JPH06326933A - Image pickup device - Google Patents

Abstract

PURPOSE:To obtain an NTSC type image pickup device capable of preventing the generation of flicker even when EE-controlled image pickup is executed under the illumination of a fluorescent lamp in an area with 50Hz power supply frequency. CONSTITUTION:A microcomputer 30 finds out the average value VA of video signal levels of the 1st field in a repeated unit consisting of three continuous fields in a video signal outputted from an A/D converter 31 by comparing it with the level value VR of a previously set reference signal. An electronic shutter 55 is controlled so that the average value of a video signal level in a field following the three fields is the same as the value VA and the average values of video signal levels after one and two fields are the same based upon respective compared results with the value VA.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus, and more specifically, to NTSC (National Television SV).
ystem Committee) method, PAL (Phase Alternation by
The present invention relates to an image pickup apparatus such as a television camera adopting the Line) method or the SECAM (Sequentiel a Memoire) method.

[0002]

2. Description of the Related Art When shooting a movie or using a TV phone indoors, the shooting is often performed with fluorescent lighting. In this case, there is no problem in the area where the power supply frequency is 60 Hz for the NTSC camera, but in the area where the power supply frequency is 50 Hz, the vertical scanning frequency of the video camera is 60 Hz (N
Vertical scanning frequency in TSC system), so 20Hz
Flicker will occur.

This phenomenon will be described more specifically. The brightness of the fluorescent lamp by the 50 Hz power source changes in a cycle of 10 ms as shown in FIG. On the other hand, CCD (Charg
Since the vertical scanning frequency of the e-coupled device) video camera is 60 Hz, the CCD is used during the scanning period of 16.6 ms.
The photocharges accumulated in the photosensitive element of (1) become a video signal. Therefore, the video signal level changes depending on which phase of the power supply frequency of 50 Hz the scanning cycle starts. For example, the video signal level becomes maximum at the timing shown in FIG. 5 (A), and the video signal level becomes minimum at the timing shown in FIG. 5 (B).

FIG. 6 shows the correspondence between the brightness of the fluorescent lamp and the average value of the video signal level for each field period. As shown in the figure, since the average value of the video signal level changes in a 3-field cycle, flicker occurs.
The flicker is repeated every 50 ms, which is the least common multiple of 10 ms and 16.6 ms.
Hz (flicker cycle: 50 ms).

Therefore, various countermeasures against flicker have been conventionally proposed. For example, by using an electronic shutter or the like, the accumulation time of photocharges on the photosensitive element of the CCD is set to 10 ms (1/100 second), which is the same as the brightness cycle, and the start of the scanning cycle and the phase of the power supply frequency of 50 Hz are set. A flicker countermeasure is known in which the image signal has a constant level as shown in FIG.
(See JP-A-55-162671, etc.).

Besides, the flicker period is 50 ms.
There is known a flicker countermeasure that controls the gain of the amplifier of the signal processing unit by utilizing the fact that it is repeated every (3 fields).

The latter flicker countermeasure will be described in detail. In a general video camera, as shown in FIG. 8, an automatic gain control amplifier (hereinafter referred to as “AGC amplifier”) 4 is provided in the signal processing unit 5 so that the signal level becomes constant.
Is provided. Then, the output level of the resistor 1 and the AGC amplifier 4 in the capacitor 2 detects the average value, the AGC amplifier so by comparing the level V _R of the reference level V ₁ by the operational amplifier 6 becomes V ₁ = V _R Feedback is applied to the gain of 4. 3 is a CCD,
Reference numeral 7 is a capacitor.

On the other hand, FIG. 9 shows the structure of a video camera having a flicker countermeasure. As mentioned above, the flicker is repeated every three fields. Therefore, each field of the repeating unit composed of three consecutive fields of the video signal output from the CCD 8 is defined as a, b, and c, and A of each field is set.
The average values of the output levels of the GC amplifier 9 will be described as V _a , V _b , and V _c (FIG. 10).

The analog switch 11 is turned on only during the field a, and the voltage of the capacitor 15 becomes V _a . The analog switch 19 is also O only during the period of field a.
N, and the result of comparing the reference levels V _R and V _a is
Feedback is applied to the AGC amplifier 9 only during the period of the field a. That is, the result of the output level of the field a is fed back only during the period of the field a and is V
become _a = V _R.

Similarly, V _b = V _R and V _c = V _R ,
As a result, V _a = V _b = V _c and flicker is reduced. That is, the gain of the AGC amplifier 9 is switched in three field cycles so that V _a , V _b , and V _c become V _R , respectively. In FIG. 9, 8 is a CCD and 10 is
Is a signal processing unit, 12, 13, 20, and 21 are analog switches, and 15, 16, 17, 22, 23, and 24 are capacitors.

By the way, although the subject to be photographed may be dark or bright, since the dynamic range of the CCD is limited, the brightness on the CCD surface is generally fixed by adding an iris to the lens. Is configured as follows. However, since an iris-equipped lens is expensive, recently an EE (Electric Exposure) control video camera that automatically changes the accumulation time of photocharges in the CCD by changing the shutter speed using an electronic shutter is available. It is being used.

[0012]

The flicker does not occur when the shutter speed is 1/100 second, but if the shutter speed is further reduced, the ratio of the image signals becomes large in the EE-controlled video camera. Therefore, there is a problem that flicker cannot be eliminated.

