JPH01246971A - Method for controlling exposure of image pickup device - Google Patents

Abstract

PURPOSE:To eliminate occurrence of flickering phenomena by setting the least common multiple period of the light emitting period and vertical scanning line period (V) as a basic image pickup period. CONSTITUTION:The F-timer 31 of an iris control circuit 3 counts vertical scanning line pulses Pv and outputs readout timing FT at every basic image pickup period F which is equal to the 3V period so as to drive a CCD image sensor 1 for reading-out by means of drive pulses phiF. The B-timer 32 of the circuit 3 outputs putting-out timing BT and puts out the CCD image sensor 1 by means of drive pulses phiS at the time when the period during which horizontal scanning line pulses can be counted and which is manually set through a volume switch Vol. Therefore, the lighting state in the effective photoelectric converting period E in the send half of the basic image pickup period F becomes coincident at every period F and image pickup signals Y free from flickering appear in the V period in the initial stage of each period F.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to an exposure control method for an imaging device equipped with an imaging device such as a CCD image sensor.

(b) Conventional technology Exposure control in conventional imaging devices, such as television cameras, is usually performed by a mechanical diaphragm mechanism inside the lens barrel, which increases costs.

For this reason, attempts have been made to electronically control exposure in television cameras using COD image sensors by utilizing the charge transfer driving principle of this image sensor.

For example, in Utility Model Application No. 61-139527, in a frame transfer type COD image sensor, in the middle of the photoelectric conversion period of each vertical scanning line period, the image charge that has been photoelectrically converted and accumulated in the light receiving part of this element is An exposure control means is provided that transfers and discharges the image charge in the opposite direction to the transfer direction for reading out the image signal, and accumulates the photoelectrically converted image charge only during the remaining photoelectric conversion period (effective photoelectric conversion period) for one screen. is proposed. Therefore, according to such an exposure control means, an optimum exposure state can be obtained by changing the timing of reverse charge transfer according to the brightness of the subject.

However, when an image of a subject illuminated by a fluorescent light or the fluorescent light itself is captured using the conventional imaging device as described above, flickering may occur on the playback screen.

The cause of such flicker will be explained based on FIG. 7.

That is, in the NTSC system adopted in Japan, the vertical scanning line period V (the period of the vertical retrace pulse Pv) is 1760 seconds, and this one period is equivalent to the mixed wave number (
The luminescence period (17
However, it is not synchronized with the luminescence cycle (1/100 seconds) of fluorescent lamps that are turned on at the commercial AC power frequency (50 Hz) in the Kanto region.

Therefore, the effective photoelectric conversion period E between the drive timing of the reverse transfer drive pulse φ, which is variably set for discharging the charge of the COD image sensor, and the drive timing of the forward transfer drive pulse φ, for reading out the charge. The exposure conditions will be different.

That is, in the case of fluorescent light illumination with a 60Hz power supply,
'), (口゛), (8゛) show that it is stable in a synchronized state, but in the case of fluorescent light illumination with a 501 (zij source), (A), (口゛), (HA) in the figure ), the fluctuations occur in an asynchronous state.In the latter case, fluctuations in the exposure amount appear as flickers in the reproduced image, causing a deterioration in the quality of the reproduced image.

(c) Problems to be Solved by the Invention The present invention provides an exposure control method for an imaging device that can suppress the occurrence of flicker as described above.

(d) Means for Solving the Problems The exposure control method for an imaging device of the present invention is an exposure control method for imaging under illumination of a periodic light source that emits light asynchronously with the vertical scanning line period, the method comprising: It consists of the following composition.

The first method of the present invention provides the least common multiple period T of the light emission period of the light source and the vertical scanning line period of the imaging device, or the period T.
Let an integer multiple period nT (n is an integer) be the basic imaging period F,
The basic imaging period F, which is longer than the imaging period required for proper exposure, or a period mF (m is an integer) that is an integral multiple of this period F is set as the effective imaging period.

A second method of the present invention is provided with a memory means for storing an image signal from an image sensor, and includes a period T that is the least common multiple of the light emission period of the light source and a vertical scanning line period of the image pickup device, or an integral multiple of the period T. The period nT (n is an integer) is the basic imaging period F
and every period F or an integer multiple period mF(
An image signal is written into the memory means during every vertical scanning line period (m is an integer), and an image signal is read from the memory means during each vertical scanning line period.

The third method of the present invention is provided with an auxiliary light source such as an incandescent lamp or an LED, and when the imaging period for each imaging cycle becomes a specific ratio or a non-integer multiple of the light emitting cycle of the periodic light source, the auxiliary light source is provided. It turns on the light source.

