JP6686191B2 - Focus detection device, imaging device, and focus detection method - Google Patents

Description

  The present invention relates to a focus detection device, an imaging device, and a focus detection method.

  There are a contrast AF method and a phase difference AF method as a general method of the focus adjustment method of the image pickup apparatus. Both the contrast AF method and the phase-difference AF method are AF methods often used in video cameras and digital still cameras, and there are those in which an image sensor is used as a focus detection sensor.

  This type of focus adjustment method may include an error in the focus detection result due to the aberration of the optical system, and various methods for reducing the error have been proposed.

  For example, Patent Document 1 discloses a method of calculating a correction value for correcting the focus detection result based on the evaluation frequency (evaluation band) of a signal used for focus detection.

  Such a focus detection error occurs not in the focus adjustment method described above but in the evaluation band of the focus adjustment signal used in the contrast AF method or the phase difference AF method.

Japanese Patent No. 5087077

  However, the configuration of the above conventional technique has a problem that the focus detection error cannot be sufficiently corrected. In Patent Document 1, as a focus detection error, a frequency band in which a focus adjustment signal is evaluated is specified, and a focus detection result is corrected using a correction value suitable for the evaluation band.

  On the other hand, the focus detection error is originally the difference between the focus state in which the observer feels that the photographed image is in the best focus state and the focus state indicated by the focus detection result. However, the focus state of the captured image is not mentioned in Patent Document 1 described above.

  In view of the above problems, the present invention provides an imaging device that performs more accurate focus adjustment by correcting the difference between the focus state of a captured image that is an essential focus detection error and the focus detection result. With the goal.

Therefore, in order to achieve the above object, according to the present invention, first information about an evaluation frequency of a signal used for acquiring a focus detection result and second information about an evaluation frequency of a signal used for a captured image are provided. a first acquisition means for acquiring a second acquisition unit for acquiring third information relating to the imaging position of the imaging optical system for each of a plurality of different spatial frequencies from said photographing optical system, and the focus detection result, It is characterized by further comprising focus detection means for outputting a corrected focus detection result based on the first information, the second information, and the third information.

  According to the present invention, more accurate focus adjustment can be performed by correcting the difference between the focus state between the captured image and the focus detection result, which is the focus detection error.

6 is a flowchart showing an AF operation procedure in the embodiment of the present invention. FIG. 1 is a block diagram showing a schematic configuration of a digital camera according to an embodiment of the present invention. FIG. 3 is a plan view of the light receiving pixels as seen from the lens unit 100 side. 3A and 3B are a plan view and a cross-sectional view illustrating a structure of a pixel for photographing. 6A and 6B are a plan view and a cross-sectional view illustrating the structure of a focus detection pixel that divides the pupil in the horizontal direction of the taking lens. It is a block diagram of a circuit which calculates various AF required evaluation values in an example of the present invention. FIG. 4 is a diagram showing an example of a situation of a focus detection area and a subject within a shooting range. 6 is a subroutine showing a flow of calculating a vertical and horizontal BP correction value (BP1) in the embodiment of the present invention. It is a figure which shows the example of vertical-horizontal BP correction information in the Example of this invention. FIG. 6 is a diagram showing a relationship between a position of a focus lens 104 and a focus evaluation value in an example of the present invention. 6 is a subroutine showing a flow for calculating a color BP correction value (BP2) in the embodiment of the present invention. It is a figure which shows the example of the color BP correction information in the Example of this invention. 6 is a subroutine showing a flow of calculating a spatial frequency BP correction value (BP3) in the embodiment of the present invention. It is a figure which shows the defocus MTF of the imaging optical system in the Example of this invention. It is a figure which shows various spatial frequency characteristics in the Example of this invention. It is a figure which shows the defocus MTF which considered the evaluation band of the picked-up image and the evaluation band of AF in the Example of this invention. It is a figure which shows the information regarding the maximum value of the defocus MTF of the imaging optical system in the Example of this invention. 9 is a subroutine showing a flow of calculating a spatial frequency BP correction value (BP3) in the third embodiment of the present invention.

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

  An example in which the image pickup apparatus of the present invention according to the embodiment of the present invention is applied to a single-lens reflex type digital camera with interchangeable lenses will be described below.

(Description of the configuration of the imaging device)
FIG. 2 is a block diagram of the digital camera of this embodiment. The digital camera of this embodiment is an interchangeable lens type single-lens reflex camera, and has a lens unit 100 and a camera body 120. The lens unit 100 is connected to the camera body 120 via a mount M shown by a dotted line in the center of the figure.

  The lens unit 100 includes a first lens group 101, an aperture / shutter 102, a second lens group 103, a focus lens group (hereinafter simply referred to as “focus lens”) 104, and a drive / control system. As described above, the lens unit 100 includes the focus lens 104 and the photographing lens that forms the image of the subject.

  The first lens group 101 is arranged at the tip of the lens unit 100 and is held so as to be able to advance and retreat in the optical axis direction OA. The diaphragm / shutter 102 not only adjusts the light amount at the time of shooting by adjusting the aperture diameter, but also functions as an exposure time adjusting shutter at the time of shooting a still image. The aperture / shutter 102 and the second lens group 103 integrally advance and retreat in the optical axis direction OA, and the zoom function is realized by interlocking with the forward and backward movement of the first lens group 101. The focus lens 104 performs focus adjustment by moving back and forth in the optical axis direction.

  The drive / control system includes a zoom actuator 111, an aperture shutter actuator 112, a focus actuator 113, a zoom drive circuit 114, and an aperture shutter drive circuit 115.

  Further, the drive / control system has a focus drive circuit 116, a lens MPU 117, a lens memory 118, a shift / tilt / rotation operation member 140, a displacement amount detection means 141, and a displacement direction detection means 142.

  The zoom actuator 111 drives the first lens group 101 and the third lens group 103 back and forth in the optical axis direction OA to perform a zoom operation. The diaphragm shutter actuator 112 controls the aperture diameter of the diaphragm / shutter 102 to adjust the photographing light amount, and also controls the exposure time when photographing a still image.

  The focus actuator 113 drives the focus lens 104 forward and backward in the optical axis direction OA to adjust the focus. The focus actuator 113 has a function as a position detection unit that detects the current position of the focus lens 104.

  The zoom drive circuit 114 drives the zoom actuator 111 according to the zoom operation of the photographer. The shutter drive circuit 115 drives and controls the aperture shutter actuator 112 to control the aperture of the aperture / shutter 102.

  The focus drive circuit 116 drives and controls the focus actuator 113 based on the focus detection result, and drives the focus lens 104 forward and backward in the optical axis direction OA to perform focus adjustment.

  The lens MPU 117 performs all calculations and controls relating to the taking lens, and controls the zoom drive circuit 114, the shutter drive circuit 115, the focus drive circuit 116, and the lens memory 118. Further, the lens MPU 117 detects the current lens position and notifies the lens position information to the request from the camera MPU 125.

  That is, in the image pickup apparatus, when the lens unit having the image pickup optical system and the image pickup unit having the image pickup element are detachable, the lens unit is incident on the image pickup element formed by the image pickup optical system with respect to the image pickup unit. Information regarding the image forming position of each spatial frequency band of the subject image is notified.

  This lens position information is the optical axis position of the focus lens, the optical axis position of the exit pupil when the photographing optical system is not moving, the diameter, the optical axis position of the lens frame that limits the light flux of the exit pupil, and the diameter. Including information such as. The lens memory 118 stores optical information necessary for automatic focus adjustment.

  The camera body 120 has an optical low pass filter 121, an image sensor 122, and a drive / control system.

  The optical low-pass filter 121 and the image pickup element 122 function as an image pickup optical system that forms a subject image by the light flux from the lens unit 100. The first lens group 101, the aperture / shutter 102, the second lens group 103, the focus lens group (hereinafter, simply referred to as “focus lens”) 104, and the optical low-pass filter 121 constitute a photographing optical system.

  The optical low-pass filter 121 reduces false color and moire in a captured image.

  The image sensor 122 is composed of a C-MOS sensor and its peripheral circuits, and has m pixels in the horizontal direction and n pixels in the vertical direction. The image sensor 122 has a part of a focus detection device and can perform phase difference detection AF. Of the obtained image data, image data corresponding to focus detection is converted into focus detection image data as a focus detection signal by the image processing circuit 124.

  On the other hand, among the obtained image data, the image data used for display, recording and TVAF are also sent to the image processing circuit 124, and a predetermined process suitable for the purpose is performed.

  The drive / control system includes an image pickup element drive circuit 123, an image processing circuit 124, a camera MPU 125, a display 126, an operation switch group 127, a memory 128, an image pickup surface phase difference focus detection unit 129, and a TVAF focus detection unit 130.

  The image sensor drive circuit 123 controls the operation of the image sensor 122, A / D-converts the acquired image signal, and transmits it to the camera MPU 125. The image processing circuit 124 performs γ conversion, color interpolation, JPEG compression, etc. on the image acquired by the image sensor 122.

  The camera MPU (processor) 125 performs all calculations and controls related to the camera body 120, and includes an image sensor drive circuit 123, an image processing circuit 124, a display 126, an operation SW 127, a memory 128, and an imaging plane phase difference focus detection unit 129. , And controls the TVAF focus detection unit 130.

  The camera MPU 125 is connected to the lens MPU 117 via the signal line of the mount M, acquires the lens position to the lens MPU 117, issues a lens drive request at a predetermined drive amount, and outputs optical information unique to the lens unit 100. To get.

  The camera MPU 125 includes a ROM 125a that stores a program for controlling the camera operation, a RAM 125b that stores variables, and an EEPROM 125c that stores various parameters.

  Further, the camera MPU 125 executes focus detection processing by the program stored in the ROM 125a. In the focus detection process, a known correlation calculation process is executed using a pair of image signals obtained by photoelectrically converting an optical image formed by light fluxes that have passed through different areas of the pupil. In addition, the camera MPU 125 also performs correction in the imaging plane phase difference AF, because when the image height at the focus detection position is large, vignetting greatly affects the reliability.

  The display 126 is composed of an LCD or the like, and displays information about the shooting mode of the camera, a preview image before shooting, a confirmation image after shooting, a focus state display image at the time of focus detection, and the like. The operation switch group 127 includes a power switch, a release (shooting trigger) switch, a zoom operation switch, a shooting mode selection switch, and the like. The memory 128 as a recording unit of the present embodiment is a removable flash memory and records a captured image.

  The imaging plane phase difference focus detection unit 129 performs focus detection processing in phase difference detection AF based on the image signal of the focus detection image data obtained by the image sensor 122 and the image processing circuit 124. More specifically, the image pickup surface phase difference focus detection unit 129 detects the image pickup surface phase difference based on the shift amount of a pair of images formed in the focus detection pixels by the light flux passing through the pair of pupil regions of the image pickup optical system. Perform AF. The method of the imaging plane phase difference AF will be described in detail later.

