JPH11258490A - Focus detecting device and its method and storage medium readable through computer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out a highly accurate detection even if the S/D of CCD output is bad, in the case where a defocused quantity is detected from the phase difference of a plurality of images respectively image picked up through a plurality of different pupils by CCD (solid image picking up element). SOLUTION: In a focus detecting method, three or more output images are picked up through CCD 9 as right and left pupils are mutually shielded with a shading plate 5, and these output images are correlation-computed to obtain a plurality of phase differences, and the defocused quantity of a focus lens 1a is obtained on each phase difference. In this case, the S/N of the above output image is judged to alter an operation expression for the above relation computation when S/N is bad.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a focus detection apparatus and method for an image pickup apparatus using an image pickup device such as a digital camera, and a computer-readable storage medium.

[0002]

2. Description of the Related Art Conventionally, a large number of phase difference detection type focus detection devices have been used as automatic focus devices used in single-lens reflex type silver halide cameras and the like. FIG. 13 is a cross-sectional view of a single-lens reflex camera having a conventional phase difference detection type focus detection device. A light beam 109a emitted from a photographing lens 100 is reflected by a light beam 109b reflected by a main mirror 102 made of a half mirror. It is divided into a transmitted light flux 109e. The reflected light flux 109b forms an image of the subject on the diffusion surface of the focus plate 103, and the photographer can use the eyepiece 105a,
It is configured to observe a subject image on the focus plate 103 via the 105b and the pentaprism 104.

On the other hand, the light beam 10 transmitted through the main mirror 102
9e is reflected by the sub-mirror 106 and guided to the focus detection device 107. The focus detection device 107
The focus state (defocus amount) of the photographing lens 100 with respect to the silver halide film 108 is detected by the light flux 109f from 00. If it is determined that the detected defocus amount is larger than the predetermined focusing width and the camera is out of focus, the focus adjusting lens of the photographing lens 100 is driven so that the detected defocus amount is canceled. Make adjustments.

Next, the principle of focus detection of a conventional focus detection device will be described with reference to FIGS. FIG. 14 (a)
Is a focused state, that is, a focused state, and a light beam 116 that has passed through two different pupils of the photographing lens 100.
a and 116b form an image on a primary image forming surface 114, and a subject image on the primary image forming surface is placed on a sensor surface on which two line sensors 113a and 113b are arranged by secondary image forming lenses 112a and 112b, respectively. Re-image. Here, the field lens 111 is disposed near the primary image forming surface 114 of the photographing lens 100, efficiently guides a light beam having a predetermined image height to the sensor surface, and prevents a decrease in the amount of light generated as the image height increases. I do. Generally, the two light beams 116a and 116b passing through different pupils of the photographing lens 100 are defined by apertures (not shown) disposed immediately before or immediately after the secondary imaging lenses 112a and 112b. No pupil-dividing member is provided.

The two images formed on the line sensors 113a and 113b are luminous fluxes that have passed through different pupils, and the relative positions of the images depend on the amount of extension of the lens.
As shown in FIG. 5, the state differs between the in-focus, front focus, and rear focus states.
FIGS. 14A and 15A show that the distance between two images formed on the line sensors 113a and 113b in the focused state is equal to the relative distance e0 between the two line sensors. It is always constant at the time of focusing.

FIGS. 14 (b) and 15 (B) show a state in which the front focus state is set by the defocus amount d1 and the distance e1 between the two images.
Is smaller than e0, and the difference δ1 between e0 and e1 increases as the defocus amount d1 increases. FIG.
(C) and FIG. 15 (c) show a state in which the back focus state is set by the defocus amount d2, and the interval e2 between the two images is larger than e0. When the defocus amount d2 increases, e2
The difference δ2 between と and e0 also increases.

As described above, the magnitude and direction of the defocus amount at that time can be determined from the distance between the two images. Therefore, the difference between the distance e between the two images in the current defocus state and the reference image distance e0 at the time of focusing, that is, the relative shift amount (phase difference) δ = e−e0 between the two images. Is calculated by correlating the output signals of the two line sensors 113a and 113b, the defocus amount and the direction of the optical system are obtained from the phase difference, and the focusing is controlled by controlling the focus lens.

However, in a conventional single-lens reflex camera, an optical member (main mirror, sub-mirror, etc.) for guiding a light beam to a light receiving element (sensor) for focus detection and a space for disposing a focus detection device are secured. In addition, the size increases, and the cost increases accordingly. Another problem is that the relative positional relationship between the film for photography and the focus detection device changes due to a change in temperature or a change in durability of the main mirror or the sub-mirror.

On the other hand, in an image pickup apparatus such as a video camera and a digital camera, a solid-state image pickup device (CCD) is used to obtain an image, and this image pickup device is also used as a focus detection sensor. The problem can be solved. Also, video cameras that detect focus by detecting the contrast of a subject image on a CCD (a hill-climbing method) are mainly used. However, this method cannot detect an accurate defocus amount, so that a high-speed method is used. However, there is a problem that high-precision focus detection cannot be performed.

