JP3091630B2 - Video camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video camera having an electronic shutter function for controlling the driving of a solid-state image pickup device to vary a shutter speed.

[0002]

2. Description of the Related Art A conventional color video camera having an electronic shutter function, such as a camera unit of a camera-integrated VTR, is constructed as shown in FIG. CCD image sensor 2
An image is formed on the light receiving surface.

The image pickup device 2 is operated by a driving pulse from a driving pulse generating section 3 to accumulate received light charges,
In the case of the NTSC system, the prescribed field period (=
The accumulated charge is read out at 1 / 59.94 seconds), and this charge is supplied to the signal separation / AGC circuit 4 as a video output.

The circuit 4 performs a double correlation sampling process on the video output by a high-speed sample and hold to reduce its noise, and then performs an AGC process on the video output so that the output level becomes constant. It is supplied to the processing circuit 5.

The circuit 5 separates a video output into a luminance component and a color component, performs a luminance process such as contour enhancement, pedestal clamping, and gamma correction on the luminance component to form a luminance signal Y. , Matrix processing, gamma correction and the like are performed to form color difference signals RY and BY.

Then, the luminance signal Y and the color difference signals RY,
BY is supplied to the encoder 6 at the next stage. This encoder 6 applies a setup level to the luminance signal Y, performs white clip processing, etc., and outputs the luminance signal CAM output from the camera.
The color signals RY and BY are subjected to color burst signal addition, modulation, and the like, and then combined to form color signals CAM and C output from the camera.
Y, CAM and C are supplied to a subsequent VTR section or the like.

Further, in order to control the operation of each part, a constant frequency oscillator 7 having a crystal oscillator configuration, a timing pulse generator 8 having an integrated circuit configuration, and a synchronizing signal generator 9 are provided.

The oscillator 7 has a frequency of 8 fsc (fs
c supplies a reference clock K ₁ color approximately 3.58MHz subcarrier frequency) to the generator 8, the generator 8 divider 1
0 by with the clock K ₁ 1/2 divided frequency 4fsc
Divided clock K ₂ is formed, and supplies the clock K ₂ inside the pulse generator 11 and the encoder 6, the generator 9 of.

[0009] The generator 9 processes the clock K ₂ by dividing the like of the counter, in FIG. 7 in synchronism with the clock _{K 1 (a), (b} ), the vertical synchronizing signal VD of (d), vertical Blanking signal VBLK, horizontal synchronization signal HD
And various synchronization signals such as a composite synchronization signal C / SYNC.

At this time, the frequency f of the synchronization signals VD and HD is
_V, f _{H is, fsc = (455/2) f H} , f H = (5
25/2) to satisfy the relationship of f _V.

Then, the synchronization signals VD and HD are supplied to the pulse generator 11, and various synchronization signals including both the synchronization signals VD and HD are supplied to the encoder 6.

Next, the generation unit 11 includes an address counter,
Formed by a gate circuit, a decoder circuit, a ROM, etc.
The reset control of the synchronization signals VD and HD and the clocks K ₁ ,
K _2, generates various timing pulses drive control synchronized with the clock K ₁ by counting the like of the decode output of the shutter speed switching signal SSW.

The shutter speed switching signal SSW is formed by a contact signal of a shutter speed switching switch based on a manual switching operation, a microcomputer output of automatic exposure / auto focus control, or a logic gate output, and instructs a shutter speed.

Then, the generation unit 11 sends the data to the generation unit 3 as shown in FIG.
(C), timing pulses for various drive controls of the image sensor 1 such as readout pulses of accumulated charges in the field cycle are supplied.

At this time, in the case of electronic shutter photography (shift shutter photography) in which the electronic shutter function is used, the charge accumulation period T for each field based on a shutter speed command.
By variably setting a, a sweep pulse of the accumulated charge shown in FIG. 7E is also formed and supplied to the creation unit 3.

This sweep pulse is a high-speed pulse generated every horizontal blanking period. The number of pulses changes according to the shutter speed, and the charge sweep period Tb of each field in FIG. 7E changes. And a read pulse of the stored charge,
The various drive pulses of the charge transfer pulse and the like of the preparation unit 3 based on the sweeping pulse and the like, the image pickup device 1 operates in synchronization with the clock K _1.

At this time, in the case of normal photographing in which the electronic shutter function is not used, the charge accumulation period Ta for each field
Is fixed to one field regulated by the read pulse of the accumulated charge, and in the case of electronic shutter imaging, the charge accumulation period Ta of each field is variably set by the discharge pulse and the read pulse of the accumulated charge.