  The TVAF focus detection unit 130 calculates various TVAF evaluation values based on the contrast component of the image information obtained by the image processing circuit 124, and performs the focus detection processing of the contrast method. In the focus detection processing of the contrast method, the focus lens 104 is moved to detect the focus lens position where the focus evaluation value reaches a peak.

  As described above, in the present embodiment, the imaging plane phase difference AF and the TVAF are combined, and they can be selectively used or combined and used depending on the situation. The imaging plane phase difference AF and the TVAF function as control means for controlling the position of the focus lens 104 using the respective focus detection results.

(Explanation of focus detection device)
The above is the configuration of the camera system including the lens unit 100 and the camera body 120. Next, details of the focus detection device using the signal of the image sensor 122 will be described. This focus detection device employs a phase difference detection AF and a contrast AF. The configuration will be described.

(Explanation of phase difference detection AF)
First, the configuration of the phase difference detection AF will be described with reference to FIGS. 3 to 5.

  FIG. 3 is a diagram showing a pixel array of the image pickup element in the present embodiment, and shows a range of 6 rows in the vertical direction (Y direction) and 8 columns in the horizontal direction (X direction) of the two-dimensional C-MOS area sensor from the photographing optical system side. The observed state is shown. A Bayer array is applied to the color filters, and green (green) and red (red) color filters are alternately provided in order from the left in pixels in odd-numbered rows. Further, the pixels of even rows are provided with blue (Blue) and green (Green) color filters alternately from the left. Circle 211i represents an on-chip microlens. Each of the plurality of rectangles arranged inside the on-chip microlens is a photoelectric conversion unit.

  In this embodiment, the photoelectric conversion units of all pixels are divided into two in the X direction, and the photoelectric conversion signal of one of the divided regions and the sum of the two photoelectric conversion signals can be independently read. The independently read signal corresponds to the signal obtained in the other photoelectric conversion region by taking the difference between the sum of the two photoelectric conversion signals and the photoelectric conversion signal in one of the divided regions. You can get a signal.

  The photoelectric conversion signals of these divided areas are used for phase-difference focus detection by a method described later, and can also generate a 3D (3-Dimensional) image composed of a plurality of images having parallax information. . On the other hand, the sum of the two photoelectric conversion signals is used as a normal captured image.

  Here, a pixel signal when performing the phase difference focus detection will be described. As will be described later, in the present embodiment, the microlens 211i of FIG. 3 and the divided photoelectric conversion units 211a and 211b divide the luminous flux emitted from the photographing optical system into pupils.

  Then, in a plurality of pixels 211 within a predetermined range arranged on the same row, the output of the photoelectric conversion unit 211a is connected and knitted, and the A image for AF is formed, and the output of the photoelectric conversion unit 211b is also connected and knitted. The obtained image is the AF B image. The outputs of the photoelectric conversion units 211a and 211b are obtained by subjecting the outputs of green, red, blue, and green in the Bayer array to signal addition processing, and pseudo outputs calculated as luminance (Y) signals are used.

  However, the AF A image and B image may be organized for each of red, blue, and green colors. By detecting the relative image shift amount between the AF A image and the B image thus generated by the correlation calculation, it is possible to detect the defocus amount in the predetermined area, that is, the defocus amount.

  In the present embodiment, either the A image for AF or the B image is not output from the image sensor, but as described above, the sum of the A image output and the B image output is output, so that the output and the other image are output. The other signal can be obtained from the output difference, and focus detection can be performed.

  The above-described image sensor can be manufactured by using the technique disclosed in Japanese Patent Laid-Open No. 2004-134867, and therefore detailed description of the structure is omitted.

(A diagram showing the configuration of the readout circuit)
FIG. 4 is a diagram showing the configuration of the readout circuit in the image sensor of this embodiment. Reference numeral 151 is a horizontal scanning circuit, and 153 is a vertical scanning circuit. The horizontal scanning lines 152a and 152b and the vertical scanning lines 154a and 154b are wired at the boundary of each pixel, and each photoelectric conversion unit reads out a signal to the outside via these scanning lines.

  The image sensor of this embodiment has the following two types of read modes. The first read mode is called an all-pixel read mode and is a mode for capturing a high-definition still image. In this case, the signals of all pixels are read out.

  The second reading mode is called a thinning-out reading mode and is a mode for only recording a moving image or displaying a preview image. In this case, the number of pixels required is less than all the pixels, so that the pixel group reads only the pixels thinned out in a predetermined ratio in both the X and Y directions. Also, when it is necessary to read at high speed, the thinning-out reading mode is used similarly. When thinning out in the X direction, signal addition processing of signals is performed to improve S / N, and in thinning out in the Y direction, the signal output of the thinned out row is ignored. Focus detection by the phase difference detection method and the contrast detection method is also normally performed in the second read mode.

(A diagram explaining the conjugate relationship)
5A and 5B are views for explaining the conjugate relationship between the exit pupil plane of the imaging optical system and the photoelectric conversion unit of the image pickup element arranged near the image height zero, that is, near the center of the image plane in the image pickup apparatus of the present embodiment. . The photoelectric conversion unit in the image pickup device and the exit pupil plane of the photographing optical system are designed to have a conjugate relationship by an on-chip microlens. The exit pupil of the photographing optical system generally coincides with the surface on which the iris diaphragm for adjusting the light amount is placed.

  On the other hand, the photographing optical system of the present embodiment is a zoom lens having a variable magnification function, but depending on the optical type, when the variable magnification operation is performed, the distance and size of the exit pupil from the image plane change. The photographic optical system in FIG. 5 shows a state in which the focal length is between the wide-angle end and the telephoto end, that is, in the middle state. Assuming that this is the standard exit pupil distance Zep, optimum design of the eccentricity parameter according to the shape of the on-chip microlens and the image height (X, Y coordinates) is performed.

  In FIG. 5A, 101 is a first lens group, 101b is a lens barrel member holding the first lens group, 105 is a third lens group, and 104b is a lens barrel member holding the focus lens 104. Reference numeral 102 denotes an aperture, 102a denotes an aperture plate that defines the aperture diameter when the aperture is opened, and 102b is an aperture blade for adjusting the aperture diameter when the aperture is narrowed down.

  It should be noted that 101b, 102a, 102b, and 104b that act as a member for restricting the light flux that passes through the imaging optical system represent optical virtual images when observed from the image plane. The synthetic aperture in the vicinity of the diaphragm 102 is defined as the exit pupil of the lens, and the distance from the image plane is Zep as described above.

  Reference numeral 2110 denotes a pixel for photoelectrically converting a subject image, which is arranged near the center of the image plane, and is called a central pixel in this embodiment. The central pixel 2110 is composed of the photoelectric conversion parts 2110a and 2110b, the wiring layers 2110e to 2110g, the color filter 2110h, and the on-chip microlens 2110i from the bottom layer.

  Then, the two photoelectric conversion units are projected onto the exit pupil plane of the photographing optical system by the on-chip microlens 2110i. In other words, the exit pupil of the photographing optical system is projected on the surface of the photoelectric conversion unit via the on-chip microlens 2110i.

  FIG. 5B shows a projected image of the photoelectric conversion unit on the exit pupil plane of the photographing optical system. The projected images of the photoelectric conversion units 2110a and 2110b are EP1a and EP1b, respectively. Further, in this embodiment, the image pickup element has a pixel capable of obtaining the output of either one of the two photoelectric conversion units 2110a and 2110b and the sum output of both.

  The output of the sum of both is obtained by photoelectrically converting the light flux that has passed through both regions of the projection images EP1a and EP1b, which are almost the entire pupil region of the photographing optical system.

  In FIG. 5A, when the outermost part of the light flux passing through the photographing optical system is indicated by L, the light flux L is regulated by the aperture plate 102a of the diaphragm, and the projected images EP1a and EP1b are almost eclipsed in the photographing optical system. Not not. In FIG. 5B, the light flux L of FIG. 5A is indicated by TL.

  Since most of the projected images EP1a and EP1b of the photoelectric conversion unit are included inside the circle indicated by TL, it can be seen that vignetting has hardly occurred. Since the light flux L is limited only by the aperture plate 102a of the diaphragm, the TL can be restated as 102a. At this time, in the center of the image plane, the vignetting states of the projected images EP1a and EP1b are symmetrical with respect to the optical axis, and the amounts of light received by the photoelectric conversion units 2110a and 2110b are equal.

  As described above with reference to FIGS. 3, 4, and 5, the image sensor 122 has not only the function of imaging only but also the function of a focus detection device. Further, as the focus detection method, since the focus detection pixel that receives the light flux obtained by dividing the exit pupil is provided, the phase difference detection AF can be performed.

  In the above description, the configuration in which the exit pupil is divided in the horizontal direction has been described, but pixels for dividing the exit pupil in the vertical direction may also be provided on the image sensor. By providing pixels that divide the exit pupil in both directions, focus detection can be performed in accordance with the contrast of the subject in the vertical direction as well as in the horizontal direction.

(Explanation of contrast method AF)
Next, the configuration of the contrast AF will be described with reference to FIG. FIG. 6 shows a flow of calculation of various AF evaluation values calculated using the camera MPU 125 and the TVAF focus detection unit 130 of FIG.

  When the digital signal converted by the A / D conversion circuit 7 is input to the TVAF focus detection unit 130, the AF evaluation signal processing circuit 401 extracts the green (G) signal from the Bayer array signal and reduces the brightness. Gamma correction processing is performed to emphasize components and suppress high-luminance components.

  In the present embodiment, the case where the TVAF focus detection is performed with the green (G) signal will be described, but all signals of red (R), blue (B), and green (G) may be used. Alternatively, the luminance (Y) signal may be generated using all RGB colors. The output signal generated by the AF evaluation signal processing circuit 401 will be referred to as a luminance signal Y in the following description regardless of the color used.

  A method of calculating the Y peak evaluation value will be described. The gamma-corrected luminance signal Y is input to the line peak detection circuit 402 for detecting the line peak value for each horizontal line. With this circuit, the Y line peak value for each horizontal line is obtained within the AF evaluation range set by the area setting circuit 412.

  Further, the output of the line peak detection circuit 402 is input to the vertical peak detection circuit 405. By this circuit, peak hold is performed in the vertical direction within the AF evaluation range set by the area setting circuit 414, and a Y peak evaluation value is generated. The Y peak evaluation value is effective for determining a high-luminance subject or a low-illuminance subject.

  A method of calculating the Y integral evaluation value will be described. The gamma-corrected luminance signal Y is input to the horizontal integration circuit 403 for detecting the integrated value for each horizontal line. By this circuit, the integrated value of Y for each horizontal line is obtained within the AF evaluation range set by the area setting circuit 412. Further, the output of the horizontal component circuit 403 is input to the vertical integration circuit 406.

  By this circuit, integration is performed in the vertical direction within the AF evaluation range set by the area setting circuit 412, and a Y integral evaluation value is generated. The Y integration evaluation value can determine the overall brightness within the AF evaluation range.

