JPH0678222A - Ccd camera and its driving method - Google Patents

Abstract

PURPOSE:To use the same optical shutter as a conventional one and to reduce a smear image essentially without high speed transmission by driving a semiconductor charge coupled device string at speed less than reference driving speed in most period until a field shift is performed after the optical shutter is opened. CONSTITUTION:A stroboscopic unit 15 makes a xenon lamp 17 emit light corresponding to a control signal. A timing circuit 11 generates a various kinds of timing signals, and supplies them to a drivier circuit 4 and a signal processing circuit 5, etc. A discrimination circuit 12 decreases the driving speed of a vertical charge transfer path in a period until the field shift is performed after the optical shutter is opened by controlling the driver circuit 4 based on a shutter driving signal or stroboscopic timing signal, and a field shift signal, etc. In other words, the output of a slow speed driver circuit 4b is set as that of the driver circuit 4. After the field shift is performed, the output of a reference driver circuit 4a is set as that of the driver circuit 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device and its driving method, and more particularly to a semiconductor photodiode as a photoelectric conversion element and a semiconductor charge coupled device (CC) as a charge transfer element.
The present invention relates to a CCD camera using D) and its driving method.

[0002]

2. Description of the Related Art As a solid-state image pickup device, a CCD transfer type is known. For example, a large number of photodiodes are arranged vertically and horizontally to form a pixel matrix. A vertical charge transfer path (VCCD) is formed near each photodiode row of this pixel matrix, and a horizontal charge transfer path (HCCD) is formed adjacent to the end of each VCCD. The charges accumulated in the photodiode according to the incident image are read out through the vertical charge transfer path and the horizontal charge transfer path.

When the amount of light in the outside world is insufficient, or when the amount of light in the outside world is sufficient, but when the amount of light in the main subject is insufficient due to backlight or the like, a strobe is used to supplement the necessary amount of light.
Since the strobe emits light in an extremely short period of time, its light intensity is high.

When light is reflected on a glass window when a strobe is used, considerably strong light enters the CCD adjacent to the photodiode and so-called smear occurs. Even when the strobe is not used, strong light is incident, and smear occurs when charge is generated in the CCD.

In CCD cameras, the CCD is usually
It is always driven. The charges accumulated in the photodiode are field-shifted from the photodiode to the VCCD via the transfer gate at a predetermined timing.
In the case of strobe exposure, a predetermined time substantially equal to the shutter speed elapses from the strobe light emission until the accumulated charge is transferred to the VCCD.

The smear image induced in the VCCD moves within the VCCD within this time. When the true image charge stored in the photodiode is field-shifted to the VCCD, the smear image induced in the VCCD is VCC.
It has moved to a different position in D. For this reason, the true image and the smear image appear on the screen with their positions shifted, and an unsightly screen is generated.

Generation of a smear image will be further described with reference to FIG. FIG. 7A schematically shows a state of the CCD camera at the time of image pickup. A large number of photodiodes PD are arranged in a matrix, and a vertical charge transfer path VCCD is formed close to each column of the photodiodes PD.
And a transfer gate TG.

It is assumed that strong light is incident on the upper center of the image pickup screen, and not only the actual image R in the photodiode PD, but also light is incident on the adjacent vertical charge transfer path VCCD to generate a smear image S. At this point, the smear image S is generated at the same position as the real image R. However, since the vertical charge transfer path VCCD is transfer-driven, the smear image S is sequentially transferred downward in the vertical direction.

FIG. 7B shows a state in which the charges of the real image R accumulated in the photodiode PD are field-shifted to the charge transfer path VCCD. The charges of the real image R accumulated in the photodiode PD are shifted to the vertical charge transfer path VCCD via the transfer gate TG.

At this time, it is assumed that the smear image S generated on the vertical charge transfer path VCCD has been transferred to the lower center of the image pickup screen. Then, the smear image S is displayed at a position different from the actual image R.

