JP3407223B2 - CCD camera and flash photography method of CCD 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 method for using a solid-state image pickup device, and more particularly to a stroboscopic image pickup method for a solid-state image pickup device using a semiconductor photodiode which is a photoelectric conversion element and a charge coupled device (CCD) which is a charge transfer element. .

[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.

Further, a vertical charge transfer path (VCCD) is formed adjacent to each photodiode row, and a horizontal charge transfer path (HCCD) is formed adjacent to the end of each VCCD. The charges accumulated in the photodiode by the incident light are read out through the vertical charge transfer path and the horizontal charge transfer path.

In order to read out and transmit all the charges accumulated in the photodiode at the same time, usually three or more transfer pulses for one pixel or one row are required. To realize transfer pulses of 3 phases or more per pixel, 3 per pixel
More electrodes are required, which is a disadvantage in terms of miniaturization.

An accordion transfer method has been proposed as a transfer method capable of transferring all pixel signals with two electrodes per pixel (PHILIPS TECHNICAL).
REVIEW Vol. 43, No. 1 / 2,198
6, A. J. P. Theuwissen and C.I. H.
L. Weijtens).

The applicant of the present invention has proposed a domino transfer method for performing similar charge transfer in a solid-state image pickup device including a photodiode matrix, a vertical charge transfer path and a horizontal charge transfer path. The drive signal is also four-phase drive similar to the interline CCD.

When the amount of light in the outside world is insufficient, or when the amount of light in the outside world is sufficient but the amount of light in the main subject is insufficient due to backlight or the like, a strobe is used to supplement the amount of light. If you use a strobe to reflect on glass, etc., a very strong light will enter the VCCD adjacent to the photodiode.
So-called smear occurs. When the peak flash time of the strobe is compared with the scanning time (V rate) of one screen,
Very short.

Since the CCD is transfer-driven, the smear image moves in the CCD. If the image signal is field-shifted from the photodiode to the CCD while the smear image is transferred in the CCD, the true image signal and the smear image overlap in the signal output as the image signal. Therefore, an unsightly screen is recorded.

Generation of a smear image will be described with reference to FIG. FIG. 5A schematically shows a state of the solid-state imaging device at the time of imaging. A large number of photodiodes PD are arranged in a matrix, a vertical charge transfer path VCCD is formed adjacent to each column of the photodiodes PD, and each photodiode PD is connected to each other by 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 the adjacent vertical charge transfer path VCCD is incident on the smear image S. At this point, the smear image S
Occurs at the same position as the real image R. However, since the vertical charge transfer path VCCD is transfer-driven, the smear image is sequentially transferred in the vertical direction.

FIG. 5B shows a state in which the charges of the real image R accumulated in the photodiode PD are field-shifted to the vertical charge transfer path VCCD. The charges of the real image R accumulated in the photodiode PD are transferred to the transfer gate TG.
Via the vertical charge transfer path VCCD.

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 as an image.

FIG. 6A is a timing chart showing the temporal relationship between the signals. The vertical drive signal VD is a pulse signal that rises every vertical scanning period. Following the vertical drive signal VD, a field shift signal FS for reading charges from the photodiode PD to the vertical charge transfer path VCCD is generated.

The period from one field shift signal FS to the next field shift signal FS represents the charge accumulation time during which charges are accumulated in the photodiode. In the middle of this charge accumulation time, the strobe is emitted as shown in the third row of FIG. The time from the strobe light emission timing to the end of the charge accumulation time is the time when the smear image is transferred in the vertical charge transfer path.

Field shift signal F after flash emission
When the charges accumulated in the photodiode by S are shifted to the vertical charge transfer path, the CCD output signal is as shown in FIG.
(A) As shown in the bottom row.

That is, the virtual image formed by the smear image S is first output, and the actual image signal (real image) R is output with a time delay corresponding to the time difference Δt from the strobe emission timing to the generation of the next field shift signal.

