JP2000032353A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device appropriately constituted so that it can control an electronic shutter with high precision and can always secure high exposure accuracy by adjusting a start time of charge accumulation of an imaging device to a time other than a horizontal blanking period. SOLUTION: A start time of charge accumulation of an imaging device is adjusted to a time other than a horizontal blanking period. Charges are accumulated in a photodiode after the generation of a subpulse to the generation of a transfer gate pulse and, by controlling this accumulation duration of the charge, an electronic shutter can be obtained. For this charge accumulation duration (an exposure duration) photometry data obtained by metering light from a subject are read by an AE circuit 11 of a CPU 8 and an appropriate exposure time is calculated on the basis of the photometry data. Then, by transmitting data to a TG 6 and setting various kinds of operation modes in accordance with this appropriate exposure duration, a generation timing of the subpulse with respect to a generation timing of the transfer gate pulse is controlled.

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 having an image pickup device capable of reading out a pixel signal, such as an electronic still camera or a video camera, and more particularly to a so-called electronic shutter function for electrically controlling an exposure time. The present invention relates to an imaging device having the same.

[0002]

2. Description of the Related Art As such an image pickup apparatus, for example, Japanese Patent Application Laid-Open No. 64-46379 discloses that a read pulse for reading out the stored signal charges after terminating the accumulation of charges in an image pickup element. In response to this readout pulse, the charge accumulated in the image sensor is swept out to the substrate in response to the readout pulse, and a sweeping pulse for starting the exposure, that is, the charge accumulation, is set to an arbitrary value within the vertical blanking period in the high-speed shutter area. At the time of
In a low-speed shutter region that deviates from the vertical blanking period, a device has been proposed that is generated within an arbitrary horizontal blanking period.

[0003]

In the above-described conventional imaging apparatus, in the high-speed shutter area, the generation timing of the sweeping pulse is variable within the vertical blanking period so that the shutter speed can be continuously varied. Therefore, the exposure time can be accurately controlled so that the signal charge reaches the proper accumulation level at the time of generation of the read pulse, and therefore, high exposure accuracy can be secured.

However, in the low-speed shutter region where the generation timing of the sweep pulse deviates from the vertical blanking period, the sweep pulse is fixedly generated within an arbitrary horizontal blanking period. Signal, that is, one horizontal line (1
It can be changed only in the time unit of H). For this reason, an error of 1H at the maximum occurs in the actual exposure time,
There is a problem that the exposure accuracy is reduced. In addition, it is conceivable to correct the excess or deficiency of the signal charge from the proper accumulation level based on the error of the exposure time by adjusting the gain of the subsequent amplifier, but since the gain adjustment of the amplifier is generally poor in linearity, There is a problem that the correction cannot be performed accurately and that the S / N varies with the gain.

The present invention has been made in view of such conventional problems, and provides an image pickup apparatus appropriately configured so that an electronic shutter can be controlled with high accuracy and high exposure accuracy can always be ensured. It is intended for.

[0006]

According to a first aspect of the present invention, there is provided an image pickup apparatus having an image pickup device capable of reading out pixel signals, wherein the start time of charge accumulation of the image pickup device is set to be horizontal. It is characterized by having accumulation control means for controlling at a time other than the blanking period.

Further, according to a second aspect of the present invention, there is provided an image pickup apparatus having an image pickup device capable of reading pixel signals.
The image processing apparatus further includes an accumulation control unit that controls a start time of the electric charge accumulation of the imaging element in a time unit shorter than an interval of a horizontal synchronization signal.

In a preferred embodiment of the invention according to claim 1 or 2, the image pickup device has a charge storage region, and the storage control means transfers the signal charges stored in the charge storage region to the charge storage region. By discharging the charge to the substrate of the image sensor, the charge accumulation of the image sensor is started.

Further, in a preferred embodiment of the invention according to claim 1 or 2, the image pickup device has a charge storage region and a transfer shift register, and the storage control means stores the charge in the charge storage region. By transferring the signal charges to the transfer shift register, the charge accumulation of the image sensor is terminated.

