JP2927970B2 - 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 imaging apparatus for obtaining a still video image of a subject, and more particularly to detection of an exposure condition.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram of an electronic still camera. In FIG. 5, 1 is a lens unit, 2 is a lens drive motor, 3 is an aperture, and 4 is an aperture drive circuit. Reference numeral 5 denotes a solid-state imaging device for converting an optical image of a subject into an electric signal, which can reset or read out accumulated charges by designating an arbitrary row in the vertical direction according to an instruction from the system control circuit 9. Reference numeral 6 denotes an A / D for performing an A / D (analog-digital) conversion of the output of the solid-state imaging device 5.
It is a conversion circuit. Reference numeral 7 denotes a field memory for storing the output of the A / D conversion circuit 6. 8 represents the blur amount E
This is an ES filter that calculates an S value (described later). 9 is a system control circuit for controlling the entire system. Reference numeral 10 denotes an imaging signal processing circuit that performs processing such as γ conversion and band limitation on the output of the memory 7. 11 is an imaging signal processing circuit 1
D for converting D / A (digital-analog) from the output of 0
/ A conversion circuit. Reference numeral 12 denotes an FM modulation circuit that performs FM modulation on the output of the D / A conversion circuit 11. Reference numeral 13 denotes a REC (recording) amplifier for current-amplifying the output of the FM modulation circuit 12. 14 is a magnetic head, 15 is a magnetic sheet as a recording medium, 16 is a motor for rotating the magnetic sheet 15, and 17 is a motor servo circuit for stabilizing the rotation of the motor 16. Reference numeral 20 denotes a release switch responsive to a release button, and when this switch is turned on, a series of photographing operations is started. Reference numeral 21 denotes an average value detection circuit that detects the average value of the signal of the A / D conversion circuit 6.

FIG. 7 shows an example of the configuration of a solid-state imaging device 5 which can designate and read an arbitrary row in the vertical direction.
1 shows a structure called a GA (floating gate array). For a detailed description of the FGA sensor, refer to the literature (IEEE TRANSACTION OF ELECTRON DEVICE VOL.35.N
O.5 MAY 1988 pp. 646-652), so only a brief explanation is given here.

In FIG. 7, reference numeral 101 denotes a light receiving section. The light receiving unit 101 includes a JFET (junction field effect transistor) and a coupling capacitance CO between a gate and a horizontal address line.
It is constituted by. Reference numeral 102 denotes a source load of the JFET constituting the light receiving unit 101, and constitutes a source follower together with the JFET of the light receiving unit 101. 10
Reference numeral 3 denotes a horizontal address line, which is capacitively coupled in common with a gate of one line of JFETs constituting the light receiving unit 101 by a capacitor CO. Reference numeral 104 denotes a vertical scanning decoder, which applies a reset pulse φVH to a horizontal address line of a line selected by the line selection data, and applies an off pulse φVL to a horizontal address line of a non-selected line. When the reset pulse φVH is low, the light receiving unit 10
One JFET turns on and the gate voltage appears at the source. When the reset pulse φVH is high, the coupling capacitance CO of the light receiving unit is charged to a predetermined charge amount, and the potential of the light receiving unit 101 is reset to a predetermined potential. When the off pulse φVL is high, the JFET of the light receiving unit 101 is turned on, and a gate voltage appears at the source. When the off pulse φVL is low, the JFET of the light receiving unit 101 is turned off, and the gate potential does not appear at the source.

[0005] Reference numeral 105 denotes a vertical signal line, which is commonly connected to the source of the JFET of each light receiving unit in the same column, and has a JFE of the light receiving unit of the line selected by the vertical scanning decoder.
The gate potential of T appears. Reference numeral 106 denotes a clamp circuit composed of clamp circuits for the number of the vertical signal lines 105, and fixes the respective potentials of the vertical signal lines 105 to the reference potential VR when the clamp pulse φc is high. 107
Is a sample / hold circuit and line memory, which is composed of hold capacitors and switches for the number of vertical signal lines 105. The potential level of each vertical signal line when φsh is high is sampled and the potential at the moment when it goes low is held. The hold capacitor separated from the vertical signal line becomes a horizontal line memory. An output amplifier 108 outputs the potential of the horizontal signal line. 109
Is a horizontal signal line. Reference numeral 110 denotes a switch for connecting a signal of the sample / hold circuit and line memory 107 to a horizontal signal line, which is scanned by a horizontal shift register 111.

