JP2015138201A - Image capturing device and image capturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image capturing device capable of making more accurate focus adjustment by correcting an essential focus detection error, which is a difference in a focusing condition between a captured image and a focus detection result.SOLUTION: An image capturing device of the present invention includes: third computation means for computing a third focus adjustment position for recording signals by correcting either of a first focus adjustment position or a second focus adjustment position using a correction value; focus adjustment means for making focus adjustment for the recording signals using the third focus adjustment position; and determination mean for determining reliability of a first focus evaluation value corresponding to the first focus adjustment position and a second focus evaluation value corresponding to the second focus adjustment position. The correction value is modified in accordance with a result of determination made by the determination means.

Description

  The present invention relates to an imaging apparatus and an imaging method, and more particularly to an imaging apparatus having an automatic focus adjustment function.

  There are a contrast AF method and a phase difference AF method as a general method for adjusting the focus of the imaging apparatus. Both the contrast AF method and the phase difference AF method are AF methods that are often used in video cameras and digital still cameras, and there are devices 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 performing focus detection by evaluating a plurality of evaluation directions of signals used for focus detection and weighting each evaluation result.

  Such a focus detection error occurs depending on the direction on the image sensor of the pixel that acquires the focus adjustment signal sequence used in the contrast AF method or the phase difference AF method, regardless of the focus adjustment method described above. This error occurs, for example, when an imaging apparatus having an optical system that generates astigmatism is used.

JP 2007-94236 A

  However, the configuration of the above prior art has a problem that the focus detection error cannot be sufficiently corrected. In Patent Document 1, in order to reduce the focus detection error, the evaluation direction of the focus adjustment signal is set to the horizontal direction and the vertical direction, and the focus detection result detected for each evaluation direction is weighted to perform focus detection. .

  On the other hand, it is also conceivable to reduce the above-described focus detection error by performing focus detection using a focus adjustment signal in only one direction and correcting the detection result with a correction value stored in advance.

  Even when focus detection in a plurality of directions is performed as in Patent Document 1 described above, if focus detection in any direction is impossible for some reason, the focus detection result has a correction value. The method of performing correction is effective.

  However, in the focus detection using the focus adjustment signal with a plurality of directions as the evaluation directions, the method for correcting the focus detection result in any direction using the focus adjustment signal in each direction is described in the above-mentioned patent. Reference 1 does not mention it.

  In view of the above-described problems, the present invention corrects a focus detection error caused by an evaluation direction by using a focus adjustment signal in a plurality of directions when performing focus detection in a plurality of evaluation directions. An object of the present invention is to provide an imaging apparatus that performs focus adjustment with high accuracy.

Therefore, in order to achieve the above object, in the present invention, an imaging device, recording means for recording a recording signal output from the imaging device, and a plurality of pixels arranged in a first direction of the imaging device Output from a plurality of pixels arranged in a second direction different from the first direction of the image sensor, and first calculation means for calculating a first focus adjustment position using an output signal output from A second calculation means for calculating a second focus adjustment position using the output signal, and a focus adjustment position of one of the first focus adjustment position and the second focus adjustment position using a correction value; Third calculation means for calculating a third focus adjustment position of the recording signal by correcting, focus adjustment means for adjusting the focus of the recording signal using the third focus adjustment position, and First focus evaluation corresponding to the first focus adjustment position And an imaging device having a determining means for determining reliability of the second focus evaluating value corresponding to the second focusing position,
The correction value is changed according to a determination result of the determination unit.

  According to the present invention, when focus detection is performed in a plurality of evaluation directions, the focus detection error caused by the evaluation direction is corrected by using the focus adjustment signals in the plurality of directions, so that focus can be performed with higher accuracy. Adjustments can be made.

It is a flowchart which shows AF operation | movement procedure in the Example of this invention. 1 is a block diagram showing a schematic configuration of a digital camera in an embodiment of the present invention. The top view which looked at the light reception pixel from the lens unit 100 side. The top view and sectional drawing explaining the structure of the pixel for imaging | photography. The top view and sectional drawing explaining the structure of the pixel for a focus detection which divides a pupil in the horizontal direction of an imaging lens. It is a block diagram of the circuit which calculates various AF required evaluation values in the Example of this invention. The figure which shows the example of the focus detection area | region in a imaging | photography range, and the condition of a to-be-photographed object. It is the subroutine which showed the flow which calculates the vertical / horizontal BP correction value (BP1) in the Example of this invention. It is a figure which shows the example of the vertical / horizontal BP correction information in the Example of this invention. It is the figure which showed the relationship between the position of the focus lens 104 in an Example of this invention, and a focus evaluation value. 7 is a subroutine showing a flow of calculating a color BP correction value (BP2) in an 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. It is a subroutine which showed the flow which calculates the spatial frequency BP correction value (BP3) in the Example of this 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 the various spatial frequency characteristics in the Example of this invention. It is a figure which shows the defocus MTF which considered the evaluation zone | band of the picked-up image in the Example of this invention, and the evaluation zone | band of AF. 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. It is a subroutine which showed the flow which calculates the spatial frequency BP correction value (BP3) in the 3rd Example of this invention.

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

  Hereinafter, an example in which the imaging apparatus of the present invention according to an embodiment of the present invention is applied to a single-lens reflex digital camera with interchangeable lenses will be described.

(Description of configuration of 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 includes a lens unit 100 and a camera body 120. The lens unit 100 is connected to the camera body 120 via a mount M indicated by a dotted line in the center of the drawing.

  The lens unit 100 includes a first lens group 101, a diaphragm 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 includes a photographing lens that forms an image of the subject.

  The first lens group 101 is disposed at the tip of the lens unit 100 and is held so as to be able to advance and retreat in the optical axis direction OA. The aperture / shutter 102 adjusts the aperture diameter to adjust the amount of light during shooting, and also functions as an exposure time adjustment shutter when shooting a still image.

  The diaphragm / shutter 102 and the second lens group 103 integrally move forward / backward in the optical axis direction OA, and realize a zoom function in conjunction with the forward / 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.

  The drive / control system includes 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 performs a zoom operation by driving the first lens group 101 and the third lens group 103 forward and backward in the optical axis direction OA. The aperture shutter actuator 112 controls the aperture diameter of the aperture / shutter 102 to adjust the amount of photographing light, and controls the exposure time during still image photographing.

  The focus actuator 113 drives the focus lens 104 back and forth in the optical axis direction OA to perform focus adjustment. 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 controls the aperture of the diaphragm shutter 102 by drivingly controlling the diaphragm shutter actuator 112.

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

  The lens MPU 117 performs all calculations and control related to the photographing lens, and controls the zoom drive circuit 114, the shutter drive circuit 115, the focus drive circuit 116, and the lens memory 118. The lens MPU 117 detects the current lens position, and notifies the lens position information in response to a request from the camera MPU 125.