Further, in a preferred embodiment of the invention according to claim 3, at the time of starting the charge accumulation of the image pickup device, at least the pixel based on information relating to the position of a pixel signal read from the image pickup device. It is characterized by having correction means for correcting a signal.

Further, in a preferred embodiment of the invention according to claim 5, the pixel signal to be corrected is corrected by the correction means based on peripheral pixel signals.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of a first embodiment of an imaging apparatus according to the present invention. This imaging apparatus is mainly intended to capture and record a still image, and includes a lens and an aperture 17.
CCD that converts the image of the subject incident through the camera into an electric signal
1, a correlated double sampling circuit (CDS) 2 for removing reset noise and the like from the output of the CCD 1, a gain control amplifier (AMP) 3 for adjusting the gain of the output of the CDS 2, and an output signal of the AMP 3. Analog-to-digital converter (A /
D) 4, a process processing circuit 5 for performing various processes on the image signal converted into the digital signal, and outputting various drive pulses for driving the CCD 1 and outputting a pulse for sample and hold in the CDS 2 A / D
4, a timing generator (TG) 6 for outputting a timing pulse for performing A / D conversion, a signal generator (SG) 7 for generating a signal for synchronizing the TG 6 with a CPU 8 described later, The CPU 8 comprises, for example, a microcomputer which constitutes a read control unit and performs various controls including timing and the like for the entire image pickup apparatus, pixel data of the CCD 1 output from the process processing circuit 5, and compression from a recording medium 16 to be described later. A DRAM 9 constituting a memory for storing image data supplied via an expansion circuit 15, an autofocus circuit (AF) 10 for controlling autofocus by a lens and an aperture 17, and an object image formed on the CCD 1 Automatic exposure control circuit for photometry (A
E) 11, an automatic white balance circuit (AWB) 12 for automatically controlling the white balance, and the liquid crystal display device 1 which is a monitor built in the imaging device.
3, an external display terminal 14 for outputting an image signal or the like to a display device such as an external monitor, and image data for one frame stored in the DRAM 9 on a recording medium 16 to be described later with a reduced data amount. A compression / expansion circuit 15 for compressing and expanding the compressed image data read from the recording medium 16, and a recording medium 16 for recording still image data.

FIG. 2 schematically shows an example of the configuration of the CCD 1 shown in FIG. The CCD 1 is of an interline type having a vertical overflow drain structure, is arranged two-dimensionally in a horizontal direction and a vertical direction, and has a photodiode 21 which constitutes a charge accumulation region for accumulating charges by light incidence. After receiving the electric charge accumulated in the photodiode 21 through the transfer gate 22, the vertical shift register 23 sequentially transfers the electric charge in the vertical direction, and the electric charge transferred by the vertical shift register 23 is sequentially transferred in the horizontal direction. It has a horizontal shift register 24 and a signal detector 25 for amplifying and outputting an output signal of the horizontal shift register 24.

The imaging apparatus shown in FIG. 1 operates as follows as a whole. That is, when a still image is recorded on the recording medium 16, the CDS2, AMP3,
The image data output through the A / D 4 and the process processing circuit 5 is supplied to, for example, the liquid crystal display device 13 and displayed. Thus, the photographer can determine the composition and the like of the subject while looking at the liquid crystal display device 13. When a release button (not shown) is pressed in this state, the image data from the process processing circuit 5 is compressed by the compression / expansion circuit 15 via the DRAM 9 and recorded on the recording medium 16 as a still image.

When reproducing the still image data recorded on the recording medium 16, the compressed image data read from the recording medium 16 is decompressed by the compression / decompression circuit 15 and written into the DRAM 9. The image data written in the DRAM 9 is supplied to the liquid crystal display device 13 via the process processing circuit 5 or to the external display device via the external display terminal 14, and is reproduced as a still image.

Here, when a still image is recorded on the recording medium 16, the CCD 1 sequentially scans from the first line to the last L line as shown in FIG. Is read. This read mode is
This is a so-called progressive scan that sequentially scans the full screen area and outputs information on all pixels, so that a high-resolution image can be obtained as a still image.

