JPH0748820B2 - Flicker removal circuit for imaging device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a flicker removing apparatus used in a video camera. The present invention is effective in obtaining a good image without flicker in an environment illuminated by a discharge lamp such as a fluorescent lamp or a mercury lamp in a video camera.

[Conventional technology]

FIG. 7 is a block diagram showing the operation principle of a known flicker removal circuit, which was announced in December, 1984, NHK Technical Bulletin, for example. In the figure, (1) corresponds to the input voltage (Vi). A variable gain amplifier that changes the gain of the output voltage (Vo) according to the level of the control voltage (Vc); (2) an arithmetic circuit that obtains a control voltage (Vc) that controls the gain of the variable gain amplifier (1); ) Is a 1-field integration circuit that integrates the video signal input (Vi) over a 1-field period, (41)
(42) (43) is a delay circuit for delaying the output of the integrating circuit (3) by one field time each, and (5) controls so as to stop the flicker correction operation when there is no correlation of three field times. It is a correlation detection circuit.

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 image pickup tubes, solid-state image pickup devices that are often used in television cameras are generally short in afterimage time.
An output voltage proportional to the amount of incident light for almost one field, that is, 1/60 second, can be obtained. On the other hand, discharge lamp lighting such as fluorescent lamps, which are often used in general households, emit light at a frequency twice the power supply frequency according to the power supply frequency. That is, the light is emitted with a light amount that changes with time as shown in FIG. 6 (L (t)). For example, in Japan, two types of power supply frequency are used, 50Hz and 60Hz.
Fluorescent lamps lit at the power supply frequency of 100Hz will be lit while blinking repeatedly at a frequency of 100Hz.
The solid-state image sensor of the television camera accumulates and averages the light amount that changes during this time every 1/60 second, so the video signal level output by the solid-state image sensor periodically fluctuates at 20 Hz,
Flicker occurs.

The conventional example shown in FIG. 7 is configured to correct the 20 Hz flicker due to the discharge lamp light source lit by such a 50 Hz power source. Under the condition that the video signal input (Vi) is illuminated by a discharge lamp such as a fluorescent lamp that is lit at 50 Hz, the output is proportional to the average value of the incident light that changes with time every 1/60 second. Become. FIG. 6 shows an example of this time change. In Figure 6, it was pinched every 1/60 second (L ₁₀ ), (L ₂₀ ),
The area of (L ₃₀ ) ... is proportional to the amount of incident light for 1/60 second, and the video signal input (Vi) is (L) for each field.
₁₀ ), (L ₂₀ ), (L ₃₀ ) ... fluctuates in proportion to the area. In FIG. 7, the 1-field integrating circuit (3) integrates the video signal input (Vi) for each field to obtain (L ₁₀ ),
Obtain an output proportional to the area of (L ₂₀ ), (L ₃₀ ) ... The delay circuits (41) (42) (43) (44) delay the output of the 1-field integration circuit (3) by 1 field time (1V period), so that (a), (b), (c), In (d), the output of the 1-field integration circuit (3) is 1V, 2V,
It is possible to obtain a delayed version of 3V or 4V. 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, and the delay circuit (41), (42)
Means that each holds the integration result 2 or 3 fields before the video signal input (Vi) input to the variable gain amplifier (1). Furthermore, in Fig. 6 (L ₁₁ = L ₁₀ ).
Considering that the average value of the incident light quantity repeats every 3 fields as shown in, the delay circuit (42)
(B) is proportional to the magnitude of the video signal input (Vi) that is just being input to the variable gain amplifier (1).

Here, the video signal input (Vi) that averages the flicker
Since the value of is obtained as ((a + b + c) / 3),
Variable gain amplifier flicker component (f _l) of the video signal is input to the (1) Input (Vi) _{is, f l = b- (a +} b + c) / 3 , and the video signal input (Vi) is the flicker component The voltage value is (1 + _fl ) times the averaged value. Therefore, the arithmetic circuit (2) is seeking the flicker component (f _l), the gain (Ga) against the variable gain amplifier (1) Ga = 1 / ( 1 + f l) that such control voltage (Vc) output To do.

