JP2015099218A - Focal point detector, focal point detector control method, imaging device, program, and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a base length while suppressing blur of a focal-point detection signal in response to a defocus amount in one photographic optical system.SOLUTION: A focal point detector includes: an imaging element that includes imaging pixels each performing photoelectric conversion on light from a photographic optical system that includes a diaphragm and generating an image of an object, and a pair of focal-point detection pixels that include a first focal-point detection pixel and a second focal-point detection element performing photoelectric conversion on luminous fluxes passing through different pupil areas of an exit pupil of the photographic optical system, respectively; generation means generating a third focal-point detection signal on the basis of a first focal-point detection signal output from the paired focal-point detection pixels if an aperture of the diaphragm has a first aperture value, and a second focal-point detection signal output from the paired focal-point detection pixels if the aperture of the diaphragm has a second diaphragm value other than the first diaphragm value; and focal-point detection means detecting a focal state of the photographic optical system on the basis of the third focal-point detection signal.

Description

  The present invention relates to a focus detection device, a control method thereof, an imaging device, a program, and a storage medium.

  As an example of an image sensor having a functional element in which a specific function is given to a part of a pixel group constituting the image sensor, a phase difference detection function of a subject image is given to the image sensor, and a dedicated AF sensor is unnecessary, and A technique for realizing high-speed phase difference AF is disclosed.

  For example, Patent Document 1 discloses a technique for providing a pupil division function by decentering the sensitivity region of the light receiving unit with respect to the optical axis of the on-chip microlens in a part of the light receiving elements (pixels) of the imaging device. Yes. In addition, it is disclosed that these pixels are used as focus detection pixels and phase difference type focus detection is performed by disposing them at a predetermined interval between imaging pixel groups.

JP 2000-292686 A

  However, in the imaging apparatus disclosed in Patent Document 1 described above, the phase difference between a pair of focus detection signals obtained from focus detection pixels may be limited by the specifications of the photographing optical system. This will be described with reference to FIG. As shown in FIG. 14A, the light beams that have passed through different regions 1405 and 1506 of the exit pupil 1404 are placed on a pair of light receiving elements 1402 and 1403 arranged corresponding to one microlens 1401, respectively. Is imaged. Here, the pair of light receiving elements 1402 and 1403 are referred to as an A image light receiving element and a B image light receiving element, respectively. At this time, the light beams refracted and incident by the microlenses of the A image light receiving element 1402 and the B image light receiving element 1403 have a predetermined incident angle range.

  The intensity distribution of the incident light beam at the incident angle is as shown in FIG. In the figure, the intensity of the light beam incident at each incident angle, where the incident angle of light incident on the light receiving element is the positive angle on the horizontal axis, and the negative angle on the horizontal axis is the incident angle from the right side. FIG. In FIG. 14B, the sensitivity distribution with respect to the incident light beam to the A image light receiving element 1402 is shown as 1411, and the sensitivity distribution with respect to the incident light beam to the B image light receiving element 1403 is shown as 1412. The sensitivity peak is the centroid position in the region where each incident light beam passes through the exit pupil, and the interval between the centroid positions is the baseline length. Further, line signals obtained by arranging the A image light receiving element and the B image light receiving element in a line shape in the base line length direction are respectively referred to as an A image and a B image. In phase-difference focus detection using focus detection pixels, the defocus amount of the optical system is calculated by calculating the relative positional deviation amount of the A and B images, which changes according to the blur amount (defocus amount) of the subject image. To detect. The larger the defocus amount, the larger the relative positional deviation amount between the A and B images, and the sensitivity of the relative positional deviation amount between the A and B images with respect to the defocus amount is limited by the baseline length.

  That is, in one imaging optical system, the maximum baseline length of the A image light receiving element and the B image light receiving element is determined according to the radius of the exit pupil when the aperture is in the open state.

  On the other hand, the A image and the B image obtained from the focus detection pixel group are easily blurred according to the defocus amount as the diaphragm is moved toward the open side, and the calculation of the relative positional deviation amount between the A image and the B image becomes difficult.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to extend the base length while suppressing blurring of a focus detection signal corresponding to a defocus amount in one photographing optical system. .

  A focus detection apparatus according to an aspect of the present invention includes imaging pixels that photoelectrically convert light from an imaging optical system having a diaphragm to generate an image of a subject, and different pupil regions among exit pupils of the imaging optical system And a pair of focus detection pixels each having a first focus detection pixel and a second focus detection pixel for photoelectrically converting each of the light beams that have passed through the aperture, and the aperture of the aperture is a first aperture value The first focus detection signal output from the pair of focus detection pixels and the pair of focus when the aperture of the aperture is a second aperture value different from the first aperture value. A generating means for generating a third focus detection signal based on the second focus detection signal output from the detection pixel, and a focus state of the photographing optical system based on the third focus detection signal And focus detection means for detecting And wherein the door.

  According to the present invention, it is possible to extend the baseline length while suppressing blurring of a focus detection signal corresponding to the defocus amount in one photographing optical system.

