JP2807255B2 - Flicker removal circuit of imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flicker removing device used for a video camera. INDUSTRIAL APPLICABILITY The present invention is effective in obtaining a good image without flicker in a video camera under an environment proven by a discharge lamp such as a fluorescent lamp or a mercury lamp.

[Conventional technology]

FIG. 3 is a block diagram showing the operation principle of a known flicker elimination circuit published in, for example, the NHK Technical Monthly Report, December 1984, in which (1) denotes an output with respect to an input voltage (Vi). A variable gain amplifier for changing the gain of the voltage (Vo) according to the level of the control voltage (Vc); (2) an arithmetic circuit for obtaining a control voltage (Vc) for controlling the gain of the variable gain amplifier (1); 3) a one-field integration circuit for integrating the video signal input (Vi) over one field period;
1) (42), (43) and (44) are delay circuits for delaying the output of the integration circuit (3) by one field time, respectively (5)
Is a correlation detection circuit that controls so as to stop the flicker correction operation when there is no correlation between the three field times.

Next, the operation will be described. It is well known that in NTSC television, a video signal is sampled every 1/60 second for one screen and converted into an electric signal.
A solid-state image sensor, which is widely used in television cameras recently, differs from an image pickup tube in general in that the image pickup time is short, and an output voltage proportional to the amount of incident light for approximately one field, that is, 1/60 second is obtained. On the other hand, discharge lamp lighting such as a fluorescent lamp, which is often used in general homes, emits light at a frequency twice the power supply frequency in accordance with the power supply frequency.
That is, light is emitted with a light amount that changes with time as shown in FIG. 2 (L). For example, in Japan, two types of commercial power sources, 50 Hz and 60 Hz, are used.A fluorescent lamp that is lit at a power frequency of 50 Hz must be lit at a frequency of 100 Hz while flickering over time. become. Since the solid-state imaging device of the television accumulates and averages the time-varying light amount every 1/60 second, the level of the video signal output from the solid-state imaging device periodically changes at 20 Hz, and flicker occurs.

The conventional example shown in FIG. 3 is configured to correct a 20 Hz flicker caused by a discharge lamp light source turned on by such a 50 Hz power supply. When the video signal input (Vi) is illuminated with a discharge lamp such as a fluorescent lamp lit at 50 Hz, the output is proportional to the average value of the time-varying incident light every 1/60 second. Become. FIG. 2 shows an example of this time change. Second
(L10), (L20), cut off every 1 / 60th of a second in the figure
The area of (L30) is proportional to the amount of incident light for 1/60 second, and the video signal input (Vi) is also
0), (L20), (L30)... In FIG. 3, a one-field integration circuit (3) integrates a video signal input (Vi) for each field, and (L10)
(L20), (L30) ... Obtain an output proportional to the area. Each of the delay circuits (41), (42), (43), and (44) delays the output of the one-field integration circuit (3) by one field period (1V period), so that (a), (b), (c), In (d), the output of the one-field integration circuit (3) is 1V, 2V,
The one delayed by 3V and 4V can be obtained. On the other hand, when the video signal input (Vi) is input to the variable gain amplifier (1), the one-field integration circuit (3) has obtained the integration result one field before that, and the delay circuit (41) (42)
Respectively hold the integration results two or three fields before the video signal input (Vi) input to the variable gain amplifier (1). Further, as shown in FIG. 2 (L11 = L10), considering that the average value of the incident light amount repeats the same value every three fields, the output (b) of the delay circuit (42) becomes the variable gain amplifier (1). ) Is proportional to the magnitude of the video signal input (Vi) that is being input.

Here, the video signal input (V
Since the value of i) is obtained as ((a + b + c) / 3), the flicker component (f) of the video signal input (Vi) input to the variable gain amplifier (1) is f = b− (a + b + c) / 3, and the video signal input (Vi) has a voltage value (1 + f) times the average value of the flicker component. Then, the arithmetic circuit (2) obtains the flicker component (f) and outputs a control voltage (Vc) to the variable gain amplifier (1) such that the gain (Ga) is Ga = 1 / (1 + f).

