JP2020003686A - Focus detection device, imaging apparatus, and interchangeable lens device - Google Patents

Abstract

To excellently correct a focus detection error caused by a phase difference detection system.SOLUTION: Focus detection devices 125 and 129 acquire a focus detection correction value used for the correction of the result of focus detection, acquire a first correction value which is a difference between a first focusing position calculated according to the characteristics of an image generated from the output of an imaging element 122 and a second focusing position calculated according to the characteristics of the focus detection, acquire a second correction value which is a correction value corresponding to a condition relating to the light reception sensitivity distribution of the imaging element and is the difference between the second focusing position and a third focusing position calculated from the result of the focus detection, and further acquire the focus detection correction value by using the first correction value and the second correction value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a focus detection technique for performing focus detection by an imaging plane phase difference detection method.

  As an automatic focus detection (AF) method for an image pickup apparatus such as a digital camera and a video camera, there is an image pickup surface phase difference detection method for performing focus detection using a phase difference detection method using an image sensor as a focus detection sensor. Further, in the phase difference detection method, since focus detection is performed using a pair of optical images formed by light from a subject, an aberration of an optical system forming the optical image may cause an error in the focus detection result. There is. For this reason, Patent Literature 1 discloses a method of correcting a focus detection error caused by a mismatch between the shapes of a pair of optical images due to aberration of an optical system in a focused state.

JP 2013-171251 A

  However, the focus detection errors include not only errors due to aberrations of the optical system but also errors depending on the color, direction, and spatial frequency of the subject. Further, if the light receiving sensitivity at each incident angle of the image sensor, that is, the light receiving sensitivity distribution differs depending on the type of the image sensor and manufacturing errors, the focus detection error amount due to the aberration of the optical system differs. Therefore, it is necessary to correct different focus detection errors for each combination of the aberration of the optical system and the light receiving sensitivity distribution of the image sensor.

  The present invention provides a focus detection device that can satisfactorily correct not only aberrations of an optical system but also focus detection errors that differ depending on characteristics of a subject, such as color, direction, and spatial frequency, and distribution of light receiving sensitivity of an image sensor. provide.

  A focus detection device according to one aspect of the present invention performs focus detection by a phase difference detection method using an image sensor. The focus detection device has a correction value acquisition unit that acquires a focus detection correction value used for correcting a result of focus detection. The correction value obtaining means is a difference between a first focus position calculated according to a characteristic of an image generated from an output of the imaging element and a second focus position calculated according to a characteristic of focus detection. The first correction value is obtained, and is a correction value corresponding to a condition regarding the light-receiving sensitivity distribution of the image sensor, and is a difference between the second focus position and a third focus position calculated from a result of focus detection. (2) acquiring a second correction value, and acquiring a focus detection correction value using the first correction value and the second correction value.

  In addition, the interchangeable lens device according to another aspect of the present invention provides a first focus position calculated based on characteristics of an image generated from an output of an imaging element and characteristics of focus detection in a phase difference detection method. A first correction value, which is a difference between the second focus position calculated in accordance with the second focus position, and a correction value corresponding to a condition relating to the light receiving sensitivity distribution of the image sensor, which is calculated from the second focus position and the result of focus detection. The imaging apparatus is mounted on an imaging device that acquires a focus detection correction value used for correcting a result of focus detection using a second correction value that is a difference from the third in-focus position. The interchangeable lens device includes a storage unit that stores information used by the imaging device to obtain at least one of the first correction value and the second correction value, and the information according to a condition regarding a light-receiving sensitivity distribution of the imaging device. And transmitting means for transmitting to the imaging device.

  A focus detection method according to another aspect of the present invention is a method of performing focus detection by a phase difference detection method using an image sensor, which is calculated according to characteristics of an image generated from an output of the image sensor. Obtaining a first correction value that is a difference between the first focus position to be calculated and a second focus position calculated in accordance with the characteristics of focus detection; and correction according to a condition relating to a light-receiving sensitivity distribution of the image sensor. Obtaining a second correction value, which is a difference between the second focus position and a third focus position calculated from the result of focus detection, using a first correction value and a second correction value. Obtaining a focus detection correction value for correcting the result of focus detection.

  Note that a computer program that causes a computer of the focus detection device or the imaging device to execute a process according to the focus detection method also constitutes another aspect of the present invention.

  According to the present invention, a focus detection error in the phase difference detection method can be corrected with high accuracy.

FIG. 1 is a block diagram illustrating a configuration of a digital camera as a first embodiment of the present invention. FIG. 2 is a diagram illustrating a configuration of an image sensor used in the camera according to the first embodiment. FIG. 4 is a diagram illustrating a relationship between a photoelectric conversion region of the image sensor and an exit pupil. FIG. 2 is a block diagram illustrating a configuration of a TVAF unit in the camera according to the first embodiment. 6 is a flowchart illustrating AF processing in the camera according to the first embodiment. 9 is a flowchart illustrating a calculation process of a focus detection correction value according to the first embodiment. FIG. 3 is a diagram illustrating a focus detection area in the camera according to the first embodiment. The figure which shows the process which calculates the difference of the focus position of a picked-up image and the focus detection focus position. FIG. 4 is a diagram for explaining a shift amount of the center of gravity of a line image intensity distribution due to defocus. The figure which shows the line image intensity distribution of a pair when vignetting is large. FIG. 4 is a diagram showing that a light receiving sensitivity distribution differs depending on a pixel size, a pupil distance, and a pupil shift amount of an image sensor. FIG. 4 is a diagram illustrating a relationship between a light receiving sensitivity condition and a second correction value according to the first embodiment. FIG. 4 is a diagram for explaining correction of a focus detection error of the phase difference AF in the first embodiment. 9 is a flowchart illustrating a calculation process of a focus detection correction value according to the second embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a lens-interchangeable digital camera (hereinafter, referred to as a camera body) 120 as an electronic apparatus (imaging apparatus) having a focus detection apparatus according to a first embodiment of the present invention, and is detachably attached to the camera body 120. 1 shows a configuration of a lens unit 100 as an interchangeable lens device. A camera system is configured by the camera body 120 and the lens unit 100.

  The lens unit 100 is mounted on the camera body 120 via a mount M indicated by a dotted line in the center of the figure. The lens unit 100 has an imaging optical system (hereinafter, referred to as a lens optical system) including a first lens 101, an aperture 102, a second lens 103, and a focus lens 104 in order from the subject side (left side in the figure). Each of the first lens 101, the second lens 103, and the focus lens 104 includes one or a plurality of lenses. The lens unit 100 has a lens drive / control system that drives and controls the lens optical system.

  The first lens 101 and the second lens 103 move in the optical axis direction OA, which is the direction in which the optical axis of the imaging optical system extends, to perform zooming. The aperture 102 has a function of adjusting the amount of light and a function as a mechanical shutter that controls the exposure time when capturing a still image. The diaphragm 102 and the second lens 103 move together in the optical axis direction OA during zooming. The focus lens 104 moves in the optical axis direction OA to change a subject distance (focus distance) at which the imaging optical system focuses, that is, performs focus adjustment.

  The lens drive / control system includes a zoom actuator 111, an aperture actuator 112, a focus actuator 113, a zoom drive unit 114, an aperture drive unit 115, a focus drive unit 116, a lens MPU 117, and a lens memory 118. The zoom drive unit 114 drives the zoom actuator 111 to move the first lens 101 and the second lens 103 in the optical axis direction OA, respectively. The aperture shutter driving unit 115 drives the aperture actuator 112 to operate the aperture 102, and controls the aperture diameter of the aperture 102 and the shutter opening / closing operation. The focus drive unit 116 drives the focus actuator 113 to move the focus lens 104 in the optical axis direction OA. The focus drive unit 116 detects the position of the focus lens 104 using a sensor (not shown) provided on the focus actuator 113.

The lens MPU 117 can communicate data and commands with a camera MPU 125 provided on the camera body 120 via a communication contact (not shown) provided on the mount M. The lens MPU 117 transmits lens position information to the camera MPU 125 in response to a request command from the camera MPU 125. The 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 of the imaging optical system in an undriven state in the optical axis direction OA, and a lens that restricts the light flux passing through the exit pupil. Information such as the position and diameter of the frame in the optical axis direction OA is included. Further, the lens MPU 117 controls the zoom drive unit 114, the aperture drive unit 115, and the focus drive unit 116 according to a control command from the camera MPU 125. Thus, zoom control, aperture / shutter control, and focus adjustment (AF) control are performed.
The lens memory (storage means) 118 stores optical information necessary for AF control in advance. The camera MPU 125 controls the operation of the lens unit 100 by executing a program stored in a built-in nonvolatile memory or the lens memory 118.

  The camera body 120 has a camera optical system including an optical low-pass filter 121 and an image sensor 122, and a camera driving / control system. An imaging optical system of the camera system is configured by the lens optical system and the camera optical system.

