JP2018018032A - FOCUS DETECTION DEVICE, FOCUS DETECTION METHOD, IMAGING DEVICE, PROGRAM, AND STORAGE MEDIUM - Google Patents

Abstract

A technique for accurately correcting a focus detection error caused by lateral chromatic aberration of a photographing optical system is realized. A focus detection apparatus includes: a first focus for each color from a first focus detection pixel in an imaging device having a plurality of focus detection pixels that receive light beams respectively passing through different pupil partial regions of an imaging optical system; An acquisition means for acquiring a detection signal and acquiring a second focus detection signal for each color from the second focus detection pixel; and focus detection using the first focus detection signal and the second focus detection signal. A focus detection unit that performs the focus detection error caused by the chromatic aberration of magnification of the imaging optical system, and the correction unit is used when the focus detection unit performs focus detection. And first correction processing means for correcting the signal for each color with respect to the second focus detection signal, and the focus detection means obtained by performing focus detection using the first and second focus detection signals. The amount of defocus At least one of the second correction processing means for correcting in accordance with the magnification chromatic aberration. [Selection] Figure 4

Description

  The present invention relates to a technique for correcting a focus detection error caused by lateral chromatic aberration of a photographing optical system.

  As one method for detecting the focus state of the photographing lens, an imaging surface phase difference type automatic focus detection method that performs pupil division type focus detection using a two-dimensional image sensor in which a microlens is formed in each pixel ( Imaging surface phase difference AF) is known. In Patent Document 1, in order to perform focus detection of the pupil division method, the photoelectric conversion unit of each pixel constituting the imaging device is divided into a plurality of parts, and the divided photoelectric conversion unit is a photographic lens via a microlens. Are configured to receive light beams that have passed through different regions of the pupil.

  The imaging plane phase difference AF can simultaneously detect the defocus direction (defocus direction) and defocus amount (defocus amount) based on a pair of image signals obtained from focus detection pixels provided in the image sensor. The focus adjustment operation can be performed at high speed. On the other hand, since the imaging surface phase difference AF performs focus detection using an image signal obtained by imaging an optical image, the aberration of the lens that forms the optical image may cause an error in the focus detection result. A method for reducing the focus detection error has been proposed.

  Patent Document 2 discloses a method for correcting a focus detection error caused by a shape of a pair of optical images formed by a pair of focus detection light beams in an in-focus state being not matched due to an aberration of an optical system. Has been. Patent Document 3 discloses an imaging apparatus capable of restoring an image signal in accordance with the vignetting state of a light beam. Patent Document 4 discloses a method of correcting a focus detection error with a correction value corresponding to a combination of information regarding the state of the photographing lens, information regarding the state of the image sensor, and image height.

JP 2008-52009 A JP 2013-171251 A JP 2010-117679 A JP 2014-222291 A

  Conventionally, in the imaging plane phase difference AF, the mechanism of the focus detection error due to the chromatic aberration of magnification of the photographing optical system has not been known in detail, and it is not known that the focus detection error is particularly strongly influenced by the characteristics of the image sensor. . In addition, the characteristics of an image sensor mounted on a product such as a camera are not far from the design value due to characteristic variations inherent to the image sensor and assembly errors. Since the correction value of the focus detection error caused by the chromatic aberration of magnification of the photographing optical system is calculated on the assumption of the design value of the image sensor, there is a problem that the focus detection error may not be accurately corrected during actual use. is there.

  The present invention has been made in view of the above problems, and an object thereof is to realize a technique for accurately correcting a focus detection error caused by lateral chromatic aberration of a photographing optical system.

  In order to solve the above-described problems and achieve the object, a focus detection apparatus according to the present invention is a first imaging device having a plurality of focus detection pixels that receive light beams respectively passing through different pupil partial regions of a photographing optical system. Acquisition means for acquiring a first focus detection signal for each color from the focus detection pixels and acquiring a second focus detection signal for each color from the second focus detection pixels; the first focus detection signal; and A focus detection unit that performs focus detection using a second focus detection signal; and a correction unit that corrects a focus detection error caused by lateral chromatic aberration of the imaging optical system. The correction unit includes the focus detection unit. First correction processing means for performing signal correction for each color with respect to the first and second focus detection signals used when the means performs focus detection; and the focus detection means for the first and second focus Focus detection using detection signal At least one of the second correction processing means for correcting the focal shift amount obtained was in the magnification chromatic aberration of the imaging optical system.

  According to the present invention, it is possible to accurately correct a focus detection error caused by lateral chromatic aberration of a photographing optical system.

The block diagram which shows the apparatus structure of this embodiment. FIG. 3 is a diagram illustrating a configuration of a pixel of an image sensor of the present embodiment. FIG. 3 is a diagram illustrating a conjugate relationship between an exit pupil plane of the imaging optical system of the present embodiment and a photoelectric conversion unit of an image sensor. 5 is a flowchart illustrating focus detection processing based on imaging surface phase difference AF according to the first embodiment. 5 is a flowchart illustrating signal correction filter calculation processing for each color in FIG. 4. FIG. 4 is an explanatory diagram of a method for adjusting the center of gravity of a signal correction filter for each color according to the first embodiment. FIG. 3 is an explanatory diagram of a method for adjusting the center of gravity of a signal correction filter according to the first embodiment. The figure which illustrates the signal strength of the focus detection signal of each color in an in-focus state. The figure which illustrates pupil intensity distribution of a focus detection signal. The figure which shows the relationship between the pupil partial area | region in peripheral image height, and the exit pupil of an imaging optical system. FIG. 4 is a diagram illustrating a focus detection area in the image sensor according to the embodiment. 9 is a flowchart illustrating focus detection processing by imaging surface phase difference AF according to the second embodiment. 13 is a flowchart showing focus detection result correction value calculation processing of FIG.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. The embodiment described below is an example for realizing the present invention, and should be appropriately modified or changed according to the configuration and various conditions of the apparatus to which the present invention is applied. It is not limited to the embodiment. Moreover, you may comprise combining suitably one part of each embodiment mentioned later.

[Embodiment 1]
In this embodiment, as an example of an imaging apparatus equipped with a focus detection apparatus, a single-lens reflex digital camera with an interchangeable lens having an automatic focus adjustment (autofocus: AF) function of a contrast method (TVAF method) and an imaging surface phase difference method However, digital cameras and digital video cameras that are not interchangeable lenses, personal computers and their types of tablets, mobile phones and their types of smartphones, PDAs (personal digital assistants), game consoles, medical devices It can be applied to equipment.

  <Apparatus Configuration> With reference to FIG. 1, the configuration and functions of the imaging apparatus of this embodiment will be described.

  The digital camera (hereinafter referred to as a camera) according to the present embodiment includes a lens unit 100 and a camera body 120. The lens unit 100 is detachably connected to the camera body 120 via a mount M indicated by a dotted line in the center of the drawing.

  A lens unit 100 that forms a subject image includes a first lens group 101, a diaphragm 102, a second lens group 103, a focus lens group (hereinafter referred to as a focus lens) 104, and a drive / control system described later. The lens unit 100 includes a focus lens 104 and forms a photographing optical system that forms an optical image of a subject.

  The first lens group 101 is disposed at the tip of the lens unit 100 and is held so as to be able to advance and retreat in the optical axis direction OA. In the following, the optical axis direction OA is the Z direction, and the direction of viewing the subject side from the camera is the positive direction. In the present embodiment, the origin 0 of the axis in the Z direction corresponds to the position of the image sensor 122 of the camera body 120 described later.

  The diaphragm 102 adjusts the light amount at the time of photographing by adjusting the aperture diameter. The aperture 102 also functions as a mechanical shutter that controls the exposure time during still image shooting. The aperture 102 and the second lens group 103 can move forward and backward in the optical axis direction OA as a unit, and realize a zoom function by moving in conjunction with the first lens group 101.

  The focus lens 104 can advance and retreat in the optical axis direction OA, and the subject distance (focus distance) at which the lens unit 100 is focused changes according to the position. In the present embodiment, by controlling the position of the focus lens 104 in the optical axis direction OA, an object focus detection (focus detection) and an autofocus function for adjusting the focus distance are realized.