  This lens position information includes the position on the optical axis of the focus lens, the position on the optical axis of the exit pupil when the imaging optical system is not moving, the diameter, the position on the optical axis of the lens frame that restricts the light flux of the exit pupil, and the diameter. Information. The lens memory 118 stores optical information necessary for automatic focus adjustment.

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

  The optical low-pass filter 121 and the imaging element 122 function as an imaging optical system that forms a subject image with the light flux from the lens unit 100. The first lens group 101, the diaphragm 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 colors and moire in the 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 by the image processing circuit 124. On the other hand, among the obtained image data, image data used for display, recording, and TVAF is also sent to the image processing circuit 124, and predetermined processing according to the purpose is performed.

  The drive / control system includes an image sensor driving circuit 123, an image processing circuit 124, a camera MPU 125, a display 126, an operation switch group 127, a memory 128, an imaging 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, and the like of 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 driving circuit 123, an image processing circuit 124, a display 126, an operation SW 127, a memory 128, and an imaging surface phase difference focus detection unit 129. The TVAF focus detection unit 130 is controlled. The camera MPU 125 is connected to the lens MPU 117 via the signal line of the mount M, and obtains the lens position, issues a lens driving request with a predetermined driving amount to the lens MPU 117, and transmits optical information specific to the lens unit 100. Or get it.

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

  Further, the camera MPU 125 executes focus detection processing by a 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 a light beam that has passed through different areas of the pupil. The camera MPU 125 also corrects the imaging surface phase difference AF because the influence of vignetting is large and the reliability decreases when the image height at the focus adjustment position is large.

  The display 126 is configured by an LCD or the like, and displays information related to the shooting mode of the camera, a preview image before shooting and a confirmation image after shooting, a focus state display image at the time of focus detection, and the like. 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. A memory 128 serving as a recording unit according to the present exemplary embodiment is a detachable flash memory that records captured images.

  The imaging surface phase difference focus detection unit 129 performs focus detection processing by the phase difference detection method AF based on the image signal of the image data for focus detection obtained by the imaging element 122 and the image processing circuit 124.

  More specifically, the imaging surface phase difference focus detection unit 129 is based on the deviation amount of the pair of images formed on the focus detection pixels by the light flux passing through the pair of pupil regions of the imaging optical system. Perform AF. The method of imaging plane phase difference AF will be described later in detail.

  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 contrast-type focus detection processing. In contrast-type focus detection processing, the focus lens 104 is moved to detect the focus lens position where the focus evaluation value reaches a peak.

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

(Description 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 apparatus using the signal of the image sensor 122 will be described. This focus detection apparatus employs phase difference detection AF and contrast AF. The configuration will be described.

(Description of phase difference detection AF)
First, the configuration of the phase difference detection method AF will be described with reference to FIGS.

  FIG. 3 is a diagram showing a pixel arrangement of the image sensor in the present embodiment. A range of 6 rows and 8 columns in the horizontal (X direction) of the two-dimensional C-MOS area sensor is viewed from the photographing optical system side. The observed state is shown. A Bayer arrangement is applied to the color filters, and green (Red) and red (Red) color filters are alternately provided in order from the left on pixels in odd rows.

  In addition, blue (Blue) and green (Green) color filters are alternately provided in order from the left in the pixels in even rows. A 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 the pixels are divided into two in the X direction, and the sum of the photoelectric conversion signal of one divided region and the two photoelectric conversion signals can be read independently. The signal read out independently 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 divided photoelectric conversion signal in one region. A signal can be obtained.

  The photoelectric conversion signals of these divided regions can be 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 two photoelectric conversion signals is used as a normal captured image.

  Here, a pixel signal in the case of performing phase difference focus detection will be described. As will be described later, in this embodiment, the exit lens of the photographing optical system is pupil-divided by the microlens 211i of FIG. 3 and the divided photoelectric conversion units 211a and 211b.

  Then, in a plurality of pixels 211 within a predetermined range arranged on the same row, the result of joining the outputs of the photoelectric conversion unit 211a and the output of the photoelectric conversion unit 211b are joined together. This is used as an AF B image. The outputs of the photoelectric conversion units 211a and 211b are obtained by adding outputs of green, red, blue, and green in a Bayer array, and are used as pseudo-yield (Y) signals.

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

  In this embodiment, either the AF A image 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. The other signal can be obtained from the output difference, and focus detection can be performed.

  Since the above-described imaging element can be manufactured using the technique disclosed in Japanese Patent Application Laid-Open No. 2004-134867, description regarding the detailed structure is omitted.

  FIG. 4 is a diagram showing a configuration of a readout circuit in the image sensor of the present embodiment. Reference numeral 151 denotes a horizontal scanning circuit, and 153 denotes a vertical scanning circuit. In addition, horizontal scanning lines 152a and 152b and vertical scanning lines 154a and 154b are wired at the boundary between the pixels, and signals are read out to the photoelectric conversion units through these scanning lines.

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

  The second readout mode is called a thinning readout mode, and is a mode for performing only moving image recording or preview image display. In this case, since the number of necessary pixels is smaller than that of all the pixels, the pixel group reads out only the pixels thinned out at a predetermined ratio in both the X direction and the Y direction.

  Also, when it is necessary to read at high speed, the thinning-out reading mode is used in the same manner. When thinning out in the X direction, signals are added to improve the S / N ratio, and thinning out in the Y direction ignores the signal output of the thinned out rows. The focus detection by the phase difference detection method and the contrast detection method is also normally performed in the second readout mode.

  5A and 5B are diagrams for explaining the conjugate relationship between the exit pupil plane of the imaging optical system and the photoelectric conversion unit of the image sensor disposed near the center of the image plane, that is, in the vicinity of the center of the image plane, in the imaging apparatus of the present embodiment. . The photoelectric conversion unit in the image sensor 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 zooming function. However, depending on the optical type, when the zooming operation is performed, the distance and size of the exit pupil from the image plane change. The photographing optical system in FIG. 5 shows a state in which the focal length is intermediate between the wide-angle end and the telephoto end, that is, a middle state.

  Assuming that this is a standard exit pupil distance Zep, an optimum design of an eccentricity parameter according to the shape of the on-chip microlens and the image height (X, Y coordinates) is made.

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

  Note that reference numerals 101b, 102a, 102b, and 104b that act as limiting members for the light beam passing through the photographing optical system indicate optical virtual images when observed from the image plane. Further, the synthetic aperture in the vicinity of the stop 102 is defined as the exit pupil of the lens, and the distance from the image plane is Zep as described above.

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

  The two photoelectric conversion units are projected onto the exit pupil plane of the photographing optical system by the on-chip microlens 2110i. In other words, the exit pupil of the photographing optical system is projected onto 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, and the projected images on the photoelectric conversion units 2110a and 2110b are EP1a and EP1b, respectively. Further, in this embodiment, the imaging device has a pixel that can obtain the output of either one of the two photoelectric conversion units 2110a and 2110b and the sum of both. The sum of both outputs is a photoelectric conversion of the light beam that has passed through both regions of the projection images EP1a and EP1b, which are almost the entire pupil region of the photographing optical system.