  A method of calculating the Max-Min evaluation value will be described. The gamma-corrected luminance signal Y is input to the line peak detection circuit 402, and the Y line peak value for each horizontal line is obtained within the AF evaluation range. The gamma-corrected luminance signal Y is input to the line minimum value detection circuit 404.

  This circuit detects the minimum value of Y for each horizontal line within the AF evaluation range of the luminance signal Y. The detected line peak value and minimum value of Y for each horizontal line are input to the subtractor, (line peak value-minimum value) is calculated, and then input to the vertical peak detection circuit 407.

  By this circuit, the peak hold is performed in the vertical direction within the AF evaluation range, and the Max-Min evaluation value is generated. The Max-Min evaluation value is effective in determining low contrast and high contrast.

  A method of calculating the area peak evaluation value will be described. The gamma-corrected luminance signal Y is passed through a BPF 408 to extract a specific frequency component and generate a focus signal. This focus signal is input to a line peak detection circuit 409, which is a peak hold unit for detecting a line peak value for each horizontal line.

  The line peak detection circuit 409 obtains a line peak value for each horizontal line within the AF evaluation range. The obtained line peak value is peak-held in the AF evaluation range by the vertical peak detection circuit 411, and the area peak evaluation value is generated.

  The area peak evaluation value does not change much even if the subject moves within the AF evaluation range, and is therefore effective for restart determination for shifting to the processing for searching the in-focus point again from the in-focus state.

  A method of calculating the total line integral evaluation value will be described. Similar to the area peak evaluation value, the line peak detection circuit 409 obtains a line peak value for each horizontal line within the AF evaluation range. Next, the line peak value is input to the vertical integration circuit 410, and integrated for all horizontal scanning lines in the vertical direction within the AF evaluation range to generate an integrated evaluation value for all lines.

  The high-frequency all-line integral evaluation value is effective as the main evaluation value of AF for detecting the in-focus position because it has a wide dynamic range and high sensitivity due to the effect of integration.

  In this embodiment, the evaluation value changes according to the defocus state, and the all-line integral evaluation value used for focus adjustment is called the focus evaluation value.

  The area setting circuit 413 generates a gate signal for an AF evaluation range for selecting a signal at a predetermined position in the screen set by the camera MPU 125.

  The gate signal is input to each of the line peak detection circuit 402, horizontal integration circuit 403, line minimum value detection circuit 404, line peak detection circuit 409, vertical integration circuits 406 and 410 vertical peak detection circuits 405, 407, and 411. .

  Then, the timing at which the brightness signal Y is input to each circuit is controlled so that each focus evaluation value is generated by the brightness signal Y within the AF evaluation range.

  Further, the area setting circuit 413 can set a plurality of areas according to the AF evaluation range.

  The AF control unit 151 takes in each focus evaluation value, controls the focus actuator 113 through the focus drive circuit 116, and moves the focus lens 104 in the optical axis direction to perform AF control.

  In the present embodiment, in addition to calculating the various AF evaluation values in the horizontal line direction as described above, they are also calculated in the vertical line direction. As a result, focus detection can be performed on the contrast information of the subject in either the horizontal or vertical direction.

  When performing the AF of the contrast method, the above-mentioned various AF evaluation values are calculated while driving the focus lens 104. Focus detection is performed by detecting the position of the focus lens at which the integral evaluation value for all lines becomes maximum.

(Explanation of focus detection area)
FIG. 7 is a diagram showing a focus detection area in the shooting range. In the focus detection area, the imaging plane phase difference AF and the TVAF are performed based on the signal obtained from the image sensor 122. The focus detection area in FIG. 7 includes a focus detection unit including pixels that perform pupil division in the horizontal direction (horizontal direction) of the taking lens shown in FIG.

  Further, a rectangle shown by a dotted line indicates a shooting range 217 in which pixels of the image sensor 122 are formed. Within the shooting range 217, three lateral focus detection areas 218ah, 218bh, and 218ch for performing the imaging plane phase difference AF are formed. In the present embodiment, the focus detection area of the phase difference detection method is configured to have a total of three locations, that is, the central portion of the imaging range 217 and two locations on the left and right as illustrated.

  In addition, focus detection areas 219a, 219b, and 219c that perform TVAF are formed so as to include each of the focus detection areas that perform three imaging plane phase difference AFs. In the focus detection area where TVAF is performed, contrast detection is performed using the focus evaluation values in the horizontal and vertical directions in FIG.

  Note that the example shown in FIG. 7 shows an example in which the focus detection areas are roughly arranged in three areas, but the present invention is not limited to three areas, and a plurality of areas may be provided at arbitrary positions. You may arrange.

(Explanation of the flow of focus detection processing)
Next, the focus detection (AF) process according to the present embodiment in the digital camera having the above configuration will be described with reference to FIG. The outline of the AF process according to the embodiment of the present invention is as follows. First, the amount of defocus (defocus amount) and the reliability are obtained for each of the focus detection areas 218ah, 218bh, and 218ch.

  Then, it is divided into a region where the defocus amount having a predetermined reliability is obtained and a region where the defocus amount is not obtained. If the defocus amount having a predetermined reliability is obtained in all the focus detection areas 218ah, 218bh, and 218ch, the focus lens 104 is driven so as to focus on the closest subject.

  On the other hand, when there is a region in which the defocus amount having the predetermined reliability is not obtained, the change amount of the focus evaluation value before and after driving the focus lens is used for the corresponding region in the focus detection regions 219a to 219c. , It is determined whether or not there is a subject on the closer side.

  Then, when it is determined that the subject is present on the closer side, the focus lens 104 is driven based on the change in the focus evaluation value. However, if the focus evaluation value has not been obtained before this, the amount of change in the focus evaluation value cannot be obtained. In that case, when there is a region in which a defocus amount having a predetermined reliability, which is larger than a predetermined defocus amount, exists, the focus lens 104 is driven so as to focus on the closest subject. To do.

  In other cases, that is, when there is no region where a defocus amount having a predetermined reliability is obtained and when the obtained defocus amount is less than or equal to a predetermined defocus amount, defocus is performed. The lens is driven by a predetermined amount regardless of the amount.

  When the defocus amount is small, the reason why the lens is driven by a predetermined amount irrelevant to the defocus amount is that the lens drive amount based on the defocus amount detects a change in the focus evaluation value at the next focus detection. This is because it is likely to be difficult to do.

  When the focus detection is completed by either method, various correction values are calculated and the focus detection result is corrected. The focus lens 104 is driven based on the corrected focus detection result, and the focus adjustment process is completed.

  Hereinafter, the AF process will be described in detail. 1A and 1B are flowcharts showing an AF operation procedure of the image pickup apparatus. The control program related to this operation is executed by the camera MPU 125. When starting the AF operation, the camera MPU 125 first sets a focus detection area for performing focus adjustment on the subject in S1. In the processing of S1, as shown in FIG. 6, three focus detection areas are set.

  Next, in S2, the closeness determination flag is set to 1. In S3, a signal required for focus detection is acquired in each focus detection area. Specifically, after exposure is performed by the image sensor 122, the image signals of the focus detection pixels in the focus detection areas 218ah, 218bh, and 218ch for the imaging plane phase difference AF are acquired.

  Here, the correction processing described in Japanese Patent Laid-Open No. 2010-117679 may be performed on the acquired image signal. Further, after exposure is performed by the image sensor 122, pixel signals in the areas of the focus detection areas 219a, 219b, and 219c used for TVAF are acquired and the focus evaluation value is calculated. The calculated focus evaluation value is stored in the RAM 125b.

  Next, in S4, it is determined whether or not the peak (maximum value) of the focus evaluation value is detected. This is for performing focus detection by the contrast detection method, and when a reliable peak is detected, focus detection is terminated, and the process proceeds to S20. For the reliability of the focus evaluation value, for example, the method described in FIGS. 10 to 13 of JP 2010-078810 A may be used.

  That is, it is determined whether or not the focus evaluation value indicating the in-focus state has a mountain shape by determining the difference between the maximum value and the minimum value of the focus evaluation value and the length of the portion that is inclined with a slope equal to or more than a constant value (SlopeThr). , And the slope of the sloped part. As a result, the reliability of the peak can be determined.

  In the present embodiment, since the AF of the phase difference detection method is used together, if the presence of a subject on the closer side is confirmed in the same focus detection area or another focus detection area, reliability of Even when a certain focus evaluation value peak is detected, the process may proceed to S5 without finishing the focus detection.

  In that case, the position of the focus lens 104 corresponding to the position of the focus evaluation value peak is stored, and if the reliable focus detection result is not obtained thereafter, the stored focus lens 104 position is set as the focus detection result. To do.

  Next, in S5, the shift amount of the obtained pair of image signals is calculated for each focus detection region for the imaging plane phase difference AF, and the defocus amount is stored using the conversion factor for the defocus amount stored in advance. Calculate the focus amount. Here, the reliability of the calculated defocus amount is also determined, and only the defocus amount of the focus detection area determined to have the predetermined reliability is used in the AF process thereafter.

  Due to the effect of the vignetting due to the photographing lens, as the defocus amount increases, the deviation amount of the detected pair of image signals includes more errors. Therefore, if the calculated defocus amount is large, the degree of matching between the shapes of the pair of image signals is low, or the contrast of the pair of image signals is low, it is determined that high-precision focus detection is impossible, in other words, Then, it is determined that the reliability of the calculated defocus amount is low.

  Hereinafter, when the calculated defocus amount has a predetermined reliability, it is expressed as “the defocus amount has been calculated”, and the defocus amount cannot be calculated for some reason, or the calculated defocus amount has reliability. When the property is low, it is expressed as “the defocus amount cannot be calculated”.

  Next, in S6, it is determined whether or not the defocus amount can be calculated for all of the plurality of focus detection areas 218ah, 218bh, and 218ch set in S1. When the defocus amount can be calculated in all the focus detection regions, the process proceeds to S20, and the focus detection region in which the defocus amount indicating the closest object among the calculated defocus amounts is calculated Then, the vertical and horizontal BP correction values (BP1) are calculated.

  Here, the reason for selecting the closest object is that, in general, the object that the photographer wants to focus is often on the closest side. The vertical / horizontal BP correction value (BP1) corrects the difference between the focus detection results when focus detection is performed on the contrast of the horizontal subject and when focus detection is performed on the contrast of the vertical subject. It is a thing.

  Generally, a subject has a contrast in both the horizontal and vertical directions, and the focus state of a captured image is evaluated in consideration of the contrast in both the horizontal and vertical directions. On the other hand, when focus detection is performed only in the horizontal direction as in the AF of the phase difference detection method described above, an error occurs between the focus detection result in the horizontal direction and the focus state of the captured image in both the horizontal and vertical directions.

  This error occurs due to astigmatism of the photographing optical system. The vertical and horizontal BP correction value (BP1) is a correction value for correcting the error. The vertical and horizontal BP correction values (BP1) are calculated in consideration of the selected focus detection area, the position of the focus lens 104, the position of the first lens group 101 indicating the zoom state, and the like. Details of the calculation method will be described later.

