JPH0943507A - Electric still camera and focusing control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To unnecessitate an optical system and a sensor both used exclusively for AF(automatic focusing) by fetching the output image of a photographing element on each moved position of a pupil and performing focusing control of an optical system based on a defocusing amount obtained by the correlation arithmetic. SOLUTION: A pupil position is moved to symmetrical positions to the optical axis of an optical system for photographing, the output image of a photographing element on each moved position of a pupil is fetched and focusing control of the optical system is performed based on a defocusing amount obtained from its correlation arithmetic. Namely, sweep-out transfer, reading out only a necessary read-out area at an ordinary speed and others at high speed, is performed. Partial high-speed reading is performed as same as a first time, the data are fetched, correlation arithmetic between them and the first held data is performed and a defocusing amount is obtained. A lens is moved in the direction of optical axis based on the defocusing amount thus obtained and a pupil diaphragm for AF is withdrawn out of the optical path. Thus, phase difference AF operation and pupil time dividing phase difference AF operation are performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic still camera for recording an image photographed by an image pickup device such as a CCD on a recording medium, and more particularly to its automatic focusing.

[0002]

2. Description of the Related Art Conventionally, in a so-called single-lens reflex type silver salt camera which images an image on a silver salt film, a phase difference detection type automatic focusing device (AF) is used in many models. The AF system of this phase difference detection system operates roughly as follows.

As shown in FIG. 10, the light incident from the lens is reflected to the lower side of the apparatus by a sub-mirror mounted behind the 45-degree mirror which is the main mirror, and is reflected by a lens of a secondary optical system called an eyeglass lens. It is separated into two images and enters the AF sensor. The AF sensors are arranged side by side as shown in FIG. 11, and the output is as shown in FIG. 11, and the distance between the two images differs depending on the focused state, the front focus state, and the rear focus state. The lens is moved and the focus is adjusted so that the image interval becomes the in-focus interval. The amount of movement of the lens, that is, the amount of movement of the image plane is 2
Calculated from the image distance. The calculation is performed by the following algorithm.

First, the outputs of the two AF sensors are fetched as data. Then, the correlation between the two sensor outputs is calculated. The method is called "MIN algorithm", and the data of the sensor 1 is A [1] -A [n],
When the data of the sensor 2 is B [1] -B [n], the correlation amount U0 is

[0005]

[Equation 1]

It is expressed as First, this U0 is calculated. next,
As shown in FIG. 12, the correlation amount U1 of the data obtained by shifting the A image by 1 bit of the AF sensor and the data of the B image is calculated. This U1 is

[0007]

[Equation 2]

[0008] In this way, the correlation amount shifted by one bit is calculated one after another. If the two images match, this correlation amount takes the maximum value, so the shift amount that takes the maximum value is obtained, and the true maximum value of the correlation amount is interpolated from the data before and after that to obtain the shift amount. Let the amount be the shift amount. Since the relationship between the shift amount and the image plane movement amount, that is, the so-called defocus amount is determined by the optical system, the defocus amount is obtained from the shift amount. From the defocus amount, the amount of lens extension is obtained, and the lens is moved and focused.

This phase difference detection type AF system is
When used in a so-called electronic still camera that captures a still image with a three-dimensional image sensor and records the video signal on some kind of recording medium, it corresponds to one pixel of the AF sensor due to the difference in size (area) between the silver salt film and the image sensor. Since the ratio of the image pickup surface becomes large, that is, the pixels become coarse and the accuracy is lowered, it is necessary to reduce the magnification of the AF optical system or reduce the size of the AF sensor itself (pixel pitch or the like).
These methods have already been proposed by the present applicant.

On the other hand, in a so-called video camera which captures a moving image with a two-dimensional image pickup device and outputs the video signal or records it on a recording medium, there are many models of AF (also called a contrast system) called a mountain climbing system. Is used for. There is a perturbation method as a kind of this method.
This AF method generally operates as follows.