  In FIG. 5A, when the outermost part of the light beam passing through the photographing optical system is denoted by L, the light beam L is regulated by the aperture plate 102a of the diaphragm, and the vignetting of the projection images EP1a and EP1b is almost generated in the photographing optical system. Not. In FIG. 5B, the light beam L in FIG. 4A is indicated by TL. Since most of the projected images EP1a and EP1b of the photoelectric conversion unit are included in the circle indicated by TL, it can be seen that almost no vignetting occurs. Since the light beam L is limited only by the aperture plate 102a of the diaphragm, TL can be restated as 102a.

  At this time, the projected state of each projection image EP1a or EP1b is symmetric with respect to the optical axis at the center of the image plane, and the amount of light received by each of the photoelectric conversion units 2110a and 2110b is equal.

  As described above with reference to FIGS. 3, 4, and 5, the image sensor 122 has not only a function of imaging but also a function as a focus detection device. In addition, as a focus detection method, since a focus detection pixel that receives a light beam obtained by dividing an exit pupil is provided, 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. However, pixels that divide 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 corresponding to the contrast of the subject in the vertical direction as well as the horizontal direction can be performed.

(Description of contrast 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 a green (G) signal from the Bayer array signal and reduces the luminance. A gamma correction process for emphasizing the component and suppressing the high luminance component is performed.

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

  A method for calculating the Y peak evaluation value will be described. The luminance signal Y subjected to gamma correction is input to a line peak detection circuit 402 for detecting a 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.

  With this circuit, peak hold is performed in the vertical direction within the AF evaluation range set by the region 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 for calculating the Y integral evaluation value will be described. The luminance signal Y subjected to gamma correction is input to a horizontal integration circuit 403 for detecting an integrated value for each horizontal line. With this circuit, the integral 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 region setting circuit 412 to generate a Y integral evaluation value. The Y integral evaluation value can determine the brightness of the entire AF evaluation range.

  A method for 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. Further, the luminance signal Y subjected to gamma correction 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 Y line peak value and minimum value for each horizontal line are input to the subtractor, and (line peak value−minimum value) is calculated and input to the vertical peak detection circuit 407.

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

  A method for calculating the region peak evaluation value will be described. A specific frequency component is extracted from the gamma-corrected luminance signal Y through the BPF 408 to generate a focus signal. This focus signal is input to a line peak detection circuit 409 which is a peak hold means 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 within the AF evaluation range by the vertical peak detection circuit 411, and an area peak evaluation value is generated.

  Since the area peak evaluation value changes little even when the subject moves within the AF evaluation range, it is effective for restart determination for shifting from the focused state to the process of searching for the focused point again.

  A method for 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 with respect to the number of all horizontal scanning lines in the vertical direction within the AF evaluation range to generate an all-line integration evaluation value.

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

  In this embodiment, the evaluation value changes according to the defocus state, and the total line integration evaluation value used for focus adjustment is referred to as a focus evaluation value.

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

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

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

  The area setting circuit 413 can set a plurality of areas in accordance with the AF evaluation range.

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

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

  When performing contrast AF, the above-described various AF evaluation values are calculated while driving the focus lens 104. Focus detection is performed by detecting the focus lens position where the total line integral evaluation value is the maximum value.

(Description of focus detection area)
FIG. 7 is a diagram showing a focus detection area in the imaging range, and imaging plane phase difference AF and TVAF are performed based on a signal obtained from the image sensor 122 in this focus detection area. The focus detection area in FIG. 7 includes a focus detection unit including pixels that perform pupil division in the horizontal direction (lateral direction) of the photographing lens shown in FIG. A rectangle indicated by a dotted line indicates an imaging range 217 in which pixels of the image sensor 122 are formed.

  Three horizontal focus detection areas 218ah, 218bh, and 218ch for performing imaging plane phase difference AF are formed in the imaging range 217. 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 left and right locations as shown in the figure. Further, focus detection areas 219a, 219b, and 219c for performing TVAF are formed so as to include each of the focus detection areas for performing three imaging surface 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.

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

(Explanation of focus detection process flow)
Next, a 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 processing according to the embodiment of the present invention is as follows. First, for each of the focus detection areas 218ah, 218bh, and 218ch, a defocus amount (defocus amount) and reliability are obtained.

  Then, the region is divided into a region where a defocus amount having a predetermined reliability is obtained and a region where the defocus amount is not obtained. If a 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 where a defocus amount having a 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 among the focus detection regions 219a to 219c. Then, it is determined whether or not the subject exists closer to the camera. 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 change amount of the focus evaluation value cannot be obtained. In that case, when there is a region where a defocus amount having a predetermined reliability greater than a predetermined defocus amount is obtained, the focus lens 104 is driven 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 equal to or less than a predetermined defocus amount, defocusing is performed. A predetermined amount of lens driving is performed regardless of the amount. The reason for driving a predetermined amount of lens that is not related to the defocus amount when the defocus amount is small is that the lens drive amount based on the defocus amount detects a change in focus evaluation value at the next focus detection. This is because it is likely to be difficult.

  When focus detection is completed by any of the methods, various correction values are calculated, and the focus detection result is corrected. Based on the corrected focus detection result, the focus lens 104 is driven to complete the focus adjustment process.

(Description of flowchart showing AF operation procedure)
Hereinafter, the AF process will be described in detail. FIG. 1A and FIG. 1B are flowcharts illustrating an AF operation procedure of the imaging apparatus. A 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 process of S1, three focus detection areas are set as shown in FIG. Next, in S2, the closeness determination flag is set to 1. In S3, a signal necessary for focus detection is acquired in each focus detection region.

  Specifically, after exposure is performed by the image sensor 122, image signals of focus detection pixels in the focus detection areas 218ah, 218bh, and 218ch for the imaging surface phase difference AF are acquired.

  Here, correction processing described in JP 2010-117679 A may be performed on the acquired image signal. Further, after exposure is performed by the image sensor 122, pixel signals in the focus detection areas 219a, 219b, and 219c used for TVAF are acquired, and focus evaluation values are 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 has been detected. This is for performing focus detection by the contrast detection method, and when a reliable peak is detected, the process proceeds to S20 in order to finish focus detection. For the reliability of the focus evaluation value, for example, a method described in FIGS. 10 to 13 of JP 2010-078810 A may be used.

  That is, whether or not the focus evaluation value indicating the in-focus state has a mountain shape is determined by the difference between the maximum value and the minimum value of the focus evaluation value, and the length of the portion inclined with a slope equal to or greater than a certain value (SlopeThr). , And the slope of the inclined portion. Thereby, the peak reliability can be determined.

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

  In that case, the focus lens 104 position corresponding to the position of the focus evaluation value peak is stored, and when the focus detection result with reliability is not obtained thereafter, the stored focus lens 104 position is used as the focus detection result. To do.

