JPH0156590B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video camera that handles video signals having flicker components. Conventionally, when a video camera is used to take pictures under, for example, fluorescent lamp illumination, flicker occurs due to changes in the amount of light from the fluorescent lamp and beats between the field frequencies of the television.

Below, we will explain the fritzker generation mechanism and some analysis regarding it. The intensity of light from a fluorescent lamp turned on by a commercial power source with a frequency of 50 Hz is modulated at 100 Hz. Therefore, when operating a television camera with a field frequency of 60Hz under fluorescent lighting, its video output will be modulated at 100Hz,
It has a 20Hz beat component.

Nowadays, when the image pickup section of a television camera consists of a conventional image pickup tube or a MOS type solid-state image sensor, photoelectrically converted charge is accumulated and read out repeatedly for each horizontal line, so it is illuminated with a fluorescent lamp. In this case, if you observe it on a monitor, if you focus on one point, it will appear to be blinking at 20Hz, and if you focus on the entire screen, you will see horizontal stripes flowing from top to bottom at a rate of 20 times per second. It looks like there is. In addition, if the imaging unit is a charge transfer device (CCD) that transfers the accumulated charge to the memory unit at once during the vertical retrace period, accumulation and reading are repeated for each field. When observed on a monitor, the entire screen appears to be blinking at 20Hz with the same phase. This kind of fritzing was not a problem in places that were lit with incandescent light bulbs, such as television studios, but in recent years, as home video cameras have become increasingly popular, it has become increasingly difficult to capture images under fluorescent lights. As opportunities have increased, countermeasures have been highlighted as a problem.

The characteristics of the light source with respect to fritska are that the light output is l
When expressed as (t), the percent fritz D of the following formula
Defined by

D=max{l(t)}-min{l(t)}/max{l(t
)}+min{l(t)}×100% (1) According to the optical output observation results of fluorescent lamps, the above change is close to that obtained by full-wave rectification of the power frequency component.
That is, the light output l(t) of the fluorescent lamp is expressed by the following equation, assuming that the power supply frequency is fp (50 Hz).

l(t)=lo {1+a|sin(2πfpt+Op)|} (2) a is a parameter representing the magnitude of flicker, and by substituting this into equation (1), the flicker D becomes the following equation.

D=a/2+a×100% (3) Each image sensor integrates the light from the fluorescent lamp for one field period Tf, and outputs a signal current proportional to this. Now, considering that no significant charge is accumulated in the charge transfer part of the vertical retrace period in one field period from nTf to (n+1)Tf, and assuming that the accumulation time is Te, the integral value of the light output of the fluorescent lamp is Fn is, Fn=∫ ^nTf+Te _oTf l(t)dt (4) Strictly speaking, you can integrate equation (2) by substituting equation (4) into equation (4), but for simplicity, in equation (2), Substituting only the fundamental wave component 2fp expanded into the Fourier series and finding an approximate value, Fn=A+Bsin (4πfp n・Tf+θp') (5) However, A=lo(1+2/πa)Te B=-2loa/3π ² fpsin2πfpTe ( From equation 5), it can be seen that the signal is modulated every three fields, that is, at 20Hz. Further, the flicker D' of the signal output is approximately given by the following equation.

D′=−2a sin(2πfpTe)/3πfp(π+2a)・Te (6) Looking at this, it can be seen that due to the integral effect of the image sensor, the flicker D given by equation (3) is suppressed to a large extent by about 14 %, but it shows that noticeable frizz occurs. What is shown in equation (6) is for the type where the signal is read out for each line, but
In the case of CCD elements, only discrete values are taken as shown in equation (5), so the amount of flicker is calculated from equation (6) as follows:
Furthermore, the value is about 15% to 25% smaller.

Since no special processing was performed on the video camera side to deal with this flickering phenomenon, flickering occurred on the television image, making it difficult to view.

In view of the above points, the present invention provides an improved video camera. The present invention detects only the flicker component from the video signal and converts this detection signal into
The present invention provides a video camera that attempts to reduce flicker in the video signal by adding it to the control terminal of the AGC circuit.

Another object of the present invention is to provide a bandpass filter 1 for passing flicker components of a video signal of a video camera caused by illumination conditions of a subject, a variable gain amplifier, and a filter for eliminating flicker components from an output signal of the variable gain amplifier. A bandpass filter 2 for passing, and the bandpass filter 1
and a video camera in which the variable gain amplifier is controlled by the output of the comparison circuit and the output of the comparison circuit.

FIG. 1 shows one embodiment of the present invention, in which 1 is an image pickup tube (or solid-state image sensor), 2 is a drive circuit for the image pickup tube 1, 3 is a preamplifier, and 4 is a low-pass filter for the video band. , 5 is a band filter that passes the flicker component, 6 is a comparison circuit that compares the flicker error component, 7 is a level setting circuit for the variable gain amplifier (hereinafter referred to as AGC circuit), and 8 is a level setting circuit for the video signal. AGC circuit controlled by the output of circuit 7, 9
is a 20Hz band filter, 10 is a return circuit, and 11 is a
The process encoder circuit that produces the MTSC signal is shown. 100 is a flicker reduction circuit,
It consists of the aforementioned band filter 5, comparison circuit 6, level setting circuit 7, AGC circuit 8, band filter 9, and feedback circuit 10.

