JP2010107664A - Stereoscopic imaging apparatus and focusing control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the speed of AF search in a stereoscopic imaging apparatus having a plurality of imaging means. <P>SOLUTION: The stereoscopic imaging apparatus includes: a parallax detection processing part 49 which detects a parallax amount corresponding to a difference between a position in the first image of an object and a position in the second image of the object by analyzing the first image obtained by a first imaging element 29R and the second image obtained by a second imaging element 29L; an approximate distance calculation part 50 which calculates an approximate distance up to the object, based on the parallax amount; a lens moving distance decision part 53 which decides the moving distance of a focus lens 19R or 19L for obtaining the focusing lens position of the focus lenses 19R and 19L, based on the approximate distance; and a focusing control part 47 which calculates the contrast value of an image, while moving the focus lens 19R or 19L in the moving range and decides the focusing lens position where the focus lens 19R or 19L focuses on the object, based on the contrast value, to move the focus lens 19R or 19L to the decided focusing lens position. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a stereoscopic imaging apparatus and a focus control method that capture and record a plurality of images corresponding to a plurality of viewpoints.

  There is known a stereoscopic imaging apparatus including a first imaging optical system and a first imaging element corresponding to the right eye, and a second imaging optical system and a second imaging element corresponding to the left eye. Each of the two photographing optical systems has a focus lens.

  As a method of autofocus (also referred to as “AF”) control, contrast AF is known. In contrast AF, a contrast value (also referred to as “AF evaluation value”) is detected from an image signal (hereinafter referred to as “captured image”) captured by the image sensor while moving the focus lens in the optical axis direction, and the contrast value is detected. Is determined to be the focus lens position, and the focus lens is moved to that position to automatically focus (focus).

  Patent Documents 1 and 2 disclose a configuration in which the focus of one imaging optical system is adjusted based on the focusing information of the other imaging optical system when the focusing lens of the two imaging optical systems is focused. Yes.

Patent Document 3 discloses a configuration in which the focus lens of two photographing optical systems is simultaneously driven, and the other focus lens is set at the focus position of the photographing optical system where the in-focus position is detected first. Here, for example, the focus lens of one photographing optical system is driven from the near point to the far point, and the focus lens of the other photographing optical system is driven from the far point to the near point.
JP-A-8-242468 JP 2005-173270 A JP 2006-162990 A

  When the so-called hill-climbing method is used as the focus lens position detection (AF search), in order to prevent focusing on only the background, not the person, the search is performed from the shortest shooting distance side to the infinity point distance side. Often done. However, on the shortest shooting distance side, since the focus position fluctuation is small with respect to the focus lens movement amount, it takes time (AF search time) until the in-focus position corresponding to the subject distance is detected, resulting in a shooting time lag.

  The present invention has been made in view of such circumstances, and provides a stereoscopic imaging apparatus and a focusing control method capable of speeding up an AF search based on an image obtained by stereoscopic imaging with a plurality of imaging means. For the purpose.

  In order to achieve the above object, the present invention provides a first imaging optical system including a focus lens and a first imaging element on which a subject image is formed via the first imaging optical system. Stereo imaging including an imaging unit, a second imaging optical system including a focus lens, and a second imaging unit having a second imaging element on which a subject image is formed via the second imaging optical system In the apparatus, the first image acquired by the first image sensor and the second image acquired by the second image sensor are analyzed, and the position of the subject in the first image and the A parallax amount detecting means for detecting a parallax amount corresponding to a difference between the position of the subject in the second image, a rough distance calculating means for calculating a rough distance to the subject based on the parallax amount, and the rough outline Based on the distance, the focus lens Lens moving range determining means for determining a moving range of the focus lens for obtaining a focus lens position, and moving the focus lens within the moving range while moving the first lens and the second image. AF search control means for performing an AF search for calculating a contrast value of at least one of the images, and the focus lens position at which the focus lens focuses on the subject based on the contrast value obtained by the AF search. There is provided a stereoscopic imaging apparatus comprising: a focusing control unit that determines and moves the focus lens to the determined focusing lens position.

  In the present invention, the aperture value of the first imaging optical system and the second imaging optical system when the amount of parallax is detected by the parallax amount detection means is used as the aperture value of the imaging optical system at the time of the AF search. There is provided a stereoscopic photographing device comprising a first aperture value adjusting means for making the value larger than the value.

  Further, according to the present invention, when the AF search control unit fails to detect the parallax amount by the parallax amount detecting unit, the focus lens is focused from the shortest shooting distance position side where the focus lens is focused on the shortest shooting distance to infinity. While performing the AF search by moving in the first direction toward the infinity position side, when the parallax amount detection unit succeeds in detecting the parallax amount, the focus lens is moved from the infinity position side to the infinity position side. There is provided a stereoscopic imaging apparatus characterized by performing the AF search by moving in a second direction toward the shortest shooting distance position.

  The present invention further includes an AF search start position calculation unit that calculates an AF search start position indicating a position of the focus lens at which the AF search is started based on the approximate distance calculated by the approximate distance calculation unit. When the parallax amount detection unit fails to detect the parallax amount, the AF search control unit moves the focus lens from the shortest shooting distance position focusing on the shortest shooting distance to the infinity position side focusing on infinity. While the AF search is performed by moving the focus lens toward the target, when the parallax amount is successfully detected by the parallax amount detection unit, the AF search start position calculated by the AF search start position calculation unit A stereoscopic imaging apparatus, wherein the AF search is performed by moving the focus lens toward an infinite position side. To provide.

  Further, in the present invention, the AF search start position calculating means narrows the moving range of the focus lens as the depth of field of the photographing optical system used for the AF search is shallower. I will provide a.

  Further, according to the present invention, the AF search control means moves the focus lens every time the contrast value is calculated during the AF search as the depth of field of the photographing optical system used for the AF search is deeper. A stereoscopic imaging device characterized by increasing a step width is provided.

  Further, the present invention provides the shortest time based on the contrast value obtained by the AF search and the position of the focus lens from which the contrast value is obtained when the focus lens is moved to the focus lens position. First subject distance calculation means for calculating a substantially accurate main subject distance to a main subject at the shooting distance position side and a substantially accurate sub-subject distance to a sub-subject behind the main subject; Based on the sub-subject distance, aperture value calculation means for calculating the aperture value of the photographing optical system so that the sub-subject falls within the depth of field by calculation of the depth of field, and calculation results of the aperture value calculation means And a second aperture value adjusting means for adjusting the aperture value.

  The present invention also provides a substantially accurate main subject up to the main subject on the shortest shooting distance position side based on the contrast value obtained by the AF search and the position of the focus lens from which the contrast value was obtained. A second subject distance calculating unit that calculates a sub-subject distance to the sub-subject behind the main subject and a distance, and the sub-subject is determined based on the main and sub-subject distances. Focusing lens position determining means for calculating a focus setting distance corrected to the infinity position side by a depth of field calculation up to a position entering inside, and determining the focusing lens position based on the calculated focus setting distance; The stereoscopic imaging apparatus according to claim 1, wherein the stereoscopic imaging apparatus is provided.

  In addition, the present invention provides a stereoscopic imaging apparatus, wherein the parallax amount detection unit detects the parallax amount based on a person image included in the first image and the second image. To do.

  The present invention also provides a first imaging optical system including a focus lens, a first imaging unit having a first imaging element on which a subject image is formed via the first imaging optical system, and a focus lens. Focusing control of the focus lens using a second imaging optical system including the second imaging device and a second imaging unit having a second imaging element on which a subject image is formed via the second imaging optical system. A focusing control method to be performed, wherein a first image acquired by the first image sensor and a second image acquired by the second image sensor are analyzed, and the first image of the subject is analyzed. A parallax amount detecting step for detecting a parallax amount corresponding to a difference between a position in the image and a position in the second image of the subject; and a rough distance for calculating a rough distance to the subject based on the parallax amount Based on the calculating step and the approximate distance A lens movement range determining step for determining a movement range of the focus lens for obtaining a focus lens position of the focus lens; and moving the focus lens within the movement range, the first image and the An AF search step for performing an AF search for calculating a contrast value of at least one of the second images, and the focusing lens that focuses the subject based on the contrast value obtained by the AF search. And a focusing step of determining a focus lens position and moving the focus lens to the determined focus lens position.