  Next, in S5, for each focus detection area for the imaging surface phase difference AF, the shift amount of the obtained pair of image signals is calculated, and the defocus amount is stored using a conversion factor to 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 subsequent AF processing. Due to the influence of vignetting caused by the taking lens, as the defocus amount increases, the detected shift amount of the pair of image signals includes more errors.

  Therefore, when the calculated defocus amount is large, when the degree of coincidence of the shape of the pair of image signals is low, or when the contrast of the pair of image signals is low, it is determined that high-precision focus detection is impossible, in other words 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 is calculated”, and the defocus amount cannot be calculated for some reason, or the calculated defocus amount is reliable. It is expressed that “the defocus amount cannot be calculated” when the property is low.

  Next, in S6, it is determined whether or not the defocus amount has been calculated in all of the plurality of focus detection areas 218ah, 218bh, and 218ch set in S1. If the defocus amount can be calculated in all the focus detection areas, the process proceeds to S20, and among the calculated defocus amounts, the focus detection area for which the defocus amount indicating the closest object is calculated. Thus, the vertical / horizontal BP correction value (BP1) is calculated. Here, the reason for selecting the closest subject is that the subject that the photographer wants to focus on is often on the close side. The vertical / horizontal BP correction value (BP1) corrects the difference between the focus detection results when the focus detection is performed on the contrast of the subject in the horizontal direction and the focus detection is performed on the contrast of the subject in the vertical direction. Is.

  In general, the subject has contrast in both the horizontal direction and the vertical direction, and the evaluation of the focus state of the photographed image is performed in view of the contrast in both the horizontal direction and the vertical direction. 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 in both the horizontal and vertical directions of the captured image. This error is caused by astigmatism of the photographing optical system.

  The vertical / horizontal BP correction value (BP1) is a correction value for correcting the error. The vertical / horizontal BP correction value (BP1) is calculated in view 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, a color BP correction value (BP2) is calculated using contrast information in one direction, vertical or horizontal, for the focus detection area that is the correction value calculation target in S20. The color BP correction value (BP2) is generated due to chromatic aberration of the photographing optical system, and is caused by the difference between the color balance of the signal used for focus detection and the color balance of the signal used for the photographed image or the developed image.

  For example, in the case of performing contrast detection type focus detection in this embodiment, since the focus evaluation value used is generated by a pixel output having a green (G) color filter, the focus position of the green wavelength is mainly determined. Will be detected.

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

  Next, in S22, a specific color space frequency BP correction value (contrast information of green or luminance signal Y is used in one of the vertical and horizontal directions with respect to the focus detection area to be corrected in S20 and S21. BP3) is calculated. The spatial frequency BP correction value (BP3) is generated mainly by spherical aberration in the photographing optical system, and the difference between the evaluation frequency (band) of the signal used for focus detection and the evaluation frequency (band) when viewing the photographed 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 readout mode, and therefore the output signal is added or thinned out. For this reason, the output signal used for focus detection has a lower evaluation band than the captured image generated using the signals of all the pixels read in the first readout mode.

  The spatial frequency BP correction value (BP3) is generated due to the difference between the evaluation bands. 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 so far, and DEF_A is calculated.
(Formula 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, the evaluation at the time of viewing a captured image uses contrast information in both vertical and horizontal directions, whereas focus detection occurs because contrast information in one direction is used. The error to be calculated is calculated.

  Next, the color BP correction value is calculated as a correction value by separating the influence of the vertical and horizontal BP, and using the contrast information in one direction as a correction value, based on the color used for the signal when viewing the captured image and detecting the focus. 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 a captured image and detecting a focus. Is calculated as a correction value.

  In this way, by calculating the three types of errors separately, the amount of calculation is reduced and the data capacity stored in the lens or camera is reduced.

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

  Next, the process proceeds to S25, where the focus detection area where the defocus amount used for driving the lens is calculated is displayed in focus on the display 126, and the AF process is terminated.

  On the other hand, if there is a focus detection area where 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 driving has never been performed since the AF operation has started, and becomes 0 when the lens driving has been performed a plurality of times. If the closeness determination flag is 1, the process proceeds to S8.

  In S8, when the defocus amount cannot be calculated in all focus detection areas, or when the defocus amount indicating the presence of the closest subject among the calculated defocus amounts is equal to or less than the predetermined threshold A The process proceeds to S9. In S9, a predetermined amount of lens driving is performed on the closest side.

  Here, the reason why the predetermined amount of lens driving is performed in the case of Yes in S8 will be described. First, the case where there is no region where the defocus amount can be calculated among the plurality of focus detection regions is a case where no subject to be focused is found at the present time. Therefore, before determining that focusing is impossible, a predetermined amount of lens driving is performed to check the presence of a subject to be focused on in all focus detection areas, and a focus evaluation value described later is obtained. Enable to determine changes.

  Also, when the defocus amount indicating the presence of the closest subject in the calculated defocus amount is equal to or smaller than the predetermined threshold A, there is a focus detection region that is almost in focus at the present time. Is the case.

  In such a situation, a predetermined amount of lens drive is performed in order to confirm that there is a subject that is not detected at the present time closer to the focus detection area where the defocus amount could not be calculated. It is possible to determine a change in focus evaluation value.

  Here, the lens driving amount may be determined in consideration of the sensitivity of the focus movement amount on the image sensor surface with respect to the F value of the photographing optical system and the lens driving amount.

  On the other hand, in the case of No in S8, that is, when the defocus amount indicating the presence of the closest subject 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 where the defocus amount is calculated, but the focus detection area is not in focus. Therefore, in S10, lens driving is performed based on the defocus amount indicating the presence of the closest subject in the calculated defocus amount.

  After driving the lens in S9 or S10, the process proceeds to S11, the closeness 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 cannot be calculated has changed by a predetermined threshold B or more before and after lens driving. 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 greater than a predetermined threshold B.

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

  Thereby, focus adjustment can be performed on a subject that has a large defocus amount and cannot be detected by the imaging plane phase difference AF.

  Here, the predetermined threshold B used for the determination result 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 the subject exists, the amount of change in the focus evaluation value increases as the lens driving amount increases. The threshold value B for each lens driving amount is stored in the EEPROM 125c.

  If the absolute value of the change amount of the focus evaluation value is equal to or greater than the predetermined threshold 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 greater than the threshold indicates the presence of the infinite object. It is determined whether or not only the area.

  When the focus detection area indicates the presence of an object at infinity, the focus evaluation value decreases when the lens drive direction is close, or the focus evaluation value increases when the lens drive direction is infinity. It is.

  If the focus detection area where the change amount of the focus evaluation value is greater than or equal to 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 driving is performed on the closest side.

  This is because there is a focus detection area indicating the presence of the near-side subject in the focus detection area where the change amount of the focus evaluation value is equal to or greater than the threshold value B. The reason for giving priority to the closest side is as described above.

  On the other hand, if the focus detection area where the amount of change in the focus evaluation value is greater than or equal to the threshold value B is only the focus detection area indicating the presence of the infinity side object in S13, the process proceeds to S15.