FIG. 8 is a driving timing chart of the FGA sensor 5. Line address data is set immediately after the start of the horizontal blanking period. Next, the off pulse φVL
Is set to low, the JFETs of the light receiving units other than the selected line are turned off, and only the signal of the selected line appears on the vertical signal line 105. The signal that appears at this time is clamped to the reference potential VR by the clamp pulse φc, and then its level is sampled and held by the sample and hold pulse φsh. Next, the clamp pulse φc goes low, and then the reset pulse φVH goes high, resetting all the charges in the light receiving section of the selected line, and changing the output of the vertical signal line 105. After the reset pulse φH goes low, the potential appearing on the vertical signal line 105 is sampled and held by the sample / hold pulse φsh, so that the change in potential before and after resetting the light receiving unit can be sampled and held by the line memory 107. To memorize. Next, the off pulse φVL becomes the intermediate potential. Next, the address of the line to be reset to control the charge accumulation time is set as line address data, and the reset pulse φVH goes high to reset the charge of the light receiving portion of the designated line. When this operation is completed, the clamp pulse goes high again, and the potential of the vertical signal line 105 is clamped. Next, scanning by the shift register of the line memory 107 is started, and the H blanking period ends. Vertical scanning can be performed at random by giving line address data. The charge accumulation time can be set by giving the address of the line to be reset several Hs prior to reading, and the electronic shutter operation of the focal plane is performed.

FIG. 9 is a diagram showing a change in output of the light receiving section.
At time t1, the output is reset by the reset pulse φH. If light is applied, the output will increase with time. At t2, the potential immediately before being reset again is sampled and held in the sample / hold circuit / line memory 107. By sampling and holding the potential immediately after the reset at t3, a read signal value is obtained in the sample / hold circuit / line memory 107.

FIG. 10 is a diagram showing an operation sequence of the electronic still camera. When the release switch is turned on at time T0, a series of photographing sequences is started. Time T0
The scanning is performed M times, that is, the photometric scanning is performed while changing the charge accumulation time with the aperture value that is between T1 and T1.
The optimal aperture value Av and the optimal shutter speed Tv are calculated from the average value of the outputs of. Between T1 and T2, the aperture is set to open, and between T2 and T3, the lens unit 1 is moved by the lens drive motor 2 to the focus position from N infinity to the infinity to the close range. , N times, that is, AF (auto focus) scanning, and the amount of blur is calculated from the output of the solid-state imaging device 5 in the N times of scanning, thereby calculating the position with the least amount of blur, that is, the optimum focus position. T3
The lens unit 1 is set to the optimum focus position at the same time as the aperture value Av is set between T4 and T4. A reset scan for resetting one line of charge is performed in one horizontal period from T4, and then a read scan is performed from T5 and a processing signal is recorded on the magnetic sheet 15. FIG. 10C is a diagram illustrating the photometric scanning portion in an enlarged manner for further detailed description. Performing K scans while changing the charge storage time by opening the aperture,
At the same time, the average value detection circuit 21 detects the average value of the output of the fixed imaging element 5 for each scan. The charge accumulation time is set to the maximum value (for example, 1/30 second) in the first scan, and is changed to half the time of the previous scan for each scan. Average value detection circuit 2
If the average value, which is the output of 1, is within a certain value range, the system control circuit 9 can calculate the shutter speed for obtaining the proper exposure amount and the aperture values Tv and Av from that value. If the average value is too large, the solid-state imaging device 5
It is considered that most of the area was saturated. If the average value is small, the S / N is too bad and the calculation error in obtaining the proper exposure amount becomes too large. Therefore, scanning is performed while changing the charge accumulation time until the average value of the image falls within an appropriate range. . If the optimum exposure amount cannot be obtained even with the minimum charge accumulation time, a plurality of scans are performed while stopping the aperture by one step and changing the charge accumulation time again. This operation is repeated until the optimum exposure amount is obtained.