  According to the present invention, it is possible to speed up AF search based on an image obtained by stereoscopic imaging with a plurality of imaging means.

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

  FIG. 1 is a front perspective view showing an external configuration of an example of a digital camera to which the stereoscopic imaging apparatus of the present invention is applied. FIG. 2 is a rear perspective view showing an external configuration of an example of the digital camera.

  The digital camera 10 includes a plurality of imaging means (two are illustrated in FIG. 1), and the same subject can be photographed from a plurality of viewpoints (two left and right viewpoints are illustrated in FIG. 1). In this example, for convenience of explanation, a case where two imaging units are provided will be described as an example, but the present invention is not limited to this. The present invention can be similarly applied even when three or more imaging units are provided. Note that the arrangement of the imaging means (mainly the imaging optical system) may not be in a horizontal row but may be two-dimensionally arranged. Stereo shooting, multi-viewpoint, or shooting in all directions may be used.

  The camera body 112 of the digital camera 10 of this example is formed in a rectangular box shape, and a pair of photographing optical systems 11R and 11L and a strobe 116 are provided on the front surface thereof as shown in FIG. Yes. On the top surface of the camera body 112, a release button 14, a power / mode switch 120, a mode dial 122, and the like are provided. On the back of the camera body 112, as shown in FIG. 2, a liquid crystal display (LCD) 13, a zoom button 126, a cross button 128, a MENU / OK button 130, a DISP button 132, a BACK button 134, and the like are provided. ing.

  The pair of left and right photographing optical systems 11R and 11L are configured to include retractable zoom lenses (18R and 18L in FIG. 3), respectively, and are fed out from the camera body 112 when the power of the digital camera 10 is turned on. In addition, since the zoom mechanism and the retracting mechanism in the photographing optical system are known techniques, a specific description thereof is omitted here.

  The LCD 13 is a display device such as a color liquid crystal panel in which a so-called lenticular lens having a semi-cylindrical lens group is arranged on the front surface. The LCD 13 is used as an image display unit for displaying captured images, and is used as a GUI during various settings. Further, at the time of shooting, an image captured by the image sensor is displayed through and used as an electronic viewfinder.

  The release button 14 is composed of a two-stroke switch composed of so-called “half press” and “full press”. When the digital camera 10 shoots a still image (for example, when a still image shooting mode is selected by the mode dial 122 or the menu), the release button 14 is pressed halfway to perform shooting preparation processing, that is, AE (Automatic Exposure), AF (Auto Focus) and AWB (Automatic White Balance) processing are performed, and when fully pressed, image shooting / recording processing is performed. Further, during moving image shooting (for example, when the moving image shooting mode is selected with the mode dial 122 or the menu), when the release button 14 is fully pressed, shooting of the moving image is started, and when the release button 14 is fully pressed again, shooting is ended. Note that, depending on the setting, the moving image can be shot while the release button 14 is fully pressed, and the shooting can be terminated when the full press is released. A release button dedicated to still image shooting and a release button dedicated to moving image shooting may be provided.

  The power / mode switch 120 (power switch and mode switch) functions as a power switch of the digital camera 10 and also functions as a switching unit that switches between the playback mode and the shooting mode of the digital camera 10. The mode dial 122 is used for setting the shooting mode. The digital camera 10 is set to a 2D still image shooting mode for shooting a 2D still image by setting the mode dial 122 to “2D still image position”, and set to “3D still image position”. The 3D still image shooting mode for shooting a 3D still image is set. Furthermore, the 3D moving image shooting mode for shooting a 3D moving image is set by setting the “3D moving image position”.

  The zoom button 126 is used for zoom operations of the photographing optical systems 11R and 11L, and includes a zoom tele button for instructing zooming to the telephoto side and a zoom wide button for instructing zooming to the wide angle side. The cross button 128 is provided so that it can be pressed in four directions, up, down, left, and right, and a function corresponding to the setting state of the camera is assigned to the pressing operation in each direction. The MENU / OK button 130 is used to call a menu screen (MENU function), and to confirm selection contents, execute a process, etc. (OK function). The DISP button 132 is used to input an instruction to switch the display contents of the LCD 13 and the BACK button 134 is used to input an instruction to cancel the input operation.

  Below, it divides into each embodiment and explains.

(First embodiment)
FIG. 3 is a block diagram illustrating a main part of the digital camera 10 according to the first embodiment.

  The digital camera 10 includes a right-eye imaging unit 12R having a right-eye imaging optical system 11R and an imaging element 29R, and a left-eye imaging unit 12L having a left-eye imaging optical system and an imaging element 29L. .

  The two photographing optical systems 11 (11R, 11L) include a zoom lens 18 (18R, 18L), a focus lens 19 (19R, 19L), and a diaphragm 20 (20R, 20L), respectively. The zoom lens 18, the focus lens 19, and the diaphragm 20 are driven by a zoom motor 22 (22R, 22L), a focus motor 23 (23R, 23L), and an iris motor 24 (24R, 24L), respectively. Each of the motors 22, 23, and 24 is a stepping motor, and is controlled by a driving pulse given from a motor driver 27 (27 R and 27 L) connected to the CPU 26.

  CCD image sensors (hereinafter simply referred to as “CCD”) 29 (29R, 29L) are disposed behind the two photographing optical systems 11 (11R, 11L), respectively. Instead of the CCD 29, a MOS type image sensor may be used. As is well known, the CCD 29 has a photoelectric conversion surface on which a plurality of photoelectric conversion elements are arranged. Subject light is incident on the photoelectric conversion surface via the photographing optical system 11 so that a subject image is formed. The A timing generator: TG31 (31R, 31L) controlled by the CPU 26 is connected to the CCD 29, and the shutter speed of the electronic shutter (the charge accumulation time of each photoelectric conversion element) is determined by a timing signal (clock pulse) input from the TG31. Is determined).

  The imaging signal output from the CCD 29 is input to the analog signal processing circuit 33. The analog signal processing circuit 33 includes a correlated double sampling circuit (CDS) 34, an amplifier (AMP) 35, and an A / D converter 36. The CDS 34 generates R, G, and B image data corresponding to the accumulated charge time of each pixel from the imaging signal. The AMP 35 amplifies the generated image data. The A / D converter 36 converts the amplified image data from analog to digital.

  The AMP 35 functions as a sensitivity adjustment unit that adjusts the sensitivity of the imaging unit 12. The ISO sensitivity of the CCD 29 is determined by the gain of the AMP 35. The digital image data output from the A / D converter 36 is temporarily stored in the SDRAM 39, which is a working memory, via the data bus 38.

  The image processing circuit 41 reads out the image data from the SDRAM 39, performs various image processing such as gradation conversion, white balance correction, γ correction processing, YC conversion processing, and stores the image data in the SDRAM 39 again. Image data that has been subjected to image processing by the image processing circuit 41 is acquired as a through image, converted into an analog signal by the LCD driver 42, and displayed on the LCD 13. Also, when the release button 14 is fully pressed, what is obtained for recording is compressed by the compression / decompression circuit 43 in a predetermined compression format (for example, JPEG format), and then the memory card via the memory card slot 15. 16 is recorded.

  The operation unit 25 is for performing various operations of the digital camera 10 and includes various buttons and switches 120 to 134 shown in FIGS. 1 and 2.

  The CPU 26 is provided for overall control of the digital camera 10. The CPU 26 controls each unit based on various control programs and setting information stored in a ROM (not shown).

  The CPU 26 also includes an AE control unit 45 that performs AE control, an AF control unit 47 that performs AF control, a parallax detection processing unit 49 that performs parallax detection on the main subject to be focused, and an approximate distance to the main subject ( An approximate distance calculation unit 50 for calculating an approximate subject distance) is provided.

  The AE control unit 45 analyzes the image (captured image) obtained by the CCD 29 when the release button 14 is half-pressed, and based on the luminance information of the subject, the aperture value of the diaphragm 20 and the electronic shutter of the CCD 29 are analyzed. The shutter speed is calculated. Based on these calculation results, the AE control unit 45 controls the aperture value via the iris motor 24 and the shutter speed via the TG 31.