The configuration includes an image pickup system including a two-dimensional image pickup device, a system control unit including a calculation unit and a lens control signal generation unit, and a lens control unit for moving the lens in the optical axis direction. It consists of a lens part. First, the image pickup section captures image light, converts it into a video signal, and sends it to the system control section, where the high-frequency component of the signal is extracted. The maximum value of the extracted signal is stored and the lens is moved in a certain direction. When the movement is completed, the image light is similarly captured and the high frequency component is extracted. Then, if the maximum value is larger than the stored value, it is determined that the moving direction of the lens is approaching the focusing surface, the current value is stored again, and the lens is moved in the same direction. If the maximum value of this time is smaller than that of the previous time, it is determined that the moving direction of the lens is moving away from the focusing surface, the current value is stored again, and the lens is moved in the opposite direction. Then, after the movement of the lens is finished, the image light is similarly taken in, the high-frequency component is extracted, the maximum value is compared, and finally the image plane is brought to the focusing surface.

Referring to FIG. 13, the horizontal axis of the figure shows the position of the image plane, the vertical axis shows the maximum value of the high frequency components, and the point a is the image plane position of the starting point and the point b is the focusing plane. Assuming that the maximum value of the high frequency component at the point is A, when the lens is moved to the right in the figure, that is, in the direction toward the in-focus plane, a '
The maximum value of the high frequency component at the point is A ', and by comparison, A <A
It becomes' and the lens continues to move in the same direction. And
During several comparisons, when the image plane position passed point b (maximum value A ″ at point a ″), it was determined that A> A ″ and that the direction was moving away from the focusing surface. , Reverse the direction of lens movement and bring the image plane to the focusing plane.

Another type of hill-climbing AF is a trial method (including a whole-area scan method). The configuration is the same as the above-mentioned perturbation method. First, the lens is sent to the closest end or the infinity end, and with that as a starting point, the lens is moved in a direction in which the lens can move at a certain image plane interval, and image light is captured by the image pickup unit, and it is converted into a video signal by the system. The signal is sent to the control unit, where the high frequency component of the signal is extracted and the maximum value is stored. This operation is repeated until the infinity end if the starting point is the closest end, and conversely if the starting point is the infinity end, until the closest end. Then, the maximum value among the stored maximum values, that is, the focus position with the highest contrast is obtained, and the lens is moved to the lens position corresponding to that point. Similar to the perturbation method, the relationship between the image plane position and the high frequency component is as shown in FIG. 14, and the focal plane is the x point. Basically, the above operation is performed.

[0014]

As described in the above-mentioned conventional example, when the phase difference detection type AF system used in a silver halide camera or the like is used in an electronic still camera, a new AF optical system or Since it is necessary to make AF sensors, they become more strict in terms of accuracy, and the accuracy of the relative position with respect to the image sensor is also strict, and the influence of deviation due to aging increases. In addition, in the case of the hill-climbing AF system used in the video camera as described above, it is not necessary to create a new optical system or the like, but one image pickup device storage / readout time is at least one vertical period. And that
Considering the calculation time and the like of the high-frequency extraction filter, the focusing time becomes long, and the shutter chance is missed, so that there is a problem that it cannot be used as an AF system of an electronic still camera.

The present invention has been made in order to solve such a problem, and in an electronic still camera, an AF system of a phase difference detection system is constructed without using an AF-dedicated optical system and sensor. The purpose is to improve the accuracy of the AF.

[0016]

In order to achieve the above object, the present invention constitutes an AF system of a phase difference detection system by using an optical system for photographing and an image pickup element. The following (1), (2), and (3) are configured, and the focus control method of the electronic still camera is configured as in (4) below.

(1) Imaging device for photographing, optical system for photographing, pupil position moving means for moving the pupil position to a position symmetrical with respect to the optical axis of the optical system, and movement by the pupil position moving means. An electronic still camera provided with a focus control means for capturing an output image of the image pickup device at each pupil position, obtaining a defocus amount by a correlation calculation thereof, and performing focus control of the optical system based on the defocus amount. .

