JP5147474B2 - Imaging apparatus and control method thereof - Google Patents

Description

  The present invention relates to an imaging apparatus that performs focus control using a phase difference detection method and a contrast detection method.

  Examples of the AF (autofocus) method of the imaging apparatus include a phase difference detection method and a contrast detection method. In the phase difference detection method, the defocus amount of the imaging optical system is detected based on the phase difference between a pair of images (two images) formed by a pair of light beams that have passed through different areas of the exit pupil in the imaging optical system. Then, the in-focus state is obtained by moving the focus lens by a movement amount corresponding to the defocus amount.

  Further, in the contrast detection method, an in-focus state is obtained by moving the focus lens to a position where the high frequency component (contrast evaluation value) included in the image signal generated using the image sensor is maximized. In many cases, a hybrid AF that uses both a phase difference detection method capable of AF at high speed and a contrast detection method capable of high-precision AF is also used.

  Further, in Patent Document 1, focusing on a phase difference detection unit is arranged on the image sensor, so that focusing is performed in comparison with a conventional phase difference detection method using a phase difference detection unit different from the image sensor. An imaging apparatus with improved accuracy is disclosed. In addition to performing AF (phase difference AF) by the phase difference detection method using the imaging element having the pixels dedicated to the phase difference detection in this way, AF (contrast AF) by the contrast detection method is also performed, thereby further increasing the level. Accurate hybrid AF is possible.

There has also been proposed an imaging apparatus that detects a subject's face from an image generated using an imaging element and performs AF so that the face is in focus. Patent Document 2 discloses an imaging apparatus that detects an eye of a subject included in an image, displays a focus frame around the detected eye, and performs AF on the focus frame. Further, Patent Document 3 discloses an imaging apparatus that estimates a subject distance based on information about a subject's face and performs focus control based on the subject distance.
JP 2000-156823 A JP 2005-128156 A JP 2006-18246 A

  An imaging apparatus that employs hybrid AF has the following problems. When the pupil separation direction for phase difference detection is, for example, the horizontal direction, and the subject has a contrast difference greater than a certain size in the horizontal direction, after performing the phase difference AF, more accurate contrast AF can be performed.

  However, when the subject has only a small contrast difference in the pupil separation direction, even if the subject has a contrast difference larger than a certain size in the vertical direction orthogonal to the pupil separation direction, high-precision contrast AF is performed on the subject. Can not do. Therefore, there is a problem that the performance as the hybrid AF varies depending on the direction in which the subject has a contrast difference.

  The present invention provides an imaging apparatus capable of performing appropriate hybrid AF corresponding to the contrast difference direction of a specific subject such as a face.

An imaging apparatus according to an aspect of the present invention includes a subject detection unit that detects a specific subject from an image generated using an imaging element, and first focus control and contrast using a phase difference detection method for the specific subject. Control means for performing second focus control by a detection method. The control means sets the phase difference detection direction according to the direction in which the contrast difference of the specific subject is large , performs the first focus control based on the phase difference detected in the phase difference detection direction, and the phase difference The second focus control is performed based on the contrast detected in the same direction as the detection direction.

According to another aspect of the present invention, there is provided a method for controlling an imaging apparatus, comprising: a step of detecting a specific subject from an image generated using an imaging device; and a first method using a phase difference detection method for the specific subject. And a control step for performing second focus control by a contrast detection method. In the control step, the phase difference detection direction is set according to the direction in which the contrast difference of the specific subject is large , the first focus control is performed based on the phase difference detected in the phase difference detection direction, and the phase difference The second focus control is performed based on the contrast detected in the same direction as the detection direction.

  According to the present invention, the phase difference AF in the phase difference detection direction corresponding to the specific subject is performed, and the contrast AF is performed by contrast detection in the same direction as the phase difference detection direction. For this reason, appropriate hybrid AF corresponding to the direction of the contrast difference of the specific subject can be performed, and a highly accurate in-focus state for the specific subject can be obtained.

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

  FIG. 1 shows a configuration of a digital still camera as an image pickup apparatus that is an embodiment of the present invention.

