JP2014123050A - Focus detection device, focus detection method, program and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable appropriate setting of a phase difference focus evaluation area even if a subject is displaced in an imaging picture as a focus lens is moved during phase difference focus control.SOLUTION: A focus detection device includes: driving means for an imaging optical system including a focus lens for forming an optical image of a subject; and obtaining means for obtaining an imaging signal obtained by photo-electrically converting the optical image by imaging means. The focus detection device sets a focus detection area in an imaging picture based on the imaging signal, performs focus adjustment by driving the focus lens by the driving means in accordance with at least a phase difference detection method, determines the amount of driving of the focus lens on the basis of an optical image corresponding to an imaging signal corresponding to the set focus detection area, and controls focus detection means in accordance with the determined amount of driving. If the position of the subject in the imaging picture is displaced due to the driving of the focus lens in accordance with the phase difference detection method, the position of the focus detection area is changed in accordance with the amount of displacement of the subject.

Description

  The present invention relates to a focus detection apparatus, and more particularly to a focus detection apparatus that performs autofocusing using a phase difference detection method and an imaging apparatus having the focus detection apparatus.

  As an AF method of an imaging apparatus such as a digital still camera or a video camera, there are an AF based on a phase difference detection method (phase difference AF), an AF based on a contrast detection method (contrast AF), and a hybrid AF combining these. In some phase difference AFs, focus detection pixels are arranged on an image sensor that receives a light beam that has passed through an imaging optical system, and AF (imaging surface phase difference AF) is performed using a phase difference detection method. In the hybrid AF, the phase difference AF is performed to move the focus lens to a position near the focus, and the focus lens is moved to the focus position by contrast AF. In such a hybrid AF, there is a type in which a region for generating a contrast evaluation value in contrast AF (hereinafter referred to as a contrast evaluation region) is set according to the result of phase difference AF. In particular, the hybrid AF of the imaging surface phase difference AF and contrast AF performs focus detection from the data obtained from the imaging device, so it is highly accurate from the viewpoint of data acquisition simultaneity, evaluation range coincidence, etc. There is a possibility of realizing high-speed hybrid AF.

  In the hybrid AF disclosed in Patent Document 1, the phase difference AF is performed by selecting any one of a plurality of focus detection areas capable of performing the phase difference AF, and the two or more selected focus detection areas are selected. The focus lens is driven to a position near the in-focus position. Then, the contrast evaluation area is set so as to include the focus detection area corresponding to the in-focus vicinity position.

  Patent Document 2 discloses the result of phase difference AF in the focus detection area when the focus detection area capable of performing phase difference AF and the contrast evaluation area overlap or are close to each other. A hybrid AF that performs contrast AF using the same is disclosed.

In addition, there is a method for setting a contrast evaluation region in which the influence of distortion of an optical image due to distortion of an imaging optical system is eliminated.
Patent Document 3 discloses contrast AF that sets a contrast evaluation area in image data before distortion correction in accordance with a focus frame set in image data that has been subjected to distortion correction.

JP 2006-350188 A JP 2007-179029 A JP 2008-118387 A

  However, just setting the contrast evaluation area so as to include the focus detection area where the phase difference AF is performed as in the hybrid AF disclosed in Patent Documents 1 and 2 causes the following problems. That is, by moving the focus lens, the image magnification in the shooting screen changes. For this reason, the subject to be focused included in the focus detection area before the phase difference AF is displaced in the photographing screen due to a change in the image magnification due to the movement of the focus lens, and is included in the focus detection area before the phase difference AF. It may not be possible. In this case, even if the contrast evaluation area is set so as to include the focus detection area before the phase difference AF, there is a possibility that the subject to be focused on is not included in the contrast evaluation area. This is a problem not only in the configuration of the hybrid AF but also in the case where focusing is performed while repeatedly performing focus detection and focus lens driving only with the phase difference AF.

  Further, when the processing for eliminating the influence of the distortion of the imaging optical system in the contrast AF disclosed in Patent Document 3 by changing the contrast evaluation area is applied to the imaging plane phase difference AF, the following problems occur. That is, the phase difference AF detects the shift amount of the optical image formed by the light beam that has passed through different pupil regions of the imaging optical system. On the other hand, distortion of the imaging optical system is called pincushion distortion and barrel distortion, and forms an optical image having an inclination with respect to the horizontal and vertical directions of the subject. Therefore, in the imaging plane phase difference AF, there is a possibility that the direction in which the optical image is shifted and the evaluation area excluding the influence of distortion become non-parallel, which may cause deterioration in focus detection accuracy.

  The present invention provides high-precision focus detection by appropriately setting a focus detection area even when a subject is displaced in a shooting screen due to a change in image magnification caused by movement of a focus lens due to phase difference AF or distortion of an imaging optical system. It is an object of the present invention to provide a focus detection device that enables the above.

  According to the present invention, focus detection includes an imaging optical system driving unit including a focus lens for forming an optical image of a subject and an acquisition unit that acquires an imaging signal obtained by photoelectrically converting the optical image by the imaging unit. The apparatus includes: a setting unit that sets a focus detection area on a shooting screen based on an imaging signal; a focus detection unit that performs focus adjustment by driving a focus lens according to at least a phase difference detection method; and a focus detection area that is set The control unit includes a control unit that determines a driving amount of the focus lens based on an optical image corresponding to a corresponding imaging signal, and controls the focus detection unit according to the determined driving amount. The control unit controls the setting unit and detects the phase difference. If the position of the subject in the shooting screen is displaced by driving the focus lens according to the method, the focus detection area To change the location.