1 is a configuration diagram of an imaging apparatus according to a first embodiment of the present invention. 1 is a block diagram of a solid-state imaging device according to a first embodiment of the present invention. It is the top view and sectional drawing of the pixel for an imaging of the image pick-up element of the 1st Embodiment in this invention. 2A and 2B are a plan view and a cross-sectional view of focus detection pixels of the image sensor according to the first embodiment of the present invention. It is a figure explaining the vignetting of the pixel for focus detection of the 1st Embodiment in this invention, and the gravity center space | interval of a focus detection light beam. FIG. 2 is an enlarged view of an arrangement area of focus detection pixels of the image sensor according to the first embodiment of the present invention. FIG. 2 is a layout diagram of focal regions of the image sensor according to the first embodiment of the present invention. It is a flowchart which shows operation | movement of the imaging device of 1st Embodiment in this invention. It is a flowchart which shows the operation | movement of the focus detection of 1st Embodiment in this invention. It is a flowchart which shows the operation | movement of imaging | photography of 1st Embodiment in this invention. It is correlation calculation explanatory drawing of 1st Embodiment in this invention. It is a figure explaining the gravity center space | interval of the focus detection light beam of 1st Embodiment in this invention. It is a figure explaining the gravity center space | interval of the focus detection light beam of the modification of the 1st Embodiment in this invention. It is a figure explaining the concept of the focus detection light beam in a focus detection pixel.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
<First Embodiment>
FIG. 1 is a configuration diagram of an image pickup apparatus (camera) according to the present invention, and shows an electronic camera 100 in which an image pickup apparatus main body (camera main body) having an image pickup element and a photographing lens (photographing optical system) are integrated. . In this embodiment, the electronic camera 100 is, for example, a digital camera or a video camera. Here, the imaging apparatus in which the photographing lens is integrated has been described as an example. However, the present invention is not limited to this, and imaging in which the photographing lens is attached to the imaging apparatus body in a replaceable manner. It is also applicable to the device. In the figure, reference numeral 101 denotes a first lens group disposed at the tip of a photographing optical system (imaging optical system, imaging optical system), and is held so as to be able to advance and retreat in the optical axis direction. Reference numeral 102 denotes an aperture / shutter (hereinafter also simply referred to as an aperture), which adjusts the light amount at the time of shooting by adjusting the aperture diameter, and also has a function as an exposure time adjustment shutter at the time of still image shooting. Reference numeral 103 denotes a second lens group. The diaphragm shutter 102 and the second lens group 103 integrally move forward and backward in the optical axis direction, and perform a zooming function (zoom function) in conjunction with the forward and backward movement of the first lens group 101.

  Reference numeral 105 denotes a third lens group (focus lens) that performs focus adjustment by advancing and retreating in the optical axis direction. Reference numeral 106 denotes an optical low-pass filter, which is an optical element for reducing false colors and moire in a captured image. Reference numeral 107 denotes an image sensor (imaging means) composed of a C-MOS sensor and its peripheral circuits. The image sensor 107 uses a two-dimensional single-plate color sensor in which a Bayer array primary color mosaic filter is formed on-chip on light receiving pixels of horizontal (horizontal) m pixels and vertical (vertical) n pixels. It is done. In this embodiment, the image sensor 107 includes an imaging pixel and a focus detection pixel as will be described later.

  A zoom actuator 111 rotates a cam cylinder (not shown) to drive the first lens group 101 or the second lens group 103 back and forth in the optical axis direction and perform a zooming operation. Reference numeral 112 denotes an aperture shutter actuator that controls the aperture diameter of the aperture / shutter 102 to adjust the amount of photographing light, and controls the exposure time during still image photographing. Reference numeral 114 denotes a focus actuator, which performs focus adjustment by driving the third lens group 105 back and forth in the optical axis direction.

  115 is an electronic flash (illuminating means) for illuminating a subject at the time of photographing, and a flash illumination device using a xenon tube is suitable, but an illumination device including LEDs that emit light continuously may be used. Reference numeral 116 denotes an AF auxiliary light device (AF auxiliary light means), which projects a mask image having a predetermined aperture pattern onto a subject field via a projection lens, and has a focus detection capability for a dark subject or a low contrast subject. Improve.

  Reference numeral 121 denotes a CPU (control means), which is an in-camera CPU that controls various controls of the camera 100, and includes a calculation unit, a ROM, a RAM, an A / D converter, a D / A converter, a communication interface circuit, and the like. Further, the CPU 121 functions as a focus detection unit of a phase difference detection method that obtains a phase difference between a pair of image signals using a correlation calculation based on an output from an image sensor driving circuit 124 and an image processing circuit 125 described later. Also have. Thus, the CPU 121 functions as a part of the focus detection device that detects the focus state of the photographic lens (shooting optical system). Further, various circuits included in the camera 100 are driven based on a predetermined program stored in the ROM, and a series of operations such as AF, photographing, image processing, and recording are executed.

  An electronic flash control circuit 122 controls lighting of the illumination unit 115 in synchronization with the photographing operation. Reference numeral 123 denotes an auxiliary light driving circuit that controls the lighting of the AF auxiliary light unit 116 in synchronization with the focus detection operation. An image sensor driving circuit 124 controls the image capturing operation of the image sensor 107 and A / D converts the acquired image signal and transmits the image signal to the CPU 121. An image processing circuit 125 performs processes such as γ conversion, color interpolation, and JPEG compression of the image acquired by the image sensor 107.