In the conventional example shown in FIG. 7, the flicker component (f _l ) three fields before the video signal input (Vi) that is just being input is calculated in this manner, and the correction is performed. 20Hz with a discharge lamp light source lit by a 50Hz power supply
It has the effect of correcting 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 scene change. The correlation detection circuit (5) finds the difference between the output (a) of the delay circuit (41) and the output (d) of the delay circuit (44) and when this exceeds a certain value, the gain variable amplifier (1) The gain (Ga) is set to 1 and the control voltage (Vc) is fixed so as not to perform correction. With such a configuration, for a 20Hz flicker caused by a discharge lamp light source turned on by a 50Hz power source, (a = d), and the gain (Ga) of the variable gain amplifier (1) is controlled, so that the flicker is reduced. When the video signal input (Vi) is corrected and otherwise changed due to a scene change or the like, (a ≠ d) is satisfied, so that an erroneous correction signal is not output.

FIG. 8 is a block diagram showing the operation principle of another conventional example shown in Japanese Patent Laid-Open No. 57-99875. In the figure, (47) is a delay circuit for delaying a video signal by one field. is there. In this embodiment, since the video signal input (Vi) itself is delayed by one field by using the video signal 1-field delay circuit (47), the magnitude of the input signal of the variable gain amplifier (1) is It is proportional to the output voltage value of the 1-field integration circuit (3) without any time difference. Therefore, if the gain (Ga) of the variable gain amplifier (1) is selected so that Ga = 1 / (Vc) by using the output (Vc) of the 1-field integration circuit (3) as a control voltage, the variable gain amplifier ( The output voltage (Vo) in 1) is kept constant. However, the configuration of FIG. 8 has a problem that a large capacity memory circuit is actually required to configure the video signal 1 field delay circuit (47).

[Problems to be Solved by the Invention]

Since the flicker removing circuit of the conventional image device is configured as described above, for example, in the conventional example of FIG. 7, it should be effective for a discharge lamp whose power supply frequency is 50 Hz and flickers at 100 Hz. Is. However, in actual photography, when the power supply frequency is 50 Hz, the phenomenon that the brightness fluctuates even in a cycle of 50 Hz with illumination such as a fluorescent lamp is observed. This 50 Hz blinking is caused by the deterioration of the efficiency of the cathode and cathode due to deterioration of the fluorescent lamp, and the subject to be shot does not receive the same amount of light from the cathode and cathode of the fluorescent lamp. , Unevenly, in other words,
This is caused by the fact that when one of the cathodes is biasedly illuminated, each cathode blinks at 50 Hz. This 50 Hz flicker causes a 10 Hz flicker with the NTSC field frequency of 60 Hz. The 10 Hz flicker component is smaller in degree than the 20 Hz flicker component described above, but has a problem that the visibility is high due to its low frequency and it is noticeable, and the image quality is remarkably deteriorated. To remove this 10 Hz flicker, it is easily inferred from the embodiment of the conventional flicker removing circuit that the conventional flicker removing circuit of the image pickup apparatus may be improved and a delay circuit may be provided for three fields. If the 10 Hz flicker is removed by such a method, the circuit scale becomes large and the apparatus becomes expensive. Also, the video signal input (Vi) is always controlled so that the value 6 fields before is constant. Since the gain is corrected by the voltage, the subject itself should be kept constant in the magnitude of the video signal input (Vi) one tenth of a second before and after the flicker of only 20Hz component and no periodic flicker. In some cases, a wrong correction voltage may be output when the value changes, causing a problem that the image quality is rather deteriorated.

Further, the conventional example of FIG. 8 is effective in that the 10 Hz flicker is corrected in exactly the same manner as the 20 Hz flicker, but since a video signal 1 field delay circuit is required, sufficient image quality is obtained. Therefore, a large-capacity memory is required, and it is difficult to configure the device at low cost.

The present invention has been made to solve the above problems, and an object thereof is to obtain a flicker removing circuit for an image pickup apparatus, which can effectively correct 10 Hz flicker and can inexpensively configure the apparatus. .

[Means for Solving the Problems]

The flicker removing circuit of the image pickup device according to the present invention obtains the average value (APL) of each field of the video signal output from the image pickup element, quantizes these average values, and from this data, a flicker component of 20 Hz, When the presence or absence of a 10Hz flicker component is detected, and when these flicker components are detected, the gain of the variable gain amplifier that amplifies the video signal is controlled so as to cancel each flicker component, and when no flicker component is detected. Is equipped with means for controlling the gain so as to keep it at a constant value.