In the conventional example shown in FIG. 3, the flicker component (f) three fields before the video signal input (Vi) that has just been input is obtained in this way, and works to correct the flicker component (f). 20 with power supply lit discharge lamp light source
It has the effect of correcting Hz flicker.

Further, in this conventional example, the correlation detection circuit (5) is configured to prevent a malfunction due to a flicker component due to a change in a scene. The correlation detection circuit (5) obtains the output (a) of the delay circuit (41) and the output (d) of the delay circuit (44), and if this exceeds a certain value, the output of the variable gain amplifier (1) is determined. The gain (Ga) is set to 1 and the control voltage (Vc) is fixed so as not to perform the correction. With this configuration, (a = d) for a 20 Hz flicker caused by a discharge lamp light source lit with a 50 Hz power supply,
The flicker is corrected by controlling the gain (Ga) of the variable gain amplifier (1), and other changes in the video signal input (Vi) due to scene changes or the like result in (a ≠ d), which is incorrect correction. No signal is output.

FIG. 4 is a block diagram showing the operation principle of another conventional example disclosed in Japanese Patent Laid-Open Publication No. 57-99875. In FIG. 4, (47) is a delay circuit for delaying a video signal by one field. is there. In this embodiment, a video signal input (Vi) itself is converted to a video signal 1 by using a video signal 1 field delay circuit (47).
Since the configuration is such that the field delay occurs, the magnitude of the input signal of the variable gain amplifier (1) is proportional to the voltage value of the output of the one field integration circuit (3) without a time difference. Therefore, if the gain (Ga) of the variable gain amplifier (1) is selected so that Ga = 1 / (Vc) using the output (Vc) of the one-field integrating circuit (3) as a control voltage, the variable gain amplifier can be obtained. The output voltage (Vo) of (1) is kept constant. However, the configuration shown in FIG. 4 has a problem that a large-capacity memory circuit is required to actually constitute the video signal 1 field delay circuit (47).

[Problems to be solved by the invention]

Since the flicker removal circuit of the conventional image pickup apparatus is configured as described above, for example, in the conventional example shown in FIG. 3, it should be effective for a discharge lamp that has a power supply frequency of 50 Hz and flickers at 100 Hz. It is. However, in actual shooting, when the power supply frequency is 50 Hz, a phenomenon in which the brightness changes even with a cycle of 50 Hz under illumination such as a fluorescent lamp is observed. The blinking of 50Hz is caused by deterioration of fluorescent lamps, etc.
What happens due to the non-uniform efficiency of the cathode bipolar, or the subject to be photographed does not receive the same amount of light from the cathode bipolar such as a fluorescent lamp, in other words, if it is uneven,
When one cathode is illuminated with a bias, each cathode is caused to blink at 50 Hz.

This flicker of 50 Hz generates a 10 Hz flicker between the NTSC field frequency of 60 Hz. This 10Hz
The flicker component has a lower frequency than the above-mentioned 20 Hz flicker component, but has a low frequency, so that the visibility is high and the image is noticeable.

In addition, the conventional example shown in FIG. 4 is effective in that the 10 Hz flicker is also corrected to be exactly the same as the 20 Hz flicker, but requires a video signal 1 field delay circuit, so that sufficient image quality can be obtained. In order to obtain it, a large-capacity memory was required, and it was difficult to configure the device at low cost.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to obtain a flicker removal circuit of an imaging apparatus which can effectively correct 10 Hz flicker and can configure the apparatus at low cost. .

[Means for solving the problem]

A flicker elimination circuit of the imaging apparatus according to the present invention includes: an integrator that integrates a video signal obtained from an imaging element in units of a field period; a first delay unit that delays an output from the integrator for a first field period; First comparing means for comparing the output from the integrator with the output from the first delay means; first calculating means for calculating a control output for correcting a flicker component before a first field period; Delay means for delaying the output from the integrator for a second field period, second comparison means for comparing the output from the integrator with the output from the second delay means, flicker before the second field period A second calculating means for calculating a control output for correcting the component, an output from the first calculating means based on an output from the first comparing means and an output from the second comparing means; The output from the computing means or any selection means for selecting the output either, is obtained by including a gain variable amplifier for varying the gain for correcting based on an output of said selection means.