The signals output from the CCD form images on the monitor screen sequentially from above, so the display on the screen is as shown in FIG. 6 (B). That is, the virtual image S is displayed above the real image R. For example, scan lines 262.
When scanning one screen with 5 lines at 1/60 seconds, if the strobe emits light 1/125 seconds before the field shift signal,
The virtual image S is displayed above the real image R at a screen length of about ½.

In order to prevent the virtual image due to such smear, the vertical charge transfer path VCC is provided before the field shift.
It is sufficient to sweep out D. For example, the horizontal scanning line 1
When the number of pixels gradually increases, such as around 000,
If the sweeping out of the VCCD is performed before the field shift, the sweeping-out time is increased, the shutter speed on the high speed side is limited, and the shooting area is narrowed down, which makes it difficult to carry out. Also, depending on the type of solid-state imaging device,
In some cases, such a charge transfer path cannot be swept out.

[0019]

As described above,
If smear occurs in the vertical charge transfer path, a virtual image due to the smear will be displayed on the screen unless the vertical charge transfer path is swept out.

An object of the present invention is to improve the image quality by substantially reducing the virtual image due to smear generated by reflection or the like at the time of exposure with a strobe without sweeping out the vertical charge transfer path VCCD. It is to provide a flash driving method of.

[0021]

According to the stroboscopic photographing method for a CCD camera of the present invention, the strobe photographing is performed by a CCD camera which transfers the accumulated charges of photodiodes arranged in a matrix to a vertical transfer path (VCCD) and reads out an image signal. In the method, before the charge is transferred from the photodiode to the VCCD, the brighter the brightness detected by the brightness detection means for detecting the reflected light from the subject is, the light is emitted from the strobe at a timing earlier in time. It is characterized by A CCD camera according to the present invention includes photodiodes arranged in a matrix, a vertical charge transfer path (VCCD) for vertically transferring accumulated charges accumulated in the photodiodes, and brightness detection for detecting reflected light from a subject. Means, a strobe that emits light before the charge is transferred from the photodiode to the VCCD, and the brighter the time detected before the charge is transferred from the photodiode to the VCCD, the earlier the time. And a control means for causing the strobe to emit light at a timing.

[0022]

[Operation] By causing the strobe to emit light immediately before the field shift of the charges from the photodiode to the CCD column,
It is possible to prevent the smear image from being almost transferred in the CCD array during the time from strobe emission to field shift. If the transfer distance of the smear image is short enough not to cause a visual problem, the smear image on the screen will not be a visual problem.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view for explaining a strobe photographing method of a CCD camera according to an embodiment of the present invention. FIG. 1A schematically shows an image pickup screen at the time of image pickup.
(B) schematically shows an image pickup screen during field shift.

FIG. 1 (A) shows a state in which the strobe is made to emit light and an image is taken. Since strong light enters, not only the image signal of the real image R is accumulated in the photodiode PD, but also the smear image S is generated in the adjacent VCCD.

It is assumed that the field shift is performed immediately after strobe light emission (for example, after one horizontal period H). At that time,
As shown in FIG. 1B, the smear image moves only one row downward in the vertical charge transfer path VCCD.

Therefore, at the time when the charges are shifted from the photodiode PD to the vertical charge transfer path VCCD via the transfer gate TG, the positions of the real image signal R and the smear image signal S are slightly deviated,
It almost overlaps. The relationship between the real image R and the virtual image S due to smear in this case will be described in more detail with reference to FIG.

FIG. 2A shows a timing chart between each signal. The vertical drive signal VD is generated in each vertical scanning period, and then the vertical charge transfer path V is generated from the photodiode PD.
A field shift signal FS for performing field shift for reading out image charges is generated in the CCD. The period from the field shift signal to the next field shift signal is the charge accumulation time for accumulating charges in the photodiode.

Strobe light emission is performed immediately before the field shift signal FS rises, as shown in the third row of FIG. Therefore, the time from when the strobe emits light and smear occurs until the field shift is performed is extremely short.