  The optical low-pass filter 121 reduces false colors and moire of a captured image. The imaging element 122 is configured by a CMOS image sensor and its peripheral portion, and photoelectrically converts (images) a subject image formed by the imaging optical system. The image sensor 122 has a plurality of m pixels in the horizontal direction and a plurality of n pixels in the vertical direction. Further, the image sensor 122 has a pupil division function described below, and uses a phase difference image signal (described later) generated from an output of the image sensor 122 to perform AF (imaging plane phase difference AF: Hereinafter, it is simply referred to as phase difference AF).

  The camera driving / control system includes an image sensor driving unit 123, an image processing unit 124, a camera MPU 125, a display 126, an operation switch group 127, a phase difference focus detection unit 129, and a TVAF focus detection unit 130. The image sensor driving unit 123 controls driving of the image sensor 122. The image processing unit 124 converts an analog image signal output from the image sensor 122 into a digital image signal, performs γ conversion, white balance processing, and color interpolation processing on the digital image signal, and outputs a video signal (image data). Is generated and output to the camera MPU 125. The camera MPU 125 displays the image data on the display 126 or records the image data in the memory 128 as captured image data. Further, the image processing unit 124 performs a compression encoding process on the image data as needed. Further, the image processing unit 124 generates a pair of phase difference image signals and TVAF image data (RAW image data) used in the TVAF focus detection unit 130 from the digital image pickup signal.

  The camera MPU 125 as control means performs necessary calculations and controls for the entire camera system. The camera MPU 125 transmits, to the lens MPU 117, a command for requesting the above-described lens position information and optical information unique to the lens unit 100, and a control command for zoom, aperture, and focus adjustment. The camera MPU 125 has a built-in ROM 125a that stores programs for performing the above calculations and controls, a RAM 125b that stores variables, and an EEPROM 125c that stores various parameters.

  The display 126 is configured by an LCD or the like, and displays the above-described image data, the imaging mode, and other information related to imaging. The image data includes preview image data before imaging, image data for focusing confirmation at the time of AF, an image for confirming imaging after imaging and recording, and the like. The operation switch group 127 includes a power switch, a release (imaging trigger) switch, a zoom operation switch, an imaging mode selection switch, and the like. The memory 128 is a flash memory that can be attached to and detached from the camera body 120, and records captured image data.

  The phase difference focus detection unit 129 performs focus detection processing in phase difference AF using the phase difference image signal obtained from the image processing unit 124. The light beam from the subject passes through the pair of pupil regions divided by the pupil division function of the exit pupil of the imaging optical system, and forms a pair of phase difference images (optical images) on the image sensor 122. . The image sensor 122 outputs a signal obtained by photoelectrically converting the pair of phase difference images to the image processing unit 124. The image processing unit 124 generates a pair of phase difference image signals from this signal, and outputs the signal to the phase difference focus detection unit 129 via the camera MPU 125. The phase difference focus detection unit 129 performs a correlation operation on the pair of phase difference image signals to obtain a shift amount (phase difference: hereinafter, referred to as an image shift amount) between the pair of phase difference image signals, and obtains the image shift. The amount is output to the camera MPU 125. The camera MPU 125 calculates the defocus amount of the imaging optical system from the image shift amount.

  The phase difference AF performed by the phase difference focus detection unit 129 and the camera MPU 125 will be described later in detail. Further, a focus detection device is configured by the phase difference focus detection unit 129 and the camera MPU 125.

  The TVAF focus detection unit 130 generates a focus evaluation value (contrast evaluation value) indicating a contrast state of the image data from the TVAF image data input from the image processing unit 124. The camera MPU 125 moves the focus lens 104 to search for a position where the focus evaluation value reaches a peak, and detects that position as the TVAF in-focus position. The TVAF is also called a contrast detection type AF (contrast AF).

  As described above, the camera body 120 of the present embodiment can perform both the phase difference AF and the TVAF (contrast AF), and can use these selectively or in combination.

  Next, the operation of the phase difference focus detection unit 129 will be described. FIG. 2A shows a pixel array of the image sensor 122, and shows a range of 6 pixel rows (Y direction) and 8 pixel columns (X direction) of the CMOS image sensor viewed from the lens unit 100 side. . The image sensor 122 is provided with a Bayer array of color filters. Green (G) and red (R) color filters are alternately arranged in the odd-numbered pixels in order from the left. Blue (B) and green (G) color filters are arranged alternately from the left. In the pixel 211, a circle with reference numeral 211i indicates an on-chip microlens (hereinafter, simply referred to as a microlens), and two rectangles with reference numerals 211a and 211b disposed inside the microlens 211i indicate photoelectric conversion units, respectively. Is shown.

  In the image sensor 122, the photoelectric conversion unit is divided into two in the X direction in all the pixels, and the photoelectric conversion signals from the individual photoelectric conversion units and the two photoelectric conversion signals from the two photoelectric conversion units of the same pixel are used. The combined signal (hereinafter, referred to as a combined photoelectric conversion signal) can be read. By subtracting the photoelectric conversion signal from one photoelectric conversion unit from the combined photoelectric conversion signal, a signal corresponding to the photoelectric conversion signal from the other photoelectric conversion unit can be obtained. The photoelectric conversion signals from the individual photoelectric conversion units are used to generate a phase difference image signal or used to generate a parallax image forming a 3D image. The combined photoelectric conversion signal is used for generating normal display image data and captured image data, and further, TVAF image data.

  A pair of phase difference image signals used for the phase difference AF will be described. The imaging element 122 divides the exit pupil of the imaging optical system by the microlens 211i illustrated in FIG. 2A and the divided photoelectric conversion units 211a and 211b. A signal obtained by joining the photoelectric conversion signals from the photoelectric conversion units 211a of the plurality of pixels 211 in a predetermined area arranged in the same pixel row is the A image signal, which is one of the pair of phase difference image signals. A signal obtained by joining the photoelectric conversion signals from the photoelectric conversion units 211b of the plurality of pixels 211 is a B image signal which is the other of the pair of phase difference image signals. When the photoelectric conversion signal from the photoelectric conversion unit 211a and the combined photoelectric conversion signal are read from each pixel, a signal corresponding to the photoelectric conversion signal from the photoelectric conversion unit 211b is obtained by converting the combined photoelectric conversion signal into the photoelectric conversion signal from the photoelectric conversion unit 211a. Obtained by subtracting the transformed signal. The A image signal and the B image signal are pseudo luminance (Y) signals generated by adding photoelectric conversion signals from pixels provided with red, blue, and green color filters. However, an A image signal and a B image signal may be generated for each of red, blue, and green colors.

  By calculating the relative image shift amounts of the A image signal and the B image signal thus generated by the correlation operation, the defocus amount in a predetermined area can be obtained.

  FIG. 2B illustrates a circuit configuration of a reading unit of the image sensor 122. A horizontal scanning line 152a, 152b and a vertical scanning line 154a, 154b are provided at a boundary between pixels (photoelectric conversion units 211a, 211b) connected to the horizontal scanning unit 151 and the vertical scanning unit 153. The signal from each photoelectric conversion unit is read out via these scanning lines.

  The camera body 120 of the present embodiment has a first read mode and a second read mode as a read mode of a signal from the image sensor 122. The first reading mode is an all-pixel reading mode, and is a mode for capturing a high-definition still image. In the first read mode, signals are read from all pixels of the image sensor 122. The second reading mode is a thinning-out reading mode in which only a moving image is recorded or a preview image is displayed. Since the number of pixels required for the second read mode is smaller than the total number of pixels, only the photoelectric conversion signals from the pixels thinned out at a predetermined ratio in the X and Y directions are read.

  The second read mode is also used when it is necessary to read data from the image sensor 122 at high speed. When thinning out pixels from which signals are read out in the X direction, signals are added to improve the S / N ratio, and when thinning out pixels in the Y direction, signals from the pixel rows to be thinned out are ignored. The phase difference AF and the TVAF are performed using the photoelectric conversion signal read in the second read mode.

  FIG. 3A illustrates the position of the exit pupil (exit pupil plane) of the imaging optical system according to the present embodiment, and the image height 0, that is, the photoelectric conversion units 211a and 211b of the imaging element 122 arranged near the center of the image plane. Shows a conjugate relationship with. The photoelectric conversion units 211a and 211b in the imaging element 122 and the exit pupil plane of the imaging optical system are conjugated by the microlens 211i. In general, the exit pupil plane of the imaging optical system substantially coincides with the plane on which the iris diaphragm for adjusting the light amount is arranged. On the other hand, the imaging optical system according to the present embodiment is a zoom lens having a zooming function. However, depending on the optical type, when zooming is performed, the distance (exit pupil distance) and size of the exit pupil from the image plane change. I do. FIG. 3A shows a state where the focal length of the imaging optical system is at the center between the wide-angle end and the telephoto end. With the exit pupil distance Zep in this state as a standard value, an eccentricity parameter corresponding to the shape and image height (X, Y coordinates) of the microlens 211i is set.