For example, when the shutter speed is 1/1000 second, the ratio of the size of the video signal becomes large as shown in FIG. 10 (B).
Even if the gain of the C amplifier 9 (FIG. 9) is switched, if the control range of the gain is insufficient, flicker cannot be eliminated. Even if it is sufficient, the gain of each field greatly changes, so that there arises a problem that the S / N changes field by field or the black level changes field by field. As described above, a video camera with a mechanical iris can eliminate the flicker by the conventional measures, but an EE-controlled video camera cannot eliminate the flicker.

Although these problems are related to the flicker of the luminance signal, there is a problem that the flicker of 20 Hz similarly occurs for the color signal. In addition, the vertical scanning frequency is 50 Hz as in the PAL system and SECAM system.
There is also a problem that flicker of 10 Hz occurs when this video camera is used under fluorescent lamp illumination in an area where the power supply frequency is 60 Hz.

The flicker of the color signal will be described more specifically in the NTSC system. For example, in a general video camera in which the shutter speed is set to 1/60 seconds without adopting the EE control method, the white balance is controlled based on the empirical rule that the entire screen is achromatic. . As shown in FIG. 13, the signal from the CCD 61 is controlled by the AGC amplifier 62 so that the average output level becomes constant, and then is decomposed into red, blue, and green signal components by the signal processing circuit 63. NT based on this
When an SC signal is created and displayed on a monitor, the image becomes reddish or bluish depending on the color temperature of the lighting, and white balance cannot be achieved. Therefore, the average value of the output of the green signal is detected by the resistor 70 and the capacitor 71 and added to the positive inputs of the operational amplifiers 73 and 74, while the outputs of the red signal and the blue signal are output from the amplifiers 64 and 65 to the resistors 66 and 68 and the capacitor, respectively. The average value is detected by 67 and 69 and added to the negative inputs of the operational amplifiers 73 and 74. And
The outputs of the operational amplifiers 73 and 74 are applied to the gain control terminals of the amplifiers 64 and 65, and the average value level of the red signal and the blue signal is controlled to be the same as the average value of the green signal. As a result, in the image output from the encoder 72, the average of the entire screen is achromatic and white balance is achieved.

Thus, white balance can be achieved when the shutter speed is 1/60 seconds. However, the brightness of a fluorescent lamp changes in a cycle of 10 ms (Fig. 4).
At the same time, as shown in FIG. 14 (A), the color temperature also changes in a cycle of 10 ms. Therefore, when the shutter speed is high like in an EE-controlled video camera, the red and blue signal levels are large in each field. Changed, fig.
As shown in (B) and (C), flicker of a color signal of 20 Hz occurs. As a result, the color changes for each field, and the white balance cannot be achieved.

The present invention has been made in view of these points, and even if an image is taken under fluorescent lamp illumination in an area where the frequency of the power source is 50 Hz, flicker does not occur and the subject is bright. An object of the present invention is to provide an NTSC-type image pickup device capable of performing EE control without flicker.

Another object of the present invention is to provide an image pickup apparatus adopting a system in which the vertical scanning frequency is different from the frequency of the power source used for fluorescent lamp illumination, and the color signal of the color signal is generated under the fluorescent lamp illumination using the power source. An object of the present invention is to provide an imaging device that can perform EE control without flicker.

[0019]

In order to achieve the above object, the image pickup device according to the first aspect of the present invention receives light with a periodical change in brightness at a frequency of 50 Hz, accumulates photocharges and displays an image. In an image pickup apparatus having a vertical scanning frequency of 60 Hz, which is equipped with an electronic shutter that changes the accumulation time of the photocharges by changing the shutter speed for an image pickup element that outputs a signal, a video signal for each field period from the video signal. The detection means for obtaining the average value of the level and the average value of the video signal level in the predetermined field obtained by the detection means are based on the average value of the video signal level in the field three fields after the field. And a control means for controlling the electronic shutter so as to approach the value.

Further, an AGC amplifier for changing the average value of the video signal level by changing the gain is provided, and the average value of the video signal level in a predetermined field obtained by the detecting means is used for the field. The control means controls the AGC amplifier together with the electronic shutter so that the average value of the video signal levels in the fields three fields after the above approaches the reference value.

Further, the image pickup device according to the second aspect of the present invention is arranged such that an image pickup device which receives light having a frequency of 50 Hz and which has a periodic change in brightness, accumulates photocharges, and outputs a video signal to the image pickup device. The vertical scanning frequency is 6 with an electronic shutter that changes the charge accumulation time by changing the shutter speed.
In an image pickup device of 0 Hz, a detection means for obtaining an average value of a video signal level for each field period from the video signal, and a video signal in a first field of a repeating unit composed of three consecutive fields of the video signal Comparing means for comparing the average value of the levels with the level value of the preset reference signal, and comparing the average value of the video signal levels in the other fields with the average value of the video signal levels in the first field, and the comparing means. A control means for controlling the electronic shutter so that the average values of the video signal levels in all the fields in the repeating unit have the same magnitude based on the comparison result obtained by the means. It is characterized by

Further, an AGC amplifier for changing the average value of the video signal level by changing the gain is provided, and the video signals in all fields in the repeating unit are based on the comparison result obtained by the comparing means. The control means controls the AGC amplifier together with the electronic shutter so that the average values of the levels are the same.