[Action]

The flicker removing circuit of the image pickup device according to the present invention is 20 when the quantized data obtained by obtaining the average value of each field of the video signal has the time correlation for every three fields.
It is judged that it has a flicker component of Hz, and a control voltage that corrects the flicker component of the average value of the field three fields before the present is given to the variable gain amplifier to cancel the flicker component of 20 Hz, and the time correlation for every six fields is calculated. If so, it is judged that the flicker component of 10 Hz is present, and a control voltage for correcting the flicker component of the average value of the field 6 fields before the present is given to the variable gain amplifier to cancel the flicker component of 10 Hz and 3 fields and 6 When there is no time correlation for each field, the gain of the variable gain amplifier is controlled to be maintained at a constant value.

Example of Invention

An embodiment of the present invention will be described below with reference to the drawings. In Fig. 1, (1) is the output voltage (V) for the video signal input (Vi).
The variable gain amplifier which changes the gain of o) by the control voltage (Vc), (3) is reset at the beginning of the field period of the television signal, and the result of integrating the video signal input (Vi) over one field period (V _A ). (6) is an A / D converter for quantizing the output (V _A ) of the 1-field integration circuit (3), and (8) is for the A / D converter (6). Based on the output (V _A ) the control voltage (V
A microcomputer for calculating c), and (7) is a D / A converter for converting the control voltage output of the microcomputer into the control voltage of the variable gain amplifier (1).

Further, FIG. 2 is a flow chart showing the operation of the program of the microcomputer (8) in one embodiment of the present invention, and FIG. 3 is a detailed description of the portion shown as (Process 1) in the flow chart of FIG. 4 is a flowchart showing the operation, FIG. 4 is a flowchart showing the detailed operation of the portion shown as (Processing 2) in FIG. 2, and FIG. 5 is the detailed operation of the portion shown as (Processing 3) in FIG. It is a flow chart which shows operation.

Next, the operation of the embodiment according to the present invention will be described. In FIG. 1, the 1-field integrating circuit (3) is reset at the start point of the field cycle of the television signal and the video signal input (Vi) is integrated over the 1-field period as in the conventional example of FIG. The result (V _A ) is A / D converted by the A / D converter (6) and taken into the microcomputer (8).

The microcomputer (8) performs a calculation based on the time variation of the output (V _A ) of the A / D converter (6) and obtains and outputs the control voltage (Vc). The control voltage (Vc) is converted into an analog voltage by the D / A converter (7) and controls the variable gain amplifier (1).

The flow chart shown in FIG. 2 shows in more detail how the microcomputer (8) calculates the control voltage (Vc) from the input (V _A ) from the A / D converter (6). In the figure, (a), (b), (c),
(D), (e), (f ₀ ), and (f ₁ ) indicate the name of the register storing the data or the value of the data stored in the register. The entire loop is synchronized with the field cycle of the television signal by the V blanking synchronization processing (86), by a timer or external synchronization, or by the signal from the A / D converter (6). Will be executed once. In the shift process (82), (f ₁ ← e, e ← d, d ←
c, c ← b, b ← a, a ← f ₀ ) are assigned in this order,
In the input process (83), the quantized output (V _A ) of the one-field integration circuit (3) is substituted into (f ₀ ). The process (82) is executed once for each field, and in the first place the output (V _A ) of the 1-field integration circuit (3)
(F ₀ ) is an electronic version of the variable gain amplifier (1)
Since each video signal input (Vi) is delayed by one field period, each output (a)
(B), (c), (d), (e), and (f ₁ ) are delayed with respect to the video signal input (Vi) by 2,3,4,5,6,7 field periods, and finally, 1, Average value (f ₀ ) (a) (b) (c) (d) (e) of the field size of the video signal input (Vi) delayed by 2,3,4,5,6,7 field periods (F ₁ ) will be obtained. In the comparison branch processing (84), ((f ₁ ) −
(F ₀ )) and the constant (K ₁ ) are compared. (F ₁ ) and (f ₀ )
, Respectively, the average value of the video signal input (Vi) is delayed by 7 fields and 1 field. Therefore, between these two data signals, (7-1) / 60 = 1/10 [sec] There is a time difference. If the time-varying component of the video signal input (Vi) is only the flicker component that repeats at a 20Hz or 10Hz cycle that is superimposed on the video signal input (Vi), then (f ₁ ) and (f ₀ )
Are the same, and if there are relatively small time-varying components other than the flicker component that repeats at 20 Hz or 10 Hz periods, (f ₁ ) − (f ₀ ) <K ₁ holds, and The processing is moved to the branch processing (85). In cases other than these cases, that is, if the video signal input (Vi) includes time fluctuations other than the flicker component that repeats at a frequency of 20 Hz or 10 Hz to a certain degree or more, (f ₁ ) − (f ₀ ) ≧ K ₁ holds. , (Processing 1) is executed.