  For example, based on the captured image (right eye image or left eye image) obtained by the CCD 29R or 29L of one of the two imaging optical systems 11R and 11L, the apertures of both the imaging optical systems 11R and 11L Calculate the value and shutter speed. Based on the captured images (right eye image and left eye image) obtained by both the photographing optical systems 11R and 11L, the aperture value and the shutter speed of the respective photographing optical systems 11R and 11L may be calculated.

  The AF control unit 47 performs AF search control for calculating the contrast value by moving the focus lenses 19R and 19L in the optical axis direction OA when the release button 14 is half-pressed, and the focusing lens position based on the contrast value. Focusing control for moving the focus lenses 19R, 19L is performed. Here, the “contrast value” is calculated based on the captured images obtained by the CCDs 29R and 29L. The “focus lens position” is the position of the focus lenses 19R and 19L at which the focus lenses 19R and 19L are focused on at least the main subject.

  For example, while moving at least one of the focus lenses 19R and 19L of the two photographic optical systems 11R and 11L by driving the motor driver 27R or 27L, the captured image (right-eye image or 11L) of the photographic optical system 11R or 11L is moved. In the left eye image), the contrast value is calculated. Based on the contrast value, the focus lens positions of the focus lenses 19R and 19L of the two photographing optical systems 11R and 11L are determined, respectively, and the motor drivers 27R and 27L are respectively driven so that the focus lenses 19R and 19L are respectively set. Move to focus lens position. An AF search may be performed in both the photographing optical systems 11R and 11L, and the respective focusing lens positions may be determined.

  The parallax detection processing unit 49 detects the amount of parallax between the photographing optical systems 11R and 11L with respect to the main subject based on the captured image (right eye image and left eye image) recorded in the SDRAM 39. Here, “main subject” Is a subject to be focused.

  In the explanatory view shown in FIG. 4, as the main subject becomes farther from the photographing optical systems 11R and 11L, the position of the specific point 250R of the main subject in the right-eye image and the left eye as shown in FIG. While the position of the specific point 250L of the main subject in the image coincides, the closer the main subject is to the photographing optical systems 11R and 11L, the more the main subject in the right-eye image as shown in FIG. The position of the specific point 250R of the subject is separated from the position of the specific point 250L of the main subject in the left eye image. That is, the larger the subject distance, the smaller the parallax amount, and the smaller the subject distance, the larger the parallax amount. Specifically, the parallax detection processing unit 49 uses a difference in position (corresponding points) between specific points (corresponding points) corresponding to both the right eye image and the left eye image for the same main subject as the amount of parallax. (Distance between points) is calculated. In other words, the difference between the position of the main subject on the right eye image and the position of the main subject on the left eye image is calculated as the amount of parallax.

  The main subject (that is, the subject to be focused) is not particularly limited. For example, when the face detection mode is set by the operation unit 25, the person H in the captured image is set as the main subject as shown in FIG. The distance between corresponding points in the face detection frame A is calculated. For example, in the right-eye image and the left-eye image, the difference in the positions of the points 251, the difference in the positions of the 252 points, the difference in the positions of the 253 points, and the points of the 254 points A difference in position is obtained, and an average value of these differences is used as the amount of parallax. In addition, although the case where the distance between corresponding points was obtained for four points of the main subject has been described as an example, the distance between corresponding points may be obtained for at least three points.

  When performing such parallax detection, parallax detection may not be possible because the face detection frame cannot be detected even if parallax detection is performed in a state where the main subject is not in focus. For this reason, in the present embodiment, when the parallax is detected, the aperture value of the aperture 20 is increased to increase the depth of field so that the main subject falls within the depth of field.

  Next, AF search control of the AF control unit 47 in the first embodiment will be described. In the following, description will be made by omitting the symbols R and L indicating the right eye and the left eye, assuming that AF search control is performed using one of the two photographing optical systems 11R and 11L.

  The focus lens 19 is movable at least between an MOD position that focuses on the shortest shooting distance (hereinafter referred to as “MOD”) and an INF position that focuses on infinity (hereinafter referred to as “INF”). The AF control unit 47 moves the focus lens 19 from the MOD position side toward the INF position side, and moves the focus lens 19 from the INF position side toward the MOD position side. However, it has a reverse search mode for calculating the contrast value. The AF control unit 47 drives the CCD 29 and the AF contrast value calculation unit 52 while moving the focus lens 19, and the AF contrast value calculation unit 52 is based on the luminance value of the image stored in the SDRAM 39 by the imaging of the CCD 29. Thus, the AF contrast value is sequentially calculated.

  When no parallax is detected, the AF control unit 47 compares the AF contrast value obtained for each predetermined lens feed amount with the previous AF contrast value in the forward direction search mode, and the AF contrast value changes from rising to falling. The so-called hill-climbing AF search is performed to calculate the lens movement and the contrast value until the AF control value 47 shifts the AF contrast value from rising to falling, and the AF contrast value peak (maximum) position is focused. The lens position is determined, and the focus motor 23 is controlled so that the focus lens 19 is moved to the focus lens position.

  On the other hand, when a parallax is detected, the AF control unit 47 of the present embodiment performs an accelerated AF search in the reverse search mode based on the parallax detection result by the parallax detection processing unit 49.

  As shown in FIG. 7, when the aperture value F = a and the aperture value F = b (where a> b) are compared, curves indicating the relationship between the focus lens position and the AF contrast value are compared. On the smaller side (b: dotted line), the variation amount of the AF contrast value with respect to the movement amount of the focus lens 19 becomes large, so that the depth of field (the in-focus range) becomes narrow (shallow). On the contrary, when the aperture value of the aperture 20 is larger (a: solid line), the variation amount of the AF contrast value with respect to the movement amount of the focus lens 19 becomes smaller, so the depth of field becomes deeper and the subject becomes deeper. There is a high possibility of entering.

  Therefore, for example, in the present embodiment, when the parallax is detected, the aperture value of the aperture 20 (“1”, “1.4”, “2”, “2.8”, “4”, “5.6”). , “8”...) Is increased by one step (two or more steps are possible) larger than the aperture value at the time of AF search. If the parallax detection fails in this state and the parallax detection fails, the aperture value of the aperture 20 is increased by one step until the face of the person H enters the depth of field and the parallax detection is successful. .

  Specifically, as shown in FIG. 8A, when the person H who is the main subject is not within the depth of field, the face of the person H is not in focus, so parallax detection is performed. Fail. When the parallax detection by the parallax detection processing unit 49 fails, the AE control unit (45 in FIG. 3) controls the iris motor 24 to increase the aperture value of the aperture 20 by one level (for example, “1.4” → “ 2 "). Next, the parallax detection processing unit 49 performs parallax detection again. Hereinafter, as shown in (B), the above process is repeated until the person H enters the depth of field and succeeds in detecting the parallax.

  Instead of increasing the aperture value of the aperture 20 one step at a time when parallax is detected, for example, the aperture value may be set to a large value from the beginning. However, when the aperture value is increased, that is, the aperture 20 is reduced to a certain extent. In this case, a phenomenon called so-called small-aperture blur may occur due to a diffraction phenomenon caused by the diaphragm 20. For this reason, it is preferable not to restrict the diaphragm 20 too much.

  When the aperture value of the aperture 20 is increased, that is, when the aperture 20 is stopped, the subject light incident on the CCD 29 decreases. Therefore, in FIG. 3, the CPU 26 increases the gain of the AMP 35 according to the increase of the aperture value of the aperture 20 and increases the ISO sensitivity of the CCD 29. As a result, a decrease in image brightness due to a decrease in the amount of subject light is corrected.

  The approximate distance calculation unit 50 calculates an approximate distance Ls to the face of the person H based on the amount of parallax calculated by the parallax detection processing unit 49. In this embodiment, the lens movement distance for moving the focus lens 19 from the INF position toward the MOD position is determined based on the calculation result of the approximate distance Ls, and the focus lens 19 is moved from the INF position by the determined lens movement distance. Perform AF search while moving. Hereinafter, the reason for moving the focus lens 19 from the INF position toward the MOD position will be described by taking the imaging optical system 11 having a 135-converted focal length of 300 m as an example.