  In FIG. 1, reference numeral 1 denotes an image pickup optical system, and reference numeral 2 denotes a focus lens constituting a part of the image pickup optical system 1. Reference numeral 4 denotes a focus motor as an actuator for moving the focus lens 2 in the optical axis direction. Reference numeral 10 denotes an image sensor composed of a CCD sensor, a CMOS sensor, or the like. Reference numeral 12 denotes an A / D converter that converts an analog imaging signal from the imaging device 10 into a digital imaging signal.

  Reference numeral 14 is a memory controller, and 15 is a memory (DRAM). The memory controller 14 controls reading / writing of data with respect to the memory 15. The memory 15 has a buffer function for temporarily storing a digital imaging signal from the A / D converter 12 and image data from a development processing unit 16 described later.

  The development processing unit 16 generates image data by performing various processes on the digital imaging signal from the A / D converter 12. The development processing unit 16 converts the image data held in the memory 15 into YUV format image data. For example, YUV image data is generated as a pre-stage for generating JPEG image data, which is a general recording format for digital cameras.

  Further, display image data sequentially generated at a predetermined cycle in the development processing unit 16 is transferred to the display unit 22 where it is displayed on a display device such as an LCD. As a result, the subject video (live view video) is displayed by the electronic viewfinder (EVF).

  Reference numeral 20 denotes a face detection unit (subject detection means) that detects the face of a subject (person) from image data after development processing and image data stored in the memory 15. A specific method of face detection will be described later.

  The face detection result (face position information) in the face detection unit 20 is sent to the display unit 22 as data indicating the face position. The display unit 22 generates face frame data surrounding an area including a face (face area), and causes the display device to display the face frame data on the display image data transferred from the development processing unit 16.

  Reference numeral 26 denotes a phase difference defocus amount acquisition unit (first focus detection means), which is a position in a focus detection area designated by an AF area control unit 28 to be described later in the image data from the development processing unit 16 or the memory 15. The defocus amount is acquired by the phase difference detection method. A defocus amount acquisition method (phase difference AF) will be described later.

  The AF area control unit 28 designates an AF area (focus detection area) to be focused in the imaging area (imaging screen). When the AF area control unit 28 receives the face detection result (face position information) from the face detection unit 20, the AF area control unit 28 specifies the face area in the image data (focus luminance data) from the development processing unit 16.

  Reference numeral 30 denotes a contrast evaluation value acquisition unit, and among the image data from the development processing unit 16 or the memory 15, a contrast evaluation value (also simply referred to as contrast) is obtained from an image signal in the AF area designated by the AF area control unit 28. Generate. When a face area is designated as the AF area, a contrast evaluation value is generated from an image signal in the face area. A method for generating the contrast evaluation value (contrast AF) will be described later.

  Reference numeral 32 denotes a focus control unit. The focus control unit 32 obtains an in-focus state with respect to a subject to be focused based on the defocus amount from the phase difference defocus amount acquisition unit 26 and the contrast evaluation value from the contrast evaluation value acquisition unit 30. The moving amount or position of the focus lens 2 is calculated. Then, the focus control unit 32 controls the focus motor 4 so as to move the focus lens 2 by the movement amount or to the position. That is, the focus control unit 32 functions as a control unit that performs contrast AF (second focus control) after performing phase difference AF (first focus control) on the subject.

  When the focus target is a face area, hybrid AF can be performed on the face area by performing contrast AF after performing phase difference AF.

  A focus motor driving unit 34 drives the focus motor 4 in response to an instruction from the focus control unit 32.

  Reference numeral 35 denotes an attitude sensor as attitude detection means. The posture sensor 35 will be described later.

[Description of Phase Difference AF by Image Sensor 10]
Next, the arrangement of the image pickup pixel (group) and the phase difference detection pixel (group) in the image pickup device 10 will be described with reference to FIG. The image sensor 10 photoelectrically converts a subject image formed by a light beam from the imaging optical system 1 and outputs a first photoelectric conversion cell group (imaging pixel group) that outputs a first signal used for image generation and contrast detection. ). In addition, the image sensor 10 photoelectrically converts a plurality of images formed by the divided light beams out of the light beams from the imaging optical system 1 and outputs a second signal used to detect a phase difference. It has a conversion cell group (phase difference detection pixel group). The first signal is used for contrast AF, and the second signal is used for phase difference AF.