In Comparative branch processing (85), - comparing the ((c) (f ₀₎₎ and the constant (K _2). (C) and (f ₀ ) are obtained by delaying the average value of the video signal input (Vi) by 4 fields and 1 field, respectively. Therefore, between these two data signals, (4-1) / 60 There is a time difference of = 1/20 [seconds]. If only the flicker component that repeats at the 20Hz cycle in which the time-varying component of the video signal input (Vi) is superimposed on the video signal input (Vi) is repeated, since (c) and (f ₀ ) match, repeat at the 20Hz cycle. If the time-varying component other than the flicker component is present and is relatively small, (c)-(f ₀ ) <K ₂ is established and (Process 2) is executed. In cases other than these cases, that is, when (f ₁ ) − (f ₀ ) <K ₁ and (c) − (f ₀ ) ≧ K ₂ are satisfied, the time-varying component of the video signal input (Vi) has a frequency of 10 Hz. The repeating flicker component is included to some extent or more, and in this case, (Processing 3) is executed.

Next, the detailed contents of each of (Process 1), (Process 2), and (Process 3) will be described with reference to the flowcharts shown in FIG. 3, FIG. 4, and FIG. FIG. 3 is a flow chart showing the processing contents of the block shown in (Process 1) in FIG. In (Process 1), a process is performed in the case where the time signal other than the flicker component repeated at a cycle of 20 Hz or 10 Hz is included in the video signal input (Vi) to some extent or more. If this condition is satisfied, it is considered that there is a time variation in the video signal input (Vi) that occurs because the video itself being shot is changing for some reason. In this case, the video signal input (Vi) It is not rational to correct the time fluctuation of and to keep the value of the video signal input (Vi) constant. Therefore, in (Process 1), in the output process (811),
The control voltage (Vc = 1) that simply sets the gain (Ga) of the variable gain amplifier (1) to (Ga = 1) is simply substituted and output, and the processing ends. By carrying out such a processing, it is possible to prevent the adverse effect of causing unnecessary fluctuations of the video signal rather than being caused by the operation of the flicker removing circuit other than the 20Hz or 10Hz flicker caused by the discharge lamp.

FIG. 4 is a flow chart showing the processing contents of the block shown in (Processing 2) in FIG. In (Processing 2), 20Hz
The processing is performed when the video signal input (Vi) includes only the time variation due to the flicker component that repeats in a cycle.
If this condition is satisfied, the size of the video signal input (Vi) will be the same size every twentieth second, that is, every three fields, so the time variation of the video signal input (Vi) is corrected. In order to keep the input (Vi) value constant, the flicker component of the video signal three fields before, which is just as large as the video signal input (Vi) input to the variable gain amplifier (1) The gain may be adjusted so that the flicker is corrected based on (f _l3 ). The substitution process (812), 3 flicker component of the field before the video signal (f _l3), determined as in the conventional example of FIG. 3 as _{f l3 = b- (a + b} + f 0) / 3, the output processing (813) Then, the control voltage (Vc) Vc = 1 / (1 + _fl3 ) is output so that the gain (Ga) of the variable gain amplifier (1) is Ga = 1 / (1 + _fl3 ). By this processing, the 20Hz flicker that repeats the same size video signal (Vi) every 3 fields
It can be completely removed.

FIG. 5 is a flowchart showing the processing contents of the block shown in (Processing 3) in FIG. In (Process 3), 10Hz
Processing is performed when the video signal input (Vi) includes a time variation due to a flicker component that repeats in a cycle. If this condition is met, the size of the video signal input (Vi) is
Since it becomes the same size every tenth of a second, that is, every six fields, it is just now necessary to correct the time variation of the video signal input (Vi) and to process the value of the video signal input (Vi) to be constant. Adjust the gain so that the flicker is corrected based on the flicker component ( _fl6 ) of the video signal 6 fields before, which is the same size as the video signal input (Vi) input to the variable gain amplifier (1). do it. Substitution process (81
In 4), the flicker component (f _l6 ) of the video signal 6 fields before is obtained as f _l6 = e− (a + b + c + d + e + f ₀ ) / 6, and in the output processing (815), the gain (Ga) of the variable gain amplifier (1) is calculated. _Output the control voltage (Vc) Vc = 1 / (1 + _fl6 ) such that _Ga ) _becomes Ga = 1 / (1 + _fl6 ). According to this processing, the 10Hz flicker that repeats the video signal (Vi) of the same size every 6 fields is
It can be completely removed.