FIG. 8A is a timing chart showing the temporal relationship between the drive signals of the CCD camera. The vertical synchronization signal VD is a pulse signal that rises every vertical scanning period. Following the vertical synchronization signal VD, a field shift signal FS for reading charges from the photodiode PD to the vertical charge transfer path VCCD is generated.

The optical shutter drive signal is supplied at a predetermined point in the vertical scanning period (before the exposure time from the field shift signal FS).
Open the optical shutter to start exposure. Although this optical shutter controls the timing of starting exposure,
The timing of ending the exposure is assumed to be performed by the field shift signal FS.

With such a structure, an optical shutter with low accuracy can be used, and the cost of the CCD camera can be reduced. That is, the exposure time is the time from the opening of the optical shutter to the field shift.

When the strobe is made to emit light, the strobe light emission timing signal rises immediately after the optical shutter is opened to make the strobe emit light. The strobe flash time is as short as 1 msec, for example, and occupies only a part of the exposure time. Furthermore, the initial light intensity of the strobe flash time is strong.

For example, the exposure time (shutter speed) is 1 /
In the case of 250 seconds, the exposure time is about 4 msec, so the strobe flash time is about 1/4 of the exposure time. Since the required amount of light is all generated within this limited time, the light intensity is high and smear is likely to occur.

It is assumed that the image of the subject has a bright spot at the center, as shown in FIG. 8 (B). When this subject is photographed with strobe exposure, it takes, for example, about 3 before the field shift is performed after the strobe emits light.
The time of msec elapses. During this time, the smear image in the VCCD is transferred downward, and when the real image is field-shifted, the positions of the real image and the smear image are considerably displaced.

Therefore, when the read image signal is displayed, it becomes as shown in FIG. Since the signals transferred downward from the VCCD are sequentially displayed from the upper part of the display screen, the smear image S is displayed above the actual image R.

FIG. 8D shows a smear image when there is a strong illuminant at one point in the screen during normal exposure without using a strobe. In this case, since a smear image is continuously generated at a certain position of the VCCD, the smear image generated during the period from the start of exposure to the field shift is such that the smear image S to the actual image R in FIG. Smear image S
It becomes 1.

Further, even after the field shift, the shutter is still open, and smear images continue to be generated at the same spot on the VCCD. Therefore, the smear image S2 also appears in the portion following the actual image R.

As described above, when the smear image is added to the actual image, the image quality is deteriorated. Therefore, it is desired to prevent smear images. In particular, smear images tend to occur during strobe exposure, and their prevention is desired.

FIG. 9 is a diagram for explaining a conventionally proposed method for preventing smear images. The vertical synchronization signal VD, the field shift signal FS, the optical shutter drive signal, and the strobe light emission signal are the same as those shown in FIG. Hereinafter, the A method and the B method for preventing smear will be described.

In the A system, the sweep-out drive of the VCCD is performed at high speed immediately before the field shift signal FS rises, and after the field shift, the read image signal is transferred at high speed. According to such a reading method, the charge of the VCCD is swept out before the image signal is read to the VCCD, so that the smear image accumulated in the VCCD disappears.

In the B method, after image pickup, the next vertical scanning period is set as the sweep-out driving period of the VCCD, and the signal charges are read out in the next vertical scanning period. In this case, it is not necessary to drive the VCCD at high speed. If the optical shutter is opened during the sweeping drive period of the VCCD, charges are accumulated subsequently to the photodiode, so the exposure time needs to be defined only by the optical shutter. For example, an optical shutter such as a focal plane shutter that can control both start and end of exposure is used.

[0024]

When strong light enters the CCD camera, smear occurs in the VCCD. If this smear is output as it is as an image signal, the image becomes unsightly.

If the above-mentioned method A is adopted to prevent smear, it is necessary to perform high-speed sweep-out transfer of VCCD after the start of exposure and before the field shift.
Therefore, the maximum shutter speed is limited by the time required for the sweep drive of the VCCD.