  FIG. 3 shows an enlarged part of the image sensor 10. Each white portion 201 surrounded by a rectangular frame indicates an imaging pixel. In addition, portions 202 and 203 surrounded by a rectangular frame and hatched on the inside thereof indicate phase difference detection pixels. The phase difference detection pixels form a pair of two pixels that are obliquely adjacent to each other, and the pairs are discretely (and periodically) arranged in the imaging element 10 (imaging pixel group).

  4 is a front view of the phase difference detection pixel 202, and the lower side of FIG. 4 is a cross-sectional view of the phase difference detection pixel 202 taken along the line B-B 'in the front view. The phase difference detection pixel 202 does not have any of the R, G, and B color filter layers of the imaging pixel 201, and the microlens 301 is provided at the position closest to the light incident side. In the front view, the microlens 301 is not shown. Reference numeral 302 denotes a smoothing layer for forming a plane for forming the microlens 301.

  Reference numeral 303 a denotes a light shielding layer, which has a diaphragm opening eccentric in one direction with respect to the center O of the photoelectric conversion region 305. 304 is a smooth layer.

  5 is a front view of the phase difference detection pixel 203, and the lower side of FIG. 5 is a sectional view of the phase difference detection pixel 203 when cut along the line BB ′ in the front view. Yes. This phase difference detection pixel 203 also has no color filter layer, and a microlens 301 is provided at a position closest to the light incident side (on the smoothing layer 302). In the front view, the microlens 301 is not shown.

  Reference numeral 303b denotes a light shielding layer, which has an aperture opening that is decentered in the opposite direction to the light shielding layer 303a provided in the phase difference detection pixel 202 with respect to the center O of the photoelectric conversion region 305. That is, the light shielding layers 303 a and 303 b of the phase difference detection pixels 202 and 203 have diaphragm openings at symmetrical positions with the optical axis (O) of each microlens 301 interposed therebetween.

  According to such a configuration, the case where the imaging optical system 1 is viewed from the phase difference detection pixel 202 and the case where the imaging optical system 1 is viewed from the phase difference detection pixel 203 is equivalent to the fact that the pupil of the imaging optical system 1 is divided symmetrically. It becomes. That is, the microlens 301 and the light shielding layers 303a and 303b constitute a so-called pupil division optical system.

  Two more approximate images are formed on the phase difference detection pixels 202 and 203 adjacent to each other as the number of pixels of the image sensor 10 increases. When the imaging optical system 1 is in focus with respect to the subject, the outputs (image signals) obtained from the phase difference detection pixels 202 and 203 coincide with each other.

  On the other hand, if the imaging optical system 1 is out of focus, a phase difference occurs in the image signals obtained from the phase difference detection pixels 202 and 203. The direction of the phase difference is reversed between the front pin state and the rear pin state.

  6 and 7 show the relationship between the phase difference and the focus state. In these figures, the phase difference detection pixels 202 and 203 are shown as S1 and S2, respectively. Further, the imaging pixel 201 is omitted, and a plurality of pairs of phase difference detection pixels 202 and 203 are shown close to each other on the same cross section. In the drawing, the pair of phase difference detection pixels S1 and S2 is shown as being covered with the same microlens 301, but the phase difference detection pixels S1 and S2 may be covered with different microlenses. Good.

  Light from a specific point of the subject passes through the pupil for the phase difference detection pixel S1 and enters the phase difference detection pixel S1, and light flux L2 enters the phase difference detection pixel S2 through the pupil for the phase difference detection pixel S2. And divided. The two light beams L1 and L2 are collected at one point on the surface of the microlens 301 as shown in FIG. 6 in a state where the imaging optical system 1 is focused on a specific point. The same image is formed on the phase difference detection pixels S1 and S2. As a result, the image signal read from the phase difference detection pixel S1 and the image signal read from the phase difference detection pixel S2 are the same.

  On the other hand, when the imaging optical system 1 is not focused on a specific point, the light beams L1 and L2 intersect at different positions from the surface of the microlens 301, as shown in FIG. The distance between the surface of the microlens 301 and the intersection of the two light beams L1 and L2, that is, the defocus amount is x. Further, it is assumed that the image shift amount (phase difference) on the phase difference detection pixels S1 and S2 generated in this state corresponds to n pixels.

