JPH04207475A - Video camera - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a DC reproduction method of video signals in a video camera.

[Prior Art] In video cameras, in order to perform DC reproduction during video signal processing, a pulse clamp circuit is used to adjust the optical black level for the optical black level period of the video signal output from the image sensor. The DC voltage value is kept constant. An example of this pulse clamp circuit can be found in "Image Electronic Circuits J, edited by Toshio Utsunomiya et al., Corona Publishing, (1978), pp. 47-4.
It is introduced on page 8. This type of pulse clamp circuit receives a control pulse and fixes the signal level to a constant DC voltage value during the control pulse period.

[Problems to be Solved by the Invention] In a video camera, it is necessary to repeat DC reproduction several times, and each time the period of the optical black level of the video signal output from the image sensor is clamped.

Each time a clamp is performed, spike-like noise is superimposed on the video signal due to the control pulse. However, in the above-mentioned conventional technology, in the second and subsequent DC reproductions, DC reproduction is performed including this noise, so that the actual video Errors occur in the signal. This error is caused by the automatic gain control circuit (A
However, since the amount of error changes depending on the amount of automatic gain control, there is a problem that the optical black level of the video signal fluctuates depending on the illuminance.

Therefore, an object of the present invention is to eliminate errors caused by the superimposition of the spike-like noise and provide a high-quality video camera.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a video camera provided with a plurality of pulse clamp circuits that regenerate the optical black level period of a video signal output from an image sensor. The pulse clamp circuits are each operated at different timings. for example,
The duty phase of the input pulse is changed to avoid spike noise caused by clamping in the preceding stage and clamping in the latter stage.

Moreover, in order to achieve the said object, this invention.

In a video camera that is equipped with a plurality of pulse clamp circuits that regenerate the period of the optical black level of the video signal output from the image sensor using DC current, the period of the optical black level of the video signal output from the previous stage pulse clamp circuit is superimposed on the optical black level of the video signal output from the previous stage pulse clamp circuit. The pulse clamp circuits are each operated at different timings to avoid the influence of spike-like noise.

Furthermore, in order to achieve the above object, the present invention provides a video camera equipped with a plurality of pulse clamp circuits that regenerate the period of the optical black level of a video signal output from an image sensor using direct current. A pulse shaping circuit is added to the pulse clamp circuit that performs reproduction.

[Operations] The present invention relates to a video camera provided with a plurality of pulse clamp circuits for DC reproduction of the optical black level period of a video signal output from an image sensor.

The DC reproduction is performed by operating the pulse clamp circuits at different timings to avoid the influence of spike-like noise superimposed on the optical black level of the video signal output from the previous stage pulse clamp circuit. This eliminates the superimposition of spike-like noise that sometimes occurs, and as a result, it is possible to prevent errors caused by fluctuations in the optical black level of the video signal.

[Example code] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention, in which 1 is an input terminal, 2a and 2b are capacitors, and 3 a
+3b is a pulse clamp circuit, 4 is an automatic gain control circuit (AGC circuit), 5 is a pulse shaping circuit, 6 is a control pulse input terminal, and 7 is a γ correction circuit.

The automatic gain control circuit 4 adjusts the signal amount of the video signal input from the input terminal 1, and the γ correction circuit 7 performs γ processing to adapt it to the input/output characteristics of the cathode ray tube.
This is the purpose of the circuit shown in FIG. In order to ensure a dynamic range or perform accurate γ processing based on the optical black level, capacitors 2a, 2a, and 2a for direct current reproduction are installed before the automatic gain control circuit 4 and the γ correction circuit 7, respectively. 2b and a pulse clamp circuit 3a,
3b is provided.

The pulse clamp circuit 3a performs DC reproduction of the video signal using the first control pulse input from the control pulse input terminal 6 during the optical black level period of the video signal. The first control pulse input during the optical black level period of the video signal is applied to the pulse shaping circuit 5, and the second control pulse output from the pulse shaping circuit 5 performs DC reproduction of the video signal. . In addition, by changing the pulse widths of the first control pulse and the second control pulse, the timing of DC regeneration is changed in the pulse clamp circuits 3a and 3b, and the DC regeneration error that occurs in the pulse clamp circuit 3b is avoided. . The situation will be explained using the timing chart shown in FIG.

When the pulse clamp circuit 3a is operated with the first control pulse input from the control pulse input terminal 6 during the optical black level period of the video signal, the first control pulse (see (1) in FIG. 2) is activated. ) is added to the optical black level of the video signal and output from the pulse clamp circuit 3a (see (2) in FIG. 2). The automatic gain control circuit 4 adjusts the signal amount of the signal output from the pulse clamp circuit 3a, and further delays the signal.
A signal obtained by adding spike noise to the optical black level of the video signal is shown as (3) in FIG. 2.

By operating the pulse clamp circuit 3b with the second control pulse shown in (4) in Figure 2 for this signal, DC regeneration is possible without being affected by the superimposed spike noise. Note that the second control pulse causes spike-like noise to be output from the pulse clamp circuit 3b. As a result, the pulse clamp circuit 3b outputs the optical black level of the video signal plus the spike-like noise caused by the first control pulse and the spike-like noise caused by the second control pulse. .

Next, a specific example of the pulse shaping circuit 5 will be explained with reference to FIGS. 3 and 4. In FIG. 3, 8 is an input terminal, 9 is a low-pass filter, and 10 is an AND circuit. Figure 4 shows
FIG. 8 is a timing chart diagram showing the waveform of the first control pulse applied to the input terminal 8; In the same figure, the control pulses of 9 jgl applied to the input terminal 8 are shown in (]).
The high frequency components of this first control pulse are attenuated by the low-pass filter 9, resulting in a waveform shown in (2). By logically ANDing the waveform shown in (2) and the first control pulse shown in (1) using the AND circuit 10, it is possible to generate the second control pulse with a different duty shown in (3). be.

