JPH09163238A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption with a wide luminance range of an object to be picked up in the image pickup device able to transfer a picked up image to a computer. SOLUTION: An optical image of an object is formed to an image pickup element 3 such as a CCD through an optical lens 1 and the image is converted into an electric signal by the element 3, and an A/D converter 9 converts the signal into a digital signal and a prescribed image signal is generated by an image pickup signal processing circuit 10. In this case, the driving of the image pickup element 3 and the image pickup signal processing circuit 10 is controlled by a timing signal from a timing signal generating circuit 4 and a synchronizing signal generating circuit 11 and a frequency of an input clock being a reference signal of the signal generating circuits 4, 11 is controlled variably by using a system control circuit 14 and a frequency divider 17. Then the frequency of the input clock is changed to control a luminous quantity of the optical image made incident into the image pickup element 3.

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 such as a digital camera connected to a computer, and more particularly to an image pickup apparatus for improving automatic exposure amount control.

[0002]

2. Description of the Related Art In recent years, the number of uses for handling images in computers has increased dramatically, and the commercialization of digital cameras for capturing images in computers has become active. The image sensor used in such a digital camera can be freely configured because it is not regulated by a video signal. However, the video sensor is required to be easily available or to reduce the product price. An image pickup device for a camera is used.

Also, as a timing generator (TG) IC for driving the image pickup device, a video IC is used. Further, the CDS / AGC, the IC for signal processing, and the IC for synchronizing signal generation (SSG) are also those for video, so that the camera constituted by these is driven at the video rate after all. .

FIG. 2 is a block diagram showing the structure of a conventional digital camera. In the figure, 1 is an optical lens for forming an image of reflected light from a subject, 2 is an optical diaphragm for controlling the amount of incident light of an optical image incident through the optical lens 1,
An image sensor 3 converts an object image formed by the optical lens 1 into an electric signal. For example, an interline CCD of a complementary color checkered color difference sequential system generally used in movie video is used.

Reference numeral 4 denotes a timing signal generation circuit (hereinafter referred to as TG) which generates a timing signal necessary for operating the image pickup device 3, and 5 shows image pickup for amplifying a signal from the TG 4 to a level capable of driving the image pickup device 3. An element drive circuit, 6 is a CDS provided for removing output noise of the image sensor 3.
A circuit, 7 is an amplifier circuit for amplifying the output signal of the CDS circuit 6, and 8 is a clamp circuit for fixing the zero (black) level of the amplified signal.

Reference numeral 9 denotes an A / D converter for converting an analog signal output from the preprocessing circuit into a digital signal, 1
Reference numeral 0 is an image pickup signal processing circuit for processing a digitized signal, 11 is a synchronizing signal generating circuit for generating a pulse or a synchronizing signal of a video signal necessary for the signal processing (hereinafter, SS).
G), 12 is an interface circuit for sending out the signal processed by the image pickup signal processing circuit 10 to a computer or a recording medium, and 13 is information on the integrated value of a specific region of the luminance signal generated by the image pickup signal processing circuit 10. Is a brightness level detection circuit for outputting a system control circuit for controlling the entire camera (hereinafter referred to as syscon), 15 is an oscillator for generating a basic clock as a reference of the whole, and 16 is for changing the aperture area of the optical diaphragm 2. It is a diaphragm drive circuit for driving the diaphragm.

The exposure control of such a camera will be described.

The exposure control is to maintain the illuminance (image surface illuminance) of the light receiving surface of the image pickup device at a constant amount by controlling the amount of light applied to the image pickup device 3 and controlling the aperture area of the diaphragm 2. The amount of light incident on the image sensor 3 can be detected as an integrated value of a specific region of the light receiving area of the image sensor, from the output signal of the image sensor 3 being a luminance signal in the image signal processing circuit 10. Then, the brightness level detection circuit 13 transmits the brightness level information to the syscon 14.

The syscon 14 compares the obtained luminance level with the reference luminance level. If the obtained luminance level is higher than the reference luminance level, the diaphragm driving circuit opens the aperture area of the optical diaphragm 2. Order 16 and squeeze 2
Drive. On the contrary, if the obtained brightness level is lower than the reference brightness level, the diaphragm drive circuit 16 is instructed to open the aperture area of the optical diaphragm 2 to drive the diaphragm 2.