  According to the present invention, even if the subject is displaced in the shooting screen due to the movement of the focus lens (change in image magnification) or distortion by phase difference focus control, the focus detection area for the subsequent focus control is set as the subject after the displacement. Can be set to include. Therefore, more accurate AF control is possible.

1 is a block diagram showing a configuration of an imaging apparatus to which a focus detection apparatus according to a first embodiment of the present invention is applied. The top view and sectional drawing of the pixel for an imaging which the image pick-up element used with the imaging device of FIG. 1 has. FIG. 3 is a plan view and a cross-sectional view of focus detection pixels included in the image sensor of FIG. 2. The figure for demonstrating the pupil division by the pixel for focus detection of FIG. FIG. 4 is a diagram illustrating a flowchart of an AF operation of the imaging apparatus according to the first embodiment of the present invention. FIG. 3 is a diagram illustrating a phase difference detection region before and after distortion correction in an AF operation of the imaging apparatus to which the focus detection apparatus according to the first embodiment of the present invention is applied. FIG. 6 is a diagram illustrating a setting example of a phase difference detection area after driving a focus lens in an AF operation of the imaging apparatus to which the focus detection apparatus according to the first embodiment of the present invention is applied. FIG. 6 is a diagram illustrating a setting example of a contrast evaluation region for a phase difference detection region in an AF operation of the imaging apparatus to which the focus detection apparatus according to the first embodiment of the present invention is applied. The figure which shows the flowchart of AF operation | movement in the imaging device to which the focus detection apparatus which concerns on 2nd Example of this invention is applied. FIG. 10 is a diagram illustrating a setting example of a contrast evaluation area for a phase difference detection area in an AF operation of an imaging apparatus to which a focus detection apparatus according to a second embodiment of the present invention is applied.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a digital camera body 138 and an interchangeable lens 137 that is detachably attached to the digital camera body as an example of an imaging apparatus having a focus detection apparatus according to the first embodiment of the present invention. 1 shows a configuration of an imaging system to be used.

  First, the configuration of the interchangeable lens 137 will be described. Reference numeral 101 denotes a first lens group which is disposed closest to the subject in the photographing optical system (imaging optical system) and is movable in the optical axis direction. Reference numeral 102 denotes an aperture, which adjusts the amount of light by changing the aperture diameter (with the aperture value being variable). Reference numeral 103 denotes a second lens group. The diaphragm 102 moves integrally with the second lens group 103 in the optical axis direction. Zooming is performed by moving the first lens group 101 and the second lens group 102 in the optical axis direction.

  Reference numeral 105 denotes a third lens group serving as a focus lens, which moves in the optical axis direction to adjust the focus. Reference numeral 111 denotes a zoom actuator that rotates a cam cylinder (not shown) around the optical axis, thereby moving the first lens group 101 and the second lens group 102 in the optical axis direction to perform zooming.

  A diaphragm actuator 112 is driven to change the aperture diameter of the diaphragm 102 to adjust the light amount. Reference numeral 114 denotes a focus actuator, which performs focusing by moving the third lens group 105 in the optical axis direction.

  Reference numeral 136 denotes a camera communication circuit that transmits information about the lens to the camera and receives information about the camera. The information regarding the lens includes a zoom state, a diaphragm state, a focus state, lens frame information, and the like. The camera communication circuit 136 transmits these pieces of information to the lens communication circuit 135 provided on the camera side.

  Next, the configuration of the camera body 138 will be described. Reference numeral 106 denotes an optical low-pass filter, which is an optical element for reducing false colors and moire in a captured image. Reference numeral 107 denotes an image sensor composed of a CMOS sensor and its peripheral circuits. The image sensor 107 has m pixels in the horizontal direction and n pixels (photoelectric conversion elements) in the vertical direction, and a Bayer array primary color mosaic filter is arranged for these pixels to form a two-dimensional single-plate color. A sensor is configured.

  Reference numeral 139 denotes a shutter unit that controls exposure time during still image shooting. Reference numeral 140 denotes a shutter actuator that operates the shutter 139.

  An electronic flash 115 has a xenon tube or LED as a light source. Reference numeral 116 denotes an AF auxiliary light emitting unit that projects an image of a mask having a predetermined opening pattern onto a subject through a light projection lens. Thereby, the AF performance for a dark subject or a low-contrast subject can be improved.

  Reference numeral 121 denotes a camera CPU as a controller, which controls various operations of the camera. The camera CPU 121 includes a calculation unit, a ROM, a RAM, an A / D converter, a D / A converter, a communication interface circuit, and the like. The camera CPU 121 controls the operation of each part in the camera according to a computer program stored in the ROM, and a series of shooting operations such as AF, imaging, image processing, and recording including detection of the focus state of the imaging optical system (focus detection). Is executed.

  Reference numeral 122 denotes an electronic flash control circuit that controls the lighting of the electronic flash 115. Reference numeral 123 denotes an auxiliary light driving circuit that performs lighting control of the AF auxiliary light emitting unit 116. An image sensor driving circuit 124 controls the operation of the image sensor 107, and A / D converts a pixel signal (image signal) output from the image sensor 107 and transmits it to the camera CPU 121. An image processing circuit 125 generates an image signal by performing image processing such as γ conversion and color interpolation on the A / D converted imaging signal, and further performs processing such as JPEG compression on the image signal. .