(f) Effect According to the first method of the present invention, the periodic light emitting type light source and the vertical scanning line period are synchronized with each other at the least common multiple period T, and therefore, this period T or integral multiple synchronization nT is the basic imaging period F, and this period F or an integral multiple period m
By setting F as the effective imaging period, there is no variation in the illumination state within each imaging period provided for each effective imaging period, and an imaging signal captured under the same illumination state is output.

According to the second method of the present invention, only the vertical scanning line pulses that provide the same illumination state are written into the memory means for the imaging signal obtained from the imaging device, and the imaging signal is read from the memory means for each vertical scanning line period. Therefore, image signals captured under the same illumination condition are output.

According to the third method of the present invention, by turning on the auxiliary light source that assists the illumination of the light source when the imaging period becomes short and the flicker phenomenon becomes strong, it is possible to relatively reduce the difference in bright and dark levels of illumination illuminance. .

Embodiment FIG. 1 shows an embodiment of an imaging apparatus employing the exposure control method of the first invention.

In the figure, (1) is a frame transfer type C
It is a CD image sensor, which includes an imaging section (11) and a storage section (
12), and a horizontal transfer section (13). (2) is the CC
This is a drive circuit that drives the D image sensor, and the imaging unit (
A forward transfer drive pulse≠r is supplied to the imaging unit (11) to perform forward transfer drive (downward in the figure) for charge readout, and a forward transfer drive pulse ≠r is supplied to the imaging unit (11) for forward transfer drive (downward in the figure) for charge discharge. )
4. Reverse direction transfer drive pulse for performing transfer drive. supply. Furthermore, this drive circuit (2) applies storage and transfer drive pulses φ3 and φ3 to the storage section (12) and horizontal transfer section (13), respectively.
Output transfer drive pulse φ4 is supplied.

(3) is an iris control circuit, and the above drive circuit (2)
The length of the effective photoelectric conversion period E is controlled to expand or contract by determining the driving pulse providing timing FT of the forward transfer driving pulse i and the driving pulse providing timing BT of the backward transfer driving pulse φ.

A feature of the embodiment of the present invention is that the iris control circuit (3) has a period that is the least common multiple of the vertical scanning line period V of 1760 seconds and the lighting period of the fluorescent light of 1/100 seconds. 3v by measuring a certain period of 1720 seconds, that is, a 3v period.
The carry signal when it reaches the above read timing FT
An F timer (31) with a counter configuration that outputs the output as FT, and a B timer (32) with a counter configuration that measures the period until the above-mentioned discharge timing BT is output according to the potential of the volume switch Vol that is reset by this FT. We are prepared.

(4) is a signal processing circuit that performs signal processing such as sample hold, clamping, synchronization signal addition, and gamma correction on the image pickup signal from the CCD image sensor and outputs a video signal Y.

Note that (9) is a monitor such as a CRT, and (10) is an interpolation circuit that interpolates the video signal Y.

The operation of the apparatus having such a configuration will be explained based on FIG. 2.

The box in Fig. 2 shows the periodic variation (1/100 second) of the illuminance of a fluorescent light turned on by a 50Hz commercial AC power supply, and the total illuminance during the variably set effective photoelectric conversion period E. is represented by a hatched area (to).

The F timer (31) counts the vertical scanning line pulses Pv, outputs the read timing FT every basic imaging cycle F of the 3v period, and drives the CCD image sensor (1) with the driving pulse -1.
Read drive is performed. On the other hand, the B timer (32) can count horizontal scanning line pulses over a period of 3V, and outputs the discharge timing BT when it reaches the value of FE set manually with the volume switch Vol. 1) is ejected using a drive pulse φ3.

Therefore, the illumination state shown by (f) in the effective photoelectric conversion period E after the basic imaging period F is the same for each period F, and the imaging signal Y is free from flicker caused by the periodic lighting of the fluorescent light. appears as the V signal y(to) in the v period at the beginning of each period F.

Such an imaging signal Y is a signal y only during the V period once every 3V.
(to) exists, so you can connect it to a regular TV monitor (9
), it is preferable that the interpolation circuit (1) repeats this y(to) twice during the remaining 2v period and converts it into an interpolated image signal X.

FIG. 3 shows an embodiment of an imaging apparatus employing the second method of the present invention, and FIG. 4 shows its operation timing.

In the device shown in the figure, the iris control circuit (3) drives the CCD image sensor (1) by operating the drive circuit (2) at a normal V cycle. That is, the drive pulse φ for reading is V in synchronization with the vertical scanning line pulse Pv.
The drive pulses for ejection, which occur periodically, are variably set and present in each V period.