  As shown in FIG. 9, since the depth of field is shallow on the MOD side, the fluctuation amount (m) of the focus position (focus setting distance) with respect to the movement amount (mm) of the focus lens 19 needs to be reduced. On the other hand, since the depth of field is deep on the INF side, the fluctuation amount of the focus position with respect to the movement amount of the focus lens 19 can be increased. For this reason, when performing an AF search, the search range (lens movement amount) of the AF search can be reduced by starting the search from the INF side where the variation amount of the focus position is large.

  FIG. 10 shows that “135 equivalent focal length” of the photographic optical system 11 and “person distance” that is the distance to the person H (face) under the condition that the image is taken from the side of the camera so that the person H enters from the waist to the head. “MOD to person”, which is the amount of lens movement when AF search is performed from the MOD side for the distance to the person H, and conversely, lens movement when AF search is performed from the INF side The relationship between the quantity “from INF to person” is shown. In FIG. 10, the height from the waist to the head of the person H is 0.85 m.

  In FIG. 10, in the “lens movement amount ratio” column, when the lens movement range necessary for focusing from the INF side to the MOD side is 100%, “MOD to person” and “INF to person”. The result of calculating the ratio of the respective lens movement amounts is entered. Further, the result of the lens movement amount ratio for each 135 equivalent focal length is graphed in FIG. In FIG. 11, the lens movement amount ratio “MOD to person” is on the left side, and the lens movement ratio is “INF to person” on the right side.

  As is clear from FIGS. 10 and 11, the assumed (usually assumed) person distance (excluding 135 equivalent focal length 28 mm and person distance 28 mm) is more than performing an AF search from the MOD side toward the INF side. The AF search time (distance) can be shortened by performing the AF search from the INF side toward the MOD side. For example, when the 135 equivalent focal length is 300 mm, the AF search time can be shortened to about 20% compared to the conventional case.

  Further, by moving the focus lens 19 from the INF position toward the MOD position at the time of AF search, the AF search time can be shortened (AF speed is increased), and the focus position of the face of the person H is detected. The focus position of the background B can also be detected before. As a result, it is possible to perform AF control that reflects the photographer's intention, such as focusing a person on both the background and the background.

In FIG. 3, when the parallax detection is performed by the parallax detection processing unit 49 and the approximate distance Ls to the face of the person H is calculated by the approximate distance calculation unit 50, the approximate distance calculation result is obtained as the lens of the AF control unit 47. This is input to the movement distance determination unit 53. The lens movement distance determination unit 53 moves the focus lens 19 to the INF position during AF search based on the result of correcting the approximate distance calculation error ΔLs (see FIG. 12) by the approximate distance calculation unit 50 with respect to the input approximate distance Ls. The lens movement distance L _AF (AF search range) to be moved from the position to the MOD position is determined.

  Here, the reason why the approximate distance calculation error ΔLs is corrected with respect to the approximate distance Ls is that the approximate distance Ls calculated by the approximate distance calculation unit 50 is different from the actual distance. In particular, when the approximate distance Ls is calculated to be shorter than the actual distance as a tendency of face recognition, the estimated focus lens position Ds (see FIG. This is because it is necessary to be closer to the MOD side than (see 12). In addition, the size of the face varies from person to person, especially for adults and children. Therefore, there is a reason that the lens movement amount considering safety must be set in consideration of this point. The magnitude of the approximate distance calculation error ΔLs may be, for example, a constant magnitude for each model of the digital camera, or may be changed according to the calculated approximate distance Ls.

AF control unit 47, when the lens movement distance _{L AF} lens movement distance determination section 53 determines, by driving the focus motor 23, a lens moving distance _{L AF} only focus lens 19 is moved toward the MOD position from the INF position However, the CCD 29 and the AF contrast value calculation unit 52 are driven. The AF contrast value calculation unit 52 performs an AF search for sequentially acquiring AF contrast values for each predetermined lens feed amount of the focus lens 19.

As shown by a solid line in FIG. 12, a curve indicating the relationship between the focus lens position obtained by the AF search and the AF contrast value (hereinafter referred to as “AF contrast curve”) has a peak position P1 corresponding to the background B. And a peak position P2 corresponding to the person H exists. As described above, the lens movement distance _LAF is a distance obtained by correcting (adding) the approximate distance calculation error ΔLs with respect to the approximate distance Ls. Therefore, the AF search end position is closer to the MOD than the estimated focus lens position Ds and the peak position P2. In the figure, D _P1 is a focus lens position (hereinafter simply referred to as “lens position”) corresponding to the peak position P1, and D _{P2 in} the figure is a lens position corresponding to the peak position P2.

AF control unit 47, based on the AF contrast curve obtained by the AF search, the most peak position of MOD side, i.e., the focus lens position for focusing the lens position D _P2 that corresponds to the peak position P2 to a person's face H Determine as. Next, the AF control unit 47 controls the focus motor 23 so that the focus lens 19 is moved to the determined focus lens position. Thus, the AF control when the parallax is detected is completed.

  In the above description, the case where there is only one main subject (in this example, a person) in the captured image obtained by the CCD 29 has been described as an example. However, for example, as illustrated in FIG. There may be two or more main subjects. In this case, the parallax detection processing unit 49 detects the area A1 where the face of the first person H1 is present and the area A2 where the face of the second person H2 is present. The amount of parallax of the second person H2 is obtained.

For example, the approximate distance calculation unit 50 selects the person H1 having the largest amount of parallax, that is, the closest person H1, and calculates the above-described approximate distance Ls based on the parallax amount of the selected person H1. Thereafter, the determination of the lens movement distance _LAF and the AF search are sequentially performed in the same manner as in the case of one main subject. In this case, as shown in FIG. 14, the AF contrast curve obtained by the AF search includes a peak position P1 corresponding to the background B, a peak position P2 corresponding to the farther person H2, and a closer person H1. And a peak position P3 corresponding to.

As described above, the AF control unit 47 determines, based on the AF contrast curve, the peak position closest to the MOD, that is, the lens position _DP3 corresponding to the peak position _P3 as the in-focus lens position, and determines the determined focus. The focus lens 19 is moved to the lens position. Even when there are three or more main subjects in the captured image, similarly, based on the parallax amount of the main subject having the largest amount of parallax, calculation of the approximate distance Ls, determination of the lens movement distance _LAF , AF search, focus The focusing position of the lens 19 is moved in order.

  FIG. 10 is a flowchart illustrating an example of a shooting process according to the first embodiment to which the focus control method of the present invention is applied. This process is executed according to the program by the CPU 26 of FIG.

  When the power of the digital camera 10 is turned on and the photographing mode is set, a through image is displayed on the LCD 13.

  In step S1, the CPU 26 determines whether or not the release button 14 is half-pressed. If it is determined that the release button 14 is not half-pressed, the CPU 26 is in a standby state until the release button is half-pressed.

  If it is determined that the release button has been half-pressed, the parallax detection processing by the parallax detection processing unit 49 is started in step S2. The detailed flow of this parallax detection process is shown in FIG. The AE control unit 45 controls the iris motor 24 to increase the aperture value of the aperture 20 by one step, thereby increasing the depth of field (step S21). Thereby, the possibility that the face of the person H falls within the depth of field increases. At the same time, the CPU 26 increases the gain of the AMP 35 and increases the ISO sensitivity of the CCD 29 in accordance with the increase of the aperture value in order to correct the decrease in image brightness due to the decrease in the amount of subject light incident on the CCD 29 (step S22). .

  The parallax detection processing unit 49 calculates the parallax amount of the face of the person H between the two images based on the right eye image and the left eye image stored in the SDRAM 39 after the aperture value and the ISO sensitivity are adjusted. (Step S23). It is determined whether or not the parallax detection has succeeded (step S24). If the parallax detection has failed, it is determined whether or not the aperture value is the maximum value (step S25). Here, when the aperture value is not the maximum value, the aperture value of the aperture 20 is further increased by one step (step S26), and after the ISO sensitivity of the CCD 29 is increased (step S22), the parallax detection is performed again. (Step S23). Thereafter, the above-described processing is repeated until the parallax detection is successful. If parallax detection fails even when the aperture value is set to the maximum value, it is determined that parallax detection is impossible (step S27). That is, it is finally determined that the parallax detection has failed.