  A focus driving circuit 126 drives the focus actuator 114 based on the focus detection result, and moves the third lens group 105 in the optical axis direction to perform focus adjustment. Reference numeral 128 denotes an aperture driving circuit that drives the aperture actuator 112 to operate the aperture 102. Reference numeral 129 denotes a zoom drive circuit that drives the zoom actuator 111 in accordance with the zoom operation of the photographer.

  Reference numeral 135 denotes the lens communication circuit described above, which communicates with the camera communication circuit 136 in the interchangeable lens 137. A shutter driving circuit 145 drives the shutter actuator 140.

  Reference numeral 131 denotes a display such as an LCD, which displays information related to the shooting mode of the camera, a preview image before shooting, a confirmation image after shooting, a focus state at the time of focus detection, and the like. When displaying a preview image before photographing, the display frame of the focus detection area is displayed so as to overlap the corrected image obtained by performing aberration correction of the photographing optical system. An operation switch group 132 includes a power switch, a release (shooting trigger) switch, a zoom operation switch, a shooting mode selection switch, and the like. Reference numeral 133 denotes a detachable flash memory that records a photographed image. Reference numeral 144 denotes an in-camera memory in which various data necessary for processing and calculation performed by the camera CPU 121 are stored.

  A camera CPU (control unit) 121 performs autofocus (phase difference focus control) by a phase difference detection method using image signals acquired from a plurality of focus detection pixels provided in the image sensor 107. Furthermore, autofocus (contrast focus control) is also performed by a contrast detection method using outputs from a plurality of imaging pixels. The autofocus (AF) based on the phase difference detection method using the image sensor 107 is hereinafter referred to as an imaging surface phase difference AF, and the AF based on the contrast detection method is hereinafter referred to as contrast AF.

  In the imaging plane phase difference AF, the camera CPU 121 performs a correlation operation on a pair of imaging signals generated by outputs from a plurality of focus detection pixels, and calculates a phase difference indicating their relative positional deviation. Then, the camera CPU 121 calculates (detects) the focus state (defocus amount) of the interchangeable lens 1 (imaging optical system) based on the phase difference. Furthermore, the camera CPU 121 calculates a drive amount to a position (near focus position) to move the third lens group 105 in order to obtain a state close to focus based on the defocus amount. The camera CPU 121 controls the focus actuator 114 through the focus drive circuit 126 so as to move the third lens group 105 by the calculated drive amount.

  In contrast AF, the camera CPU 121 controls the focus actuator 114 to move the third lens group 105 and outputs high-frequency components of image signals generated by outputs from a plurality of imaging pixels at a predetermined cycle. Extract and calculate a contrast evaluation value. Then, the camera CPU 121 moves the third lens group 105 to a position (focus position) where the contrast evaluation value is maximized.

  Next, the structure of the imaging pixels and focus detection pixels arranged on the imaging element 107 will be described with reference to FIGS. 2 and 3. In the image sensor 107 of this embodiment, pixels having G (green) spectral sensitivity are arranged at two diagonal positions in four pixels of 2 rows × 2 columns, and R (red) and B (blue) are arranged at the other two locations. A Bayer array in which one pixel having a spectral sensitivity of 1) is arranged. A plurality of focus detection pixels are dispersedly arranged among the plurality of imaging pixels arranged in such a Bayer array.

  FIG. 2 shows a plan view and a cross-sectional view of the imaging pixel. FIG. 2A is a plan view of 2 × 2 imaging pixels located in the center of the image sensor 107. As described above, two G pixels are arranged at two diagonal positions, and an R pixel and a B pixel are arranged at the other two positions.

FIG. 2B shows a cross section AA of FIG. ML is an on-chip microlens arranged in front of each pixel, CF _R denotes a color filter of R (Red). CF _G is a color filter of G (Green). PD schematically shows the photoelectric conversion unit of the CMOS sensor described in FIG. CL is a wiring layer for forming signal lines for transmitting various signals in the CMOS sensor. TL schematically shows the photographing optical system.

  Here, the on-chip microlens ML and the photoelectric conversion unit PD of the imaging pixel are configured to capture the light flux that has passed through the photographing optical system TL as effectively as possible. In other words, the exit pupil EP of the photographing optical system TL and the photoelectric conversion unit PD are arranged in a conjugate relationship by the microlens ML, and the effective area of the photoelectric conversion unit PD is set to be large. FIG. 2B shows the structure of the R pixel, but the G pixel and the B (Blue) pixel also have the same structure. Therefore, the exit pupil EP corresponding to the RGB pixels for imaging has a large diameter, and efficiently takes in the light flux from the subject to improve the S / N of the image signal.

  FIG. 3 shows a plan view and a cross-sectional view of focus detection pixels for dividing the pupil of the photographing optical system in the x direction. FIG. 4A is a plan view of 4 pixels of 2 rows × 2 columns including a focus detection pixel located at the center of the image sensor 107.

When obtaining an imaging signal, the output from the G pixel is the main component of the luminance information. Since human image recognition characteristics are sensitive to luminance information, if G pixels are lost, image quality degradation is likely to be recognized. On the other hand, the R pixel or the B pixel is a pixel that acquires color information. However, since humans are insensitive to color information, pixels that acquire color information are less likely to notice deterioration in image quality even if some loss occurs. Therefore, in this embodiment, two G pixels out of four pixels of 2 rows × 2 columns are left as imaging pixels, and focus detection pixels are arranged at a certain ratio at positions of R pixels and B pixels. . In FIG. 5A, focus detection pixels are denoted by S _HA and S _HB .

In this way, the plurality of focus detection pixels S _HA dispersedly arranged in the image sensor 107 correspond to the first pixel group, and the plurality of focus detection pixels _SHB correspond to the second pixel group. The plurality of focus detection pixels S _HA and S _HB are collectively referred to as a focus detection pixel group.