(2) Image pickup device for photographing, optical system for photographing, pupil position moving means for moving the pupil position to a position symmetrical with respect to the optical axis of the optical system, and movement by the pupil position moving means. First focus control means for capturing the output image of the image sensor at each pupil position, obtaining a defocus amount by the correlation calculation, and performing focus control of the optical system based on the defocus amount; Subsequent to the focus control by the first focus control means, the output image of the image pickup device is captured with the pupil position as the optical axis position of the optical system, and the focus control of the optical system is performed so that the high frequency component becomes maximum. An electronic still camera having two focus control means.

(3) The second focus control means is the first focus control means.
Each time the focusing lens is moved by a predetermined image plane distance from the end point of the required front and rear range in the optical axis direction of the optical system with the position of the focusing lens moved by the focus control means as the center, Capture the output image of
The operation of extracting the high frequency component is repeatedly executed to the other end point of the required range, the maximum value of the repeatedly extracted high frequency component group is detected, and the focusing lens is placed at the position showing the maximum value. The electronic still camera according to (2) above, which moves the camera.

(4) The first step of performing the phase difference detection type autofocus control using the output image of the image pickup device for photographing, and the hill climbing type autofocus control using the output image of the image pickup device. A focus control method for an electronic still camera, comprising: a second step.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to Examples. In this embodiment, the pupil positions of the phase difference detection method are set to the left and right with respect to the center of the photographing lens.
However, the present invention is not limited to this, and it is possible to set the pupil position in an arbitrary direction or to set three or more pupil positions.

In the embodiment, the video signal is recorded on the recording medium, but the present invention is not limited to this, and the video signal can be output to a personal computer or the like via a line.

In the embodiment, the phase difference detection type AF is
The method is supplemented by a trial method, which is a type of mountain climbing method, but the method is not limited to this, and the method may be supplemented by a perturbation method, which is another type of mountain climbing method.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the configuration of an "electronic still camera" which is an embodiment. In FIG. 1, 1 is a photographic optical system to which image light is input, 2 is a motor for moving a focus lens and a zoom lens of the photographic optical system 1 and its driver unit, 3 is a shutter diaphragm system including a pupil position moving mechanism, 4 is an image pickup signal processing system such as a CCD that photoelectrically converts image light into a video signal, and 5 is A for digitizing the video signal.
A -D converter, 6 is a digital signal processing unit for performing various digital signal processing of the digital video signal converted by the A-D converter 5, 7 is a system control unit for the entire camera, 8
Is a PC connected to a recording medium, function card, etc.
An MCIA-compliant slot and its controller section, 9 is a buffer memory such as a DRAM used for temporarily storing digital video signals, 10 is an electronic viewfinder (EVF), 11 is an EVF driver section,
12 is a D- for sending an analog signal to the driver unit 11.
The A converter, 13 holds the image to be displayed on the EVF, and D-
VRAM that outputs a digital signal to the A converter 12, 14
Is an external black and white liquid crystal (EXT.LCD) for displaying the mode data of the camera, and 15 is the EXT.LCD. Reference numeral 16 denotes a controller such as a controller for displaying on the LCD 14 and a driver, and an operation unit such as a shutter button and a dial outside the camera.

The operation will be described below with reference to the flow charts of FIGS. The CPU of the system control unit 7 performs calculations and judgments in these flowcharts.

First, when the shutter button of the operation unit 16 is pressed halfway, that is, when SW1 is turned on (S1, YES), the system control unit 7 detects it and starts the AF operation. First, pupil time division phase difference AF (S2) is performed. This A
The sequence flow of F is shown in FIG. First, the system control unit 7 sends a control signal to the shutter diaphragm system 3,
The shutter diaphragm system 3 is set to a pupil diaphragm for AF. As shown in FIG. 5A, this is a spectacle-shaped hole for halving the aperture diameter for photography in the horizontal direction, which is the optical axis (center of the aperture hole for photography).
Are arranged symmetrically with each other, for example, one of the holes, for example, the hole on the right side of the figure is closed by a light shielding plate (S11), and only the light flux on the left side of the lens is made incident on the CCD of the image pickup signal processing system 4 such as CCD. First, photometry for setting exposure conditions is performed (S12). This photometry or data reading for fetching AF data is not a full screen but one part, and it is necessary to perform it at high speed.