As another reading mode, in order to improve the frame rate, not all pixels but a central portion of the screen, for example, j + line from j + 1 line in FIG.
Reads out the accumulated charges only in the effective area of the continuous k lines up to the k lines, and reads out the accumulated charges in the sweeping area from the first line to the jth line and the j + k + 1th line to the last L line at the top and bottom of the screen at a high speed. There is also a mode. Image data obtained in this read mode is used for processing such as AE, AF, and AWB.

FIG. 4 is a partial detailed view of FIG. 1, showing signals supplied from the SG 7 and the CPU 8 to the TG 6, and signals supplied from the TG 6 to the CCD 1. CPU 8
By three signals of the communication lines SSTRB, SDCLK and SDATA, T
Data communication is performed with the G6 in the data communication format shown in FIG. 5, and various operation modes of the TG 6 are set. Further, the CPU 8 supplies the reset signal RST and the standby signal STBY to the TG 6 to initialize the TG 6 and control the TG 6 to be in a non-operation state.

The SG 7 supplies the TG 6 with the vertical synchronizing signal VD and the horizontal synchronizing signal HD. TG6 is SG
The sub-pulse SUB, the transfer gate pulse TGP, and the vertical shift register transfer pulse VT are supplied to the CCD 1 based on the vertical synchronizing signal VD, the horizontal synchronizing signal HD, and various operation modes set by the CPU 8. Control of the charge storage and charge readout operations.

The sub-pulse SUB is a pulse for discharging charges generated in the photodiode 21 of the CCD 1 shown in FIG. 2 in the vertical direction of the substrate.
While B is being output, the charge is discharged. Also, the transfer gate pulse TGP
Is a pulse that determines the timing for transferring the charge stored in the photodiode 21 to the vertical shift register 23. Note that this transfer gate pulse T
In the embodiment, the GP generation timing is fixed to, for example, a predetermined horizontal blanking period within a vertical blanking period. Also, the vertical shift register transfer pulse VT
Is a pulse for driving the vertical shift register 23 to transfer electric charges to the horizontal shift register 24 side.

Therefore, the charge is accumulated in the photodiode 21 during the period from the generation of the sub-pulse SUB to the generation of the transfer gate pulse TGP, and the effective exposure time is reduced by controlling the charge accumulation time. A so-called electronic (element) shutter to be controlled is realized.

The charge accumulation time (exposure time) is determined by the CPU 8 as AE as shown in the flowchart of FIG.
The circuit 11 reads photometric data obtained by photometry of the subject image (step S1), calculates an appropriate exposure time based on the photometric data (step S2), and stores the appropriate exposure time in the TG 6 in accordance with the calculated appropriate exposure time. By transmitting data and setting various operation modes, the sub-pulse SU with respect to the generation timing of the transfer gate pulse TGP is set.
The generation timing of B is controlled.

FIG. 7 shows that in this embodiment, the CPU 8 transmits a signal T via the communication line SDATA according to the proper exposure time.
The transmission data to be transmitted to the G6, in this embodiment, the relationship between 12 bits (SD11 to SD0) and various operation modes of the TG6 set thereby.

In FIG. 7, in the shutter SUB fine adjustment setting mode, a minute exposure time tSUBM (where tSUBM is the number of horizontal clocks) from the falling point of the horizontal synchronizing signal HD to the generation point of the sub-pulse SUB is set and the charge is set. The start time of the accumulation is controlled. In this embodiment,
The data DSUBM of the lower 3 bits (D2 to D0) of the setting data is allocated to the lower 3 bits (SD2 to SD0) of the transmission data and transmitted. 1) Set by. Note that α is the number of clocks slightly larger than the number of horizontal clocks during the horizontal blanking period, and
Here, for example, 130 is set.