According to the above-mentioned method B, the exposure time needs to be controlled only by the optical shutter, which requires an accurate and expensive optical shutter. An object of the present invention is to provide a CCD camera and a driving method thereof which can use the same optical shutter as the conventional one without performing high-speed transfer and can substantially reduce the unpleasantness of smear images. Is.

[0027]

According to a method of driving a CCD camera of the present invention, charges accumulated in photodiodes arranged in a matrix with an optical shutter opened are stored in a CCD.
A method of driving a CCD camera that field-shifts to a column and reads out an image signal, after an optical shutter is opened,
It is characterized in that the CCD array is driven at a driving speed lower than the standard driving speed for at least most of the period until the field shift is performed.

[0028]

Most of the period after the optical shutter is opened until the field shift is performed, the CCD transfers at a driving speed slower than the normal standard driving speed. Therefore, even when the field shift is performed, the smear image generated at the beginning of the exposure time has not moved much. Therefore, the real image and the smear image appear at positions close to each other, and the unsightlyness of the screen is substantially reduced.

[0029]

1 shows the structure of a CCD camera according to an embodiment of the present invention. Lens 1, iris 2 on the optical axis of the camera
Are arranged and driven by motors M1 and M2, respectively, to adjust the focal length and the exposure amount.

The iris 2 also has a light-shielding portion and also has a function of an optical shutter. The image of the subject focused by the lens 1 is formed on the image plane of the CCD image pickup chip 3. The CCD imaging chip 3 has a photodiode matrix, a transfer gate, a vertical charge transfer path, a horizontal charge transfer path, and the like, is driven by the driver circuit 4, and the read image signal is supplied to the signal processing circuit 5.

The driver circuit 4 includes a standard driver circuit 4a for driving the vertical charge transfer path at the standard driving speed, a low speed driver circuit 4b for driving the vertical charge transfer path at a slower driving speed lower than the standard driving speed, and a transfer from the photodiode. It includes a field shift driver circuit 4c for shifting accumulated charges to a vertical charge transfer path via a gate and a horizontal driver circuit 4e for driving a horizontal charge transfer path.

The signal processing circuit 5 processes the read charge signal in an analog manner and, when magnetically recording on a magnetic tape or the like, directly records the image signal on the magnetic recording medium 13.

The signal processing circuit 5 further includes an analog / digital converter 6, which converts the analog signal into a digital signal and outputs the digital signal. This digital signal is supplied to the image signal processing circuit 7 and undergoes processing such as data compression by the numerical operation processor 8 and the like to generate a digital image signal.
This digital image signal is recorded in, for example, the memory card 9 or the like.

The system control unit 14 has a C
This circuit controls the entire CD camera and generates various control signals. The switch circuit 19 is a circuit including switches such as the first contact S1, the second contact S2, and the power switch S3 of the release switch.

The strobe unit 15 includes a strobe module 16, a xenon lamp 17, a light receiving diode 18, and the like, and causes the xenon lamp 17 to emit light in response to control signals from the system control unit 14, such as strobe timing and strobe light emission amount.

The timing circuit 11 generates various timing signals and supplies them to the driver circuit 4, the signal processing circuit 5 and the like. The determination circuit 12 controls the driver circuit 4 to control the drive speed of the vertical charge transfer path during the period from the opening of the optical shutter to the field shift based on the shutter drive signal, the strobe timing signal, the field shift signal, or the like. Lower. That is, the output of the low speed driver circuit 4b is used as the output of the driver circuit 4. After the field shift, the output of the standard driver circuit 4a is used as the output of the driver circuit 4.

Incidentally, what is important here is that most or all of the exposure time is driven at a low speed, and then the standard drive is performed after the field shift. The low speed drive may start earlier.

2 and 3 are diagrams for explaining the driving of the vertical charge transfer path. FIG. 2A shows a vertical charge transfer path (VC
6 is a timing chart showing a waveform of a (CD) drive signal. The unit of the time axis (horizontal axis) changes between standard drive and low speed drive.