By such a feedback operation, the exposure amount is maintained at an appropriate amount. The driving unit of the diaphragm 2 is usually composed of a meter including a coil and a magnet, a stepping motor, or the like. If the amount of incident light is insufficient even if the aperture diameter of the diaphragm 2 is maximized, a method of increasing the gain of the amplifier circuit 7 is used.

Here, as one trend of digital cameras, there are low price and low power consumption. As a camera that realizes this, there is a camera without an aperture, or a camera in which one or more fixed apertures are prepared and manually switched. The exposure control of these cameras is performed by controlling the electronic shutter of the image sensor. Next, this method will be described.

FIG. 3 is a block diagram of a generalized interline CCD for movie video. In the figure, reference numeral 20 denotes a photoelectric conversion unit that transmits light in a specific wavelength range and converts the incident light into an electric charge, and includes a plurality of photodiodes (P
D). Reference numeral 21 is a vertical transfer unit for vertically transferring the charges stored in each pixel, 22 is a horizontal transfer unit for transferring the charges transferred from the vertical transfer unit 21 for each horizontal line, and 23 is a horizontal transfer unit. It is a floating diffusion amplifier that converts the charges transferred from 22 into a voltage signal and outputs the voltage signal.

FIG. 4 shows the details of the pixel section.
(A) shows the cross-sectional structure of the pixel portion, and (b) shows the potential profile.

As shown in the figure, a vertical overflow drain is used as a mechanism of the anti-blooming and electronic shutter. In addition, the substrate potential is usually an appropriate saturation charge amount and a potential V at which anti-blooming functions appropriately.
It is adjusted to sub (DC). And further ΔV
When the sub pulse is applied, the signal charges already accumulated in the PD can be discarded.

FIG. 5 is a timing chart of the vertical transfer pulses ΦV1 to ΦV4 and the electronic shutter pulse ΦVsub immediately before the charge is read from the PD to the VCCD and immediately after the charge is read from the next PD to the VCCD. Is usually added during the horizontal blanking period.

Time from the last electronic shutter pulse to the next PD to VCCD charge read pulse in the period (1V or one field) from the PD to VCCD charge read pulse to the next PD to VCCD charge read pulse. te is the accumulation time (exposure time or shutter speed).

Therefore, when the electronic shutter is used for exposure control, the electronic shutter pulse from the charge read pulse from the PD to the VCCD is normally controlled. That is, the brightness level information from the brightness detection circuit 12 is compared with the reference brightness level, and if the obtained brightness level is higher than the reference brightness level, the TG 4 is instructed to shorten the exposure time and the electronic shutter pulse is output. Is increased (the number of charge read pulses from PD to VCCD increases and the exposure time shortens). Conversely, if the obtained brightness level is lower than the reference brightness level, the TG 4 is instructed to lengthen the exposure time, and the number of electronic shutter pulses is reduced. By such a feedback operation, the exposure amount is maintained at an appropriate amount.

[0018]

However, the conventional image pickup apparatus as described above has the following problems particularly in the exposure control.

(1) When a mechanical aperture meter or a motor is mounted, the volume and weight of the camera increase and the power consumption increases. This is fatal in the type of digital camera which is powered by a computer.

(2) Since the video rate is limited, the exposure time is 1/60 sec at maximum and 1/5000 sec at minimum.
However, if the exposure is adjusted only by controlling the exposure time, it cannot withstand actual use. The exposure adjustment range can be increased by preparing two or three fixed apertures and making them switchable, but this is not sufficient. Particularly on the low brightness side, if the exposure time can be increased only up to 1/60 sec, the minimum illuminance of the subject as a camera becomes high, which makes it difficult to shoot indoors.

(3) Therefore, on the low brightness side, the gain of the amplifier for amplifying the output signal of the image pickup device is set to 6 dB to 18 dB.
Although it can be improved to some extent, this results in S / N.
The ratio increases, resulting in a poor image.