As explained above, in the first embodiment of the present invention,
Accurate DC reproduction is possible, and a video signal with no optical black level fluctuation due to illuminance can be obtained.

Next, a second embodiment of the present invention will be described with reference to FIG. 5. In this embodiment, a pulse shaping circuit and a pair of pulse clamping circuits are provided in the same integrated circuit.
This prevents inadvertent leakage of control pulses due to wiring.

11 is an input terminal, 2c and 2d are capacitors, 3c is a pulse clamp circuit, 4 is an automatic gain control circuit, 12 is an A/D
converter.

13 is a γ correction circuit, 14 is a comparator, 15 is a low pass filter (LPF) 6, and the parts inside the dotted line are provided within the same integrated circuit.

The video signal input from the input terminal 11 is transferred to the capacitor 2.
After DC regeneration is performed by the pulse clamp circuit 3c and the pulse clamp circuit 3c, the signal amount is adjusted by the automatic gain control circuit 4. After that, A/D
After converting into a digital signal with a converter, the γ correction circuit 13
In this embodiment, DC regeneration is performed using a feedback clamp method. That is, the comparator 14 outputs digital data DB of a predetermined optical black level and digital data D output from the A/D converter 12. Compare with 11.

The comparison is performed during the period in which the second control pulse input to the comparator 14 is H, and according to the comparison result, the comparator 14
outputs H or L.

That is, when DB>Dos, the comparator 14
When Da≦DoB, the comparator 14 outputs L (note that when D11=DOB, the output of the comparator 14 can be set to high impedance and not output from the comparator 14.) The output signal of this comparator 14 is passed through a low-pass filter 15 and fed back to the input section of the A/D converter [12].

As a result, when I)oB is lower, the A/D converter 1
The input voltage of 2 is raised and I) oe becomes D
When higher than B, the input voltage of the A/D converter 12 is lowered. As a result, it is possible to set the digital data to a constant value D9 according to the second control pulse input to the comparator 14. In this embodiment as well, the operation of the pulse shaping circuit 16 is the same as in the previous embodiment, and the explanation thereof will be omitted. In this embodiment, by configuring the pulse shaping circuit 16 in the same integrated circuit as the comparator 14, the second control pulse generated by the pulse shaping circuit 16 can be inadvertently connected to the input section of the pulse clamp circuit J13c, etc. Prevent leakage.

This suppresses errors caused by clamping. the result,
Fluctuations in optical black level due to changes in illuminance can be eliminated.

Note that the pulse shaping circuit 16 has a control pulse input terminal 17.
An example was shown in which a second control pulse with a different phase and duty is generated based on the first control pulse input to the
It is obvious that the second control pulse may be generated in the integrated circuit by another reference pulse in order to avoid noise spikes. Also, for the same reason, as shown in FIG.

In the first embodiment of the present invention, the spike noise (see (1) in FIG. 6) superimposed on the optical black level of the video signal output from the automatic gain control circuit 4 is corrected. The second control pulse may be provided before the spike-like noise (see (2) in Figure 6), or the second control pulse may be provided after the negative spike-like noise among the spike-like noises. (Please refer to (3) in Figure 6.)
, the second control pulse may be provided to include spike-like noise (see (4) in FIG. 6).

[Effects of the Invention] The present invention provides a video camera equipped with a plurality of pulse clamp circuits that regenerate the optical black level period of a video signal output from an image sensor using direct current. Since DC reproduction is performed by operating the pulse clamp circuit at different timings to avoid the influence of spike-like noise superimposed on the optical black level of the signal, errors due to fluctuations in the optical black level of the video signal are avoided. It has the effect of preventing

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention;
3 is a block diagram of the pulse shaping circuit, FIG. 4 is a timing chart diagram of the pulse shaping circuit, and FIG. 5 is a timing chart diagram for explaining the first embodiment of the present invention. FIG. 6 is another timing chart for explaining the first embodiment of the present invention. 2a, 2b... Capacitor, 3a, 3b...
...Pulse clamp circuit, 4...Automatic IH
IJ control circuit, 5... Pulse shaping circuit, 9, 15
...Low pass filter, 1o...AND circuit, 12...A/D converter, 13...
...γ correction circuit, 14... comparator. Figure 1 Figure 12 Figure 3 O Figure 4 Figure 5 Figure 6

Claims (1)

[Scope of Claims] 1. In a video camera provided with a plurality of pulse clamp circuits for direct current reproduction of the optical black level period of a video signal output from an image sensor, each of the pulse clamp circuits is operated at a different timing. A video camera characterized by: 2. In a video camera equipped with a plurality of pulse clamp circuits that regenerate the period of the optical black level of the video signal output from the image sensor using direct current, the optical black level of the video signal output from the previous stage pulse clamp circuit is A video camera characterized in that each of the pulse clamp circuits is operated at different timings to avoid the influence of superimposed spike-like noise. 3. In the video camera according to claim 1, a pulse shaping circuit generates a control pulse for the pulse clamp circuit that performs second and subsequent DC regenerations based on a control pulse that operates the pulse clamp circuit that performs the first DC regeneration. A video camera characterized by being provided with. 4. The video camera according to claim 3, wherein the pulse shaping circuit is paired with a pulse clamping circuit to be operated, and each of the pulse shaping circuits is provided in the same integrated circuit.