  The drive / control system of the lens unit 100 includes a zoom actuator 111, an aperture / shutter actuator 112, a focus actuator 113, a zoom drive unit 114, an aperture / shutter drive unit 115, and a focus drive unit 116 as a drive system. In addition, a lens MPU 117 and a lens memory 118 are provided as a control system for controlling the drive system.

  The zoom actuator 111 performs zoom control to drive the first lens group 101 and the second lens group 103 forward and backward in the optical axis direction OA and change the angle of view of the photographing optical system. The aperture / shutter actuator 112 controls the aperture diameter of the aperture 102 to adjust the amount of photographing light, and controls the opening / closing operation of the aperture 102 to control the exposure time during photographing. The focus actuator 113 performs an autofocus operation by driving the focus lens 104 back and forth in the optical axis direction OA, and also has a function of detecting the current position of the focus lens 104.

  The zoom drive unit 114 drives the zoom actuator 111 according to the zoom operation of the photographer or the control value of the lens MPU 117. The aperture / shutter driver 115 drives the aperture / shutter actuator 112 to control the aperture diameter or opening / closing operation of the aperture 102. The focus driving unit 116 drives the focus actuator 113 to drive the focus lens 104 forward and backward in the optical axis direction OA to perform an autofocus operation.

  The lens MPU 117 performs all calculations and control related to the photographing optical system, and controls the zoom driving unit 114, the aperture / shutter driving unit 115, the focus driving unit 116, and the lens memory 118. The lens MPU 117 is connected to the camera MPU 125 via the mount M so that commands and data can be communicated. For example, the lens MPU 117 detects the current position of the focus lens 104 and notifies lens position information in response to a request from the camera MPU 125. This lens position information includes the position of the focus lens 104 in the optical axis direction OA, the position and diameter of the exit pupil in the optical axis direction OA when the optical system is not moving, and the optical axis of the lens frame that restricts the luminous flux of the exit pupil. Contains information such as position and diameter in direction OA. The lens MPU 117 controls the zoom driving unit 114, the aperture / shutter driving unit 115, and the focus driving unit 116 in response to a request from the camera MPU 125. The lens memory 118 stores in advance optical information necessary for the imaging plane phase difference AF of the present embodiment. Further, the lens memory 118 stores, for example, a defocus map indicating a correspondence relationship between the position and movement amount of the focus lens 104 and the defocus amount. As will be described later, the defocus map calculates an image shift amount at each pixel position of the first focus detection signal (AF A image) and the second focus detection signal (AF B image) by correlation calculation. However, it is generated by converting the image shift amount into a defocus amount. Accordingly, when the lens MPU 117 receives a request to change the defocus amount by a predetermined amount from the camera MPU 125, the lens MPU 117 refers to the defocus map stored in the lens memory 118 and only the distance corresponding to the predetermined defocus amount. It is possible to control the focus actuator 113 so as to move the focus lens 104. The camera MPU 125 controls the operation of the lens unit 100 by executing a program stored in the ROM 125a or the lens memory 118, for example. The lens memory 118 also stores information on the chromatic aberration of magnification of the photographing optical system of the present embodiment.

  The camera body 120 includes an optical low-pass filter 121, an image sensor 122, and a drive / control system described later. The optical low-pass filter 121 reduces false colors and moire in the captured image.

  The image sensor 122 is composed of, for example, a CMOS image sensor and its peripheral circuits. The CMOS image sensor has a photoelectric conversion element provided in each pixel that receives light, and has a pixel group (imaging surface) in which a plurality of unit pixels are arranged two-dimensionally with each pixel as a unit pixel. The imaging element 122 has a plurality of focus detection pixels that receive light beams that pass through different pupil regions of the imaging optical system, and can output independent signals for each pixel. Thereby, it is possible to calculate the defocus amount by the imaging surface phase difference AF. In addition, the imaging element 122 includes a plurality of imaging pixels that generate a subject image signal (image signal) by receiving light beams passing through the entire exit pupil of the photographing optical system that forms the subject image.

  The drive / control system of the camera body 120 includes an image sensor drive unit 123, an image processing unit 124, a camera MPU 125 that controls the entire camera body 120, a display unit 126, an operation switch 127, a memory 128, a first focus detection unit 129, and a first focus detection unit 129. A bifocal detection unit 130 is included. The image sensor driving unit 123 controls the charge accumulation operation of the image sensor 122, converts the image signal read from the image sensor 122 into a digital signal, and sends the digital signal to the camera MPU 125. The image processing unit 124 performs various image processes such as gamma conversion, color interpolation, and JPEG compression on the image signal read from the image sensor 122. The image processing unit 124 also generates an image signal for focus detection using an imaging surface phase difference method, which will be described later, and an evaluation value for TVAF using a contrast method.

  The camera MPU 125 includes a microprocessor and performs all calculations and controls related to the camera body 120. Thus, the image sensor driving unit 123, the image processing unit 124, the display unit 126, the operation switch 127, the memory 128, the first focus detection unit 129, and the second focus detection unit 130 are controlled. The camera MPU 125 is connected to the lens MPU 117 via a signal line arranged on the mount M. As a result, a request for acquiring the lens position is issued to the lens MPU 117, a request for zoom driving, aperture driving, and lens driving with a predetermined driving amount is issued, and optical information specific to the lens unit 100 is provided. Issue a request to get.

  The camera MPU 125 includes a ROM 125a that stores a program for controlling the operation of the camera, a RAM 125b that stores variables, and an EEPROM 125c that stores various parameters. The camera MPU 125 reads a program stored in the ROM 125a, develops it in the RAM 125b, and executes it, thereby executing a focus detection process described later. The EEPROM 125c stores sensitivity information of RGB colors described later.

  The display unit 126 includes a display device such as an LCD (liquid crystal) panel or an organic EL, and displays various types of information regarding each operation mode of the camera. The operation mode of the camera includes, for example, a shooting mode for shooting a still image or a moving image, and a playback mode for playing back a captured image stored in the memory 128. In the case of the shooting mode, information on the shooting mode of the camera, a preview image before shooting and a confirmation image after shooting, a focus state image at the time of focus detection, and the like are displayed. In addition, the moving images being shot are sequentially displayed.

  The operation switch 127 includes a shutter switch, a power switch, a zoom switch, a mode switch, and the like. The memory 128 is a flash memory that can be attached to and detached from the camera, and records captured images.

  The first focus detection unit 129 performs phase difference type focus detection using the image signal for focus detection obtained by the image processing unit 124 (phase difference AF). Specifically, the image processing unit 124 generates a pair of focus detection image signals formed by light beams passing through the pair of pupil regions of the photographing optical system, and the first focus detection unit 129 detects the pair of focus detections. A defocus amount is detected based on the image shift amount of the image signal for use. As described above, the first focus detection unit 129 of the present embodiment performs phase difference AF (imaging surface phase difference AF) based on the output of the image sensor 122 without using a sensor dedicated to AF.

  The second focus detection unit 130 performs a contrast type focus detection process (contrast AF) based on the TVAF evaluation value (contrast information of the image data) generated by the image processing unit 124. Since the contrast AF is a known technique for moving the focus lens 104 and detecting the focus lens position where the evaluation value reaches a peak as the in-focus position, a detailed description is omitted.

  FIG. 11A illustrates a focus detection area set in the image sensor 122. Imaging surface phase difference AF and contrast AF are performed based on the image signal obtained from the image sensor 122 within the focus detection region. In FIG. 11, a rectangle indicated by a dotted line indicates the imaging surface 1110 of the imaging element 122. In the imaging surface 1110, three lateral focus detection areas 1111ah, 1111bh, and 1111ch for performing imaging surface phase difference AF are formed. In the present embodiment, the focus detection area for the imaging surface phase difference AF is configured to have a total of three locations, that is, the central portion of the imaging surface 1110 and the left and right two locations. Further, focus detection areas 112a, 1112b, and 1112c for performing contrast AF are formed so as to include each of the three focus detection areas 1111ah, 1111bh, and 1111ch for the imaging surface phase difference AF. Note that FIG. 11 shows a configuration in which focus detection areas are arranged roughly in three areas. However, the present invention is not limited to this, and a plurality of areas may be arranged at arbitrary positions.

  As described above, the camera of the present embodiment is equipped with the phase difference type and contrast type AF functions, and either one can be selectively executed according to the shooting situation or the like, and both can be executed in combination. it can.

