JPH0478273A - Flicker elimination circuit for image pickup device - Google Patents

Abstract

PURPOSE:To realize the sufficient effect of flicker correction even at high speed electronic shutter operation by providing a gain variable amplifier and a gain control circuit to the flicker elimination circuit. CONSTITUTION:A video signal proportional to luminous quantities L10a, L20a, L30a sampled for a period shorter than 1/60sec from a time change in an incident light at high speed electronic shutter operation is obtained and since the degree of a change in the luminous quantities L10a, L20a, L30a is large because a time averaging the luminous quantity is short. Thus, it is required to control largely a gain variable range of a gain variable amplifier more than that at a normal operation. A high speed electronic shutter discrimination signal S is used to set a control range of a control voltage VC outputted from a gain control circuit 3 to a range larger than that at the normal operation to increase the gain variable range of the gain variable amplifier 1 thereby attaining sufficient flicker correction even to the video signal whose luminous quantity is largely changed for each field.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention provides a video camera that uses a high-speed electronic shutter in an environment illuminated with a discharge lamp such as a fluorescent lamp or a mercury lamp.
The present invention relates to a flicker removal circuit for an imaging device suitable for obtaining a good flicker-free image.

[Conventional technology]

FIG. 3 is a block diagram showing the operating principle of a known flicker removal circuit published, for example, in the December 1980 issue of NHK Giken Monthly Report. In the figure, 1 is the output voltage ■ for the input voltage ■. 2 is a control circuit for determining a control voltage vc for controlling the gain of the variable gain amplifier 1;

Next, the operation will be explained. It is well known that in NTSC television, video signals are sampled every 1/60th of a second for one screen and converted into electrical signals.

Unlike image pickup tubes, solid-state image sensors, which have recently been widely used in TV cameras, generally have a short afterimage time and can provide an output voltage proportional to the amount of incident light over a field, that is, 1/60th of a second.

On the other hand, discharge lamp lighting such as fluorescent lamps, which are often used in general homes, emit light at a frequency twice the power supply frequency, depending on the power supply frequency.

That is, in FIG. 4, light is emitted with a light amount that changes over time as shown by L (t). For example, in Japan, two types of power supply frequencies are used as commercial power sources: 50Hz and 607, but a fluorescent lamp that is lit at a power frequency of 50Hz is lit at a frequency of 100Hz while repeatedly flickering over time. become.

The solid-state image sensor of a television camera accumulates and averages the amount of light that changes over time every 1/60th of a second, so the video signal level output from the solid-state image sensor fluctuates periodically over 20 lines, causing flicker. do.

The conventional example shown in FIG. 3 is configured to correct such 50) [20) fz flicker caused by the discharge lamp light source turned on by the z power supply. Video signal power ■8 is under the condition that the lighting is with a discharge lamp such as a fluorescent lamp turned on at 507.
The output is proportional to the average value of the temporally varying incident light every 1/60th of a second.

In Fig. 4, Ll·, separated every 1/60th of a second,
The areas of Lzo, L3゜... are proportional to the amount of incident light for 1/60th of a second, and the video signal input is also Ll for each field. +Lt. + L 3°... fluctuates in proportion to the area.

In the conventional example shown in FIG. 3, the control circuit 2 is designed based on the consideration that the average value of the incident light amount repeats the same value every three fields as shown by (L, I=L, .) in FIG. Part 3 for the video signal that is being input manually
Since the output of the variable gain amplifier 1 is controlled to obtain the pre-field pre-field power component and correct it, the 50 &
It has the effect of compensating for the 20 refres force caused by the discharge lamp light source lit by the power supply.

[Problem to be solved by the invention]

Since the flicker removal circuit of the conventional imaging device is configured as described above, for example, in the conventional example shown in FIG. It should be effective.

However, during a so-called high-speed electronic shutter operation in which the solid-state image sensor uses a video signal obtained by sampling every 1/60th of a second for a period shorter than 1/60th of a second, Ll
. @＋L! 6a+ L S. The ratio of change in video signal level indicated by the area of , . . . is Ll in FIG. .

Lzo, Lx. Since the area of the solid-state image sensor indicated by . Unless it is set significantly larger than the original value, a sufficient flicker correction effect cannot be obtained.

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

In order to satisfy both of these conditions, there are problems such as an expensive device, and it has been difficult to obtain a sufficient flicker correction effect both during normal shutter operation and during high-speed electronic shutter operation.

This invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain a flicker removal circuit for an imaging device that can obtain a sufficient flicker correction effect even during high-speed electronic shutter operation. .