  3A, the lens unit 100 includes a lens barrel member 101b that holds the first lens 101, a third lens 105, and a lens barrel member 104b that holds the focus lens 104. In addition, the lens unit 100 includes an aperture plate 102a that defines an aperture diameter of the aperture 102 when the aperture 102 is open, and an aperture blade 102b that adjusts the aperture diameter of the aperture 102 when the aperture 102 is stopped down. Note that the lens barrel members 101b and 104b, the aperture plate 102a, and the aperture blade 102b that function as a restricting member for a light beam passing through the imaging optical system are shown as optical virtual images when observed from the image plane. The synthetic aperture near the stop 102 is defined as the exit pupil of the imaging optical system, and the distance from the image plane is defined as the exit pupil distance Zep.

  The pixel 211 is arranged near the center of the image plane, and is hereinafter referred to as a center pixel. The central pixel 211 includes, in order from the lowest layer, photoelectric conversion units 211a and 211b, wiring layers 211e to 211g, a color filter 211h, and a microlens 211i. The two photoelectric conversion units 211a and 211b are projected on the exit pupil plane of the imaging optical system by the microlenses 211i. In other words, the exit pupil of the imaging optical system is projected on the surfaces of the photoelectric conversion units 211a and 211b via the microlenses 211i.

  FIG. 3B shows a projected image of the photoelectric conversion units 211a and 211b on the exit pupil plane of the imaging optical system. Projection images of the photoelectric conversion units 211a and 211b on the exit pupil plane are shown as EP1a and EP1b, respectively. The center pixel 211 can output the photoelectric conversion signal from one of the two photoelectric conversion units 211a and 211b and the sum of the photoelectric conversion signals from both (a combined photoelectric conversion signal). The combined photoelectric conversion output corresponds to a signal obtained by photoelectrically converting a light beam that has passed through both regions of the projected images EP1a and EP1b over substantially the entire exit pupil of the imaging optical system.

  In FIG. 3A, the outermost ray of the light beam passing through the imaging optical system is indicated by L. The light flux L is restricted by the aperture plate 102a of the stop 102, and the projected images EP1a and EP1b have almost no vignetting in the imaging optical system. In FIG. 3B, the light beam L in FIG. 3A is indicated by TL. Since most of the projected images EP1a and EP1b of the photoelectric conversion units 211a and 211b are included in a circle indicated by TL, vignetting hardly occurs. Since the light beam L is limited only by the aperture plate 102a of the stop 102, the circle TL can be rephrased as the aperture plate 102a. At this time, at the center of the image plane, the vignetting state of the projected images EP1a and EP1b is symmetric with respect to the optical axis indicated by the dashed line in FIG. 3A, and the light amounts received by the two photoelectric conversion units 211a and 211b are mutually different. equal.

  When performing the phase difference AF, the camera MPU 125 controls the sensor driving unit 123 so as to read out the above-described two types of outputs (one photoelectric conversion signal and the combined photoelectric conversion signal) from the image sensor 122. The camera MPU 125 gives the information of the focus detection area set in the imaging area to the image processing unit 124, and generates an A image signal and a B image signal from the output of the pixels included in the focus detection area to generate a position. A command is supplied to the phase difference focus detection unit 129 to supply the phase difference focus detection unit 129. The image processing unit 124 generates an A image signal and a B image signal according to the instruction, and outputs the signals to the phase difference focus detection unit 129. The image processing unit 124 supplies the RAW image data to the TVAF focus detection unit 130.

  As described above, the image sensor 122 constitutes a part of the focus detection device in both the phase difference AF and the TVAF. In the present embodiment, the case where the exit pupil is divided into two in the horizontal direction (that is, the pupil division direction is the horizontal direction) has been described. However, the exit pupil may be divided into two in some of the pixels in the vertical direction. . By dividing the exit pupil in the vertical direction (that is, the pupil division direction is the vertical direction), phase difference AF can be performed on a subject having a contrast not only in the horizontal direction but also in the vertical direction. Further, the exit pupil may be divided into both the horizontal and vertical directions to be divided into four.

  Next, TVAF (contrast AF) will be described with reference to FIG. TVAF is realized by the camera MPU 125 and the TVAF focus detection unit 130 repeating the driving of the focus lens 104 and the calculation of the focus evaluation value in cooperation with each other. As described above, the RAW image data is input from the image processing unit 124 to the TVAF focus detection unit 130. In the TVAF focus detection unit 130, the AF evaluation signal processing unit 401 extracts a green (G) signal from the Bayer array signal of the RAW image data, and emphasizes a low luminance component of the G signal to suppress a high luminance component. A luminance signal Y is generated by performing a gamma correction process. In this embodiment, the case where the luminance signal Y is generated using the G signal will be described. However, the luminance signal may be generated using the red (R) signal and the blue (B) signal. Alternatively, a luminance signal may be generated using all of the R, G, and B signals.

  The camera MPU 125 sets one or a plurality of focus detection areas in the area setting unit 413 in the TVAF focus detection unit 130. The area setting unit 413 generates a gate signal for selecting a signal in the set focus detection area. Then, the gate signal is input to the line peak detection unit 402, the horizontal integration unit 403, the line minimum value detection unit 404, the line peak detection unit 409, the vertical integration units 406 and 410, and the vertical peak detection units 405, 407 and 411. . The area setting unit 413 controls the timing at which the luminance signal Y is input to each of the units so that the focus evaluation value is generated using the luminance signal Y in the focus detection area. The line peak detection unit 402 to the vertical peak detection units 405, 407, and 411 calculate a Y peak evaluation value, a Y integration evaluation value, a Max-Min evaluation value, an area peak evaluation value, and a total line integration evaluation value.

  A method for calculating the Y peak evaluation value will be described. The luminance signal Y that has been subjected to the gamma correction processing is input to the line peak detection unit 402. The line peak detection unit 402 obtains a Y line peak value which is a peak value of the luminance signal Y for each horizontal line in the focus detection area set by the area setting unit 413. The vertical peak detector 405 generates a Y peak evaluation value by vertically holding the Y line peak value of each horizontal line output from the line peak detector 402 in the focus detection area. The Y peak evaluation value is an effective index for determining a high-luminance subject or a low-illuminance subject.

  Next, a method of calculating the Y integral evaluation value will be described. The luminance signal Y that has been subjected to the gamma correction processing is input to the horizontal integration section 403. The horizontal integration unit 403 obtains an integrated value (Y integrated value) of the luminance signal Y for each horizontal line in the focus detection area. The vertical integration unit 406 integrates the Y integration value in the focus detection area output from the horizontal integration unit 403 in the vertical direction to generate a Y integration evaluation value. The Y integral evaluation value is used as an index for determining the brightness of the entire focus detection area.

  Next, a method of calculating the Max-Min evaluation value will be described. The luminance signal Y that has been subjected to the gamma correction processing is input to the line peak detection unit 402. The line peak detector 402 calculates a Y line peak value for each horizontal line in the focus detection area. The luminance signal Y that has been subjected to the gamma correction processing is input to the line minimum value detection unit 404. The line minimum value detection unit 404 detects the minimum value (Y minimum value) of the luminance signal Y for each horizontal line in the focus detection area. The Y line peak value and the Y minimum value for each horizontal line are input to a subtractor (-). As a result, (line peak value−minimum value) for each horizontal line is input to the vertical peak detection unit 407. The vertical peak detection unit 407 generates a Max-Min evaluation value by peak-holding (line peak value−minimum value) for each horizontal line in the focus detection area in the vertical direction. The Max-Min evaluation value is an index effective for determining the level of the contrast.

  Next, a method of calculating the area peak evaluation value will be described. When the luminance signal Y that has been subjected to the gamma correction process passes through the BPF 408, a specific frequency component is extracted, thereby generating a focus signal. This focus signal is input to the line peak detection unit 409. The line peak detection unit 409 obtains a line peak value which is a peak value of a focus signal for each horizontal line in the focus detection area. The vertical peak detection unit 411 generates a region peak evaluation value by peak-holding a line peak value for each horizontal line in the focus detection region. The area peak evaluation value is an effective index for restart determination to determine whether or not to shift from the in-focus state to the process of searching for the in-focus position again because the change is small even if the subject moves within the focus detection area. is there.

  Next, a method of calculating the integral evaluation value of all lines will be described. Similarly to the area peak evaluation value, the line peak detection unit 409 obtains a line peak value for each horizontal line in the focus detection area. The vertical integrator 410 integrates the line peak value of each horizontal line in the focus detection area for all horizontal lines in the vertical direction to generate an integrated evaluation value of all lines. The integral evaluation value of all lines is a main focus evaluation value because the dynamic range is wide and the sensitivity is high due to the effect of integration. In the following description, unless otherwise specified, the focus evaluation value means an integrated evaluation value of all lines.

  The AF control unit 151 in the camera MPU 125 acquires the focus evaluation value from the TVAF focus detection unit 130, and moves the focus lens 104 by a predetermined amount in the optical axis direction through the lens MPU 117. Then, a focus evaluation value is newly acquired from the TVAF focus detection unit 130, and the position of the focus lens 104 at which the focus evaluation value becomes the maximum value (TVAF in-focus position) is detected.

  In this embodiment, the focus evaluation value is calculated in each of the horizontal direction and the vertical direction. This makes it possible to perform TVAF using the contrast of the subject in the horizontal and vertical directions.