  Section (B) of FIG. 3 (a) is shown in FIG. The microlens ML and the photoelectric conversion unit PD have the same structure as the imaging pixel shown in FIG.

In this embodiment, signals from the focus detection pixel is not used for image generation, a transparent film (white film) CF _W instead of a color separation color filter is disposed.

Further, in order to perform pupil division in the x direction, the opening of the wiring layer CL is biased in the x direction with respect to the center line of the microlens ML. Specifically, the opening _{OP HA} of focus detection pixels _{S HA} for biased towards the -x direction, the photoelectric conversion unit PD of the focus detection pixels _{S HA} is the photographic optical system TL left (+ x side) The light beam that has passed through the exit pupil region (first pupil region) EP _HA is received. Further, since the biased opening _{OP HB} of the focus detection pixels _{S HB} is in the + x direction, the photoelectric conversion unit PD of the focus detection pixels _{S HB} is an exit pupil area of the right imaging optical system TL (-x side) (Second pupil region) The light beam that has passed through the EP _HB is received.

A subject image acquired by photoelectric conversion by a plurality of focus detection pixels S _HA (first pixel group) regularly arranged in the x direction is defined as an A image (first image). A subject image acquired by a plurality of focus detection pixels S _HB (second pixel group) regularly arranged in the x direction is defined as a B image (second image). Then, by detecting the relative positional deviation amount (phase difference) between the A image and the B image, the defocus amount of the photographing optical system TL with respect to the subject can be calculated based on the phase difference.

  FIG. 4 shows a state of pupil division of the image sensor 107 in the present embodiment. TL is a photographing optical system, 107 is an image sensor shown in FIG. 1, OBJ is a subject, and IMG is a subject image.

As shown in FIG. 2, the imaging pixel receives the light beam that has passed through the entire exit pupil EP of the imaging optical system TL. On the other hand, the focus detection pixel S _HA shown in FIG. 3 among the focus detection pixels receives the light beam that has passed through the pupil region EP _HA on the + x side of the exit pupil EP. Similarly, the focus detection pixel S _HB receives the light beam that has passed through the exit pupil region EP _HB . Then, by distributing the focus detection pixels over the entire area of the image sensor 107, focus detection can be performed over the entire effective image pickup area.

  However, the actual imaging plane phase difference AF is 1 selected by the photographer or by the camera CPU 121 in accordance with a predetermined algorithm from among a plurality of focus detection areas provided in the imaging screen corresponding to the effective imaging area of the imaging device 107. Alternatively, it is performed only in two or more focus detection areas.

Further, focus detection is possible for a subject having a luminance distribution in the x direction of the photographing screen, for example, a line extending in the y direction, by the focus detection pixels S _HA and S _HB , but the luminance distribution is in the y direction. Focus detection is impossible for a subject, for example, a line extending in the x direction. In this embodiment, although not shown, a plurality of focus detection pixels that perform pupil division are also provided in the y direction of the photographing optical system TL so that focus detection can be performed for the latter.

Further, the contrast AF is also performed in an area (contrast evaluation area described later) that is selectively set to a part of the shooting range.
In this embodiment, the configuration in which the focus detection pixels are arranged in the imaging device for photographing is taken as an example, but a configuration in which an imaging device for focus detection is separately provided may be used. In that case, the configuration of the focus detection pixels is not limited to the configuration illustrated in FIG. 3, and may be a pupil division configuration in which a plurality of photoelectric conversion elements are associated with one microlens.

  The flowchart of FIG. 5 shows the flow of the AF operation that the camera CPU 121 executes according to the computer program in this embodiment. When the photographer turns on the power switch of the camera body, the camera CPU 121 confirms the operation of the actuator (such as the shutter actuator 140) and the image sensor 107 in the camera 138 body. Further, the camera CPU 121 initializes the memory contents and the execution program, and reads information necessary for AF, such as a focus detection area selected as a focus detection area where the imaging plane phase difference AF is performed. The focus detection area where the imaging plane phase difference AF is performed is hereinafter referred to as a phase difference detection area.

  In step S <b> 501, the camera CPU 121 communicates with the camera communication circuit 136 in the interchangeable lens 137 via the lens communication circuit 135. The camera CPU 121 confirms the operation of the interchangeable lens 137 through this communication, and initializes the memory contents in the interchangeable lens 137 and the execution program. Further, the camera CPU 121 acquires various characteristic data of the interchangeable lens 137 necessary for AF and photographing, and stores it in the in-camera memory 144. Then, the process proceeds to step S502.

  In step S502, the camera CPU 121 determines whether or not an imaging preparation switch (S1) (not shown) has been turned on by the photographer. If not, the camera CPU 121 maintains the imaging standby state in step S502. On the other hand, when the imaging preparation switch is turned on, the process proceeds to step S503.

  In step S503, the camera CPU 121 drives the shutter actuator 140 to open the shutter 139, and starts the photoelectric conversion operation by the image sensor 107.

  In step S504, the camera CPU 121 sets a phase difference detection area. One or a plurality of phase difference detection areas are set according to the setting of the photographer.

  In the present invention, the region size (number of pixels) and the position of the focus detection pixel are set from the phase difference detection region set by the photographer and the distortion information calculated from the lens information obtained in step S501.

  FIG. 6A shows an example of the phase difference detection area set by the photographer. FIG. 6B shows an example in which the position or size (number of pixels) of the phase difference detection region is changed due to the influence of distortion.