  <Description of Focus Detection Operation Using Imaging Surface Phase Difference Method> Next, the focus detection operation by the first focus detection unit 129 of the present embodiment will be described with reference to FIG.

  FIG. 2A shows a pixel arrangement of the image sensor 122 of the present embodiment, and the range of 6 rows and 8 columns in the horizontal (X direction) of the two-dimensional C-MOS area sensor is shown on the lens unit 100 side. The state seen from. The image sensor 122 is provided with a Bayer color filter. In the Bayer arrangement according to the present embodiment, for example, green (G) and red (R) color filters are alternately arranged in the X direction from the left for pixels in odd rows, and from the left for pixels in even rows. In order, blue (B) and green (G) color filters are alternately arranged in the X direction. In the pixel 211, a circle 211i represents an on-chip microlens, and a plurality of rectangles 211a and 211b arranged inside the on-chip microlens represent photoelectric conversion units, respectively.

  The image sensor 122 of the present embodiment includes a first focus detection pixel and a second focus detection pixel that receive light beams that pass through different pupil partial regions of the photographing optical system. In this embodiment, the photoelectric conversion units of all the pixels of the image sensor are divided into two in the X direction, and the sum of the photoelectric conversion signal of one divided region and the two photoelectric conversion signals can be read independently. The configuration may be divided into a plurality of sections in the X direction and the Y direction. Further, by subtracting the photoelectric conversion signal of one region divided from the sum of two photoelectric conversion signals, a signal corresponding to the photoelectric conversion signal of the other region can be obtained. The photoelectric conversion signals of these divided regions can be used for phase difference focus detection described later, and can also generate a 3D (3-Dimensional) image composed of a plurality of images having parallax information. On the other hand, the sum of two photoelectric conversion signals is used as a normal captured image.

  Here, the image signal for focus detection (focus detection signal) will be described. In this embodiment, the microlens 211i in FIG. 2A and the divided photoelectric conversion units 211a and 211b divide the emitted light beam of the photographing optical system into pupils. Then, for a plurality of pixels 211 within a predetermined range arranged in the same pixel row, an A image for AF is formed by joining the outputs of the photoelectric conversion unit 211a, and the output of the photoelectric conversion unit 211b is joined. This is used as an AF B image. The outputs of the photoelectric conversion units 211a and 211b are pseudo luminances calculated by adding the outputs of green (G), red (R), blue (B), and green (G) included in the unit array of the color filter. Y) Use the signal. However, an AF A image and an AF B image may be knitted for each of red, blue, and green colors. By obtaining the relative image shift amount between the AF A image and the AF B image generated in this way by correlation calculation, the defocus amount (defocus amount) of the predetermined region can be detected. In the present embodiment, the sum of the output of one photoelectric conversion unit and the output of all the photoelectric conversion units is read from the image sensor 122. For example, when the output of the photoelectric conversion unit 211a and the sum of the outputs of the photoelectric conversion units 211a and 211b are read, the output of the photoelectric conversion unit 211b is obtained by changing the output of the photoelectric conversion unit 211a from the sum of the outputs of the photoelectric conversion units 211a and 211b. Obtained by subtraction. In this way, the imaging plane phase difference AF is realized by acquiring both the AF A image and the AF B image. Note that the imaging surface phase difference AF using the imaging device of the present embodiment is known as disclosed in, for example, Japanese Patent Application Laid-Open No. 2004-134867, and thus detailed description thereof is omitted.

  FIG. 2B illustrates the configuration of the readout circuit of the image sensor 122 of this embodiment. Reference numeral 151 denotes a horizontal scanning circuit, and 153 denotes a vertical scanning circuit. Horizontal scanning lines 152a and 152b and vertical scanning lines 154a and 154b are wired at the boundary between the pixels, and signals are read out to the photoelectric conversion units through these scanning lines.

  Note that the imaging device of the present embodiment has the following two types of readout modes in addition to the readout method in the pixel described above. The first readout mode is called an all-pixel readout mode and is a mode for capturing a high-definition still image. In this case, signals of all pixels are read out.

  The second readout mode is called a thinning readout mode and is a mode for performing only moving image recording or display of a preview image. In this case, since the number of pixels required is smaller than that of all the pixels, the pixel group reads out only the pixels thinned out at a predetermined ratio in both the X direction and the Y direction. Also, when it is necessary to read at high speed, the thinning-out reading mode is used in the same manner. When thinning out in the X direction, signals are added to improve the S / N ratio, and thinning out in the Y direction ignores the signal output of the thinned out rows. The imaging plane phase difference AF and contrast AF are also usually performed based on the signal read in the second readout mode.

  <Conjugate relationship between exit pupil plane of photographic optical system and photoelectric conversion unit of image pickup device> Next, referring to FIG. 3, the exit pupil plane of the photographic optical system and the image height zero, that is, the image in the camera of this embodiment. The conjugate relationship of the photoelectric conversion units of the image sensor arranged near the center of the surface will be described. The photoelectric conversion unit of the image sensor and the exit pupil plane of the imaging optical system are designed to have a conjugate relationship by an on-chip microlens. The exit pupil of the photographic optical system generally coincides with the surface on which the iris diaphragm for adjusting the amount of light is placed. On the other hand, the photographing optical system of the present embodiment is a zoom lens having a zoom function. However, depending on the optical type, when the zoom operation is performed, the distance and size of the exit pupil from the image plane change. FIG. 3 shows a state where the focal length of the lens unit 100 is at the center between the wide-angle end and the telephoto end. Using the exit pupil distance Zep in this state as a standard value, the optimum design of the eccentricity parameter according to the shape of the on-chip microlens and the image height (X, Y coordinates) is made. A set pupil distance of the image sensor 122 designed in accordance with the exit pupil distance Zep is defined as Ds.

  In FIG. 3A, 101 is a first lens group, 101 b is a lens barrel member that holds the first lens group, 104 is a focus lens, and 104 b is a lens barrel member that holds the focus lens 104. Reference numeral 102 denotes an aperture, reference numeral 102a denotes an aperture plate that defines an aperture diameter when the aperture is opened, and reference numeral 102b denotes an aperture blade for adjusting the aperture diameter when the aperture is closed. Note that reference numerals 101b, 102a, 102b, and 104b that act as limiting members for the light flux passing through the photographing optical system indicate optical virtual images when observed from the image plane. Further, the synthetic aperture in the vicinity of the stop 102 is defined as the exit pupil of the lens, and the distance from the image plane is Zep as described above.

  The pixel 2110 in FIG. 3A is disposed in the vicinity of the center of the image plane, and is referred to as a center pixel in this embodiment. The center pixel 2110 is composed of photoelectric conversion units 2110a and 2110b, wiring layers 2110e to 2110g, a color filter 2110h, and an on-chip microlens 2110i from the bottom layer. The two photoelectric conversion units are projected onto the exit pupil plane of the photographing optical system by the on-chip microlens 2110i. In other words, the exit pupil of the imaging optical system is projected onto the surface of the photoelectric conversion unit via the on-chip microlens 2110i.

  FIG. 3B shows a projected image of the photoelectric conversion unit on the exit pupil plane of the photographing optical system, and the projected images on the photoelectric conversion units 2110a and 2110b in FIG. 3A are EP1a and EP1b, respectively. In the present embodiment, the imaging device has a pixel that can obtain the output of either one of the two photoelectric conversion units 2110a and 2110b and the sum of both. The sum of both outputs is a photoelectric conversion of the light beam that has passed through both regions of the projection images EP1a and EP1b, which are almost the entire pupil region of the photographing optical system.

  In FIG. 3A, when the outermost part of the light beam passing through the photographing optical system is denoted by L, the light beam L is regulated by the aperture plate 102a of the diaphragm, and the projected images EP1a and EP1b are vignetted by the photographing optical system. Almost no occurrence. In FIG.3 (b), the light beam L of Fig.3 (a) is shown by TL. Since most of the projected images EP1a and EP1b of the photoelectric conversion unit are included in the circle indicated by TL, it can be seen that almost no vignetting occurs. Since the light beam L is limited only by the aperture plate 102a of the diaphragm, TL can be restated as 102a. At this time, at the center of the image plane, the projected states EP1a to EP1b are symmetrical with respect to the optical axis, and the light amounts received by the photoelectric conversion units 2110a and 2110b are equal.

