplifier circuit, 17... 1st operational amplifier, 22... 2nd operational amplifier, 34... focal amount detection circuit Fig. 2

Claims (2)

[Claims] (1) A first variable gain amplification circuit, a second variable gain amplification circuit connected in series with the first variable gain amplification circuit, and a first variable gain amplification circuit whose output level varies according to the output level of the first variable gain amplification circuit; and a comparison circuit that receives a first control signal for controlling the first variable gain amplifier circuit so that the voltage is constant, and generates a second control signal for controlling the second variable gain amplifier circuit. camera. (2) inputting the high frequency component of the output video signal of the first variable gain amplifier circuit from the stage before the second variable gain amplifier circuit;
2. The video camera according to claim 1, further comprising a focus amount detection circuit for detecting the degree of focus accuracy.