[0010] Therefore, with higher speed and higher accuracy than the hill climbing method,
In addition, as a solution to the above-described problem of the conventional phase difference method, a movable pupil is inserted into a photographing optical system, and the pupil is moved to form an optical image including light beams having different pupil regions. A phase difference method (pupil time division phase difference AF) in which an image is formed on an image pickup element for photographing, a phase difference between a plurality of images having different pupil regions obtained thereby, and a defocus amount of the photographing lens is detected. Have been.

[0011]

As described above, conventionally, in order to use both an image pickup device for photographing and a sensor for focus detection, images are taken in time series using pupil position moving means. Images with different pupils are obtained. Therefore, if there is a relative motion between the camera and the subject, the phase difference obtained from the image includes a phase shift component due to defocus and a phase shift component due to the relative motion between the camera and the subject. Therefore, in order to reduce a focus detection error due to relative movement between the camera and the subject (such as camera shake or movement of the subject), a plurality of phase differences are obtained using three or more phase difference detection signals, and a plurality of phase differences are obtained. The phase difference due to defocus is obtained by correcting the phase detection error from the phase difference.

However, the S / S of the output signal of the image sensor is
When N is bad, there is a problem that the dispersion of a plurality of phase differences used for performing the correction operation becomes large, so that the focus detection accuracy is reduced.

An object of the present invention is to provide an output signal S of an image sensor.
When / N is poor, the focus detection accuracy is reduced by changing a correction formula for obtaining a phase difference due to defocus from a plurality of phase differences.

[0014]

According to the present invention, there is provided a focus detection apparatus, comprising: an image pickup means for picking up an optical image of a subject formed on an image pickup surface and outputting an image signal; Optical system means for forming an image on an imaging surface; moving means for moving the pupil region to a plurality of positions; and a plurality of phase differences by correlating three or more image signals obtained by imaging at the plurality of positions. Calculating means for obtaining a defocus amount of the optical system means based on the phase difference, and control means for changing an arithmetic expression for obtaining the phase difference according to an output signal of the imaging means. I have.

In the focus detection method according to the present invention, an image pickup procedure for picking up an optical image of an object formed on an image pickup surface and outputting an image signal, and an optical system for forming the optical image on the image pickup surface A plurality of phase differences are obtained by a moving procedure for moving the pupil region to a plurality of positions and a correlation operation of three or more image signals obtained by imaging at the plurality of positions, respectively, and the optical system is determined based on the phase differences. And a control procedure for changing an arithmetic expression for calculating the phase difference in accordance with an output signal from the imaging procedure.

In the storage medium according to the present invention, an image pickup process for picking up an optical image of a subject formed on an image pickup surface and outputting an image signal, and a pupil in an optical system for forming the optical image on the image pickup surface A moving process of moving an area to a plurality of positions, a phase difference between three or more image signals obtained by imaging at each of the plurality of positions is obtained by a correlation operation, and defocusing of the optical system is performed based on the phase difference. A program for executing a calculation process for obtaining an amount and a control process for changing a calculation formula for obtaining the phase difference according to an output signal from the imaging process is stored.

[0017]

FIG. 1 is a view showing an embodiment of a focus detecting device and a camera using the same according to the present invention, wherein 1b is a focusing lens group of a photographing lens, and 1a is a focusing lens group of the photographing lens. The lens group 2 other than the lens group 1b is a lens extension mechanism for extending the focus lens group 1b, and includes a motor for moving the lens. Reference numeral 3 denotes a focus detection aperture, 4 denotes a motor for inserting the focus detection aperture 3 into an optical path, and 5 denotes a light shield for shielding one of the two openings 3a and 3b in the focus detection aperture 3. Reference numeral 6 denotes a motor for moving the light shielding plate 5. Reference numeral 7 denotes an optical low-pass filter, reference numeral 8 denotes an infrared cut filter, and reference numeral 9 denotes a CCD as an image pickup device which photoelectrically converts an optical image formed on an image pickup surface into an electric signal. The imaging surface of the CCD 9 is provided with a color filter shown in FIG.

Reference numeral 10 denotes an amplifier for amplifying the output from the CCD 9, reference numeral 11 denotes an A / D converter for digitizing an analog signal amplified by the amplifier 10 with a predetermined gain, and reference numeral 12
Is a digital signal processing unit that performs various digital signal processing of the A / D converted digital signal, 13 is a system control unit that controls the entire camera, and 14 is a drive control of the CCD 9 and a setting of an amplification factor of the amplifier 10. C for
A CD driver 15 is a lens control unit for controlling the extension of the focusing lens group 1b.