  A focus drive circuit 126 controls the focus actuator 114 based on the focus detection result, and adjusts the focus by driving the third lens group 105 back and forth in the optical axis direction. Reference numeral 128 denotes an aperture shutter drive circuit (aperture control means), which controls the aperture shutter actuator 112 to control the aperture of the aperture / shutter 102. Reference numeral 129 denotes a zoom drive circuit that drives the zoom actuator 111 in accordance with the zoom operation of the photographer.

  Reference numeral 131 denotes a display device (display means) such as an LCD, which displays information related to the shooting mode of the camera, a preview image before shooting and a confirmation image after shooting, a focus state display image at the time of focus detection, and the like. Reference numeral 132 denotes an operation switch group (operation means), which includes a power switch, a release (shooting trigger) switch, a zoom operation switch, a shooting mode selection switch, and the like. Reference numeral 133 denotes a detachable flash memory (storage means) that records captured images.

FIG. 2 shows a block diagram of the image sensor 107. Note that the block diagram of FIG. 2 illustrates a minimum configuration that can explain the reading operation, and a pixel reset signal and the like are omitted. In FIG. 2, reference numeral 201 denotes a photoelectric conversion unit of the image sensor 107. The plurality of photoelectric conversion units 201 are abbreviated as PDmn in FIG. Here, m is an X-direction address, and m = 0, 1,... M−1. N is a Y-direction address, and n = 0, 1,... N−1. Each photoelectric conversion unit PDmn includes a photodiode (PD), a pixel amplifier, a reset switch, and the like. In the imaging device of the present invention, m × n photoelectric conversion units are two-dimensionally arranged. Since the code is complicated, it is added only in the vicinity of the photoelectric conversion unit PD _{00 in the} upper left.

  Reference numeral 202 denotes a switch for selecting the output of the photoelectric conversion unit PDmn, which is selected for each row by a vertical scanning circuit 208 described later.

  Reference numeral 203 denotes a line memory for temporarily storing the output of the photoelectric conversion unit PDmn, and stores the output of the photoelectric conversion unit for one row selected by the vertical scanning circuit 208. For the line memory 203, a capacitor is usually used.

  A switch 204 is connected to the horizontal output line to reset the horizontal output line to a predetermined potential VHRST, and is controlled by a signal HRST.

Reference numeral 205 denotes a switch for sequentially outputting the output of the photoelectric conversion unit PDmn stored in the line memory 203 to the horizontal output line. The switches from H ₀ to H _m−1 are sequentially scanned by the horizontal scanning circuit 206 described later. As a result, the output of photoelectric conversion for one row is read out.

Reference numeral 206 denotes a horizontal scanning circuit which sequentially operates the outputs of the photoelectric conversion units stored in the line memory 203 and outputs them to the horizontal output line. The signal output to the horizontal output line is output as the signal VOUT through the output amplifier 207. The signal PHST is a data input of the horizontal scanning circuit 206, PH1 and PH2 are shift clock inputs, and data is set when PH1 = H, and data is latched at PH2. PH1, by inputting the shift clock PH2, can be by sequentially shifting the PHST, are sequentially turned on of the switches _{H m-1} from _{H 0.} SKIP is a control terminal input for setting during thinning readout. By setting the SKIP terminal to the H level, the horizontal scanning circuit can be skipped at predetermined intervals.

Reference numeral 208 denotes a vertical scanning circuit, which can select the selection switch 202 of the photoelectric conversion unit PDmn by sequentially scanning and outputting V ₀ to V _n−1 . The control signal is controlled by the data input PVST, the shift clocks PV1 and PV2, and the thinning reading setting SKIP as in the horizontal scanning circuit. Since the operation is the same as that of the horizontal scanning circuit, detailed description thereof is omitted. In the figure, the control signal is not shown.

  3, 4, and 5 are diagrams illustrating the structures of the imaging pixels and focus detection pixels provided in the imaging element 107 of the present embodiment. In this embodiment, out of 4 pixels of 2 × 2, pixels having a spectral sensitivity of G (green) are arranged in two diagonal pixels, and R (red) and B (blue) spectra are arranged in the other two pixels. A Bayer arrangement in which one pixel having sensitivity is arranged is employed. Further, focus detection pixels having a structure to be described later are arranged in a distributed manner between the Bayer arrays.

  FIG. 3 shows the arrangement and structure of the imaging pixels. FIG. 2A is a plan view of 2 × 2 imaging pixels. As is well known, in the Bayer array, G pixels are arranged diagonally, and R and B pixels are arranged in the other two pixels. The structure of 2 rows × 2 columns is repeatedly arranged.

A cross section AA of FIG. 4A is shown in FIG. ML denotes an on-chip microlens arranged in front of each pixel, CF _R is a color filter, CF _G of R (Red) is a color filter of G (Green). PD is a schematic diagram showing the photoelectric conversion unit of the C-MOS sensor, and CL is a wiring layer for forming signal lines for transmitting various signals in the C-MOS sensor. TL schematically shows the photographing optical system. EP indicates the exit pupil of the photographing optical system TL.