  Next, the AF processing in the present embodiment will be described. In the present embodiment, first, the camera MPU 125 performs focus detection by phase difference AF or TVAF in the focus detection area to obtain a defocus amount that is a distance between the current position of the focus lens 104 and the focus position. When the focus detection is completed, the camera MPU 125 calculates a focus detection correction value for correcting the defocus amount as a result of the focus detection, and corrects the defocus amount using the focus detection correction value. Then, the camera MPU 125 performs focus control for moving the focus lens 104 to a more accurate focusing position through the lens MPU 117 in accordance with the corrected defocus amount.

  Details of the above AF processing will be described with reference to the flowcharts of FIGS. FIG. 5 shows the flow of the entire AF process, and FIG. 6 shows the process of calculating the focus detection correction value in step S5 in FIG. Mainly, the camera MPU 125 executes the AF processing according to the computer program.

  First, in step S1, the camera MPU 125 sets the focus detection area 219 for the main subject 220 on the imaging screen (imaging element 122) as shown in FIG. Note that the focus detection area set here may be a preset focus detection area such as the center of the imaging screen. The camera MPU 125 sets coordinates (x1, y1) representing the focus detection area 219. The representative coordinates (x1, y1) are set, for example, at the position of the center of gravity of the focus detection area 219.

  Next, in step S2, the camera MPU 125 acquires a focus detection signal used for focus detection. When performing the phase difference AF, the camera MPU 125 acquires the A image signal and the B image signal from the outputs of a plurality of pixels included in a predetermined range in the same pixel row in the focus detection area 219 as focus detection signals. When performing TVAF, the camera MPU 125 acquires a focus evaluation value from the TVAF focus detection unit 130 as a focus detection signal.

  Next, in step S3, when performing the phase difference AF, the camera MPU 125 calculates an image shift amount of the A image signal and the B image signal, and calculates a defocus amount as a focus detection result from the image shift amount. When performing TVAF, the camera MPU 125 moves the focus lens 104 to detect a position at which the focus evaluation value reaches a peak (TVAF in-focus position).

  Next, in step S4, the camera MPU 125 as a correction value acquisition unit acquires a correction value calculation condition necessary for calculating a focus detection correction value. The correction value calculation condition referred to here includes the position of the focus lens 104, the position of the first lens 101 indicating the zoom state, the state of the imaging optical system (lens optical system) such as the aperture value, and the position coordinates (x1) of the focus detection area. , Y1). The correction value calculation condition includes a contrast direction (horizontal, vertical: hereinafter, simply referred to as a direction), a color (R, G, B) and a spatial frequency, and further includes a direction, a color, and a color shown in FIG. It also includes the magnitude (weighting factor) of the weighting for the spatial frequency.

  Next, in step S5, the camera MPU 125 calculates a focus detection correction value as follows. First, the camera MPU 125 determines an imaging in-focus position (first in-focus position) calculated in accordance with characteristics of a captured image described below (hereinafter, referred to as image characteristics) and characteristics of a focus detection signal (hereinafter, referred to as focus detection characteristics). A first correction value, which is a difference from the focus detection in-focus position (second in-focus position) calculated from the above, is calculated. Further, the camera MPU 125 calculates a second correction value that is a difference between the focus detection focus position and a phase difference focus position (third focus position) calculated according to phase difference correction information described later. Then, the camera MPU 125 calculates a focus detection correction value from the first correction value and the second correction value. Details of the method of calculating the focus detection correction value in step S5 will be described later with reference to FIG.

  Next, in step S6, the camera MPU 125 corrects the defocus amount DEF_0, which is the focus detection result, by the following equation (1) using the focus detection correction value BP calculated in step S5, and the corrected defocus amount DEF. Is calculated.

DEF = DEF_0 + BP (1)
In step S7, the camera MPU 125 drives the focus lens 104 to a focus position corresponding to the corrected defocus amount DEF.

  Next, in step S8, the camera MPU 125 determines whether the in-focus state has been obtained. If it is determined that the in-focus state has not been obtained, the process returns to step S1, and it is determined that the in-focus state has been obtained. Ends the AF process.

  The method of calculating the focus detection correction value in step S5 will be described with reference to FIG. Steps S101 to S104 are processing (first step) relating to the calculation of the first correction value as the difference between the imaging focus position and the focus detection focus position, and steps S107 to S110 are the phase correction and the focus detection focus position. This is a process (second step) for calculating a second correction value as a difference from the focal position. Step 111 is a process of calculating a focus detection correction value (third process).

  First, in step S101, the camera MPU 125 transmits, from the lens memory 118, information indicating the state of aberration of the imaging optical system (mainly the lens optical system) as information for obtaining the first correction value (hereinafter, referred to as aberration information). It is obtained through the lens MPU 117 as a transmission unit. The aberration information in the present embodiment is, for example, information on the imaging position of the imaging optical system for each color, direction, and spatial frequency. The aberration information changes according to the state of the imaging optical system described above.

  The aberration information for each spatial frequency stored in the lens memory 118 will be described with reference to FIGS. FIG. 8A shows a defocus MTF of the imaging optical system. The horizontal axis indicates the position of the focus lens 104, and the vertical axis indicates the MTF intensity. The four curves in FIG. 8A are defocus MTF curves for each spatial frequency, and show the defocus MTF when the spatial frequency changes from low to high in the order of MTF1, MTF2, MTF3 and MTF4. I have. The defocus MTF curve of the spatial frequency F1 (lp / mm) shown in FIG. 8B is MTF1, and the defocus MTF curve of the spatial frequencies F2, F3, F4 (lp / mm) is MTF2, MTF3, MTF4. It is. Further, LP4, LP5, LP6, and LP7 in FIG. 8A indicate positions of the focus lens 104 at which each defocus MTF has a maximum value (hereinafter, referred to as a defocus MTF peak position).

  FIG. 8B shows aberration information in the present embodiment, and shows the position MTF_P_RH of the focus lens 104 at which the defocus MTF in FIG. The aberration information includes the spatial frequency f and the position coordinates (x, x) of the focus detection area on the image sensor 122 for each of the six combinations of three colors (R, G, B) and two directions (horizontal and vertical directions). It is expressed by the following equation (2) using y) as a variable.

MTF_P_RH (f, x, y)
= (Rh (0) × x + rh (1) × y + rh (2)) × f ²
+ (Rh (3) × x + rh (4) × y + rh (5)) × f
+ (Rh (6) × x + rh (7) × y + rh (8)) (2)
rh (n) (0 ≦ n ≦ 8) is a coefficient of each term in the above functional expression (2) indicating aberration information, n is an index of the coefficient, and 0 ≦ n ≦ 8. In the present embodiment, rh (n) is stored in the lens memory 118 in advance, and the camera MPU 125 requests the lens MPU 117 to acquire this rh (n). However, rh (n) may be stored in the non-volatile area of the camera RAM 125b.

  Equation (2) shows the defocus MTF peak position MTF_P_RH for each spatial frequency in the horizontal (H) direction for the R signal, but the signal of another color and the H direction and the vertical (V) direction The combination is also represented by the same equation.

  In addition, in order to correct a manufacturing error included in the first correction value, manufacturing error correction information rhd (n) of the first correction value for rh (n) is stored in the lens memory 118 or the nonvolatile area of the camera RAM 125b. It is desirable to keep. When performing the manufacturing error correction of the first correction value, the camera MPU 125 acquires rhd (n) from the non-volatile area of the lens memory 118 or the camera RAM 125b, and adds rhd (n) to rh (n). To correct the manufacturing error.

  Coefficients (rv, gh, gv, bh, bv) for each combination of R and V (MTF_P_RV), G and H (MTF_P_GH), G and V (MTF_P_GV), B and H (MTF_P_BH), and B and V (MTF_P_BV) Can be obtained similarly. As described above, by converting the aberration information into a function and storing the coefficient of each term as the aberration information, the amount of data stored in the lens memory 118 or the camera RAM 125b is reduced, and the aberration information corresponding to the state of the imaging optical system is reduced. Can be stored.

  FIG. 8D shows an example of a weighting coefficient for the direction (H, V), color (R, G, B) and spatial frequency as the correction value calculation condition acquired in step S4 in FIG. The weighting coefficients shown in FIG. 8D are used for calculating the imaging focus position and the focus detection focus position.

In steps S102 and S103 in FIG. 6, the camera MPU 125 determines the imaging focus position P_IMG and the focus detection focus position from the weighting coefficients shown in FIG. 8D obtained in step S4 and the aberration information obtained in step S101. Calculate P_AF. Specifically, first, the position coordinates (x1, y1) of the focus detection area are substituted for x and y in Expression (2). By this calculation, equation (2) is represented in the form of equation (3) below.
MTF_P_RH (f) = Arh × f2 + Brh × f + Chr (3)
The camera MPU 125 calculates MTF_P_RV (f), MTF_P_GH (f), MTF_P_GV (f), MTF_P_BH (f) and MTF_P_BV (f) in the same manner. FIG. 8B shows an example of the aberration information after substituting the position coordinates of the focus detection area in step S1, where the horizontal axis indicates the spatial frequency and the vertical axis indicates the defocus MTF peak position. As shown in the figure, when the chromatic aberration is large, the defocus MTF curve for each color deviates, and when the vertical and horizontal differences are large, the defocus MTF curves in the H direction and the V direction deviate. As described above, in this embodiment, for each combination of the color (R, G, B) and the direction (H, V), there is information (defocus MTF information) of the defocus MTF curve corresponding to the spatial frequency.