  In S15, it is determined whether or not there is a focus detection area for which the defocus amount is calculated. When there is a focus detection area for which the defocus amount is calculated (Yes in S15), the result of the imaging plane phase difference AF is given priority over the presence of the infinitely far side object based on the focus evaluation value. Proceed to S20 of a).

  If there is no focus detection area for which the defocus amount is calculated (No in S15), the information indicating the presence of the subject is only a change in the focus evaluation value. A predetermined amount of lens is driven to the side. After driving a predetermined amount of lens to the infinity side, the process returns to S3 in FIG.

  The driving amount of the lens driving performed in S14 and S16 may be determined in view 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 drive amount is set in advance so that the subject cannot be detected and passed by the lens drive from a state where the focus cannot be detected.

  If the absolute value of the change amount of the focus evaluation value is less than the predetermined threshold 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 is calculated. If there is no focus detection area for which the defocus amount is calculated, the process proceeds to S18, the lens is driven to a predetermined fixed point, and then the process proceeds to S19, where the in-focus display is performed on the display 126 and the AF process is terminated. To do.

  This is a case where there is no focus detection area where the defocus amount is calculated, and there is no focus detection area where the focus evaluation value changes before and after lens driving. In such a case, since there is no information indicating the presence of the subject, focusing is impossible and the AF process is terminated.

  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 to correct the detected defocus amount (S20 to S23). The focus lens 104 is driven to the focal position. Thereafter, in-focus display is performed on the display 126 in S25, and the AF processing is terminated.

(Calculation method of vertical / horizontal BP correction value)
Next, a method for calculating the vertical / horizontal BP correction value (BP1) performed in S20 of FIG. 1 will be described with reference to FIGS.

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

  In S100, vertical / 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 the vertical position (second direction) of the focus position in the horizontal direction (first direction). Difference information.

  FIG. 9 shows an example of vertical / 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 design focus detection correction values are equal for the focus detection regions that are symmetrical with respect to the optical axis of the imaging optical system. Therefore, it is only necessary to store two focus detection correction value tables for the three focus detection regions. If the correction value does not change greatly depending on the position of the focus detection area, it may be stored as a common value.

  That is, a common table value is used for the correction value for the first focus adjustment position and the correction value for the second focus adjustment position.

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

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

  In S100, the zoom position and the correction value corresponding to the focus position corresponding to the focus detection result to be corrected are acquired.

  Next, in S101, it is determined whether a reliable focus detection result is obtained in either the horizontal direction or 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, reliable focus detection results in both the horizontal and vertical directions are obtained in the case of the contrast detection method. Therefore, in the following description regarding the vertical / horizontal BP correction value, the description will be made assuming the contrast detection method, but the same processing is performed when the phase difference detection type focus detection is possible in both the horizontal direction and the vertical direction. Just do it. If it is determined in S101 that the reliability of the focus detection result in both the horizontal direction and the vertical direction is equal to or greater than a predetermined value, the process proceeds to S102.

  In S102, it is determined whether or not the difference between the focus detection result in the horizontal direction and the focus detection result in the vertical direction is appropriate. This is a process performed to deal with the perspective conflict problem that occurs when an object at a distance close to an object at a distance is included in the focus detection area.

  For example, consider a case where there is a subject with contrast in the horizontal direction at a long distance and a subject with contrast in the vertical direction at a short distance.

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

  Thus, when the difference between the horizontal focus detection result (first focus adjustment position) and the vertical focus detection result (second focus adjustment position) is significantly different from the determination value C. Judge that they are competing with each other.

  Then, the horizontal direction or the vertical direction is selected as the direction indicating the closer focus detection result, and the process proceeds to S104.

  The determination value C may be uniquely determined to determine a value that cannot be a correction value for the above-described reason, or may be set using the correction information obtained in S100.

  If it is determined in S102 that the difference between the horizontal focus detection result (first focus adjustment position) and the vertical focus detection result (second focus adjustment position) is appropriate, the process proceeds to S103, where BP1 = The subroutine for calculating vertical and horizontal BP correction values is completed. In this case, focus detection is performed using focus detection results in the horizontal and vertical directions without using correction values.

  In the case of the contrast detection method, the focus detection result is weighted according to the magnitude relationship such as the ratio of the maximum value of the focus evaluation value in the horizontal direction and the vertical direction, and the focus detection result including the horizontal direction and the vertical direction ( Focus adjustment position). Similarly, in the case of the phase difference detection method, the focus detection result may be weighted using the correlation amount used for the correlation calculation.

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

  That is, when the difference between the first focus adjustment position and the second focus adjustment position is larger than the predetermined threshold value, the focus adjustment unit adjusts the focus adjustment on the closest side of the first focus adjustment position and the second focus adjustment position. The focus of the recording signal is adjusted using the position.

  Next, in S105, it is determined whether or not weighting in the horizontal direction and the vertical direction is possible. When performing the determination in S105, a reliable focus detection result in both the horizontal direction and the vertical direction has not been obtained from the viewpoint of the reliability of the focus evaluation value and the perspective conflict, but in S105, A determination for calculating the vertical / horizontal BP correction value 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 indicating changes in the horizontal focus evaluation value and the vertical focus evaluation value detected by the contrast detection method. LP1, LP2, and LP3 each indicate a focus lens position.

  FIG. 10 shows a case where LP3 is obtained as a reliable focus detection result from the focus evaluation value E_h in the horizontal direction, and LP1 is obtained as a reliable focus detection result from the focus evaluation value E_v in the vertical direction. Yes. Since the focus lens positions of LP1 and LP3 are greatly different, that is, in a perspective conflict state, the focus detection result LP3 in the horizontal direction, which is the focus detection result on the closer side, is selected in S104.

  Under such circumstances, 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 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. 8, is acquired as the vertical / horizontal BP correction information.

Using the horizontal focus evaluation value E_hp at the position LP3 in FIG. 10 and the vertical focus evaluation value E_vp at LP1, the vertical / horizontal BP correction value BP1 is calculated by the following equation.
(Formula 2)
BP1 = BP1_B × E_vp / (E_vp + E_hp) × (+1)

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

  As is obvious from Equations 2 and 3, information indicating that the focus evaluation value is large is determined to be that there is a lot of contrast information included in the subject, and a vertical and horizontal BP correction value (BP1) is calculated. As described above, the vertical / horizontal BP correction information is (difference in focus adjustment position of subject having contrast information only in the vertical direction) − (focus adjustment 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. When the process of S106 is completed, the vertical / horizontal BP correction value calculation subroutine ends.

  On the other hand, if there is no vertical focus detection result in the vicinity of the selected horizontal focus detection result LP1 in S105, the process proceeds to S103. In S103, since it is determined that the contrast information included in the subject is generally only in one direction, BP1 = 0 is set. When the process of S107 is completed, the vertical / horizontal BP correction value calculation subroutine ends.

  Thus, since the correction value is calculated according to the contrast information for each direction of the subject, it is possible to calculate the correction value with high accuracy according to the pattern of the subject.