  When performing imaging surface phase difference AF, the camera MPU 125 controls the imaging device driving unit 123 so as to read the above-described two types of outputs from the imaging device 122. Then, the camera MPU 125 gives information related to the focus detection area to the image processing unit 124, generates an AF A image and an AF B image from the output of the pixels in the focus detection area, and supplies them to the first focus detection unit 129. In this manner, the image processing unit 124 is controlled. The image processing unit 124 generates an AF A image and an AF B image according to the control of the camera MPU 125 and outputs them to the first focus detection unit 129.

  In the present embodiment, the configuration in which the exit pupil is divided into two in the horizontal direction is illustrated. However, for some pixels in the image sensor, the exit pupil may be split in two in the vertical direction. Further, the exit pupil may be divided in both the horizontal and vertical directions. By providing pixels that divide the exit pupil in the vertical direction, it is possible to perform imaging plane phase difference AF corresponding to the subject contrast in the vertical direction as well as in the horizontal direction.

  As described above, the image sensor 122 of the present embodiment has not only a function of capturing an image but also a function as a focus detection device. In addition, as a focus detection method, since the focus detection pixel which receives the light beam which divided | segmented the exit pupil is provided, it is possible to perform imaging surface phase difference AF.

  <Imaging surface phase difference AF processing sequence> Next, the imaging surface phase difference AF processing of this embodiment will be described with reference to FIGS.

  First, an outline of AF processing will be described. The camera MPU 125 acquires the defocus amount using the AF A image and the AF B image under the shooting conditions described later. The AF A image and the AF B image are signals corrected by the first signal correction filter for each color and the second signal correction filter for each color according to the present embodiment in accordance with the chromatic aberration of magnification of the lens. . Then, the camera MPU 125 drives the focus lens 104 based on the defocus amount.

  Next, details of the imaging surface phase difference AF process described above will be described with reference to FIGS. 4 and FIG. 5 are executed mainly by the camera MPU 125, unless other main entities are specified. When the camera MPU 125 drives and controls the lens unit 100 by transmitting a command or the like to the lens MPU 117, the operation subject may be described as the camera MPU 125 for the sake of simplicity. The same applies to FIGS. 12 and 13.

  In step S401, the camera MPU 125 sets shooting conditions such as a shutter time Tv, an aperture value F, and a focus detection area. The focus detection area to be set may be determined according to the main subject or may be set in advance. In the present embodiment, as shown in FIG. 11B, representative coordinates (x1, y1) are set for the focus detection area corresponding to the face area 1114 of the main subject 1113, and the representative coordinates are shown in FIG. A description will be given as the coordinates of the center of the focus detection area 1111ch of a).

  In step S402, the camera MPU 125 acquires an AF signal used for the imaging plane phase difference AF. An A image for AF (AF_A (i)) formed by joining the outputs of the photoelectric conversion unit 211a and the output of the photoelectric conversion unit 211b for a plurality of pixels 211 within a predetermined range arranged in the same pixel row of the image sensor 122. A B image for AF (AF_B (i)) knitted by joining together is acquired. In S402, the AF image signal is a signal immediately after being acquired for each RGB from the image sensor 122, and has each RGB value individually (AF_A (i) = {rA (i), gA (i)). , BA (i)}, AF_B (i) = {rB (i), gB (i), bB (i)}).

  In step S403, the camera MPU 125 communicates with the lens MPU 117, and performs signal correction for each color based on the shooting conditions (lens exit pupil distance, aperture value: F, image height: (x1, y1)) set in step S401. Determine whether to do it. The exit pupil distance of the lens varies depending on the zoom state and focus state of the lens. Among the shooting conditions, if the exit pupil distance of the lens is greater than or equal to the set pupil distance of the image sensor, the set aperture is less than a predetermined value, or the set image height is less than a predetermined value, it is determined that color sensitivity correction is not performed. The process proceeds to S406. Also, among the shooting conditions, if the exit pupil distance of the lens is less than the set pupil distance, the set aperture is greater than or equal to a predetermined value, and the set image height is greater than or equal to a predetermined value, the lens memory 118 is stored using the shooting conditions. The magnification chromatic aberration information that matches the photographing conditions is acquired from the lens information. Then, it is determined whether or not signal correction for each color is performed using the acquired magnification chromatic aberration information. If it is determined that the focus detection error due to the magnification chromatic aberration is large and signal correction for each color is performed, the process proceeds to S404. . If it is determined that the focus detection error due to the chromatic aberration of magnification is small and signal correction for each color is not performed, the process proceeds to S406.

  In step S404, the camera MPU 125 calculates a signal correction filter for each color for performing signal correction for each color. In this embodiment, the RGB sensitivity ratios corresponding to the AF A image and the AF B image are made uniform. Here, the signal correction filter calculation processing for each color according to the present embodiment will be described with reference to FIGS.

In step S <b> 501, the camera MPU 125 matches the pupil intensity distribution of the AF A image and the AF B image stored in the EEPROM 125 c and information on the photographing optical system (lens vignetting information, etc.) stored in the lens memory 118. Thus, the first line image distribution function LSF_xA (i) for each color of the AF A image and the AF B image at coordinates (x1, y1), which are representative values of the focus detection area 1111ch, and the second color-specific second image distribution function LSF_xA (i). A line image distribution function LSF_xB (i) (x represents an RGB subscript) is calculated. Here, i represents the X coordinate within the focus detection range.
AF A images: LSF_rA (i), LSF_gA (i), LSF_bA (i)
B image for AF: LSF_rB (i), LSF_gB (i), LSF_bB (i)
The A image for AF and the B image for AF correspond to the RGB A and B images in FIG.

  In S502, the camera MPU 125 sets the line image distribution functions LSF_xA (i) and LSF_xB (i) for each color of the AF A image and the AF B image created in S501 to the provisional defocus amount stored in the EEPROM 125c. Accordingly, the integrated light quantity is changed so as not to change, and line image distribution functions LSF_xA ′ (i) and LSF_xB ′ (i) at the time of provisional defocusing are calculated.

Next, details of the processing from S503 to S505 will be described with reference to FIGS. In S503, the camera MPU 125 calculates the center-of-gravity X coordinates Cog_xXA 'and Cog_xXB' of the line image distribution functions LSF_xA '(i) and LSF_xB' (i) at the time of provisional defocus created in S502 (FIG. 6). Further, the line image distribution functions LSF_xA ′ (i) and LSF_xB ′ (i) at the time of provisional defocus created in S502 are sampled for each sampling pitch Fil_p stored in the EEPROM 125c, and the sampling line images LSF_xA ″ ( i) The centroid X coordinates Cog_xXA ″ and Cog_xXB ″ of LSF_xB ″ (i) are calculated. Then, centroid differences ΔCog_xXA and ΔCog_xXB are calculated from the calculated centroids Cog_xXA ″, Cog_xXB ″, Cog_xXA ″, and Cog_xXB ″.
ΔCog_XA = {Cog_rXA′−Cog_rXA ″, Cog_gXA′−Cog_gXA ″, Cog_bXA′−Cog_bXA ″}
ΔCog_XB = {Cog_rXB′−Cog_rXB ″, Cog_gXB′−Cog_gXB ″, Cog_bXB′−Cog_bXB ″}
Furthermore, the signal correction filter length is calculated using the calculated barycenter differences ΔCog_xXA and ΔCog_xXB. As the signal correction filter length to be calculated, an X coordinate range including the centroid differences ΔCog_xXA and ΔCog_xXB is set.

  In S504, the camera MPU 125 calculates the X coordinates Fil_xXA (i) and Fil_xXB (i) after the centroid adjustment of the signal correction filters Fil_xA (i) and Fil_xB (i). This is because the centroid differences ΔCog_xXA and ΔCog_xXB calculated in S503 are subtracted from the common X coordinates LSF_xXA (i) and LSF_xXB (i) in the sampling line images LSF_xA ″ (i) and LSF_xB ″ (i) calculated in S503. Thus, the X coordinates Fil_xXA (i) and Fil_xXB (i) after the center of gravity adjustment of the signal correction filter are calculated.