Next, the camera MPU 125 weights the aberration information using the weighting coefficient (FIG. 8D) acquired in step S4. Thereby, the aberration information is weighted with respect to the color and the direction evaluated in the focus detection and the captured image. Specifically, the camera MPU 125 calculates a spatial frequency characteristic MTF_P_AF (f) for focus detection and a spatial frequency characteristic MTF_P_IMG (f) for a captured image using Expressions (4) and (5), respectively. K_AF is a weighting coefficient for focus detection, and K_IMG is a weighting coefficient for a captured image.
MTF_P_AF (f)
= K_AF_R x K_AF_H x MTF_P_RH (f)
+ K_AF_R × K_AF_V × MTF_P_RV (f)
+ K_AF_G × K_AF_H × MTF_P_GH (f)
+ K_AF_G × K_AF_V × MTF_P_GV (f)
+ K_AF_B × K_AF_H × MTF_P_BH (f)
+ K_AF_B × K_AF_V × MTF_P_BV (f) (4)

MTF_P_IMG (f)
= K_IMG_R x K_IMG_H x MTF_P_RH (f)
+ K_IMG_R × K_IMG_V × MTF_P_RV (f)
+ K_IMG_G × K_IMG_H × MTF_P_GH (f)
+ K_IMG_G × K_IMG_V × MTF_P_GV (f)
+ K_IMG_B × K_IMG_H × MTF_P_BH (f)
+ K_IMG_B × K_IMG_V × MTF_P_BV (f) (5)
FIG. 8C shows the defocus MTF peak positions LP4_AF, LP5_AF, LP6_AF, LP7_AF obtained by substituting into the equation (4) for the discrete spatial frequencies F1 to F4 shown on the horizontal axis. ing.

  The camera MPU 125 calculates the imaging focus position P_IMG calculated from the image characteristics of the captured image and the focus detection focus position P_AF calculated from the focus detection characteristics of the phase difference AF by using the following Expressions (6) and (7). Calculate using That is, the spatial frequency characteristics (maximum value of the defocus MTF) MTF_P_AF (f) and MTF_P_IMG (f) for each of the spatial frequencies F1 to F4 shown in FIG. 8C obtained by Expressions (4) and (5). Are weighted and added using the weighting coefficients K_IMG_FQ (n) and K_AF_FQ (n) for each spatial frequency obtained in step S4.

P_IMG
= MTF_P_IMG (1) × K_IMG_FQ (1)
+ MTF_P_IMG (2) × K_IMG_FQ (2)
+ MTF_P_IMG (3) × K_IMG_FQ (3)
+ MTF_P_IMG (4) × K_IMG_FQ (4) (6)

P_AF
= MTF_P_AF (1) × K_AF_FQ (1)
+ MTF_P_AF (2) × K_AF_FQ (2)
+ MTF_P_AF (3) × K_AF_FQ (3)
+ MTF_P_AF (4) × K_AF_FQ (4) (7)
Here, the image characteristics and the focus detection characteristics will be described. The image characteristics mean characteristics relating to the evaluation when a person observes a captured image and evaluates the captured image. Further, the focus detection characteristic means a characteristic relating to focus detection, that is, evaluation of AF processing. Specific examples are shown below.
The weighting coefficients K_AF_H, K_AF_V, K_IMG_H, and K_IMG_V for the directions shown in FIG. 8D are, for example, when the pupil division direction is only the H direction,
K_AF_H = 1
K_AF_V = 0
K_IMG_H = 0.5
K_IMG_V = 0.5
Is set. This is because the evaluation of the focus position obtained by the AF process is greatly affected by aberrations in the H direction, while the evaluation of the focus position when a person observes a captured image is based on aberrations in the H direction and the V direction. Is generally averaged at a ratio of 1: 1.

The weighting coefficients K_AF_R, K_AF_G, K_AF_B, K_IMG_R, K_IMG_G, and K_IMG_B for the color are, for example,
K_AF_R = 0.25
K_AF_G = 0.5
K_AF_B = 0.25
K_IMG_R = 0.3
K_IMG_G = 0.5
K_IMG_B = 0.2
Is set. This is because the focus position is evaluated based on the signal obtained from the image sensor 122 in which the color filters are arranged in the Bayer array at the time of focus detection, but the chromatic aberration of each color weighted according to a desired white balance coefficient is obtained in the captured image. This is because the in-focus position changes under the influence of.

The weighting coefficients K_AF_fq (1) to K_AF_fq (4) and K_IMG_fq (1) to K_IMG_fq (4) for the spatial frequency are, for example,
AF_fq (1) = 0.8
AF_fq (2) = 0.2
AF_fq (3) = 0
AF_fq (4) = 0
K_IMG_fq (1) = 0
K_IMG_fq (2) = 0
K_IMG_fq (3) = 0.5
K_IMG_fq (4) = 0.5
Is set. This is because, in general, at the time of focus detection, the focus position is evaluated in a low spatial frequency band, and the focus position is evaluated in a captured image in a high spatial frequency band.

  In step S104 of FIG. 6, the camera MPU 125 calculates a first correction value BP1, which is a component that depends on the color, direction, and spatial frequency of the subject in the focus detection correction value BP, using the following equation (8).

BP1 = P_AF-P_IMG (8)
In the present embodiment, processing relating to the position, color, and direction of the focus detection area is performed prior to processing relating to the spatial frequency. This is because when the user arbitrarily sets the position of the focus detection area, the frequency of changing the position, color, and direction of the focus detection area is low. On the other hand, the spatial frequency is frequently changed by the reading mode of the image sensor, selection of a digital filter for obtaining a focus evaluation value, and the like. For example, in a low illuminance environment where the signal S / N is reduced, it is conceivable to change the pass frequency range of the digital filter to a lower frequency range. In this embodiment, after calculating and storing a coefficient (position, color, and direction) having a low change frequency, a coefficient (spatial frequency range) having a high change frequency is calculated as necessary, and the first correction value is calculated. calculate. Thus, the amount of calculation can be reduced when the user arbitrarily sets the position of the focus detection area.

  Next, in step S105, manufacturing error correction information of the first correction value is held for each state of the imaging optical system, and manufacturing error correction information corresponding to a correction value calculation condition as a focus detection condition is acquired. Then, the manufacturing error is corrected for the first correction value. Note that the manufacturing error correction information of the first correction value may be held only in a specific state, and the state not held may be calculated from the rate of change between the states of the first correction value.

  Next, in step S106, the camera MPU 125 determines whether or not the focus detection method that has performed focus detection in step S3 is phase difference AF. If the focus detection method is phase difference AF, the process proceeds to step S107. On the other hand, if it is not the phase difference AF, that is, if the second correction value BP2 that is the difference between the focus detection focus position P_AF and the phase difference focus position P_AF2 obtained by the phase difference AF cannot be obtained, the camera MPU 125 proceeds to step S112. Then, the second correction value is set to 0 (BP2 = 0), and the process proceeds to step S111. By determining the focus detection method and calculating the focus detection correction value in this manner, the defocus amount can be corrected with high accuracy according to the focus detection method.

  In step S107, the camera MPU 125 determines a correction value calculation condition. That is, the camera MPU 125 determines whether or not the difference between the focus detection focus position P_AF and the phase difference focus position P_AF2 is smaller than a predetermined value. If the difference is smaller, the camera MPU 125 sets the second correction value to 0 (BP2 = 0) and proceeds to step S111. On the other hand, if the difference between the focus detection focus position P_AF and the phase difference focus position P_AF2 is not smaller than the predetermined value, the camera MPU 125 proceeds to step S108.

  Here, the conditions under which the difference between the focus detection focus position P_AF and the phase difference focus position P_AF2 becomes small will be described. In the phase difference AF, an amount of shift of the center of gravity of a pair of line image intensity distributions due to defocus is detected as an amount of image shift, and a defocus amount and a phase difference in-focus position are calculated from the amount of image shift.

  The center-of-gravity shift amount of the line image intensity distribution due to defocus will be described with reference to FIG. FIG. 9 shows a state in which there is no aberration (for example, coma aberration) that gives an error to at least one of the above-described center-of-gravity deviation amount and the positional deviation amount of the line image intensity distribution that is the result of the correlation operation, and there is no vignetting of the light beam due to the diaphragm 102 or the like. ing. In the state shown in FIG. 9, no difference occurs between the focus detection focus position P_AF and the phase difference focus position P_AF2.

  The defocus positions 1201_P and 1202_P indicate different positions. A pair of line image intensity distributions 1201_A and 1201_B indicate a pair of line image intensity distributions corresponding to the photoelectric conversion units (211a and 211b) divided at the defocus position 1201_P. A pair of line image intensity distributions 1202_A and 1202_B indicate a pair of line image intensity distributions corresponding to the photoelectric conversion units (211a and 211b) divided at the defocus position 1202_P.