When the pixel pitch is d, the distance between the centers of gravity of the two pupils is Daf, and the distance from the principal point of the imaging optical system 1 to the focal position is u, the defocus amount x is
x = n × d × u / Daf (1)
Is required.

Since u is considered to be substantially equal to the focal length f of the imaging optical system 1, the defocus amount x is
x = n × d × f / Daf (2)
You can also ask for it.

  FIG. 8 shows image signals read from each of the phase difference detection pixels S1 and S2. A shift amount (that is, an image shift amount) n × d is generated in the pair of image signals.

  The phase difference defocus amount acquisition unit 26 obtains a shift amount (phase difference) n × d between a pair of image signals using a correlation calculation method, and further obtains a defocus amount x by the expression (1) or (2).

  The focus control unit 32 calculates a movement amount of the focus lens 2 for keeping the defocus amount x within a predetermined range (preferably zero) based on the calculated defocus amount. Then, the focus control unit 32 moves the focus lens 2 in the imaging optical system 1 to a focus position corresponding to the calculated movement amount. Thereby, a focused state by phase difference AF is obtained.

  Note that the development processing unit 16 may interpolate image pixel data corresponding to the phase difference detection pixels based on outputs from a plurality of imaging pixels arranged in the vicinity of the phase difference detection pixels. As a result, image data having no missing pixels is generated.

  As described above, in this embodiment, among the light beams from the imaging optical system 1, the light beams L1 and L2 passing through different pupils are divided using the pupil division optical system, and two images formed by the light beams L1 and L2 are obtained. By providing the phase difference detection pixels S1 and S2 so as to receive light, phase difference AF is enabled.

[Description of face detection]
As a method of detecting a human face (specific subject) by the face detection unit 20, there are a method using an eigenface by principal component analysis, and a method using facial feature points such as eyes, nose and mouth. . The former is described in MA Turk and APPentland, “Face recognition using eigenfaces”, Proc. Of IEEE Conf. On Computer Vision and Pattern Recognition, pp. 586-591, 1991. The latter is described in, for example, Japanese Patent Application Laid-Open No. 09-251534. In these face detection methods, it is determined whether or not the input image is a human face by a pattern matching method between the input image and a plurality of standard patterns. In this embodiment, pattern matching is performed between a standard pattern of a human face stored in advance in the memory 15 and image data from the development processing unit 16 or the memory 15.

  Then, the AF area control unit 28 designates a face area on the image data based on the face position information from the face detection unit 20, and the display unit 22 superimposes a face frame surrounding the face area on the image data. indicate.

  However, the present invention is not limited to the face detection method described above, and other face detection methods may be used. For example, the human eye included in the image data disclosed in Patent Document 2 shown above is detected, and the face frame is set based on the information indicating the detected position and size of the eye. Also good.

[Description of contrast AF]
The contrast evaluation value acquisition unit 30 extracts the high-frequency component included in the image data by passing the image data obtained using the image sensor 10 through a band-pass filter, and determines the contrast state of the image data from the high-frequency component. A contrast evaluation value is generated. Then, the contrast evaluation value is acquired while moving the focus lens 2 within a predetermined range, and the focus lens position where the contrast evaluation value is maximized is determined as the in-focus position. By moving the focus lens 2 to the focus position, a focus state by contrast AF is obtained.

[Description of hybrid AF for face area]
Next, hybrid AF for the face area in the present embodiment will be described with reference to FIGS.

  FIG. 2 shows a scene in which there are two persons in the foreground and a building behind them. FIG. 10 shows contrast evaluation values in a wide area including one person and the background building in the scene of FIG. In this figure, the contrast evaluation value for the background building is higher than the contrast evaluation value for the face. That is, the contrast evaluation value is maximized at a distance farther than the distance of the person (face) due to the influence of the background. For this reason, even if contrast AF is performed, the face is out of focus (the building is in focus).

  FIG. 9 shows contrast evaluation values acquired only from the face area F of one person in the scene of FIG. In this figure, the contrast evaluation value is maximum at the distance of the person's face (specific subject). For this reason, the face is focused by contrast AF.