Further, in the image pickup device according to the third aspect of the present invention, based on the video signal obtained under the illumination of the fluorescent lamp having the power supply frequency of 50 Hz, the average value of the luminance signal level for each field period is for all the fields. An image pickup apparatus of an EE control method which controls so as to be equal to each other and performs image pickup at a vertical scanning frequency of 60 Hz, and a first detection unit for obtaining an average value of a green signal level from the image signal for each field period, and the image. Second detection means for obtaining the average value of the signal levels of the color signals other than the green signal among the three primary color signals from the signal for each field period, and the green signal level obtained by the first detection means for a predetermined field Is compared with the average value of the color signal levels obtained by the second detection means, and the average value of Wherein the average value of the color signal level and a control means for controlling the amplifier gain so as to approach the mean value of the green signal level, the.

In the image pickup device according to the fourth aspect of the present invention, the average value of the luminance signal level for each field period is calculated for all fields based on the video signal obtained under the illumination of the fluorescent lamp with the power supply frequency of 60 Hz. An image pickup apparatus of an EE control system which controls so as to be equal to each other and picks up an image at a vertical scanning frequency of 50 Hz, comprising: first detection means for obtaining an average value of green signal levels from the video signal every one field period; Second detection means for obtaining the average value of the signal levels of the color signals other than the green signal among the three primary color signals from the signal for each field period, and the green signal level obtained by the first detection means for a predetermined field Is compared with the average value of the color signal levels obtained by the second detecting means, and the previous value in the field 5 fields after the field is compared. Wherein the average value of the color signal level and a control means for controlling the amplifier gain so as to approach the mean value of the green signal level, the.

[0025]

When the image is picked up by the image pickup device having the vertical scanning frequency of 60 Hz under the light having the periodical change of the brightness of the frequency of 50 Hz, the flicker of 3 field period occurs in the image. According to the configuration, with respect to the average value of the video signal level in the predetermined field obtained by the detecting means, the average value of the video signal level in the field three fields after the field approaches the reference value, Since the electronic shutter is controlled, 3 consecutive video signals
Between repeating units consisting of one field, the average value of the video signal level is fed back to the next repeating unit for each field, and the same magnitude is obtained not only between repeating units but also within any repeating unit. become. Moreover, since the electronic shutter is controlled as described above, the size ratio of the video signal does not increase even if the subject is bright.

Further, according to the second configuration, the average value of the video signal levels in the first field of the repeating unit is compared with the level value of the preset reference signal, and the video signals in the other fields are compared. Based on the comparison result obtained by comparing the average value of the level with the average value of the video signal level in the first field, all the average values of the video signal level in all the fields in the repeating unit are the same. Since the electronic shutter is controlled so as to have the same size, the same size is obtained not only in the repeating unit but also in any field between the repeating units. Moreover, since the electronic shutter is controlled as described above, the size ratio of the video signal does not increase even if the subject is bright.

In any of the above configurations, if the gain is changed by using the AGC amplifier together with the electronic shutter,
The average value of the video signal level in each field within the repeating unit and between the repeating units can be more surely made the same.

Since the green signal is similar to the luminance signal and is not related to the color temperature of illumination, eliminating the flicker of the luminance signal eliminates the flicker of the green signal. Therefore, the third
According to the configuration, when performing image pickup at a vertical scanning frequency of 60 Hz under fluorescent lamp illumination with a power supply frequency of 50 Hz, in a predetermined field of a color signal (that is, a red signal or a blue signal) other than the green signal among the three primary color signals. The amplifier gain of the red or blue signal is controlled so that the average value of the red or blue signal level in the field three fields after that field approaches the average value of the green signal level with respect to the average value of the color signal level of Therefore, the average value of the level of the red signal or the blue signal is field-backed to the next repeating unit between repeating units consisting of three consecutive fields, not only between repeating units but also within the repeating unit. Is the same in any of the fields. Moreover, since the amplifier gain is controlled as described above, the size ratio of the color signals does not increase even if the subject is bright.

Further, similar to the third configuration, according to the fourth configuration, when the vertical scanning frequency of 50 Hz is imaged under the fluorescent lamp illumination of the power source frequency of 60 Hz, the signals other than the green signal of the three primary color signals are used. The average value of the red or blue signal level in the field 5 fields after the average value of the color signal level in the predetermined field of the color signal (that is, the red signal or the blue signal) is the average of the green signal level. Since the amplifier gain of the red or blue signal is controlled so as to approach the value, the average value of the level of the red signal or the blue signal for each field is set as the next repeating unit among the repeating units consisting of five consecutive fields. It is field-backed and becomes the same not only between repeating units but also in any field within a repeating unit. Moreover, since the amplifier gain is controlled as described above, the size ratio of the color signals does not increase even if the subject is bright.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention having a characteristic of a flicker reduction system will be described below with reference to the drawings. Since the video camera of the embodiment according to the present invention adopts the NTSC system, the vertical scanning frequency is 60H as described above.
z. The light used for imaging is light from a fluorescent lamp that emits light with a power source having a frequency of 50 Hz, and is accompanied by a periodic change in brightness of 50 Hz.