  Here, the microlens ML and the photoelectric conversion unit PD of the imaging pixel are configured to capture the light beam that has passed through the photographing optical system TL as effectively as possible. In other words, the exit pupil EP of the photographing optical system TL and the photoelectric conversion unit PD are conjugated with each other by the microlens ML, and the effective area of the photoelectric conversion unit is designed to be large. Further, in FIG. 5B, the incident light beam of the R pixel has been described, but the G pixel and the B (Blue) pixel have the same structure. Accordingly, the exit pupil EP corresponding to each of the RGB pixels for imaging has a large diameter, and the S / N of the image signal is improved by efficiently capturing the light flux from the subject.

FIG. 4 shows the arrangement and structure of focus detection pixels for performing pupil division in the horizontal direction (lateral direction) of the photographing optical system. Here, the definition of the horizontal direction or the horizontal direction indicates a direction along a straight line that is orthogonal to the optical axis and extends in the horizontal direction when the camera is held so that the optical axis of the photographing optical system is horizontal. FIG. 5A is a plan view of 2 × 2 pixels including focus detection pixels. When obtaining an image signal for recording or viewing, the main component of luminance information is acquired with G pixels. Since human image recognition characteristics are sensitive to luminance information, image quality degradation is easily perceived when G pixels are missing. On the other hand, the R or B pixel is a pixel that acquires color information (color difference information). However, since human visual characteristics are insensitive to color information, the pixel that acquires color information may have some loss. Image quality degradation is difficult to recognize. Therefore, in this embodiment, among the pixels of 2 rows × 2 columns, the G pixel is left as an imaging pixel, and the R and B pixels are replaced with focus detection pixels. The focus detection pixels are denoted by S _HA (first focus detection pixel) and S _HB (second focus detection pixel) in FIG. Further, S _HA (first focus detection pixel) and S _HB (second focus detection pixel) are referred to as a pair of focus detection pixels. Although not shown, the present embodiment may be provided with focus detection pixels for pupil division in the vertical direction (longitudinal direction) of the photographing optical system. Here, the definition of the vertical direction or the vertical direction means that when the imaging apparatus is held so that the optical axis of the imaging optical system and the long side of the imaging area are parallel to the ground, the optical axis extends perpendicularly to the optical axis. The direction along a straight line.

A cross section AA in FIG. 4A is shown in FIG. The microlens ML and the photoelectric conversion unit PD have the same structure as the imaging pixel shown in FIG. In this embodiment, since the signal of the focus detection pixel is not used for image creation, a transparent film CF _W (White) is disposed instead of the color separation color filter. Moreover, since pupil division is performed by the image sensor, the opening of the wiring layer CL is biased in one direction with respect to the center line of the microlens ML. Specifically, since the opening OP _HA of the pixel S _HA is biased to the right side, the light beam that has passed through the left exit pupil EP _HA of the imaging optical system TL is received. Similarly, since the opening OP _HB of the pixel S _HB is biased to the left side, the light beam that has passed through the right exit pupil EP _HB of the imaging optical system TL is received. Thus, the pixel S _HA and the pixel S _HB respectively receive (photoelectrically convert) light beams that have passed through different pupil regions of the exit pupil of the photographing optical system. Pixels _SHA are regularly arranged in the horizontal direction, and a subject image acquired by these pixel groups is defined as an A image. In addition, the pixels _SHB are also regularly arranged in the horizontal direction, and if the subject image acquired by these pixel groups is a B image, the relative positions of the A image and the B image are detected and converted with respect to the image shift amount. By multiplying by the coefficient, it is possible to calculate the amount of defocus (defocus amount) of the subject image.

  Here, how to obtain the conversion coefficient for calculating the defocus amount from the image shift amount will be described. The conversion coefficient can be calculated based on the aperture information of the photographing optical system and the sensitivity distribution of the focus detection pixels. A light flux limited by some components such as a lens holding frame of the photographing lens TL and a diaphragm / shutter 102 is incident on the image sensor 107. FIG. 5 is a diagram showing a state in which the light beam used for focus detection is limited by the vignetting of the photographing optical system. This figure shows a state in which the light flux is limited by the diaphragm / shutter 502 of the photographing optical system located at the position of the exit pupil plane 501 with respect to the pixel near the center of the image sensor (imaging device). In FIG. 5A, reference numerals 503 and 504 denote image sensors (503 indicates a state at a planned imaging plane position), 505 denotes an optical axis, and 506 denotes an optical axis position on the image sensor. Reference numerals 507 and 508 denote light beams when the light beam is limited by the diaphragm shutter 502 (in a state where the diaphragm is stopped), and reference numerals 509 and 510 denote light beams when the light beam is not limited (when the diaphragm is opened). Yes. Focus detection light beams 511 and 512 with respect to the light beams 507 and 508, and centroid positions of the focus detection light beams are indicated by 515 and 516. Similarly, reference numerals 513 and 514 denote focus detection light fluxes with respect to the light fluxes 509 and 510, and reference numerals 517 and 518 denote gravity center positions of the focus detection light fluxes.

