JP2547273B2 - Flicker removal circuit for imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention obtains a good image without flicker when a high speed electronic shutter is used in a video camera under an environment illuminated by a discharge lamp such as a fluorescent lamp or a mercury lamp. The present invention relates to a flicker removing circuit of an image pickup apparatus suitable for the above.

[Conventional technology]

FIG. 3 is a block diagram showing the operating principle of a known flicker removing circuit, which was announced in, for example, the December issue of NHK STRL, 1984. In the figure, 1 indicates the output voltage V _o with respect to the input voltage V _i . variable gain amplifier for varying the gain according to the level of the control voltage V _c, 2 denotes a control circuit for obtaining the control voltage V _c for controlling a gain of the variable gain amplifier 1.

Next, the operation will be described. It is well known that in an NTSC system television, a video signal is sampled every 60th of a second for conversion into an electric signal.

Unlike the image pickup tube, the solid-state image pickup device that has been widely used in television cameras in recent years generally has a short afterimage time, and can obtain an output voltage proportional to the amount of incident light for almost one field, that is, 1/60 second.

On the other hand, discharge lamp lighting such as fluorescent lamps, which are often used in homes, have a power supply frequency of 2% depending on the power supply frequency.
It emits light at twice the frequency.

That is, in FIG. 4, light is emitted with a light amount that changes with time as indicated by L (t). For example, in Japan, two types of power supply frequencies, 50Hz and 60Hz, are used as commercial power supplies, but a fluorescent lamp lit at a power supply frequency of 50Hz is 100H.
It is lit while repeatedly blinking at the frequency of z.

Since the solid-state image sensor of the television camera accumulates and averages the amount of light that changes during this time every 1/60 second, the video signal level output by the solid-state image sensor periodically fluctuates at 20 Hz, causing flicker. .

The conventional example of FIG. 3 is configured to correct the 20 Hz flicker due to the discharge lamp light source that is turned on by such a 50 Hz power source. Under the condition that the video signal input V _i is illuminated by a discharge lamp such as a fluorescent lamp lit at 50 Hz, the output becomes proportional to an average value of incident light that changes with time every 1/60 second. .

In FIG. 4, L ₁₀ , L ₂₀ , divided every 1 / 60th of a second,
The area of L ₃₀ ... is proportional to the amount of incident light for 1/60 second, and the video signal input V _i is also L ₁₀ , L ₂₀ , L ₃₀ ... for each field.
Fluctuates in proportion to the area of.

In the conventional example of FIG. 3, considering that the average value of the incident light amount repeats every three fields, as shown by (L ₁₁ = L ₁₀ ) in FIG. 4, the control circuit 2 is just inputting. The flicker component three fields before is obtained for the video signal input V _i that has been generated, and the output of the variable gain amplifier 1 is controlled so as to correct this, so that the discharge lamp light source that is turned on by the 50 Hz power supply is used. It has the effect of correcting 20Hz flicker.

[Problems to be Solved by the Invention]

Since the flicker removing circuit of the conventional image pickup device is configured as described above, for example, in the conventional example of FIG. 3, as compared with the case of a discharge lamp in which the power supply frequency is 50 Hz and the illumination light flickers at 100 Hz. Should be effective.

However, during the so-called high-speed electronic shutter operation in which the solid-state image sensor uses a video signal obtained by sampling every 1/60 second for a period shorter than 1/60 second, L _10a , L in FIG.
_20a, L _30a ... L ₁₀ ratio of the change in the video signal level indicated by the area of the fourth diagram of, L _20, L ₃₀ ... solid-state imaging device shown in area of 60
The flicker correction is sufficient unless the gain variable range of the variable gain amplifier 1 is set to be significantly larger than that during normal shutter operation, because it is larger than during normal shutter operation that uses a video signal obtained by averaging the light amount for one second. Cannot be obtained.

On the other hand, the gain variable range of the variable gain amplifier at the time of operating at the normal shutter speed may be small, but in order to obtain a sufficient flicker correction effect, it is necessary to precisely control within this gain variable range.

To satisfy these conditions, there is a problem that the apparatus becomes expensive, and it is difficult to obtain a sufficient flicker correction effect in both the normal shutter operation and the high-speed electronic shutter operation.

The present invention has been made to solve the above problems, and an object of the present invention is to obtain a flicker removing circuit of an image pickup apparatus capable of obtaining a sufficient flicker correction effect even during high-speed electronic shutter operation. .

[Means for solving the problem]

A flicker removing circuit of an image pickup apparatus according to the present invention controls a variable gain amplifying means for changing an output voltage of a video signal for each field according to a video signal level output from an image pickup element, and an output voltage of the video signal. A gain control means for switching the control voltage to be set in the gain variable amplification means, wherein the gain control means uses a normal electronic shutter based on a determination signal output from the image pickup device during operation of the high-speed electronic shutter. It is characterized in that the flicker component in the video signal is removed by setting the control voltage so that the variable gain range of the variable gain amplifying means becomes larger than that at the time of operating at speed.