  Next, in S21, the color BP correction value (BP2) is calculated for the focus detection area for which the correction value has been calculated in S20, using the vertical or horizontal one-way contrast information. The color BP correction value (BP2) is generated by the chromatic aberration of the photographing optical system, and is generated by the difference between the color balance of the signals used for focus detection and the color balance of the signals used for the photographed image or the developed image. For example, when performing the focus detection of the contrast detection type in the present embodiment, the focus evaluation value used is generated by the pixel output having the green (G) color filter, and therefore the focus position of the green wavelength is mainly determined. It will be detected.

  On the other hand, since the captured image is generated using all RGB colors, when the focus position of red (R) or blue (B) is different from that of green (G), there is a shift from the focus detection result based on the focus evaluation value ( Error). The correction value for correcting the error is the color BP correction value (BP2). Details of the method for calculating the color BP correction value (BP2) will be described later.

  Next, in S22, with respect to the focus detection area that is the correction target of S20 and S21, a specific color space frequency BP correction value (vertical or horizontal) using a contrast information of green or luminance signal Y ( Calculate BP3). The spatial frequency BP correction value (BP3) is generated mainly by the spherical aberration of the photographing optical system, and is the difference between the evaluation frequency (band) of the signal used for focus detection and the evaluation frequency (band) when viewing the captured image. Caused by.

  As described above, at the time of focus detection, the mode in which the output signal is read from the image sensor is the second read mode, so the output signals are added or thinned. Therefore, the evaluation band of the output signal used for focus detection is lower than that of the captured image generated using the signals of all pixels read in the first read mode. The spatial frequency BP correction value (BP3) is generated due to the difference in the evaluation band. The details of the method of calculating the spatial frequency BP correction value (BP3) will be described later.

Next, in S23, the focus detection result DEF_B is corrected by the following equation using the three types of correction values (BP1, BP2, BP3) calculated up to this point to calculate DEF_A.
(Equation 1)
DEF_A = DEF_B + BP1 + BP2 + BP3

  In the first embodiment, the correction value for correcting the focus detection result is divided into three stages and calculated in the order of vertical and horizontal, color and spatial frequency.

  First, by calculating the vertical and horizontal BP correction values, contrast information in both vertical and horizontal directions is used for evaluation when viewing a captured image, whereas focus detection occurs because contrast information in one direction is used. Calculate the error.

  Next, with respect to the color BP correction value, the influence of the vertical and horizontal BPs is separated, and the difference between the in-focus positions due to the colors used for the signals during viewing of the captured image and during focus detection is calculated as the correction value in the contrast information in one direction. is doing.

  Further, the spatial frequency BP correction value is contrast information in one direction, and for a specific color such as green or a luminance signal, a difference in focus position caused by a difference in evaluation band between viewing of a captured image and focus detection. Is calculated as a correction value.

  By dividing and calculating the three types of errors in this way, the amount of calculation and the amount of data stored in the lens or the camera are reduced.

  In S24, the focus lens 104 is driven based on the corrected defocus amount DEF_A calculated by Expression 1 (focus control).

  Next, in S25, the focus detection area for which the defocus amount used for driving the lens has been calculated is displayed on the display device 126, and the AF process ends.

  On the other hand, if there is a focus detection area in which the defocus amount cannot be calculated in S6, the process proceeds to S7 in FIG.

  In S7, it is determined whether or not the closeness determination flag is 1. The closeness determination flag is a flag that becomes 1 when the lens has not been driven since the AF operation started, and becomes 0 when the lens has been driven a plurality of times. If the closeness determination flag is 1, the process proceeds to S8.

  In S8, if the defocus amount cannot be calculated in all the focus detection areas, or if the defocus amount indicating the existence of the closest object is a predetermined defocus amount A or less among the calculated defocus amounts. To proceed to S9. In S9, a predetermined amount of lens is driven to the close side.

  Here, the reason why the lens is driven by a predetermined amount in the case of Yes in S8 will be described. First, the case where there is no area where the defocus amount can be calculated among the plurality of focus detection areas is the case where the subject to be focused is not found at the present moment. Therefore, in order to confirm the presence of a subject to be focused on all focus detection areas before determining that focusing is impossible, a predetermined amount of lens drive is performed and Be able to judge changes.

  Further, in the case where the defocus amount indicating the presence of the closest object in the calculated defocus amounts is equal to or less than the predetermined threshold value A, the focus detection area in the almost in-focus state exists at the present time. This is the case.

  In such a situation, a lens is driven by a predetermined amount in order to confirm that there is a subject that is not detected at this moment in the focus detection area where the defocus amount could not be calculated. Change in the focus evaluation value to be determined.

  It should be noted that the lens driving amount here may be determined in consideration of the F value of the photographing optical system and the sensitivity of the focus moving amount on the image pickup element surface with respect to the lens driving amount.

  On the other hand, if No in S8, that is, if the defocus amount indicating the presence of the closest object in the calculated defocus amount is larger than the predetermined threshold A, the process proceeds to S10. In this case, there is a focus detection area for which the defocus amount has been calculated, but that focus detection area is not in focus.

  Therefore, in S10, the lens is driven based on the defocus amount indicating the presence of the closest object among the calculated defocus amounts.

  After the lens is driven in S9 or S10, the process proceeds to S11, the close-up determination flag is set to 0, and the process returns to S3 in FIG.

  If the closeness determination flag is not 1 (0) in S7, the process proceeds to S12. In S12, it is determined whether or not the focus evaluation value of the focus detection area for TVAF corresponding to the focus detection area for which the defocus amount could not be calculated has changed by a predetermined threshold value B or more before and after driving the lens. Here, the focus evaluation value may increase or decrease, but it is determined whether or not the absolute value of the change amount of the focus evaluation value is equal to or larger than a predetermined threshold value B.

  In S12, when the absolute value of the change amount of the focus evaluation value is equal to or larger than the predetermined threshold value B, the defocus amount cannot be calculated, but the change in the blur condition of the subject can be detected by the increase or decrease of the focus evaluation value. It means that. Therefore, in the present embodiment, even if the defocus amount due to the imaging plane phase difference AF cannot be detected, the presence of the subject is determined based on the increase or decrease of the focus evaluation value, and the AF process is continued.

  This makes it possible to perform focus adjustment on a subject that has a large defocus amount and cannot be detected by the imaging plane phase difference AF.

  Here, the predetermined threshold value B used for the determination is changed according to the lens driving amount performed in advance. When the lens driving amount is large, a larger value is set as the threshold value B, and when the lens driving amount is small, a smaller value is set as the threshold value B.

  This is because when there is a subject, the amount of change in the focus evaluation value increases as the amount of lens drive increases. The threshold value B for each lens driving amount is stored in the EEPROM 125c.

  When the absolute value of the change amount of the focus evaluation value is equal to or larger than the predetermined threshold value B, the process proceeds to S13, and the focus detection area in which the change amount of the focus evaluation value is equal to or larger than the threshold value indicates focus detection indicating the existence of the infinity side subject. It is determined whether or not there is only a region.

  The case where the focus detection area indicates the presence of a subject on the infinity side means that the focus evaluation value decreases when the lens driving direction is the closest direction or the focus evaluation value increases when the lens driving direction is infinity. Is.

  When the focus detection area in which the change amount of the focus evaluation value is equal to or more than the threshold value B is not only the focus detection area indicating the presence of the infinity side subject, the process proceeds to S14, and a predetermined amount of lens drive is performed on the close side. This is because the focus detection area in which the amount of change in the focus evaluation value is equal to or greater than the threshold value B is the focus detection area indicating the presence of the close-up side subject. The reason for prioritizing the near side is as described above.

  On the other hand, in S13, when the focus detection area in which the amount of change in focus evaluation value is equal to or greater than the threshold value B is only the focus detection area indicating the presence of the infinity side subject, the process proceeds to S15. In S15, it is determined whether or not there is a focus detection area for which the defocus amount has been calculated.

  When the focus detection area for which the defocus amount has been calculated is present (Yes in S15), the result of the imaging plane phase difference AF is prioritized over the presence of the infinity side subject based on the focus evaluation value. Proceed to S20 of a).

  If the focus detection area for which the defocus amount has been calculated does not exist (No in S15), since the information indicating the presence of the subject is only the change in the focus evaluation value, that information is used to infinity in S16. A predetermined amount of lens is driven to the side. After the lens is driven to the infinity side by a predetermined amount, the process returns to S3 in FIG.

  The drive amount of the lens drive performed in S14 and S16 may be determined in consideration of the defocus amount that can be detected by the imaging surface phase difference AF. Although the defocus amount that can be detected differs depending on the subject, a lens driving amount that prevents the subject from passing without being detected when the lens is driven from a state in which focus detection is not possible is set in advance.

  If the absolute value of the change amount of the focus evaluation value is less than the predetermined threshold value B (No in S12), the process proceeds to S17. In S17, it is determined whether or not there is a focus detection area for which the defocus amount has been calculated. If there is no focus detection area for which the defocus amount has been calculated, the process proceeds to S18, the lens is driven to a predetermined fixed point, and then the process proceeds to S19, in-focus display is performed on the display 126, and the AF process ends. To do. This is a case where there is no focus detection area in which the defocus amount is calculated, and there is no focus detection area in which the focus evaluation value changes before and after the lens driving. In such a case, since there is no information indicating the presence of the subject, it is determined that focusing is impossible, and the AF process ends.

  On the other hand, if there is a focus detection area in which the defocus amount can be calculated in S17, the process proceeds to S20 in FIG. 1A, the detected defocus amount is corrected (S20 to S23), and in S24. The focus lens 104 is driven to the in-focus position. Then, in step S25, the focus display is performed on the display device 126, and the AF process ends.

(Method of calculating vertical and horizontal BP correction values)
Next, a method of calculating the vertical and horizontal BP correction values (BP1) performed in S20 of FIG. 1 will be described with reference to FIGS.

  FIG. 8 is a subroutine showing the flow of calculating the vertical and horizontal BP correction values (BP1) showing the details of the processing performed in S20 of FIG.

  In S100, the vertical and horizontal BP correction information is acquired. The vertical / horizontal BP correction information is information obtained through the lens MPU 117 in response to a request from the camera MPU 125, and indicates the vertical (second direction) focus position with respect to the horizontal (first direction) focus position. This is difference information.

  FIG. 9 shows an example of vertical and horizontal BP correction information stored in the lens memory 118. FIG. 9 shows correction values corresponding to the focus detection areas 219a and 218ah in the center of FIG. Similarly, focus detection correction values are stored for the other two focus detection areas. However, the focus detection correction values in the design are the same in the focus detection areas symmetrical with respect to the optical axis of the imaging optical system.

  Therefore, it suffices to store two focus detection correction value tables for the three focus detection areas. If the correction value does not change significantly depending on the position of the focus detection area, it may be stored as a common value.