  Areas 101 to 105 in FIG. 6A are phase difference detection areas set by the photographer. The photographer selects the display frame of the detection area superimposed on the image in which various aberrations of the photographing optical system displayed on the display 131 are corrected. In FIG. 6A, Aera 101 to 105 are indicated by rectangles that are long in the horizontal direction, but this indicates a phase difference detection area that can detect the phase difference in the horizontal direction of the subject, and is displayed on the display 131. Does not necessarily match the display frame to be displayed. In this embodiment, since the phase difference of the subject can be detected both in the horizontal direction and in the vertical direction, display centering on the intersection of both phase difference detection areas may be performed. Here, five phase difference detection areas are set, and phase difference detection AF is performed. Areas 101h to 105h in FIG. 6B are the positions on the image sensor 107 calculated from the distortion information calculated from the lens information and the position and size information of the phase difference detection areas Area101 to 105 set by the photographer. This is a phase difference detection area (focus detection is a pixel readout range).

  As shown in FIG. 6B, the phase difference detection area Area103 at the center of the shooting screen is hardly affected by the distortion. On the other hand, the phase difference detection areas Area101, 102, 104, and 105 arranged at high image height positions are changed in size, position, and inclination under the influence of distortion. Based on this information, the camera CPU (focus control means) 121 performs phase difference focus control using the output of the pixels of the focus detection pixels on the image sensor 107 that overlap the phase difference detection areas Area101h to 105h.

Conversion of the detected defocus amount and lens driving amount performed in the phase difference focus control is performed using the following equation.
L = K × cos θ × Def (Formula 1)
Here, L represents a lens driving amount, Def represents a detected defocus amount, and K represents a conversion coefficient between the defocus amount and the lens driving amount. Further, θ represents the angle (acute angle) formed by the pupil division direction (horizontal direction in FIG. 6) of the focus detection pixels and the phase difference detection areas (Area 101h to 105h) after distortion correction. This is because the center of gravity of the focus detection pixel output of the optical image formed by the photographing optical system moves in the pupil division direction of the focus detection pixel by defocusing, while the pixel group used for focus detection is horizontal, Since they are arranged at an inclination, the amount of movement is largely calculated. For example, when a pixel group whose pupil division direction is horizontal forms a phase difference detection region inclined by 45 degrees, the movement of the optical image due to defocusing is detected by multiplying by √2. Therefore, in this embodiment, the conversion factor between the defocus amount and the lens driving amount is corrected in consideration of the inclination of the phase difference detection region after distortion correction. Thereby, more accurate phase difference focus control can be realized.

  Next, in step S505, the camera CPU 121 performs imaging plane phase difference AF on a subject included in the selected phase difference detection region (hereinafter referred to as a subject to be focused). That is, the defocus amount is calculated from the phase difference between a pair of image signals obtained using the output from the focus detection pixel group in the phase difference detection region. When there are a plurality of selected phase difference detection areas, a phase difference detection area indicating a closer subject is selected from the calculated defocus amount, and the third difference from the defocus amount to the near focus position is selected. The driving amount of the lens group 105 is calculated.

  In step S507, the camera CPU 121 determines whether the defocus amount calculated in step S506 is smaller than a threshold that is a predetermined value corresponding to the in-focus vicinity state. That is, it is determined whether or not the AF method is switched from the imaging surface phase difference AF to the contrast AF. If the defocus amount is smaller than the threshold, the process proceeds to step S508 to switch to contrast AF. On the other hand, if the defocus amount is larger (or more) than the threshold value, the process proceeds to step S506, and the camera CPU 121 drives the focus actuator 114 to move the third lens group 105 by the drive amount calculated in step S505. . Thereafter, the process returns to step S503 again, and the imaging surface phase difference AF control is repeated.

  In the present embodiment, when the phase difference detection area set in step S504 is set again, the phase difference detection area is set in consideration of the imaging surface phase difference AF and the lens driving situation in advance. A method for setting the phase difference detection area will be described with reference to FIG.

  FIG. 7A shows an example in which the position and size of the phase difference detection area are not changed. FIG. 7B shows an example in which the position and size of the phase difference detection area are changed in step S104.

  Area 201h, Area 202h, and Area 202z are phase difference detection areas on the image sensor 107. Area 202h represents a phase difference detection area with a large defocus amount, and Area 202z represents a phase difference detection area with a small defocus amount.

  As shown in FIG. 7A, when focus detection is performed at the center portion of the shooting screen, even if the defocus amount changes in the phase difference detection area Area 201h, that is, the movement of the third lens group 105 according to the defocus amount ( Hereinafter, it does not change even if the image magnification is changed by driving the focus lens). In other words, even if the image magnification is changed by driving the focus lens, the subject existing at the center of the shooting screen is not displaced from the center portion of the shooting screen. For this reason, when the camera CPU 121 sets the phase difference detection area again, it sets the phase difference detection area of the same size at the same position as the Area 201h.

  On the other hand, as shown in FIG. 7B, when focus detection is performed in the peripheral portion of the shooting screen, the phase difference detection area Area202h is positioned by the change in the image magnification caused by the large focus lens drive that greatly changes the defocus amount. It moves to the phase difference detection area Area202z. In other words, when the image magnification is changed by driving the focus lens, the subject existing around the shooting screen is displaced toward the center of the shooting screen. For this reason, the camera CPU 121 determines the amount of displacement of the subject based on the position of the phase difference detection area and the amount of change in image magnification each time step S504 is executed. Then, it is determined whether to change the position of the phase difference detection area based on the determined displacement amount and the current position of the focal area, and resetting is performed according to the result.