FIG. 12 shows an example of the number of aperture stages that can be set. In an electronic still camera, since the exposure latitude of a solid-state imaging device is generally smaller than that of a silver halide film, high accuracy is required for the amount of exposure. Therefore, an aperture having a round hole and high precision but a small number of steps is often combined with a so-called electronic shutter function by a charge accumulation time variable function of the solid-state imaging device. Therefore, as shown in FIG. 12, there are many cases where the aperture value is about three types of F2 (release), F5.6, and F16. FIG. 13 is a diagram showing an example of setting the shutter speed. The shutter speed can be set in increments of one horizontal scanning period (hereinafter referred to as "H"), and the correspondence between the shutter speed in seconds and the charge accumulation time in H units is shown in FIG.
become that way. If the charge storage time is too short with an electronic shutter using the charge storage time variable function of the solid-state imaging device, false signals generally called smears increase,
The lightning accumulation time at the time of photographing is at least about 8H. However, at the time of photometric scanning, there is no problem even if smear is present, so that the charge accumulation time can be reduced to 1H.

FIG. 14 shows an example of a combination of a shutter speed and an aperture during photometric scanning. Camera specifications are the longest exposure time 1/30 seconds, the shortest exposure time 1/2000 seconds, release F
2. Assuming that the minimum aperture is F16, first, the charge accumulation time can be varied from 512H to 1H at F2, and then the entire exposure range can be checked by varying the charge accumulation time from 4H to 2H at F5.6. become. Therefore, FIG.
The photometric scanning described with reference to FIG. 0 (c) may be sequentially set and scanned as shown in FIG.

FIG. 15 shows one of the methods for detecting the amount of blur.
FIG. 2 is a diagram for explaining one ES method. The ES method is disclosed in U.S. Pat. No. 4,804,831 and will be described only briefly. In the figure, (a) is a video signal (amplitude), and an edge stands when in focus, and the edge falls when out of focus. (B) is the absolute value D of the differential waveform of the video signal. (C) and (d) are the delayed signals DL1 and DL2 of the differential waveform D, respectively, and (e) is the integrated waveform I, which represents the contrast of the etch portion of the video signal.
By dividing D by I as shown in (f), the ES value indicating the sharpness of the edge is represented. FIG. 6 is a configuration example of the ES filter 8. 6, reference numeral 201 denotes a differentiating circuit;
2 is an absolute value circuit, 203 is a delay circuit, 204 is an integration circuit, and 205 is a division circuit. 206 is a peak hold circuit. The value having the highest ES value in the image information is determined as the ES value of the subject.

FIG. 16 is a diagram showing changes in the lens position and the ES value when performing AF scanning to find the in-focus position. In this example, the lens feed is continuously performed from the minimum position to the maximum position, during which the image information is accumulated in the solid-state imaging device 5 every one vertical scanning (hereinafter referred to as “V”) period, the signal is scanned, and Finding ES value from image information
The position where the value is large is set as the focus position.

FIG. 11 is a timing chart showing a conventional example of driving of the solid-state imaging device 5 during photometric scanning. As shown in FIG. 11, after the V blanking period ends, read scanning of all pixels is performed, and reset scanning of all pixels is also performed at the same time. As shown in FIG. 8, these scanning addresses are designated in the vertical direction after the line address of the reset scanning performed for each horizontal blanking period is designated and read out, and the time difference between the scanning address designation (horizontal scanning). (Which can be set in a period unit) is the exposure charge accumulation time. Assuming that the address Y of the reading start position is set immediately after the end of the V period, for example, at time t3, the accumulation time becomes the maximum (1V period) by setting the address Y of the reset scanning start position to t1, and the storage period becomes t3. By setting, the charge accumulation time becomes minimum (0).