FIG. 1 shows a block diagram of a schematic configuration of an embodiment according to the present invention. Note that each of the repeating units consisting of three consecutive fields of the signal output from the CCD 25 is A, B, and C (FIG. 2), and the average value of the output level of the CCD 25 in each field (1 A from the A / D converter 31 for each field period
(Corresponding to the average value of the D / D conversion outputs) will be described as V _A , V _B , and V _C.

The CCD 25 receives light from a fluorescent lamp (not shown), accumulates photocharges, and outputs a video signal. The electronic shutter 55 changes the accumulation time of the photocharge with respect to the CCD 25 by changing the shutter speed.
It is controlled by a microcomputer (hereinafter referred to as “microcomputer”) 30.

The output from the CCD 25 is A after the horizontal transfer clock is removed by the correlated double sampling circuit 26.
The signal passes through the GC amplifier 27 and the signal processing unit 28 and is output as a video signal. On the other hand, the correlation double sampling circuit 26
After passing through a low-pass filter consisting of a resistor 32 and a capacitor 33 having a time constant of about 1 ms,
It is input to the / D converter 31. The output from the A / D converter 31 is input to the microcomputer 30. The microcomputer 30
Each time the horizontal synchronizing signal HD is input from the timing generator 29, the A / D conversion result is fetched from the A / D converter 31 and integrated for one field period.

When one field is completed, the microcomputer 30
Is obtained by dividing the integrated result by the number of integrations to obtain the average value V _A of the output level of the CCD 25 in one field period.
In the case of field A, the microcomputer 30 compares V _A with the level value V _{R of the} reference signal. If V _A is larger than V _R by V _H or more, the shutter speed of field A of the next repeating unit is set. Make it faster If V _A is smaller than V _H ,
The shutter speed of the field A of the next repeating unit is decreased.

Thus, the first characteristic of this embodiment is that A /
With respect to the average value V _A of the video signal level in the field A obtained by D converter 31 and the like, so that the average value of the video signal level in the field A after 3 fields from the field A approaches V _R The electronic shutter 55 is controlled by the microcomputer 30.

By repeating this control, V _A becomes a level between V _R -V _H and V _R + V _H. Where V
The width _H is provided because the shutter speed cannot be changed continuously, and can only be changed in units of 1H (about 63 μs). In other words, without this width, the final shutter speed will cause hunting.

The above control is performed by the CCD 25 in the field A.
The feedback is applied to the shutter speed in the field A of the next repeating unit on the basis of the average value V _A of the output level of. Therefore, if feedback is similarly applied to the fields B and C, the fields A and
Since the average values of the output levels of the CCD 25 in B and C change so as to be the same, flicker can be eliminated.

However, in this embodiment, the target level is set to V _A instead of V _R for the fields B and C, and other control is performed in the same manner as the field A. The target level may be set to V _R for the fields B and C, but in this case, the maximum difference between V _A and V _B or V _C is 2 V _H. If the target level is V _A as described above, the difference between V _A and V _B or V _C can be suppressed within the maximum V _H.

As described above, the second characteristic of the present embodiment is that the average value V _A of the video signal level in the first field A of the repeating unit consisting of three consecutive fields of the video signal is preset. was compared to the level value V _R of the reference signal, the other field B, the average value V _B of the video signal level in C, and compared with the average value V _a and V _C, based on the comparison results obtained by this , The electronic shutter 55 so that the average values of the video signal levels in all the fields A, B and C in the repeating unit have the same magnitude.
Is controlled by the microcomputer 30.

As described above, changing the shutter speed
The flicker can be greatly improved by performing feedback in units of the fields A, B, and C. FIG. 2 shows that the average value of the video signal levels is controlled to be the same by changing the shutter speed as described above.

As described above, since the shutter speed cannot be changed continuously, there is a possibility that flicker of maximum level V _H remains between the fields. But,
Regarding this, as described in the conventional example, the operational amplifier 4
Since the control of the gain of the AGC amplifier 27 for each field using 0 or the like is also used, the average value of the video signal level in each field can be made the same. Therefore, it is possible to surely eliminate flicker.

The control operation of this embodiment will be described below with reference to the flow chart shown in FIG. First, the integration value ΣY of the video signal level and the number of integrations CT for each one field period are reset (# 10). Waiting for the horizontal synchronizing signal HD to be input (# 20), the process proceeds to step # 30. The A / D conversion output (that is, the video signal level for each one field period) Y from the A / D converter 31 is input (# 30). Next, Y is incremented by ΣY, and the integration count CT is incremented by +1.
Is incremented (# 40). Waiting for the vertical synchronizing signal VD to be input (# 50), the process proceeds to step # 60.
If VD is not input, the process returns to step # 20.

Whether or not it is the field A is determined (# 60). If it is the field A, the process proceeds to step # 70, and if it is not A, the process proceeds to step # 100. At step # 70, ΣY / CT which is the average value of the output level of the CCD 25 is set to V _A. Next, it is judged whether or not V _A > V _R + V _H (# 8
0), set so as to increase the shutter speed in V _A> V _R + V _H is long if field A after three fields (#
180), and returns to step # 10. V If _A ≦ V _R + V _H determines whether _{V A <V R -V H (} # 90), V A <V R -
If it is V _H , the shutter speed in field A after three fields is set to be slow (# 190), and the process returns to step # 10. If V _A ≧ V _R −V _H , V _A is at the target level, so the process returns to step # 10 to continue the control for the next field B.