  However, in order to focus on the face with high accuracy by contrast AF, it is necessary to acquire a contrast evaluation value in a direction in which the face has a contrast difference. Furthermore, it is necessary that the acquisition (detection) direction of the contrast evaluation value is the same as the pupil division direction that is the phase difference detection direction in the phase difference AF. The pupil division direction is the light beam division direction by the above-described pupil division optical system, in other words, the separation direction of the first and second phase difference sensors.

  In the present embodiment, the image sensor 10 is provided with a phase difference sensor (horizontal phase difference sensor) in which the phase difference detection direction (pupil division direction), that is, the direction in which the phase difference can be detected is horizontal, as shown in FIG. 11A. Provided. Furthermore, the image sensor 10 is provided with a phase difference sensor (vertical phase difference sensor) whose phase difference detection direction is the vertical direction as shown in FIG. 11B.

  Such horizontal and vertical phase difference sensors are discretely arranged at predetermined intervals over the entire image sensor 10. Specifically, about 1% of all the pixels of the image sensor 10 are allocated to the phase difference sensor.

  Regarding the phase difference detection direction (pupil division direction), horizontal phase difference sensor, and contrast detection, the horizontal direction means a direction along the long side of the image sensor 10, and the vertical direction means along the short side of the image sensor 10. Means the direction.

  For subjects with a greater contrast difference in the horizontal direction than in the vertical direction, after performing phase difference AF using a horizontal phase difference sensor, contrast AF is performed by detecting the contrast in the horizontal direction. Hybrid AF can be performed. On the other hand, for a subject having a larger contrast difference in the vertical direction, after performing phase difference AF using a vertical phase difference sensor, contrast AF is performed by contrast detection in the vertical direction, thereby achieving high accuracy for the subject. Hybrid AF can be performed.

  The contrast evaluation value acquisition unit 30 can acquire the contrast evaluation values in the horizontal direction and the vertical direction by using different band pass filters in the horizontal direction and the vertical direction for the image data.

  Here, in general, the face has a larger contrast difference in the direction orthogonal to the direction of both eyes (longitudinal direction of the face) than in the direction of both eyes. Therefore, as shown in FIG. 2, when the subject is in an upright state and the camera is held in a normal posture (hereinafter referred to as a horizontal position), the phase difference AF using the vertical phase difference sensor and the vertical direction The accuracy of focusing is higher when contrast AF is performed by contrast detection.

  However, when the subject is in an upright state and the camera is held in a horizontal position (hereinafter referred to as a vertical position), the phase difference AF using a horizontal phase difference sensor and the contrast AF by contrast detection in the horizontal direction. The accuracy of focusing is higher when performing.

  As described above, in the present embodiment, for the face area, after performing the phase difference AF by setting the phase difference detection direction corresponding to the face direction with respect to the camera, the phase difference detection direction is the same as the phase difference detection direction. Contrast AF based on contrast detection is performed. Specifically, when the longitudinal direction of the face is the direction along the short side of the image sensor 10, the phase difference detection direction is set to the direction along the long side of the image sensor 10. When the longitudinal direction of the face is the direction along the long side of the image sensor 10, the phase difference detection direction is set to the direction along the short side of the image sensor 10.

  Thereby, the consistency of evaluation of the focus state in the phase difference AF and the contrast AF with respect to the face area can be obtained, and high focusing accuracy can be obtained by making full use of the performance of the hybrid AF.

  The camera of this embodiment is provided with a posture sensor 35 for detecting whether the camera is in the horizontal position or the vertical position. The position (orientation) of the camera is detected by the attitude sensor 35, and a phase difference detection direction and a contrast detection direction that is the same direction as this are set, so that the phase difference corresponding to the face direction relative to the camera is set. A detection direction and a contrast detection direction can be set.

  When the subject is lying down even when the camera is in the horizontal position (when the face is lying down), the phase difference AF using the horizontal phase difference sensor and the contrast AF based on the contrast detection in the horizontal direction are performed. The focusing accuracy is higher. In such a case, the appropriate phase difference detection direction and contrast detection direction described above cannot be set even using the attitude sensor 35.

  Therefore, in this embodiment, the face detection unit 20 also acquires face tilt information, sets the phase difference detection direction and the contrast detection direction appropriately based on the tilt information, and uses the phase difference AF using the horizontal phase difference sensor. Contrast AF is performed by detecting contrast in the horizontal direction.