  In step S <b> 505, the camera MPU 125 calculates signal correction filter values Fil_xA (i) and Fil_xB (i) after the center of gravity adjustment, and deforms them to make the signal correction filters for each color. Here, a method of calculating the signal correction filter values Fil_xA (i) and Fil_xB (i) after the center of gravity adjustment will be described with reference to FIG. The camera MPU 125 uses the line image distribution functions LSF_xA ′ (i) and LSF_xB ′ (i) in which the intensity at the filter length calculated in S503 is transformed in S502 for each sampling pitch Fil_p of the signal correction filter stored in the EEPROM 125c. Calculate by integrating the area. At this time, the integration range differs depending on the magnitude relationship between the sampling pitch Fil_p of the signal correction filter and the pitch LSF_p of the line image distribution functions LSF_xA ′ (i) and LSF_xB ′ (i).

  FIG. 7 is an explanatory diagram in the case of Fil_p> LSF_p. In this case, the value of the calculated j-th signal correction filter Fil_xA (j) is the area of the line image distribution functions LSF_xA ′ (i) and LSF_xB ′ (i) in the range of ± Fil_p / 2 with respect to Fil_xA (j). Is calculated by integrating. Then, the area is calculated by the signal correction filter length calculated in S503, the values of the signal correction filters Fil_xA (i) and Fil_xB (i) after the centroid adjustment are calculated, and the first signal correction filter for each color is calculated. The second signal correction filter for each color is used. In this way, after calculating the first signal correction filter for each color and the second signal correction filter for each color, the process proceeds to S405 in FIG.

  In this embodiment, the RGB intensities corresponding to the AF A image and the AF B image at coordinates (x1, y1), which are representative values of the focus detection area 1111ch, are R_Ap (rAp / gAp, 1, bAp / gAp) and R_Bp. Although described as a format of (rBp / gBp, 1, bBp / gBp), it may be a format of R_Ap (rAp, gAp, bAp) and R_Bp (rBp, gBp, bBp) normalized by G pixels.

Returning to FIG. 4, in step S405, the camera MPU 125 performs signal correction for each color using the signal correction filter for each color calculated in step S404. Details of the signal correction for each color in S405 will be described with reference to FIG. FIG. 8A shows the RGB intensities of the AF A image and the AF B image before the color-by-color signal correction, and FIG. 8B shows the RGB intensities of the AF A image and the AF B image after the color-by-color signal correction. Sensitivity. The camera MPU 125 acquires the first signal correction filter Fil_xA ′ (i) for each color and the second signal correction filter Fil_xB ′ (i) for each color calculated in S404 in S402 illustrated in FIG. 8A. The corrected AF A image (AF_A (i)) and AF B image (AF_B (i)) are corrected by performing convolution integration on each of R, G, and B, and the AF A after color-by-color signal correction shown in FIG. An image (AF_A ′ (i)) and an AF B image (AF_B ′ (i)) are generated.
AF_A ′ (i) = {(AF_rA (i) * Fil_rA), (AF_gA (i) * Fil_gA), (AF_bA (i) * Fil_bA)}
AF_B ′ (i) = {(AF_rB (i) * Fil_rB), (AF_gB (i) * Fil_gB), (AF_bB (i) * Fil_bB)}
As described above, the AF A image (first focus detection signal) after the signal correction for each color is convolved with the second signal correction filter for each color, and the AF B after the signal correction for each color is performed. The RGB intensity correction of the AF A image and the AF B image can be performed by convolving and integrating the first signal correction filter for each color with respect to the image (second focus detection signal).

  In step S406, the camera MPU 125 performs Bayer addition on the AF A image and the AF B image before or after the color signal correction by the image processing unit 124. If it is determined in S403 that signal correction for each color is performed, the AF A image and the AF B image corrected in S405 are used. If it is determined in S403 that the signal correction for each color is not performed, the AF A image and the AF B image acquired in S402 are used.

  In step S407, the camera MPU 125 performs shift processing based on the shift amount stored in the EEPROM 125c by the first focus detection unit 129, and the first focus detection unit 129 uses a known correlation calculation method or the like. An image shift amount representing the degree of coincidence is calculated and converted into a defocus amount.

  In S <b> 408, the camera MPU 125 communicates with the lens MPU 117 based on the defocus amount obtained in S <b> 407 and sends a control command to the focus driving unit 116. Then, based on the control command, the focus driving unit 116 drives the focus lens 104 via the focus actuator 113, and the AF process is ended.

  <Mechanism of generation of focus detection error due to lateral chromatic aberration> Next, a mechanism for generating a focus detection error due to lateral chromatic aberration will be described. The lateral chromatic aberration is a phenomenon in which light emitted from the same subject causes a color shift on the image sensor 122 due to a difference in refractive index depending on a wavelength.

  FIG. 8 illustrates color line image distribution functions of the AF A image and the AF B image at the in-focus position when the focus detection area is the peripheral image height. FIG. 8A shows each color line image before the signal correction for each color, and FIG. 8B shows each color line image after the signal correction for each color. In both FIG. 8A and FIG. 8B, the vertical axis represents sensitivity, and the AF A image and the AF B image are normalized by G sensitivity. The horizontal axis corresponds to lateral chromatic aberration, and the barycentric position of the line image is different between RGB. Each line image barycenter position of the AF A image and the AF B image in the same color is substantially the same at the focus detection focus position. The focus detection focus position is a correct focus position as AF, and is an MTF peak position.

  Comparing the sensitivities of R and G in FIG. 8A, R has a smaller signal intensity than G in the AF A image. On the other hand, in the AF B image, R is more sensitive than G. Regarding B, in comparison with G, the A image for AF and the B image for AF are almost the same. The reason why the RGB color sensitivity ratio in the AF A image is different from the RGB color sensitivity ratio in the AF B image is that the pupil intensity distribution (incident angle distribution of the light receiving rate) of the image sensor 122 differs depending on the wavelength.

  FIG. 9 shows pupil intensity distributions in the R and G image sensors 122 of the AF A image and the AF B image. The horizontal axis is the incident angle, and the right side is positive. The vertical axis represents the signal intensity corresponding to the light reception rate, and is normalized at the intersection of the AF A image and the AF B image. The AF A image takes the maximum intensity when the incident angle is negative, and the AF B image takes the maximum intensity when the incident angle is positive. The shape of the pupil intensity distribution of R and G differs depending on the difference in refractive index depending on the wavelength.

  As described above, since the eccentric parameter is designed with the set pupil distance Ds as the standard value, the incident angle θc of the intersection corresponds to the exit pupil distance Zep. The exit pupil distance Zep is a state in which the focal length of the lens unit 100 is at the center between the wide-angle end and the telephoto end. Therefore, the closer the lens unit 100 is to the wide-angle end or the telephoto end, the more the incident angle of the light incident on the focus detection pixel deviates from the angle of the intersection.

  Since the change rate of the signal intensity with respect to the incident angle is different between R and G in FIG. 9, the signal intensity ratio of R and G is different between the A image for AF and the B image for AF in a region outside the angle of the intersection. I understand. For example, when the incident angle is more negative than the intersection, R has a smaller signal intensity than G in the AF A image. On the other hand, in the B image for AF, R has a higher signal intensity than G. In this case, the signal intensity ratio of R and G is different between the AF A image and the AF B image.

  FIG. 10 shows the relationship between the first pupil partial region 1001 of the photoelectric conversion unit 211a, the second pupil partial region 1002 of the photoelectric conversion unit 211b, and the exit pupil 1011 of the imaging optical system at the peripheral image height of the image sensor. In FIG. 10, the horizontal direction of the exit pupil 1011 is the X axis, and the vertical direction of the pupil is the Y axis.

  FIG. 10A shows a case where the exit pupil distance Dl of the photographing optical system and the set pupil distance Ds of the image sensor are the same. In this case, the first pupil partial region 1001 and the second pupil partial region 1002 divide the exit pupil 1011 of the photographing optical system substantially equally. Considering the pupil intensity distribution, the light incident angle θ at each image height is substantially equal to the incident angle θc at the intersection of the AF A image and the AF B image (θ = θc). The RGB signal intensity ratio in the B image is substantially equal.