Therefore, the illumination state of the fluorescent light during each effective photoelectric conversion period E changes as shown in (D), (E), and (E), and this is 3V.
Since it is repeated at regular intervals, the image pickup signal Y output from the signal processing circuit (4) is y (y), y (d).

y (e) is repeated at a 3v cycle.

If this imaging signal Y is left as it is, it will cause flicker due to the presence of signals y (he), y (d), and y (e) that are subject to illuminance fluctuations caused by the fluorescent light.

The embodiment of the present invention is characterized by an A/D converter (5
), a memory circuit (
6). That is, the write control circuit <8> attached to the memory circuit (6) sets the 3v period corresponding to the least common multiple period T explained in the first method of the present invention as the basic imaging period F, and The signal WE that makes the memory circuit (6> ready for writing) is sent to the memory circuit (6) only during the first V period.
), and the memory circuit (6) writes only the ■signal y (to) that appears in the digitized image signal Y at a 3V cycle, and updates this at a 3V cycle. On the other hand, the image signal is read out from the memory (6) every V period, converted into an analog signal, and outputted as a converted image signal X. Therefore, this converted imaging signal or illumination state is (
Since it consists of only the highly unified V signal y (f), flicker in the image signal Y before being input to the memory circuit (6) can be eliminated.

In the method of the present invention explained above, FIGS.
In any of the devices shown in the figure, the emission period of the fluorescent light (171
The basic imaging period F is set to the least common multiple period T (=3V) of the V period (00 seconds) and the V period.
=6V), 3T (=9■), . . . are set as F, similar effects can be obtained. If an imaging period longer than the basic imaging period F is required to set a long effective photoelectric conversion period E, 2F, 3F, . . . may be reset as the adaptive imaging period. However, this basic imaging period F
As the time becomes longer, the video playback image becomes close to a time-lapse image.

FIG. 5 shows an external appearance of a video telephone device which is an embodiment of an imaging device employing the third method of the present invention, and FIG. 6 shows its configuration. In addition, in a videophone device, a monitor terminal connected to one telephone device and a monitor terminal connected to the other telephone device are connected to a telephone line with an intervening exchange, but only one monitor terminal is shown in the figure. ing. The television camera CAM shown in Fig. 5 is for taking a self-portrait of the sender, and the CC
It includes a D image sensor (1), a drive circuit (2), an iris control circuit (3), a signal processing circuit (4), a lens mechanism (not shown), and the like.

Further, the television monitor (9) is a CRT that displays a self-portrait taken by the television camera CAM or an image of the other party.

The key switch KEY is used to operate the monitor terminal, and includes a power switch, a transmission switch, and the like.

The modem MOD is a transmitting/receiving means that controls transmission and reception of still image signals between the telephone line and the monitor terminal.

The controller CON is a microcomputer that controls the operation of the monitor terminal according to a built-in program based on the operation of the key switch KEY.

The interface IF performs image signal processing and connects the controller CON, TV camera CAM, and TV monitor 9)
act as intermediary between

The memory circuit (6) connects the TV camera CAM, TV monitor (9) and controller C via the interface IF.
This is a video RAM that stores a still image signal of the self-portrait or the other party's image digitally encoded by the interface IF.

The line relay SW is controlled by the controller CON to temporarily switch the connection of the telephone line of the telephone equipment from the telephone equipment to the modem MOD. That is, this line relay SW normally connects a telephone line and a telephone device, and controls the period during which the currently taken self-portrait is transmitted to the other party's monitor terminal via the telephone line by operating the transmission switch of the key switch KEY, as well as the period when the other party's monitor The telephone line and modem MOD are connected only during the period when the other party's image signal from the terminal is received via the telephone line.

In the video telephone device having such a configuration, when the power switch of one of the monitor terminals is turned on, a self-portrait imaged by the television camera CAM is displayed on the television monitor (9). Then, when you turn on the transmission switch of the key switch KEY while dialing the other party's telephone on the telephone device and connecting the lines of both telephones, the controller CON switches the line relay S.
Connect W to the modem MOD side, and at this time connect the TV monitor (
9) The self-portrait still image signal displayed in the memory circuit (
6), and sends out this self-portrait signal to the telephone line via the modem MOD, and transmits it to the other party's monitor terminal.

Conversely, when receiving the other party's image from the other party's monitor terminal, the controller CON connects the line relay SW to the telephone equipment side, stores the received other party's image signal in the memory circuit (6) via the modem MOD, and sends it to the TV monitor. (9) is switched from the self-portrait up to this point to the other party's image.

Since the videophone device described above is configured to be used indoors, unless a lens mechanism with a low (bright) F value is used, it will not work when indoor lighting such as fluorescent lights is dark. Since this results in insufficient exposure, an infrared light source consisting of an infrared LED and a driving inverter In are provided to compensate for this.