  Further, as a result of acquiring the face inclination information in the face detection unit 20, when the face is inclined obliquely with respect to the camera (the longitudinal direction of the face is inclined with respect to the long side and the short side of the image sensor), The phase difference detection is performed by each of the horizontal phase difference sensor and the vertical phase difference sensor. Furthermore, contrast detection is performed in each of the horizontal direction and the vertical direction. When the phase difference and contrast evaluation value obtained in each direction are appropriately weighted according to the face inclination angle, the phase difference and contrast evaluation value actually used in AF are determined. Good.

  The size of the pixel area for determining the face by the face detection unit 20 is set to, for example, about 20 × 20 pixels with respect to the size of the display image on the display unit 22 of horizontal 320 × vertical 240 pixels. That's fine. Assuming that about 1% of all pixels of the image sensor 10 are used as a phase difference sensor, if a pair of phase difference detection pixels corresponding to the same phase difference detection direction are arranged at oblique positions close to each other, the horizontal position is set at an interval of 20 pixels. A phase difference sensor and a vertical phase difference sensor can be arranged.

  When the horizontal phase difference sensor and the horizontal phase difference sensor are alternately arranged almost uniformly over the entire image sensor, the image sensor with 10 million pixels (horizontal 3648 × vertical 2736 pixels) has 500 pixels in the face area. About a phase difference detection pixel can be arranged. In the phase difference detection pixels of about 500 pixels, when the horizontal phase difference sensor and the vertical phase difference sensor are alternately arranged in the horizontal and vertical directions, 130 horizontal and vertical phase difference sensors can be arranged respectively. By arranging 130 horizontal and vertical phase difference sensors in the face area described above, the phase difference AF can be performed with good accuracy for the face.

  Next, the face detection process by the face detection unit 20 will be described using the flowchart shown in FIG. This process is executed according to a computer program stored in the memory in the face detection unit 20. Here, it is assumed that a person as a subject is in an upright state as shown in FIG.

  In step S450, display of the subject video by EVF on the display unit 22 is started after the camera is activated.

  Next, in step S452, the face detection unit 20 determines whether or not there has been a scene change as a start condition for the face detection sequence. When there is no change in the light from the subject received by the image sensor 10, it is assumed that the same face as the face detected before is present, and a scene change is awaited. Immediately after the start of EVF display in step S450, it is handled as a scene change.

  If there is a scene change in step S452, the process proceeds to step S454, and the face detection unit 20 reads a signal indicating the position (posture) of the camera from the posture sensor 35. In step S456, it is determined based on the signal from the attitude sensor 35 whether the camera is in the vertical position or the horizontal position. If it is the vertical position, the process proceeds to step S458, and if it is the horizontal position, the process proceeds to step S468.

  In step S458, the face detection unit 20 detects a face by a procedure suitable for face detection in the vertical position using the face detection method described above. In step S460, the number of faces and the position of each face are detected. Then, the process proceeds to step S472.

  On the other hand, in step S468, the face detection unit 20 detects a face by a procedure suitable for face detection in the horizontal position using the face detection method described above. In step S470, the number of faces and the position of each face are detected. Then, the process proceeds to step S472.

  In step S472, the face detection unit 20 determines whether or not the imaging preparation switch (SW1) that is turned on by half-pressing the release button of the camera is turned on. If SW1 is not ON, the process returns to step S452, and if SW1 is ON, the process proceeds to step S474, and the process proceeds to step S500 shown in FIG.

  FIG. 13 shows a flowchart of hybrid AF for the face area performed by the focus control unit 32. This process is executed according to a computer program stored in a memory in the focus control unit 32.

  In step S500, the AF sequence is started on the condition that SW1 in step S474 of FIG. 12 is turned on. Note that the AF is started regardless of whether the EVF is in a display state or a non-display state.

  In step S <b> 502, the focus control unit 32 reads a signal indicating the position (posture) of the camera from the posture sensor 35. In step S504, based on the signal from the attitude sensor 35, it is determined whether the camera is in the vertical position or the horizontal position. If it is the vertical position, the process proceeds to step S510, and if it is the horizontal position, the process proceeds to step S540.

  In step S510, the focus control unit 32 sets the face area including the face detected by the face detection process (step S458) performed by the face detection unit 20 before the SW1 is turned on as the AF area. When a plurality of faces are detected, the face located at the closest distance is set as the main face, and the face area including the main face is set as the AF area.