Reference numeral 16 denotes a buffer memory such as a DRAM used for temporarily storing digital signals, for example.
Reference numeral 17 denotes a card slot connected to a recording medium or a function card or the like and its control unit, 18 denotes an electronic viewfinder (EVF), 19 denotes a driver unit of the LCD, and 20 denotes a D / D for sending an analog signal to a driver unit 19. An A converter 21 holds an image to be displayed on the EVF 18 and outputs a digital signal to the D / A converter 20.
AM and 22 are external black and white liquid crystals (LCD) for displaying the settings of the camera, etc., 23 is an LCD driver for displaying the LCD, and 24 is an operation switch for detecting the setting of the shooting mode of the camera and the release operation. is there.

Next, a focus detection method and a focus detection device directly related to the present invention will be described with reference to FIG. Now, it is assumed that the power of the camera is turned on and the camera is in a photographable state. In order to perform pupil time division phase difference AF, the focus detection diaphragm 3 has two openings (hereinafter, referred to as CCs) having the same shape in the horizontal direction.
When viewed from the side of D9, the left opening has a left pupil 3a and the right opening has a right pupil 3b), and is inserted into the optical path of the photographing lens by a motor at the time of focus detection. By moving the light-shielding plate 5 to shield either the left pupil 3a or the right pupil 3b, an optical image composed of light beams passing through different pupil regions can be formed on the CCD 9.

In order to perform the pupil time-division phase difference AF, the focus detection diaphragm 3 is inserted into the optical path in accordance with an instruction from the system control unit 13. FIG. 2 is a diagram showing a positional relationship between the focus detection diaphragm 3 and the light shielding plate 5. FIG. 2A shows a state at the time of photographing, in which the focus detection diaphragm 3 and the light shielding plate 5 are at positions retracted outside the optical path of the photographing lens. Reference numeral 25 denotes a pupil shape when the taking aperture of the taking lens is opened.

First, as shown in FIG. 2 (b), the right pupil 3b of the focus detection aperture is closed with a light shielding plate 5, the left pupil 3a of the taking lens is opened, and an optical image composed of a light beam passing therethrough. Is imaged on the CCD 9 to capture an image. At this time, the image data for focus detection composed of the light beam that has passed through the left pupil 3a is referred to as a left image 1. Next, in order to obtain focus detection image data composed of light beams passing through different pupil regions, the motor 6 is driven to move the light shielding plate 5 as shown in FIG. 2C, and the right pupil 3b of the photographing optical system is moved. The optical image composed of the light beam that has been released and passed through the image is formed on the CCD 9 to capture the image. At this time, the image data for focus detection composed of the light beam that has passed through the right pupil 3b is defined as the right image 2.

Further, the light shielding plate 5 is moved again as shown in FIG. 2 (b) in order to take in focus detection image data composed of a light beam having passed through the same left pupil 3a as the left image 1, and at this time, the CCD 9 An image to be imaged is captured. At this time, the image data for focus detection composed of the light beam that has passed through the left pupil 3a is referred to as a left image 3. Similarly, right image 4, left image 5
Take in. Exposure when capturing image data for focus detection is performed by an electronic shutter, a mechanical shutter (not shown), gain adjustment of the amplifier 10, addition reading in the CCD 9 described later, and in some cases, auxiliary light is prepared. The adjustment is performed using the above.

By the way, the left image 1, right image 2, left image 3, right image 4, and left image 5, which are image data for focus detection, are taken in and focus detection is performed. In order to reduce the focus detection error due to relative movement between the camera and the subject (such as camera shake or movement of the subject), it is desirable that the capture interval of each image be as short as possible. Therefore, reading out the image data for focus detection requires a long time to read out the entire screen of the CCD 9 as in the case of reading out an image for photographing. Therefore, only a part of the image necessary for focus detection is usually read. Is read out faster than in the case of the main shooting.

The above reading method will be described below. FIG. 3 shows a schematic view of an interline CCD. 3
1 is a pixel, 32 is a vertical charge transfer element, 33 is a horizontal charge transfer element, and 34 is an output unit. The signal charge photoelectrically converted by each pixel 31 is sent to the vertical charge transfer element 32, and the four-phase drive pulses φV1, φV2, φV3 and φV
4 sequentially transfers in the direction of the horizontal charge transfer element 33. The horizontal charge transfer element 33 transfers the signal charges for one horizontal line transferred from the vertical charge transfer element 32 to the output unit 4 by the two-phase driving pulses φH1 and φH2, where the signal charges are converted into voltages and output.

FIG. 4 is a schematic view of an image pickup area of a CCD.
In the present embodiment, in order to speed up the read operation, only the read area necessary for focus detection is read at a normal speed,
Otherwise, high-speed sweep transfer is performed. In FIG. 4, reference numeral 41 denotes an area for reading at a normal speed used for focus detection, and reference numerals 42 and 43 denote high-speed sweep transfer areas in the first half and the second half, respectively.