FIG. 2B is a schematic band diagram showing the movement of charges. , I correspond to the timings a, b, ... i in FIG. 2 (A). The CCD imaging chip shown in FIG. 1 has photodiodes arranged in rows and columns and vertical charge transfer paths (VCCD) formed adjacent to each photodiode row. The electrodes of the VCCD are grouped in groups of four from the upper side to the lower side, and V1, V2, V
3 and V4 are displayed. Drive signal φ to these electrodes
V1, φV2, φV3, and φV4 are applied.

In FIG. 2 (B), the charges at V1 at the timing a are moved to V3 at the timing i, and all the charges move downward.
FIG. 3 is a timing diagram illustrating drive speed modulation. The vertical drive signal VD is a pulse signal that rises at the beginning of each vertical scanning period. The drive signal φV schematically represents a signal applied to each column electrode of the VCCD. At the beginning of each vertical scanning period V, a high level is taken to form the field shift signal FS, and then the VCCD is driven at the standard driving speed. A vertical line shift pulse is input every horizontal scanning period H. 1H
The signal waveform inside is shown in FIG.

After the predetermined timing within the vertical scanning period V, the cycle of the drive signal φV becomes longer, and in the illustrated case, the cycle is 3
Is doubled. Therefore, the driving speed of VCCD is 1 /
It will be 3. This low speed drive continues until the end of the vertical scanning period. In addition, the drive speed of low speed drive can be set arbitrarily,
In terms of the circuit, it is preferable that it is an integral fraction of the vertical scanning drive speed.

FIG. 4 is a schematic diagram showing the charge transfer of the vertical charge transfer path within the exposure time by the strobe exposure.
In FIGS. 4A and 4B, a large number of photodiodes P
Ds are arranged in a matrix. A vertical charge transfer path VCCD is formed adjacent to each column of the photodiodes PD. A transfer gate TG is arranged between the photodiode PD and the vertical charge transfer path VCCD to control charge transfer from the photodiode PD to the vertical charge transfer path VCCD.

The VCCD is driven from the upper side to the lower side at a standard driving speed prior to exposure. An exposure start signal is given, the optical shutter is opened and exposure is started, and the driving speed of the VCCD is reduced from the standard driving speed to the low speed as shown in FIG. 4 (A).

At the same time when the exposure is started, the strobe flashes and the electric charge R of the actual image is accumulated in the photodiode PD.
It is assumed that the smear image S also occurs in the VCCD. This VC
The smear image S in the CD slowly moves downward in the figure in accordance with the low speed transfer of the vertical charge transfer path VCCD.

When the exposure time elapses, field shift is performed as shown in FIG. When the field shift is performed, the charges of the real image R accumulated in the photodiode PD are transferred to the VCCD. At this time,
The smear image S transferred to the VCCD is at a position not far from the original position because the driving speed of the VCCD has been switched to a low speed. Therefore, the real image R and the smear image S exist in a range in which the observer can almost see each other. When such an image signal is displayed on the display, the smear image S is prevented from being displayed separately from the actual image R, and the adverse effect of the smear image is substantially reduced.

After the field shift, the transfer speed of the VCCD is returned to the standard drive speed, and normal charge transfer is performed. FIG. 5 shows a flow chart of control for realizing such charge transfer. When the power of the CCD camera is turned on in step A1, step A
Proceed to step 2 and the system will be on standby. The VCCD starts the transfer at the standard drive speed. Then, in step A3, it is determined whether or not the first contact S1 of the release switch is turned on.

NO when the switch S1 is not turned on
Follow the arrow to return to step A2. If the switch S1 is on, the process proceeds to step A4 according to the YES arrow to start the operation of automatic exposure / automatic distance measurement (AE / AF).