  FIG. 10B shows a case where the exit pupil distance Dl of the photographing optical system is shorter than the set pupil distance Ds of the image sensor. FIG. 10C shows a case where the exit pupil distance Dl of the photographing optical system is longer than the set pupil distance Ds of the image sensor. In either case of FIG. 10B or FIG. 10C, a pupil shift between the exit pupil of the imaging optical system and the entrance pupil of the imaging element occurs at the peripheral image height of the imaging element, and the exit pupil 1011 of the imaging optical system is The pupil is divided unevenly. Considering the pupil intensity distribution, the light incident angle θ in FIGS. 10B and 10C is shifted from the incident angle θc at the intersection of the AF A image and the AF B image as the image height increases. Therefore, as the deviation between the exit pupil distance of the lens unit 100 and the set pupil distance Ds increases and the image height increases, the difference in RGB signal intensity between the AF A image and the AF B image increases.

  The incident angle θc at the intersection of the AF A image and the AF B image is strongly affected by variations in characteristics of the image sensor 122 and assembly errors. Therefore, even if the state of the lens unit 100 and the focus detection area are the same, the RGB signal intensity ratio between the AF A image and the AF B image differs depending on the state of the image sensor 122.

  In the imaging plane phase difference AF, focus detection processing is performed using a focus detection signal obtained from focus detection pixels. As described above, the defocus amount (defocus amount) is based on the relative image shift amount of the pseudo luminance (Y) signal calculated by adding the outputs of the RGB AF A image and the RGB AF B image. Is detected. That is, the phase difference AF is determined to be in focus when the gravity center Ga of the AF A image and the gravity center Gb of the AF B image coincide.

Using FIG. 8A, the centroid G (A) of the AF A image and the centroid G (B) of the AF B image are calculated with respect to the luminance (Y) signal. First, let Xr, Xg, and Xb [mm] be the centroid positions of RGB line images corresponding to the horizontal axis of FIG. Further, the signal intensities of RGB colors corresponding to the vertical axis in FIG. 8A are Sr, Sg, and Sb. From the RGB weighting at the time of luminance (Y) signal creation, each color contribution ratio Pi at the time of calculating the center of gravity is obtained by the following equation 1.
(Formula 1)
Pr (A) = Sr (A) / (Sr (A) + 2Sg (A) + Sb (A))
Pg (A) = 2Sg (A) / (Sr (A) + 2Sg (A) + Sb (A))
Pb (A) = Sb (A) / (Sr (A) + 2Sg (A) + Sb (A))
Pr (B) = Sr (B) / (Sr (B) + 2Sg (B) + Sb (B))
Pg (B) = 2Sg (B) / (Sr (B) + 2Sg (B) + Sb (B))
Pb (B) = Sb (B) / (Sr (B) + 2Sg (B) + Sb (B))
It becomes. Note that (A) shows the value in the AF A image, and (B) shows the value in the AF B image. The centroid G (A) of the AF A image and the centroid G (B) of the AF B image are obtained by the following equation (2) based on the product sum of the RGB line image centroid and each color contribution ratio Pi.
(Formula 2)
G (A) = ΣXi (A) × Pi (A) where i = R, G, B
G (B) = ΣXi (B) × Pi (B) where i = R, G, B
ΔG = G (A) −G (B) [mm]
It becomes. Xi (A) is the line image centroid in the AF A image, and Xi (B) is the line image centroid in the AF B image. ΔG is the difference in the center of gravity between the AF A image and the AF B image at the focus detection focus position.

The line image barycentric positions of the AF A image and the AF B image in the same color are substantially equal at the focus detection focus position.
Xi (A) = Xi (B) where i = R, G, B
Therefore, the condition that the centroid G (A) of the AF A image and the centroid G (B) of the AF B image for the luminance (Y) signal coincide is the contribution of each color of the AF A image and the AF B image. The rate Pi matches. Therefore, if the RGB signal intensity ratio in the focus detection area matches between the AF A image and the AF B image, the centroid G (A) of the AF A image and the centroid G (B) of the AF B image match. The focus detection result of the imaging plane phase difference AF coincides with the focus detection focus position. On the contrary, when the RGB signal intensity ratio in the focus detection region is different between the A image and the B image, a centroid difference occurs between the centroid G (A) and the centroid G (B) of the AF B image. The focus detection result of AF does not coincide with the focus detection focus position, and a focus detection error occurs.

  As described above, since the eccentricity parameter of the image sensor 122 is designed with the exit pupil distance Zep as a standard value, the RGB sensitivity ratio between the A image and the B image increases as the exit pupil distance of the lens unit 100 becomes farther from the standard value Zep. Are different. Since the deviation of the exit pupil distance has a larger effect as the image height is higher, the focus detection error due to the chromatic aberration of magnification becomes larger as the image height is higher.

  As described above, the higher the image height, the centroid positions of the pair of focus detection signals are different for each RGB color due to lateral chromatic aberration. In addition, when the exit pupil distance Dl of the imaging optical system and the set pupil distance Ds of the image sensor 122 are separated, the intensity of the pair of focus detection signals differs for each RGB color depending on the characteristics of the image sensor 122. For this reason, if focus detection is performed using a pair of focus detection signals obtained by adding the focus detection signals of RGB colors, a focus detection error occurs.

  Therefore, in the present embodiment, the second signal correction filter for each color and the color-specific second signal correction filter that performs signal correction for each color on the AF A image and the AF B image according to the information about the chromatic aberration of magnification of the photographing optical system. By using the first signal correction filter, it is possible to correct the focus detection error caused by the chromatic aberration of magnification of the photographing optical system with high accuracy. In addition, asymmetry due to the aberration of the photographing optical system of the AF A image and the AF B image is corrected, and the focus detection error can be corrected with high accuracy.

  [Embodiment 2] Next, the imaging surface phase difference AF processing sequence of Embodiment 2 will be described.

  In the first embodiment, signal correction for each color is performed on the AF image signal before focus detection in order to reduce the focus detection error caused by the lateral chromatic aberration described in FIG. On the other hand, in the present embodiment, the defocus amount as the focus detection result is calculated using the defocus amount correction value (focus detection result correction value) regarding the chromatic aberration of magnification obtained according to the chromatic aberration of magnification of the photographing optical system. to correct. That is, the timing for performing the correction in the focus detection process is different from that of the first embodiment.

  Then, according to the present embodiment, the focus detection error can be accurately corrected by calculating the correction value of the focus detection error using the information regarding the chromatic aberration of magnification of the photographing optical system and the information regarding the color sensitivities specific to the image sensor. Can do.

  Note that the configuration of the camera and image sensor of this embodiment is the same as that shown in FIGS. Further, the mechanism for generating the focus detection error due to the lateral chromatic aberration is as described with reference to FIGS.

  First, an outline of AF processing will be described. The camera MPU 125 acquires the amount of defocus using the AF A image and the AF B image under shooting conditions described later. Thereafter, the camera MPU 125 calculates and corrects a focus detection result correction value for correcting the defocus amount. Then, the camera MPU 125 drives the focus lens 104 based on the corrected defocus amount.

  Next, the details of the imaging surface phase difference AF process described above will be described with reference to the flowcharts of FIGS. In this embodiment, an example using a correction value for correcting the focus detection error caused by the chromatic aberration of magnification of the photographing optical system will be described. However, the focus detection result correction value caused by other aberrations of the photographing optical system is described. And may be combined. For example, it may be combined with a correction value for correcting a focus detection error caused by astigmatism, coma aberration, spherical aberration or the like of the photographing optical system. Further, a correction value for correcting a difference between a focus state that the user feels in the best focus state in the captured image and a focus state indicated by the focus detection result may be combined.

  In S <b> 1201, the camera MPU 125 sets a focus detection area of the image sensor 122. In the present embodiment, as shown in FIG. 11B, representative coordinates (x1, y1) are set for the focus detection area corresponding to the face area 1114 of the main subject 1113, and the representative coordinates are shown in FIG. A description will be given as the coordinates of the center of the focus detection area 1111ch of a).

  In S1202, the camera MPU 125 acquires an AF signal used for the imaging plane phase difference AF. Here, for a plurality of pixels 211 within a predetermined range arranged in the same pixel row, the AF A image formed by connecting the outputs of the photoelectric conversion units 211a corresponding to the detection pixels and the output of the photoelectric conversion unit 211b are connected. A B image for AF knitted together is acquired.