FIG. 5 shows that the vertical charge transfer device 32 of the CCD is
A timing chart for one vertical synchronization period in the case of phase driving is shown. VD is a vertical synchronization signal, a vertical blanking period is indicated by a LOW potential, and HD is a horizontal synchronization signal, and a horizontal blanking period is indicated by a LOW potential. φV
1, φV2, φV3 and φV4 denote four-phase driving pulses of the vertical charge transfer element 32, and 51 and 52 denote readout pulses for transferring the signal charges photoelectrically converted by the pixels 31 to the horizontal charge transfer element 33. 53 and 54 of the four-phase drive pulses are 42 and 43 in FIG. 4, respectively.
A high-speed sweeping transfer pulse for transferring the signal charges read out to the vertical charge transfer elements 32 in the area of the area at a high speed. By sweeping out the area other than the necessary read area at high speed in this manner, the partial read operation can be speeded up.

When reading out the focus detection signal,
The signal charges of a plurality of lines are added using the horizontal charge transfer element 33, and the addition and reading of the plurality of lines can be performed. This is to compensate for the light quantity shortage that occurs at the time of focus detection because the pupils 3a and 3b of the focus detection aperture 3 are smaller than when the shooting aperture is opened at the time of actual shooting.
It is used to increase the sensitivity together with the gain of the amplifier 3.

Using the focus detection image data left image 1, right image 2, left image 3, right image 4, and left image 5 thus read out at high speed, a correlation operation between the images is performed. By detecting the phase difference between the images, focus detection is performed.However, unlike a monochrome sensor dedicated to focus detection such as that used in a single-lens reflex type silver halide camera, an image sensor for photographing is used. When the sensor also serves as a focus detection sensor, since a color filter is built in a single-plate color sensor that is an imaging element for photographing, an output signal from the CCD is used as a phase difference detection signal. In order to use it, signal processing must be performed.

As described above, it is possible to use a luminance signal generated by using a luminance signal processing circuit for photographing as a signal for detecting a phase difference, but the luminance signal for photographing is subjected to a predetermined matrix operation. Considering the time required for focus detection, the shorter the time for the arithmetic processing for generating the phase difference detection signal from the output signal of the image sensor, the better, but using a luminance signal processing circuit for photography. There is a problem that it takes too much time to calculate the phase difference detection signal.

A description will now be given of an arithmetic process for obtaining a phase difference detection signal for focus detection from the output signal of the CCD.
FIG. 6A is a diagram showing a color filter array formed on a CCD. Ye, Cy, M constituting color filter
g, G (yellow, cyan, magenta, green) 4
When the colors are added one pixel at a time, Ye + Cy + Mg + G =
Since 2B + 3G + 2R, 1 of adjacent 2 × 2 pixels
The average of the outputs of the blocks is used as a phase difference detection signal.

Actually, as described above, line addition reading is possible when reading from the CCD 9, so by performing two-line addition reading, two vertical pixels are added in the CCD (FIG. 6B), and this analog signal is output. A / D converter 1
The digital signal is converted into a digital signal by 1 and the operation of two pixels in the horizontal direction is performed in the digital signal processing unit 12 (FIG. 6C).
A phase difference detection signal is obtained by averaging the outputs of one block of × 2 pixels.

In FIG. 6, the pitch of the phase difference detection signal is p with respect to the pixel pitch p of the CCD.
Further, in this embodiment, the vertical addition is performed in the CCD in order to improve the S / N. However, the readout may be performed without performing the line addition, and the vertical addition may also be performed by digital signal processing.

Next, a phase difference is obtained by performing a correlation operation using the phase difference detection signal obtained as described above. FIG.
8 and 9 are views for explaining the focus detection principle of the pupil time division phase difference AF according to the present invention. FIG. 7 shows a focused state, that is, a focused state. In the photographing state of FIG. 7C, the light flux 27 transmitted through the photographing lens 1 is CC.
Focus is on the light receiving surface of D9, and the defocus amount is zero.

FIG. 7A shows a state in which the focus detecting diaphragm 3 is inserted on the optical path of the photographing lens, the right pupil 3b is shielded by the light shielding plate 5, and the left pupil 3a is opened with the left pupil 3a opened. The luminous flux 27a forms an image at a position zero away from the optical axis 26 on the light receiving surface of the CCD 9. FIG. 7B shows a state in which the left pupil 3 a is shielded by the light shielding plate 5 and the right pupil 3 b is opened, and the light beam 27 a passing through the right pupil 3 b is separated from the optical axis 26 by zero on the light receiving surface of the CCD 9. Image at the position. As described above, in the focused state, the optical images composed of the light beams that have passed through the two different pupils 3a and 3b are both incident on the light receiving surface of the CCD 9 from the optical axis 26 at the same zero position. Is zero.

FIG. 8 shows a state in which the defocus amount is in the front focus state by d, and in the photographing state of FIG.
The light flux 27 passing through is focused before the light receiving surface of the CCD 9 by d. FIG. 8A shows a state in which the focus detection diaphragm 3 is inserted on the optical path of the photographing lens 1 and the left pupil 3a is opened.
Is formed at a position + δ / 2 away from the optical axis 26 on the light receiving surface of. FIG. 8B shows a state in which the right pupil 3b is opened, and the light beam 27a passing through the right pupil 3b forms an image on the light receiving surface of the CCD 9 at a position separated by -δ / 2 from the optical axis 26. Thus, in the front focus state, two different pupils 3a, 3b
The phase difference between the two images composed of the luminous flux passing through is (+ δ
/ 2)-(-δ / 2) = δ.