The charge stored in the charge storage period Ta is read out from the image sensor 1 in each field. Also, the generation unit 1
A sample / hold pulse, a clamp pulse and the like are supplied from 1 to the circuits 4 and 5.

[0019]

In the case of the conventional video camera shown in FIG. 6, especially when photographing with an electronic shutter using an electronic shutter function, if the illuminating light source of the subject is a discharge lamp such as a fluorescent lamp, the luminance and the luminance are not improved. Flicker is generated in the color camera output based on the blinking change of the illumination light. That is, a discharge lamp such as a fluorescent lamp as an illumination light source flickers at a frequency that is an integral multiple of that of a commercial AC power supply or the like as its power supply.

[0020] Then, if the illuminating light source a fluorescent lamp that lights at the commercial AC power supply of 60 Hz, the light luminance, hue of FIG. 8, for example (a), power supply period T _1, as shown in (b) ( 1/2 cycle T ₂ (1/120 second)
Seconds) and changes in synchronization with the commercial AC power supply.

On the other hand, the amount of charge accumulated in each field of the image pickup device 1 depends on the charge accumulation period Ta. This period Ta is determined by the timing of the read pulse of the accumulated charge shown in FIG. becomes one field time T _3, when the electronic shutter shooting the timing and drawing the read pulse of sweeping pulses of accumulated charge (d) time T ₄ (= Tb)
The time T ₅ (= T ₃ −T ₄ ) is determined by:

This type of video camera is often driven by a battery power source or the like, operates asynchronously with the blinking of the illumination light, and has a one-field time (field period) determined by a vertical synchronization signal VD. Assuming that T ₃ is equal to the prescribed field period T _V of the television system, in the case of the NTSC system, T _V = 1 / 59.94 seconds. Therefore, with respect to the power period T ₁ (= 1/60 seconds). somewhat shifted the field period T ₃ Te.

[0023] Incidentally, there is a similar displacement may be a television system other than the NTSC system, for example, a field period T _V defined if the PAL system is 1/50 sec, the deviation is higher than the NTSC system growing.

Therefore, this type of video camera operates asynchronously with the blinking of the illumination light, and in this case, the charge storage time T ₅
Timing (phase) changes at a cycle corresponding to the phase difference between the field period T ₃ based on blink cycle T ₂ and the reference clock K ₁ of the illumination light.

Based on this change, the amount of charge accumulated in each field greatly changes, for example, as shown in FIG. 9 during electronic shutter photography in which the influence of the phase difference is large.
FIG. 9 shows a change in hue, and the amount of integration in the shaded portion of each field is the amount of accumulated charge. In addition, a change similar to that in FIG. 9 occurs in the luminance.

Then, based on the change in the amount of accumulated charge in each field, flicker occurs in the video output of the image sensor at a period corresponding to the phase difference, and the flicker of the video output causes the luminance signal CAM / Y of the camera output. , Color signal CAM
C has a problem that luminance and color flickers occur as shown in FIG. FIG. 10 shows the flicker fluctuation of the hue, and the cycle _TF thereof will be specifically described below.

The power supply period T ₁ of the FIG. 9, blink cycle T _2, the field period T ₃ 1/60 sec, 1/120 sec, T _V (1
/59.94 seconds) and the phase difference between the field period T ₃ and the blink period T ₂ is ΔT, ΔT is expressed by the following equation (1).

[0028]

ΔT = T _V (= T ₃ ) −2 T ₂ (= T ₁ ) = 1 / 59.94-1 / 60 = 1.67 × 10 ⁻⁵ sec

The flicker period T _F is equal to the phase difference ΔT
Of a period until the addition value reaches the blink cycle T _2, the phase difference [Delta] T is increased for each field by [Delta] T, calculated from Expression 2 below.

[0030]

T _F = (T ₂ / ΔT) T _V = T ₂ · T _V / (1 / T ₂ -2 / T _V ) = 1 / (120−2 / 59.94) = 1 / ｛2 (60−59.94)｝ = 8.33 seconds

An object of the present invention is to prevent flickering of a camera output when photographing an electronic shutter under illumination of a discharge lamp such as a fluorescent lamp.