(4) When the exposure amount is adjusted by the electronic shutter, the electronic shutter pulse 1 is set on the short time side (high brightness side).
The ratio of output change due to increase / decrease of emission becomes high and the adjustment amount becomes rough. (Since the electronic shutter pulse is issued in the horizontal synchronization period so as not to add noise to the image signal, a pulse is added every horizontal period, On the side, the ratio of one horizontal period to the total exposure time is high).

The present invention has been made in view of the above problems, and an object thereof is to obtain an image pickup apparatus which has a wide luminance range capable of photographing, does not require aperture adjustment, and consumes little power.

[0024]

An image pickup apparatus according to the present invention is configured as follows.

(1) An image pickup device for converting an optical image of a subject into an electric signal, a signal processing circuit for processing an output signal of the image pickup device to generate a predetermined image signal, and the image pickup device and the signal processing circuit. A timing signal generating circuit for generating a timing signal necessary for operation and a control means for arbitrarily variably controlling the frequency of an input clock serving as a reference of the timing signal generating circuit are provided.

(2) An image pickup device for converting an optical image of a subject into an electric signal, a signal processing circuit for processing an output signal of the image pickup device to generate a predetermined image signal, and the image pickup device and the signal processing circuit. A timing signal generating circuit that generates a timing signal necessary for operation, and a control unit that controls the amount of light of an optical image incident on the image sensor by changing the frequency of an input clock that is a reference of the timing signal generating circuit. It was

(3) In the image pickup device of the above (2), the control means lowers the frequency of the input clock serving as the reference of the timing signal generation circuit when the light quantity of the optical image when entering the image pickup element is small.

(4) In the image pickup device of (2) or (3) above, the control means increases the frequency of the input clock serving as the reference of the timing signal generation circuit when the light quantity of the optical image incident on the image pickup element is large. I did it.

(5) An image sensor for converting an optical image of an object into an electric signal, a signal processing circuit for processing an output signal of the image sensor to generate a predetermined image signal, and the image sensor and the signal processing circuit. A timing signal generating circuit that generates a timing signal necessary for operation, and a control unit that controls the amount of light of an optical image incident on the image sensor by changing the frequency of an input clock that is a reference of the timing signal generating circuit. Further, the image pickup device has an electronic shutter function, and the control means controls the electronic shutter function of the image pickup device by changing a frequency of an input clock serving as a reference of the timing signal generating circuit so as to enter the image pickup device. The light quantity of the optical image is controlled.

(6) In the image pickup device of the above (5), the control means lowers the frequency of the input clock which is the reference of the timing signal generating circuit when the brightness of the subject is lower than a predetermined value.

(7) In the image pickup device according to (5) or (6), the control means increases the frequency of the input clock which is the reference of the timing signal generating circuit when the brightness of the subject is higher than a predetermined value. .

(8) An image sensor for converting an optical image of an object into an electric signal, a signal processing circuit for processing an output signal of the image sensor to generate a predetermined image signal, and the image sensor and the signal processing circuit. A timing signal generating circuit that generates a timing signal necessary for operation, and a control unit that controls the amount of light of an optical image incident on the image sensor by changing the frequency of an input clock that is a reference of the timing signal generating circuit. The image pickup device has an electronic shutter function of removing the signal charge of the pixel by applying a high-potential pulse to the substrate, and the control means controls the frequency of the input clock serving as the reference of the timing signal generation circuit. By changing the electronic shutter function of the image sensor, the light amount of the optical image incident on the image sensor is controlled.

(9) In the image pickup apparatus according to the above (8), the control means lowers the frequency of the input clock serving as the reference of the timing signal generation circuit when the electronic shutter pulse of the image pickup element becomes a predetermined number or less.

(10) In the image pickup device according to (8) or (9), the control means raises the frequency of the input clock which is the reference of the timing signal generation circuit when the electronic shutter pulse of the image pickup element exceeds a predetermined number. I chose

[0035]

1 is a block diagram showing the configuration of an embodiment of the present invention, showing the internal configuration of a digital camera connected to a computer, and the same reference numerals as those in FIG. 2 denote the same components. There is.

In FIG. 1, 1 is an optical lens for forming an optical image of a subject, and 2 is an optical diaphragm, which is a fixed diaphragm. Reference numeral 3 denotes an image pickup element for converting an optical image of an object into an electric signal, and 4 denotes a TG for generating a timing signal necessary for the operation of the image pickup element 3 and the like, and the image pickup signal processing circuit 10 is a digital processing circuit here.