FIG. 9 shows a state in which the defocus amount is in the back focus state by d. In the photographing state shown in FIG.
The light flux 27 passing through is focused behind the light receiving surface of the CCD 9 by d. FIG. 9A shows a state in which the focus detection diaphragm 3 is inserted into the optical path of the photographing lens 1 and the left pupil 3a is opened.
Is formed at a position -δ / 2 away from the optical axis 26 on the light-receiving surface of the light-emitting device. 9B, with the right pupil 3b opened, the light beam 27a passing through the right pupil 3b forms an image on the light receiving surface of the CCD 9 at a position away from the optical axis 26 by + δ / 2. Thus, in the front focus state, two different pupils 3a, 3b
The phase difference between the two images composed of the luminous flux passing through is (−δ
/ 2)-(+ δ / 2) =-δ. As described above, 2 composed of the light beam that has passed through the left pupil 3a and the right pupil 3b
The focus state can be detected by calculating the phase difference between the phase difference detection signals of the two images.

Next, the algorithm for calculating the phase difference will be described. First, for simplicity of explanation, a case where the relative position between the subject and the photographing optical system has not moved will be described as an example. A phase difference between a phase difference detection signal (left image) composed of a light beam having passed through the left pupil region and a phase difference detection signal (right image) composed of a light beam having passed through the right pupil region is obtained by a correlation operation. Now, as shown in FIG. 10, the phase difference detection signal is composed of M (horizontal) × N (vertical) signals, and m × n signals are cut out of these signals to perform a correlation operation.

As shown in the following equation (1), the position of the left image: a is fixed, and the right image: b
Calculates the integral value C (τx, τy) of the product of a and b (τx, τy are integer variables) while sequentially shifting the phase (τx, τy) with respect to the left image, and calculates each phase (τx, τy). A value C (τx, τy) obtained for each τy) is defined as a correlation amount between the two images.

[0040]

(Equation 1)

The correlation amount C (τx, τy) takes a minimum value, and the phase (τx, τy) at this time is the phase difference (δx, δy) between the data a of the left image and the data b of the right image. Equivalent to. Further, the phase (τx,
τy) is not an integer value (the signal pitch of the phase difference detection signal is the same as the pixel pitch of the CCD as shown in FIG. 6).
In order to obtain the value below the decimal point, the phase difference may be calculated by interpolation using the minimum value of the correlation amount and values before and after the minimum value.

When the relative position between the subject and the photographing optical system has not moved, if there is no influence of noise or the like,
δy becomes zero in principle. In addition, to reduce the effects of subject pattern, contrast, etc., the effects of differences in shooting conditions, the effects of the color filter array built into the solid-state image sensor, and the effects of noise, the filter processing is performed on the phase difference detection signal. , A correlation operation may be performed.

Since the relationship between the phase difference and the amount of movement of the image plane and the amount of defocus are determined by the optical system, the amount of defocus is obtained from the phase difference, and the amount of extension necessary for focusing is obtained. Is performed, and focus is achieved.
Up to this point, if there is no relative movement between the subject and the optical system,
The method of performing focus detection using two images composed of light beams that have passed through different pupil regions has been described.

Next, a description will be given of a phase difference calculation algorithm in the case where there is a relative movement between the subject and the optical system. The phase difference can be obtained from two images (left image and right image) composed of light beams of different pupil regions. In the present embodiment, the left image and the right image are chronologically captured, and the subject If there is a relative movement of the optical system (such as camera shake or movement of a subject), a focus detection error is included due to the influence.

Therefore, as described above, the readout of the focus detection image data does not involve reading out the entire screen of the CCD as in the case of reading out the image for photographing, but only a part of the image necessary for focus detection. The reading is performed at a higher speed than in the case of the normal main photographing, and the image capturing interval is devised as short as possible. However, the operation of capturing the signals of the left image and the right image is temporally different, and if there is a relative movement between the camera and the subject during this time, it is inevitable that an error occurs in the phase difference detection.

Therefore, in the present embodiment, as described above, the left image 1, the right image 2, the left image 3, the right image 4, the left image 5, and the five Using a plurality of phase differences obtained from the captured images and between the images, detection errors due to relative movement between the camera and the subject (such as camera shake or subject movement) are corrected. When the camera and the subject move relatively, the effect appears in the phase difference (δx, δy) between the two images. Here, δy is the phase difference in the vertical direction of the image and is a direction perpendicular to the phase shift direction generated in accordance with the optical defocus amount, so that the phase shift component due to defocus is not included, and the relative position between the camera and the subject is not included. There is only a phase shift component due to movement. Therefore, the value of δy is used as it is as the correction amount of the vertical image movement due to the relative movement between the camera and the subject.