  In step S508, the camera CPU 121 drives the focus actuator 114 to move the third lens group 105 from the drive amount calculated in step S505 to the switching point to contrast AF. Here, since switching to contrast AF is performed, smooth switching without passing through the in-focus point can be realized by driving with a driving amount smaller than the calculated defocus amount.

  Next, in step S509, the camera CPU 121 determines the position of an area (hereinafter referred to as a contrast evaluation area) for acquiring a contrast evaluation value in contrast AF from the defocus amount calculated in step S505 immediately before starting contrast AF. Determine whether to change the size. That is, when the defocus amount calculated in step S505 immediately before the start of contrast AF is larger than the predetermined threshold, the third lens 105 is moved when the third lens group 105 is moved in step S508 or the subsequent contrast AF is performed. It is considered that the subject to be focused is displaced in the shooting screen due to the change in image magnification accompanying the driving of the group 105 and is out of the phase difference detection area in step S504. In this case, it is determined that the position or size of the contrast evaluation area is changed. On the other hand, when the defocus amount is smaller than the threshold value, it is considered that the subject to be focused is hardly displaced in the shooting screen even if the image magnification is changed, and is present in the phase difference detection region in step S504. In this case, it is determined that the position and size of the contrast evaluation area are not changed.

  If it is determined that the position or size of the contrast evaluation area is not changed, the camera CPU 121 sets the position of the contrast evaluation area to the same position as the phase difference detection area in step S504, and the size is also a predetermined standard size ( Set to a predetermined size). Thereafter, the process proceeds to step S110.

  On the other hand, if it is determined that the position or size of the contrast evaluation area is to be changed, the camera CPU 121 proceeds to step S511. In step S511, the camera CPU 121 calculates the displacement amount of the subject to be focused that has been displaced by the change in the image magnification, from the defocus amount obtained in step S505 and the lens information obtained in step S501. Then, the position and size of the contrast evaluation area are changed (set) based on the calculation result.

  FIG. 8A shows an example in which the position and size of the contrast evaluation area are not changed. FIG. 8B shows an example in which the position and size of the contrast evaluation area are changed in step S511.

  Area01, Area11, and Area11 'are phase difference detection areas. In this embodiment, the phase difference can be detected in both the horizontal and vertical directions, so Area 01, Area 11, and Area 11 ′ indicate areas near the intersection of the phase difference detection areas in both the horizontal and vertical directions. Area 11 indicates a phase difference area with a large defocus amount, and Area 11 ′ indicates a phase difference detection area with a small defocus amount. Area02 and Area12 are standard size contrast evaluation areas in contrast AF.

  As shown in FIG. 8A, when focus detection is performed at the center portion of the shooting screen, even if the defocus amount changes in the phase difference detection area Area01, that is, the movement of the third lens group 105 according to the defocus amount ( Hereinafter, it does not change even if the image magnification is changed by driving the focus lens). In other words, even if the image magnification is changed by driving the focus lens, the subject existing at the center of the shooting screen is not displaced from the center portion of the shooting screen. Therefore, the camera CPU 121 sets the contrast evaluation area when the AF method is switched from the imaging surface phase difference AF to the contrast AF to the contrast evaluation area Area02 at the same position as the phase difference detection area Aerea01. That is, the contrast evaluation area Area02 is set so as to include the phase difference detection area Areaa01.

  On the other hand, when focus detection is performed in the peripheral portion of the shooting screen as shown in FIG. 8B, the phase difference detection area Area11 is caused by a large change in image magnification due to a large focus lens drive that greatly changes the defocus amount. Move to the phase difference detection area Area11 ′. In other words, when the image magnification is changed by driving the focus lens, the subject existing around the shooting screen is displaced toward the center of the shooting screen. For this reason, the camera CPU 121 sets the contrast evaluation area when the AF method is switched from the imaging plane phase difference AF to the contrast AF to the contrast evaluation area Area12 including the phase difference detection area Area11 ′ after the imaging plane phase difference AF. .

  Note that “inclusion” here means a state in which a part of the phase difference detection region does not protrude from the contrast evaluation region, and the entire phase difference detection region is completely included in the contrast evaluation region. Furthermore, in this case, it is more preferable that the center of the phase difference detection region and the center of the contrast evaluation region coincide.

  In step S510 of FIG. 5, the camera CPU 121 performs contrast AF within the contrast evaluation area set in step S509 or step S511. When the in-focus state is obtained by contrast AF, a series of AF processing is completed, and a recording image is generated in response to turning on an imaging start switch (not shown), and this is recorded or displayed. Or

  As described above, according to the present embodiment, even when the phase difference detection area corresponding to the subject to be focused is moved by the imaging surface phase difference AF, the position after the movement is again performed when focus detection is performed again. The focus detection area can be set so as to include the phase difference detection area. Therefore, more accurate AF control is possible.

  Further, by eliminating the influence of the distortion of the photographing optical system by setting the phase difference detection area and correcting the conversion coefficient between the defocus amount and the lens driving amount, more accurate AF control can be performed.

  A second embodiment of the present invention will be described. Since the configuration of the imaging apparatus to which the focus detection apparatus of the present embodiment is applied is the same as that of the first embodiment, description thereof is omitted here. In this embodiment, a phase difference detection area is set using face detection, imaging surface phase difference AF is repeatedly performed on the setting area, and switching from imaging surface phase difference AF to contrast AF is performed.