In step # 100, it is determined whether or not it is the field B. If it is the field B, the process proceeds to step # 110, and if it is not B, the process proceeds to step # 140. In step # 110, ΣY / CT which is the average value of the output level of the CCD 25 is set to V _B. Next, it is determined whether or not V _B > V _A + V _H (# 120), and if V _B > V _A + V _H , the shutter speed in field B after three fields is set to be high ( # 180) and the process returns to step # 10.
If V _B ≦ V _A + V _H , it is determined whether V _B <V _A −V _H.
(# 130), set to a slower shutter speed in the field B after 3 fields if _{V B <V A -V H (} # 190), the flow returns to step # 10. V _B ≧ V _A −V
_{If H} , then V _B is at the desired level, so step #
Returning to 10, the control is continued for the next field C.

In step # 140, it is determined whether or not it is the field C. If it is the field C, the process proceeds to step # 150, and if it is not C, the process returns to step # 10. Step #
At 150, ΣY / CT which is the average value of the output level of the CCD 25 is set to V _C. Next, it is determined whether or not V _C > V _A + V _H (# 160), and if V _C > V _A + V _H , the shutter speed in field C after three fields is set to be high ( # 180) and the process returns to step # 10. V
_{If C} ≦ V _A + V _H , it is determined whether V _C <V _A −V _H (#
170), and if V _C <V _A −V _H , set the shutter speed in field C after 3 fields to be slow.
(# 190), the process returns to step # 10. If V _C ≧ V _A −V _H , since V _C is at the target level, step # 1
It returns to 0 and continues the control for the next field A.

Next, an embodiment having a feature in the color signal flicker reduction system will be described with reference to the drawings. Since the video camera of this embodiment also adopts the NTSC system, the vertical scanning frequency is 60 Hz as described above. The light used for imaging is light from a fluorescent lamp that emits light with a power source having a frequency of 50 Hz, and is accompanied by a periodic change in brightness of 50 Hz.

FIG. 11 shows a block diagram of this embodiment. C
The respective fields of the repeating unit composed of three consecutive fields of the signal output from the CD 81 are designated as F1, F2 and F3 as shown in FIG. Average value of red signal level in each field F1 to F3
(A / D from the A / D converter 90 for each field period)
The average value of the green signal levels of the respective fields F1 to F3 (corresponding to the average value of the D conversion output) is defined as R1, R2 and R3 (of the A / D conversion output from the A / D converter 89 for each one field period). Equivalent to the average value)
This will be described as B3.

The CCD 81 receives light from the fluorescent lamp, accumulates photocharges, and outputs a video signal. The electronic shutter 80 changes the accumulation time of the photocharge with respect to the CCD 81 by changing the shutter speed. When the subject becomes bright and the shutter speed becomes fast, flicker occurs in the luminance signal and the color signal in the above-described conventional example (FIG. 10), but in the present embodiment, the flicker in the luminance signal is Similar to 1), it is assumed that the electronic shutter 80 has disappeared by changing the shutter speed of the electronic shutter 80 and the gain of the AGC amplifier 83 in three field cycles.

That is, the measure against the flicker of the luminance signal is C
This is performed by utilizing the fact that the luminance signal level from the CD 81 (FIG. 11) has a 3-field cycle (FIG. 10 (B)). The average value of the brightness signal levels in each field period is detected, and the average value of the brightness signal levels in the predetermined field obtained is the average value of the brightness signal levels in the field three fields after this field. The electronic shutter speed and AGC amplifier gain are controlled so as to approach the reference value. This makes it possible to eliminate the flicker of the luminance signal (see FIG. 2).

The output from the CCD 81, after the horizontal transfer clock is removed by the correlated double sampling circuit 82,
After the signal level is adjusted to an appropriate level by the AGC amplifier 83,
The signal processing circuit 84 converts the signals into red, green and blue signals.

After passing through the amplifier 85, the red signal passes through a low-pass filter composed of a resistor 91 and a capacitor 92 having a time constant of about 1 ms, and then input to the A / D converter 90. The output from the A / D converter 90 is the microcomputer 1
00 is input. The microcomputer 100 receives the A / A signal every time the horizontal synchronizing signal HD from the timing generating unit 99 is input.
The result of D conversion is fetched from the A / D converter 90 and integrated for one field period.

On the other hand, the blue signal, after passing through the amplifier 86, passes through a low-pass filter consisting of a resistor 93 and a capacitor 94 having a time constant of about 1 ms, and thereafter, the A / D converter 8
9 is input. The output from the A / D converter 89 is input to the microcomputer 100. The microcomputer 100 fetches the result of A / D conversion from the A / D converter 89 every time the horizontal synchronizing signal HD from the timing generator 99 is input,
Integrate for one field period.

When one field is completed, the microcomputer 10
0 is divided by the number of times of integration, and the average value of the red signal level for each one field period and the average value of the blue signal level for each one field period are obtained. For example, in the case of the field F1, these average values are the average values R1 and B1, respectively.

On the other hand, the green signal is input to the A / D converter 88 after passing through a low pass filter composed of a resistor 95 and a capacitor 96 having a time constant of about 200 ms. A /
The output from the D converter 88 is input to the microcomputer 100, and the average value G of the green signal levels for each one field period is obtained.