Therefore, in the image signal transferred in the vertical charge transfer path, the real image R and the virtual image S due to smear are only slightly displaced. FIG. 2B shows a real image R and a virtual image S due to smear on the screen. Most of the real image R and the virtual image S due to the smear coincide with each other, and the virtual image S due to the smear is slightly shifted upward. Therefore,
Smear is rarely recognized independently, and image deterioration due to smear is reduced.

FIG. 3 schematically shows the structure of a CCD camera for performing such stroboscopic photography. Optical unit 1
Includes a lens 3 and a diaphragm 5. Light incident from the outside world
An image is formed on the image plane through the lens 3 and the aperture of the diaphragm 5. The lens 3 and the diaphragm 5 are driven by motors 7 and 9, respectively.

A CCD chip 11 including a photodiode and a CCD is arranged on the image plane to pick up an image. CCD
The chip 11 is driven by the CCD driving unit 13. The CCD drive unit 13 includes a CCD driver circuit 15 and a timing generation circuit 17 that controls the CCD driver circuit 15.

The output signal of the CCD chip 11 is supplied to the signal processing circuit 21. The signal processing circuit 21 is provided with a sensitivity setting amplifier 23, and performs sensitivity setting according to the exposure amount. The image signal processed by the signal processing circuit 21 is recorded in the recording circuit 25.

The operation of the entire CCD camera is controlled by the central processing unit CPU 27. A drive signal for driving the motor 7 for driving the lens 3 and the motor 9 for driving the diaphragm 5 is generated from the CPU 27, and a control signal for driving the CCD drive unit 13, for example, a shutter speed signal is supplied.

Further, from the CPU 27 to the sensitivity setting amplifier 23
Is supplied with a control signal for setting the circuit gain, and the signal processing circuit 21 supplies the CPU 27 with signals for automatic exposure and automatic focusing.

The CPU 27 also uses the flash unit 31.
A strobe emission amount and a strobe emission timing signal for controlling are supplied. The strobe unit 31 includes a light source 33, a strobe module 35 that drives the light source 33, a photodiode 37 that detects reflected light from a subject, and the like.

As shown in FIGS. 1 and 2, if the strobe is made to emit light immediately before the field shift signal FS, the strobe emission must be extinguished during the field shift depending on the light emission timing.

In such a case, the amount of light returning from the subject is reduced as compared with the case where the total amount of flash light emission is used. The CPU 27 controls the aperture, the shutter speed, the circuit gain, and the like based on the strobe light emission timing and the strobe light emission amount so as to obtain an optimum image signal.

FIG. 4 is a diagram for explaining the control performed by the CPU. CCD camera has about 1000 horizontal scanning lines
Suppose you have a book. FIG. 4A shows a flowchart of control. When photographing is performed, it is determined in step S1 whether or not strobe light emission is performed.

When strobe light emission is to be performed, the process proceeds to step S2 according to the YES arrow to determine the light emission timing. For example, in consideration of the fact that the background is often dark with respect to a low-illuminance subject, so that even a slight smear is noticeable, the light emission timing is before the number H of field shifts (for example, 1 to 4H, H is a horizontal scanning period). Set the flash to fire.

Also, when the background is bright such as during daytime synchro, slight smear is relatively unnoticeable, so the strobe light emission timing is a field shift, for example, 10.
Approximately 16 hours before. However, even in the daytime synchronization, when the upper part of the screen is dark, it is preferable to set the flash emission timing to be short as in the case of low illuminance.

From the visual point, there are 26 scanning lines in one field.
When there are about 2.5 lines, it is preferable that the strobe emission timing be performed at least within 16H before the field shift. Especially when the background is dark, it is preferable to perform the heating within 4 hours.

When the light emission timing is determined in step S2, the flow advances to step S3 to determine the strobe light emission amount and the light amount correction value. When the light emission timing is very close to the field shift, it is preferable to increase the strobe light emission amount. Since the strobe is extinguished at the time of field shift, the light amount correction value is determined according to the time from the strobe emitting light until extinguishing.