[0014] However, in the conventional example requires a maximum of 12 times the area scanned before determining the optimum exposure amount (see FIG. 1 4), only the photometric scanning it takes more time 200 ms, the throttle AF even if switching time is ignored
It takes 400 ms or more together with scanning, and the release time lag is a problem.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to provide an imaging apparatus which requires a short photometric scanning time and a small release time lag.

[0016]

In order to achieve the above-mentioned object, according to the present invention, an imaging device is configured as described in the following (1 ) .

[0017] (1) classification result and the image pickup element scanning line of arbitrary that can specify reset and read, all or part of the scan line of the image sensor into a plurality of light metering blocks
Both partitions the respective scan lines in said metering block into a plurality of drive means, each of which is divided for each of the measuring light block the reset and read so that a different charge storage time, all the metering block From
Imaging device having, an exposure detection unit which detects the exposure condition by comparing the read different charge accumulation time of the signal.

[0018]

According to the configuration of the action] (1), in one area scan, obtained the information of a number of charge accumulation time, the photometric scanning is short no.

[0019]

The present invention will be described below in detail with reference to examples.

FIGS. 1 and 2 are views for explaining the operation of an "electronic still camera" according to a first embodiment of the present invention. This embodiment is configured in the same manner as FIG. 5 except for the method of driving the solid-state imaging device and the method of determining the exposure condition. FIG. 1 is a diagram showing a photometric area during photometric scanning of the solid-state imaging device in the present embodiment. In this example, the vertical scanning lines of the solid-state imaging device 5 are 480 lines, which are equally divided into 48 blocks of 10 lines in the vertical direction, and 24 blocks selected every other block are photometric blocks. Used to detect information.

FIG. 2 is a diagram showing the charge accumulation time of 10 scan lines belonging to one photometry block. In this way, ten scan lines are set for ten different charge accumulation times. The different charge accumulation time is made possible because the time required from reset to reading can be freely changed at the timing of giving an address. Since these 10 scanning lines are close to each other, the correlation of the image is strong. Therefore, the same photometric information as when the same image is exposed many times by changing the charge accumulation time can be obtained at the same time. 3 and 4 are diagrams showing photometric scanning timings of the solid-state imaging device 5 in the present embodiment. FIG. 3 shows a photometric scan performed with the aperture released (F2). In the figure, INT (512H) reset is the charge accumulation time 51
The timing at which the reset address of 24 lines in the 2H group is given is shown.

INT (512H) read is a charge accumulation time of 512H
The timing at which a read address of 24 lines of the group is given. The data of 24 lines belonging to each charge storage time group take an average value for each charge storage time group in the average value detection circuit 21 and are sent to the system control circuit 9 as photometric information. In this manner, as shown in FIG. 3, photometric information in which the shutter speed is changed in ten steps in the 2V period is obtained. If the optimal exposure amount could not be detected from the photometric information in FIG.
At 5.6, the photometric scanning shown in FIG. 4 is performed. If the photometric scanning of FIG. 4 is performed, photometric information of all combinations shown in FIG. 14 can be obtained. The case where the aperture is not obtained under the optimum exposure condition when the aperture is released is limited to a considerably bright case. In most cases, the photometric scanning is completed only with the aperture release condition.

Then, A which is performed following the photometric scanning
The F-scan is performed in the state of the aperture finally set during the photometric scanning. At the time of AF scanning, it is easier to obtain the in-focus position by setting the aperture as close as possible to the open state. This is because the difference in the ES value depending on the position of the lens increases because the depth of field is shallower when the lens is closer to the release. At the end of the photometric scanning, if the charge storage time is set to a certain value, it is guaranteed that the output of the solid-state imaging device 5 falls within a certain range, and the optimal charge storage time is already known. In addition, since the aperture is in a state close to the open state, the state is suitable for AF scanning. Therefore, AF scanning is performed with the optimal charge accumulation time obtained by photometric scanning without changing the aperture. In this way, the total release time lag can be reduced by the amount that the aperture is not changed.