  The center of gravity positions 1201_GA and 1201_GB indicate the center of gravity of the pair of line image intensity distributions 1201_A and 1201_B. The centroid positions 1202_GA and 1202_GB indicate the centroid positions of the paired line image intensity distributions 1202_A and 1202_B. Further, the center-of-gravity shift amount 1201_difG indicates a difference between the center-of-gravity positions 1201_GA and 1201_GB, and the center-of-gravity shift amount 1202_difG indicates a difference between the center of gravity positions 1202_GA and 1202_GB. Further, as shown in FIG. 9, when there is no aberration or vignetting due to the stop 102 or the like, the center-of-gravity shift amounts 1201_difG and 1202_difG increase in proportion to the defocus amount. The phase difference AF calculates the defocus amount by acquiring the center-of-gravity deviation amount.

  Next, a case where the aberration of the imaging optical system and the vignetting due to the stop 102 and the like are large will be described. FIG. 10A shows a pair of line image intensity distributions in a case where aberrations of the imaging optical system and vignetting due to the stop 102 and the like are large. A line image intensity distribution 1301_A corresponding to the photoelectric conversion unit 211a is indicated by a broken line, and a line image intensity distribution 1301_B corresponding to the photoelectric conversion unit 211b is indicated by a solid line. The dashed line G_A indicates the position of the center of gravity of the line image intensity distribution 1301_A, and the dashed line G_B indicates the position of the center of gravity of the line image intensity distribution 1301_B.

  As shown in FIG. 10A, the line image intensity distributions 1301_A and 1301_B have an asymmetric shape such that each line image intensity distribution extends to one side under the influence of aberration. In such an asymmetric line image intensity distribution, the barycentric position is shifted on the side where the line image intensity distribution extends.

  In addition, the line image intensity distributions 1301_A and 1301_B are affected by vignetting due to the aperture 102 and the like, and a light amount difference occurs. The line image intensity distribution 1301_A, which is more affected by vignetting, is also more affected by aberration, and the degree of asymmetry is greater. As described above, the degree of asymmetry is different between the line image intensity distribution 1301_A and the line image intensity distribution 1301_B, so that the shift amounts of the respective gravity centers G_A and G_B are different, and a difference in the center of gravity shift occurs.

  A line image intensity distribution 1301_IMG illustrated in FIG. 10B is a line image intensity distribution obtained by adding the line image intensity distributions 1301_A and 1301_B, and is the sum of the photoelectric conversion signals from the photoelectric conversion units 211a and 211b (the combined photoelectric conversion signal). 7) is a line image intensity distribution corresponding to ()).

  1302_A and 1302_B illustrated in FIG. 10C and 1302_IMG illustrated in FIG. 10D have different defocus positions from the states of 1301_A, 1301_B and 1301_IMG, and are indicated by a solid line and a line image intensity of 1302_A indicated by a broken line. This shows a state in which the barycenter positions for the line image intensity of 1301_B match. 1302_IMG, like 1301_IMG, represents a line image intensity distribution obtained by adding 1302_A and 1302_B.

  Comparing the line image intensity distributions 1301_IMG and 1302_IMG, the line image intensity distribution 1301_IMG, which is the sum of the line image intensity distributions 1301_A and 1301_B having different barycentric positions, is better than the line image intensity distributions 1302_A and 1302_B whose barycentric positions match each other. The distribution shape is sharper than the line image intensity distribution 1302_IMG which is the sum.

  The position where the shape of the line image intensity distributions 1301_IMG and 1302_IMG corresponding to the signal of the captured image is the sharpest means the in-focus position. For this reason, a state where the barycentric positions are different from each other as in the line image intensity distributions 1301_A and 1301_B is a focus state, and a state where the barycenter positions match as in the line image intensity distributions 1302_A and 1302_B is out of focus (defocus). State. In other words, when the degree of asymmetry is different between the paired line image intensity distributions and a difference in the center of gravity is generated, the position where the center of gravity coincides is not the in-focus position, and the position where the center of gravity is different is the in-focus position. Position.

  As described above, when the aberration of the imaging optical system such as the line image intensity distributions 1301_A and 1301_B and the vignetting due to the diaphragm 102 are large, the degree of asymmetry of the line image intensity distribution is determined in addition to the amount of the center of gravity shift due to defocus. This causes a difference in the amount of displacement of the center of gravity. As a result, the phase difference AF detects an out-of-focus state at a defocus position where the in-focus state should be detected.

  Further, in the correlation calculation used when detecting the defocus amount by the phase difference AF, a detection error occurs when there is a shape difference like the line image intensity distributions 1301_A and 1301_B. If there is no shape difference, the correlation amount indicating the degree of coincidence of the signal becomes 0 when the paired line image intensity distributions completely overlap. However, since the line image intensity distributions 1301_A and 1301_B having a shape difference do not completely overlap each other, the correlation amount does not become 0, and the correlation amount becomes a minimum value when it is slightly shifted from each other. Thus, when there is a shape difference between the paired line image intensity distributions, a detection error occurs.

  From the above, the condition that the difference between the focus detection focus position P_AF and the phase difference focus position P_AF2 is small is when aberration of the imaging optical system and vignetting due to the diaphragm 102 and the like are small. Further, when the position coordinates (x1, y1) of the focus detection area are near the center image height, it is common that the aberration of the imaging optical system is small and the vignetting due to the aperture 102 and the like is small. Therefore, the fact that the position coordinates (x1, y1) of the focus detection area is near the center image height is also a condition for reducing the difference between the focus detection focus position P_AF and the phase difference focus position P_AF2.

  In step S108 in FIG. 6, the camera MPU 125 changes the condition of the image sensor 122 that changes the light sensitivity distribution, which is the light sensitivity at each incident angle of the image sensor 122, in other words, the condition regarding the light sensitivity distribution of the image sensor (hereinafter, the light sensitivity). ) Is acquired from the EEPROM 125c. The light receiving sensitivity condition information z includes a pixel size of the image sensor 122, a pupil distance that is a distance from the image sensor 122 to an entrance pupil of the image sensor 122, and a pupil shift amount. As shown by dx in FIG. 11E, the pupil shift amount is a shift amount of the center of gravity of the pupil due to a variation in assembling the camera and a variation in manufacturing the imaging device. The pupil shift amount differs for each camera individual. If the pixel size, the pupil distance, and the pupil shift amount are different, the light receiving sensitivity distribution in the light beam passing area, which is an area through which light passes without vignetting due to a lens frame or a diaphragm, is different. Since the shape of the line image intensity distribution depends on the light receiving sensitivity distribution in the light beam passage area, if the light receiving sensitivity distribution differs, the difference between the focus detection focus position P_AF and the phase difference focus detection focus position P_AF2 also differs.

  With reference to FIGS. 11A to 11E, a description will be given of how the light receiving sensitivity distribution in the light beam passage area differs depending on the pixel size, pupil distance, and pupil shift amount of the image sensor 122. FIG. The pixel size, pupil distance, and pupil shift amount in the light reception sensitivity distribution shown in FIG. With respect to this criterion, FIG. 11B shows a light receiving sensitivity distribution with different pixel sizes, FIG. 11C shows a light receiving sensitivity distribution with different pupil distances due to manufacturing errors, and FIG. 11D shows a different design pupil distance. FIG. 11E shows light receiving sensitivity distributions having different pupil shift amounts.

  Dl in the figure indicates the exit pupil distance of the imaging optical system, and Ds and Ds' indicate the pupil distance of the image sensor 122. dx indicates the pupil shift amount of the image sensor 122, and the pupil shift amount in FIGS. 11A to 11E is zero. Further, the light passage areas are indicated by reference numerals 1101 to 1105.

  When the pixel size shown in FIG. 11B is different from that in FIG. 11A, the light ray passing area 1102 is the same as the light ray passing area 1101 in FIG. Since it is different from (A), the light receiving sensitivity distribution of the light beam passage area 1102 is different.

  When the pupil distance is different from that in FIG. 11A due to a manufacturing error as shown in FIG. 11C, the shape of the light receiving sensitivity distribution is the same, but the pupil distance Ds ′ is the pupil distance in FIG. Due to the difference from Ds, the light passage area 1103 is different from the light passage area 1101 in FIG. Thus, the light-receiving sensitivity distribution in the light-passing region 1103 differs from that in FIG.

  When the design pupil distance is different from that in FIG. 11A as shown in FIG. 11D, the light receiving sensitivity distribution has a shape obtained by scale conversion by the pupil distance ratio Ds' / Ds. Further, since the pupil distance Ds' is different from Ds, the light ray passing area 1104 is different from the light ray passing area 1101 in FIG. Since the shape of the light reception sensitivity distribution and the light passage area are different from each other, the light reception sensitivity distribution of the light passage area 1104 is different from that in FIG.