  In step S3 of FIG. 15, it is determined whether or not the parallax detection is successful in the parallax detection processing unit 49, and when the parallax detection is successful, that is, when the parallax amount is calculated, in this embodiment, the reverse direction AF Perform a search.

In step S <b> 4, the approximate distance calculation unit 50 calculates the approximate distance Ls to the face of the person H based on the calculation result of the parallax amount, and inputs the calculation result to the lens movement distance determination unit 53. As described above, when a plurality of faces are detected by the parallax detection processing unit 49, the approximate distance Ls to the face with the largest amount of parallax is calculated. Then, in step S5, the lens movement distance determination unit 53, based on the result obtained by correcting the approximate distance calculation error of ΔLs respect approximate distance Ls, determines the lens movement distance L _AF. When the lens moving distance _{L AF} is determined at step S6, AF control section 47 drives the focus motor 23, while moving toward the MOD position of the lens movement distance _{L AF} only the focus lens 19 from the INF position Then, the CCD 29 and the AF contrast value calculation unit 52 are driven. Thus, an AF search for sequentially calculating the AF contrast value for each predetermined lens feed amount is performed until the focus lens 19 is moved by the lens movement distance _LAF .

  In step S7, it is determined whether or not the AF search is completed. When the AF search is completed, the AF control unit 47 determines the peak position of the AF contrast value on the most MOD side based on the AF contrast curve obtained by the AF search. Is determined as the in-focus lens position (see FIG. 12). In step S8, the AF control unit 47 controls the focus motor 23 to move the focus lens 19 to the determined focus lens position. This completes the AF control.

  When it is determined in step S3 that the parallax detection has failed, a normal forward AF search is performed. That is, in step S16, the AF control unit 47 drives the focus motor 23 to perform the AF search while moving the focus lens 19 from the MOD position toward the INF position. In step S17, it is determined whether or not the AF search is completed. When the AF search is completed, the AF control unit 47 determines the lens position corresponding to the peak position of the AF contrast value closest to the MOD based on the AF contrast curve. Is determined as the focus lens position. In step S18, the AF control unit 47 controls the focus motor 23 to move the focus lens 19 to the determined focus lens position.

  Also, the image data stored in the SDRAM 39 is analyzed, and the aperture value of the aperture 20, the electronic shutter of the CCD 29, and the ISO sensitivity of the CCD 29 are controlled by AE so that the optimum shooting conditions are obtained based on the luminance information of the subject. Calculated by the unit 45, the CPU 26, etc. (step S9). Based on these calculation results, the aperture value, electronic shutter speed, and ISO sensitivity are controlled (step S10). This completes the shooting preparation process.

  Thereafter, the CPU 26 determines whether or not the release button 14 has been fully pressed. If it is determined that the button is not fully pressed, the standby state is maintained until the button is fully pressed. If it is determined that the release button 14 has been fully pressed, the CPU 26 causes the CCD 29 to perform imaging (step S11). The imaging signal output from the CCD 29 is converted into digital image data by the analog signal processing circuit 33. The image data is subjected to various image processing / compression processes by the image processing circuit 41, the compression / decompression circuit 43, and the like, and then stored in the memory card 16 via the memory card slot 15. It is determined whether or not there is a next shooting (step S12). If there is a next shooting, the above-described processing may be repeated.

  As described above, in the present embodiment, when the parallax is detected, the aperture value is set to be larger than that in the AF search so that the depth of field is deepened. Therefore, there is a possibility that the subject enters the depth of field. This increases the probability of successfully detecting parallax (parallax detection rate).

  In the present embodiment, when the aperture value is increased, the ISO sensitivity of the CCD 28 is increased, so that it is possible to correct a decrease in image brightness due to the illusion of the amount of subject light incident on the CCD 29.

In this embodiment, the focus lens 19 is moved from the INF position where the variation amount of the in-focus position is large toward the MOD position by the lens movement amount (lens movement distance L _AF ) determined based on the parallax detection result. Since the AF search is performed, the AF search time can be shortened.

  In the present embodiment, when a plurality of main subjects are detected during parallax detection, the approximate distance Ls is calculated based on the parallax amount of the main subject having the largest parallax. The focus lens 19 can be reliably focused on the subject.

(Second Embodiment)
Next, an example of a digital camera according to the second embodiment to which the present invention is applied will be described.

  As shown in FIG. 18, the digital camera of the present embodiment includes a CPU denoted by reference numeral 60 instead of the CPU denoted by reference numeral 26 shown in FIG. This CPU 60 is basically the same as the CPU 26. However, the CPU 60 includes an AF control unit 64 provided with a subject distance calculation unit 63 (first subject distance calculation unit) and a depth of field calculation unit 65 (aperture value calculation unit).

The subject distance calculation unit 63 determines the main subject (in this example, the person H based on the AF contrast value (AF contrast curve) obtained by the AF search and the position of the focus lens when each AF contrast value is obtained. ) And a substantially accurate main subject distance LA to the sub-subject (background B in this example) are calculated (see FIG. 19). As these calculation methods, for example, the subject distance calculation unit 63 includes lens positions DP ₁ and DP ₂ corresponding to the peak positions P 1 and P ₂ of the AF contrast curve, and predetermined arithmetic expressions or data tables stored in advance in the CPU 60. Based on the above, both subject distances LA and LB are calculated. When there are a plurality of main subjects (persons in this example), the subject distance calculation unit 63 obtains the main subject distance LA to the main subject (person) on the MOD side. The calculation results of both subject distances LA and LB are input to the depth of field calculation unit 65.

  As shown in FIG. 19, the depth-of-field calculating unit 65 sets the subject distances LA and LB at the focusing lens position where the focus lens 19 focuses on the main subject H (person H) at the main subject distance LA. Based on the calculation result, the aperture value of the aperture 20 is calculated by the depth of field so that the sub-subject (background B) having the subject distance LB is also within the depth of field (rear field depth Lr) of the photographing optical system 11. Ask. For this depth of field calculation, the well-known equation 1 below is used to determine the rear depth of field Lr.

[Equation 1]
Lr = σFL ² / (f ² −σFL)
Here, σ is a permissible circle of confusion that indicates the permissible blur amount when forming an image on the CCD 29, F is a diaphragm value of the diaphragm 20, L is a distance LA to the person H, and f is a photographing optical system. 11 focal lengths.

  Among the above parameters, σ and f are known in advance before photographing. σ is stored in a ROM (not shown) or the like in the depth of field calculation unit 65, and f is input to the depth of field calculation unit 65 from the AF control unit 64. Then, the depth-of-field calculating unit 65 calculates F (aperture value) from the following formula 2 in which the main subject distance LA and the sub-subject distance LB are substituted for L and Lr in formula 1, respectively.

[Equation 2]
LB = σF (LA) ² / {f ² −σF (LA)}
From the above equation 2, the aperture value is calculated such that the sub-subject distance LB, that is, the background B falls within the depth of field (rear field depth Lr) when the focus lens 19 is at the above-described focusing lens position. You may make it perform the correction | amendment which considered safety | safety so that the background B might enter in the depth of field reliably. The calculated aperture value is input to the AE control unit 45.

  The AE control unit 45 controls the iris motor 24 based on the input aperture value and adjusts the aperture value of the aperture 20. As described above, when the aperture value of the aperture 20 is increased, the subject light incident on the CCD 29 decreases. For this reason, the CPU 60 increases the ISO sensitivity of the CCD 29 by increasing the gain of the AMP 35 in accordance with the increase of the aperture value of the aperture 20 as in the case of parallax detection.

  When the luminance value of the subject is lower than a predetermined amount, the amount of light received by the CCD 29 is insufficient with the aperture value obtained by Equation 2. For this reason, it is preferable to determine the aperture value in consideration of the balance between the shutter speed of the electronic shutter of the CCD 29 and the ISO sensitivity.

  FIG. 20 is a flowchart showing an example of a shooting process according to the second embodiment to which the focus control method of the present invention is applied. This process is executed according to the program by the CPU 60 of FIG.

