JPS63215173A - Signal processing device for video camera - Google Patents

Abstract

PURPOSE:To obtain a video camera capable of responding to a large difference in an incident light quantity, by assembling an amplifier in which a gain can be switched in an automatic gain control and automatic iris control loop. CONSTITUTION:The titled device is constituted in such a way that the amplifier 13 is provided at the rear stage of an automatic gain control circuit 12, and the gain of the automatic gain control circuit 12 and the aperture angle of the iris of an optical lens is controlled so as to always keep the output of the amplifier 13 constant. The amplifier 13 is the amplifier capable of switching the gain, and the connection/disconnection of switching is controlled by a switch 8, and the gain control signal of the switch 8 is not added on the amplifier 13 until the maximum gain of the automatic gain control circuit 12 can be obtained at a prohibition circuit 16. As a result, since the amplifier 13 is operated as the amplifier of 0dB until illuminace goes to a low illuminance where the maximum gain of the automatic gain control circuit 12 can be obtained, an operating point is not changed at a bright place, therefore, no problem such as deterioration in an S/N with ordinary illuminance or white clipping is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to signal processing for a video camera, and particularly to a signal processing device for a video camera suitable for photographing under low illumination.

[Conventional technology]

Unlike broadcast cameras, it is rare for home video cameras to be able to take pictures under good lighting conditions. So, in a dark place,
For example, there is an increasing demand for images to be sufficiently enjoyable even when photographing under illuminance of about 10 to 100 Lux. In particular, image tube type video cameras have high sensitivity, so even when used in the dark place mentioned above, the S/N ratio is still high.
has a % characteristic that does not deteriorate that much.

FIG. 2 shows a signal processing circuit of a frequency separation type video camera for low-light photography, which is used in a conventional video camera.

This operation will be explained below with reference to FIG.

First, the preamplifier 1 amplifies the signal current obtained from the image pickup tube (not shown) to a level appropriate for signal processing, and filters it through a low-pass filter (hereinafter referred to as LPF') to obtain the wideband luminance signal YH.
(abbreviated as )3. The color signal is processed by a color separation filter installed on the photoelectric conversion surface of the image pickup tube, which converts the input optical image into a high frequency (
For example, since the signal is sampled at a spatial frequency of 4.3 MHz), by using a one horizontal scanning period (1H) delay line, the red (CR) signal and the blue (CB) signal can be obtained separately.

The output signal of BPF 3 is applied to the color separation circuit described above and R
Separate the signal and B signal. These R and B signals are combined with a narrowband luminance signal Y output from the LPF 5 to which the output of the preamplifier 1 is applied, and a color difference signal (R-yL
), CB-Yr) signal. This color difference signal (R-YL
), (E-YL) are added to the balanced modulation circuit 7 to modulate 3, 58 &#z subcarriers having a phase difference of 90° from each other, and add them at a predetermined mixing ratio to obtain a carrier suppressed color signal. This carrier suppressed color signal is applied to an amplifier 9 whose gain is controlled by a switch 8. On the other hand, the broadband luminance signal Y is applied to an amplifier 10 whose gain is controlled by the switch 8, and added to the carrier suppressed color signal outputted from the amplifier 9 by an adder 11 to form an NTSC composite signal. The switch 8
When turned on when there is darkness, amplifiers 9 and 10 operate to increase the gain, giving the required gain, respectively,
You can get clear images even in dark places.

In addition, as related to such technology, the
No. 9-46159 is mentioned.

[Problem that the invention seeks to solve]

However, with the above configuration, if switch 8 is turned on when taking a picture of a bright place from a dark place, the white clip that clips the high-brightness part will work, and the bright part will be clipped. Information about the bright part will be lost. However, there is a problem in that it is not possible to obtain faithful images.

SUMMARY OF THE INVENTION An object of the present invention is to provide a signal processing device for a video camera in which bright areas are not clipped even when a bright area is photographed while the video camera is set in a state suitable for photographing a dark area.

[Means for solving problems]

The problem with the conventional method is that it focuses only on dark areas.