Δx is the phase difference in the horizontal direction of the image, which corresponds to the phase shift direction generated in accordance with the optical defocus amount. Therefore, the value δx obtained from the two images including the relative movement of the camera and the subject includes: A phase shift component due to defocus and a phase shift component due to relative movement between the camera and the subject are included.

FIG. 11 shows the position of the image in the horizontal direction (x direction) due to the relative movement of the camera and the subject after correcting the image movement due to the relative movement of the camera and the subject in the vertical direction, and the phase difference between the images. The relationship is shown. Solid lines L1, R2,
L3, R4, and L5 are left images 1, right images 2,
A left image 3, a right image 4, and a left image 5, where t = t1, t
2, t3, t4, and t5 are capture times of the respective images, and the capture time intervals of the respective images are equal. Dashed line R
1 ', L2', R3 ', L4', R5 'are L
1, R2, L3, R4, and L5 indicate the position of an image composed of light fluxes that have passed through different pupils when the capturing is performed at the same time. A signal that cannot be captured in practice. It is.

M1, m2, m3, and m4 are the amounts of movement on the image due to the relative movement of the camera and the subject during each image capturing time, and δ is a phase shift component due to defocus of the optical system. This is the phase difference to be obtained as focus detection.

First, images L1 and R2 composed of different pupils,
The respective phase differences δ1, δ2, δ3, δ4 of R2 and L3, L3 and R4, and R4 and L5 are determined based on the left image.
As can be seen from FIG. 15, each phase difference obtained here includes a phase shift component due to defocus and a phase shift component due to relative movement between the camera and the subject.

FIG. 12 is a diagram for explaining a method of correcting a phase difference detection error. The horizontal axis is the time axis t, and the vertical axis is the horizontal position x of the subject image. L1, R2, L3, R
4. L5 is the position of the subject image captured in time series, and while capturing this signal, the movement of the subject image due to the relative motion between the camera and the subject is approximated by a quadratic function, so that the left image at times t2 and t4 is obtained. Subject position L2 ', L
Find the position of 4 '. And the phase difference δ between L2 ′ and R2.
The average value of 2 ′ and the phase difference δ4 ′ between L4 and R4 ′ is defined as the finally obtained phase difference δ.

(T1, x1), (t3, x3), (t
5, x5), the quadratic function y = At ² + Bt is calculated as t1 =
0, x1 = 0, and the finally obtained phase difference δ is δ
When obtained from the average value of 2 ′ and δ4 ′, since the capture interval of each image is now equal, the corrected phase difference δ is given by the following equation (2). δ = (δ1 + 3 × δ2 + 3 × δ3 + δ4) / 8 (2)

Next, the case where the S / N of the output signal of the image pickup device (CCD 9 in FIG. 1) is poor will be described. When the S / N of the output signal of the image sensor is poor, the dispersion of the plurality of phase differences δ1, δ2, δ3, and δ4 used for obtaining the corrected phase difference δ increases. If this variation is greater than the phase shift component between the camera and the subject due to relative motion,
It is not appropriate to use the correction operation expression (2) for obtaining the corrected phase difference δ because only the weights of δ2 and δ3 are large.

Therefore, in the first embodiment of the present invention,
When the S / N exceeds a predetermined value, the correction operation equation (2) is converted into a plurality of phase differences δ1, δ2, δ3, δ as shown in the following equation (3).
The arithmetic mean of No. 4 is the corrected phase difference δ. δ = (δ1 + δ2 + δ3 + δ4) / 4 (3)

As the means for determining the S / N of the output signal of the image sensor, the result of AF AE is used. AE for AF
Before inserting the left image 1 of the phase difference detection signal, that is, inserting the focus detection diaphragm 3 in the optical path of the photographing lens,
The right pupil 3b of the photographing lens is closed by the light shielding plate 5, an optical image composed of a light beam passing through the left pupil 3a of the photographing lens is formed on the CCD, and the focus is set in the same optical state as that for taking in the phase difference detection signal. This is performed using signals in the same area as used for detection. The output signal from the CCD is subjected to the same processing as that for calculating the phase difference detection signal. If the exposure level obtained from this signal is darker than a predetermined value, the exposure conditions are changed.

In the pupil time-division phase difference AF, since the focus detection diaphragm 3 is inserted in the optical path of the photographing lens, the diaphragm value is fixed and cannot be changed while the phase difference detection signal is being captured. Therefore, the exposure is adjusted by adjusting the accumulation time in the CCD and the output gain of the CCD. However, if the adjustment time is longer than the predetermined time, the equation (2)
Even if the correction of the phase difference detection error due to the relative motion between the camera and the subject is performed, the focus detection may be adversely affected, and therefore, the correction may be performed by adjusting the output gain of the CCD.