  Next, in step S512, the focus control unit 32 causes the phase difference defocus amount acquisition unit 26 to perform phase difference detection (defocus amount calculation) using a horizontal phase difference sensor with respect to the AF area, and from the defocus amount. The amount of movement of the focus lens 2 is calculated. In step S514, the focus control unit 32 moves the focus lens 2 by the calculated movement amount. Thereby, a focused state by phase difference AF is obtained.

  In step S516, the focus control unit 32 checks whether or not the focus lens 2 has moved within a predetermined range (phase difference focus range) with respect to the focus position. If it is within the phase difference in-focus range, in the next step S518, the focus lens 2 is finely moved (scanned) by a predetermined amount within a predetermined range (for example, within the phase difference in-focus range or slightly larger than this). Contrast AF is performed on the AF area. The detection direction of the contrast evaluation value at this time is the same horizontal direction as the phase difference detection direction in the phase difference AF in step S512. By scanning in the vicinity of the phase difference focusing range, it is possible to detect the focusing position (contrast focusing position) by contrast AF for the AF area (face) in a short time.

  In step S520, the focus control unit 32 moves the focus lens 2 to the contrast focus position detected in step S518. Thus, when a highly accurate in-focus state is obtained for the AF area (face), in-focus determination is performed in step S560, and AF is completed in step S562.

  On the other hand, in step S540, the focus control unit 32 sets the face area including the face detected by the face detection process (step S468) performed by the face detection unit 20 before SW1 is turned on as the AF area. . When a plurality of faces are detected, the face area including the main face is set as the AF area.

  Next, in step S542, the focus control unit 32 causes the phase difference defocus amount acquisition unit 26 to perform phase difference detection (defocus amount calculation) using a vertical phase difference sensor with respect to the AF area, and further, from the defocus amount. The amount of movement of the focus lens 2 is calculated. In step S544, the focus control unit 32 moves the focus lens 2 by the calculated movement amount. Thereby, a focused state by phase difference AF is obtained.

  In step S546, the focus control unit 32 checks whether or not the focus lens 2 has moved within the phase difference focusing range with respect to the focusing position. If it is within the phase difference in-focus range, in the next step S548, the focus lens 2 is finely moved (scanned) by a predetermined amount within a predetermined range (for example, within the phase difference in-focus range or a slightly larger range). Contrast AF is performed on the AF area. The detection direction of the contrast evaluation value at this time is the same vertical direction as the phase difference detection direction in the phase difference AF in step S542. By scanning in the vicinity of the phase difference focusing range, it is possible to detect the focusing position (contrast focusing position) by contrast AF for the AF area (face) in a short time.

  In step S550, the focus control unit 32 moves the focus lens 2 to the contrast focus position detected in step S548. Thus, when a highly accurate focus state is obtained for the AF area (face), focus determination is performed in step S60, and AF is completed in step S562.

  According to the present embodiment, phase difference AF is performed in the phase difference detection direction corresponding to the face direction, and contrast AF is performed by contrast detection in the same direction. For this reason, hybrid AF corresponding to the direction of the face, that is, the direction in which the face has a larger contrast difference can be performed, and a highly accurate in-focus state with respect to the face can be obtained.

  Each of the embodiments described above is merely a representative example, and various modifications and changes can be made to the above-described embodiments when the present invention is implemented.

  For example, in the above-described embodiment, the case has been described in which the position (posture) of the camera is detected using the posture sensor, and the orientation of the face relative to the camera is specified based on the detected position of the camera. However, the orientation of the face relative to the camera may be determined during the face detection process using the image data.

  In the above embodiment, the face is detected as the specific subject, and the phase difference detection direction and the contrast detection direction are determined according to the direction. In this regard, if the subject is suitable for phase difference detection and contrast detection when the subject is scanned horizontally instead of scanning the subject vertically, for example, when detecting a subject with a vertical line as the specific subject, It may be as follows. That is, a subject with a vertical line is detected as the specific subject, and the phase difference detection direction and the contrast detection direction are determined according to the direction.