[0032]

In order to achieve the above object, in a video camera according to the present invention, a flicker detection sensor for detecting a blinking change of illumination light of a subject, and an illumination light based on a detection output of the sensor. A voltage-controlled oscillator that generates a reference clock based on an error signal between a blinking phase of the reference clock and a phase of a vertical synchronizing signal formed by dividing the reference clock.
And a flicker synchronizing unit for performing L control and forming a reference clock in synchronization with flickering of the illumination light.

[0033]

In the video camera of the present invention configured as described above, since the reference clock is formed by the flicker synchronization section in synchronization with the flicker of the illumination light, the vertical synchronization formed by dividing the reference clock is formed. The signal is also synchronized with the flickering of the illumination light.

Therefore, the field cycle of the video camera determined by the vertical synchronizing signal is synchronized with the flickering of the illumination light, and even during electronic shutter shooting, the charge accumulation period of the image sensor in each field is based on the flickering of the illumination light. It occurs at almost the same timing. Therefore, the amount of charge accumulated in each field of the image sensor becomes equal, and flicker of the camera output during electronic shutter shooting under discharge lamp illumination is prevented.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment will be described with reference to FIGS. 1, the same reference numerals as those in FIG. 6 denote the same or corresponding elements, and the points different from the conventional camera in FIG. 6 are as follows.

(I) A flicker detection sensor 12 having an optical sensor configuration for detecting a flickering change of illumination light is provided.

(Ii) A flicker of a PLL circuit configuration for generating a reference clock K ₁ ^* by PLL control of an error signal between a blinking phase of illumination light based on a detection output of the sensor 12 and a phase of a vertical synchronization signal VD of the generator 9. A point provided with a synchronization unit 13.

(Iii) A flicker synchronization mode terminal 14 to which a flicker synchronization mode signal FSW whose level is inverted by turning on / off the flicker synchronization mode is provided.

(Iv) A first clock selection switch 15 that is switched by the mode signal FSW is provided. When the flicker synchronization mode is turned on, the input clock of the frequency divider 10 and the generator 11 of the generator 8 is changed to the reference clock K of the oscillator 7. ₁ to synchronization unit 1
3 is switched to the reference clock K ₁ ^* .

(V) A second clock selection switch 16 which switches in conjunction with the switch 15 and a constant frequency oscillator 17 having a frequency of 4 fsc in the form of a crystal oscillator are provided to separate the input clock of the encoder 6 when the flicker synchronization mode is turned on. to point switched from the divided clock signal K ₂ of divider 10 to a constant frequency clock K ₂ ^*.

The sensor 12 is formed of an optical sensor having sensitivity in the visible light range, and is provided in the camera in the same shape and mounting method as a conventional white balance sensor or the like so as to receive the illumination light of the subject as much as possible. .

The detection output of the current of the sensor 12 changes in real time according to the brightness of the illuminating light, and at the time of photographing under a discharge lamp such as a fluorescent lamp, the sensor 12 detects the flickering change of the illuminating light. .

The detection output of the sensor 12 is output to the synchronization unit 1
The amplifier 18 converts the voltage signal into a voltage signal and amplifies the voltage signal. The amplifier 18 supplies the voltage signal of FIG. Incidentally, T ₂ in FIG. 2 FIG. 8 shows a similar example blink cycle of 1/120 seconds in the case of FIG.

The generator 19 is formed by a comparator or the like. The input signal is processed into a rectangular wave pulse signal shown in FIG. 3 and supplied to a frequency divider 20 having a flip-flop configuration. set for each rise of the pulse signal, changes alternately 1/2 divides the input pulse signal to the reset, to form a reference pulse signal with a period T ₁ shown in FIG. In addition,
The cycle T ₁ is a power cycle of 1/60 second, similar to the case of FIGS. 8 and 9.

The reference pulse signal and the vertical synchronizing signal VD of the generator 9 are supplied to a phase comparator 21. The comparator 21 synchronizes this signal with the vertical direction with reference to the phase of the reference pulse signal. A phase difference from the signal VD is detected, and a phase error signal proportional to the phase difference is supplied to the low-pass filter 2.
Feed to 2.

The filter 22 forms a DC control voltage signal by smoothing the phase error signal, and supplies this signal to a voltage controlled oscillator 23 to control the oscillation frequency. The reference clock K ₁ ^* of the oscillator 23 based on this control is supplied to the switch 15.

On the other hand, the signal FSW of the terminal 14 is formed by a contact signal of a synchronous mode switch which is switched by a mode selection operation, and the level is inverted when the flicker synchronous mode is turned on and off.