The microcomputer 100 compares the average values R1 and B1 with the average value G, respectively, and when R1 and B1 are larger than G, the D / A converter in the field F1 of the next repeating unit. Amplifier 8 via 97, 98
Reduce the gain of 5,86. When the average values R1 and B1 are smaller than the average value G, the gains of the amplifiers 85 and 86 are increased via the D / A converters 97 and 98 in the field F1 of the next repeating unit. By repeating this control, the average values R1 and B1 are made equal to the average value G.

The above control is carried out by the red signal in the field F1,
Feedback is applied to the gains of the amplifiers 85 and 86 in the field F1 of the next repeating unit based on the average values R1 and B1 of the green signal. Therefore, if feedback is similarly applied to the fields F2 and F3, the average values of the red and blue signal levels in each of the fields F1, F2 and F3 are the same as the average value G of the green signal level, so that the red signal and the blue signal are the same. For all of the above, flicker can be eliminated in all fields. As a result, the video output from the encoder 87 is white-balanced in all fields.

As described above, in the present embodiment, FIG.
As can be seen from the relationship with (A), the electronic shutter 80 is set to E at a timing effective as a measure against flicker of the luminance signal.
When the E control is performed, the color temperature of the light of the fluorescent lamp (in other words, the color signal levels of the red signal and the blue signal obtained by processing the signal of the CCD 81) is equal to the period of three fields (see FIG. 14 (B) (C)) is used.

That is, the feature of this embodiment is that the average value of the green signal level is obtained from the video signal by the A / D converter 88 or the like every one field period, and the average value of the green signal level is obtained from the video signal by the A / D converters 89, 90 or the like. Of the three primary color signals, the average value of the signal levels of color signals other than the green signal (that is, the red signal, the blue signal) is obtained for each field period, and the obtained average value of the green signal level in the predetermined field, Compare the average signal level of the red or blue signal in that field, and adjust the amplifier gain so that the average value of the color signal level in the field three fields after that field approaches the average value of the green signal level. It is controlled by the microcomputer 100.

As described above, the control based on the green signal is that the green signal is close to the luminance signal and is not related to the color temperature of the illumination. Therefore, if the flicker of the luminance signal is eliminated, the green signal is controlled. This is because there is no flicker. By this control, the average value of the red signal or the blue signal is fielded back to the next repeating unit between repeating units consisting of three consecutive fields, and not only between repeating units but also within repeating units. Is the same in any of the fields. Moreover, since the gains of the amplifiers 85 and 86 are controlled as described above, the ratio of the color signals does not increase even if the subject is bright. Therefore, white balance can be achieved by eliminating the flicker of each color signal.

The control operation for the red signal of this embodiment will be described below with reference to the flow chart shown in FIG. First, the integrated value ΣR of the red signal level for each field period
And the number of integration CT is reset (S10). Wait for the horizontal synchronizing signal HD to be input (S20), and then step S30
Proceed to. The A / D conversion output (that is, the red signal level for each one field period) R from the A / D converter 90 is input (S30). Next, ΣR is incremented by R, and the number of integrations CT is incremented by +1 (S40). Waiting for the vertical synchronizing signal VD to be input (S50), the process proceeds to step S55. If VD is not input, step S20
Return to.

In step S55, the A / D conversion output (that is, the average value of the green signal level for each one field period) G from the A / D converter 88 is input. Then field F
Whether it is 1 or not is determined (S60). If it is the field F1, the process proceeds to step S70, and if it is not the field F1, the process proceeds to step S100. In step S70, ΣR / CT, which is the average value of the red signal, is set in R1. Next, R1> G
It is determined whether or not (S80), and if R1> G, the gain of the amplifier 85 in the field F1 after three fields is set to be small (S180), and the process returns to step S10. If R1 ≦ G, it is determined whether or not R1 <G (S9
0), if R1 <G, field F after 3 fields
Set to increase the gain of the amplifier 85 at 1
(S190), and returns to step S10. If R1 ≧ G, the gain of the amplifier 85 in field 1 after three fields is not changed, and the process returns to step S10 and the next field F
Control of 2 is continued.

In step S100, it is determined whether or not it is the field F2, and if it is the field F2, step S11.
0, and if it is not the field F2, step S140
Proceed to. In step S110, Σ which is the average value of the red signal
Set R / CT to R2. Next, it is determined whether or not R2> G (S120), and if R2> G, the gain of the amplifier 85 in the field F2 after three fields is set to be small (S180), and the process returns to step S10. . R2
If ≦ G, it is determined whether R2 <G (S130), and R2
If <G, set to increase the gain of the amplifier 85 in the field F2 after three fields (S19
0), and returns to step S10. If R2 ≧ G, the gain of the amplifier 85 in the field 1 after three fields is not changed and the process returns to step S10 to continue the control for the next field F3.

In step S140, it is determined whether or not it is the field F3, and if it is the field F3, step S15.
If the field F3 is not reached, the process returns to step S10. In step S150, ΣR, which is the average value of the red signal
Set / CT to R3. Next, it is determined whether or not R3> G (S160). If R3> G, the gain of the amplifier 85 in the field F3 after three fields is set to be small (S180), and the process returns to step S10. . R3 ≦
If G, it is determined whether R3 <G (S170) and R3 <
If it is G, it is set to increase the gain of the amplifier 85 in the field F3 after three fields (S190),
It returns to step S10. If R3 ≧ G, the gain of the amplifier 85 in the field 1 after three fields is not changed,
Returning to step S10, the control for the next field F3 is continued.