  When the pupil shift amount is different from that in FIG. 11A as shown in FIG. 11E, the pupil distance Ds is the same, so that the ray passage area 1105 is the same as the ray passage area 1101 in FIG. It is. However, since the pupil shift amount dx is different from 0 in FIG. 11A, the barycentric position of the light-receiving sensitivity distribution is shifted by dx from FIG. 11A even though the shape of the light-receiving sensitivity distribution is the same. Since the barycentric position of the light-receiving sensitivity distribution is different as described above, the light-receiving sensitivity distribution in the light beam passage area 1105 is different from FIG.

  Next, it will be described with reference to FIG. 12 that when the light receiving sensitivity conditions are different, the second correction value, which is the difference between the focus detection focus position P_AF and the phase difference focus position P_AF2, is different. FIG. 12 shows the relationship between the light receiving sensitivity condition and the second correction value. The horizontal axis shows the light receiving sensitivity condition (information z), and the vertical axis shows the second correction value. From this figure, it can be seen that the second correction value also changes with the change in the light receiving sensitivity condition.

  In FIG. 12, the pixel size, the pupil distance, and the pupil shift amount of the image sensor 122 are collectively used as the light receiving sensitivity condition. However, the second correction value changes with each change in the pixel size, the pupil distance, and the pupil shift amount. .

  As described above, when the light receiving sensitivity conditions are different, the light receiving sensitivity distribution in the light beam passage area changes, and the second correction value that is the difference between the focus detection focus position P_AF and the phase difference focus position P_AF2 also differs. Therefore, in order to calculate the second correction value corresponding to the light receiving sensitivity condition, in step S108, the camera MPU 125 acquires the light receiving sensitivity condition information z.

  Further, the lens memory 118 stores the second correction value, which is the difference between the focus detection in-focus position P_AF and the phase difference in-focus position P_AF2, using a function using the position coordinates (x, y) of the focus detection area as a variable. Function coefficients (hereinafter, referred to as second correction value coefficients) are stored for each of the position of the focus lens 104, the position of the first lens 101 (zoom state), the aperture value, and the light receiving sensitivity condition. The function and the second correction value coefficient will be described later. In step S108, the lens MPU 117 acquires the light receiving sensitivity line information z from the EEPROM 125c through the camera MPU 125.

  Next, in step S109, the camera MPU 125 obtains phase difference correction information as information used for obtaining a second correction value. The phase difference correction information is information on the phase difference in-focus position obtained by the phase difference AF. Specifically, the phase difference correction information includes the position of the focus lens 104, the position (zoom state) and the aperture value of the first lens 101 obtained in step S4 of FIG. 5, and the light receiving sensitivity obtained in step S108 of FIG. This is a second correction value coefficient corresponding to the information z. By storing the second correction value coefficient for each light receiving sensitivity condition in the lens memory 118 in this way, even when the lens unit 100 is mounted on various camera bodies having different light receiving sensitivity conditions from each other, the second correction value coefficient can be accurately corrected. Two correction values can be calculated.

  In the lens memory 118, the discrete position of the focus lens 104, the position of the first lens 101, the aperture value, the light receiving sensitivity condition (pixel size, pupil distance and pupil shift amount), and the position coordinates (x , Y) may be stored in advance. In this case, the camera MPU 125 may calculate a second correction value coefficient to be obtained by interpolation from a plurality of second correction value coefficients stored in the lens memory 118. For example, as shown in FIG. 12, when the second correction value changes linearly with respect to the light receiving sensitivity condition (information z), linear interpolation of the second correction value coefficient discretely stored is performed. A second correction value coefficient corresponding to the light receiving sensitivity condition at that time can be calculated.

  In this embodiment, a case is described in which the lens memory 118 stores second correction value coefficients corresponding to a plurality of light receiving sensitivity conditions, such as a pixel size, a pupil distance, and a pupil shift amount. However, only the second correction value coefficient corresponding to the representative value of the pixel size, the pupil distance, and the pupil shift amount is stored in the lens memory 118, and the stored second correction value coefficient is received regardless of the actual light receiving sensitivity condition. It may be used as a second correction value coefficient corresponding to the sensitivity condition.

Next, in step S110, the camera MPU 125 calculates a second correction value BP2, which is a component that depends on the phase difference AF of the focus detection correction value BP, using the above-described function represented by the following equation (9). In equation (9), a ₀₀ , a ₀₂ , a ₂₀ , and a ₂₂ are the second correction value coefficients acquired in step S109.

^{_{BP2 = a 00 + a 02 y}} 2 + a 20 x 2 + a 22 x 2 y 2 (9)
As described above, the camera MPU 125 acquires the second correction value coefficient corresponding to the light receiving sensitivity condition from the lens unit 100 and calculates the second correction value BP2. This makes it possible to acquire the second correction value BP2 for favorably correcting (decreasing) the difference between the focus detection focus position P_AF and the phase difference focus position P_AF2 even when the light receiving sensitivity distribution is different.

  In this embodiment, the camera MPU 125 obtains a second correction value coefficient, which is a coefficient of a function having the position coordinate (x, y) of the focus detection area as a variable, and calculates a second correction value using the function. However, a second correction value calculated in advance for each image height and stored in the lens memory 118 may be obtained.

Next, in step S111, the camera MPU 125 calculates the focus detection correction value BP by using the first correction value BP1 and the second correction value BP2 according to the following equation (10).
BP = BP1 + BP2 (10)
At this time, if the second correction value BP2 is set to 0 in step S112, the focus detection correction value BP is calculated from only the first correction value BP1 without using the second correction value BP2.

  As described above, in the present embodiment, the focus detection correction value BP is divided into the first correction value BP1 depending on the color, direction, and spatial frequency of the subject, and the second correction value BP2 depending on the phase difference AF. And calculate. Thereby, the defocus amount in the phase difference AF can be corrected with high accuracy.

  The fact that the defocus amount can be corrected with high accuracy by separately calculating the first correction value BP1 and the second correction value BP2 will be described with reference to FIG. P_IMG in FIG. 13 indicates the imaging focus position calculated by the camera MPU 125 in step S102. P_AF indicates the focus detection in-focus position calculated by the camera MPU 125 in step S103. BP1 indicates the first correction value calculated by the camera MPU 125 in step S104, BP2 indicates the second correction value calculated by the camera MPU 125 in step S112, and BP indicates the focus detection correction value calculated in step S114. . BP ′ indicates a correction value calculated by the processing illustrated in FIG. 6 based on the line image intensity distribution at the imaging focus position P_IMG without separating the first correction value and the second correction value. . δBP indicates a difference (BP′−BP) between the correction value BP ′ and the correction value to be calculated originally. The horizontal axis represents actual def (actual defocus amount), and the vertical axis represents detection def (defocus amount detected by phase difference AF).

  When the relationship between the actual def and the detected def is not linear as shown in FIG. 13, when the correction value BP is calculated by converting the detected image shift amount between the A image signal and the B image signal into a defocus amount, The correction value calculated due to the non-linear relationship between the actual def and the detected def becomes a correction value BP ′, and an error δBP occurs. On the other hand, when the second correction value BP2 is calculated using the LSF at the focus detection focus position P_AF calculated from the focus detection characteristics, the calculated second correction value BP2 is smaller than the correction value BP. Therefore, the influence of an error due to the nonlinear relationship between the actual def and the detected def is reduced.

  As described above, in the present embodiment, the focus detection correction value BP is divided into the first correction value BP1 depending on the color, direction, and spatial frequency of the subject, and the second correction value BP2 depending on the phase difference AF. To get. In the present embodiment, the second correction value BP2 is calculated according to the light receiving sensitivity condition of the image sensor 122. Thereby, the defocus amount in the phase difference AF can be corrected with high accuracy.

  Next, a second embodiment of the present invention will be described. The second embodiment differs from the first embodiment in the method of obtaining the first correction value and the method of calculating the second correction value. Note that the configurations of the camera body 120 and the lens unit 100 in the present embodiment are the same as those in the first embodiment, and the same components as those in the first embodiment are denoted by the same reference numerals.

  In the first embodiment, the camera MPU 125 calculates the first correction value from the imaging focus position P_IMG and the focus detection focus position P_AF calculated from the aberration information acquired in step S101. On the other hand, in the second embodiment, a first correction value, which is a difference between the previously calculated imaging focus position P_IMG and the focus detection focus position P_AF, is stored in the EEPROM 125c. Then, the camera MPU 125 reads and acquires the first correction value corresponding to the position of the focus lens 104, the position of the first lens 101, and the aperture value acquired in step S4 of FIG. 4 from the EEPROM 125c.

  In the first embodiment, the camera MPU 125 obtains a coefficient (second correction value coefficient) for each light receiving sensitivity condition in a function using the position coordinate (x, y) of the focus detection area as a variable, and uses this to obtain a second correction value coefficient. Two correction values were calculated. On the other hand, in the second embodiment, the position coordinates (x, y) of the focus detection area and the coefficient of a function for calculating the second correction value for each light receiving sensitivity condition (hereinafter also referred to as the second correction value) Is stored in the EEPROM 125c. Then, the camera MPU 125 calculates the second correction value by using the above and the function described above.