Reference numeral 5 is an image pickup element drive circuit, 6 is a noise eliminating CDS circuit, 8 is a clamp circuit for fixing a black level, and 9 is a circuit.
Is an A / D converter for converting an analog signal into a digital signal, 10 is an image pickup signal processing circuit for processing an output signal of the image pickup device 3 to generate a predetermined image signal, and 11 is an operation of the image pickup signal processing circuit 10. SSG (timing signal generation circuit) that generates a necessary timing signal (synchronization signal), 1
2 is an interface (I / F) circuit, 13 is a brightness level detection circuit, 14 is a system controller for controlling the whole,
Reference numeral 15 is an oscillator for generating a basic clock, 17 is an oscillator 1
It is a frequency divider that changes the basic clock from 5 to the reference clock of an arbitrary frequency by the instruction of the syscon 14.

Here, the syscon 14 and the frequency divider 17 are provided.
Constitutes a control means for arbitrarily variably controlling the frequency of the input clock serving as the reference of TG4 and SSG11,
By changing the frequency of the input clock, the illuminance (light amount) of the optical image incident on the image sensor 3 is controlled. At that time, when the illuminance of the optical image incident on the image sensor 3 is low (the amount of light is small), the frequency of the input clock serving as the reference of the TG 4 and the SSG 11 is lowered, and the illuminance of the optical image incident on the image sensor 3 is high ( When the light intensity is large) TG4 and SS
The frequency of the input clock that is the reference of G11 is increased.

When the image pickup device 3 has an electronic shutter function, the above-mentioned control means are TG4 and SSG1.
The electronic shutter function of the image pickup device 3 is controlled by changing the frequency of the input clock serving as the reference of 1. At this time, if the brightness of the subject is lower than a predetermined value (control of the illuminance of the optical image incident on the image sensor 3 becomes impossible), TG4
And when the frequency of the input clock that is the reference of the SSG 11 is lowered and the brightness of the subject is higher than a predetermined value (the illuminance of the optical image incident on the image sensor 3 cannot be controlled), TG
4 and the frequency of the input clock serving as the reference of the SSG 11 is increased.

When the image pickup device 3 has an electronic shutter function of removing the signal charge of the pixel by applying a high potential pulse to the substrate, the above-mentioned control means is the same as the above-mentioned TG4 and TG4. The electronic shutter function of the image sensor 3 is controlled by changing the frequency of the input clock that is the reference of the SSG 11, and at this time, if the electronic shutter pulse of the image sensor 3 becomes an arbitrary predetermined number or less, TG4 and SSG
The frequency of the input clock serving as the reference of No. 11 is lowered, and the frequency of the input clock serving as the reference of TG4 and SSG11 is increased when the number of electronic shutter pulses of the image sensor 3 becomes an arbitrary predetermined number or more.

Next, a method of adjusting the exposure amount in this embodiment will be described. As this adjusting method, the method of controlling the accumulation time by changing the number of pulses of the electronic shutter shown in the conventional example is adopted.

The frequency of the output clock from the frequency divider 17 of FIG. 1 is set to fs [Hz] which is normally used. However, since the digital camera for a computer is not restricted by the video signal standard, it is not necessarily the reference clock frequency fv [Hz] required to make the timing for satisfying the video signal standard. Therefore, fs is arbitrarily determined according to the purpose of use of the camera, specifications, and the like.

TG4 and SSG depending on the frequency fs
When photographing is performed under the condition that 11 is driven, even if the electronic shutter of the image sensor 3 is set to the maximum exposure time (no electronic shutter pulse), only an exposure amount less than or equal to the proper exposure amount is obtained, that is, from the brightness detection circuit 12. If the information of the luminance level is lower than the reference luminance level, the syscon 14 commands the frequency divider 17 to halve the output frequency, and the frequency divider 17 outputs a pulse of fs / 2 [Hz]. (Needless to say, the outputs of TG4 and SSG11 all have a doubled cycle, and therefore HD, VD, and the interval between electronic shutter pulses ΦVsub also doubled).