By controlling as described above, the average values R1 to R3 of the red signal levels in the fields F1 to F3.
Becomes the same as the average value G of the green signal level. As a result, it is possible to achieve white balance in all fields even when imaging is performed under fluorescent lamp illumination in an area where the power supply frequency is 50 Hz.

Although only the control operation for the red signal has been described here, the control operation is similarly performed for the blue signal. In that case, in the flowchart of FIG.
Control is performed by reading R as B, ΣR as ΣB, R1 as B1, R2 as B2, and R3 as B3. By controlling only one of the red signal and the blue signal, there is an effect of achieving white balance even if the flicker is eliminated only for that color signal, but it is possible to control both the red and blue color signals as described above. preferable.

In this embodiment, the countermeasure in the primary color signal processing (converting once into red, blue and green and then generating the NTSC signal) has been described. However, the color difference signal processing (the signal processing is performed with the color difference signal as it is). .), The same processing can be performed by controlling each field so that the average value of the color difference signals R-Y and B-Y becomes zero.

In each of the above embodiments, the NTSC signal
It is assumed that a video camera with a vertical scan frequency of 60 Hz is used under fluorescent lighting with a power supply frequency of 50 Hz. However, a video camera with a PAL signal or SECAM signal (vertical scan frequency of 50 Hz) is used with a power supply frequency of 60 Hz. When used under fluorescent lighting, flicker of 100 ms cycle (that is, 5 field cycle), which is the least common multiple of 20 ms and 8.3 ms, will occur.
Flicker countermeasures can be taken by setting all three fields in the countermeasure described for the C signal to five fields.

[0068]

As described above, according to the image pickup apparatus of the first aspect of the present invention, with respect to the average value of the video signal level in the predetermined field obtained by the detecting means, three fields after that field, Since the electronic shutter is controlled by the control means so that the average value of the video signal level in the field approaches the reference value, there is no difference in the average value of the video signal level in each field that causes flicker. As a result, the frequency of the power supply is 50Hz
It is possible to realize an imaging device in which flicker does not occur even when imaging is performed under fluorescent lamp illumination in the area.

According to the image pickup apparatus of the second invention,
The average value of the video signal level in the first field of the repeating unit of three consecutive fields of the video signal is compared with the preset level value of the reference signal by the comparison means, and the video signal in the other fields is compared. The average value of the video signal levels in the first field is compared with the average value of the video signal levels in the first field, and based on the obtained comparison result, the average value of the video signal levels in all the fields in the repeating unit has the same magnitude. The electronic shutter is controlled by the control means so that the difference in the average value of the image signal level in each field, which causes flicker, is eliminated, and as a result, in a region where the power supply frequency is 50 Hz. It is possible to realize an image pickup apparatus in which flicker does not occur even when image pickup is performed under the illumination of the fluorescent lamp.

In the case of performing EE control using an electronic shutter, in the conventional image pickup apparatus, when the subject is bright and the shutter speed is high, the ratio of the size of the video signal becomes large, which causes a large flicker. ,
Even in such a case, according to the first or second configuration, since the size ratio of the video signal can be suppressed to a small value by changing the shutter speed, EE control can be performed without flicker even if the subject is bright. Further, since it is not necessary to use a lens with an iris, there is an effect that cost can be reduced.

Further, in any of the above configurations, the flicker can be more surely prevented by using the AGC amplifier together with the electronic shutter to change the gain.

According to the image pickup apparatus of the third and fourth inventions,
In an image pickup device that employs a method in which the vertical scanning frequency is different from the frequency of a power supply used for fluorescent lamp illumination, an image pickup device that can perform EE control without flicker of color signals under fluorescent lamp illumination using the power supply is provided. Can be realized. That is, in the third configuration, when the EE-controlled NTSC image pickup device is photographed under fluorescent lamp illumination with a power supply frequency of 50 Hz, color signal flicker can be eliminated and white balance can be achieved in all fields. , 4th
With this configuration, when an EE-controlled PAL system or SECAM system imaging device is used to shoot under fluorescent lighting with a power supply frequency of 60 Hz, color signal flicker can be eliminated and white balance can be achieved in all fields.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a video camera in which an embodiment of the present invention is used.

FIG. 2 is a diagram showing a correspondence relationship between a cycle of brightness of a fluorescent lamp and an average value of CCD output for each field period in the embodiment of the present invention.

FIG. 3 is a flowchart showing a control operation in the embodiment of the present invention.

FIG. 4 is a diagram showing the relationship between the brightness of a fluorescent lamp and time when the power supply frequency is 50 Hz.

FIG. 5 is a diagram showing a scanning cycle when the video signal of the conventional example becomes maximum / minimum under illumination of a fluorescent lamp by a 50 Hz power supply.

FIG. 6 is a diagram showing a correspondence relationship between the brightness of a fluorescent lamp using a 50 Hz power supply and an average value of video signal levels for each field period in a conventional example.

FIG. 7 is a diagram showing a correspondence relationship between the brightness of a fluorescent lamp using a 50 Hz power supply and the average value of video signal levels for each field period in another conventional example in which the shutter speed is set to 1/100 second.