As described above, when the exposure is adjusted by the output gain of the CCD, when the gain is increased, the S / N of the image is increased.
Gets worse. Therefore, if the result of the AF AE is darker than a predetermined value with respect to the proper exposure, an image having a poor S / N is obtained, and thus an image having a poor S / N is determined. That is, if the exposure of the phase difference detection signal is lower than the proper exposure, the image obtained by the CCD is dark and the S / N is poor, so the phase difference detection signal is darker than a predetermined value. In the case of performing the capture, the determination is made that the S / N ratio is poor, and the correction operation expression is switched from Expression (2) to Expression (3).

From the thus obtained phase difference δ corrected for the relative movement between the camera and the subject, the amount of extension necessary for focusing is obtained, and the focus control of the optical system is performed. Until the focus detection is repeated until focusing is performed, shooting is performed. In the case of a camera system that falls within a predetermined allowable defocus amount in the first focus detection and focus control of the optical system, the second focus detection for confirmation is not performed (close-out focusing), and shooting starts. Is also good.

After focusing has been performed in this manner, the focus detection diaphragm 3 is retracted from the optical path of the photographing lens, and photographing is performed. Then, the data of the CCD 9 is read for recording, subjected to image signal processing by the digital signal processing unit 12, subjected to processing such as image data compression if necessary, and recorded on a recording medium via the card slot 13. At this time, the image data is subjected to video processing for finder display in the digital signal processing unit 12,
Displayed in F18. This allows the photographer to check the subject image.

In this embodiment, the method of using the AE result for AF has been described as a method of determining the S / N for the output signal of the image sensor. S / N may be determined. In this case, if the previous variation of the plurality of phase differences δ1, δ2, δ3, δ4 exceeds a predetermined value, it is determined that the S / N is poor, and the correction calculation equation is calculated from Equation (2) to Equation (3). Switch to

Further, the S / N may be determined based on the change in the phase difference δ after correction, which is the focus detection result up to the previous time. If the focus detection result does not converge within the allowable defocus amount despite the focus detection being repeated a predetermined number of times or more, this may be due to poor S / N. Switches the correction operation expression from Expression (2) to Expression (3).

Next, a second embodiment will be described. Second
In the embodiment, when the S / N of the output signal of the image sensor is poor, the number of times of taking in the phase difference detection signal used for obtaining the phase difference δ is increased. Hereinafter, only different points from the first embodiment will be described, and the description of the same portions as the first embodiment will be omitted. When the S / N of the output signal of the image sensor is poor, the dispersion of the plurality of phase differences δ1, δ2, δ3, and δ4 used for the correction operation increases, and the focus detection accuracy decreases. Therefore, if the number of acquisitions of the phase difference detection signal necessary for obtaining the plurality of phase differences is increased, the number of the plurality of phase differences is increased, and the average value thereof is obtained as the corrected phase difference δ, the variation is reduced. It is possible to suppress a decrease in focus detection accuracy due to a large value.

Therefore, if it is determined that the S / N is poor based on the result of the AF AE or the focus detection result up to the previous time, the number of times of taking in the phase difference detection signal is increased from 5 times to 10 times. Image L with pupil switched in time series
1, R2, L3, R4, L5, R6, L7, R8, L
9, taking R10, L1 and R2, R2 and L3, L3
, R4 and L5, R5 and L6, L6 and R7, R7 and L8, R8 and L9, L9 and R10, respectively.
1 to δ9 are obtained. Then, the arithmetic expression of the correction is calculated by calculating the arithmetic mean of the plurality of phase differences as shown in the following equation (4).
And δ = (δ1 + δ2 + δ3 + δ4 + δ5 + δ6 + δ7 + δ8 + δ9) / 9 (4)

The case where the number of captures is increased from five to ten has been described, but the number of captures is not limited to this.

The system using the functional blocks shown in FIG. 1 may be configured as hardware, or may be configured as a microcomputer system including a CPU, a memory, and the like. When configured in a microcomputer system,
The memory constitutes a storage medium according to the present invention. The storage medium stores a program for executing each of the above-described processes. The storage medium is RO
A semiconductor memory such as M or RAM, an optical disk, a magneto-optical disk, a magnetic medium, or the like may be used. These are CD-RO
M, a floppy disk, a magnetic tape, a nonvolatile memory card, or the like.

[0066]

As described above, according to the present invention,
By changing an arithmetic expression for obtaining the defocus amount from a plurality of phase differences according to the imaging output, for example, by changing to an arithmetic average of a plurality of phase differences when the S / N is poor, focus detection accuracy can be improved. Can be suppressed. Also,
By increasing the number of times of capturing images for obtaining the phase difference, it is possible to suppress the influence of variations in a plurality of phase differences due to poor S / N, and to suppress a decrease in focus detection accuracy.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a focus detection device and a camera using the same according to the present invention.

FIG. 2 is a configuration diagram illustrating a positional relationship between a focus detection diaphragm and a light shielding plate.

FIG. 3 is a configuration diagram of an interline CCD.