[Work]

In the present invention, the control gain of the gain control circuit is switched so as to be different from that at the operation at the normal shutter speed by the high-speed electronic shutter determination signal output at the time of the high-speed electronic shutter operation, so that the imaging at the time of the high-speed electronic shutter operation is performed. An appropriate control gain is obtained to remove the flicker component in the video signal obtained from the element, and the flicker is removed during the high-speed electronic shutter operation.

〔Example〕

An embodiment of a flicker removing circuit of an image pickup apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the embodiment.

In FIG. 1, reference numeral 1 is a variable gain amplifier that changes the gain of the output voltage V _o with respect to the input voltage V _{i according} to the level of the control voltage V _c , and 3 is a high-speed electronic shutter determination signal S output during high-speed electronic shutter operation. , A gain control circuit having a function of switching the control gain and for obtaining a control voltage V _c for controlling the gain of the variable gain amplifier 1.

Next, the operation will be described. Also in the embodiment of FIG. 1, the basic operation of correcting the 20 Hz flicker by the discharge lamp light source turned on by the 50 Hz power source is the same as that of the conventional example of FIG.

In the embodiment of FIG. 1, the high-speed electronic shutter determination signal S is in the state of indicating the normal shutter during the operation at the normal shutter speed in which the image signal proportional to the average value of the incident light every 1/60 second is obtained. In this case, the same operation as in the conventional example is performed.

During high-speed electronic shutter operation, as shown in FIG.
A video signal proportional to the light quantity L _10a , L _20a , L _30a obtained by sampling the time change of the incident light in a period shorter than 1/60 second can be obtained, but it is clear by comparing FIG. 2 and FIG. such as, light quantity L _10a, L _20a, degree of L _30a ... change of light intensity L _10, L _20,
The rate of change is large because the period of averaging the light amount is short compared to the degree of change of L ₃₀ ... Therefore, the gain of the variable gain amplifier is higher during high-speed electronic shutter operation than during normal shutter speed operation. It is necessary to control the variable range largely.

In this embodiment, during such a high-speed electronic shutter operation, the control range of the control voltage V _c output from the gain control circuit 3 is made larger than that during the normal shutter speed operation by using the high-speed electronic shutter determination signal S. The gain variable range of the variable gain amplifier 1 is widened by setting the range.

That is, when the high-speed electronic shutter determination signal S indicates the high-speed electronic shutter operation, the gain control circuit 3 expands the gain control range of the variable gain amplifier 1, and the light amount shown in FIG.
It is possible to perform a sufficient flicker correction operation even for a video signal in which the light amount greatly changes for each field such as L _10a , L _20a , L _30a .

In the above embodiment, the method of realizing the gain control circuit 3 by an electric circuit has been described, but the control voltage V _c for controlling the variable gain amplifier 1 may be obtained by software.

Further, not only the 20 Hz flicker but also the 10 Hz flicker component can be configured to correct the flicker component 6 fields before, and the same effect as in the above embodiment can be obtained.

Further, by setting the control gain according to the speed of the electronic shutter, it is possible to remove the flicker component corresponding to a wide range of speeds of the electronic shutter, and the control system is configured so that the output of the gain variable amplifier 1 is controlled by the gain control circuit 3. A feedback control system for input may be used, and in this case also, the same effect as that of the above-described embodiment is exhibited.

〔The invention's effect〕

As described above, according to the present invention, the control voltage is set by the gain control circuit so that the gain variable range of the gain variable amplifier is increased by the high speed electronic shutter determination signal during the high speed electronic shutter operation. The flicker component can be removed not only when operating at the normal shutter speed but also when operating at a high-speed electronic shutter.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a flicker removing circuit of an image pickup apparatus according to an embodiment of the present invention, and FIG. 2 shows an image pickup apparatus when a discharge lamp is turned on at a power supply frequency of 50 Hz during high-speed electronic shutter operation. FIG. 3 is an explanatory diagram showing the relationship between the field period and the amount of emitted light, FIG. 3 is a block diagram showing the configuration of a flicker removing circuit of a conventional image pickup device, and FIG. 4 is a discharge lamp lit at a power supply frequency of 50 Hz during normal shutter operation. FIG. 3 is an explanatory diagram showing a relationship between a field period and the amount of emitted light of the image pickup apparatus in the case of being present. 1 ... Variable gain amplifier, 3 ... Gain control circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. A variable gain amplifying means for varying an output voltage of a video signal for each field according to a video signal level output from an image pickup device, and a control voltage for controlling an output voltage of the video signal by switching the control voltage. A gain control means for setting the gain variable amplification means, wherein the gain control means is based on a discrimination signal output when the image pickup device is operating a high-speed electronic shutter, A flicker removing circuit for an image pickup apparatus, characterized in that the flicker component in the video signal is removed by setting the control voltage so that a variable gain range in the variable gain amplifying means becomes large.