  The basic flow of the AF processing in the present embodiment is the same as the AF processing described in the first embodiment with reference to FIG. 5, but the calculation processing of the focus detection correction value performed by the camera MPU 125 in step S5 is different. FIG. 14 shows the calculation processing of the focus detection correction value in the present embodiment. Step S201 in FIG. 14 is processing (first step) related to calculation of a first correction value that is a difference between the imaging focus position and the focus detection focus position. Steps S203 to S206 are steps S203 to S206. This is a process (second step) related to calculation of a second correction value that is a difference between focus detection focus positions. Step 207 is processing for calculating a focus detection correction value (third step).

  In step S201, the camera MPU 125 sets the position coordinates (x, y) of the focus detection area set in step S1, the position of the focus lens 104, the position of the first lens 101 (zoom state), and the aperture value obtained in step S4. A first correction value is obtained accordingly. In the present embodiment, the first correction value stored in advance is acquired as described above. However, the position coordinates (x, y) of the focus detection area and the coefficient of the function for calculating the first correction value are stored. And the first correction value may be calculated using them.

  Next, in step S202, the camera MPU 125 determines whether or not the focus detection method that has performed focus detection in step S3 is phase difference AF. If the focus detection method is phase difference AF, the process proceeds to step S203. On the other hand, if it is not the phase difference AF, that is, if the second correction value BP2 cannot be obtained, the camera MPU 125 sets the second correction value to 0 (BP2 = 0) in step S208, and proceeds to step S207. By determining the focus detection method and calculating the focus detection correction value in this manner, the defocus amount can be corrected with high accuracy according to the focus detection method.

  In step S203, the camera MPU 125 determines a correction value calculation condition. That is, the camera MPU 125 determines whether or not the difference between the focus detection focus position P_AF and the phase difference focus position P_AF2 is smaller than a predetermined value. If the difference is smaller, the camera MPU 125 sets the second correction value to 0 (BP2 = 0) and proceeds to step S111. On the other hand, if the difference between the focus detection focus position P_AF and the phase difference focus position P_AF2 is not smaller than the predetermined value, the camera MPU 125 proceeds to step S204. The condition under which the difference between the focus detection focus position P_AF and the phase difference focus position P_AF2 is small is as described in the first embodiment.

  In step S204, the camera MPU 125 acquires the light receiving sensitivity condition information z of the image sensor, as in step S108 of the first embodiment.

  Next, in step S205, the camera MPU 125 acquires phase difference correction information. As described in step S109 of the first embodiment, the phase difference correction information is information on the phase difference in-focus position obtained by the phase difference AF. However, the phase difference correction information in the present embodiment is a second correction value coefficient of a function using the position coordinates (x, y) of the focus detection area and the light-receiving sensitivity condition information z acquired in step S204 as variables. , The position of the first lens 101 (zoom state), and a coefficient according to the aperture value. The camera MPU 125 acquires the second correction value coefficient corresponding to the position of the focus lens 104, the position (zoom state) of the first lens 101 and the aperture value acquired in step S4 of FIG. 5 from the EEPROM 125c.

Next, in step S206, the camera MPU 125 calculates a second correction value BP2, which is a component depending on the phase difference AF of the focus detection correction value BP, using a function represented by the following equation (11). In Expression (11), a ₀₀ (z), a ₀₂ (z), a ₂₀ (z), and a ₂₂ (z) are the second correction value coefficients acquired in Step S205. Each second correction value coefficient is a function using the light receiving sensitivity condition information z as a variable.

^{_{BP2 = a 00 (z) +}} a 02 (z) y 2 + a 20 (z) x 2 + a 22 (z) x 2 y 2 (10)
As described above, the camera MPU 125 obtains the second correction value coefficient corresponding to the light-receiving sensitivity condition information z, and calculates the second correction value from the second correction value coefficient. Thereby, even when the light receiving sensitivity conditions are different, it is possible to acquire the second correction value for satisfactorily correcting the difference between the focus detection focus position P_AF and the phase difference focus position P_AF2 with high accuracy.

  Next, in step S207, the camera MPU 125 calculates the focus detection correction value BP using Expression (10), as in the first embodiment. At this time, if the second correction value BP2 is set to 0 in step S208, the focus detection correction value BP is calculated from only the first correction value BP1 without using the second correction value BP2.

  As described above, also in this embodiment, the focus detection correction value BP is divided into the first correction value BP1 depending on the color, direction, and spatial frequency of the subject, and the second correction value BP2 depending on the phase difference AF. To get. Further, also in the present embodiment, the second correction value BP2 is calculated according to the light receiving sensitivity condition information of the image sensor 122. Thereby, the defocus amount in the phase difference AF can be corrected with high accuracy.

  In each of the above embodiments, the case where the camera MPU 125 calculates both the first and second correction values has been described. However, at least one of the first and second correction values is calculated by the lens MPU 117 and the camera MPU 125 calculates the first and second correction values. May be sent. That is, the camera MPU 125 may acquire at least one of the first and second correction values from the lens MPU 117.

In each of the embodiments described above, the interchangeable lens type digital camera has been described. However, the imaging apparatus as another embodiment of the present invention also includes a lens integrated camera and a video camera. Another embodiment of the present invention also includes an imaging device mounted on an electronic device such as a mobile phone, a personal computer, and a game machine.
(Other Examples)
The present invention supplies a program for realizing one or more functions of the above-described embodiments to a system or an apparatus via a network or a storage medium, and one or more processors in a computer of the system or the apparatus read and execute the program. It can also be realized by the following processing. Further, it can also be realized by a unit (for example, an ASIC) that realizes one or more functions.

  Each of the embodiments described above is merely a representative example, and various modifications and changes can be made to each embodiment in practicing the present invention.

120 Camera main body 122 Image sensor 125 Camera MPU
129 Phase difference focus detection unit

Claims (11)

A focus detection device that performs focus detection by a phase difference detection method using an imaging element,
A correction value acquisition unit that acquires a focus detection correction value used for correcting the result of the focus detection,
The correction value acquiring means,
A first correction value, which is a difference between a first focus position calculated according to the characteristics of an image generated from the output of the image sensor and a second focus position calculated according to the characteristics of the focus detection, Acquired,
Obtaining a second correction value, which is a correction value according to a condition relating to a light-receiving sensitivity distribution of the image sensor and is a difference between the second focus position and a third focus position calculated from a result of the focus detection. And
A focus detection device, wherein the focus detection correction value is obtained using the first correction value and the second correction value.   The focus detection apparatus according to claim 1, wherein the condition regarding the light-receiving sensitivity distribution of the image sensor includes at least one of a pixel size, a pupil distance, and a pupil shift amount of the image sensor.   3. The apparatus according to claim 1, wherein the first focus position and the second focus position are calculated using information on aberration of an optical system that forms a subject image on the image sensor. 4. Focus detection device.   When the focus detection by the phase difference detection method is not performed, the correction value acquiring unit may acquire the third correction value using the first correction value without using the second correction value. The focus detection device according to claim 1, wherein the focus detection device is a display device.   When the difference between the second in-focus position and the third in-focus position is smaller than the predetermined value, the correction value obtaining means uses the first correction value without using the second correction value, and The focus detection apparatus according to claim 1, wherein the focus detection apparatus obtains three correction values.   6. The apparatus according to claim 1, wherein at least one of the first correction value and the second correction value is obtained from an interchangeable lens device having an optical system that forms a subject image on the image sensor. The focus detection device according to claim 1. An image sensor;
A focus detection device according to any one of claims 1 to 6,
Control means for performing focus control using the focus detection result corrected by the third correction value. An interchangeable lens device detachable from an imaging device having an imaging element,
The image pickup apparatus includes a first focus position calculated according to characteristics of an image generated from an output of the image sensor, and a second focus position calculated according to characteristics of focus detection in a phase difference detection method. And a third focus position calculated from the second focus position and the result of the focus detection, wherein the first focus value is a difference between the first focus value and the second focus position. And a second correction value, which is a difference from the above, to obtain a focus detection correction value used for correcting the result of the focus detection,
The interchangeable lens device,
Storage means for storing information used by the imaging device to acquire at least one of the first correction value and the second correction value;
An interchangeable lens device comprising: a transmission unit configured to transmit the information according to a condition regarding a light-receiving sensitivity distribution of the imaging element to the imaging device.   9. The interchangeable lens device according to claim 8, further comprising a calculating unit configured to calculate at least one of the first correction value and the second correction value and transmit the calculated value to the imaging device. A focus detection method for performing focus detection by a phase difference detection method using an imaging element,
A first correction value, which is a difference between a first focus position calculated according to the characteristics of an image generated from the output of the image sensor and a second focus position calculated according to the characteristics of the focus detection, Obtaining,
Obtaining a second correction value, which is a correction value according to a condition relating to a light-receiving sensitivity distribution of the image sensor and is a difference between the second focus position and a third focus position calculated from a result of the focus detection. Steps to
Obtaining a focus detection correction value for correcting a result of the focus detection using the first correction value and the second correction value. A computer program for causing a computer of a focus detection device or an imaging device to execute a process according to the focus detection method according to claim 10.