Since a series of processes for calculating and outputting these control voltages (Vc) are repeated for each field, the micro computer (8) in this embodiment has a component varying in 10 Hz in the video signal input (Vi). Flicker is included, it is detected that the video signal input (Vi) has a correlation for every 6 fields, and a control voltage (Vc) for removing the flicker having the same magnitude as the flicker component 6 fields before is detected. ) To output the video signal input (Vi)
If only the flicker of the component that fluctuates at 10 Hz is not included and the flicker of the component that fluctuates at 10 Hz is included, it is detected that the video signal input (Vi) has correlation for every three fields, and the flicker of the three fields before that is detected. It operates to output the control voltage (Vc) for removing the flicker of the same magnitude as the component, and when the time fluctuation of the video signal input (Vi) does not include the flicker of the component that fluctuates at 10Hz and 20Hz. Detects that the video signal input (Vi) has no time correlation for every 6 and 3 fields, and operates so as to output a control voltage (Vc) that does not change the gain for correction.

Further, in FIG. 1, a microcomputer (8)
The control voltage (Vc) output by the D / A converter (7)
A / A conversion is performed, and the flicker component is removed by controlling the gain (Ga) of the variable gain amplifier (1) to a predetermined value. As a result, in this embodiment, the flicker included in the video signal input (Vi) includes 10 Hz component, 20 Hz component only, and no periodic flicker component.
By switching the correction voltage dynamically, 10Hz flicker
20Hz flicker is also removed, and a system that does not adversely affect the image quality is realized.

In the above embodiment, the method of realizing the one-field integration circuit (3) by an electric circuit has been shown, but the video signal input (Vi) may be directly A / D converted and the result may be added as a digital signal. Also, the same effect can be obtained even if the addition is performed by software. Furthermore, in the above embodiment, the variable gain amplifier is configured to be controlled by the output of the D / A converter as the means for varying the gain (Ga), but the video signal input is input as the reference voltage of the D / A converter. With the above method, a variable gain amplifier may be configured and the same effect can be obtained.

〔The invention's effect〕

As described above, according to the present invention, the 10 Hz flicker and the 20 Hz flicker in the video signal are similarly removed, and the video signal is disturbed when the subject itself changes other than the periodic flicker by the discharge light source. Such an erroneous operation is prevented, and since the image frame memory or the like is not used, the image quality is not adversely affected, and the flicker removing circuit of the image pickup apparatus can be realized at low cost.

[Brief description of 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, FIG. 2 is a flow chart showing an operation of a program of a microcomputer in an embodiment of the present invention, and FIG. 2 is a flowchart showing the detailed operation of the part shown as (Process 1) in the flowchart of FIG. 2, FIG. 4 is a flowchart showing the detailed operation of the part shown as (Process 2) in FIG. 2, and FIG.
FIG. 6 is a flow chart showing the detailed operation of the portion shown as (Processing 3) in FIG. 2, and FIG. 6 is a time change of the light emission amount of discharge lamp illumination such as a fluorescent lamp which is often used in general households. FIG. 4 is a schematic diagram showing the relationship between the field period of the imaging device and the amount of emitted light when the light source is turned on at a power supply frequency of 50 Hz. FIG. 7 is a block diagram showing a configuration example of a flicker removal circuit of a conventional image pickup device, and FIG. 8 is a block diagram showing a configuration of a flicker removal circuit of another conventional image pickup device. In the figure, (1) is a variable gain amplifier, (3) is a one-field period integrator, (6) is an A / D converter, (7) is a D / A converter, and (8) is a microcomputer. In the drawings, the same reference numerals indicate parts having the same or corresponding functions.

Claims (1)

[Claims] 1. A variable gain amplifier for amplifying a video signal output from an image pickup device, means for obtaining an average value of the video signal for each field period, and quantization of these average values.
A / D converter, and detecting the presence or absence of 20Hz flicker component and 10Hz flicker component contained in the video signal from the output of this A / D converter, and when these flicker components are detected, these flicker components are detected. A flicker removing circuit for an image pickup device, comprising means for controlling the gain of the variable gain amplifier so as to cancel the component, and controlling the gain of the variable gain amplifier to maintain a constant value when these flicker components are not detected.