Means for Solving CtJB] The flicker removal circuit of the imaging device according to the present invention includes a variable gain amplifier for adjusting the magnitude of the video signal obtained from the imaging device, a high-speed electronic shutter discrimination signal, and a high-speed electronic A gain circuit m11 is provided which has a function of switching the control gain to an appropriate value during shutter operation and outputs a control voltage for controlling the gain of the variable gain amplifier.

[Function] In this invention, the high-speed electronic shutter is operated by switching the control gain of the gain control circuit to be different from that when operating at the normal shutter speed, using the high-speed electronic shutter discrimination signal that is output during the high-speed electronic shutter operation. An appropriate control gain is obtained to remove flicker components in a video signal obtained from an image sensor during operation, and flicker is removed during high-speed electronic shutter operation.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a flicker removal circuit for an imaging device according to the present invention will be described below with reference to the drawings. The first part is a block diagram showing the configuration of one embodiment.

In this FIG. 1, 1 is the output voltage (■) with respect to the input voltage V. A variable gain amplifier 3 changes the gain of the variable gain amplifier L according to the level of the control voltage VC; Control m'rix pressure■. This is a gain control circuit that calculates

Next, the operation will be explained. In the embodiment shown in FIG. 1 as well, the basic operation for correcting the 20 Hz flicker caused by the discharge lamp light source lit by the 507 power source is the same as in the conventional example shown in FIG.

In the embodiment shown in FIG. 1, when operating at a normal shutter speed in which a video signal proportional to the average value of incident light every 1/60th of a second is obtained, the high-speed electronic shutter discrimination signal S is in a state indicating a normal shutter. In this case, the operation is exactly the same as in the conventional example.

During high-speed electronic shutter operation, as shown in FIG. 2, the light intensity is measured by sampling the temporal change in incident light over a period shorter than 1/60th of a second. 1L worker. 1. L. , but as is clear from a comparison of FIG. 2 and FIG. 4, the light amount L1°1. L! . 1. L. 1・
The degree of change in ... is the amount of light L1゜+LZ. + L 2
Since the period for averaging the light intensity is short compared to the degree of change in ゜..., the rate of change is large. Therefore, when operating the high-speed electronic shutter, the variable gain amplifier needs more power than when operating at the normal shutter speed. It is necessary to greatly control the gain variable range.

In this embodiment, during such high-speed electronic shutter operation, the high-speed electronic shutter discrimination signal S is used to control the control voltage vc output from the gain control circuit 3 to a wider range than when operating at the normal shutter speed. The gain variable range of the variable gain amplifier 1 is widened.

That is, when the high-speed electronic shutter discrimination signal S is in a state indicating high-speed electronic shutter operation, the 1M gain gate circuit 3 expands the gain control range of the variable gain amplifier 1, and the light amount L1 in FIG.
゜,,L2゜,,L,. It is possible to perform a sufficient flicker correction operation even for video signals in which the amount of light varies greatly from field to field, such as in the case of .

In the above embodiment, a method is shown in which the gain control circuit 3 is realized by an electric circuit, but a configuration may also be adopted in which the control voltage V for controlling the variable gain amplifier 1 is determined by software.

Furthermore, if the structure is configured to correct not only the 207 flicker but also the 10 Hz flicker component, the flicker component of 6 fields before can provide the same effect as in the above embodiment.

Furthermore, by setting the control gain according to the speed of the electronic shutter, it is possible to remove flicker components that correspond to a wide range of electronic shutter speeds. A feedback control system may be configured as an input, and in this case, the same effect as that of the above embodiment can be achieved.

〔Effect of the invention〕

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

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a flicker removal circuit of an imaging device according to an embodiment of the present invention, and FIG. 2 is a block diagram showing the imaging device when the discharge lamp is lit at a power frequency of 507 during high-speed electronic shutter operation. Fig. 3 is a block diagram showing the structure of a flicker removal circuit of a conventional image pickup device, and Fig. 4 is an explanatory diagram showing the relationship between the field period and the amount of light emitted. FIG. 7 is an explanatory diagram showing the relationship between the field cycle and the amount of emitted light of the imaging device when the image pickup device is turned on. 1... variable gain amplifier, 3... gain control circuit. In addition, the same symbols in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] A variable gain amplifier inputs a video signal obtained from an image sensor and controls the gain so as to remove flicker components in the video signal by varying it field by field using a control voltage; and a gain control circuit that sets the control voltage so that the variable gain range of the variable gain amplifier is wider when the shutter is operating than when operating at a normal electronic shutter speed.