  In the above embodiment, the case where the contrast AF is performed after the phase difference AF is described, but the focus control in the present invention is not limited to this. For example, phase difference AF and contrast AF may be performed at the same time, and the focus lens position may be converged using both results. Also, when the subject changes suddenly while performing contrast AF in moving image capturing, if there is no change in the face position, the phase difference AF in the same direction in the area where contrast detection was performed immediately before May be performed.

  In the above-described embodiment, the case where the specific subject is a “face” has been described. However, the present invention can be applied to the case where hybrid AF is performed on various specific subjects as well as the face.

1 is a block diagram illustrating a configuration of a digital camera that is an embodiment of the present invention. The figure which shows the example of the scene imaged with the camera of an Example. FIG. 3 is a diagram illustrating a pixel array of an image sensor used in the camera of the embodiment. The front view and sectional drawing of the phase difference detection pixel provided in the said image sensor. The front view and sectional drawing of another phase difference detection pixel provided in the said image sensor. The figure which shows the relationship between the phase difference obtained by the phase difference detection pixel in an Example, and a focus state (focusing state). The figure which shows the relationship between the phase difference obtained by the phase difference detection pixel in an Example, and a focus state (defocus state). The figure which shows a pair of image signal read from each of a phase difference detection pixel. The figure which shows the contrast evaluation value acquired only in the face area | region among the scenes of FIG. The figure which shows the contrast evaluation value acquired in the area | region including a background among the scenes of FIG. The figure which shows the horizontal phase difference sensor in an Example. The figure which shows the vertical phase difference sensor in an Example. The flowchart which shows the face detection process in an Example. The flowchart which shows the AF process in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image pick-up optical system 2 Focus lens 10 Image pick-up element 16 Development processing part 20 Face detection part 28 AF area control part 26 Phase difference defocus amount acquisition part 30 Contrast evaluation value acquisition part 32 Focus control part 35 Posture sensor F Face area R, G , B Imaging pixels S1, S2 Phase difference detection pixels

Claims (7)

Subject detection means for detecting a specific subject from an image generated using an image sensor;
Control means for performing a first focus control by a phase difference detection method and a second focus control by a contrast detection method for the specific subject,
The control means sets a phase difference detection direction according to a direction in which the contrast difference of the specific subject is large , performs the first focus control based on the phase difference detected in the phase difference detection direction, and An image pickup apparatus that performs the second focus control based on a contrast detected in the same direction as a phase difference detection direction. Having an attitude detection means for detecting the attitude of the imaging device;
The imaging apparatus according to claim 1, wherein the control unit sets the phase difference detection direction based on the detected posture.   The imaging apparatus according to claim 1, wherein the specific subject is a face. When the longitudinal direction of the face is a direction along the short side of the image sensor, the control means sets the phase difference detection direction to a direction along the short side of the image sensor,
When the longitudinal direction of the face is a direction along the long side of the image sensor, the control unit sets the phase difference detection direction to a direction along the long side of the image sensor. The imaging device according to claim 3.   When the longitudinal direction of the face is inclined with respect to the long side and the short side of the image sensor, the control means sets the phase difference detection direction along the direction along the long side and the short side of the image sensor. The imaging apparatus according to claim 3, wherein the first focus control and the second focus control are performed using a phase difference and a contrast detected in each direction. The imaging device includes a first photoelectric conversion cell group that photoelectrically converts a subject image formed by a light beam from an imaging optical system and outputs a first signal used for generating an image and detecting the contrast; A second photoelectric conversion cell group that photoelectrically converts a plurality of images formed by the divided light beams out of the light beams from the imaging optical system and outputs a second signal used to detect the phase difference; ,
The second photoelectric conversion cell group detects the phase difference in the direction along the long side of the image sensor, and detects the phase difference in the direction along the short side of the image sensor. The imaging device according to claim 1, further comprising: a photoelectric conversion cell that performs the operation. Detecting a specific subject from an image generated using an image sensor;
A control step for performing a first focus control by a phase difference detection method and a second focus control by a contrast detection method on the specific subject,
In the control step, a phase difference detection direction is set according to a direction in which the contrast difference of the specific subject is large , the first focus control is performed based on the phase difference detected in the phase difference detection direction, and A control method for an imaging apparatus, wherein the second focus control is performed based on a contrast detected in the same direction as a phase difference detection direction.