Further, the integrator integrates the video signal obtained from the image sensor over one field period, the first delay means delays the output from the integrator for three field periods, and the second delay means delays the output from the integrator. The output is delayed for six field periods.

[Action]

The flicker removal circuit of the imaging device according to the present invention includes:
When the selecting means has a correlation for each first field period, the output of the integrator of the video signal input from the first arithmetic means for correcting the flicker component of the output before the first field period is used to control the gain of the variable gain amplifier. Adjust the gain,
When there is a correlation every second field period, the gain of the variable gain amplifier is adjusted by the output from the second calculating means for correcting the flicker component of the output before the second field period of the video signal input integrator. Also, when there is no correlation between the first field period and the second field period, the correction is not performed.

Further, it works so as to correspond to six fields as the first field period and three fields as the second field period.

(Example of the invention)

An embodiment of the present invention will be described below with reference to the drawings. First
In the figure, (1) is a variable gain amplifier that changes the gain of the output voltage (Vo) with respect to the video signal input (Vi) according to the control voltage (Vc), and (3) is the average of the video signal input (Vi). A one-field integration circuit for integrating a video signal input (Vi) over one field period to obtain blood; (41) (42)
(43) (44) (45) (46), shall apply in the delay circuit, each to one field period delays the output (f0) of one field integrating circuit (3), (f ₀₎ is the video signal input (Vi) , Each output (a), (b), (c), (d), (e), and (f ₁ ) is 2, 2 with respect to the video signal input (Vi), respectively. Delayed by 3,4,5,6,7 field periods. (21) and (22) are addition means (21)
Is the sum of three fields (a), (b) and (f ₀ ), and (22) is the sum of six fields (a), (b), (c), (d), (e) and (f ₀ ). (23) and (24) are arithmetic means,
(23) calculates the flicker component (f ₃ ) three fields before the video signal input (Vi) from the ratio of (b) and the adding means (21) to f ₃ = b− as in the conventional example of FIG. calculated as _{(a + b + f 0)} / 3, (24) is, (e) and said adding means the ratio of the previous 6 fields of the video signal input (Vi) from (22) Furitsuka component (f ₆₎ to f ₆ = e + ( obtained as a + b + c + d + e + f 0) / 6. The operation means (23) and (24) each provide a gain (Ga) of the variable gain amplifier (1) for the variable gain amplifier (1).
Is output as a control voltage (Vc) such that Ga = 1 / (1 + f ₃ ) or Ga = 1 / (1 + f ₆ ). (51) (5
2) is comparison means for detecting a correlation with respect to the output time of the one-field integration circuit (3), (53) and (54) are switching means, and (51) is two signals (c) having a time difference of three field periods. ) and the difference between the (f _0), if certain level, switching the switching means (53), (52) the difference between the two signals in time difference 6 field periods (f ₀₎ and (f ₁₎ is constant If so, the switching means (54) is switched.

Next, the operation of the embodiment according to the present invention will be described.
In FIG. 1, the one-field integration circuit (3) is reset at the start of the field cycle of the television signal, and the video signal input (Vi) is over one field period, as in the conventional example of FIG. Is integrated. The output of the one-field integrator (3) is a delay circuit (41) (42) (43) (44)
(45) Since it is delayed by (46), each video signal input (V
With respect to i), the average value (f ₀ ) (a) (b) (c) of the size of each field of the video signal input (Vi) before 1, 2, 3, 4, 5, 6, and 7 fields (D) (e) (f ₁ ) is obtained.