Then, in step S4, the shutter speed and aperture are determined. FIG. 4B is a graph showing changes over time in the typical strobe light emission amount and integrated light emission amount. The luminescence amount rises rapidly at the same time as the luminescence, and is about 0.
The peak value is reached in about 1 msec. After that, the light emission amount decreases, but the tail portion extends for 2 msec or more.

The integrated light emission amount reaches about half in about 0.3 msec, but thereafter, the increasing rate becomes gradually gentle,
It is about 87% in 0.7 msec. For example, when the integrated light emission amount is used at about 1/4 of the total light emission amount, in the case of correcting it by the aperture, it is sufficient to shoot with the aperture opened by 2 apertures more than usual.

Since the diaphragm is converted into the amount of light and changes by a factor of two, fine adjustment cannot be performed. In the next step S5, the circuit gain is determined, and fine adjustment that cannot be adjusted by the diaphragm is executed. In this way, the adjustment for stroboscopic light emission is completed, and the process proceeds to the shooting sequence.

In this way, immediately before the field shift,
By causing the strobe to emit light within 16H at the longest, the smear generated can be made unobtrusive.

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.

[0048]

As described above, according to the present invention,
Even if smear occurs in the vertical charge transfer path due to stroboscopic light emission, the virtual image due to the smear is arranged very close to the real image, so that deterioration of image quality is reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining a strobe photographing method of a CCD camera according to an embodiment of the present invention.

2A and 2B are schematic diagrams for explaining the photographing method of FIG. 1 and the result thereof.

FIG. 3 is a CCD for carrying out the embodiment shown in FIGS.
It is a block diagram which shows the structure of a camera.

4A and 4B are a flowchart and a graph for explaining control performed by the CCD camera of FIG.

FIG. 5 is a schematic diagram for explaining smear by stroboscopic photography according to a conventional technique.

FIG. 6 is a schematic diagram for explaining the flash photography in FIG. 5 and the result thereof.

[Explanation of symbols]

PD photodiode TG transfer gate VCCD vertical charge transfer path 1 Optical unit 3 lenses 5 aperture 7, 9 motor 11 CCD chip 13 CCD drive unit 15 CCD driver 17 Timing generation circuit 21 Signal processing circuit 23 Sensitivity setting amplifier 25 recording circuit 27 CPU 31 Strobe unit 33 light source 35 Strobe module 37 Photodiode

Claims (5)

(57) [Claims] 1. A method for transferring accumulated charges of photodiodes arranged in a matrix to a vertical transfer path (VCCD) and stroboscopically photographing with a CCD camera for reading out an image signal, wherein the charge is transferred from the photodiodes to VCCD. A strobe photographing method for a CCD camera, characterized in that the strobe is caused to emit light at a timing earlier in time as the brightness detected by the brightness detecting means for detecting the reflected light from the subject becomes brighter. 2. When the brightness detection unit determines that the brightness is bright, the flash light emission is 1 before field shift.
2. The strobe photographing method for a CCD camera according to claim 1, wherein the stroboscopic photographing method is performed from 0 horizontal scanning period to 16 horizontal scanning period. 3. The strobe of a CCD camera according to claim 1, wherein when the brightness detecting means determines that the strobe is dark, the strobe emits light before a field shift for one horizontal scanning period to four horizontal periods. How to shoot. 4. The stroboscopic photographing method for a CCD camera according to claim 1, wherein the strobe is extinguished during field shift. 5. Photodiodes arranged in a matrix, vertical charge transfer paths (VCCD) for vertically transferring the accumulated charges accumulated in the photodiodes, and brightness detection means for detecting reflected light from a subject. A strobe that emits light before the charge is transferred from the photodiode to the VCCD; and a brighter time detected by the detecting means before the charge is transferred from the photodiode to the VCCD, at a timing earlier in time. A CCD camera comprising: a control unit that causes the strobe to emit light.