The operation of the embodiment configured as described above will be explained.
An output signal 1α of the image pickup tube 1 driven by the drive circuit 2 is amplified by the preamplifier circuit 3, and a video signal 2a is obtained by the low-pass filter 4. Generally, the low-pass filter 4 is constructed of a filter that passes the entire band of the video signal. This video signal 2a includes a flicker component caused by the fluorescent lamp, and a flicker signal 3a can be obtained by using a filter 5 having a band characteristic of 20 Hz. Flicker signal 3 in comparison circuit 6
A and a flicker signal 4a obtained from the AGC circuit, a 20 Hz band filter 9, and a feedback circuit 10 are compared to detect a flicker error.

The output signal 5a of the comparison circuit 6 is sent to the level setting circuit 7.
The voltage 6a is converted into an appropriate voltage 6a and guided to the gain control terminal of the AGC circuit 8, forming a loop. Therefore, the AGC circuit 8 changes the gain of the video signal 2a in a direction that reduces flicker using the output voltage 6a of the level setting circuit.

AGC signal 7a is process encoder circuit 1
1 becomes the NTSC signal 8a.

With such a configuration example, even if the video signal contains flicker under fluorescent lamp illumination, the effect of not perceiving flicker on the television image can be obtained due to the function of the flicker reduction circuit.

Next, another embodiment according to the present invention is shown in FIG.
21 is an image pickup tube (or solid-state image sensor), 22 is a drive circuit for the image pickup tube 21, 23 is a preamplifier, 24 is a low-pass filter for the video band, 25 is a band filter that passes flicker components, and 26 is a variable gain amplifier. 27 is a variable gain amplifier that amplifies the output of the low-pass filter 24;
It is controlled by the output of the level setting circuit 26. 2
8 shows a process encoder circuit that generates the MTSC signal.

The operation of the embodiment configured as described above will be explained.
The output signal 21α of the image pickup tube 21 driven by the drive circuit 22 is amplified by the preamplifier circuit 23,
A video signal 22a is obtained by the low-pass filter 24. In general, this low-pass filter 24 is constructed of a filter that passes the entire band of the video signal.This video signal 22a contains a flicker component due to the fluorescent light, and is filtered by the filter 25 with a band characteristic of 20Hz.
A flicker signal 23a can be obtained.

The output signal 23a of the filter 25 is converted into a voltage 24a having the above-mentioned value by the level setting circuit 26.
It is guided to the gain control terminal of the AGC circuit 27. Therefore, the AGC circuit 27 changes the gain of the video signal 22a in a direction that reduces flicker using the output voltage 24a of the level setting circuit 26.

Next, another embodiment according to the present invention will be described. 1st
In the embodiment shown in FIGS. 2 and 2, the flicker detection signal is added to the flicker-containing video signal in reverse phase. Naturally, unlike this electrical processing method, a mechanical method applied to an aperture mechanism is also possible. Therefore, in the next embodiment, a flicker detection signal is applied to an auto iris (diaphragm mechanism) to reduce flicker. 31 is an image pickup tube (or solid-state image sensor), 32 is a drive circuit for the image pickup tube 31, 33 is a preamplifier, 34 is a video band low-pass filter, 35
is a bandpass filter that passes the flicker component, 36
37 is a variable gain amplifier that amplifies the video signal, and 38 is a process encoder that produces an NTSC signal. The operation of the embodiment configured as described above will be explained.

An output signal 31α of the image pickup tube 31 driven by the drive circuit 32 is amplified by the preamplifier circuit 33, and a video signal 32a is obtained by the low-pass filter 34. In general, this low-pass filter 34 is constructed of a filter that passes the entire band of the video signal. This video signal 32a includes a flicker component caused by the fluorescent lamp, and a flicker signal 33a can be obtained by using a filter 35 having a band characteristic of 20 Hz. The flicker detection signal 33a is amplified by the auto-iris drive circuit 36 and drives an auto-iris (not shown). Therefore, the AGC circuit 37 reduces flicker and amplifies the video signal 2a, and the process encoder 38 outputs the NTSC signal 34a.

As described above, according to the present invention, flicker can be reduced.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the invention, FIG. 2 is a block diagram of another embodiment of the invention, and FIG. 3 is a block diagram of another embodiment of the invention. 6... Comparison circuit, 8... Variable gain amplifier, 36
...Auto iris drive circuit.

Claims (1)

[Claims] 1. A video characterized by comprising: flicker detection means for detecting a flicker component contained in reflected light from a subject; and gain control means for controlling the gain of a video signal in response to the output of the flicker detection means. camera.