FIG. 6B is a diagram showing a change in the position of the center of gravity due to vignetting on the exit pupil plane 501 of the focus detection pixel at the center of the image sensor. In the figure, reference numerals 523 and 524 denote the pupil regions of the light beams 507 and 508 in the aperture state and the light beams 509 and 510 in the open state with respect to the central pixel of the image sensor, and reference numerals 525 and 526 denote the focus detection pixels S. The sensitivity distribution of _HA and _SHB is shown. The focus detection pixels S _HA and S _HB receive a light beam that has passed through the inside of the shapes indicated by 523 and 524 with respect to the sensitivity distribution indicated by 525 and 526. Therefore, by obtaining the distribution centroids of the focus detection light fluxes that have passed through the inside of the shapes indicated by 523 and 524, the respective baselines are determined from the state in which the light flux used for focus detection is narrowed and the centroid interval in the open aperture state. You can ask for the length.

  By obtaining the sensitivity distribution information of the focus detection pixel and the aperture information of the photographing optical system from the measurement and calculation and storing them in a memory (aperture information storage means, sensitivity distribution storage means) (not shown) or the like, the image shift amount Thus, a conversion coefficient for calculating the defocus amount can be obtained.

  In FIG. 9A, the defocus amount 519 is DEF, and the distance 520 from the image sensor 503 to the exit pupil plane 501 is L. In addition, the base line length when the light beam used for focus detection is narrowed and when the diaphragm is opened are G2 (distance between 515 and 516) and G1 (distance between 517 and 518), respectively. Further, when the image displacement amounts are PRED2 (521) and PRED1 (522), and the conversion coefficients for converting the image displacement amount into the defocus amount are K2 and K1, the defocus amount is obtained by the following expression.

DEF = K1 × PRED1 = K2 × PRED2
Conversion coefficients K1 and K2 for converting the image shift amount into the defocus amount are obtained by the following equations, respectively.

K1 = G1 / L
K2 = G2 / L
A section AA of the sensitivity distribution in FIG. 10B is shown in FIG. In FIG. 8C, (c) -1 is a full aperture and (c) -2 is a diagram showing sensitivity distributions (533, 534) in a state where the aperture is closed. In the figure, the horizontal axis represents the light incident angle, and the vertical axis represents the sensitivity distribution. Comparing the two figures, it can be seen that the base length is longer and the incident angle width with sensitivity is wider in the fully open state. Since the base line length is proportional to the image shift amounts of the A image and the B image with respect to defocus, the sensitivity of the image shift amount to defocus increases as the base line length increases. Further, when the incident angle width having sensitivity is increased, the blur amount and image vignetting of the A image and the B image with respect to defocusing are increased. In general, as an image signal from a focus detection pixel, an image signal having high sensitivity of image shift amount with respect to defocus, small blur amount, and small image vignetting is desired. In other words, in order to perform AF with high accuracy, it is desired that the blur is small and the edge of the subject is standing, and that the base length (image shift amount) is large.

  Here, FIG. 5C is used to explain the concept of a method for extending the baseline length while suppressing the blur amount of the focus detection signal corresponding to the defocus amount in one photographing optical system that is characteristic of the present invention. I will explain.

  In the present invention, as shown in (c) -1 and (c) -2, by subtracting the pixel value of the focus detection signal obtained by varying the aperture state, as shown in FIG. In addition, a focus detection signal corresponding to an optical image formed by the light flux that has passed through the region 531 and the region 532 is acquired. In other words, the sensitivity distribution with respect to the incident angle of the light flux becomes 535 due to the subtraction, and the sensitivity is relatively high with respect to the light from the outer periphery of the lens, so the distance between the centers of gravity of the light flux passage area in the exit pupil (baseline length) ) Can be extended more than the center-of-gravity distance in the fully open state. In addition, since the incident angle width of the sensitivity distribution can be reduced, the amount of blur of the focus detection image with respect to defocus can be reduced. Thereby, the precision of imaging surface phase difference AF can be improved.

  Note that in the case of a photographing optical system in which the aperture diameter and the exit pupil diameter match, as shown in FIGS. 5A to 5C, the region where the light beam reaching the light receiving region of the focus detection pixel passes through the exit pupil. The distances between the centers of gravity (baseline lengths) G1, G2, and G3 are as follows.

G1 = D1 / 2
G2 = D2 / 2
G3 = G1 + G2
Here, D1 is the aperture diameter when the aperture is fully open, and D2 is the aperture diameter in the aperture state.

  Further, the conversion coefficient for converting the image shift amount into the defocus amount is obtained by the following equation.

K3 = G3 / L
Further, the output Pb of the focus detection pixel in the case of FIG. 5 varies depending on the optical performance of the photographing optical system and the light condensing performance due to the arrangement of the microlens and the light receiving element of the imaging unit. Based on Pa,
Pa × (D2 / D1) ≦ Pb ≦ Pa × (D2 / D1) 2
Included in the range. In this case, the output Pc in the subtracted image data is
Pc = Pa-Pb
It becomes.

FIG. 6 is a diagram showing the arrangement of the imaging pixel group and the focus detection pixel group. In the figure, G is a pixel to which a green filter is applied, R is a pixel to which a red filter is applied, and B is a pixel to which a blue filter is applied. In the figure, S _HA is a focus detection pixel formed by horizontally deviating the aperture of the pixel portion, and is a reference for detecting a horizontal image shift amount with the _SHB pixel group described later. It is a pixel group. Further, S _HB is the S _HA pixel aperture of the pixel, a pixel formed by biased in the reverse direction, the horizontal direction reference pixel group for detecting the image shift amount of the S _HA pixel group It is. The white portions of the S _HA and S _HB pixels indicate the opening positions of the biased pixels.