Such a reading method is as follows. FIG. 6 shows a schematic diagram of an interline CCD. 61 is a pixel, 62 is a vertical charge transfer element, 64 is a horizontal charge transfer element, and 65 is an output section. The signal charges photoelectrically converted by the pixels are sent to the vertical charge transfer element 62 and sequentially transferred in the direction of the horizontal charge transfer element 64 by the four-phase drive pulses φV1, φV2, φV3 and φV4. The horizontal charge transfer element 64 transfers the signal charge for one horizontal line transferred from the vertical charge transfer element 62 to the output section 65 by the two-phase drive pulses φH1 and φH2, and is converted into a voltage and output there.

FIG. 7 shows a schematic view of the image pickup area of the CCD.
In this embodiment, in order to speed up the read operation, only the necessary read area is read at a normal speed, and the sweep transfer is performed at a high speed in other areas. Reference numeral 71 is an area to be read out as usual, and 72 and 73 are high speed sweep transfer areas in the first half and the second half, respectively. FIG. 8 shows a timing chart for one vertical synchronization period when the vertical charge transfer element 62 of the CCD is driven by four phases. VD is a vertical synchronizing signal and indicates a vertical blanking period with a LOW potential.
Is a horizontal synchronizing signal and indicates a horizontal blanking period by a LOW potential. .phi.V1, .phi.V2, .phi.V3 and .phi.V4 are four-phase drive pulses for the vertical charge transfer elements, and 81 and 82 are read pulses for transferring the signal charges photoelectrically converted in the pixels to the vertical charge transfer elements. 8 out of 4 phase drive pulses
Reference numerals 3 and 84 respectively indicate high-speed sweep transfer pulses for transferring the signal charges read out to the vertical charge transfer element 62 in the regions 72 and 73 in FIG. 7 at high speed.
By thus sweeping out the area other than the necessary read area at high speed, the speed of the partial read operation can be increased.
The exposure condition is set by the partial data thus read (S14), and the first exposure for AF is performed (S1).
5). At this time, depending on the photometric value, it may be determined that distance measurement is impossible due to low luminance (S13, YES), but at that time, although not shown as a sequence flow, FIG.
Use a diaphragm hole with a large pupil area as shown in (b). Another method is to emit auxiliary light (not shown). At that time, set the exposure condition for the auxiliary light (S
21), the auxiliary light is emitted (S22), and exposure is performed. In addition, high-speed reading is performed in the same manner as during photometry, and the data is stored in the camera (S23). Then again CC
D is reset to open the blocked aperture hole, close the other aperture hole, and set the exposure condition (S16,
S24) The second exposure is performed. For the aperture hole, use the same type as the one used the first time, that is, the same diameter.
If the auxiliary light is emitted during the first exposure, the exposure conditions for the auxiliary light are set for the second exposure, and the auxiliary light is emitted for exposure (S24, S25). Then, the partial high-speed reading is performed in the same manner as in the first time, the data is taken in (S17), the correlation calculation with the held data in the first time is performed, and the defocus amount is obtained (S18). The calculation method is the same as the conventional phase difference AF, but when a plurality of lines are used as data, for example, the correlation calculation is performed for each corresponding line, and the average of the obtained correlation value groups is calculated. Alternatively, the defocus amount is determined by averaging a plurality of line data in the vertical direction to obtain data for one line before performing the correlation calculation and then performing the correlation calculation. A lens for focusing according to claim 1, which refers to a lens (the focus lens in the case of a zoom lens, the entire lens in the case of a single focus lens, or a lens related to focusing such as a front lens) based on the calculated defocus amount. (Corresponding to) in the optical axis direction (S19),
The AF pupil stop is retracted from the optical path (S20). Of course, this retracting operation may be performed while the lens is moving. The above is a series of operations of pupil time division phase difference AF. This behavior
The process is repeated until the image surface is within the range near the in-focus state. The number of times depends on the initial position of the lens and the range setting value in the vicinity of focus, but when the initial position of the lens is in the vicinity of focus, 1
Otherwise, at least twice (in the first time, the lens is moved to the vicinity of the in-focus state, and in the second time, it is determined that the image surface is in the vicinity of the in-focus state). When it is determined that the image surface is in the vicinity of the in-focus state and is in the in-focus surface, the AF operation ends there, the in-focus display is performed, and the shooting standby state, that is, the SW2 ON state is set.