FIG. 17 is a diagram showing a technique for further reducing the time for obtaining the optimum exposure amount. An example according to this method will be described as a second embodiment of the present embodiment. In this embodiment, since the information is read from the information having the shortest charge accumulation time, the average information of the image of the group having the shortest charge accumulation time in the aperture open state at the time t3 in FIG. 17 is obtained. If the image is equal to or more than a certain value, it is certain that it is necessary to further reduce the number of steps by one, so that information of the charge accumulation time 2H or more is not necessary. Therefore, if the average value of the images of the group of the 1H accumulation time exceeds a certain value, the operation of immediately stopping down the aperture by one step is started. Immediately after the end of the aperture changing operation, scanning of the group with the accumulation time 2H from 111 and 4H
Scan of the group. Data read during the aperture changing operation is ignored or no scanning is performed. In this way, when the brightness of the subject is very large, the first
The time of photometric scanning can be shorter than in the embodiment.

In each of the above embodiments, as shown in FIG. 1, half of the scanning area of the image sensor is used as the photometry area. However, the present invention is not limited to this. The entire area may be a photometric area, or the center of the area may be a photometric area (center-weighted photometry). Further, the detection of the focusing condition is not limited to the ES method, and the TTL (thru
gh the lenses), and the solid-state imaging device may be driven back and forth by a piezoelectric element or the like instead of driving the lens. In addition, the present invention is not limited to the recording means of the video signal, and may have a separate recording means and transmit the video signal to the recording means.

[0026]

As described above, according to the present invention,
An average value of images in a plurality of types of charge accumulation times can be obtained by one scan in one direction (for example, a vertical direction) of a solid-state imaging device, and the time required for photometry can be significantly reduced, and a release time lag can be achieved. that it is possible to ing to significantly reduce.

[Brief description of the drawings]

FIG. 1 is a diagram showing a photometry area according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a charge accumulation time of each scanning line in each photometry block of FIG. 1;

FIG. 3 is a diagram showing the timing of photometric scanning of the solid-state image sensor in the first embodiment.

FIG. 4 is a diagram showing the timing of photometric scanning of the solid-state imaging device in the first embodiment.

FIG. 5 is a block diagram of an electronic stell camera.

FIG. 6 is a block diagram of an ES filter 8;

FIG. 7 is a diagram showing a drive circuit of an FGA sensor.

FIG. 8 is a diagram showing drive timing of an FGA sensor.

FIG. 9 is a diagram showing an output change of a light receiving unit of the FGA sensor.

FIG. 10 is an operation sequence diagram of the electronic still camera.

FIG. 11 is a diagram showing a photometric scanning timing of a conventional example.

FIG. 12 is a diagram showing an example of the number of stops of the aperture that can be set in the electronic still camera.

FIG. 13 is a diagram showing a setting example of a shutter speed.

FIG. 14 is a diagram showing a combination of a shutter speed and an aperture during photometric scanning.

FIG. 15 is an explanatory diagram of the ES method.

FIG. 16 is an explanatory diagram of AF scanning.

FIG. 17 is a diagram showing the timing of photometric scanning in the second embodiment.

[Explanation of symbols]

 5 Solid-state image sensor 9 System control circuit

Claims (1)

(57) [Claims] An imaging element as claimed in claim 1] which can specify the scan lines of arbitrary reset and read, as well as partitioning the whole or part of the scan line of the image sensor into a plurality of light metering blocks, each of said metering block
The scanning line in the block is divided into a plurality of
Driving means for resetting and reading so that each of the divided sections in the block has a different charge accumulation time,
Different charge accumulation times read from all photometric blocks
Imaging apparatus characterized by having, an exposure detection unit which detects the exposure condition by comparing the signal.