  Note that the flow of processing from when the release button is pressed halfway down until the parallax detection is successful, the AF search is completed, and the focus lens 19 is moved to the in-focus lens position (steps S101 to S108), and parallax detection. Since the process flow (steps S116 to S119) in the case of failure is the same as that in the first embodiment described above, description thereof is omitted.

  After the focus lens 19 is moved to the focus lens position in step S108, the subject distance calculation unit 63 of the AF control unit 64 determines the AF contrast value (AF contrast curve) obtained by the AF search in step S109. The main subject distance LA and the sub-subject distance LB are calculated based on the position of the focus lens when each AF contrast value is obtained, and these calculation results are input to the depth-of-field calculating unit 65. To do.

  In step S110, the depth-of-field calculating unit 65, the allowable confusion circle diameter σ stored in advance, the focal length f of the photographing optical system 11 input from the AF control unit 64, and both subject distances LA, LB. And substituting into the above formula 2, the aperture value of the aperture 20 so that the background B falls within the depth of field of the photographing optical system 11 is obtained by depth of field calculation. The aperture value calculation result is input to the AE control unit 45.

  In step S111, when the aperture value is increased, the CPU 60 calculates the ISO sensitivity of the CCD 29 so that the optimum photographing condition is obtained. Thereby, when the aperture value of the aperture 20 is increased, the ISO sensitivity of the CCD 29 is increased, so that a decrease in image brightness due to a decrease in the amount of subject light incident on the CCD 29 is corrected. At the same time, the AE control unit 45 calculates the shutter speed of the electronic shutter of the CCD 29 so as to obtain the optimum shooting condition.

  Thereafter, similarly to the first embodiment, the aperture value, electronic shutter speed, and ISO sensitivity are controlled (step S112), and the imaging preparation process is completed. Since the subsequent processing (steps S113 to S114) is the same as that in the first embodiment, description thereof will be omitted.

  As described above, in the second embodiment, after the focus lens 19 is moved to the focus lens position, the main subject distance LA and the sub-subject distance LB are calculated based on the result of the AF search, and based on the calculation result. Since the aperture value that allows the background B to fall within the depth of field is obtained by the calculation of the depth of field, the background B can be focused when the person H is photographed. Since the AF search control is the same as that in the first embodiment, the same effects as those described in the first embodiment can be obtained, such as shortening the AF search time.

(Third embodiment)
Next, an example of a digital camera according to a third embodiment to which the present invention is applied will be described.

  As shown in FIG. 21, the digital camera of this embodiment includes a CPU denoted by reference numeral 70 instead of the CPU denoted by reference numeral 26 shown in FIG. This CPU 70 is basically the same as the CPU 26. However, the CPU 70 includes an AF control unit 75 provided with a subject distance calculation unit 72 (second subject distance calculation unit) and a focusing lens position determination unit 73 (focusing lens position determination unit).

  The subject distance calculation unit 72 is the same as the subject distance calculation unit (63 in FIG. 18) described in the second embodiment. Based on the result of the AF search, the subject distance calculation unit 63 is the same as the subject distance calculation unit 63. A distance LA and a sub-subject distance LB are calculated. These calculation results are input to the depth-of-field calculation circuit 76 of the focusing lens position determination unit 73.

  The depth-of-field calculation circuit 76 sets a “focus setting distance” such that the background B (sub-subject distance LB) also falls within the depth of field of the photographing optical system 11 based on the calculation results of both the subject distances LA and LB. Obtained by depth of field calculation. In the depth of field calculation, the above formula 1 for obtaining the rear depth of field Lr and the following formula 3 for obtaining the front depth of field Lf are used.

[Equation 3]
Lf = σFL ² / (f ² + σFL)
Among the parameters of Equations 1 and 3, the allowable confusion circle diameter σ, the focal length f, and the aperture value F are known in advance before photographing. Then, the depth-of-field calculation circuit 76 calculates the “focus” so that the distance after the main subject distance LA (person H) is within the depth of field by Expression 4 obtained by substituting the main object distance LA into Lf of Expression 3. A set distance “L1” is calculated (see FIG. 22). Here, the focus set distance L1 is set so that the main subject distance LA (person H) is forward when the focus lens 19 is focused on the focus set distance L1 (hereinafter referred to as “focus” if necessary). This is the distance that enters the depth of field Lf.

[Equation 4]
LA = σF (L1) ² / {f ² + σF (L1)}
Further, the depth-of-field calculating circuit 76 is configured to focus the distance within the sub-subject distance LB (background B) within the depth of field according to the following formula 5 by substituting the sub-subject distance LB for Lr in formula 1. A set distance L2 is calculated (see FIG. 22). Here, the focus setting distance L2 is a distance at which the sub-subject distance LB (background B) enters the rear depth of field Lr when the focus setting distance L2 is focused.

[Equation 5]
LB = σF (L2) ² / {f ² −σF (L2)}
When the focus setting distances L1 and L2 are calculated, the focusing lens position determination unit 73 compares the sizes of L1 and L2. As shown in FIG. 22A, in the case of L1 ≧ L2, by focusing on the focus setting distance between L1 and L2, all the distances between the main subject distance LA and the sub subject distance LB are obtained. The subject enters the depth of field. Accordingly, the depth-of-field calculating circuit 76 determines the photographing focus setting distance (focus setting position) LC by taking the average of the focus setting distances L1 and L2 based on the following equation (6). The left-pointing arrow indicates the range of the front depth of field, and the right-pointing arrow indicates the range of the rear depth of field.

[Equation 6]
LC = (L1 + L2) / 2 + L2
As shown in FIG. 23, when L1 = L2, it is possible to focus on both the person H and the background B within the limit of the allowable confusion circle diameter σ. That is, both the person H and the background B can be placed within the depth of field. Here, a symbol _DLC in the figure is a lens position (focusing lens position) corresponding to the focus setting distance LC.

  As shown in FIG. 22B, when L1 <L2, there is no solution in which all subjects between the main subject distance LA and the sub subject distance LB fall within the depth of field. For this reason, the focusing lens position determination unit 73 sets the focus setting distance L1 as the focus setting distance LC for photographing as shown in the following Equation 7 in order to focus on the person.

[Equation 7]
LC = L1
In addition, since it is necessary to focus the person H on the main rather than the background B, a weighting factor may be added so that the person H is emphasized with respect to the expressions 6 and 7.

  When the shooting focus setting distance LC is determined, the focusing lens position determination unit 73 determines the lens position of the focus lens 19 corresponding to the shooting setting distance LC as the focusing lens position. Then, the AF control unit 75 drives the focus motor 23 to move the focus lens 19 to the determined focus lens position.

  FIG. 24 is a flowchart illustrating an example of a shooting process according to the third embodiment to which the focus control method of the present invention is applied. This process is executed according to the program by the CPU 70 of FIG.

  The process flow from when the release button is pressed halfway down until the parallax detection is successful and the AF search is completed (steps S201 to S207), and the process flow when the parallax detection fails (steps S217 to S219). ) Is the same as in the first embodiment described above, and a description thereof will be omitted.

  If the parallax detection is successful and it is determined in step S207 that the AF search is completed, in step S208, the subject distance calculation unit 72 of the AF control unit 75 determines the main subject distance LA and the sub subject based on the result of the AF search. The distance LB is calculated, and these calculation results are input to the depth of field calculation circuit 76.

  In step S209, the depth-of-field calculating circuit 76 determines the permissible circle of confusion σ and the focal length f stored in advance in the AF control unit 75, the previously calculated both subject distances LA and LB, and AE control. Substituting the aperture value F of the aperture 20 input from the unit 45 into Equations 4 and 5, the focus setting distances L1 and L2 are calculated by depth of field calculation.

  When the focus setting distances L1 and L2 are obtained, the focus lens position determination unit 73 compares the sizes of L1 and L2 in step S210. Based on the equation 6, the photographing focus setting distance LC is calculated. If L1 <L2, the photographing focus setting distance LC is calculated based on the equation 7 in step S212. Next, in step S213, the focusing lens position determination unit 73 determines the lens position corresponding to the photographing focus setting distance LC as the focusing lens position. The AF control unit 75 drives the focus motor 23 to move the focus lens 19 to the determined focus lens position.