As a result, as shown in FIGS. 8 and 9, from the falling edge of the horizontal synchronizing signal HD, there are eight types of minute exposure times in units of 268 horizontal clocks, which correspond to the data contents of the DSUBM. The minute exposure time tSUBM is set. FIG. 8 shows the data content of DSUBM and the sub-pulse SUB from the falling point of the horizontal synchronization signal HD.
9 shows the relationship between the number of horizontal clocks at the time of falling and rising, and FIG. 9 shows a timing chart of each sub-pulse SUB and the horizontal synchronizing signal HD. Here, the pulse width of the low level section of the sub-pulse SUB is set to 40 horizontal clocks, and the number of horizontal clocks in 1H is set to 2145 clocks.

Therefore, in the shutter SUB fine adjustment setting mode, the sub-pulse SUB can be generated in a time unit other than the horizontal blanking period in units of 268 horizontal clocks shorter than 1H.

In FIG. 6, in the shutter SUB setting mode, the generation timing of the sub-pulse SUB is made variable in units of 1H. In this embodiment, among the shutter SUB setting data, the data DSUBH of the upper 2 bits (D10, D9) and the data DSU of the lower 9 bits (D8 to D0)
And BL as separate transmission data. That is, the data DSUBH of the upper 2 bits (D10, D9) is allocated to the lower 2 bits (SD1, SD0) of one transmission data and transmitted.
The lower 9 bits (D8 to D0) of data DSUBL are assigned to the lower 7 bits (SD6 to SD0) of other transmission data and transmitted. Thus, the exposure time tSUB (where tSUB
Is set to tSUB = DSUBH × 2 ⁹ + DSUBL (2) using the data DSUBH and DSUBL.

Therefore, in the shutter SUB setting mode, the exposure time tSUB is set to 1 within the range of 0 to 2047H.
It can be set in H units.

The shutter V setting mode controls the exposure time in units of one frame (V). In this embodiment, of the shutter V setting data, the data DVH of the upper 7 bits (D11 to D5) and the lower 5 bits (D4 to D5)
0) and the data DVL are transmitted as separate transmission data. That is, the data DVH of the upper 7 bits (D11 to D5)
Is assigned to the lower 7 bits (SD6 to SD0) of one transmission data and transmitted, and the lower 5 bits (D4 to D0) of the data D
VL is transmitted by allocating it to the lower 5 bits (SD4 to SD0) of other transmission data. Thus, the exposure time tv
(However, tv is the number of frames)
Using VL, tv = DVH × 2 ⁵ + DVL (3)

Therefore, in the shutter V setting mode, the exposure time for long-time exposure can be set in the range of 0 to 4095 V in units of 1 V.

As described above, if the various operation modes of the TG 6 are set by the CPU 8 in accordance with the appropriate exposure time, the exposure time tR from the time when the sub-pulse SUB is generated to the time when the transfer gate pulse TGP is generated is determined.
(Where tR is the number of horizontal clocks), where n is the number of horizontal clocks in 1H, tR = LRnＬtv + n ・ tSUB-tSUBM (4) Therefore, assuming that the time of one horizontal clock is msec, the shutter speed Tsp is as follows: Tsp = 1 / (m · tR) (5)

FIG. 7 also shows a mechanical shutter drive time setting mode when a mechanical shutter for controlling the exposure time is provided in cooperation with the electronic shutter, and transmission data for setting the mode. Here, the description is omitted.

FIG. 10 is a timing chart showing the operation of the CCD 1 according to this embodiment.
Horizontal synchronization signal HD, vertical shift register transfer pulse V
T, sub-pulse SUB, transfer gate pulse T
GP and CCD which is a read signal from CCD1
The signal is shown. The exposure time tR is calculated according to the above (1)
In the expression (2), DSUBH = 0,
It is assumed that DSUBL = 11, and the expression (3) is the time when DVH = 0 and DVL = 0.

In this embodiment, the generation timing of the transfer gate pulse TGP is synchronized with, for example, a predetermined horizontal blanking period of a vertical blanking period, and the sub-pulse SUB is set to a horizontal blanking period other than the exposure time tR. At the start of the exposure time tR, the time tSUBM (the number of horizontal clocks) from the fall of the horizontal synchronizing signal HD is generated variably within 1H outside the horizontal blanking period. Thus, the shutter speed can be finely adjusted, so that the exposure time tR (the number of horizontal clocks) can be accurately controlled to a time at which the charge accumulation level becomes an appropriate accumulation level.