This occurs because the idea is to increase the gain of the amplifier only in that case. Therefore, the above problem can be solved by creating a configuration that not only increases the gain of the amplifier but also controls the gain to vary according to the amount of incident light so that it can be used in both bright and dark places.

[Effect]

An amplifier is provided after the automatic gain control circuit, and the gain of the automatic gain control circuit and the aperture angle of the iris of the optical lens are controlled so that the output of the amplifier is always constant. The amplifier is a gain-switchable amplifier whose connection/disconnection is controlled by a switch, and the gain control signal of the switch is not applied to the amplifier by an inhibit circuit until the gain of the automatic gain control circuit is maximized. As a result, the amplifier operates as an OdJ amplifier until the illuminance reaches a low level where the gain of the automatic gain control circuit is maximized, so the operating point in a bright place does not change, so there is no S/N deterioration at normal illuminance. Problems such as white clips do not occur.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. First, the preamplifier 1 amplifies the signal current obtained from the image pickup tube to a level suitable for signal processing. Thereafter, in addition to the automatic gain control (hereinafter abbreviated as AGC) circuit 12, the signal is applied to an amplifier 13 having a gain of about 6 dB. The output of the amplifier 13 is applied to the AGC circuit 12 and the iris control circuit 14, and the gain of the AGC circuit 12 and the iris (not shown) of the optical lens in front of the image pickup tube are applied so that the output of the amplifier 16 is always constant. The aperture angle of the iris control circuit 14
Control with.

Also, the output of the amplifier 16 is tpp2 as in the example of FIG.
．． Bpps and Bpps are applied to obtain a wideband luminance signal Y, a narrowband luminance 4M signal YL, and a carrier signal, respectively. Add the carrier signal to the color separation circuit 4 to obtain the R signal and B signal. (R-YL) and (BYt) are balanced-modulated by the encoder 15 and added to the wideband luminance signal YH to form an NTSCa signal.

Furthermore, the amplifier 16 is a gain-switchable amplifier, and when the switch 8 is turned on, it becomes an AGC circuit with a gain control range of 6 dB, and when the switch 8 is turned off, the gain is OdB. The control signal is controlled by the AGC signal 17, which is the gain control signal of the AGC circuit 12, so that the gain of the AGC circuit 12 is not applied to the amplifier 13 until the gain or ti of the AGC circuit 12 reaches the maximum. Since the amplifier 13 operates only as a 0 dlJ amplifier until the illuminance reaches a low level where the gain becomes MAX, the operating point in a bright place remains the same, so an image with the same S/N as before can be obtained at normal illuminance. Further, the gain control of the amplifier 13 is controlled by the gain of the AGC circuit 12 or MAX.
It is controlled by the AGC signal 17 to operate after detecting that the

As described above, according to this embodiment, when the switch 8 is turned on when photographing a dark place, a bright image can be obtained by the gain of the amplifier 15. Also, even if you take a picture of a bright place,
Since the AGC circuit and the auto-iris adjustment circuit operate in accordance with the output of the amplifier 13 so as to always maintain a predetermined level, it is possible to avoid the conventional problem of clipping of the brightness level. Furthermore, since the inhibition circuit 16 operates after the AGC circuit 12 reaches its maximum gain, the change in output level is also very small, and natural response characteristics can be obtained.

〔Effect of the invention〕

According to the present invention, by incorporating a gain-switched amplifier into the AGC and auto-iris control loops,
This has the effect of providing a video camera with a high dynamic range that can cope with the difference in the amount of incident 'yc more than ever before.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing an embodiment of the present invention, 2g2
The figure is a block diagram showing an example of a signal processing circuit of a conventional low-light video camera.

Claims (1)

[Claims] 1. In the signal processing device of a video camera, at the stage after the automatic gain control circuit that processes the signal obtained from the imaging means,
A gain control circuit having a predetermined gain and capable of switching the gain is arranged, and the gain control circuit is controlled to be switched by detecting that the gain of the automatic gain control circuit has reached a maximum. A signal processing device for a video camera, characterized in that the automatic gain control circuit and the automatic iris control circuit are controlled according to the magnitude of the output signal of the gain control circuit.