  Thereafter, similarly to the first embodiment, the aperture value, electronic shutter speed, and ISO sensitivity are controlled (S214), and the photographing preparation process is completed. Subsequent processing (steps S215 to 216) is the same as that in the first embodiment described above, and thus description thereof is omitted.

  As described above, in the third embodiment, the main subject distance LA and the sub-subject distance LB are calculated based on the AF search result, and the position where the background B falls within the depth of field is calculated based on the calculation result. By determining the focusing lens position of the focus lens 19 based on the result of calculating the focus setting distance LC for photographing corrected to the background side (INF position side) by the depth of field calculation until the second implementation described above Similarly to the form, when the person H is photographed, the background B can be focused. In addition, the same effects as those described in the first embodiment, such as shortening the AF search time, can be obtained.

(Fourth embodiment)
Next, an example of a digital camera according to a fourth embodiment to which the present invention is applied will be described.

  As shown in FIG. 25, the digital camera of this embodiment includes a CPU denoted by reference numeral 80 in place of the CPU denoted by reference numeral 26 shown in FIG. This CPU 80 is basically the same as the CPU 26. However, the CPU 80 includes an AF control unit 84 provided with a depth of field calculation unit 81, an AF search start position calculation unit 82, and a lens movement width determination unit 83.

  The depth of field calculation unit 81 calculates the depth of field of the photographic optical system 11 based on the aperture value of the diaphragm 20 of the photographic optical system 11 and the like.

Based on the approximate distance to the main subject calculated by the approximate distance calculation unit 50, the AF search start position calculation unit 82 calculates an AF search start position that indicates the position of the focus lens 19 that starts the AF search. In this embodiment, when the parallax detection is successful, the forward AF search for calculating the contrast value while moving the focus lens 19 from the MOD side toward the INF side is performed. If the parallax detection is successful in this AF search, the position D _ST (see FIG. 26) obtained by correcting the approximate distance calculation error ΔLs with respect to the approximate distance Ls is set as the AF search start position from the MOD side to the INF side. AF search (referred to as “parallax detection AF search”) is performed.

  The AF search when the parallax detection fails is the same as in the first embodiment, and an AF search (referred to as “normal AF search”) is performed from the MOD position toward the INF side.

  Similar to the normal AF search, the parallax detection AF search detects the first peak position where the contrast value reverses from rising to falling. However, in the parallax detection AF search, since the AF search is performed from the AF search start position calculated based on the approximate distance of the main subject (person H), even when an object is present at a closer distance than the person H, It is possible to reliably detect the lens position that focuses on the person H.

  The AF search start position is preferably calculated based on the depth of field calculated by the depth of field calculation unit 81. In this case, as the depth of field is shallower, the AF search start position calculation unit 82 makes the AF search start position closer to the lens position Ds (estimated focus lens position) corresponding to the approximate distance (the approximate distance to the main subject). To do. That is, as the depth of field is shallower, the movement range of the focus lens 19 in the AF search is narrowed.

  When the parallax detection is successful, the lens movement width determination unit 83 determines the movement width (step width) of the focus lens 19 during AF search based on the depth of field calculated by the depth of field calculation unit 81. To do. The lens movement width determination unit 83 increases the movement width of the focus lens 19 (that is, the interval between positions of the focus lens 19 to be moved each time an AF contrast value is calculated during AF search) as the depth of field is deeper.

  The AF search is based on an image acquired by at least one of the two photographing optical systems 11 (11R and 11L) while moving only the focus lens (19R or 19L) of the one photographing optical system. A contrast value may be calculated. In this case, the focusing lens positions of the two photographing optical systems 11R and 11L are obtained based on the contrast curve (AF contrast value) of one photographing optical system 11, respectively, and the focus lens 19R of the two photographing optical systems 11R and 11L. And 19L are moved to the respective focusing lens positions. Further, while moving the focus lenses 19R and 19L of both the photographing optical systems 11R and 11L, the AF contrast values are calculated by both the photographing optical systems 11R and 11L, and the respective focusing lens positions are obtained. Also good.

  FIG. 27 is a flowchart showing an example of a shooting process according to the fourth embodiment to which the focus control method of the present invention is applied. This process is executed according to the program by the CPU 80 in FIG.

  The flow of processing from when the release button is pressed halfway down until parallax detection is successful and the approximate distance of the main subject (person H) is calculated (steps S301 to S304), and processing when parallax detection fails The flow (steps S316 to S318) is the same as the processing (steps S1 to S4 and steps S16 to S18) of the first embodiment shown in FIG.

If the parallax detection of the main subject (person H in this example) is successful, in step S306, the AF search start position calculator 82 calculates the approximate distance calculation error ΔLs with respect to the approximate distance Ls as shown in FIG. the position _{D ST} with the corrected, calculated as AF search start position. In this example, ΔLs is determined so that the AF search start position D _ST is positioned on the MOD side of the lens position D _P2 corresponding to the subject distance of the main subject (that is, the lens position D _P2 corresponding to the peak position _P2 ). Yes. In step S308, the AF control unit 84 drives the focus motor 23 to move the focus lens 19 from the AF search start position _DST toward the INF position (infinity) side, and then the CCD 29 and the AF contrast. The value calculation unit 52 is driven. Thereby, an AF search for sequentially calculating an AF contrast value for each predetermined lens feed amount (“step width”) is performed.

In step S309, it is determined whether or not the AF contrast value is reversed from rising to falling, that is, whether or not the AF search is completed. When the AF search is completed, in step S310, the AF control unit 84 performs AF based on the AF contrast curve obtained by the search, determining the lens position D _P2 corresponding to the peak position P2 of the contrast values of the side closest to the AF search start position D _ST as the in-focus lens position (see Figure 26). Then, the AF control unit 84 controls the focus motor 23 to move the focus lens 19 to the determined focus lens position. This completes the AF control.

  FIG. 28 is a flowchart illustrating another example of the shooting process according to the fourth embodiment. This process is executed according to the program by the CPU 80 in FIG.

28, the depth of field calculation unit 81 of the AF control unit 84 calculates the depth of field of the photographic optical system 11 based on the aperture value of the diaphragm 20 of the photographic optical system 11 and the like. Then, at step S306, AF search start position calculating section 82 of the AF control unit 84, based on the approximate distance Ls and the depth of field, it calculates the AF search start position _{D ST.} That is, the AF search start position _DST is calculated by correcting the approximate distance Ls with the correction value ΔLs considering the depth of field. As shown in FIG. 29, as the depth of field is shallow, closer to the lens position Ds corresponding to AF search start position D _ST in approximate distance Ls (estimated focus lens position). That is, as the depth of field is shallower, the movement range of the focus lens 19 in the AF search is narrowed.

  The other steps are as described with reference to FIG. 27, and the description is omitted here.

  FIG. 30 is a flowchart illustrating another example of the shooting process according to the fourth embodiment. This process is executed according to the program by the CPU 84 in FIG.

  In S307 of FIG. 30, the lens movement width determination unit 83 of the AF control unit 84 determines the movement width (step width) of the focus lens 19 at the time of AF search based on the depth of field. Specifically, as the depth of field is deeper, the movement width of the focus lens 19 (that is, the lens position interval for calculating the AF contrast value) is increased.

  The other steps are the same as the photographing process shown in FIG. 28, and the description thereof is omitted here.

  In the first to fourth embodiments described above, the person H and the background B are described as examples of the main subject and the sub-subject in the captured image, respectively, but the present invention is not limited to this. Absent. For example, the main subject may be an animal other than a person, a plant, a building, a vehicle, or the like. In this case, a parallax detection processing unit 49 that can also detect parallax of these various main subjects may be provided. The sub-subject may be anything such as a background person, animal, plant, building, or vehicle.

  In addition, a selection switch for selecting whether or not a sub-subject such as the background B is placed within the depth of field may be provided in the operation unit 25.

  In the first to fourth embodiments, the shutter speed of the CCD 29 is adjusted by the electronic shutter at the time of AE control. However, the present invention is not limited to this, and a mechanical shutter may be used. Good.

  In the first to fourth embodiments, the digital camera has been described as an example. However, the present invention is not limited to this, and an AF search is performed to bring the focus lens into the focus lens position. The present invention can be applied to various imaging devices such as a mobile phone with camera and a PDA with camera.