  The flowchart in FIG. 9 shows the flow of the AF operation that the camera CPU 121 executes according to the computer program in the imaging apparatus to which the focus detection apparatus according to the present embodiment is applied.

  Since the processing from step S901 to step S903 is the same as the processing from step S501 to step S503 in the first embodiment (FIG. 5), description thereof is omitted here.

  In step S904, the camera CPU 121 performs face detection processing for detecting a human face as a specific subject existing in the shooting screen as subject detection means. Various methods of face detection processing have been proposed in the past, and any method may be adopted in this embodiment. The specific subject is not limited to a person's face.

  In step S905, the camera CPU 121 sets a detection area for the imaging plane phase difference AF using the face position information detected in step S904. That is, the focus detection pixel group included in the phase difference detection area corresponding to the face position after distortion correction is set. Next, in step S906, a defocus amount is calculated from a phase difference between a pair of image signals obtained using the output from the set pixel group, and the third lens group 105 from the defocus amount to a position near the in-focus position. Is calculated. Then, the process proceeds to step S908.

  In step S908, as in step S507 of the first embodiment, it is determined whether or not the AF method is switched from the imaging surface phase difference AF to the contrast AF. If the defocus amount is smaller than the threshold value, the process proceeds to step S910 to switch to contrast AF. On the other hand, if the defocus amount is larger (or more) than the threshold value, the process advances to step S907, and the camera CPU 121 drives the focus actuator 114 so as to move the third lens group 105 by the drive amount calculated in step S906. . Thereafter, the process returns to step S903 again, and the imaging surface phase difference AF control is repeated. The determination of whether or not to reset the phase difference detection area in this repetition is the same as in the first embodiment, and thus the description thereof is omitted here.

  Here, an outline of setting the phase difference detection area performed in step S905 from the face detection in this embodiment again or setting the contrast evaluation area in the contrast AF from the face detection will be described with reference to FIG. FIG. 10 shows an example in which the position and size of the evaluation area are not changed.

  Area 21 and Area 21 'are focus detection areas (phase difference detection areas) of the imaging plane phase difference AF. Area 22 is a phase difference detection area of imaging plane phase difference AF when setting again, or a contrast evaluation area of contrast AF after switching. Area 21 indicates a phase difference detection region with a large defocus amount, and Area 21 ′ indicates a phase difference detection region with a small defocus amount.

  As shown by the dotted line in FIG. 10, when there is a face that is a specific subject in the periphery of the shooting screen, the face is displaced closer to the center of the shooting screen due to the change in image magnification caused by the focus lens drive. The phase difference detection area corresponding to the position moves from Area 21 to Area 21 ′. In this embodiment, in such a case, the phase difference detection area of the imaging plane phase difference AF and the contrast evaluation area Area22 when set again are set so as to include both the phase difference detection areas Area21 and Area21 '. This makes it possible to maintain focus detection accuracy even when the position of the specific subject is displaced.

  Since the processing from step S909 to step S912 is the same as the processing from step S508 to step S511 of the first embodiment, description thereof is omitted here. When the in-focus state is obtained by contrast AF in step S911, a series of shooting operations is completed, and a recording image is generated and recorded in response to turning on an imaging start switch (not shown). And display.

  As described above, according to the present embodiment, even if the phase difference detection area corresponding to the face to be focused is moved by the imaging plane phase difference AF, before and after the movement in the subsequent imaging plane phase difference AF. The phase difference detection area of the imaging plane phase difference AF is set so as to include the phase difference detection area of the imaging plane. Therefore, more accurate phase difference AF and AF control are possible.

  The control of the system control circuit 1 may be performed by one hardware, or the entire apparatus may be controlled by a plurality of hardware sharing the processing.

  Further, in the above-described embodiment, the case where the present invention is applied to a digital camera has been described as an example, but this is not limited to this example. That is, the present invention may be applied to devices such as an imaging device such as a video camera, or a system including an imaging device with a focus detection function and a computer.

  Each means constituting the recording apparatus and each step of the recording method in the embodiment of the present invention described above can be realized by operating a program stored in a RAM or ROM of a computer. This program and a computer-readable storage medium storing the program are included in the present invention.

  In addition, the present invention can be implemented as, for example, a system, apparatus, method, program, storage medium, or the like. Specifically, the present invention may be applied to a system including a plurality of devices. The present invention may be applied to an apparatus composed of a single device.

  In the present invention, a software program for realizing the functions of the above-described embodiments (in the embodiment, a program corresponding to the flowcharts shown in FIGS. 5 and 9) may be supplied directly or remotely to the system or apparatus. Including. This includes the case where the system or the computer of the apparatus is also achieved by reading and executing the supplied program code.

  Accordingly, since the functions of the present invention are implemented by computer, the program code installed in the computer also implements the present invention. In other words, the present invention includes a computer program itself for realizing the functional processing of the present invention. In that case, as long as it has the function of a program, it may be in the form of object code, a program executed by an interpreter, script data supplied to the OS, and the like.

  Examples of the storage medium for supplying the program include a flexible disk, a hard disk, an optical disk, and a magneto-optical disk. Further, there are MO, CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, DVD (DVD-ROM, DVD-R) and the like.

  As another program supply method, there is a method of connecting to a homepage on the Internet using a browser of a client computer. It can also be supplied by downloading the computer program itself of the present invention or a compressed file including an automatic installation function from a homepage to a storage medium such as a hard disk.

  It can also be realized by dividing the program code constituting the program of the present invention into a plurality of files and downloading each file from a different homepage. That is, a WWW server that allows a plurality of users to download a program file for realizing the functional processing of the present invention on a computer is also included in the present invention.