Since (f ₀ ) and (f ₁ ) have the average value of the video signal input (Vi) delayed by 1 field and 7 fields, respectively, there is a following equation between these two signals: (7-1) / 60 = There is a time difference of 1/10 [second]. (F ₀ ) and (c) are similarly 1
Since the signal is delayed from the field by 4 fields, there is a time difference of (4-1) / 60 = 1/20 [sec] between the two signals.

If a flicker component that is repeated at a period of 10 Hz is superimposed on the video signal input (Vi), the video signal input (Vi) becomes the same every 1/10 [second] (f ₀ ).
There is no difference between and (f ₁ ).

Further, when a flicker component repeated at a cycle of 20 Hz is superimposed on the video signal input (Vi), the video signal input (Vi) becomes the same every 1/20 [second] (f There is no difference between ( ₀ ) and (c), and there is no difference between (f ₀ ) and (f ₁ ). If the difference between (f ₀ ) and (f ₁ ) is smaller than a certain value, the 6-field comparison (52) switches the control signal (CP ₆ ) to switch the switching circuit (54) to the upper side in FIG. Output, otherwise the switching circuit (5
4) outputs a fixed value. (F ₀ ) and (f ₁ ) only in the case of the change due to the flicker component repeated at a cycle of 20 Hz or the flicker component repeated at a cycle of 10 Hz in the time change superimposed on the video signal human power (Vi) Otherwise, the switching circuit (54)
Is 20 Hz because the control voltage (Vc) is fixed and the gain (Ga) of the variable gain amplifier (1) is fixed at (Ga = 1).
Or, when the gain changes due to a change in a signal other than flicker caused by illumination of a discharge lamp such as a fluorescent lamp which changes at a cycle of 10 Hz, a malfunction does not occur.

The difference between (f ₀ ) and (f ₁ ) is smaller than a certain value, and
If the difference between (f ₀ ) and (c) is smaller than a certain value, the 3-field comparison (51) outputs the control signal (CP ₃ ) so as to switch the switching circuit (53) to the upper side in FIG. Then, the output of the arithmetic circuit (23) is selected as the control circuit (Vc). Otherwise, the switching circuit (53) selects the output of the arithmetic circuit (24) as the control voltage (Vc). Video signal input (V
In the case where the time change superimposed on i) is only a change due to a flicker component repeated at a cycle of 20 Hz, (f ₀ )
Since the difference between (c) and (c) becomes smaller, the output of the arithmetic circuit (23) is selected. In this case, the difference between (f ₀ ) and (c) becomes large and the output of the arithmetic circuit (24) is selected.

Gain of the operational circuit (23) correcting the gain variable amplifier 3 field before Furitsuka component of the video signal input (Vi) (f ₃₎ is (1) a (Ga) and (Ga = 1 / (1 + f ₃₎₎ The control circuit (24) corrects the flicker component (f ₆ ) six fields before the video signal input (Vi) and corrects the gain (Ga) of the variable gain amplifier (1). To (Ga = 1 /
(1 + f ₆ )) to output the control voltage (Vc).
Therefore, when the video signal input (Vi) has a flicker component, and this flicker component changes at a cycle of 20 Hz, the variable gain amplifier (1) is immediately turned on by the output of the arithmetic circuit (23). Input video signal input (Vi)
The gain (Ga) is adjusted to (Ga = 1 / (1 + f ₃ )) so that flicker is corrected based on the flicker component (f ₃ ) of the video signal three fields before, which has the same size as that of. If the video signal input (Vi) has a flicker component and the flicker component includes a component that changes at a cycle of 10 Hz, the gain of the variable gain amplifier (1) is determined by the output of the arithmetic circuit (24).
The gain (Ga) is set to (Ga = 1) so that flicker is corrected based on the flicker component (f6) of the video signal six fields before, which is the same size as the video signal input (Vi) just input. Adjust to / (1+ (f6)).