FIG. 8 is a block diagram showing a schematic configuration of a general video camera.

FIG. 9 is a diagram showing a configuration in which a countermeasure is taken by controlling a gain of an AGC amplifier in a general video camera.

FIG. 10 shows a shutter speed of 1/1 in the configuration of FIG.
The figure which shows the correspondence of the brightness | luminance of the fluorescent lamp by a 50 Hz power supply at the time of 000 second, and the average value of the video signal level for every 1 field period.

FIG. 11 is a block diagram of a video camera in which another embodiment of the present invention is used.

FIG. 12 is a flowchart showing a control operation in another embodiment of the present invention.

FIG. 13 is a block diagram showing white balance processing according to a conventional example.

FIG. 14 is a diagram showing a correspondence relationship between a color temperature of a fluorescent lamp using a 50 Hz power source and average values of red signal and blue signal levels for each field period.

[Explanation of symbols]

 25 CCD 26 Correlation Double Sampling Circuit 27 AGC Amplifier 28 Signal Processing Section 29 Timing Generation Section 30 Microcomputer (Microcomputer) 31 A / D Converter 32 Resistor 33 Capacitor 34, 35, 36 Analog Switch 37, 38, 39 Capacitor 40 Operational Amplifier 41 resistance 42, 43, 44 analog switch 45, 46, 47 capacitor 55 electronic shutter 80 electronic shutter 81 CCD 82 correlated double sampling circuit 83 AGC amplifier 84 signal processing circuit 85, 86 amplifier 87 encoder 88, 89, 90 A / D Converter 91,93,95 Resistor 92,94,96 Capacitor 97,98 D / A converter 99 Timing generator 100 Microcomputer

Claims (6)

[Claims] Claim: What is claimed is: 1. An image pickup device, which receives a light having a frequency of 50 Hz and which has a periodical change in brightness, accumulates photocharges and outputs a video signal. In an image pickup device having an electronic shutter with a vertical scanning frequency of 60 Hz, a detection unit for obtaining an average value of video signal levels for each field period from the video signal, and a predetermined field obtained by the detection unit. Control means for controlling the electronic shutter so that the average value of the video signal level in a field three fields after the field approaches the reference value with respect to the average value of the video signal level. Image pickup device. 2. An AGC amplifier for changing the average value of the video signal level by changing a gain is provided, and the average value of the video signal level in a predetermined field obtained by the detecting means is set, 2. The image pickup device according to claim 1, wherein the control unit controls the AGC amplifier together with the electronic shutter so that an average value of video signal levels in a field three fields after the field approaches a reference value. apparatus. 3. An image pickup device for accumulating photocharges and outputting a video signal by receiving light having a frequency of 50 Hz with periodic brightness changes, and changing the accumulation time of the photocharges by changing the shutter speed. In an image pickup apparatus having a vertical scanning frequency of 60 Hz equipped with an electronic shutter, the detection means for obtaining the average value of the video signal level for each field period from the video signal, and the repetition comprising three consecutive fields of the video signal Of the units, the average value of the video signal level in the first field is compared with the level value of the preset reference signal, and the average value of the video signal levels in other fields is compared with the level of the video signal level in the first field. Comparison means for comparing with the average value, and based on the comparison result obtained by the comparison means, all fields in the repeating unit Imaging apparatus characterized by the average value of the video signal level and a control means for controlling the electronic shutter as both become the same size of the. 4. An AGC amplifier for changing an average value of the video signal level by changing a gain is provided, and based on a comparison result obtained by the comparing means, all fields in the repeating unit are changed. 4. The image pickup apparatus according to claim 3, wherein the control unit controls the AGC amplifier together with the electronic shutter so that the average values of the video signal levels are the same. 5. A vertical scanning frequency of 60 Hz is controlled on the basis of a video signal obtained under illumination of a fluorescent lamp with a power supply frequency of 50 Hz so that the average value of the luminance signal level for each field period becomes equal for all fields. An EE control type image pickup apparatus for performing the image pickup of 1), the first detection means obtaining an average value of a green signal level from the video signal for each field period, and a green signal of the 3 primary color signals from the video signal Second detecting means for obtaining the average value of the signal level of the color signal for each field period, and the average value of the green signal level obtained by the first detecting means for a predetermined field, and the second detecting means. The obtained average value of the color signal levels is compared, and the average value of the color signal levels in the field three fields after the field is compared with the green signal level. Imaging apparatus characterized by and a control means for controlling the amplifier gain so as to approach the average value. 6. A vertical scanning frequency of 50 Hz is controlled based on a video signal obtained under illumination of a fluorescent lamp having a power supply frequency of 60 Hz so that the average value of the luminance signal level for each field period becomes equal for all fields. An EE control type image pickup apparatus for performing the image pickup of 1), the first detection means obtaining an average value of a green signal level from the video signal for each field period, and a green signal of the 3 primary color signals from the video signal Second detecting means for obtaining the average value of the signal level of the color signal for each field period, and the average value of the green signal level obtained by the first detecting means for a predetermined field, and the second detecting means. The obtained average value of the color signal levels is compared, and the average value of the color signal levels in the field five fields after the field is compared with the green signal level. Imaging apparatus characterized by and a control means for controlling the amplifier gain so as to approach the average value.