Note that R in the figure is a voltage dividing resistor. The infrared light source LED is used as an auxiliary light source in this way.
This is because D is provided close to the television camera CAM and the television monitor (9), so that the sender, who is the subject, will not feel uncomfortable due to glare. Therefore, the above TV camera C
As an AM solid-state image sensor, an image sensor having imaging sensitivity in the visible light wave and infrared light region, in this case a frame transfer type CCD image sensor (1), is used.

The feature of the embodiment of the present invention is that the infrared light source L
ED is not only used as an auxiliary light source to compensate for insufficient illuminance, but also when flicker occurs due to the lighting cycle of indoor fluorescent lights even if there is sufficient illuminance on average. , the infrared light source LED has been repurposed as a flicker countermeasure.

That is, the turning on and off of the infrared light source LED can be controlled by a manual switch (not shown), but also by the iris control circuit (3).

The iris control circuit (3) in FIG. 6 uses, for example, the drive pulse φ2 in FIG. The CCD image sensor (1) is driven at the same timing as φ, and an image signal similar to the image signal Y in FIG. 4 is sent from the signal processing circuit (4) to the interface IF.
The reproduced image is sent to the television monitor (9) through the monitor (9), and the reproduced image is monitored. The iris control in this case is operated by a manual volume switch Vol as shown in FIG.
An effective photoelectric conversion period E, which is an imaging period corresponding to the set potential of this switch Vol, is variably set for each period V, which is an imaging period.

Therefore, when this effective photoelectric conversion period E is an integral multiple of the luminescence period of the fluorescent lamp, there is no flicker phenomenon, and when this period E is long enough to correspond to many luminescence periods (spanning multiple V periods), there is no flicker phenomenon. (This is possible if the imaging cycle can be set) also makes the flicker phenomenon relatively small. Therefore, flicker countermeasures are required when this period E is small and is not an integral multiple of the luminescence period of the fluorescent light. The infrared light source LED is configured to turn on when the time is shorter than /100 seconds.

As a result, the infrared light source LE is
Since the auxiliary illumination light D illuminates the sender's face, the periodic brightness level difference of the fluorescent light illumination becomes relatively small, and the flicker phenomenon is suppressed.

In addition, according to the above description, although a fluorescent lamp was illustrated as an example of a periodic light emission type light source, the present invention is not limited to this.

(G) Effects of the Invention According to the exposure control method for an imaging device of the present invention, it is possible to implement electronic iris control and eliminate the flickering phenomenon of reproduced images that could not be avoided conventionally.

[Brief explanation of the drawing]

1 and 2 are a configuration diagram and an operation timing diagram of an imaging apparatus employing the exposure control method of the present invention;
4 and 4 are block diagrams and operation timing diagrams of an imaging device adopting the second method of the present invention, and FIGS. 5 and 6 show the method of the third present invention (1) COD image sensor , (2)...Drive circuit, (3)...Iris control circuit, (4)...Signal processing circuit, (6)...
Memory circuit, (8)...Write control circuit, (9).
...TV monitor, LED...infrared light source. Figure 5 Figure 7

Claims (3)

[Claims] (1) The vertical scanning line period of an imaging device refers to the light emission period of the light source and the vertical scanning of the imaging device in an exposure control method for an imaging device that performs imaging under illumination of a periodic light source that emits light asynchronously. The least common multiple period T with the line period or the integral multiple period nT (n
is an integer) as the basic imaging period F, and the basic imaging period F, which is longer than the imaging period necessary for proper exposure, or the period mF (m is an integer) that is an integral multiple of the period F, is set as the adaptive imaging period. Exposure control method for the device. (2) The vertical scanning line period of an imaging device refers to the period of vertical scanning lines used to store imaging signals from an imaging device in an exposure control method for an imaging device that performs imaging under illumination of a periodic light source that emits light asynchronously. a memory means, the least common multiple period T of the light emission period of the light source and the vertical scanning line period of the imaging device or an integral multiple period n of the period T;
T (n is an integer) is a basic imaging period F, and an image signal is written to the memory means in one vertical scanning line period every period F or every integral multiple period mF (m is an integer) of the period F. An exposure control method for an imaging apparatus, characterized in that an image signal is read out from the memory means and outputted for each vertical scanning line period. (3) The vertical scanning line period of an imaging device is an exposure control method for an imaging device that performs imaging under illumination of a periodic light source that emits light asynchronously, and is equipped with an auxiliary light source such as an incandescent lamp or an LED. An exposure control method for an imaging device, characterized in that an auxiliary light source is turned on when an imaging period for each imaging cycle becomes a specific ratio or a non-integer multiple of the luminescence cycle of the periodic light emitting type light source.