  FIG. 7 is an example showing a focus detection area on the imaging screen. In the drawing, the focus detection area has the pixel arrangement shown in FIG. In this embodiment, the focus detection area is set at the center on the imaging screen. However, a plurality of focus detection areas are arranged, and an image is sampled with focus detection pixels from the subject image formed in each area. It may be.

  8 to 10 are flowcharts for explaining camera focus adjustment and photographing steps. The control flow after FIG. 7 will be described with reference to the respective drawings described above. Note that each step in this flow is executed by a computer constituted by the CPU 121 according to a computer program.

  FIG. 8 is a flowchart showing the operation of the camera in this embodiment.

  When the photographer turns on the power switch of the camera in step S801, in step S802, the CPU 121 confirms the operation of each actuator and image sensor in the camera, initializes the memory contents and the execution program, and performs the shooting preparation operation. Run. In step S803, the imaging operation of the image sensor is started, and a low-pixel moving image for preview is output. In step S804, the read moving image is displayed on the display 131 provided on the back of the camera, and the photographer visually determines the composition at the time of photographing by viewing the preview image.

  In step S805, a focus detection area is determined from the image area. In this embodiment, as shown in FIG. 7, since the distance measuring points are arranged only in the center, the center area is selected. Thereafter, the process proceeds to step S901, and a focus detection subroutine is executed.

  FIG. 9 is a flowchart of the focus detection subroutine. Jump to this subroutine from step S901 of the main flow. When jumping to a subroutine, focus detection pixel signals are read out at two different aperture values in steps S902 and S903, respectively.

  In step S902, the CPU 121 sets the aperture value to an open side value (first aperture value) such as F2.0 and reads the focus detection pixel signal, and stores the obtained aperture open side data in the RAM (focus detection). (Pixel storage means). In subsequent S903, the CPU 121 sets the aperture value to a closed-side value such as F8.0 (second aperture value different from the first aperture value), reads the focus detection pixel signal, and obtains the obtained aperture value. Closed data is stored in RAM. Here, the aperture size at the first aperture value is larger than the aperture size at the second aperture value. In the present embodiment, the first aperture value is set to an aperture value that is reduced by one step from the open aperture value, and the second aperture value is set to an aperture value that is larger than the first aperture value (for example, 4 from the first aperture value). The aperture value is set to a stepped aperture value). In this embodiment, the first aperture value is set to the aperture value obtained by reducing the first aperture value by one step from the open aperture value. However, the present invention is not limited to this, and the first aperture value may be set to the open aperture value. In this way, the first aperture value is set to a value near the full aperture value. Further, in order to appropriately remove the light beam component on the aperture close side from the aperture open side focus detection pixel signal, when reading the focus detection pixel signal on the aperture close side, with respect to the exposure at the time of aperture open side readout, Read with the same exposure time. Further, in order to eliminate the change in the exposure of the preview image always displayed on the display 131, when the aperture is closed side read, a preview image whose gain is controlled to be the same as the exposure at the time of aperture open side reading is displayed.

  In step S904, the CPU 121 (generation unit and focus detection unit) subtracts the focus detection signal (second focus detection signal) on the aperture close side from the focus detection signal (first focus detection signal) on the aperture opening side. Run.

  In step S905, the correlation calculation of the focus detection signals (subtraction focus detection signal, third focus detection signal) obtained by subtraction is performed to calculate the relative positional shift amount (image shift amount) of the two images. A correlation calculation shown in the following equation is performed on a pair of image signals (a1 to an, b1 to bn: n is the number of data) read from the focus detection pixel column, and a correlation amount Corr (l) is calculated. .

  In the equation, l represents an image shift amount, and the number of data when the image is shifted is limited to n−1. The image shift amount l is an integer, and is a relative shift amount with the data interval of the data string as a unit. As shown in FIG. 11, when the correlation between a pair of data is the highest, the correlation amount Corr (l) is a minimum as shown in FIG. Further, the correlation amount Corr (m) (the minimum shift amount m) and the correlation amount calculated with a shift amount close to m are used, and a minimum with respect to the continuous correlation amount is obtained using a three-point interpolation method. A shift amount d giving a value Corr (d) is obtained.

  In step S906, the reliability of the correlation calculation result is calculated. Here, reliability refers to the degree of coincidence FLVL of two images. The coincidence degree FLVL of the two images is a value Corr (d) when the correlation is the highest with respect to the correlation amount Corr (l) calculated by the same equation. When the defocus amount is large, the asymmetry between the A image and the B image increases, so the degree of coincidence FLVL between the two images is large and the reliability deteriorates. In general, the degree of coincidence FLVL between two images with respect to the defocus amount is calculated such that the degree of coincidence FLVL between the two images is lower as the lens position is closer to the in-focus position, and the reliability tends to be higher.

  In subsequent steps S907 and 908, the defocus amount DEF is calculated by multiplying the image shift amount calculated in S905 by a predetermined defocus conversion coefficient. In step S907, the above-described defocusing state information by referring to the aperture opening side and closing side aperture state information from the sensitivity detection information of the focus detection pixels and the aperture information of the photographing optical system stored in advance is referred to. A focus conversion coefficient K3 is calculated. In step S908, the detected defocus amount DEF is obtained by using the defocus conversion coefficient K3 and the image shift amount calculated in S905.