Then, TG4, SSG with the above clock
Under the condition that 11 is driven, the exposure amount is adjusted again by controlling the electronic shutter. At this time, if fs / 2 [H
z], even if the maximum exposure time is reached, if the exposure amount less than the proper exposure amount is obtained, the output frequency of the frequency divider 17 is further set to 1/2 fs / 4 [Hz]. Commands the frequency divider 17.

By controlling in this manner, it is possible to realize a camera with a wide range of subject luminance that can be photographed without providing a mechanical diaphragm for adjusting the exposure amount in an analog manner. Further, since the gain of the amplifier circuit is not increased, the S / N of the photographed image of the low-luminance subject is not deteriorated, and the amplifier circuit for amplification at low luminance becomes unnecessary.

Here, in the above method, it is assumed that the clock is constantly switched in the case of a subject whose brightness is near the switching of the output clock of the frequency divider 17. Therefore, instead of changing the clock frequency when the exposure amount below the proper exposure amount is obtained even when the electronic shutter is set to the maximum exposure time, the clock frequency is switched when the electronic shutter pulse becomes n or less. Thus, the exposure control in the vicinity of the switching of the clock frequency and the brightness can be made smooth.

Next, the exposure control on the high brightness side will be described. In the shooting under the condition that the TG4 and the SSG11 are driven by the above-mentioned frequency fs, when the exposure amount more than the proper exposure amount is obtained even if the electronic shutter is set to the minimum exposure time (the maximum number of electronic shutter pulses), that is, the brightness When the brightness level information from the detection circuit 12 is higher than the reference brightness level, the syscon 14 commands the frequency divider 17 to double the output frequency, and the frequency divider 17 outputs a pulse of 2 · fs [Hz]. Is output.

Then, with this clock, TG4, SSG1
Under the condition that 1 is driven, the exposure amount is adjusted again by controlling the electronic shutter. At this time, if the exposure amount is not less than the proper exposure amount even at 2 · fs [Hz], the value is further doubled to 4 · fs [Hz].

By controlling in this way, it is possible to realize a camera with a wider range of subject illuminance that can be photographed. Also,
Since the clock frequency is increased, the interval between the electronic shutter pulses is shortened, the amount of change in the exposure amount due to the increase or decrease of one electronic shutter pulse is also reduced, and the accuracy of the exposure amount control for a high-luminance subject can be increased. .

Here, in the exposure control on the high brightness side, the amount of change in the exposure amount becomes large when the number of electronic shutter pulses is increased or decreased in the vicinity of the maximum number of electronic shutter pulses.
It becomes difficult to adjust the exposure amount. Therefore, if the switching of the output clock frequency is performed when the number of electronic shutter pulses is m or more, it is possible to eliminate the luminance band in which the exposure adjustment is rough.

As described above, by changing the basic clocks of the TG4 and SSG11 as a means of automatic exposure control (AE), a digital camera with no aperture (or fixed aperture) having a wide photographic brightness range is realized. be able to.

It should be noted that, although the above-mentioned clock frequency switching has been described in the case of a positive multiple, it is also possible to control the exposure amount with high accuracy by making the frequency switching more fine. Exposure control is also possible, which controls both the clock frequency and the clock frequency.

In some cases, it may be more effective to make the clock frequency switching interval rougher than in the above case.
If the appropriate clock frequency switching width, maximum clock frequency, and minimum clock frequency are properly set in consideration of the purpose of use of the camera, the characteristics of the image pickup element 3, and the characteristics of other circuit systems, it is a camera without a diaphragm, A camera capable of shooting a wide range of subject brightness can be realized.

Although the fixed diaphragm has been described in the embodiment, a plurality of fixed diaphragms (two or three) are prepared and switched to further widen the photographable subject luminance range.

[0055]

As described above, according to the present invention,
Since the control means for variably controlling the frequency of the input clock which is the reference of the timing signal generating circuit for generating the timing signal necessary for the operation of the image sensor and the signal processing circuit is provided, the incidence of the image sensor by changing the input clock frequency. The amount of light can be controlled, the brightness range that can be photographed is widened, aperture adjustment is not required, and power consumption is small.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional example.