During normal photographing when the flicker synchronization mode is turned off, the switches 15 and 16 are switched to the off contact α, and the reference clock K ₁ of the oscillator 7 is passed through the switch 15 to the frequency divider 10 of the generator 8. , And the divided clock K ₂ of the frequency divider 10 is supplied to the switch 16.
, The reference clock K ₁ ^* is not used, and the camera of FIG. 1 is equivalent to FIG.
Has the same circuit configuration as that of the conventional camera, and operates similarly to the conventional camera.

Next, in order to perform electronic shutter photography under the illumination of a discharge lamp such as a fluorescent lamp, the flicker mode is turned on.
Switches to switches 15 and 16 is on the contact beta, reference clock K ₁ ^* switch 15 instead of the reference clock K ₁
Is supplied to the frequency divider 10 and the generation unit 11 via the.

At this time, the divided clock K ₂ is a clock obtained by dividing the reference clock K ₁ ^* by 、, and in synchronization with this clock, the generator 9 outputs various synchronous signals such as the synchronous signals HD and VD. Form.

Then, since the synchronization signal VD is returned to the comparator 21 of the synchronization unit 13, the reference clock K ₁ ^{* is formed} by the loop of the synchronization unit 13, the switch 15, the frequency divider 10, and the generator 9 ^.
Is formed, and the synchronization signal VD is phase-synchronized with the blinking of the illumination light. In addition, since the reference clock K ₁ ^* is PLL-controlled, other synchronization signals other than the synchronization signal VD such as the synchronization signal HD are also phase-synchronized with the blinking of the illumination light.

If the illuminating light source is a fluorescent lamp operating with a commercial AC power source of 60 Hz and having a blinking period T ₂ = 1/120 seconds, the synchronizing signal VD has a power supply period T twice as long as the blinking period T _2.
Synchronize with ₁ (1/60 second).

Further, since the synchronization signals VD and HD and the clocks K ₁ ^* and K ₂ are synchronized with the flickering of the illumination light, the generation unit 1
Timing pulses for various drive controls of the image sensor 1 supplied from 1 to the creation unit 3 are also synchronized with the blinking change of the illumination light.

Since the timing of the readout pulse of the accumulated charge of the image sensor 1 and the charge sweeping period are synchronized with the flickering of the illumination light, 1 is determined by the readout pulse as shown in FIG.
The field period (field cycle) T ₃ is the power cycle T
₁ and the charge storage time T ₅ (=
T ₃ −T ₄ ) occurs at the same timing in synchronization with the blinking of the illumination light.

Therefore, the accumulated charge amount in each field determined by the area of the hatched portion in FIG. 5 becomes constant without being affected by the blinking change of the illumination light, and the luminance signal CA of the camera output is obtained.
The appearance of flicker due to the flickering change of the illumination light as in the conventional MY and color signals CAM / C is prevented.

Next, the divided clock K ₂ is formed in synchronization with the flickering of the illumination light, and the divided clock K ₂
Since the encoder 6 performs various signal formation and processing on the basis of, a half of the blinking period T ₂ greatly deviates from, for example, a prescribed field period (= 1 / 59.94 seconds) of the NTSC system. As a result, the divided clock K ₂ becomes 4 fs
c (approximately 14.32 MHz) it becomes so greatly deviated from the partial frequency division color subcarrier signal of the clock K ₂ was criteria prescribed frequency fsc of the encoder 6 (approximately 3.68
MHz), there is a possibility that a color disappearance in which a reproduced image based on the color signals CAM and C output from the camera does not have a color.

Therefore, when shooting with the electronic shutter, the switch 1 is used.
5, the switch 16 is switched to the ON contact β,
Generation of a divided constant frequency clock of 4fsc instead to the oscillator 17 clock K ₂ K ₂ ^* is supplied to the encoder 6 disappeared colors described above can be prevented.

Therefore, in the case of the above embodiment, if the flicker synchronization mode is turned on at the time of electronic shutter shooting, the flicker of the camera output and the flicker of the camera output based on the flickering of the illumination light can be prevented without any adverse effect such as so-called color fading. The image quality is significantly improved.