  In FIG. 10, the case where there is a perspective conflict has been described, but the maximum value is detected one by one in the horizontal direction and the vertical direction, and the correction value is similarly set even when the focus detection result of one side is not reliable. 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 correction value calculation method is not limited to this. For example, in the case where focus detection can be performed only in the horizontal direction, as in the focus detection of the phase difference detection method of the first embodiment, it is assumed that the amount of contrast information in the horizontal and vertical directions of the subject is the same. 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-described Expressions 2 and 3. By performing such processing, the correction accuracy is reduced, but the load of 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. As a weighting coefficient when calculating the correction value, a change amount of the correlation amount calculated by the correlation calculation of the phase difference detection method may be used.

  This utilizes the fact that the amount of change in the correlation amount increases as the contrast information of the subject increases, such as when the contrast of the subject is large or the number of edges having the contrast is large. As long as the evaluation value can obtain the same relationship, various evaluation values may be used without being limited to the change amount of the correlation amount.

  In this way, by correcting the focus detection result using the vertical and horizontal BP correction values, high-precision 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.

  Also, when the focus detection results for each direction differ greatly, the influence of perspective conflict can be reduced by not calculating the vertical and horizontal BP correction values using these focus detection results. Furthermore, even when perspective conflict is assumed, more accurate correction can be performed by weighting the correction value according to the magnitude of the focus evaluation value for each direction.

(Calculation method of color BP correction value)
Next, a method for 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 a flow of calculating the color BP correction value (BP2) indicating the details of the processing performed in S21 of FIG.

  In 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), blue) with respect to the in-focus position detected using the green (G) signal. (B)) is in-focus position difference information detected using the signal. FIG. 12 shows an example of color BP correction information stored in the lens memory 118.

  FIG. 12 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 design focus detection correction values are equal for the focus detection regions that are symmetrical with respect to the optical axis of the imaging optical system. Therefore, it is only necessary to store two focus detection correction value tables for the three focus detection regions. If the correction value does not change greatly depending on the position of the focus detection area, it may be stored as a common value.

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

  The focus detection correction values BP211 to BP288 in FIG. 12A are outputs of pixels having a red (R) color filter with respect to a focus detection result detected using an output signal of a pixel having a green (G) color filter. This is a difference between focus detection results detected using a signal. The focus detection correction values BP311 to BP388 in FIG. 12B are output of the pixel having the blue (B) color filter with respect to the focus detection result detected using the output signal of the pixel having the green (G) color filter. This is a difference between focus detection results detected using a signal.

  In the first embodiment, green (G), red (R), and blue (B) mean signals obtained for each of the color filters applied to the pixels on the image sensor described above. Is not limited to this. For example, a spectral detection unit that separately detects spectral information of a subject is provided, and the wavelengths or wavelength ranges of green (G), red (R), and blue (B) are set according to the output of the spectral detection unit. Also good.

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

  In S200, the zoom position and the correction value corresponding to the focus position corresponding to the focus detection result to be corrected are acquired.

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

  K_R and K_B are coefficients for the correction information of each color. For a subject that contains many red colors, K_R takes a large value and is blue for a value that correlates with the magnitude relationship of red (R) and blue (B) information with respect to green (G) information contained in the subject. For a subject that contains many colors, K_B takes a large value.

  For a subject containing a lot of green, both K_R and K_B take small values. K_R and K_B may be set in advance based on spectral information representative of the subject. Alternatively, when the spectral information of the subject can be acquired using 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 best focus correction value used for focus detection is stored for each focus detection area as shown in FIGS. 9 and 12, but the correction value storage method is not limited to this. Absent. For example, coordinates are set with the intersection of the optical axis of the imaging device and the imaging optical system as the origin and the horizontal and vertical directions of the imaging device as the X axis and the Y axis, and the correction value at the center coordinate of the focus detection area is set as X You may obtain | require with the function of Y. In this case, the amount of information to be stored as the focus detection correction value can be reduced.

  In the first embodiment, the correction value used for focus detection calculated using the vertical / horizontal BP correction information and the color BP correction information is calculated based 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 correction value calculation method is not limited to this. Similar to a method for calculating a spatial frequency BP correction value described later, a correction value that matches the spatial frequency component of the subject may be calculated using vertical / horizontal BP correction information and color BP correction information for each spatial frequency.

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

  FIG. 13 is a subroutine showing a flow of calculating the spatial frequency BP correction value (BP3) indicating 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 indicates the position of the focus lens 104, and the vertical axis indicates the intensity of the MTF. The four types of curves depicted in FIG. 14 are MTF curves for each spatial frequency, and show a case where the spatial frequency changes from lower to higher 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. LP4, LP5, LP5, and LP6 indicate the positions of the focus lens 104 corresponding to the maximum values of the defocus MTF curves.

  In FIG. 14, although shown by a continuous curve, the spatial frequency BP correction information stored in the lens memory 118 is obtained by discretely sampling the curve of FIG. In the first embodiment, MTF data is sampled for 10 focus lens positions with respect to one MTF curve. For example, for MTF1, MTF1 (n) (1 ≦ n ≦ 10). ) 10 data are stored.

  Spatial frequency BP correction information is stored for each position of the focus detection area in the same manner as vertical and horizontal BP correction information and color BP correction information. Further, the zoom position and the focus position of the photographing optical system are divided into eight zones, and spatial frequency BP correction information is provided for each of the divided zones. Similar to the vertical / horizontal BP correction information and color BP correction information described above, the number of focus detection areas, the number of divisions of the zoom position, and the focus position may be freely set. As the number of settings increases, the amount of memory necessary for data storage increases, but high-precision 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 zoom position and the correction value corresponding to the focus position corresponding to the focus detection result to be corrected are acquired.

  In step S301, a signal band used for focus detection (AF) in 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 influence of the subject, the photographing optical system, the sampling of the image sensor, and the digital filter used for evaluation. A method for 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 S302, the photographed image evaluation band is calculated in consideration of the influence of the subject, the photographing optical system, the sampling of the image sensor, and the evaluation band of the viewer of the photographed image.

  The calculation of the AF evaluation band (second evaluation band) and the captured image evaluation band (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, with the horizontal axis indicating the spatial frequency and the vertical axis indicating the intensity.

  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 the Nyquist frequency determined by the pixel pitch of the image sensor. F1 to F4 and Nq are similarly shown in FIGS. 15B to 15F described later.

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

  In the first embodiment, the spatial frequency characteristics of the subject stored in advance are used. However, the spatial frequency characteristics of the subject to be used may be changed according to the subject for which focus detection is performed. By performing processing such as FFT processing on the captured image signal, spatial frequency information of the subject can be obtained.

  Such processing increases the amount of calculation processing, but a correction value corresponding to the subject for which focus detection is performed can be calculated, so that highly accurate focus adjustment can be performed. Further, several types of spatial frequency characteristics stored in advance may be properly used depending on the magnitude 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 this time may be a spatial frequency characteristic for each defocus state or only a spatial frequency characteristic at the time of focusing. Since the spatial frequency BP correction value is calculated in the vicinity of the in-focus state, the correction can be performed with high accuracy by using the spatial frequency characteristic at the time of in-focus state.