Subsequently, in step A5, it is determined whether or not the AE / AF operation is completed. If not completed, the process returns to step A4 following the NO arrow. If the AE / AF operation is completed, the shutter speed, the exposure intensity, etc. are determined, so the flow advances to step A6 according to the YES arrow.

At step A6, it is determined whether or not the second contact S2 of the release switch is on. When the switch S2 is not turned on, the process returns to step A4 following the NO arrow. YES if switch S2 is on
Following the arrow, the process proceeds to step A7, the optical shutter is opened, and exposure is started.

Immediately following step A7, step A8 is immediately executed.
Is performed. That is, the driving frequency of the vertical charge transfer path VCCD is modulated at the same time as the exposure is started, and the low speed driving is performed. For example, the driving speed of the VCCD is reduced to 1/3 or less as compared with the standard driving. When performing flash photography, the flash is flashed immediately after the optical shutter is opened or after a short time. During the exposure time, the VCCD continues to drive at low speed.

Then, the process proceeds to step A9, and it is determined whether or not the exposure is completed. When the exposure is not completed,
Repeat step A9 according to the NO arrow. When the exposure is completed, follow the YES arrow to step A10.
Then, the drive speed of the vertical charge transfer path VCCD is returned to the standard drive speed.

Since the field shift is performed upon completion of the exposure, the field-shifted signal of the real image R is transferred in the VCCD at the standard driving speed and read out as an image signal via the horizontal charge transfer path HCCD. It

During the exposure time, since the VCCD is driven at a low speed slowly downward, the smear image S slowly moves downward. Due to the movement, the output image is prevented from being scratched, and the driving speed is reduced, so that the smear image is prevented from being largely separated from the actual image. When the field shift signal FS rises after the exposure time has elapsed, the real image R from the photodiode is read out and the VCCD is returned to the standard drive.

Since the VCCD is driven at a low speed during the exposure time, the smear image S is located close to the actual image R.
Therefore, the real image R and the smear image S are usually partially overlapped with each other, and the harmful effect of the smear image S is substantially reduced. The output image is generated as an inverted image of the image in the VCCD.

Whether or not the drive speed modulation for incorporating the low speed drive in the normal exposure is performed is arbitrary. The read image signal is recorded in a digital recording device such as a magnetic floppy disk or a memory card in the next step A11. In this way, the exposure operation is completed.

FIG. 6 is a timing chart showing an exposure operation performed according to the control flow chart shown in FIG. The vertical drive signal VD, the field shift signal FS, the shutter control signal, and the strobe light emission control signal are the same as those described in FIG.

That is, the vertical synchronizing signal VD is a pulse signal which rises every vertical scanning period. Vertical sync signal V
D from the photodiode PD to the vertical charge transfer path V
Field shift signal F for reading charge to CCD
S occurs.

The optical shutter drive signal is given at a predetermined point in the vertical scanning period (before the exposure time from the field shift signal FS).
Open the optical shutter to start exposure. Although this optical shutter controls the timing of starting exposure,
The timing of ending the exposure is assumed to be performed by the field shift signal FS. The VCCD has been standardly driven before exposure.

For example, when strobe light is emitted,
The exposure time t is preset and the field shift signal FS
The strobe is fired at a time point t which is before the rising timing of.

When the shutter is opened or the flash is emitted,
The VCCD is switched from the standard drive to the low speed drive, and the VCCD continues the low speed drive until the field shift signal FS falls. When the field shift signal FS falls, the VCCD returns to the standard drive again.

Under such control, the smear image in the VCCD behaves as shown in FIG. 6 (B).
When strobe light is emitted, a smear image in the VCCD is generated at the same position as the actual image. At this time, the VCCD is switched to the low speed drive, and the charges in the VCCD are slowly transferred. The smear image does not move much even after the exposure time elapses, and if the pattern is large to some extent, the smear image partially overlaps the actual image.

FIG. 6C shows the behavior of the smear image when the driving speed of the VCCD is modulated during the normal exposure. It is assumed that the irradiation intensity is high at one point on the screen and a smear image is generated.