  The present invention is not limited to the examples described in the present specification and the examples illustrated in the drawings, and various design changes and improvements may be made without departing from the spirit of the present invention.

Front perspective view of an example of a digital camera to which the present invention is applied The rear perspective view of an example of a digital camera to which the present invention is applied Block diagram of an example of a digital camera to which the present invention is applied Explanatory diagram showing the relationship between multiple shooting optical systems and subject distance Explanatory drawing used to explain the correspondence between subject distance and parallax amount Explanatory drawing used to explain recognition of main subject Explanatory drawing showing an example of the relationship between the focus lens position and the AF contrast position according to the aperture value Explanatory diagram for explaining that the parallax detection rate increases by increasing the aperture value Explanatory diagram showing an example of the relationship between the amount of movement of the focus lens and the focus position The figure which shows an example of the correspondence of a focal distance and a lens movement amount Graph showing the lens movement ratio by focal length Explanatory drawing which shows an example of AF contrast curve in 1st Embodiment Explanatory drawing used for explanation of parallax detection when there are a plurality of main subjects Explanatory drawing which shows an example of a contrast curve when a plurality of main subjects are detected The flowchart which shows the flow of an example of the imaging | photography process in 1st Embodiment. Flowchart showing an exemplary flow of parallax detection processing Explanatory drawing for demonstrating the case where a focus lens is moved toward the INF position side from a MOD position. Functional block diagram of the CPU of the digital camera of the second embodiment Explanatory diagram for explaining that the background also falls within the depth of field by increasing the aperture value The flowchart which shows the flow of an example of the imaging | photography process in 2nd Embodiment. Functional block diagram of the CPU of the digital camera of the third embodiment Explanatory diagram for explaining that the background also falls within the depth of field by correcting the focus setting distance for shooting to the background side Explanatory drawing for demonstrating an example of AF contrast curve The flowchart which shows the flow of an example of the imaging | photography process in 3rd Embodiment. Functional block diagram of the CPU of the digital camera of the fourth embodiment Explanatory drawing used to explain the AF search start point The flowchart which shows the flow of the 1st example of the imaging | photography process in 4th Embodiment. The flowchart which shows the flow of the 2nd example of the imaging | photography process in 4th Embodiment. Explanatory drawing used to explain the correspondence between depth of field and AF search start point The flowchart which shows the flow of the 3rd example of the imaging | photography process in 4th Embodiment. Explanatory diagram used to explain the correspondence between depth of field and lens movement width

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Digital camera, 11 (11R, 11L) ... Shooting optical system, 12 (12R, 12L) ... Imaging means, 19 (19R, 19L) ... Focus lens, 20 (20R, 20L) ... Aperture, 26, 60, 70 80 ... CPU, 29 (29R, 29L) ... CCD image sensor, 45 ... AE control unit, 47 ... AF control unit, 49 ... parallax detection processing unit, 50 ... approximately distance calculation unit, 52 ... AF contrast value calculation unit, 53. Lens moving distance determining unit

Claims (10)

A first imaging optical system including a focus lens, a first imaging unit having a first imaging element on which a subject image is formed via the first imaging optical system, and a second imaging including a focus lens In a stereoscopic imaging apparatus comprising: an optical system; and a second imaging unit having a second imaging element on which a subject image is formed via the second imaging optical system,
The first image acquired by the first image sensor and the second image acquired by the second image sensor are analyzed, and the position of the subject in the first image and the subject Parallax amount detection means for detecting a parallax amount corresponding to a difference from a position in the second image;
An approximate distance calculating means for calculating an approximate distance to the subject based on the parallax amount;
A lens movement range determining means for determining a movement range of the focus lens for obtaining a focus lens position of the focus lens based on the approximate distance;
An AF search control means for performing an AF search for calculating a contrast value of at least one of the first image and the second image while moving the focus lens within the moving range;
On the basis of the contrast value obtained by the AF search, a focus control unit that determines the focus lens position at which the focus lens focuses on the subject and moves the focus lens to the determined focus lens position. When,
A stereoscopic imaging apparatus comprising:   The aperture value of the first imaging optical system and the second imaging optical system when the amount of parallax is detected by the parallax amount detection means is set to be larger than the aperture value of the imaging optical system at the time of the AF search. The stereoscopic photographing apparatus according to claim 1, further comprising a single aperture value adjusting unit.   When the parallax amount detection unit fails to detect the parallax amount, the AF search control unit shifts the focus lens from the shortest shooting distance position focusing on the shortest shooting distance to the infinity position side focusing on infinity. While the AF search is performed by moving in the first direction, the focus lens is moved from the infinity position side to the shortest shooting distance position side when the parallax amount detection unit succeeds in detecting the parallax amount. The stereoscopic imaging apparatus according to claim 1, wherein the AF search is performed by moving in a second direction toward the head. An AF search start position calculating means for calculating an AF search start position indicating a position of the focus lens for starting the AF search based on the approximate distance calculated by the approximate distance calculating means;
When the parallax amount detection unit fails to detect the parallax amount, the AF search control unit moves the focus lens from the shortest shooting distance position focusing on the shortest shooting distance to the infinity position side focusing on infinity. The focus lens is moved to perform the AF search, and when the parallax amount detection unit succeeds in detecting the parallax amount, the infinite number of times is determined from the AF search start position calculated by the AF search start position calculation unit. The stereoscopic imaging apparatus according to claim 1, wherein the AF search is performed by moving the focus lens toward a far position.   5. The stereoscopic imaging apparatus according to claim 4, wherein the AF search start position calculation unit narrows the moving range of the focus lens as the depth of field of the photographing optical system used for the AF search is shallower. .   The AF search control means increases the step width for moving the focus lens each time the contrast value is calculated during the AF search, as the depth of field of the photographing optical system used for the AF search is deeper. The three-dimensional imaging device according to claim 4, wherein: When the focus lens is moved to the in-focus lens position, it is on the shortest shooting distance position side based on the contrast value obtained by the AF search and the position of the focus lens from which the contrast value is obtained. First subject distance calculation means for calculating a substantially accurate main subject distance to the main subject and a substantially accurate sub subject distance to the sub subject behind the main subject;
Aperture value calculation means for calculating an aperture value of the photographing optical system based on the main and sub-subject distances so that the sub-subject falls within the depth of field by depth-of-field calculation;
Second aperture value adjusting means for adjusting the aperture value based on the calculation result of the aperture value calculating means;
The stereoscopic imaging apparatus according to claim 1, further comprising: Based on the contrast value obtained by the AF search and the position of the focus lens from which the contrast value was obtained, a substantially accurate main subject distance to the main subject on the shortest shooting distance position side, and the main A second subject distance calculating means for calculating a substantially accurate sub subject distance to a sub subject behind the subject;
Based on the main and sub-subject distances, the focus setting distance corrected to the infinity position side to the position where the sub-subject enters within the depth of field is calculated by the depth-of-field calculation, and the calculated focus setting distance The stereoscopic imaging apparatus according to claim 1, further comprising: a focusing lens position determining unit that determines the focusing lens position based on the focus lens position.   The parallax amount detection unit detects the parallax amount based on a person image included in the first image and the second image. The three-dimensional imaging device described in 1. A first imaging optical system including a focus lens, a first imaging unit having a first imaging element on which a subject image is formed via the first imaging optical system, and a second imaging including a focus lens A focus control method for performing focus control of the focus lens using an optical system and a second imaging unit having a second imaging element on which a subject image is formed via the second imaging optical system. There,
The first image acquired by the first image sensor and the second image acquired by the second image sensor are analyzed, and the position of the subject in the first image and the subject A parallax amount detection step of detecting a parallax amount corresponding to a difference from a position in the second image;
An approximate distance calculating step of calculating an approximate distance to the subject based on the parallax amount;
A lens movement range determination step for determining a movement range of the focus lens for determining a focus lens position of the focus lens based on the approximate distance;
An AF search step of performing an AF search for calculating a contrast value of at least one of the first image and the second image while moving the focus lens within the moving range;
A focusing step of determining the focus lens position at which the focus lens focuses on the subject based on the contrast value obtained by the AF search, and moving the focus lens to the determined focus lens position; ,
A focusing control method comprising:

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