  However, although the calculation load increases, focus adjustment can be performed with higher accuracy by using the spatial frequency characteristics for each defocus state. Which defocus state spatial frequency characteristic is used may be selected using a defocus amount obtained by focus detection by the phase difference detection method.

  In FIG. 15B, the spatial frequency characteristic (O) of the photographing optical system is drawn with a curve, but has discrete 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. 15 (c), the spatial frequency characteristic (L) of the optical low-pass filter 121 is drawn as a curve, but has discrete values corresponding to the spatial frequencies F1, F2, F3, and F4. L (n) (1 ≦ n ≦ 4).

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

  On the other hand, in the second reading mode, that is, the thinning-out reading mode, the spatial frequency characteristics change when generating a signal. As described above, a signal is added at the time of decimation in the X direction to improve the S / N, so that a low-pass effect due to the addition occurs. M2 in FIG. 15D indicates the spatial frequency characteristics during signal generation in the second readout mode. Here, the influence of thinning is not taken into account, and the low-pass effect by addition is shown.

  In FIG. 15 (d), the spatial frequency characteristics (M1, M2) due to signal generation are drawn as curves, but discretely have values corresponding to the spatial frequencies F1, F2, F3, F4. M1 (n) and M2 (n) (1 ≦ n ≦ 4) are represented.

  FIG. 15E shows the spatial frequency characteristic (D1) indicating 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 at the time of appreciating a photographed image is affected by individual differences among viewers, viewing environments such as image size, viewing distance, and brightness. In the first embodiment, the sensitivity for each spatial frequency during 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 reading mode, aliasing noise of the frequency component of the signal occurs due to the influence of thinning. In consideration of the influence, D2 shows the spatial frequency characteristics of the digital filter.

  In FIG. 15 (e), the spatial frequency characteristic (D1) at the time of viewing and the spatial frequency characteristic (D2) of the digital filter are drawn with curves, but discretely correspond to the spatial frequencies F1, F2, F3, and F4. It is expressed as 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 equations.
(Formula 5)
W1 (n) = I (n) × O (n) × L (n) × M1 (n) × D1 (n) (1 ≦ n ≦ 4)
(Formula 6)
W2 (n) = I (n) × O (n) × L (n) × M2 (n) × D2 (n) (1 ≦ n ≦ 4)

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

  The information stored in the camera may store W1 and W2 calculated in advance. As described above, by calculating each correction, the correction value can be calculated flexibly when the digital filter or the like used for AF evaluation is changed. On the other hand, if they are stored in advance, calculations such as Equation 5 and Equation 6 and the storage capacity of various data can be omitted.

  In addition, since it is not necessary to finish all calculations in advance, for example, only the spatial frequency characteristics of the photographing optical system and the subject are calculated in advance and stored in the camera, thereby reducing the data storage capacity and the calculation amount. May be reduced.

  In FIG. 15, the four spatial frequencies (F1 to F4) are used to simplify the description. However, as the number of spatial frequencies having data increases, the spatial frequency characteristics of the captured image and the evaluation band of the AF are increased. Can be accurately reproduced, and a highly accurate correction value can be calculated.

  On the other hand, the amount of calculation can be reduced 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 photographed image and the AF evaluation band, and perform subsequent calculations.

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

In S303, a spatial frequency BP correction value (BP3) is calculated. In 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 formula using the defocus MTF information obtained in S300 and the evaluation bands W1 and W2 obtained in S301 and S301.
(Formula 7)
C1 (n) = MTF1 (n) × W1 (1) + MTF2 (n) × W1 (2) + MTF3 (n) × W1 (3) + MTF4 (n) × W1 (4)
(Formula 8)
C2 (n) = MTF1 (n) × W2 (1) + MTF2 (n) × W2 (2) + MTF3 (n) × W2 (3) + MTF4 (n) × 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 captured image or AF evaluation band calculated in S301 and S302, and the defocus of the captured image is performed. C1 as the MTF and C2 as the AF defocus MTF 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 imaging 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 imaging 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.
(Formula 9)
BP3 = P_AF-P_img

  According to Expression 9, it is possible to correct a correction value for correcting an error that may occur between the focus position of the captured image and the focus position detected by the AF. As described above, the in-focus position of the photographed image is 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 varies depending on the spatial frequency characteristics indicating sensitivity.

  In addition, it varies depending on image processing 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 going back to the process of generating the captured image. For example, the in-focus position of the photographed image is changed by the recording size when the photographed image is recorded, the super-resolution processing performed in the image processing, the sharpness, or the like.

  In addition, when the captured image is recorded, it is possible to know in advance how much the image size and enlargement ratio can be viewed, and the viewing distance when viewing the image, which affects the evaluation band of the viewer. As the image size is increased and the viewing distance is shortened, the viewer's evaluation band is set to have a characteristic that emphasizes the high frequency component. As a result, the in-focus position of the captured image is also changed.

  On the other hand, the focus position detected by the AF is similarly the spatial frequency characteristics of the subject, the spatial frequency characteristics of the photographing optical system, the spatial frequency characteristics of the optical low-pass filter, the spatial frequency characteristics at the time of signal generation, and the digital filter used for AF evaluation. It varies depending on 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 characteristics going back to the process of generating the signal used for the AF.

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

  Further, since the image pickup apparatus described in the first embodiment is an interchangeable lens type single-lens reflex camera, the lens unit 100 can be replaced. When the 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 in-focus position of the photographed image and the in-focus position detected by the 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 characteristics of the photographing optical system to the camera body 120. The method of using the information is as described above.

  Similarly, when the camera body 120 is replaced, the pixel pitch, the characteristics of the optical low-pass filter, and the like may change. As described above, even in such a case, a correction value that matches the characteristics of the camera body 120 is calculated, so that 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 correction value may be calculated by the lens MPU 117. In this case, the camera MPU may transmit various information described with reference to FIG. 15 to the lens MPU, and the correction value may be calculated using the defocus MTF information or the like in the lens MPU. . In that case, the lens MPU may correct the focus position transmitted from the camera MPU 125 and drive the lens in S24 of FIG.

  In this embodiment, the AF correction value 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 data storage capacity and calculation load.

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

  However, since the defocus MTF information has a large amount of data and a large storage capacity and calculation load, in the second embodiment, the spatial frequency BP correction value is calculated using the maximum value information of the defocus MTF. . Thereby, the data capacity in the lens memory 118 can be reduced, the communication capacity between the lens and the camera can be reduced, and the calculation load performed by the camera MPU 125 can be reduced.

  In addition, the block diagram (FIG. 2) of the imaging device in the first embodiment, the explanatory diagrams of the respective focus detection methods (FIGS. 3 to 6), the explanatory diagram of the focus detection area (FIG. 7), and the flowchart of the focus detection process (FIG. With respect to FIG. 1), the second embodiment also has the same configuration and will not be described.