  In step S909, it is determined whether or not the calculation up to the detected defocus amount has been completed for all the distance measurement lines in the distance measurement point. If not completed, the process returns to step S902, and the calculation is executed from step S904 in order.

  When the defocus calculation has been completed for all the distance measurement lines in the distance measurement point, the process proceeds to the next step S910, where the reliability (FLVL) of the plurality of focus detection lines in the distance measurement area is high. (Small) information is preferentially used, and a final distance measurement result is determined.

  In subsequent step S911, the process returns to step S807 in the main flow of FIG.

  In step S807 of FIG. 8, it is determined whether or not the detected defocus amount is equal to or less than an allowable value (that is, whether or not the focus is achieved). If the detected defocus amount is larger than the allowable value, it is determined that the subject is out of focus, the focus lens is driven in step S808, and then steps S901 to S807 are repeatedly executed. If it is determined in step S807 that the in-focus state has been reached (that is, the detected defocus amount is equal to or less than the allowable value), in-focus display is performed in step S809, and the process proceeds to step S810.

  In step S810, it is determined whether or not the shooting start switch has been turned on. If the switch has not been turned on, the shooting standby state is maintained in step S810. When the shooting start switch is turned on in step S810, the process proceeds to step S1001, and a shooting subroutine is executed.

  FIG. 10 is a flowchart of the photographing subroutine. When the photographing start switch is operated, via step S1001, in step S1002, the light amount adjustment diaphragm is driven to perform aperture control of the mechanical shutter that defines the exposure time. In step S1003, image reading for high-pixel still image shooting, that is, reading of all pixels is performed. In step S1004, defective pixel interpolation of the read image signal is performed. That is, the output of the focus detection pixel does not have RGB color information for imaging, and corresponds to a defective pixel in obtaining an image. Therefore, an image signal is created by interpolation from information on surrounding imaging pixels. To do.

  In step S1005, image processing such as image gamma correction and edge enhancement is performed, and in step S1006, a captured image (image signal) is recorded in the flash memory 133. In step S1007, the captured image is displayed on the display 131, and the process returns to the main flow in FIG. 8 in step S1008.

  Returning to the main flow of FIG. 8, the series of photographing operations is terminated in step S812.

The embodiments described above are merely representative examples, and various modifications and changes can be made to the embodiments when the present invention is implemented.
<< Modification of First Embodiment >>
In the first embodiment, a focus detection signal for performing a correlation calculation is generated by performing subtraction as it is on the focus detection pixel signals read respectively in two types of aperture states.

  FIG. 12 is a diagram showing the sensitivity distribution when subtracting two types of aperture states in FIG. 5B. As shown in the figure, as in the first embodiment, when subtraction of focus detection pixel signals obtained in two types of aperture states is performed, the angle of the sensitivity region 1201 and 1202 in the horizontal direction is close to 0 degrees and is vertical. It has sensitivity in the sensitivity region with the incident angle in the direction. Therefore, it is difficult to perform ideal pupil separation. Here, reference numeral 1203 in the figure denotes a light-receivable area of the focus detection pixel.

  As a first modification for performing the above ideal pupil separation, when subtraction is performed on the focus detection pixel signals read out in the two types of aperture states, the focus detection signal on the closed aperture side is used. To correct the gain. That is, in the present modification, the CPU 121 has a function as a signal correction unit that corrects the focus detection signal on the diaphragm close side. More specifically, based on the aperture information of the photographing optical system when reading the focus detection pixel and the sensitivity distribution characteristic with respect to the incident light angle of the focus detection pixel, the gain detection signal (gain) ) Make corrections. Then, subtraction focus detection is performed by subtracting the focus detection signal after gain correction (second focus detection signal after gain correction) after gain correction from the focus detection signal (first focus detection signal) at the aperture opening side. A signal (third focus detection signal) is obtained. Setting the amount of gain correction value corresponding to the sensitivity region 1203 in FIG. 12 can improve the above-described pupil separation performance.

  As a second modification for performing the ideal pupil separation, it is conceivable to limit the light receiving area of the focus detection pixels. In FIG. 12, the light-receivable region of the pair of focus detection pixels has a shape that is divided into two in the base line length direction in the unit pixel. FIG. 13 shows a shape (1301) in which the boundary of the light-receiving area is provided in the diagonal direction of the unit pixel with respect to the optical axis of the microlens when the light-receiving area divided into right and left is provided. More specifically, the aperture shape of the focus detection pixel is configured to be an arc shape with respect to the optical axis of the microlens. In this way, the focus detection pixels are set so that the sensitivity distribution shapes in the vicinity of the optical axis of the microlens of the focus detection pixel are the same in the state controlled to the first aperture value and the state controlled to the second aperture value. Design the opening shape. In other words, the aperture shape of the focus detection pixel is designed so that the sensitivity distribution shape in a predetermined range from the optical axis of the microlens is the same. However, “the same shape” as used herein includes not only a case where they completely match, but also a case where they can be regarded as matching although there is a slight difference in the range of manufacturing errors. By adopting the shape shown in the figure, it is possible to eliminate factors that deteriorate the pupil separation performance, such as the sensitivity region 1202 in FIG.