FIG. 4 is a configuration diagram of an imaging area of a CCD.

FIG. 5 is a timing chart for one vertical synchronization period when a vertical charge transfer element of a CCD is driven in four phases.

FIG. 6 is a configuration diagram for explaining arithmetic processing when a phase difference detection signal is obtained.

FIG. 7 is a diagram for explaining the principle of focus detection.

FIG. 8 is a diagram for explaining the principle of focus detection.

FIG. 9 is a diagram for explaining the principle of focus detection.

FIG. 10 is a configuration diagram for explaining how to take a correlation when a phase difference is obtained by a correlation operation.

FIG. 11 is a waveform diagram showing a relationship between a horizontal position of an image due to a relative movement between a camera and a subject and a phase difference between the images.

FIG. 12 is a characteristic diagram for explaining a method of correcting a phase difference detection error.

FIG. 13 is a configuration diagram of a single-lens reflex camera having a conventional phase difference detection type focus detection device.

FIG. 14 is a configuration diagram for explaining a conventional focus detection principle.

FIG. 15 is a waveform chart for explaining a conventional focus detection principle.

[Explanation of symbols]

1a Focusing lens group of photographing lens 1b Lens group other than focusing lens group 1b of photographing lens 2 Lens extension mechanism 3 Focus detection aperture 4 Motor 5 Shield plate 6 Motor 9 CCD 12 Digital signal processing unit 13 System control unit 14 CCD Driver 24 Operation switch

Claims (12)

[Claims] An imaging unit configured to capture an optical image of a subject formed on an imaging surface and output an image signal; an optical system configured to form the optical image on the imaging surface through a pupil region; Moving means for moving the region to a plurality of positions; and calculating a plurality of phase differences by correlation calculation of three or more image signals obtained by imaging at the plurality of positions,
A focus detection device, comprising: a calculation unit that calculates a defocus amount of the optical system unit based on the phase difference; and a control unit that changes a calculation formula that calculates the phase difference according to an output signal of the imaging unit. 2. An apparatus according to claim 1, further comprising: a determination unit configured to determine an S / N of an output signal of the imaging unit, wherein the control unit determines the phase difference when the S / N of the output signal of the imaging unit is determined to be bad. 2. The focus detection device according to claim 1, wherein the number of times of acquiring the image signal to be obtained is increased. 3. The focus detection apparatus according to claim 1, wherein said control means changes said arithmetic expression according to S / N of an output signal of said imaging means. 4. The apparatus according to claim 1, wherein said control means sets said arithmetic expression to an arithmetic mean of said plurality of phase differences when the S / N of an output signal of said imaging means is poor. Focus detection device. 5. An imaging procedure for capturing an optical image of a subject formed on an imaging surface and outputting an image signal, and a pupil region in an optical system for forming the optical image on the imaging surface at a plurality of positions. A moving procedure for moving, and a plurality of phase differences are calculated by a correlation operation of three or more image signals obtained by imaging at the plurality of positions,
A focus detection method comprising: a calculation procedure for obtaining a defocus amount of the optical system based on the phase difference; and a control procedure for changing a calculation formula for obtaining the phase difference in accordance with an output signal from the imaging procedure. 6. A determination procedure for determining the S / N of an output signal according to the imaging procedure is provided, and when the S / N of the output signal according to the imaging procedure is determined to be poor by the control procedure,
6. The focus detection method according to claim 5, wherein the number of times of acquiring the image signal for obtaining the phase difference is increased. 7. The focus detection method according to claim 5, wherein the arithmetic expression is changed in accordance with the S / N of an output signal in the imaging procedure according to the control procedure. 8. The arithmetic procedure according to claim 5, wherein the arithmetic expression is an arithmetic average of the plurality of phase differences when the S / N of an output signal obtained by the imaging procedure is poor.
The focus detection method as described above. 9. An image pickup process for picking up an optical image of a subject formed on an image pickup surface and outputting an image signal, and pupil regions in an optical system for forming the optical image on the image pickup surface at a plurality of positions. A moving process of moving, and a calculating process of obtaining a phase difference between three or more image signals obtained by imaging at the plurality of positions by a correlation calculation, and calculating a defocus amount of the optical system based on the phase difference. A computer-readable storage medium storing a program for executing a control process of changing an arithmetic expression for obtaining the phase difference according to an output signal from the imaging process. 10. An S / N ratio of an output signal obtained by the imaging process.
A determination process for determining the phase difference, and when the control process determines that the S / N of the output signal by the imaging process is poor, increasing the number of times of acquiring the image signal for obtaining the phase difference. Item 10. A computer-readable storage medium according to item 9. 11. The computer-readable storage medium according to claim 9, wherein the arithmetic expression is changed according to the S / N of an output signal by the imaging process by the control process. 12. The computer according to claim 9, wherein the arithmetic expression is set to an arithmetic mean of the plurality of phase differences when the S / N of an output signal obtained by the imaging process is poor due to the control process. A readable storage medium.