  In FIG. 9, the zoom position and the focus position of the photographing optical system are divided into eight zones, and the focus detection correction values BP111 to BP188 are provided for each of the divided zones. Therefore, the configuration is such that a highly accurate correction value can be obtained according to the positions of the focus lens 104 and the first lens group 101 of the photographing optical system.

  The vertical and horizontal BP correction information can be used for both the contrast detection method and the phase difference detection method.

  In S100, a correction value corresponding to the zoom position and the focus position according to the focus detection result that is the correction target is acquired.

  Next, in step S101, it is determined whether a reliable focus detection result is obtained in both the horizontal direction and the vertical direction in the focus detection area to be corrected. The method of determining the reliability of the focus detection result is as described above for both the phase difference detection method and the contrast detection method. In the first embodiment, it is the case of the contrast detection method that reliable focus detection results can be obtained in both the horizontal and vertical directions.

  Therefore, the following description regarding the vertical and horizontal BP correction values will be made assuming the contrast detection method, but the same processing is performed even when focus detection by the phase difference detection method is possible in both the horizontal direction and the vertical direction. I'll do it. In S101, when there is reliability in both the horizontal and vertical focus detection results, the process proceeds to S102.

  In S102, it is determined whether or not the difference between the horizontal focus detection result and the vertical focus detection result is appropriate. This is a process performed to deal with the problem of perspective competition that occurs when a subject at a long distance and a subject at a short distance are included in the focus detection area.

  For example, this is the case where there is a subject having a horizontal contrast in a long distance and a subject having a vertical contrast in a short distance.

  In that case, an absolute value may be larger than an error generated by astigmatism of the photographing optical system, or a difference in focus detection results having opposite signs may occur.

  As described above, when the difference between the horizontal focus detection result and the vertical focus detection result is significantly different from the determination value C, it is determined that there is a perspective conflict, and focus detection on the closer side is performed. The horizontal direction or the vertical direction is selected as the direction indicating the result, and the process proceeds to S104. For the above-mentioned reason, the judgment value C may be uniquely determined in order to judge an impossible correction value, or may be set using the correction information obtained in S100.

  When it is determined in S102 that the difference between the horizontal focus detection result and the vertical focus detection result is valid, the process proceeds to S103, BP1 = 0 is set, and the vertical and horizontal BP correction value calculation subroutine ends. In this case, focus detection is performed using the focus detection results in the horizontal and vertical directions without using the correction value.

  In the case of the contrast detection method, the focus detection results are weighted according to the magnitude relationship such as the ratio of the maximum values of the focus evaluation values in the horizontal direction and the vertical direction, and the focus detection results considering the horizontal direction and the vertical direction are added. obtain. Similarly, in the case of the phase difference detection method, the focus detection result may be weighted using the correlation amount used in the correlation calculation.

  On the other hand, if there is reliability in only one horizontal or vertical direction in S101, or if only one horizontal or vertical direction is selected in S102, the process proceeds to S104. In S104, the direction of the focus detection result is selected. The direction in which the reliable focus detection result is calculated or the direction in which the focus detection result corresponding to the subject on the closer side is calculated in the perspective competition determination is selected.

  Next, in S105, it is determined whether or not weighting in the horizontal and vertical directions is possible. When the determination is made in S105, a reliable focus detection result is not obtained in both the horizontal direction and the vertical direction from the viewpoint of the reliability of the focus evaluation value and perspective competition, but in S105, The determination for calculating the vertical and horizontal BP correction values is performed. This will be described in detail with reference to FIG.

  FIG. 10 is a diagram showing the relationship between the position of the focus lens 104 in the selected focus detection area and the focus evaluation value. E_h and E_v in the figure are curves showing changes in the focus evaluation value in the horizontal direction and the focus evaluation value in the vertical direction detected by the contrast detection method.

  Further, LP1, LP2, and LP3 indicate focus lens positions, respectively. FIG. 10 shows a case where LP3 is obtained as a reliable focus detection result from the horizontal focus evaluation value E_h and LP1 is obtained as a reliable focus detection result from the vertical focus evaluation value E_v. There is.

  Since the focus lens positions of LP1 and LP3 are largely different, that is, because there is a near-far conflict condition, the horizontal focus detection result LP3, which is the focus detection result on the closer side, is selected in S104.

  In such a situation, in S105, it is determined whether or not there is a vertical focus detection result in the vicinity of the selected horizontal focus detection result LP1. In the situation as shown in FIG. 10, since LP2 exists, the process proceeds to S106, and the correction value of the focus detection result LP3 is calculated in consideration of the influence of the focus detection result LP2.

  In S106, BP1_B which is one element in FIG. 9 is acquired as the vertical and horizontal BP correction information.

The vertical / horizontal BP correction value BP1 is calculated by the following equation using the horizontal focus evaluation value E_hp at the position LP3 and the vertical focus evaluation value E_vp at LP1 in FIG.
(Formula 2)
BP1 = BP1_B × E_vp / (E_vp + E_hp) × (+1)

In the first embodiment, the correction value BP1 is calculated using Expression 2 in order to calculate the correction value for the focus detection result in the horizontal direction. However, when correcting the focus detection result in the vertical direction, the following expression is used. It is calculated by.
(Formula 3)
BP1 = BP1_B × E_hp / (E_vp + E_hp) × (-1)

  As is obvious from Expressions 2 and 3, the information that the focus evaluation value is large is determined to have a large amount of contrast information included in the subject, and the vertical and horizontal BP correction values (BP1) are calculated.

  As described above, the vertical and horizontal BP correction information is (focus detection position of subject having contrast information only in the vertical direction)-(focus detection position of subject having contrast information only in the horizontal direction). Therefore, the signs of the correction value BP1 for correcting the focus detection result in the horizontal direction and the correction value BP1 for correcting the focus detection result in the vertical direction are opposite to each other. When the process of S106 is completed, the subroutine of vertical and horizontal BP correction value calculation is completed.

  On the other hand, in S105, when there is no vertical focus detection result in the vicinity of the selected horizontal focus detection result LP1, the process proceeds to S103. In S103, the contrast information included in the subject is determined to be approximately in only one direction, so BP1 = 0. When the processing of S107 is completed, the subroutine of vertical and horizontal BP correction value calculation is completed.

  In this way, since the correction value is calculated according to the contrast information for each direction of the subject, it is possible to perform highly accurate correction value calculation according to the pattern of the subject.

  In FIG. 10, the case where there is a perspective conflict has been described. However, even when one maximum value is detected in the horizontal direction and one maximum value in the vertical direction, and one of the focus detection results is unreliable, the correction value is similarly set. calculate.

  In the first embodiment, the correction value is calculated based on the contrast information for each direction of the subject in S105, but the method of calculating the correction value is not limited to this. For example, when focus detection can be performed only in the horizontal direction, such as the focus detection of the phase difference detection method of the first embodiment, it is assumed that the information amount of the contrast in the horizontal direction of the subject is the same as that in the vertical direction. The correction value may be calculated.

  In that case, the correction value can be calculated by substituting E_hp = E_vp = 1 in the above Expressions 2 and 3. By performing such processing, although the correction accuracy is lowered, the load of the correction value calculation can be reduced.

  In the above description, the focus detection result of the contrast detection method has been described, but the same processing can be performed on the focus detection result of the phase difference detection method. The amount of change in the correlation amount calculated by the correlation calculation of the phase difference detection method may be used as the weighting coefficient when calculating the correction value.

  This utilizes the fact that the more the contrast information of the subject is, such as the case where the contrast of the subject is large or the number of edges having the contrast is large, the change amount of the correlation amount is also large. Various evaluation values may be used without being limited to the change amount of the correlation amount as long as the evaluation values can obtain the same relationship.

  In this way, by correcting the focus detection result using the vertical and horizontal BP correction values, highly accurate focus detection can be performed regardless of the amount of contrast information for each direction of the subject. Further, since the correction values in the horizontal direction and the vertical direction are calculated using the common correction information as shown in FIG. 9, the correction information is stored as compared with the case where each correction value is stored for each direction. The capacity can be reduced.

  Further, when the focus detection result for each direction is significantly different, the effect of perspective competition can be reduced by not calculating the vertical and horizontal BP correction values using these focus detection results. Further, even when perspective competition is expected, more accurate correction can be performed by weighting the correction value according to the magnitude of the focus evaluation value for each direction.

  That is, the first evaluation band includes a plurality of evaluation regions, and the focus adjustment unit performs the focus adjustment of the recording signal using the information obtained by weighting the information regarding the image forming positions of the plurality of evaluation bands. ing.

(Calculation method of color BP correction value)
Next, a method of calculating the color BP correction value (BP2) performed in S20 of FIG. 1 will be described with reference to FIGS.

  FIG. 11 is a subroutine showing the flow of calculating the color BP correction value (BP2) showing the details of the processing performed in S21 of FIG.

  In step S200, color BP correction information is acquired. The color BP correction information is information obtained through the lens MPU 117 in response to a request from the camera MPU 125, and other colors (red (R) and blue for the in-focus position detected using the green (G) signal. It is the difference information of the in-focus position detected using the signal of (B)).

  FIG. 12 shows an example of the color BP correction information stored in the lens memory 118. FIG. 12 shows correction values corresponding to the central focus detection areas 219a and 218ah in FIG. Similarly, focus detection correction values are stored for the other two focus detection areas.

  However, the focus detection correction values in the design are the same in the focus detection areas symmetrical with respect to the optical axis of the imaging optical system. Therefore, it suffices to store two focus detection correction value tables for the three focus detection areas. If the correction value does not change significantly depending on the position of the focus detection area, it may be stored as a common value.

  12, similarly to FIG. 9, the zoom position and the focus position of the photographing optical system are divided into eight zones, and the focus detection correction values BP211 to BP288 and BP311 to 388 are provided for each of the divided zones. Therefore, the configuration is such that a highly accurate correction value can be obtained according to the positions of the focus lens 104 and the first lens group 101 of the photographing optical system.

  Focus detection correction values BP211 to BP288 in FIG. 12A are outputs of pixels having a red (R) color filter with respect to focus detection results detected using output signals of pixels having a green (G) color filter. It is the difference between the focus detection results detected using the signal.

  Focus detection correction values BP311 to BP388 in FIG. 12B are outputs of pixels having a blue (B) color filter with respect to a focus detection result detected by using output signals of pixels having a green (G) color filter. It is the difference between the focus detection results detected using the signal.

  Green (G), red (R), and blue (B) in the first embodiment mean the signals obtained for each color filter applied to the pixels on the above-described image sensor, but the definition of each color. Is not limited to this. For example, a separate spectral detection unit for detecting spectral information of the subject is provided, and wavelengths or wavelength ranges of green (G), red (R), and blue (B) are set in accordance with the output of the spectral detection unit. Good.

  The color BP correction information can be used for both the contrast detection method and the phase difference detection method.

  In S200, a correction value corresponding to the zoom position and the focus position according to the focus detection result that is the correction target is acquired.