As a result, in the flicker removing circuit of the image pickup apparatus according to this embodiment, when the flicker of the component that changes at 10 Hz is included in the video signal input (Vi), the video signal input (Vi) has a correlation every six fields. And operates to remove the flicker of the same size as the flicker component six fields before that, and only the flicker of the component that changes at 20 Hz without the flicker of the component that changes at 10 Hz in the video signal input (Vi) Is included, the video signal input (V
i) detects that there is a correlation every three fields, and operates to remove flicker of the same size as the flicker component three fields before the three fields. When flicker of the changing component is not included, 6 or 3 is applied to the video signal input (Vi).
Since there is no time correlation for each field, this is detected and an operation is performed so as not to perform a gain change for correction.

In this embodiment, as described above, when the flicker included in the video signal input (Vi) includes the 10 Hz component, when the flicker includes only the 20 Hz component, and when the flicker does not include the periodic flicker component, By dynamically switching the correction voltage,
Both a 10Hz flicker and a 20Hz flicker are eliminated as well, and a system that does not adversely affect the image quality is realized.

The addition circuits (21) and (22), the operation circuits (23) and (24), and the delay circuits (41), (42) and (43) surrounded by a dotted line in the above embodiment (FIG. 1). , (44), (45), (4
6) The three-field comparison circuit (51), the six-field comparison circuit (52), and the switching circuits (53) and (54) can be realized by an A / D converter, a microcomputer, and software. The configuration has an effect that the device can be configured at a lower cost at any time.

[Effects of the Invention] As described above, according to the present invention, the presence or absence of flicker in a video signal without using a large capacity image memory,
Since the video signal can be controlled according to the type of periodic flicker, it is possible to remove only an arbitrary flicker component without suffering image quality deterioration due to the image memory, and to remove the video signal other than the flicker component. Can be prevented from being erroneously corrected.

In addition, 10 Hz flicker and 20 Hz flicker caused by the discharge lamp light source in the video signal can be similarly removed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a flicker removing circuit of an image pickup apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram showing a change over time of the amount of light emitted from a discharge lamp such as a fluorescent lamp which is widely used in general homes. FIG. 3 is a schematic diagram showing the relationship between the field cycle of the imaging apparatus and the amount of emitted light when the power is turned on at a power supply frequency of 50 Hz. FIG. 3 is a block diagram showing a configuration example of a flicker removal circuit of a conventional imaging apparatus.
FIG. 4 is a block diagram showing a configuration of a flicker removing circuit of another conventional image pickup apparatus. In the figure, (1) is a variable gain amplifier for inputting a video signal (V
The gain (Ga) of the output voltage (Vo) with respect to i) is controlled by the control voltage (V
Vary according to c). (3) is a one-field integration circuit for integrating the video signal input (Vi) over one field period. (51), (52)
Reference numerals 53 and 54 denote switching circuits for switching the method of obtaining the control voltage (Vc) depending on the result of the comparison circuit. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (2)

(57) [Claims] An image signal obtained from an image sensor is input,
A flicker elimination circuit of an image pickup apparatus having a variable gain amplifier that changes and outputs a signal according to a control signal, comprising: an integrator that integrates a video signal obtained from an image sensor in units of a field period; and outputs an output from the integrator to a first field. First delay means for delaying a period, first comparing means for comparing the output from the integrator with the output from the first delay means, calculating a control output for correcting a flicker component before a first field period. A first calculating means, a second delay means for delaying an output from the integrator for a second field period, a second comparing means for comparing an output from the integrator with an output from the second delay means A second calculating means for calculating a control output for correcting a flicker component before a second field period; an output from the first comparing means and the second comparing means; Based on the output from the output from the first calculating means, second
A flicker elimination circuit for an image pickup apparatus, comprising: a selection unit that selects either an output from the calculation unit or an arbitrary output; and a variable gain amplifier that changes a gain to be corrected based on the output of the selection unit. . 2. An integrator integrates a video signal obtained from an image pickup device over one field period, a first delay means delays an output from the integrator for three field periods, and a second delay means integrates the integration. 2. The flicker elimination circuit according to claim 1, wherein an output from the detector is delayed for a period of six fields.