Then, the detection sensor 1 separate from the image pickup device 1
In order to detect the blinking change of the illumination light from the analog continuous detection output of No. 2, the blinking change of the illumination light having a blinking cycle shorter than the field cycle which is difficult to detect from the video output of the image sensor 1 formed in the field cycle. Easy and reliable detection,
It is possible to reliably prevent flicker of the luminance and color of the camera output. The switches 15 and 16 are high-speed switch elements,
For example, it is preferable to be formed by a semiconductor switch element such as an analog switch element. Further, the generators 8, 9 and the synchronizing unit 13 can be realized by software of a microcomputer.

Furthermore, the flicker synchronization mode may be automatically turned on when the illumination light flickers. In this case, the output signals Y, RY, B-
Y, a flicker detection circuit for detecting the flickering of the illumination light based on the output signal of the amplifier 18 and the pulse generator 19 of the synchronizing unit 13 and the shutter speed switching signal SSW is provided, and the signal FSW is supplied to the terminal 14 from the detection circuit. I just need.

In the above embodiment, the television system is set to NT
The case where the SC method is used and the illumination light flickers at a blinking cycle T ₂ = 1/120 seconds, which is about twice the prescribed field period (1 / 59.54 seconds), based on a power supply frequency of 60 Hz has been described. The present invention can be applied to various television systems such as a television system.

The blinking period T ₂ of the illumination light is
Considering the pull-in capability of the vertical synchronization of a monitor television such as a color monitor based on the luminance signal CAM / Y and the color signal CAM / C of the camera output, 1 / N (N is 2 within ± 5% of the specified field period) , 3,...) Can be applied. In this case, the frequency divider 21 of the synchronization unit 13 is 1 / N
It is formed by a frequency divider.

Further, when the illumination light source is a mercury lamp other than a fluorescent lamp,
Of course, it can be applied to the case of a sodium lamp or the like.
Further, in the above embodiment, the flicker detection sensor is formed by an optical sensor. However, when the illumination light source is limited to a fluorescent lamp using a commercial AC power supply, the flicker detection sensor is formed by an electromagnetic wave sensor such as an antenna. Blinking light can also be detected. Further, in the above embodiment, the present invention is applied to a color video camera, but can be applied to a monochrome video camera.

[0064]

Since the present invention is configured as described above, the following effects can be obtained. An error signal between the flickering phase of the illumination light based on the detection output of the flicker detection sensor 12 and the phase of the vertical synchronization signal causes the flicker synchronization section 1
3 is controlled by PLL, and based on this control, the flicker synchronization unit 13 forms the reference clock for the operation of the solid-state imaging device 1 in synchronization with the blinking of the illumination light. The vertical synchronizing signal thus formed also synchronizes with the flickering of the illumination light.

Therefore, the field period of the video camera determined by the vertical synchronization signal is synchronized with the flickering of the illumination light,
Even during electronic shutter shooting, the charge storage time of the image sensor 1 in each field occurs at substantially the same timing based on the blinking of the illumination light, and the amount of charge stored in the image sensor 1 in each field becomes equal. It is possible to prevent the flicker of the camera output due to the blinking change of the illumination light at the time of photographing the electronic shutter under the discharge lamp illumination.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a video camera according to the present invention.

FIG. 2 is an output waveform diagram of an amplifier 18 of FIG.

FIG. 3 is an output waveform diagram of the rectangular wave pulse generator 19 of FIG.

FIG. 4 is an output waveform diagram of the frequency divider 20 of FIG.

FIG. 5 is an explanatory diagram of an accumulated charge amount in each field of FIG. 1;

FIG. 6 is a block diagram of a conventional camera.

FIG. 7 is a first timing chart for explaining the operation of FIG. 6;

FIG. 8 is a second timing chart for explaining the operation of FIG. 6;

FIG. 9 is an explanatory diagram of the accumulated charge amount for each field in FIG. 6;

FIG. 10 is an explanatory diagram of flicker of the camera output of FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid-state image sensor 12 Flicker detection sensor 13 Flicker synchronizing part 23 Voltage controlled oscillator

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 5/235 H04N 5/335

Claims (1)

(57) [Claims] 1. A flicker detection sensor for detecting flickering of illumination light of a subject in a video camera with an electronic shutter function for driving a solid-state imaging device based on a vertical synchronization signal formed by dividing a reference clock. PLL control of a voltage controlled oscillator that generates the reference clock based on an error signal between a blinking phase of the illumination light based on a detection output of the sensor and a phase of the vertical synchronization signal, and sets the reference clock to blinking of the illumination light And a flicker synchronizing unit formed in synchronization with the video camera.