JP2987457B2 - Imaging device - Google Patents

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, and more particularly to an image pickup apparatus having improved image quality.

[0002]

2. Description of the Related Art In general, in an image pickup apparatus having an electronic shutter function, unnecessary charges accumulated up to that time in all pixels of a photoelectric conversion unit are simultaneously discharged by a discharge pulse, and thereafter, an exposure corresponding to a desired shutter speed is performed. Exposure is performed by reading out the signal charges accumulated at the time with a readout pulse. If the signal charges of all the pixels are simultaneously read at the time of this reading, the reference potential in the device is fluctuated, and the remaining effective charges are left unread. Like that.

[0003] This will be described with reference to FIGS. FIG.
FIG. 2 is a schematic diagram showing a configuration of an interline CCD, in which photoelectric conversion units 11a, 11b, 11c, and 11 are two-dimensionally arranged.
, 11i, 11j, 11k, 11m,..., vertical transfer registers 12a, 12b,.
Transfer charges of these registers 12a, 12b,... Are collected in the horizontal transfer register 13 and sequentially output.

FIG. 4 is a block diagram of a conventional image pickup apparatus using the CCD image pickup device shown in FIG. 3 described above. The image pickup optical system 1 forms an object light on a light receiving surface of the CCD image pickup device 2 described below. A CCD image pickup device 2 for photoelectrically converting subject light transmitted through the optical system 1 into an electric signal; a camera process processing unit 3 for processing a CCD output output from the image pickup device 2 to output a video signal; An exposure control unit 5 for controlling exposure by receiving exposure information (usually luminance information is used) from the processing unit 3; and an electronic shutter (exposure time) control signal from the control unit 5 to control the CCD image sensor 2 A CCD drive signal generator 4 for outputting a CCD drive signal for causing an electronic shutter operation at a desired shutter speed, and a flash light emitter for emitting a flash light in response to a strobe light emission control signal from the exposure controller 5. The main portion is composed of a.

FIG. 5 is a timing chart of the photoelectric conversion operation in the image pickup apparatus shown in FIG. 4, and a period in which the vertical blanking signal VBLK is at "L" level is a vertical blanking period. During this vertical blanking period, the read pulse S corresponding to the end of the exposure, that is, the end of the signal charge accumulation period.
The discharge pulse SUB is transmitted back by the signal charge accumulation time from the transmission of the read pulse so that G1 and SG2 can be transmitted. These readout pulses SG1 and SG2 are normally superimposed on the transfer pulse and sent out. If they are output simultaneously, the reference potential of the CCD fluctuates as described above, resulting in unread signal charges and image quality. Is usually deteriorated by several μSec.

That is, each pixel 11 in the first row shown in FIG.
a, 11i,... and the third row of pixels 11c, 11k,..., and the signal charges accumulated in the odd rows of the pixels are read by the first read pulse SG1, and the second row of pixels 11b,
, And the signal charges accumulated in the pixels of the even-numbered rows, such as the pixels 11d, 11m,... Of the fourth row, are read by the second read-out pulse SG2 having a deviation of several μS from the read-out pulse SG1. I'm trying to put it out. The above several μSe in the period near the end of the signal charge accumulation period
The signal charge accumulation in c is a normal shutter speed of 1/60 to 1/20
In about 00 seconds, the signal charge accumulation in the entire signal charge accumulation period can be neglected, so the time difference of several μSec does not matter.

[0007]

However, when the shutter speed is high, such as when the shutter speed exceeds 1/2000 second, the signal charge accumulation due to the several μSec in the period near the end of the signal charge accumulation period is caused by the image pickup device. The signal charge accumulation during the entire signal charge accumulation period cannot be ignored, resulting in luminance unevenness and hue shift, which adversely affects image quality. This applies, for example, to the case where the exposure is terminated by the readout pulses SG1 and SG2 during the flash emission, for example, during the flash emission, and is particularly noticeable when the flash is short-distance.

Accordingly, an object of the present invention is to solve the above-mentioned problem, and to describe a ratio of signal charge accumulation in a period near the end of a signal charge accumulation period of an image pickup device to signal charge accumulation in the entire signal charge accumulation period. Regardless of the above, an object of the present invention is to provide an imaging device with little image quality deterioration.