On the other hand, when it is determined that the image plane is near the in-focus state, but it is determined that it is not the in-focus plane (S4, N
O), and then the partial whole area scan AF is performed to move the image plane to the in-focus plane (S5).

The flow of this AF sequence is shown in FIG. This is to perform the full-area scan AF (trial method) partially between image planes as shown in the conventional example, and is conceptually as shown in FIG. Assuming that the lens moving position in the pupil time division phase difference AF is a point and the moving direction of the lens up to that point is the right direction in the figure, first move the lens from point a to the left by the image plane distance A.
Just move. Then, with that as a starting point, the image plane distance is shifted to the right by B, and exposure is performed at each position. This is performed from the point a to the point A on the image plane distance. B
The shift positions are R (0), R (1) ... R (N),
(R (n) -R (n-1) = B, N = 2 * A / B), the maximum high frequency component data at each position is M
(0), M (1) ... M (N), the maximum value in the maximum value data group is obtained, and if it is M (N '), the image plane position R (N ′) Is determined to have the highest contrast, that is, R (N ′) becomes the focusing surface x.

In order to find such an in-focus surface, the sequence shown in the flowchart of FIG. 4 is used. First,
The exposure pupil position is returned to the lens center (S31). This means that the AF pupil stop during the pupil time division phase difference AF is retracted out of the optical path. Next, the lens position is moved from the current position, that is, the lens position moved by the pupil time division phase difference AF, to the image plane distance A in the direction opposite to the moving direction up to that point (S32). As the moving distance A, the focusing surface must be included in the scanning range without fail, for example, the same distance as the in-focus vicinity range. After the movement, photometry is performed as in the pupil time division phase difference AF (S33). This can be done before moving the lens.
Based on this photometric result, exposure conditions are set (S35) and exposure is performed. Then, the accumulated data is read, the high frequency component of the signal is extracted, and the maximum value is stored (S3).
6). Then, after that, the lens is moved by the image plane distance B (S37). Although the accuracy of the value B should be as small as possible, the smaller the value B, the more the number of times of exposure increases, the longer the AF operation time becomes, and the AF system becomes unusable. On the contrary, B
If is set too large, the accuracy will naturally decrease, and this will also become unusable as a system. Also, since the moving speed of the lens and the reading speed of the CCD are related,
It cannot be decided unconditionally, but it must be carefully decided after looking at the entire system. Next, it is determined whether the lens position after moving the lens B is within the scanning range, and if it is within the range (S38, NO), a series of operations from the exposure of the CCD are repeated (S40, S35 to S3).
8). When it is out of the range (S38, YES), a series of repeated operations are stopped, the high frequency component maximum value data group stored up to that point is called, and the maximum value among them is obtained. Since it is determined that the image plane position at which the obtained maximum value is obtained is the in-focus plane, the lens is moved to that position (S39). Further, here, as in the case of the pupil time division phase difference AF, when it is determined that the photometric result is low luminance (S3
4, NO), and set the exposure conditions for auxiliary light (S4
1) After the auxiliary light is emitted (S42), exposure is performed to perform a series of operations (S43, S44). The above operation is performed to focus the lens, the AF operation is ended there, the focus display is performed, and the shooting standby state, that is, the SW2 onable state is set.

As described above, in the AF operation of a so-called electronic still camera in which an image is captured by the two-dimensional CCD and recorded as a video signal and recorded on some recording medium, first, the exposure pupil position is left and right with a time difference. To perform the phase difference AF using the signals exposed and read by each, and performing the pupil time division phase difference AF, it is not necessary to provide a new AF optical system or AF sensor, and With the pupil time division phase difference AF, the lens is moved to the vicinity of the in-focus state to perform the AF coarse adjustment. Next, before and after that movement position,
By scanning the entire area for the required image plane distance at a certain predetermined image plane pitch, moving the lens to the in-focus plane, and setting the shooting standby state, it is possible to narrow the scanning range. The time required for the AF is short, and it is possible to prevent the time required for the entire AF sequence, that is, the focusing time from increasing.