Next, in S201, a color BP correction value is calculated. In S200, when BP_R is acquired as one element in FIG. 12A and BP_B is acquired as one element in FIG. 12B, the color BP correction value BP2 is calculated by the following formula.
(Equation 4)
BP2 = K_R × BP_R + K_B × BP_B

  K_R and K_B are coefficients for the correction information of each color. It is a value that correlates with the magnitude relationship of the red (R) and blue (B) information with respect to the green (G) information included in the subject. For a subject that includes many red colors, K_R has a large value and blue. K_B has a large value for a subject including many colors. For a subject including a large amount of green, both K_R and K_B have small values.

  K_R and K_B may be set in advance based on the spectral information representative of the subject. Alternatively, if the spectral information of the subject can be obtained by using the means for detecting the spectral of the subject, K_R and K_B may be set according to the spectral information of the subject. When the calculation of the color BP correction value is finished in S202, this subroutine is finished.

  In the first embodiment, the correction value used for focus detection is stored in the table data for each focus detection area as shown in FIGS. 9 and 12, but the method of storing the correction value is not limited to this. For example, coordinates are set with the intersection of the optical axis of the image sensor and the optical axis of the imaging optical system as the origin, and the horizontal and vertical directions of the image pickup device are set as the X axis and the Y axis, and the correction value at the center coordinate of the focus detection area is X. It may be obtained by a function of Y. In this case, the amount of information to be stored as the focus detection correction value can be reduced.

  Further, in the first embodiment, the correction value used for focus detection calculated using the vertical and horizontal BP correction information and the color BP correction information is calculated not to depend on the spatial frequency information of the subject pattern. Therefore, highly accurate correction can be performed without increasing the amount of correction information to be stored. However, the method of calculating the correction value is not limited to this. Similar to the method of calculating the spatial frequency BP correction value described below, the vertical and horizontal BP correction information and the color BP correction information for each spatial frequency may be used to calculate the correction value that matches the spatial frequency component of the subject.

(Calculation method of spatial frequency BP correction value)
Next, a method of calculating the spatial frequency BP correction value (BP3) performed in S22 of FIG. 1 will be described with reference to FIGS. 13 to 16.

  FIG. 13 is a subroutine showing the flow of calculating the spatial frequency BP correction value (BP3) showing the details of the processing performed in S22 of FIG.

  In S300, the spatial frequency BP correction information is acquired. The spatial frequency BP correction information is information obtained through the lens MPU 117 in response to a request from the camera MPU 125, and is information regarding the imaging position of the photographing optical system for each spatial frequency of the subject.

  An example of the spatial frequency BP correction information stored in the lens memory 118 will be described with reference to FIG. FIG. 14 shows the defocus MTF of the photographing optical system. The horizontal axis represents the position of the focus lens 104, and the vertical axis represents the MTF intensity. The four types of curves depicted in FIG. 14 are MTF curves for each spatial frequency, and show the case where the spatial frequency changes from the lower side to the higher side in the order of MTF1, MTF2, MTF3, and MTF4.

  The MTF curve of the spatial frequency F1 (lp / mm) corresponds to MTF1, and similarly, the spatial frequencies F2, F3 and F4 (lp / mm) correspond to MTF2, MTF3 and MTF4. Further, LP4, LP5, LP5, and LP6 indicate the position of the focus lens 104 corresponding to the maximum value of each defocus MTF curve.

  Although shown as a continuous curve in FIG. 14, the spatial frequency BP correction information stored in the lens memory 118 is obtained by discretely sampling the curve in FIG.

  In the first embodiment, MTF data is sampled for 10 focus lens positions for one MTF curve. For example, for MTF1, MTF1 (n) (1 ≦ n ≦ 10). ), 10 data are stored.

  The spatial frequency BP correction information is stored for each position of the focus detection area, like the vertical and horizontal BP correction information and the color BP correction information. Further, the zoom position and the focus position of the photographing optical system are divided into eight zones, and each divided zone has spatial frequency BP correction information.

  Similar to the vertical / horizontal BP correction information and the color BP correction information described above, the number of focus detection areas and the number of divisions of zoom positions and focus positions may be set freely. As the number of settings increases, the amount of memory required to store data increases, but highly accurate correction can be expected.

  The spatial frequency BP correction information can be used for both the contrast detection method and the phase difference detection method.

  In S300, the correction information corresponding to the zoom position and the focus position according to the focus detection result that is the correction target is acquired.

  Next, in step S301, a band of a signal used when performing focus detection (AF) by the contrast detection method or the phase difference detection method is calculated. In the first embodiment, the AF evaluation band is calculated in consideration of the effects of the subject, the photographing optical system, the sampling of the image sensor, and the digital filter used for the evaluation. A method of calculating the AF evaluation band will be described later.

  Next, in S302, the band of the signal used for the captured image is calculated. Similar to the calculation of the AF evaluation band in S301, the captured image evaluation band is calculated in consideration of the effects of the subject, the shooting optical system, the sampling of the image sensor, and the evaluation band of the viewer of the captured image.

  Calculation of the AF evaluation band (the second evaluation band of the focus adjustment signal) and the captured image evaluation band (the first evaluation band of the recording signal) performed in S301 and S302 will be described with reference to FIG. FIG. 15 shows the intensity for each spatial frequency, the horizontal axis shows the spatial frequency, and the vertical axis shows the intensity.

  When the first evaluation band of the recording signal is switched by the switching means, the correction value of the image forming position is changed.

  FIG. 15A shows the spatial frequency characteristic (I) of the subject. F1, F2, F3, and F4 on the horizontal axis are spatial frequencies corresponding to the MTF curves (MTF1 to MTF4) in FIG. Nq represents a Nyquist frequency determined by the pixel pitch of the image sensor. F1 to F4 and Nq are also shown in FIGS. 15 (b) to 15 (f), which will be described later.

  In the first embodiment, the spatial frequency characteristic (I) of the subject uses a representative value stored in advance. In FIG. 15A, the spatial frequency characteristic (I) of the subject is drawn by a curve, but discretely has values corresponding to the spatial frequencies F1, F2, F3, and F4, and I (n) ) (1 ≦ n ≦ 4).

  Further, in the first embodiment, the spatial frequency characteristic of the subject stored in advance is used, but the spatial frequency characteristic of the subject to be used may be changed depending on the subject for which focus detection is performed. The spatial frequency information of the subject can be obtained by performing processing such as FFT processing on the captured image signal.

  Although the content of the arithmetic processing is increased by such processing, since the correction value according to the subject for which focus detection is performed can be calculated, highly accurate focus adjustment can be performed. Further, several types of pre-stored spatial frequency characteristics may be selectively used depending on the size of the contrast information of the subject.

  FIG. 15B is a spatial frequency characteristic (O) of the photographing optical system of the photographing optical system. This information may be obtained through the lens MPU 117 or may be stored in the RAM 125b in the camera. The information stored at that time may be the spatial frequency characteristic for each defocus state or only the spatial frequency characteristic at the time of focusing.

  Since the spatial frequency BP correction value is calculated in the vicinity of the focus, the correction can be performed with high accuracy by using the spatial frequency characteristic at the time of focus. However, although the calculation load increases, the focus adjustment can be performed with higher accuracy by using the spatial frequency characteristic for each defocus state.

  Which defocused state spatial frequency characteristic is used may be selected by using the defocus amount obtained by the focus detection of the phase difference detection method.

  In FIG. 15B, the spatial frequency characteristic (O) of the photographing optical system is drawn by a curve, but discretely has values corresponding to the spatial frequencies F1, F2, F3, and F4, (N) (1 ≦ n ≦ 4).

  FIG. 15C shows the spatial frequency characteristic (L) of the optical low pass filter 121. This information is stored in the RAM 125b in the camera. In FIG. 15C, the spatial frequency characteristic (L) of the optical low-pass filter 121 is drawn by a curve, but discretely has values corresponding to the spatial frequencies F1, F2, F3, and F4, and It is expressed as L (n) (1 ≦ n ≦ 4).

  FIG. 15D shows the spatial frequency characteristics (M1, M2) due to signal generation. As described above, the image sensor of the first embodiment has two types of read modes. In the first read mode, that is, the all-pixel read mode, the spatial frequency characteristic does not change during signal generation.

  M1 in FIG. 15D shows the spatial frequency characteristic in the first read mode. On the other hand, in the second read mode, that is, the thinned-out read mode, the spatial frequency characteristic changes during signal generation. As described above, the signals are added during thinning in the X direction to improve the S / N, so that a low pass effect is generated by the addition.

  M2 in FIG. 15D shows the spatial frequency characteristic at the time of signal generation in the second read mode. Here, the effect of thinning is not added, and the low-pass effect due to addition is shown.

  In FIG. 15D, the spatial frequency characteristic (M1, M2) by signal generation is drawn by a curve, but discretely has values corresponding to the spatial frequencies F1, F2, F3, F4, and Represented as M1 (n) and M2 (n) (1 ≦ n ≦ 4).

  FIG. 15E shows the spatial frequency characteristic (D1) showing the sensitivity for each spatial frequency when viewing a captured image and the spatial frequency characteristic (D2) of the digital filter used when processing the AF evaluation signal.

  Sensitivity for each spatial frequency when viewing a shot image is affected by individual differences among viewers, viewing environment such as image size, viewing distance, and brightness. In the first embodiment, the sensitivity for each spatial frequency at the time of viewing is set and stored as a representative value.

  The viewing distance means the distance from the user to the display on which the recorded image is displayed, and the distance from the user to the paper on which the recorded image is printed.

  On the other hand, in the second read mode, aliasing noise of the frequency component of the signal occurs due to the influence of thinning. D2 shows the spatial frequency characteristic of the digital filter in consideration of the influence.

  In FIG. 15E, the spatial frequency characteristic (D1) at the time of viewing and the spatial frequency characteristic (D2) of the digital filter are drawn by curves, but discretely correspond to the spatial frequencies F1, F2, F3, F4. Which are represented by D1 (n) and D2 (n) (1 ≦ n ≦ 4).

As described above, by storing various information in either the camera or the lens, the evaluation band W1 and the AF evaluation band W2 of the captured image are calculated using the following formulas.
(Equation 5)
W1 (n) = I (n) × O (n) × L (n) × M1 (n) × D1 (n) (1 ≦ n ≦ 4)
(Equation 6)
W2 (n) = I (n) × O (n) × L (n) × M2 (n) × D2 (n) (1 ≦ n ≦ 4)

  FIG. 15F shows the evaluation band W1 (first evaluation band of the recording signal) and the AF evaluation band W2 (second evaluation band of the focus adjustment signal) of the captured image. By performing calculations such as Expression 5 and Expression 6, it is possible to quantify how much influence each spatial frequency has on the factor that determines the focused state of the captured image. Similarly, it is possible to quantify how much the error included in the focus detection result has an influence degree for each spatial frequency.