  The method for calculating various BP correction values (FIGS. 8 to 12) in the first embodiment is the same as that in the second embodiment, and the same operation is performed.

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

  A subroutine showing a flow of 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 spatial frequency BP correction information stored in the lens memory 118 of FIG. 14 in which the processing content performed in the second embodiment is different from that of the first embodiment will be described with reference to FIG.

  FIG. 17 shows the position of the focus lens 104 indicating the maximum value of the defocus MTF for each spatial frequency, which is a characteristic of the photographing optical system. Lens positions LP1, LP2, LP3, and 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 in FIG. 17 corresponding thereto. In the second embodiment, the lens memory 118 stores four 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, correction values corresponding to the zoom position and the focus position corresponding to the focus detection result to be corrected are acquired in S300.

  Next, in S301 and S302, processing similar to that in the first embodiment is performed.

Next, in S303, a 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 the defocus MTF information obtained in S300 and in S301 and S301. Using the evaluation bands W1 and W2, the following formula is used.
(Formula 10)
P_img = MTF_P (1) × W1 (1) + MTF_P (2) × W1 (2) + MTF_P (3) × W1 (3) + MTF_P (4) × W1 (4)
(Formula 11)
P_AF = MTF_P (1) × W2 (1) + MTF_P (2) × W2 (2) + MTF_P (3) × W2 (3) + MTF_P (4) × W2 (4)

  In Expressions 10 and 11, the photographic image calculated in S301 and S302 and the AF evaluation band are weighted on 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.
(Formula 9)
BP3 = P_AF-P_img

  By performing the processing as described above, the spatial frequency BP correction value can be calculated. In the first embodiment, since the defocus MTF information is used, the correction value can be calculated with higher accuracy. On the other hand, by configuring as in 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 performed by 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 calculation method of the spatial frequency BP correction value is different. In the first embodiment, the defocus MTF information is used as a value representing the characteristic for each spatial frequency of the photographing optical system, and the correction value is calculated every time focus detection is performed.

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

  In addition, the block diagram (FIG. 2) of the imaging device in the first embodiment, the explanatory diagrams of the respective focus detection methods (FIGS. 3 to 6), the explanatory diagram of the focus detection area (FIG. 7), and the flowchart of the focus detection process (FIG. With respect to FIG. 1), the third embodiment also has the same configuration, so that the description thereof is omitted.

  The method for calculating various BP correction values (FIGS. 8 to 12) in the first embodiment is the same as that in the third embodiment, and the same operation is performed.

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

  The difference between the processing contents performed in the third embodiment and 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 portions that perform the same processing as in FIG. 13, and description thereof is omitted.

  FIG. 18 is a subroutine showing a 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 to calculate a correction value. 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, the smaller the correction amount.

  Therefore, in the third embodiment, when it is known in advance that the difference between the two evaluation bands is small, the calculation of the correction value is omitted.

  Specifically, in the spatial frequency characteristics by signal generation, when the signal used for AF is also a signal read out in the first readout mode, the evaluation band of the captured image is equal to the AF evaluation band.

  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 when processing the AF evaluation signal, the spatial frequency characteristic during viewing and the digital filter Spatial frequency characteristics are equal. Such a situation occurs when an image to be displayed on the display 126 is enlarged and displayed.

  Similarly, when the captured image is generated with a signal read in the second readout mode, it is assumed that the evaluation band of the captured image is equal to the AF evaluation band. Such a situation occurs when the recording image size of the captured image is set small.

  In S3000, in such a case, it is determined that there is no need to calculate a correction value, 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 terminated.

  On the other hand, the subsequent processing performed when it is determined in S3000 that the correction value needs to be calculated is the same as that in the first embodiment, and thus the description thereof is omitted.

  With this configuration, when it is not necessary to calculate the spatial frequency BP correction value, the processing can be omitted. As a result, it is possible to reduce the amount of data communication and the calculation load.

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

DESCRIPTION OF SYMBOLS 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 surface phase difference focus detection unit 130 TVAF focus detection unit

Claims (6)

First focus adjustment using an imaging device, recording means for recording a recording signal output from the imaging device, and output signals output from a plurality of pixels arranged in a first direction of the imaging device A second focus adjustment position is calculated using first calculation means for calculating a position and output signals output from a plurality of pixels arranged in a second direction different from the first direction of the image sensor. Third focus adjustment of the recording signal is performed by correcting the focus adjustment position of either the first focus adjustment position or the second focus adjustment position using the second calculation means and the correction value. Third calculation means for calculating a position, focus adjustment means for performing focus adjustment of the recording signal using the third focus adjustment position, and first focus evaluation corresponding to the first focus adjustment position Value and a second focus corresponding to the second focus position Determining means for determining reliability of the evaluation value, an imaging device having,
An imaging apparatus, wherein the correction value is changed according to a determination result of the determination unit.   When it is determined by the determination means that the reliability of the first focus adjustment position and the second focus adjustment position is smaller than a predetermined value, the first focus adjustment position and the second focus adjustment position are corrected using a correction value. One of the focus adjustment positions is corrected, and the determination means determines that the reliability of the first focus adjustment position and the second focus adjustment position is greater than or equal to the predetermined value. In this case, the third focus adjustment position of the recording signal is not calculated by correcting one of the first focus adjustment position and the second focus adjustment position using a correction value. Item 2. The imaging device according to Item 1.   When the determination means determines that the reliability of the first focus adjustment position is equal to or higher than a predetermined value and the reliability of the second focus adjustment position is lower than the predetermined value, the first focus adjustment position is determined. The imaging apparatus according to claim 1, wherein a third focus adjustment position of the recording signal is calculated by performing correction using the correction value.   4. The imaging apparatus according to claim 1, wherein a common table value is used for the correction value for the first focus adjustment position and the correction value for the second focus adjustment position. 5.   When the difference between the first focus adjustment position and the second focus adjustment position is greater than a predetermined threshold, the focus adjustment unit is located on the closest side of the first focus adjustment position and the second focus adjustment position. The imaging apparatus according to claim 1, wherein focus adjustment of the recording signal is performed using the focus adjustment position. A first focus adjustment position is calculated using a recording step of recording a recording signal output from the image sensor and output signals output from a plurality of pixels arranged in the first direction of the image sensor. And a second calculation step of calculating a second focus adjustment position using output signals output from a plurality of pixels arranged in a second direction different from the first direction of the image sensor. And calculating a third focus adjustment position of the recording signal by correcting one of the first focus adjustment position and the second focus adjustment position using the correction value. 3 calculation step, focus adjusting means for adjusting the focus of the recording signal using the third focus adjustment position, a first focus evaluation value corresponding to the first focus adjustment position, and the second focus adjustment value. Of the second focus evaluation value corresponding to the focus adjustment position of A determination step, an imaging method with,
An imaging method, wherein the correction value is changed according to a determination result of the determination step.

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