  As another method, the program of the present invention is encrypted, stored in a storage medium such as a CD-ROM, distributed to users, and encrypted from a homepage via the Internet to users who have cleared predetermined conditions. Download the key information to be solved. It is also possible to execute the encrypted program by using the key information and install the program on a computer.

  Further, the functions of the above-described embodiments are realized by the computer executing the read program. Furthermore, based on the instructions of the program, an OS or the like running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments can be realized by the processing.

  As another method, a program read from a storage medium is first written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Then, based on the instructions of the program, the CPU or the like provided in the function expansion board or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are also realized by the processing.

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

Claims (13)

In a focus detection apparatus having an imaging optical system driving means including a focus lens for forming an optical image of a subject and an acquisition means for acquiring an imaging signal obtained by photoelectrically converting the optical image by the imaging means.
Setting means for setting a focus detection area on a shooting screen based on the imaging signal;
Focus detection means for performing focus adjustment for driving the focus lens by the drive means according to at least a phase difference detection method;
Control means for determining a drive amount of the focus lens based on an optical image corresponding to the imaging signal corresponding to the set focus detection area, and controlling the focus detection means according to the determined drive amount. ,
The control means controls the setting means, and when the position of the subject in the shooting screen is displaced by driving the focus lens according to the phase difference detection method, the focus detection area according to the amount of displacement of the subject. A focus detection device characterized by changing the position of the lens.   The control means determines a displacement amount of the subject based on a change in image magnification of the subject by driving a focus lens by the driving means, and based on the determined displacement amount and a current focus detection region position, The focus detection apparatus according to claim 1, wherein it is determined whether to change a position of the focus detection area. Detecting means for detecting a specific subject included in the shooting screen;
The control means controls the setting means to set the focus detection area according to the position of the specific subject detected by the detection means, and sets the image magnification of the specific subject by driving the focus lens by the driving means. A displacement amount of the specific subject is determined based on a change, and whether to change the position of the focus detection region is determined based on the determined displacement amount and the current position of the focus detection region. The focus detection apparatus according to claim 1.   The imaging unit has a plurality of focus detection pixels, and the control unit sets the position and the number of pixels for the focus detection based on the position of the focus detection region set by the setting unit. The focus detection apparatus according to claim 1, wherein the acquisition unit acquires an imaging signal obtained from the set focus detection pixels.   The photographing screen is a screen in which distortion of an optical image by the photographing optical system is corrected, and the control unit is configured to detect the focus detection pixel based on the focus detection region set by the setting unit and the correction of the distortion. The focus detection apparatus according to claim 4, wherein the position and the number of pixels are set.   The control means is based on the angle between the image shift amount and the image shift direction of the optical image in the focus detection area set by the setting means and the direction of the focus detection area set based on the distortion, 6. The focus detection apparatus according to claim 5, wherein a driving amount of the focus lens is determined.   The focus detection unit further performs focus adjustment for driving the focus lens by the drive unit according to a contrast method, and the control unit performs the position adjustment according to the drive amount determined in the focus adjustment according to the phase difference detection method. Decide whether to switch focus adjustment according to the phase difference detection method to focus adjustment according to the contrast method, and when switching to focus adjustment according to the contrast method is determined, control the setting means, The focus detection apparatus according to claim 1, wherein a focus detection area for focus adjustment according to the contrast method is set according to the drive amount. A focus detection method in a focus detection apparatus having an imaging optical system driving means including a focus lens for forming an optical image of a subject and an acquisition means for acquiring an imaging signal obtained by photoelectrically converting the optical image by the imaging means. And
A setting step of setting a focus detection area on a shooting screen based on the imaging signal;
A focus detection step for performing focus adjustment for driving the focus lens by the driving means according to at least a phase difference detection method;
A control step of determining a drive amount of the focus lens based on an optical image corresponding to the imaging signal corresponding to the set focus detection region and controlling the focus detection unit according to the determined drive amount. ,
The control step controls the setting step, and when the position of the subject in the photographing screen is displaced by driving the focus lens according to the phase difference detection method, the focus detection area according to the amount of displacement of the subject. A focus detection method comprising the step of changing the position of the focus. For controlling a focus detection apparatus having an imaging optical system driving means including a focus lens for forming an optical image of a subject and an acquisition means for acquiring an imaging signal obtained by photoelectrically converting the optical image by the imaging means. Program,
Computer
Setting means for setting a focus detection area on a shooting screen based on the imaging signal;
Focus detection means for performing focus adjustment for driving the focus lens by the drive means according to at least a phase difference detection method;
The focus lens drive amount is determined based on an optical image corresponding to the imaging signal corresponding to the set focus detection region, the focus detection unit is controlled according to the determined drive amount, and the phase difference detection is performed. Control means for controlling the setting means and changing the position of the focus detection area according to the amount of displacement of the subject when the position of the subject in the photographing screen is displaced by driving the focus lens according to a method Program to function as.   A computer-readable storage medium storing the program according to claim 9.   The program which makes a computer function as each means of the focus detection apparatus as described in any one of Claims 1 thru | or 7.   A storage medium storing a program for causing a computer to function as each unit of the focus detection apparatus according to any one of claims 1 to 7. A photographing optical system including a focus lens for forming an optical image of a subject;
Imaging means for photoelectrically converting the optical image to obtain an imaging signal;
A focus detection device according to any one of claims 1 to 7,
The said control means controls the photoelectric conversion of the said optical image by the said imaging means, The imaging device characterized by the above-mentioned.

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