Therefore, the exposure accuracy can be greatly improved not only in the high-speed shutter region but also in the low-speed shutter region.

By the way, in the case shown in FIG.
Since the sub-pulse SUB is generated during the output of the L-4th line of the signal, the CCD signal may be affected by count noise of the counter that determines the timing or noise due to fluctuations in the potential of the substrate of the CCD 1. here,
The pixel signal affected by the noise is one line (L-4th line in this case) of the entire screen L line, for example, 100
In the case of a 10,000-pixel CCD, the number of pixels is at most about several pixels including pixels synchronized with the fall or rise of the sub-pulse SUB in one of 1,000 lines. Therefore, when a moving image is picked up and displayed on the liquid crystal display device 13 or the like, it is almost inconspicuous and does not cause any visual problem. However, in the second embodiment of the present invention, the moving image is affected by such noise. The corrected pixel signal is also corrected.

For this reason, in the second embodiment, in the configuration shown in FIG.
The exposure time is set by PU8. In the flowchart shown in FIG. 11, photometry data obtained by photometry of a subject image by the AE circuit 11 is read (step S11), and an appropriate exposure time is calculated based on the photometry data (step S11).
12) Until the data is transmitted to the TG 6 in accordance with the calculated appropriate exposure time (step S13), step S13 of the flowchart in the first embodiment shown in FIG.
Same as 1 to S3.

In this embodiment, after the processing in step S13, it is determined whether or not the sub-pulse SUB has an effect on the CCD signal to be read (step S14). Here, when the sub-pulse SUB is generated within the horizontal blanking period, during the main exposure for recording a still image on the recording medium 16 (in this case, during the accumulation operation, the transfer path is swept out at a high speed and the CCD is Signal is not read), and AE,
In the read mode in which processing such as AF and AWB is performed, when the sub-pulse SUB is generated during the operation of sweeping out the accumulated charges in the sweep area at the top and bottom of the screen, it is determined that there is no influence, and the pixel signal correction processing is not performed.

On the other hand, except for the above cases, it is determined that the line is affected, and the line affected by the line
The line information is stored in the memory in the PU 8 (step S15), and the line information is transmitted to each block of the process processing circuit 5, the AF circuit 10, the AE circuit 11, and the AWB circuit 12 (step S16).

In the process processing circuit 5, based on the line information affected by the CPU 8,
After reading the D signal, the pixel signal is corrected using peripheral pixel signals. For example, if the affected line
As shown in FIG. 12A, at line L-4, CCD 1
12B has the Bayer array color filter shown in FIG. 12B, the G0 pixel signal on the L-4th line is compared with the average value of the peripheral G1, G2, G3, and G4 pixel signals. If the difference is equal to or more than a predetermined value and the reliability is low, the average value is replaced with the pixel signal of G0, and if the difference is less than the predetermined value and the reliability is high, it is left as it is. Similarly, the reliability is determined by comparing the pixel signal of R0 with the average value of the pixel signals of the surrounding R1 and R2. If the reliability is low, the average value is replaced.

As described above, when photographing a still image,
Of the CCD signals of all pixels, the pixel signals of the line affected by noise are corrected and written to the DRAM 9, and then the image is compressed by the compression / expansion circuit 15 and written to the recording medium 16.

The AF circuit 10, AE circuit 11, AW
The B circuit 12 selectively performs the pixel signal correction processing in the same manner as described above based on the line information affected by the CPU 8, and performs the AE, AF, and AWB processing.

As described above, by correcting the pixel signal affected by the noise of the sub-pulse SUB, it is possible to reduce the influence of noise in still image shooting and AE, AF, and AWB processing.