FIG. 3 is an explanatory diagram showing a configuration of an image sensor.

FIG. 4 is an explanatory diagram showing details of a pixel portion of an image sensor.

FIG. 5 is a drive timing diagram of the image sensor

[Explanation of symbols]

 1 Optical Lens 2 Optical Aperture 3 Image Sensor 4 Timing Signal Generation Circuit 5 Image Sensor Drive Circuit 9 A / D Converter 10 Imaging Signal Processing Circuit 11 Synchronous Signal Generation Circuit (Timing Signal Generation Circuit) 14 System Control Circuit (Control Means) 15 Oscillator 17 frequency divider (control means)

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Takeshi Watanabe 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Masayoshi Sekine 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Yuji Koide 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (10)

[Claims] 1. An image sensor for converting an optical image of a subject into an electric signal, a signal processing circuit for processing an output signal of the image sensor to generate a predetermined image signal, and operations of the image sensor and the signal processing circuit. An image pickup apparatus comprising: a timing signal generating circuit for generating a timing signal necessary for the above; and control means for arbitrarily variably controlling the frequency of an input clock serving as a reference of the timing signal generating circuit. 2. An image pickup device for converting an optical image of a subject into an electric signal, a signal processing circuit for processing an output signal of the image pickup device to generate a predetermined image signal, and operations of the image pickup device and the signal processing circuit. A timing signal generating circuit for generating a timing signal necessary for the above, and a control means for controlling the light amount of the optical image incident on the image pickup device by changing the frequency of the input clock which is the reference of the timing signal generating circuit. An imaging device characterized by the above. 3. The image pickup apparatus according to claim 2, wherein the control means lowers a frequency of an input clock which is a reference of the timing signal generating circuit when the light quantity of the optical image when entering the image pickup element is small. 4. The image pickup apparatus according to claim 2, wherein the control means raises the frequency of the input clock serving as the reference of the timing signal generating circuit when the light quantity of the optical image incident on the image pickup element is large. . 5. An image sensor for converting an optical image of a subject into an electric signal, a signal processing circuit for processing an output signal of the image sensor to generate a predetermined image signal, and operations of the image sensor and the signal processing circuit. A timing signal generating circuit for generating a timing signal necessary for the, and a control means for controlling the light amount of the optical image incident on the image sensor by changing the frequency of the input clock that is the reference of the timing signal generating circuit, Further, the image pickup device has an electronic shutter function, and the control means controls the electronic shutter function of the image pickup device by changing the frequency of an input clock serving as a reference of the timing signal generating circuit, thereby making the optical element incident on the image pickup device. An image pickup apparatus characterized by controlling the light quantity of an image. 6. The image pickup apparatus according to claim 5, wherein the control means lowers the frequency of the input clock serving as a reference of the timing signal generation circuit when the brightness of the subject is lower than a predetermined value. 7. The image pickup apparatus according to claim 5, wherein the control means increases the frequency of the input clock serving as the reference of the timing signal generating circuit when the brightness of the subject is higher than a predetermined value. 8. An image sensor for converting an optical image of a subject into an electric signal, a signal processing circuit for processing an output signal of the image sensor to generate a predetermined image signal, and operations of the image sensor and the signal processing circuit. A timing signal generating circuit for generating a timing signal necessary for the, and a control means for controlling the light amount of the optical image incident on the image sensor by changing the frequency of the input clock that is the reference of the timing signal generating circuit, Moreover, the image pickup device has an electronic shutter function of removing the signal charge of the pixel by applying a high potential pulse to the substrate, and the control means changes the frequency of the input clock which is the reference of the timing signal generation circuit. An image pickup apparatus characterized by controlling the electronic shutter function of the image pickup element to control the light amount of the optical image incident on the image pickup element. 9. The image pickup apparatus according to claim 8, wherein the control means lowers a frequency of an input clock which is a reference of the timing signal generating circuit when the electronic shutter pulse of the image pickup element becomes equal to or less than a predetermined number. 10. The image pickup apparatus according to claim 8, wherein the control means raises the frequency of the input clock serving as the reference of the timing signal generating circuit when the electronic shutter pulse of the image pickup element exceeds a predetermined number.