  As described above, the pupil separation performance can be further improved by implementing the first and second modifications.

According to the present invention, in an imaging device including an imaging pixel group and a focus detection pixel group, blurring of an image can be suppressed while extending a base length of a focus detection signal.
(Other embodiments)
The object of the present invention can also be achieved as follows. That is, a storage medium in which a program code of software describing a procedure for realizing the functions of the above-described embodiments is recorded is supplied to an apparatus (for example, an imaging apparatus). The computer (or CPU, MPU, etc.) of the device reads out and executes the program code stored in the storage medium.

  In this case, the program code itself read from the storage medium realizes the novel function of the present invention, and the storage medium and program storing the program code constitute the present invention.

  Examples of the storage medium for supplying the program code include a flexible disk, a hard disk, an optical disk, and a magneto-optical disk. Further, a CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD-R, magnetic tape, nonvolatile memory card, ROM, or the like can also be used.

  Moreover, the function of the above-described embodiment is realized by making the program code read by the computer executable. Further, based on the instruction of the program code, an OS (operating system) or the like running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments may be realized by the processing. included.

  Furthermore, the following cases are also included. First, the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Thereafter, based on the instruction of the program code, the CPU or the like provided in the function expansion board or function expansion unit performs part or all of the actual processing.

  The present invention can be suitably used for camera systems such as compact digital cameras, single-lens reflex cameras, and video cameras.

102 Shutter combined with shutter 107 Image sensor 121 CPU

Claims (12)

An imaging pixel that photoelectrically converts light from a photographing optical system having an aperture to generate an image of a subject, and a first light that photoelectrically converts light beams that have passed through different pupil regions of the exit pupil of the photographing optical system. An imaging device having a pair of focus detection pixels each having a focus detection pixel and a second focus detection pixel;
A first focus detection signal output from the pair of focus detection pixels when the aperture of the aperture is a first aperture value and a second focus aperture signal different from the first aperture value Generating means for generating a third focus detection signal based on the second focus detection signal output from the pair of focus detection pixels when the aperture value is set;
And a focus detection unit configured to detect a focus state of the photographing optical system based on the third focus detection signal.   The focus detection apparatus according to claim 1, wherein the generation unit generates the third focus detection signal by subtracting the second focus detection signal from the first focus detection signal. . Aperture information storage means for storing aperture information of the imaging optical system when reading the first focus detection signal and the second focus detection signal;
Sensitivity distribution storage means for storing sensitivity distribution characteristics with respect to an incident light angle of the focus detection pixels;
Signal correction means for correcting the second focus detection signal based on the aperture information and the sensitivity distribution characteristic;
The generation means generates the third focus detection signal by subtracting the second focus detection signal corrected by the signal correction means from the first focus detection signal. The focus detection apparatus according to 1 or 2.   4. The exposure time when reading the first focus detection signal and the exposure time when reading the second focus detection signal are the same length. 5. The focus detection apparatus described.   The aperture shape of the focus detection pixel is a sensitivity within a predetermined range from the optical axis of the micro lens of the focus detection pixel in a state controlled to the first aperture value and a state controlled to the second aperture value. The focus detection apparatus according to claim 1, wherein the focus detection apparatus is designed to have the same distribution shape.   The focus detection apparatus according to claim 5, wherein an aperture shape of the focus detection pixel is an arc shape with respect to an optical axis of the microlens.   The focus detection apparatus according to claim 1, wherein the second aperture value is larger than the first aperture value.   The focus detection apparatus according to claim 7, wherein the first aperture value is an open aperture value. A taking optical system including an aperture;
First focus detection that photoelectrically converts imaging pixels that photoelectrically convert light from the imaging optical system to generate an image of a subject and light beams that have passed through different pupil regions of the exit pupil of the imaging optical system An image sensor having a pair of focus detection pixels each having a pixel for detection and a second focus detection pixel;
Aperture control means for controlling the aperture of the aperture to a first aperture value and a second aperture value different from the first aperture value;
A first focus detection signal output from the pair of focus detection pixels when the aperture of the aperture is the first aperture value and the aperture when the aperture of the aperture is the second aperture value Generating means for generating a third focus detection signal based on the second focus detection signal output from the pair of focus detection pixels;
An image pickup apparatus comprising: focus detection means for detecting a focus state of the photographing optical system based on the third focus detection signal. An imaging pixel that photoelectrically converts light from a photographing optical system having an aperture to generate an image of a subject, and a first light that photoelectrically converts light beams that have passed through different pupil regions of the exit pupil of the photographing optical system. A control method of a focus detection apparatus having an image pickup device including a focus detection pixel and a pair of focus detection pixels having a second focus detection pixel,
A first focus detection signal output from the pair of focus detection pixels when the aperture of the aperture is a first aperture value and a second focus aperture signal different from the first aperture value A generating step of generating a third focus detection signal based on the second focus detection signal output from the pair of focus detection pixels when the aperture value is set;
And a focus detection step of detecting a focus state of the imaging optical system based on the third focus detection signal.   A computer-executable program in which a procedure of a control method for a focus detection apparatus according to claim 10 is described.   A computer-readable storage medium storing a program for causing a computer to execute the steps of the focus detection apparatus control method according to claim 10.