  In addition, the information stored in the camera may store W1 and W2 calculated in advance. As described above, by performing the calculation for each correction, the correction value can be flexibly calculated when the digital filter or the like used in the AF evaluation is changed.

  On the other hand, if it is stored in advance, it is possible to omit the calculation such as Expression 5 and Expression 6 and the storage capacity of various data.

  Also, since it is not necessary to complete all the calculations in advance, for example, only the shooting optical system and the spatial frequency characteristics of the subject are calculated in advance and stored in the camera to reduce the data storage capacity and the amount of calculation. May be reduced.

  In FIG. 15, four spatial frequencies (F1 to F4) are used for simplification of description. However, the larger the number of spatial frequencies having data, the spatial frequency characteristic of the evaluation band of the captured image or AF. Can be accurately reproduced, and an accurate correction value can be calculated.

  On the other hand, it is possible to reduce the amount of calculation by reducing the spatial frequency for weighting. It is also possible to have one spatial frequency representative of the spatial frequency characteristics of the evaluation band of the captured image and the AF evaluation band, and to perform the subsequent calculation.

  Returning to FIG. 13, the description of the contents of the subroutine will be continued.

  In S303, the spatial frequency BP correction value (BP3) is calculated. When calculating the spatial frequency BP correction value, first, the defocus MTF (C1) of the captured image and the defocus MTF (C2) of the focus detection signal are calculated.

C1 and C2 are calculated by the following formulas using the defocus MTF information obtained in S300 and the evaluation bands W1 and W2 obtained in S301 and S301.
(Equation 7)
C1 (n) = MTF1 (n) x W1 (1) + MTF2 (n) x W1 (2) + MTF3 (n) x W1 (3) + MTF4 (n) x W1 (4)
(Equation 8)
C2 (n) = MTF1 (n) x W2 (1) + MTF2 (n) x W2 (2) + MTF3 (n) x W2 (3) + MTF4 (n) x W2 (4)

  In Expressions 7 and 8, the defocus MTF information for each spatial frequency shown in FIG. 14 is weighted and added to the photographed image and the AF evaluation band calculated in S301 and S302 to defocus the photographed image. The MTF C1 and the AF defocus MTF C2 are obtained.

  FIG. 16 shows the obtained two defocus MTFs C1 and C2. The horizontal axis represents the position of the focus lens 104, and the vertical axis represents the MTF value added by weighting for each spatial frequency.

  The camera MPU 125 detects the maximum value position of each MTF curve as an image forming position calculation means. P_img (first imaging position) is detected as the position of the focus lens 104 corresponding to the maximum value of the curve C1. P_AF (second image formation position) is detected as the position of the focus lens 104 corresponding to the maximum value of the curve C2.

In S303, the spatial frequency BP correction value BP3 is calculated by the following equation.
(Equation 9)
BP3 = P_AF-P_img

  With Expression 9, the best focus correction value (BP correction value) for correcting an error that may occur between the focus position of the captured image and the focus position detected by AF can be corrected. As described above, the focus position of the captured image is determined by the spatial frequency characteristic of the subject, the spatial frequency characteristic of the photographing optical system, the spatial frequency characteristic of the optical low-pass filter, the spatial frequency characteristic at the time of signal generation, and the frequency at the time of viewing. It changes according to the spatial frequency characteristics indicating the sensitivity.

  In addition, it also changes depending on the image processing content applied to the captured image. In the first embodiment, the in-focus position of the captured image can be calculated with high accuracy by calculating the spatial frequency characteristic retroactively to the process of generating the captured image.

  For example, the focus position of the captured image is changed according to the recording size when recording the captured image, the super-resolution processing performed in the image processing, the sharpness, the display size, and the like. In addition, if the user knows in advance how much image size and magnification the image will be viewed after being recorded, and the viewing distance at the time of viewing, it will affect the viewer's evaluation band.

  As the image size becomes larger and the viewing distance becomes shorter, the viewer's evaluation band has a characteristic in which high-frequency components are emphasized. As a result, the focus position of the captured image is also changed.

  The first evaluation band of the recording signal is changed according to the interval between the pixels of the image sensor of the recording signal and the signal addition processing of the recording signal performed in the image sensor.

  The first evaluation band of the recording signal is changed according to the signal thinning processing of the recording signal performed in the image sensor and the image processing content performed on the recording signal.

  The first evaluation band of the recording signal is changed according to the image size of the recording signal and the display size of the recording signal.

  The first evaluation band of the recording signal is changed according to the viewing distance of the recording signal and the brightness of the image of the recording signal.

  Similarly, the second evaluation band of the focus adjustment signal is changed according to the distance between the pixels of the image sensor of the focus adjustment signal.

  The second evaluation band of the focus adjustment signal is changed according to the signal addition process performed in the image sensor, the signal thinning process performed in the image sensor, and the filter process performed on the focus adjustment signal.

  On the other hand, similarly, the in-focus position detected by the AF is also the spatial frequency characteristic of the subject, the spatial frequency characteristic of the photographing optical system, the spatial frequency characteristic of the optical low-pass filter, the spatial frequency characteristic at the time of signal generation, and the digital filter used for AF evaluation. It changes according to the spatial frequency characteristics. In the first embodiment, the in-focus position detected by the AF can be calculated with high accuracy by calculating the spatial frequency characteristic retroactively in the process of generating the signal used for AF.

  For example, it is possible to flexibly deal with AF in the first read mode. In that case, the weighting coefficient may be calculated by changing the spatial frequency characteristic at the time of signal generation to the characteristic corresponding to the first read mode.

  Further, since the image pickup apparatus described in the first embodiment is the interchangeable lens type single-lens reflex camera, the lens unit 100 can be exchanged. When exchange is performed, defocus MTF information corresponding to each spatial frequency is transmitted to the camera body 120 for each photographing optical system, and the focus position of a captured image and the focus position detected by AF are calculated. Therefore, a highly accurate correction value can be calculated for each interchangeable lens.

  The lens unit 100 may transmit not only the defocus MTF information but also information such as the spatial frequency characteristic of the photographing optical system to the camera body 120. The method of utilizing the information is as described above.

  Similarly, when the camera body 120 is replaced, the pixel pitch and the characteristics of the optical low-pass filter may change. As described above, even in such a case, since the correction value that matches the characteristics of the camera body 120 is calculated, the correction can be performed with high accuracy.

  In the above description, the correction value is mainly calculated by the camera MPU 125, but the calculation means is not limited to this. For example, the lens MPU 117 may calculate the correction value. In that case, the camera MPU may transmit the various types of information described with reference to FIG. 15 to the lens MPU, and the correction value may be calculated in the lens MPU using the defocus MTF information or the like. . In that case, in S24 of FIG. 1, the lens MPU may correct the in-focus position transmitted from the camera MPU 125 and drive the lens.

  In the present embodiment, the correction value for AF is calculated by paying attention to the characteristics (vertical / horizontal, color, spatial frequency band) of the signal used for focus detection. Therefore, the correction value can be calculated by the same method regardless of the AF method. Since it is not necessary to have a correction method and data used for correction for each AF method, it is possible to reduce the data storage capacity and the calculation load.

  The second embodiment of the present invention will be described below with reference to FIG. The main difference from the first embodiment is that the method of calculating the spatial frequency BP correction value is different. In the first embodiment, defocus MTF information is used as a value that represents the characteristics of the photographing optical system for each spatial frequency.

  However, since the defocus MTF information has a large amount of data, a large storage capacity, and a large calculation load, the spatial frequency BP correction value is calculated using the maximum value information of the defocus MTF in the second embodiment. .

  As a result, it is possible to reduce the data capacity in the lens memory 118, the communication capacity between the lens and the camera, and the calculation load of the camera MPU 125.

  The block diagram (FIG. 2) of the image pickup apparatus in the first embodiment and the explanatory diagrams (FIGS. 3 to 6) of each focus detection method are the same as those in the second embodiment, and therefore the description thereof is omitted. .

  Regarding the explanatory diagram (FIG. 7) of the focus detection area in the first embodiment, the flow chart of the focus detection processing (FIG. 1), and the calculation method of various BP correction values (FIGS. 8 to 12), the second embodiment will be described. Since the configuration is the same as, the description will be omitted.

  Also, the subroutine for calculating the spatial frequency BP correction value (FIG. 13) and the explanatory diagram of each evaluation band (FIG. 15) have the same configuration and perform the same operation, and therefore the description thereof is omitted.

  A subroutine showing a flow for calculating the spatial frequency BP correction value (BP3) in the second embodiment will be described.

  In S300, the spatial frequency BP correction information is acquired.

  The processing contents of the second embodiment will be described with reference to FIG. 17 regarding the spatial frequency BP correction information stored in the lens memory 118 of FIG. 14 different from that of the first embodiment.

  FIG. 17 shows the position of the focus lens 104 showing the maximum value of the defocus MTF for each spatial frequency, which is the characteristic of the photographic optical system. The lens positions LP1, LP2, LP3, LP4 corresponding to the maximum values of the defocus MTF for each spatial frequency (F1 to F4) in FIG. 14 are shown on the vertical axis of FIG. 17 correspondingly. In the second embodiment, the lens memory 118 stores four pieces of data as MTF_P (n) (1 ≦ n ≦ 4). As in the first embodiment, the stored information corresponds to the position of the focus detection area, the zoom position, and the focus position.

  In the second embodiment, in a subroutine for calculating the spatial frequency BP correction value, in S300, the correction information corresponding to the zoom position and the focus position according to the focus detection result to be corrected is acquired.

  Next, in S301 and S302, the same processing as in the first embodiment is performed.

Next, in S303, the spatial frequency BP correction value (BP3) is calculated. When calculating the spatial frequency BP correction value, first, the in-focus position (P_img) of the captured image and the in-focus position (P_AF) detected by the AF are obtained in S301 and S301 with the defocus MTF information obtained in S300. It is calculated by the following formula using the evaluated bands W1 and W2.
(Equation 10)
P_img = MTF_P (1) × W1 (1) + MTF_P (2) × W1 (2) + MTF_P (3) × W1 (3) + MTF_P (4) × W1 (4)
(Equation 11)
P_AF = MTF_P (1) × W2 (1) + MTF_P (2) × W2 (2) + MTF_P (3) × W2 (3) + MTF_P (4) × W2 (4)

  In Expression 10 and Expression 11, the captured image calculated in S301 and S302 and the evaluation band of AF are weighted with respect to the maximum value information of the defocus MTF for each spatial frequency shown in FIG. Thereby, the focus position (P_img) of the captured image and the focus position (P_AF) detected by the AF are calculated.

In S303, the spatial frequency BP correction value BP3 is calculated by the following equation, as in the first embodiment.
(Equation 9)
BP3 = P_AF-P_img

  By processing as described above, the spatial frequency BP correction value can be calculated. Since the defocus MTF information is used in the first embodiment, the correction value can be calculated with higher accuracy. On the other hand, with the configuration of the second embodiment, it is possible to reduce the data capacity in the lens memory 118, the communication capacity between the lens and the camera, and the calculation load of the camera MPU 125.