[0009]

According to the present invention, there is provided an image pickup apparatus which outputs each read pulse having substantially no timing shift with respect to a part and another part of all photoelectric conversion units of an image pickup device. The signal charge readout operation of the first mode in which the readout is performed and the signal charge is read out, and each readout pulse which is substantially shifted in timing is given to a part and another part of all the photoelectric conversion units of the image sensor. A signal charge readout means capable of selectively executing the signal charge readout operation of the second mode for reading out the signal charge, and the imaging being performed in a period near the end of the signal charge accumulation period of the image pickup device. Depends on whether the imaging in the first mode or the imaging in the second mode different from the first mode has a relatively large ratio of signal charge accumulation in the entire signal charge accumulation period. When shooting the aspect The signal charge reading means tightening perform signal charge read operation of the first embodiment, the second in the signal charge reading means at the time of imaging of the second aspect
And a signal charge readout mode selecting means for performing the signal charge readout operation of the above aspect.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram of a main part of an image pickup apparatus according to an embodiment of the present invention. The difference from FIG. The point is that a read mode switching signal SGMD is applied in addition to the shutter control signal. Except for this point, there is no difference from the above-described conventional example. Therefore, the same components are denoted by the same reference numerals, and description thereof will be omitted. Only the mode switching signal will be described below.

The read mode switching signal SGMD is
For example, at the time of a high-speed shutter of 1/2000 second or more, the ratio of signal charge accumulation in the period near the end of the signal charge accumulation period of the image sensor to the signal charge accumulation in the entire signal charge accumulation period cannot be ignored. The read pulse SG is set according to the time of flash emission or the like, and the case of a normal shutter speed of, for example, about 1/60 to 1/2000 seconds at which the above ratio can be ignored.
1, SG2, which is a signal for performing a switching operation for substantially eliminating the shift in the transmission timing or providing the shift in timing as in the conventional example.

The read mode switching signal SG
According to MD, when the ratio of signal charge accumulation in the period near the end of the signal charge accumulation period of the image pickup device to the signal charge accumulation in the entire signal charge accumulation period is relatively large, all the photoelectric conversion units of the image pickup device A first mode of performing a signal charge readout operation of a first mode in which a signal charge is read out by applying a separate readout pulse having substantially no timing shift to a part and the other part of the signal charges is performed. .

On the other hand, when the above occupying ratio is relatively small, each read pulse with a substantially shifted timing is given to a part and another part of all the photoelectric conversion units of the image sensor. Photographing is performed in the second mode for performing the signal charge readout operation in the second mode for reading out signal charges.

It should be noted that there is a substantial difference in timing between some and all of the photoelectric conversion units of the image sensor, for example, the odd-numbered photoelectric conversion units and the even-numbered photoelectric conversion units in FIG. The signal charge readout operation of the first mode in which the signal charge is read out by giving each other readout pulse, and each of the signal charge readout operations substantially deviated in timing with respect to a part and the other part of all the photoelectric conversion units of the imaging device A signal charge readout unit configured to selectively execute a signal charge readout operation according to a second mode of reading out a signal charge by giving another readout pulse, and that the photographing is performed at the end of the signal charge accumulation period of the image sensor. Whether the imaging in the first mode or the imaging in the second mode different from the first mode, in which the ratio of signal charge accumulation in the nearby period to the signal charge accumulation in the entire signal charge accumulation period is relatively large. Accordingly, the first state When the photographing is performed, the signal charge reading means performs the signal charge reading operation of the first mode. When the photographing of the second mode is performed, the signal charge reading means performs the signal charge reading operation of the second mode. A signal charge readout mode selecting means for performing an operation;
It comprises a drive signal generator 4 and an exposure controller 5.

The operation of the embodiment constructed as described above will be described with reference to the timing chart of FIG. For example, 1/60 ~
At a normal shutter speed of about 1/2000 seconds, the read mode switching signal SGMD is set to the "H" level. Then, in each photoelectric conversion unit, the discharge pulse SUB31
Is applied and the unnecessary charge is discharged, the signal charge accumulating operation is started, and the transmission timing of the read pulses SG1 and SG2 for entering the vertical blanking period and terminating the accumulating operation is set to 32 and 33. As shown, there is a shift of about 5 μSec as in the conventional case.

On the other hand, at the time of a high-speed shutter of 1/2000 seconds or more, or at the time of strobe light emission, the read mode switching signal SGMD is set to the "L" level. In this case, the read pulse SG for terminating signal charge accumulation after the discharge pulse SUB34 in each photoelectric conversion unit is transmitted.
1 and SG2 are set at substantially the same timing, such as 35 and 36.