  In step S1203, the camera MPU 125 performs focus detection based on the imaging surface phase difference AF by the first focus detection unit 129.

  In step S1204, the camera MPU 125 acquires a calculation condition necessary for calculating a focus detection result correction value. The focus detection result correction value includes a change in the photographing optical system and a change in the focus detection optical system, such as the position of the focus lens 104, the position of the first lens group 101 indicating the zoom state, and the position coordinates (x1, y1) of the focus detection area. It changes with. Therefore, the camera MPU 125 acquires information such as the position of the focus lens 104, the position of the first lens group 101 indicating the zoom state, and the position coordinates (x1, y1) of the focus detection region in S1202.

  In S1205, the camera MPU 125 calculates a focus detection result correction value from the magnification chromatic aberration information of the lens unit 100 and the RGB color sensitivity information of the image sensor 122 in the correction value calculation condition acquired in S1204. Details of the focus detection result correction value calculation method in step S1205 will be described later with reference to FIG.

  In S1206, the camera MPU 125 corrects the focus detection result DEF_0 by the following formula 3 using the correction value (BP) for correcting the result of automatic focus detection calculated in S1205, and the corrected focus detection result DEF. Is calculated.

DEF = DEF_0 + BP (3)
In step S <b> 1207, the camera MPU 125 communicates with the lens MPU 117, and sends a control command for driving the focus lens 104 to the focus position of the corrected focus detection result DEF to the focus driving unit 116. Based on the control command, the focus driving unit 116 drives the focus lens 104 via the focus actuator 113.

  In S1208, the camera MPU 125 performs in-focus determination. If it is determined not to be in focus, the process returns to S1201, and if it is determined in-focus, the AF processing is terminated.

<Description of Focus Detection Result Correction Value Calculation Method>
In the imaging plane phase difference AF, the relative image shift amount between the AF A image and the AF B image is multiplied by the conversion value K of the image shift amount and the focus shift amount to obtain the defocus amount (defocus amount). Ask. Therefore, the focus detection error amount resulting from the lateral chromatic aberration is a value obtained by multiplying the gravity center difference ΔG at the focus detection focus position by the conversion value K. Since the calculation method of the conversion value K is well known, the description thereof is omitted in the present embodiment, but basically, the image height is higher, and the higher the F value of the lens, the higher. In general, chromatic aberration of magnification hardly changes even when the F value increases. Therefore, when the F value increases, the amount of focus detection error increases as the value of K increases.

  As described above, the difference between the RGB color sensitivity ratios in the AF A image and the AF B image increases as the deviation between the exit pupil distance of the lens unit 100 and the set pupil distance Ds increases and the image height increases. Therefore, the focus detection error amount due to the chromatic aberration of magnification increases as the deviation between the exit pupil distance of the lens unit 100 and the set pupil distance Ds increases and the image height increases.

  FIG. 13 shows a focus detection result correction value calculation process for correcting the focus detection result in S1205 of FIG.

  In S1301, the camera MPU 125 determines whether or not a focus detection result correction value is necessary from the state of the lens unit 100 acquired in S1204 and the focus detection area. Here, for example, when the chromatic aberration of magnification by the lens unit 100 is smaller than the reference value and correction is not necessary, the focus detection result correction value BP is set to zero and the process proceeds to S1304. On the other hand, if it is determined that the focus detection result correction value is necessary, the process proceeds to S1302. Note that the determination process in S1301 may be omitted.

  In step S1302, the camera MPU 125 acquires the line image centroids Xr, Xg, and Xb of each color of RGB as the magnification chromatic aberration information of the lens unit 100. Although the value of the line image centroid varies depending on the focus detection area, in this embodiment, the line image centroid is the line image centroid at the focus detection area center (10 mm, 0 mm). The line image centroid may be acquired for each of the AF A image and the AF B image, or may be the same value for the AF A image and the AF B image. Note that the line image centroid data is stored in the EEPROM 125c of the camera MPU 125.

  In S <b> 1303, the camera MPU 125 acquires information Sr, Sg, Sb related to the sensitivity of each RGB color of the AF A image and the AF B image in the focus detection region of the image sensor 122. In the present embodiment, since the RGB ratio related to the sensitivity of the AF A image and the AF B image is important, a value normalized by the sensitivity of G is used (Sg = 1). Further, sensitivity information of each color of RGB under the D65 light source is stored in the EEPROM 125c of the camera MPU 125. The sensitivity information of each color of RGB is a value unique to the image sensor 122, and for example, a value measured before being mounted on the camera body 120 is stored. The light source is not limited to D65. From the viewpoint of accuracy, it is desirable to acquire sensitivity information for each of the RGB colors of the A image and the B image according to the color of the subject, but in this embodiment, a specific light source stored in the camera MPU 125 is considered from the viewpoint of processing speed. The value below is used.

  In S1304, the camera MPU 125 calculates a focus detection result correction value K · ΔG. As the focus detection result correction value, ΔG is calculated from the gravity center of each color line image acquired in S1302 and S1303 and the sensitivity information of each color of RGB of the A image and the B image using the above-described equations 1 and 2, and the image shift amount and the focus. It is calculated by multiplying the conversion value K of the deviation amount. The converted value K is stored in the EEPROM 125c of the camera MPU 125, and an appropriate value corresponding to the state of the lens unit 100 and the focus detection area is used. The converted value K of the image shift amount and the focus shift amount is also stored as a value unique to the image sensor 122 mounted on the camera body 120.

  Table 1 illustrates each parameter in the present embodiment. The focus detection result correction value K · ΔG is calculated by multiplying the center-of-gravity difference ΔG by the conversion value K of the image shift amount and the focus shift amount. Note that the value of K varies depending on the state of the lens unit 100, the state of the image sensor 122, and the position of the focus detection region in the image sensor 122, and may be about 1000 when it is large.

  In the present embodiment, the focus detection result correction value is the defocus amount, but the correction may be performed at the stage of the image shift amount.

  [Modification 1 of Embodiment 2] Next, Modification 1 of Embodiment 2 will be described focusing on differences from Embodiment 2. FIG.

<Information on lateral chromatic aberration>
In this embodiment, the line image centroids Xr, Xg, and Xb of each color of RGB at the focus detection focus position are stored in the EEPROM 125c of the camera MPU 125 as information on the chromatic aberration of magnification, but the lens memory 118 of the lens unit 100, etc. You may memorize | store in another element.

  In the second embodiment, the line image center of gravity is shown as an absolute value. However, since it is sufficient for the chromatic aberration of magnification to know the relative aberration amount of each color of RGB, for example, only the difference when G is used as a reference, that is, specific It is only necessary to store a relative value based on the color or wavelength. In order to suppress a decrease in memory capacity, fewer parameters are better.

  As shown in Table 2 below, in this embodiment, Xr and Xb are stored as the difference amounts with G as a reference. Although Xg is also shown in Table 2, in this embodiment, Xg is always 0, so it is not necessary to store Xg.

  In addition, when the information Sr, Sg, and Sb related to the sensitivities of the RGB colors of the A image and the B image are also stored as values normalized by G, Sg is always 0, so it is not necessary to store them.

  In the present embodiment, the difference amounts Xr and Xb with G as a reference are stored in the lens memory 118 as information on the chromatic aberration of magnification, and the camera MPU 125 acquires information on the chromatic aberration of magnification from the lens unit 100. The center-of-gravity difference ΔG in this embodiment is shown in Table 2, and the same result as in Embodiment 1 can be obtained. Note that the chromatic aberration of magnification information stored in the lens unit 100 may be a design value, but it is preferable to measure and store an actual value unique to the lens.

<Information on each color sensitivity specific to the image sensor>
In this embodiment, values measured before being mounted on the camera main body 120 are stored in the EEPROM 125c of the camera MPU 125 as information relating to each color sensitivity unique to the image sensor, but information relating to each color sensitivity is the pupil intensity of the image sensor 122. If distribution is obtained, it can be calculated. Therefore, the color pupil intensity distribution unique to the image sensor may be measured before being mounted on the camera body, and stored in the EEPROM 125c of the camera MPU 125. Each color sensitivity ratio of the A image and the B image at the time of focus detection is calculated by the camera MPU 125 from each color pupil intensity distribution.