  The third embodiment of the present invention will be described below with reference to FIG. The main difference from the first embodiment is that the method of calculating the spatial frequency BP correction value is different. In the first embodiment, the defocus MTF information is used as a value representing the characteristic of the imaging optical system for each spatial frequency, and the correction value is calculated each time focus detection is performed.

  However, the calculation of the spatial frequency BP correction value requires a large amount of data to be handled, a large storage capacity, and a large calculation load. Therefore, in the third embodiment, when there is no need to calculate the spatial frequency BP correction value, Do not calculate. As a result, the communication capacity between the lens and the camera can be reduced, and the calculation load of the camera MPU 125 can be reduced.

  Regarding the block diagram (FIG. 2) of the image pickup apparatus in the first embodiment, the explanatory diagrams of each focus detection method (FIGS. 3 to 6), and the explanatory diagrams of the focus detection area (FIG. 7), the third embodiment will be described. Since it is the same as, the description will be omitted.

  The flow chart of the focus detection processing (FIG. 1) and the method of calculating various BP correction values (FIGS. 8 to 12) in the first embodiment are the same as those in the third embodiment, and therefore the description thereof is omitted.

  Further, the explanatory diagrams (FIGS. 14 to 16) used when calculating the spatial frequency BP correction value also have the same configuration and perform the same operation, and therefore the description thereof will be omitted.

  Differences in processing contents performed in the third embodiment from the subroutine for calculating the spatial frequency BP correction value (BP3) in the first embodiment will be described with reference to FIG. In FIG. 18, the same step numbers are assigned to the portions that perform the same processing as in FIG. 13, and the description will be omitted.

  FIG. 18 is a subroutine showing the flow of calculating the spatial frequency BP correction value (BP3) in the third embodiment showing the details of the processing performed in S22 of FIG.

  In S3000, it is determined whether or not the correction value is calculated. As can be seen from the description in the first embodiment, the more similar the evaluation band of the captured image and the AF evaluation band are, the smaller the correction amount is. Therefore, in the third embodiment, the calculation of the correction value is omitted when it is known in advance that the difference between the two evaluation bands is smaller than the predetermined value.

  That is, when the difference between the first evaluation band and the second evaluation band is smaller than the predetermined value, the correction value is not performed.

  When the difference between the first evaluation band and the second evaluation band is greater than or equal to a predetermined value, the correction value is calculated using the information about the first evaluation band of the recording signal and the information about the second evaluation band of the focus adjustment signal. to correct.

  Specifically, in the spatial frequency characteristic by signal generation, when the signal used for AF is also the signal read in the first read mode, the evaluation band of the captured image and the AF evaluation band are equal.

  Furthermore, when a digital filter having a spatial frequency characteristic similar to the spatial frequency characteristic indicating the sensitivity for each spatial frequency when viewing a captured image is used during processing of the AF evaluation signal, the spatial frequency characteristic at the time of viewing and the digital filter Spatial frequency characteristics become equal.

  Such a situation occurs when an image displayed on the display 126 is enlarged and displayed.

  Similarly, it is assumed that the evaluation band of the captured image and the AF evaluation band are equal when the captured image is generated by the signal read in the second read mode. Such a situation occurs when the recorded image size of the captured image is set small.

  In S3000, in such a case, it is determined that the correction value need not be calculated, and the process proceeds to S3001.

  In S3001, since the correction value is not calculated, 0 is substituted for BP3, and the subroutine for calculating the spatial frequency BP correction value (BP3) is ended.

  On the other hand, the subsequent processing performed when it is determined in S3000 that the calculation of the correction value is necessary is the same as that in the first embodiment, and thus the description thereof is omitted.

  With this configuration, the process can be omitted when the calculation of the spatial frequency BP correction value is unnecessary. As a result, it is possible to reduce the amount of data communication and the calculation load.

  Further, in the third embodiment, the spatial frequency BP correction value has been described, but the same applies to the vertical and horizontal BP correction values and the color BP correction value. When the focus detection is performed in the vertical direction and the horizontal direction, the calculation of the vertical and horizontal BP correction values may be omitted. If the color signal used for the captured image and the color signal used for focus detection are the same, the calculation of the color BP correction value may be omitted.

100 lens unit 104 focus lens 113 focus actuator 117 lens MPU
118 lens memory 120 camera body 122 image sensor 125 camera MPU
129 Imaging plane phase difference focus detection unit 130 TVAF focus detection unit

Claims (18)

A first acquisition unit that acquires first information about an evaluation frequency of a signal used to acquire a focus detection result and second information about an evaluation frequency of a signal used in a captured image;
Second acquisition means for acquiring, from the photographing optical system, third information relating to the imaging position of the photographing optical system for each of a plurality of different spatial frequencies;
It has a focus detection means which outputs a corrected focus detection result based on the focus detection result, the first information, the second information, and the third information. Focus detection device.   The focus detection apparatus according to claim 1, further comprising a control unit that controls movement of a focus lens included in the imaging optical system based on the corrected focus detection result.   The focus detection means uses the third information to calculate an image-forming position corresponding to an evaluation frequency of a signal used to acquire the focus detection result, and the third information to calculate the image formation position. The focus detection device according to claim 1, wherein the focus detection device outputs a corrected focus detection result based on a result of calculating an imaging position corresponding to an evaluation frequency of a signal used for a captured image. The evaluation frequency of the signal used to obtain the focus detection result, and the evaluation frequency of the signal used in the captured image, each has a band,
The focus detection means has a maximum value of an MTF curve corresponding to an evaluation frequency of a signal used to acquire the focus detection result, and a maximum value of an MTF curve corresponding to an evaluation frequency of a signal used for the captured image. Is added to the values of the MTFs corresponding to the plurality of different spatial frequencies by weighting based on the intensity of each of the evaluation frequencies, and is calculated, and the result of the imaging optical system corresponding to the calculated maximum value is calculated. The focus detection device according to claim 3, wherein a corrected focus detection result is output using the difference between the image positions. A first acquisition unit that acquires first information about an evaluation frequency of a signal used to acquire a focus detection result and second information about an evaluation frequency of a signal used in a captured image;
Second acquisition means for acquiring, from the photographing optical system, third information relating to the imaging position of the photographing optical system for each of a plurality of different spatial frequencies;
Calculating means for calculating a correction value for correcting the focus detection result based on the first information, the second information, and the third information;
A focus detection apparatus comprising: a control unit that controls the movement of a focus lens included in the imaging optical system based on the focus detection result and the correction value.   The calculation means uses the third information to calculate the imaging position corresponding to the evaluation frequency of the signal used to obtain the focus detection result, and the third information to perform the imaging. The focus detection device according to claim 5, wherein a correction value is calculated based on a result of calculating an image formation position corresponding to an evaluation frequency of a signal used for an image. The evaluation frequency of the signal used to obtain the focus detection result, and the evaluation frequency of the signal used in the captured image, each has a band,
The calculating means calculates a maximum value of an MTF curve corresponding to an evaluation frequency of a signal used to acquire the focus detection result and a maximum value of an MTF curve corresponding to an evaluation frequency of a signal used for the captured image. , The MTF values corresponding to the plurality of different spatial frequencies are weighted and added based on the intensities of the respective evaluation frequencies to be calculated, and the imaging of the photographing optical system corresponding to the calculated local maximum values. The focus detection device according to claim 6, wherein the correction value is calculated using the difference between the positions.   8. The third information is information regarding an image forming position of the photographing optical system corresponding to each of the MTF curves for different spatial frequencies, respectively. The focus detection device according to item.   The imaging positions of the photographing optical system corresponding to the MTF curves for the different spatial frequencies, respectively, are the imaging positions corresponding to the maximum values of the MTF corresponding to the different spatial frequencies. The focus detection device according to claim 8, wherein the focus detection device is information of   The first information is an image from an image sensor selected from a plurality of read modes, the spatial frequency characteristic (I) of the subject, the spatial frequency characteristic (O) of the photographing optical system, the spatial frequency characteristic (L) of the optical low-pass filter. 10. The method according to claim 1, which is based on at least one of a spatial frequency characteristic (M2) in a second read mode for reading data and a spatial frequency characteristic (D2) of a digital filter for AF evaluation. The focus detection device according to item 1.   The first information is at least the pixel interval of the image sensor, the signal addition process performed in the image sensor, the signal thinning process performed in the image sensor, and the signal filter process for obtaining the focus detection result. The focus detection device according to claim 1, wherein the focus detection device is changed according to one.   The second information is an image from an image sensor selected from a plurality of read modes, the spatial frequency characteristic (I) of the subject, the spatial frequency characteristic (O) of the photographing optical system, the spatial frequency characteristic (L) of the optical low-pass filter. It is based on at least one of a spatial frequency characteristic (M1) in a first read mode for reading data and a spatial frequency characteristic (D1) showing sensitivity for each spatial frequency when viewing a captured image. Item 10. The focus detection device according to any one of items 1 to 9.   The second information is used for the interval between pixels of the image sensor, signal addition processing of signals used in the captured image, signal thinning processing of signals used in the captured image performed in the image sensor, and the captured image. Of image processing performed on the captured signal, the image size of the signal used for the captured image, the display size of the signal used for the captured image, the viewing distance of the signal used for the captured image, and the signal used for the captured image. The focus detection device according to any one of claims 1 to 9, wherein the focus detection device is changed according to at least one of the brightness of the image.   The focus detection device according to claim 1, wherein the focus detection result is a defocus amount. The focus detection device according to any one of claims 1 to 4 ,
An image pickup device for picking up a subject image by the photographing optical system and outputting image data, wherein the focus detection unit obtains the focus detection result based on the image data output from the image pickup device. An imaging device that outputs a corrected focus detection result based on the acquired focus detection result, the first information, the second information, and the third information. . The focus detection device according to any one of claims 1 to 14,
An image pickup device for picking up a subject image by the photographing optical system to output image data, and a focus detection unit for outputting the focus detection result based on the image data output from the image pickup device. Image pickup device. A first acquisition step of acquiring first information about an evaluation frequency of a signal used to acquire a focus detection result and second information about an evaluation frequency of a signal used for a captured image;
A second acquisition step of acquiring, from the photographing optical system, third information regarding the imaging position of the photographing optical system for each of a plurality of different spatial frequencies;
A focus detection step of outputting a corrected focus detection result based on the focus detection result, the first information, the second information, and the third information. Focus detection method. A first acquisition step of acquiring first information about an evaluation frequency of a signal used to acquire a focus detection result and second information about an evaluation frequency of a signal used for a captured image;
A second acquisition step of acquiring, from the photographing optical system, third information regarding the imaging position of the photographing optical system for each of a plurality of different spatial frequencies;
A calculation step of calculating a correction value for correcting the focus detection result based on the first information, the second information, and the third information;
A focus detection method comprising: a control step of controlling movement of a focus lens included in the photographing optical system based on the focus detection result and the correction value.

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