In this case, even in a low-speed shutter operation, in photographing in which strobe light is emitted in the latter half of the shutter opening time, signal charge accumulation in the period near the end of the signal charge accumulation time is caused by the signal charge accumulation period. Since the ratio becomes relatively large with respect to the total signal charge accumulation, it is preferable to use the first mode of imaging in which the timing deviation of the read pulse is eliminated.

According to the above embodiment, the ratio of the signal charge accumulation in the period near the end of the signal charge accumulation period of the image pickup device to the signal charge accumulation in the entire signal charge accumulation period is negligible. At the time of the normal photographing of 1/60 to 1/2000 second, the transmission timing of the read pulses SG1 and SG2 in the period near the end of the signal charge accumulation period is shifted, so that
By performing the imaging in the second mode, it is possible to obtain the same image quality as that of the related art in which no unread portion occurs. On the other hand, when the occupying ratio cannot be relatively neglected, for example, at the time of a high-speed shutter or strobe light emission of 1/2000 second or more, the transmission timing is matched to perform the shooting in the first mode, so that the remaining readout is reduced. It is possible to prevent luminance unevenness and color shift due to a difference in exposure amount, which greatly affects image quality deterioration.

In the above embodiment, the exposure is controlled using the exposure information from the camera process processing unit. However, the exposure is controlled by using an external photometric element such as a photometric sensor without using the exposure information from the CCD. Of course, the present invention can be applied to a control system. As for the solid-state imaging device of CCD, a frame interline type CCD is used.
As described above, a frame interline transfer type CCD and a frame transfer type CCD
It is needless to say that the present invention can be similarly applied. Further, it has been described that when the signal charge accumulation operation is started, the invalid charges that have been accumulated up to that time are simultaneously performed by one ejection pulse. However, for example, the present invention is also applicable to a method of performing the ejection operation using a transfer path. Can be applied. Although the description has been made with reference to a general video movie, the present invention can be applied to an electronic still camera that handles still image information.

[0021]

As described above, according to the present invention, the ratio of signal charge accumulation in the period near the end of the signal charge accumulation period of the image pickup device to the signal charge accumulation in the entire signal charge accumulation period is large. For example, a signal charge is read out by giving each read pulse having substantially no timing shift to a part and the other part of all the photoelectric conversion units of the image pickup device. Signal charges are read out by giving each read pulse with a substantially shifted timing to a part and the other part of all the photoelectric conversion units, so that the image quality is deteriorated regardless of the above ratio. The remarkable effect of being able to reduce is exhibited.

[Brief description of the drawings]

FIG. 1 is a timing chart of an exposure operation in an imaging apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram of a main part of the embodiment.

FIG. 3 is a schematic diagram of a conventional image sensor.

FIG. 4 is a block diagram of a main part of a conventional imaging device.

FIG. 5 is a timing chart of the exposure operation in FIG. 4;

[Explanation of symbols]

2 ... CCD image pickup device (image pickup device) 4 ... CCD drive signal generation unit (signal charge readout unit, signal charge readout mode selection unit) 5 ... Exposure control unit (signal charge readout unit, signal charge readout mode selection unit) 11a, 11b , 11c, 11d, 11i, 11j, 1
1k, 11m: photoelectric conversion unit SG1, SG2: read pulse

Claims (1)

(57) [Claims] 1. A signal charge according to a first mode, in which a signal charge is read by giving each other read pulse having substantially no timing shift to a part and another part of all photoelectric conversion units of an image sensor. A readout operation, and a signal charge readout operation according to a second mode in which signal charges are read out by giving individual readout pulses substantially deviated in timing to some and all of the photoelectric conversion units of the image sensor. And a signal charge readout means that can be selectively executed; and the imaging is such that the signal charge accumulation in the period near the end of the signal charge accumulation period of the image sensor is smaller than the signal charge accumulation in the entire signal charge accumulation period. Depending on whether the imaging of the first aspect or the imaging of the second aspect different from the first aspect is relatively large, the signal charge reading means performs the imaging of the first aspect. The signal power of the first aspect A signal charge readout mode selecting means for performing the readout operation and performing the signal charge readout operation of the second mode when performing the imaging in the second mode. Characteristic imaging device.