<Correction conditions>
As described above, the focus detection error due to the chromatic aberration of magnification increases as the deviation between the exit pupil distance of the lens unit 100 and the set pupil distance Ds increases and the image height increases. Moreover, it becomes large, so that the F value of a lens is large. Therefore, from the viewpoint of processing speed, the focus detection result may be corrected only when the difference between the exit pupil distance and the set pupil distance Ds is large. Specifically, whether or not to perform correction is switched according to the zoom magnification, and correction is performed only at the wide-angle end and the telephoto end.

  [Modification 2 of Embodiment 2] Next, Modification 2 of Embodiment 2 will be described focusing on differences from Embodiment 2. FIG.

<Information on subject color>
In the present embodiment, from the viewpoint of processing speed, the information regarding the sensitivity of each color of RGB of the A image and the B image under a specific light source stored in the EEPROM 125c of the camera MPU 125 is acquired. On the other hand, the accuracy of the focus detection result correction value is improved by acquiring the color of the subject with the image processing unit 124 of the camera body 120 and calculating information on the sensitivity of each RGB color based on the color of the subject. Can do.

  In the present embodiment, the color of the subject is estimated from the RGB intensity distribution of the focus detection area of the image sensor 122, and the subject is determined by comparing the estimated intensity information of each RGB color of the subject with the intensity information of each RGB color under the D65 light source. The sensitivity ratio of each RGB color is calculated on the basis of the colors. For example, it is assumed that the R / G intensity ratio R / G of the subject is 0.8 times the R / G intensity ratio R / G under the D65 light source. In this case, the value obtained by multiplying the R sensitivity ratio information Sr (A) and Sr (B) by 0.8 corresponds to the sensitivity ratio of each of the RGB colors of the A image and the B image along the color information of the subject.

  According to each of the embodiments described above, at least one of the signal-by-color correction processing (first correction processing) of the first embodiment and the focus detection result correction processing (second correction processing) of the second embodiment is executed. By doing so, it is possible to accurately correct a focus detection error caused by lateral chromatic aberration of the photographing optical system.

[Other Embodiments]
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in the computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

DESCRIPTION OF SYMBOLS 100 ... Lens unit, 117 ... Lens MPU, 120 ... Camera body, 122 ... Image sensor, 125 ... Camera MPU, 129 ... 1st focus detection part (imaging surface phase difference system), 130 ... 2nd focus detection part (contrast system) )

Claims (24)

A first focus detection signal for each color is acquired from a first focus detection pixel in an imaging device having a plurality of focus detection pixels that receive light beams respectively passing through different pupil partial regions of the photographing optical system, and the second Obtaining means for obtaining a second focus detection signal for each color from the focus detection pixels;
Focus detection means for performing focus detection using the first focus detection signal and the second focus detection signal;
Correction means for correcting a focus detection error caused by lateral chromatic aberration of the photographing optical system,
The correction unit includes a first correction processing unit that performs signal correction for each color on the first and second focus detection signals used when the focus detection unit performs focus detection, and the focus detection unit includes: It has at least one of the 2nd correction process means which correct | amends the amount of focus shift | offset | difference obtained by performing focus detection using the said 1st and 2nd focus detection signal according to the magnification chromatic aberration of the said imaging optical system. Feature focus detection device. The first correction processing unit corrects the first focus detection signal for each color using a first signal correction filter for each color, and uses the second signal correction filter for each color for each color. Correcting the second focus detection signal of
The focus detection unit calculates an image shift amount from the corrected first focus detection signal and the second focus detection signal, and converts the image shift amount into a focus shift amount. The focus detection apparatus described in 1. The first correction processing means includes:
For each color, the first line image distribution function for each color and the second line image distribution function for each color corresponding to the first focus detection signal for each color and the second focus detection signal for each color. Filter calculating means for calculating the first signal correction filter and the second signal correction filter for each color;
The first focus detection signal for each color is convolved with the second signal correction filter for each color, and then added to calculate a first focus detection signal, whereby the second focus detection for each color is calculated. 3. The focus according to claim 2, further comprising: a signal correction unit configured to calculate a second focus detection signal by convolving and integrating the first signal correction filter for each color with the signal and then adding the signal. Detection device.   The focus detection apparatus according to claim 3, wherein the first and second signal correction filters for each color are calculated using a representative value in a focus detection region of the image sensor.   The focus detection apparatus according to claim 4, wherein the representative value in the focus detection area is a coordinate in the center of the focus detection area.   The focus detection apparatus according to claim 3, further comprising a determination unit that determines whether to perform signal correction for each color by the signal correction unit.   The focus detection apparatus according to claim 6, wherein the determination unit determines whether or not to perform signal correction for each color from optical information of the photographing optical system.   The focus detection apparatus according to claim 7, wherein the optical information is information related to chromatic aberration of magnification of the photographing optical system.   The determination means determines whether or not to perform signal correction for each color when the difference between the set pupil distance of the image sensor and the exit pupil distance of the lens is a predetermined value or more. The focus detection apparatus described in 1.   The focus detection apparatus according to claim 6, wherein the determination unit determines to perform signal correction for each color when the image height is equal to or greater than a predetermined value.   The focus detection apparatus according to claim 6, wherein the determination unit determines to perform signal correction for each color when an aperture value of the photographing optical system is equal to or greater than a predetermined value. The second correction processing means includes:
First acquisition means for acquiring a defocus amount of the photographing optical system using the first and second focus detection signals;
Second acquisition means for acquiring a correction value of a defocus amount based on information on chromatic aberration of magnification of the photographing optical system and information on sensitivity of each color unique to the image sensor in the plurality of focus detection pixels; Have
The focus detection apparatus according to claim 1, wherein the defocus amount is corrected using the correction value.   The focus detection apparatus according to claim 12, wherein the second correction processing unit determines whether or not to correct the defocus amount according to a chromatic aberration of magnification of a lens of the photographing optical system. The photographing optical system includes a zoom lens,
The focus detection apparatus according to claim 13, wherein the second correction processing unit determines whether to correct the defocus amount according to a zoom state of the zoom lens.   15. The focus detection apparatus according to claim 14, wherein the second correction processing unit corrects the defocus amount when the zoom lens is at least at a telephoto end or a wide angle end.   16. The focus detection apparatus according to claim 1, wherein information relating to chromatic aberration of magnification of the photographing optical system is stored in a storage unit included in the photographing optical system.   The focus detection apparatus according to claim 16, wherein the information regarding the chromatic aberration of magnification of the photographing optical system is a relative value based on a specific color or wavelength.   18. The focus detection apparatus according to claim 17, wherein the information on the chromatic aberration of magnification of the photographing optical system is information on the chromatic aberration of magnification inherent to a lens included in the photographing optical system.   13. The information regarding the sensitivity of each color unique to the image sensor is information regarding the sensitivity of each color under a specific light source, and is stored in a storage unit included in the focus detection device. Focus detection device.   The focus detection apparatus according to claim 12, wherein the information regarding the sensitivity of each color unique to the image sensor is calculated by the focus detection apparatus according to a color of a subject. An imaging device having a plurality of focus detection pixels that receive light beams respectively passing through different pupil partial regions of the imaging optical system;
The focus detection apparatus according to any one of claims 1 to 20,
An image pickup apparatus comprising: a focus adjustment unit that adjusts a focus state of the photographing optical system using a focus detection result obtained by the focus detection apparatus. An acquisition unit acquires a first focus detection signal for each color from a first focus detection pixel in an imaging device having a plurality of focus detection pixels that receive light beams respectively passing through different pupil partial regions of the photographing optical system. Obtaining a second focus detection signal for each color from the second focus detection pixels;
A focus detection unit performing focus detection using the first focus detection signal and the second focus detection signal;
A correcting unit correcting a focus detection error caused by lateral chromatic aberration of the photographing optical system,
In the correcting step, a first correction process for correcting a signal for each color with respect to the first and second focus detection signals used when performing the focus detection; The focus is characterized by executing at least one of a second correction process for correcting a defocus amount obtained by performing focus detection using the second focus detection signal in accordance with the chromatic aberration of magnification of the photographing optical system. Detection method.   A program for causing a computer to execute the focus detection method according to claim 22.   A computer-readable storage medium storing a program for causing a computer to execute the focus detection method according to claim 22.

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