It should be noted that the present invention is not limited to the above-described embodiment, and various modifications or changes can be made. For example, in the above-described embodiment, the set minimum resolution of the sub-pulse SUB is set to 268 horizontal clocks. However, the resolution may be further increased by increasing the number of set data bits, or may be continuously variable in an analog manner. The correction processing of the pixel signal affected by the noise of the sub-pulse SUB can also be performed by a known defective pixel correction method.

[0045]

According to the present invention, the start time of the charge accumulation of the image pickup device is controlled to a time other than the horizontal blanking period. In particular, the start time is set to be longer than the interval of the horizontal synchronization signal. By controlling in short time units,
The electronic shutter can be controlled with high accuracy, and high exposure accuracy can always be ensured.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a first embodiment of an imaging device according to the present invention.

FIG. 2 is a diagram schematically showing a configuration of an example of the CCD shown in FIG.

FIG. 3 is a diagram for explaining a read mode when a still image is recorded.

FIG. 4 is a partial detailed view of FIG. 1;

5 is a diagram illustrating an example of a format of data communication between a CPU and a TG illustrated in FIG. 4;

FIG. 6 is a flowchart showing an exposure time setting operation according to the embodiment shown in FIG. 1;

FIG. 7 is a diagram showing a relationship between transmission data transmitted from the CPU to the TG and various operation modes of the TG set thereby in FIG.

8 is a diagram illustrating setting data contents of a shutter SUB fine adjustment setting mode transmitted from the CPU to the TG in FIG. 4, and horizontal lines at the falling and rising points of the sub-pulse from the falling point of the horizontal synchronization signal corresponding to the data contents. FIG. 4 is a diagram illustrating a relationship with a clock number.

FIG. 9 is a timing chart showing a relationship between a sub-pulse set in a shutter SUB fine adjustment setting mode and a horizontal synchronization signal.

FIG. 10 is a timing chart showing the operation of the CCD according to the embodiment shown in FIG.

FIG. 11 is a flowchart showing an exposure time setting operation according to a second embodiment of the present invention.

FIG. 12 is a diagram for explaining a pixel signal correction process according to the second embodiment.

[Explanation of symbols]

 Reference Signs List 1 CCD 2 correlated double sampling circuit (CDS) 3 gain control amplifier (AMP) 4 analog-to-digital converter (A / D) 5 process processing circuit 6 timing generator (TG) 7 signal generator (SG) 8 CPU 9 DRAM 10 auto Focus circuit (AF) 11 Automatic exposure control circuit (AE) 12 Auto white balance circuit (AWB) 13 Liquid crystal display device 14 External display terminal 15 Compression / expansion circuit 16 Recording medium 17 Lens and aperture 21 Photodiode 22 Transfer gate 23 Vertical shift Register 24 Horizontal shift register 25 Signal detector

Claims (6)

[Claims] 1. An image pickup apparatus having an image pickup device capable of reading out a pixel signal, comprising an accumulation control means for controlling a start time of charge accumulation of the image pickup device to a time other than a horizontal blanking period. Imaging device. 2. An image pickup apparatus having an image pickup device capable of reading out a pixel signal, comprising an accumulation control means for controlling a start time of charge accumulation of the image pickup device in a time unit shorter than an interval between horizontal synchronization signals. Characteristic imaging device. 3. The image pickup device according to claim 1, wherein the image pickup device has a charge accumulation region, and the accumulation control means converts a signal charge accumulated in the charge accumulation region into a charge of the image pickup device. By sweeping out to the substrate,
An image pickup apparatus, wherein charge accumulation of the image pickup element is started. 4. The image pickup device according to claim 1, wherein the image pickup device has a charge storage region and a transfer shift register, and the storage control unit converts the signal charge stored in the charge storage region into An image pickup apparatus, wherein the charge transfer of the image pickup device is terminated by transferring to the transfer shift register. 5. The image pickup apparatus according to claim 3, wherein, at the time of starting the charge accumulation of the image pickup device, based on information relating to a position of a pixel signal read from the image pickup device.
An imaging device comprising at least a correction unit for correcting the pixel signal. 6. The imaging apparatus according to claim 5, wherein the correction unit corrects a pixel signal to be corrected based on peripheral pixel signals.