At the start of exposure, the smear image S is generated at a position where the light intensity is high. Since the vertical charge transfer path VCCD is driven at a low speed after the start of exposure, the smear image generated at the fixed position is slowly stretched downward in the VCCD state to S1.

When the field shift is performed and the real image R is read out, the smear image S2 becomes a continuous form of the real image R. After that, transfer of standard drive speed is performed,
When the read image signal is displayed as an output image, an image like the right end in the figure is displayed. If the point with high light intensity has not disappeared, the smear image continues to be generated even at the time of the last standard drive, so the shape of S3 is also drawn below the actual image R.

In the case of normal exposure, the smear image has a wider form unless the driving speed of the VCCD is modulated. Therefore, the range in which the smear image is generated is reduced by the driving method described above.

It should be noted that the influence of the smear image is reduced as the speed at which the VCCD is driven at a low speed is low at least for most of the exposure time. However, if the VCCD is stopped at all, white scratches may occur. Therefore,
In order to reduce the influence of smear images, it is preferable to drive at a speed as low as possible within the range where the occurrence of white scratches can be prevented.

The present invention has been described above with reference to the embodiments.
The present invention is not limited to these. For example,
It will be apparent to those skilled in the art that various changes, improvements, combinations and the like can be made.

[0068]

As described above, according to the present invention,
Even if a smear image occurs during strobe exposure, the effect of the smear image can be reduced.

[Brief description of drawings]

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

FIG. 2 is a diagram illustrating vertical transfer driving in a VCCD of the CCD camera shown in FIG.

FIG. 3 is a diagram illustrating drive speed modulation of the CCD camera shown in FIG.

FIG. 4 is a schematic diagram showing movement of image charges in a VCCD.

FIG. 5 is a flowchart of control of a CCD camera.

FIG. 6 is a conceptual diagram for explaining an operation under the control of FIG.

FIG. 7 is a conceptual diagram for explaining a smear image according to a conventional technique.

FIG. 8 is a timing diagram and a conceptual diagram for explaining a smear image according to a conventional technique.

FIG. 9 is a timing diagram illustrating a smear image prevention technique according to a conventional technique.

[Explanation of symbols]

 1 Lens 2 Iris 3 CCD Imaging Chip 4 Driver Circuit 4a Standard Driver Circuit 4b Low Speed Driver Circuit 4c Field Shift Driver Circuit 5 Signal Processing Circuit 6 A / D Converter 7 Image Signal Processing Circuit 8 Numerical Operation Processor 11 Timing Circuit 12 Discrimination Circuit 14 System control unit 15 Strobe unit 16 Strobe module circuit 17 Xenon lamp 18 Photodiode R Actual image S Smear image t Exposure time

Claims (3)

[Claims] 1. The charge accumulated in photodiodes arranged in a matrix with an optical shutter opened is CC
CCD that field-shifts to column D and reads image signals
A method of driving a camera, characterized in that the CCD row is driven at a driving speed lower than a standard driving speed for most of the period after the optical shutter is opened until the field shift is performed. Driving method. 2. The driving method of a CCD camera according to claim 1, wherein the low driving speed is an integer fraction of a standard driving speed. 3. Photodiodes (PD) arranged in a matrix, CCD columns (VCCD) arranged in proximity to each column of the photodiodes, and light incident from the external environment selectively on the photodiodes (PD). An optical shutter (2) for transmission, a strobe unit (15) that can emit light after the optical shutter is opened, and the CCD array can be driven at a standard driving speed or a lower driving speed. Drive circuit (4a, 4b)
A discriminating circuit (12) for generating a signal for switching the drive speed of the drive circuit to a low drive speed by substantially starting the exposure time; and, after the exposure time elapses after the optical shutter is opened, accumulation in the photodiode. CCD camera having means (4c) for field shifting the generated charges to the CCD column.