As described above, according to this embodiment,
The phase difference detection AF can be performed by using an optical system and an image pickup device for photographing, and the AF focusing accuracy of the phase difference detection method can be supplemented by the AF of the partial whole area scan method.

[0034]

As described above, according to the present invention,
The AF of the phase difference detection method can be performed without using a new AF optical system and AF sensor, and by supplementing the AF of the phase difference detection method with the AF of the partial hill climbing method, it is possible to achieve higher accuracy. AF can be performed in a short time.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment.

FIG. 2 is a flowchart showing the basic sequence of the embodiment.

FIG. 3 is a flowchart showing a (a) pupil time division phase difference AF sequence in FIG.

FIG. 4 is a flowchart showing (b) partial whole-area scan AF sequence in FIG.

FIG. 5 is a diagram showing a configuration of a pupil diaphragm for phase difference AF according to an embodiment.

FIG. 6 is a diagram showing a schematic configuration of an interline solid-state image sensor.

FIG. 7 is a diagram showing an outline of an image pickup area of a solid-state image pickup element.

FIG. 8 is a timing chart for one vertical synchronization period when the vertical charge transfer device of the solid-state image sensor is driven by four phases.

FIG. 9 is a diagram showing a relationship between the image plane position of a lens and a high frequency component by a partial whole area scanning method.

FIG. 10 is a diagram showing a schematic configuration of a phase difference AF optical system.

FIG. 11 is a diagram showing an AF sensor and its output.

FIG. 12 is an explanatory diagram of correlation calculation (MIN algorithm)

FIG. 13 is a diagram showing a relationship between a lens image plane position and a high frequency component by a perturbation method.

FIG. 14 is a diagram showing a relationship between an image plane position of a lens and a high frequency component by a trial method.

[Explanation of symbols]

 1 Photographic optical system 3 Shutter diaphragm system 7 System control section

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shigeki Okauchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Innovator Nobuo Fukushima 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (72) Inventor Yoshiro Udagawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Futoshi Kobayashi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. ( 72) Inventor Hiroshi Saruwatari 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Tsunefumi Tanaka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. An image pickup device for photographing, an optical system for photographing, a pupil position moving means for moving a pupil position to a position symmetrical with respect to an optical axis of the optical system, and a pupil position moving means for moving the pupil position. In addition, a focus control unit that captures an output image of the image sensor at each pupil position, obtains a defocus amount by a correlation calculation thereof, and performs focus control of the optical system based on the defocus amount is provided. Electronic still camera. 2. An image pickup device for photographing, an optical system for photographing, a pupil position moving means for moving a pupil position to a position symmetrical with respect to an optical axis of the optical system, and a pupil position moving means for moving the pupil position. The first focus control means for fetching the output image of the image pickup device at each pupil position, obtaining the defocus amount by the correlation calculation, and performing the focus control of the optical system based on the defocus amount, and the first focus control means. Second focus control is performed so that the output image of the image pickup device is captured with the pupil position as the optical axis position of the optical system and the high frequency component is maximized. An electronic still camera, comprising: 3. The second focus control means has a predetermined image from an end point of a required front-back range in the optical axis direction of the optical system centering on the position of the focusing lens moved by the first focus control means. Each time the focusing lens is moved by the surface distance, the output image of the image sensor is captured, and the operation of extracting the high frequency component is repeatedly executed to the other end point of the required range, and the repeatedly extracted high frequency band is extracted. 3. The electronic still camera according to claim 2, wherein the maximum value of the frequency component group is detected, and the focusing lens is moved to a position showing the maximum value. 4. A first step of performing a phase difference detection type autofocus control using an output image of an image pickup device for photographing, and a first step of performing a hill climbing type autofocus control using an output image of the image pickup device. 2. A focus control method for an electronic still camera, comprising: