JP2009092747A - Imaging apparatus and imaging method - Google Patents

Abstract

To keep in focus on an intended subject.
A subject is focused, and a distance Df from the focused focus lens position F to the subject is calculated. Next, assuming the maximum speed Vf_max at which the subject moves, the distance to the subject that has moved per unit time (for example, 1 second) is assumed. The focus lens position corresponding to the distance to the subject moved is obtained, and based on these differences, the maximum drive speed Vaf_max_far in the far direction of the focus lens and the maximum in the near direction of the focus lens The drive speed Vaf_max_near is calculated and set to the maximum follow-up speed of the AF operation. The present invention can be applied to a digital video camera, a digital still camera, and the like.
[Selection] Figure 2

Description

  The present invention relates to an imaging apparatus and an imaging method, and more particularly to an imaging apparatus and an imaging method suitable for detecting a subject such as a human face from an image and automatically focusing on the detected subject.

  Conventionally, there are many digital cameras having an autofocus function.

  In a digital camera having an autofocus function, a focus detection area is provided in the center of an image generated by an image sensor such as a CCD, or a plurality of focus detection areas are provided on the image, and the image in the focus detection area is passed through a high-pass filter. Thus, contrast information is extracted, and focus control is performed using the extracted contrast information as a focus evaluation value. That is, when the focus of the digital camera is focused on the subject, the focus lens is moved so that the contrast information (focus evaluation value) is maximized based on the sharp contrast of the image in the focus detection area. This realizes the autofocus function.

  By the way, in general camera photography, a person is often the main subject. However, a person as a main subject does not necessarily exist in the focus detection area in the composition.

  Therefore, by analyzing the image to detect the human face and providing a focus detection area on the detected face, it is possible to focus on the subject wherever the subject (human face) exists in the image. The technique which can be performed is proposed (for example, refer patent document 1).

  However, in reality, the contrast of a human face is relatively small, and it is difficult to perform focus control based on the contrast information of the face. Therefore, the focus detection area is expanded to include the detected face contour, or the focus detection area is expanded to include the neck and shoulders that exist below the detected face. A technique for focusing is proposed (for example, see Patent Document 1).

JP 2003-107335 A JP 2006-227080 A

  By the way, when the focus detection area is set so as to include the outline of the face, it takes some processing time to detect the face, so the photographer suddenly changes the shooting direction (steep pan, tilt, etc.) ), Or when the subject person moves quickly, the face may not exist in the focus detection area set as the face is present.

  In such a case, as shown in FIG. 1A, when an object having a strong contrast (in the case of FIG. 1A) exists in the background, the influence is focused on an unintended object (in the case of FIG. 1A) Can occur.

  Alternatively, as shown in FIG. 1B, when an obstacle (in the case of FIG. 1B, another person) passes temporarily in front of the person to be followed, it focuses on an unintended obstacle due to the influence. Can occur.

  The present invention has been made in view of such a situation, and even if an object with a high contrast exists in the background of the intended subject or an obstacle appears in front of the intended subject, the effect is reduced. This makes it possible to continue focusing on the intended subject without receiving it.

  An imaging apparatus according to an aspect of the present invention, in an imaging apparatus having an autofocus function, detects a subject from a captured image and drives a focus lens to focus the detected subject. Focus control means, estimation means for estimating the detected moving speed of the subject, acquisition means for acquiring the detected distance to the subject, estimated moving speed of the subject, and the acquired subject Determining means for determining an upper limit value of the driving speed of the focus lens based on the distance up to.

  The detection means may detect the face of the subject from the captured image.

  The acquisition unit may acquire the detected distance to the subject based on the size of the face of the subject detected from the captured image.

  The acquisition unit may acquire the detected distance to the subject based on the adjustment position of the focus lens.

  The determining means may determine the upper limit value in the close direction of the driving speed of the focus lens to a value larger than the upper limit value in the far direction.

  The estimation means can determine the feature of the detected subject and estimate the movement speed of the subject by referring to the determined feature of the subject with a table prepared in advance. .

  An imaging method according to an aspect of the present invention includes a detection unit that detects a subject from a captured image, and a focus control unit that drives a focus lens to focus the detected subject. In the imaging method of the imaging apparatus having a function, the movement speed of the detected subject is estimated, the distance to the detected subject is acquired, the estimated movement speed of the subject, and the acquired subject Determining an upper limit value of the driving speed of the focus lens based on the distance.

  In one aspect of the present invention, the moving speed of the detected subject is estimated and the distance to the subject is acquired. Based on the estimated moving speed of the subject and the acquired distance to the subject, the focus lens An upper limit value of the driving speed is determined.

  According to one aspect of the present invention, focus can be controlled based on contrast information of a focus detection area.

  In addition, according to one aspect of the present invention, even if an object with high contrast exists in the background of the intended subject or an obstacle appears in front of the intended subject, the intention is not affected. It is possible to keep focusing on the subject to be focused.

  Embodiments of the present invention will be described below. Correspondences between the constituent elements of the present invention and the embodiments described in the specification or the drawings are exemplified as follows. This description is intended to confirm that the embodiments supporting the present invention are described in the specification or the drawings. Therefore, even if there is an embodiment which is described in the specification or the drawings but is not described here as an embodiment corresponding to the constituent elements of the present invention, that is not the case. It does not mean that the form does not correspond to the constituent requirements. Conversely, even if an embodiment is described here as corresponding to a configuration requirement, that means that the embodiment does not correspond to a configuration requirement other than the configuration requirement. It's not something to do.

  An imaging apparatus according to one aspect of the present invention is a detection unit (for example, the face of FIG. 4) that detects a subject from an image captured in an imaging apparatus (for example, the digital video camera 10 of FIG. 1) having an autofocus function. A detection unit 51), a focus control means (for example, the focus control unit 56 in FIG. 4) for driving a focus lens to focus the detected subject, and an estimation for estimating the detected moving speed of the subject. Means (for example, the feature determination unit 52 in FIG. 4), acquisition means (for example, the distance calculation unit 53 in FIG. 4) for acquiring the detected distance to the subject, the estimated moving speed of the subject, and Determination means for determining an upper limit value of the driving speed of the focus lens based on the acquired distance to the subject (for example, the tracking speed in FIG. 4). Including a tough 54) and.

  Hereinafter, specific embodiments to which the present invention is applied will be described. Before that, a basic outline of the present invention will be described.

  The present invention limits the speed at which the focus lens is driven (hereinafter referred to as the AF operation tracking speed) after focusing on the intended object (reducing the AF operation tracking speed), thereby reducing the intended object. Even if an object with a high contrast exists in the background of an object or an obstacle appears in front of the intended subject, it is not affected by this and continues to focus on the intended subject. is there.

  Such limitation of the tracking speed of AF operation is limited in the movement speed of the person who is the intended subject, and the relative speed between the imaging device and the person who is the subject is not so high in general human photography. Therefore, it is based on the fact that there is no inconvenience even if the tracking speed of AF operation is reduced.

  Specifically, the intended subject is focused, and the distance Df to the subject is calculated based on the focus lens position F in the focused state (or the distance Df to the focused subject is optically calculated). taking measurement). Next, assuming the maximum speed Vf_max at which the subject moves, the distance to the subject moved in unit time (for example, 1 second) is assumed. Then, referring to the optical system characteristic curve of the imaging apparatus (the horizontal axis indicates the focus lens position, and the vertical axis indicates the in-focus distance) as shown in FIG. 2, the focus lens corresponding to the distance to the moved subject, respectively. Determine the position, and based on these differences, calculate the maximum driving speed Vaf_max_far in the far direction of the focus lens and the maximum driving speed Vaf_max_near in the near direction of the focus lens to follow the AF operation Set to the maximum speed.

  As is clear from FIG. 2, the maximum driving speed of the focus lens toward the Far side is different from the maximum driving speed Vaf_max_near of the focus lens toward the Near side, and the maximum driving speed of the focus lens toward the Near side is different. Speed Vaf_max_near has a larger value.

  Next, a configuration example of a digital video camera according to an embodiment of the present invention will be described with reference to FIG. The digital video camera 10 mainly includes an imaging lens 11 that condenses an optical image of a subject on an image sensor 12, an image sensor 12 that converts the collected optical image into an electrical image signal, and predetermined analog image processing. An analog signal processing unit 13 that performs digital image processing, an A / D conversion unit 14 that digitizes an image signal, and a digital signal processing unit 15 that performs predetermined digital image processing.

  The digital video camera 10 includes a liquid crystal panel 16 that displays captured images and various types of information, a viewfinder 17 that is used for determining a composition, and a recording device 18 that records captured image signals. The

  Furthermore, the digital video camera 10 includes a control unit 23 that controls each unit of the digital video camera 10, an operation unit 24 that receives various operations from the user, and a distance measurement sensor 28 that optically measures the distance to the subject. .

  The imaging lens 11 includes a zoom lens that can continuously change the focal length, a focus lens that is moved to focus on the subject, an iris that changes the diameter of the aperture, an ND mechanism that inserts an ND filter, and camera shake during imaging. It consists of a shift anti-shake type camera shake correction lens.

  The image sensor 12 is configured by CCD or CMOS, generates an analog image signal by photoelectric conversion of the collected optical image, and outputs the analog image signal to the analog signal processing unit 13. The analog signal processing unit 13 performs analog image processing such as noise removal on the image signal from the image sensor 12 and outputs the image signal to the A / D conversion unit 14.

  The digital signal processing unit 15 performs digital image processing such as gamma correction on the image signal digitized by the A / D conversion unit 14.

  The recording device 18 records an image signal on a removable recording medium such as a semiconductor memory, a disk-shaped recording medium, or a tape-shaped recording medium.

  The timing generator (TG) 19 controls the charge discharge timing (that is, the image signal generation timing) to the image sensor 12. The motor driver 20 controls a motor 21 that drives a focus lens included in the imaging lens 11 and a motor 22 that drives a zoom lens.

  The operation unit 24 includes buttons and switches provided on the casing of the digital video camera 10 or a touch panel provided so as to be superimposed on the liquid crystal panel 16, and accepts a recording start / stop operation, a zoom operation, and the like from the user. The corresponding operation signal is output to the control unit 23.

  The control unit 23 controls various processes performed by the digital video camera 10 by the built-in CPU executing programs stored in the program ROM 26.

  Specifically, for example, the control unit 23 detects a face of a person who is a subject from an image supplied from the digital signal processing unit 15, an AF process for focusing on the detected face, and brightness adjustment AE processing for performing white balance and WB processing for performing white balance. Further, the control unit 23 performs a follow-up speed determination process for determining the follow-up speed of the AF operation.

  The EEPROM 25, which is a non-volatile memory, stores image signals, various auxiliary information, and setting information. The program ROM 26 stores various calculation parameters and the like in addition to a program executed by the CPU built in the control unit 23. The RAM 27 stores a program executed by the CPU built in the control unit 23, parameters that change as appropriate in the execution of the program, and the like.

  FIG. 4 is a functional block diagram for performing the various processes described above, which is realized by the control unit 23 executing a program.

  The face detection unit 51 detects a face of a person as a subject from the image supplied from the digital signal processing unit 15, and performs face detection processing for outputting the size, position, angle, and face image as face detection information. Do.

  In order to detect a human face from an image, a plurality of reduced images obtained by reducing the captured image at a plurality of different reduction ratios are generated, and a plurality of template groups in which brightness distribution information of the prepared face is recorded This can be realized by matching. Note that the template group includes a template in which luminance distribution information with the face tilted is recorded. This template is inclined with respect to each of the XYZ axes of the three-dimensional orthogonal coordinate system of the face, and the face inclination in the image can be determined by matching with this template. Further, the face position can be determined by matching the reduced image with the template while gradually shifting the reduced image. Furthermore, the face size can be obtained from the reduction rate of the matched reduced image. Note that a method disclosed in Japanese Patent Application Laid-Open No. 2004-133737 may be applied to a method for detecting a human face from an image.

  When a plurality of faces are detected in the image, the user selects one of the plurality of faces as the subject of interest, or selects a subject that matches a condition preset by the user. Alternatively, one is selected by the face detection unit 51.

  Examples of the conditions set in advance by the user include priority orders such as race, selection, and age.

  In order for the face detection unit 51 to select one of a plurality of faces, for example, there is a method using the size of each face and the distance from the center of the screen as indices. That is, for example, a plurality of faces whose size exceeds a predetermined threshold value is selected, and the largest face among the selected faces is selected. When there are a plurality of largest faces, the face with the shortest distance from the center of the image is selected. If there is no face whose size exceeds a predetermined threshold, the face with the shortest distance from the center of the image is selected.

  The feature determination unit 52 extracts a facial feature amount based on the face detection information from the face detection unit 51, and determines the race, sex, age, and physique of the person who becomes the subject based on the extracted feature amount. . Furthermore, the moving speed of the person who is the subject is estimated based on these determination results.

  The distance calculation unit 53 calculates the distance to the face detected by the face detection unit 51 (details will be described later). Note that the distance measured by the distance measuring sensor 28 may be adopted.

  The tracking speed determination unit 54 determines the tracking speed of the AF operation based on the distance to the detected face calculated by the distance calculation unit 53 and the moving speed of the person who is the subject estimated by the feature determination unit 52. Follow-up speed determination processing is performed (details will be described later).

  The focus determination unit 55 determines whether the image supplied from the digital signal processing unit 15 is in focus. Specifically, if the difference between the distance calculated by the distance measuring sensor 28 and the current in-focus distance such as the imaging lens 11 is within the depth of field, it is determined that the in-focus state is reached. Alternatively, a focus detection area is set for the detected face, and when the contrast information (focus evaluation value) in the focus detection area is maximum, it is determined that the focus state is achieved.

  The focus control unit 56 controls the motor driver 20 that controls the motor 21 that drives the focus lens based on the determination result by the focus determination unit 55, but at this time, the maximum value of the determined following speed is not exceeded. Control to follow. Note that the focus control unit 56 holds a restriction mode flag indicating whether or not the following speed is restricted, and restricts the following speed when the restriction mode flag is valid. If it is invalid, the tracking speed is not limited. In the initial state, the restriction mode flag is invalid. Note that the restriction mode flag valid / invalid switching will be described later.

  Here, two types of methods for calculating the distance to the face detected by the face detection unit 51 by the distance calculation unit 53 will be described.

  In the first type of method, the focus lens position F when the focus determination unit 55 determines that the face detected by the face detection unit 51 is in focus is acquired, and the imaging lens 11 illustrated in FIG. The focus distance Df is calculated based on the characteristic curve (the horizontal axis indicates the focus lens position, and the vertical axis indicates the focus distance), and is set as the distance to the face.

In the second type of method, using the detected face size WF, focal length f, and basic physical laws of the optical system shown in FIG. The distance Df can also be obtained.
Df = Wref × (f / Wi) × (Ww / Wf) (1)
Wref: Human face size standard value
Wi: Image sensor size f: Focal length
Wf: Face size [pixel] (detection value)
Ww: Size of all images used for face detection [pixels]

  However, the method using the basic physical law of the optical system shown in FIG. 6 has a problem that an error occurs in the distance Df to the face. That is, as shown in FIG. 7, the focus lens position F when the in-focus evaluation value is maximum, ΔFn is assumed to be the shift in the closest direction, ΔFf is the shift in the far direction, and the focus lens position (F− This is when the focus distance Dff corresponding to ΔFf) spreads out in the farthest direction. Conversely, the focus distance Dfn corresponding to the focus lens position (F + ΔFn) is when the error spreads in the closest direction.

  The cause of this error is that all subjects existing within the depth of field are in focus, so when the depth of field is deep, the change in the focus evaluation value becomes dull and the resolution of the focusing distance is low. There are two points, that is, that a resolution equal to or higher than the drive unit of the focus lens cannot be obtained.

  Furthermore, the method using the basic physical laws of the optical system shown in FIG. 6 has the following problems because it uses the size of the face. That is, the size of the face may vary depending on the race, gender, age, physique, etc. of the person, and there are limits on the ability of template matching used for face detection (resolution of the actual image reduction ratio, etc.). Can be mentioned.

  The first problem described above can be dealt with by having multi-dimensional table data that gives an appropriate error range to the standard value Wref of the face size. As shown in FIG. 8, this multidimensional data table is a set of tables having data in independent dimensions for each race difference, sex difference, age difference, and physique difference.

  In the feature determination unit 52, it is possible to perform race discrimination, gender discrimination, age (may be age) discrimination, and physique discrimination by using facial part recognition and individual authentication techniques. The range can be estimated small. Note that it is not essential to discriminate all of race, sex, age, and physique. If one or more of these items can be discriminated, the error range can be reduced.

  In the case of FIG. 8, the error range (variation) of the standard value Wref of the face size is obtained using the person type table, and the error range (variation) of the standard value Wref is obtained using the gender table with the race as a parameter. The error range (variation) of the standard value Wref is obtained from the age-specific table with the species and gender as parameters, and the error range (variation) of the standard value Wref is obtained from the physique-specific table with the race, gender and age as the parameters. .

  The second problem described above can be dealt with by having a face detection error rate table. Face detection error is a problem that can occur independently regardless of race, gender, age, or physique. Although an increase in the number of templates and an increase in the number of positions for confirming the matching between the reduced image and the template can be expected to improve the accuracy of face detection, there is a limit. In particular, when the face is dark, the error increases, and when the face tilt increases, the error increases.

  Accordingly, it is necessary to prepare a face detection error rate table corresponding to the three items of the limit of performance, the brightness that is disadvantageous for detection, and the tilt of the face. In addition, it is necessary to consider an error in the size of the detected face. Therefore, in this error rate table, face brightness, face tilt, and face size are used as parameters.

  When the countermeasures for the two problems described above are integrated, the relationship shown in FIG. 9 is obtained.

  First, with respect to the detected face size Wf, the brightness, inclination, and size of the face are used as parameters, and the face size Wsmall when it is determined to be small as an error is determined to be large as an error. Find the big face size Wbig.

  Next, the variation of the standard value Wref of the face size is obtained. The standard value of the face size without deviation is Wref_default, the deviation in the assumed large direction is ΔWref_big, and the deviation in the small direction is ΔWref_small.

And in Wref and Wf of equation (1),
Wref = Wref_default + ΔWref_big
Wf ＝ Wsmall
Is substituted to calculate the value Dff when the far-direction error of the distance to the face is most widened.

Also,
Wref = Wref_default−ΔWref_small
Wf = Wbig
Is substituted to calculate a value Dfn when the error in the closest direction of the distance to the face is most widened.

  Note that a combination of two methods for calculating the distance Df to the detected face may be used. That is, when the distance Df is estimated from the focus lens position F at which the focus evaluation value is maximum as in the first type of method, the depth of field is deep particularly on the wide angle side, and the focus lens is driven. It is difficult to estimate an accurate distance under the influence of the low resolution of the focusing distance for the unit.

  Therefore, for example, the second type method may be applied on the wide angle side, and the first type method may be applied on the telephoto side. Thus, by using a combination of two types of methods, the distance Df to the face can be calculated more accurately.

  Next, a tracking speed determination process for determining the tracking speed of the AF operation by the tracking speed determination unit 54 will be described.

  In the tracking speed determination process, as outlined with reference to FIG. 2, the maximum speed Vf_max at which the subject moves is assumed, and the distance to the subject that has moved per unit time (for example, 1 second) is assumed. The focus lens position corresponding to the distance to the subject is obtained, and based on these differences, the maximum drive speed Vaf_max_far in the far direction of the focus lens and the maximum drive in the near direction of the focus lens The speed Vaf_max_near is calculated.

  Note that the maximum speed Vf_max at which the subject moves, as shown in FIG. 10, is a table prepared in advance corresponding to the race, sex, age, and physique determined for the subject person, It is determined (estimated) by the feature determination unit 52 with reference to a table prepared in advance corresponding to the shooting mode (snow mode, sports lesson mode, portrait, etc.) in which the movement of the flying value is estimated.

  As apparent from FIG. 2, due to the characteristics of the imaging optical system, the amount of change of the focus lens with respect to the change of the focus distance on the near side is larger than that on the far side, so the limit speed Vaf_max_near in the near direction is Set to a value greater than the direction limit speed Vaf_max_far.

  For the same reason, when considering the error of the distance to the face, if the AF tracking speed is calculated based on the in-focus distance Dfn corresponding to the state with the most variation on the closest side, the variation will occur. It is possible to deal with all the ranges where can occur.

  Next, a process of limiting the tracking speed of the AF operation (referred to as a tracking speed limiting process) by the control unit 23 will be described with reference to the flowchart of FIG.

  In step S1, the focus control unit 56 determines whether or not to limit the follow-up speed of the AF operation based on the limit mode flag held by itself, and if it determines not to limit, the process proceeds to step S2. On the other hand, if it is determined to be restricted, the process proceeds to step S7.

  In this determination, when the restriction mode flag is valid, it is determined that the tracking speed of the AF operation is limited. When the restriction mode flag is invalid, it is determined that the tracking speed of the AF operation is not limited. In this case, since it is an initial state, the restriction mode flag is invalid. Therefore, it is determined not to limit the tracking speed of the AF operation, and the process proceeds to step S2.

  In step S <b> 2, the focus control unit 56 determines whether or not a face is detected by the face detection unit 51 from the captured image. If it is determined that a face has been detected, the process proceeds to step S3. In step S3, the focus control unit 56 determines the detected face as a tracking target (subject). When a plurality of faces are detected, one face is selected and determined as a tracking target.

  In step S4, the focus determination unit 55 determines whether or not the tracking target (detected face) is focused, and notifies the focus control unit 56 of the determination result. If it is determined that the subject is in focus, the process proceeds to step S5. In step S5, the focus control unit 56 changes the restriction mode flag held from invalid to valid. Thereafter, the process proceeds to step S11, and the upper limit of the following speed (maximum speed on the near side and the far side) is determined.

  Details of the process of step S11 will be described with reference to the flowchart of FIG.

  In step S31, the distance calculation unit 53 obtains (calculates or measures) a distance Df to the tracking target. In step S <b> 32, the feature determination unit 52 assumes a maximum speed Vf_max at which the subject moves with respect to the maximum movement speed with respect to the tracking target (the person with the face that became the face). In step S33, the tracking speed determination unit 54 determines the maximum driving speed Vaf_max_far in the far direction of the focus lens and the near direction of the focus lens based on the distance Df to the tracking target and the maximum speed Vf_max. The maximum drive speed Vaf_max_near is calculated.

  Thereafter, the process proceeds to step S12 in FIG. 11 to perform the AF process. Then, the process returns to step S1.

  If it is determined in step S4 that the subject to be tracked is not in focus, the process proceeds to step S6. In step S6, the focus control unit 56 sets the fastest speed without limiting the AF tracking speed. Thereafter, the process proceeds to step S12, and an AF operation is performed.

  In step S1 again, it is determined whether to limit the tracking speed of the AF operation. If the restriction mode flag is valid, it is determined that the follow-up speed of the AF operation is restricted, and the process proceeds to step S7.

  In step S <b> 7, the face detection unit 51 determines whether or not the tracking target is recognized (detected), and notifies the focus control unit 56 of the determination result. If it is determined that the tracking target is recognized (detected), the process proceeds to step S8.

  In step S8, the focus control unit 56 resets the recognition count value for the current tracking target to a predetermined maximum value. Here, the recognition count value is a value provided in order to allow time to return to the fastest speed without immediately stopping the tracking speed limit even when the tracking target cannot be recognized temporarily. is there.

  In step S <b> 9, the focus determination unit 55 determines whether or not the tracking target is focused, and notifies the focus control unit 56 of the determination result. If it is determined that the subject to be tracked is in focus, the process proceeds to step S10.

  In step S10, the focus control unit 56 resets the focus count value for the current tracking target to a predetermined maximum value. Here, the in-focus count value is provided in order to allow time to return to the fastest speed without immediately stopping the limit of the follow-up speed even when the object to be followed cannot be focused temporarily. Value.

  Thereafter, the process proceeds to step S11, and based on the latest distance Df to the tracking target and the maximum speed Vf_max, the maximum driving speed Vaf_max_far in the far direction of the focus lens and the focus lens near (Near) The maximum driving speed Vaf_max_near in the direction is updated.

  If it is determined in step S7 that the tracking target cannot be recognized (detected), the process proceeds to step S13. In step S13, the focus control unit 56 decrements the recognition count value for the current tracking target by one. In step S14, the focus control unit 56 determines whether or not the recognition count value for the current tracking target has become 0. If the recognition count value has not become 0, the process proceeds to step S11.

  On the other hand, when the recognition count value becomes 0, the process proceeds to step S15, and the retained restriction mode flag is changed from valid to invalid. Thereafter, the process proceeds to step S6.

  Also, if it is determined in step S9 that the subject to be tracked is not in focus, the process proceeds to step S13. In step S13, the focus control unit 56 decrements the in-focus count value for the current tracking target by 1. In step S14, the focus control unit 56 determines whether or not the focus count value for the current tracking target has become 0. If the focus count value is not 0, the process proceeds to step S11. Proceed.

  On the other hand, when the focus count value becomes 0, the process proceeds to step S15, and the retained restriction mode flag is changed from valid to invalid. Thereafter, the process proceeds to step S6.

  This follow-up speed limiting process is repeatedly executed while shooting is being performed. This is the end of the description of the follow-up speed limiting process.

  As described above, according to the digital video camera 10 to which the present invention is applied, an autofocus operation that follows the face of a person can be performed stably and accurately.

  In this embodiment, a human face is detected and focused and followed. However, a part other than the face may be detected and focused and followed.

  Further, the present invention is not limited to capturing moving images, but can be applied to capturing still images.

  According to the digital video camera 10 to which the present invention is applied, even when there are a plurality of people in the image, it is possible to stably focus on the intended person.

  In this embodiment, a human face is detected and followed, but a part other than the face may be detected and followed.

  The present invention can be applied to an imaging apparatus such as a digital still camera having an AF function in addition to a digital video camera.

  The embodiments of the present invention are not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.

It is a figure for demonstrating the conventional problem. It is a figure which shows an optical system characteristic curve. It is a block diagram which shows the structural example of the digital video camera to which this invention is applied. It is a figure which shows the structural example of the functional block implement | achieved by the control part of FIG. It is a figure which shows the characteristic curve of an imaging lens. It is a figure for demonstrating the method of calculating | requiring the distance to a face based on the magnitude | size of a face, and a focal distance. It is a figure for demonstrating the error of the distance to the face in FIG. It is a figure which shows the example of the dispersion | variation table according to the feature of the detected face. It is a figure which shows the difference | error of the distance to the face of a far side and a near side. It is a figure for demonstrating the process which estimates the maximum speed of a to-be-photographed object. It is a flowchart explaining a follow-up speed restriction process. It is a flowchart explaining follow-up speed upper limit determination processing.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Digital video camera, 11 Imaging lens, 12 Image sensor, 13 Analog signal processing part, 14 A / D conversion part, 15 Digital signal processing part, 20 Motor drive, 23 Control part, 24 Operation part, 28 Distance sensor, 51 Face detection unit, 52 feature determination unit, 53 distance calculation unit, 54 tracking speed determination unit, 55 focus determination unit, 56 focus control unit

Claims (7)

In an imaging device having an autofocus function,
Detection means for detecting a subject from the captured image;
Focus control means for driving a focus lens to focus on the detected subject;
Estimating means for estimating the moving speed of the detected subject;
Obtaining means for obtaining a distance to the detected subject;
An imaging apparatus comprising: a determining unit that determines an upper limit value of the driving speed of the focus lens based on the estimated moving speed of the subject and the acquired distance to the subject. The imaging apparatus according to claim 1, wherein the detection unit detects a face of the subject from a captured image. The imaging apparatus according to claim 2, wherein the acquisition unit acquires the detected distance to the subject based on the size of the face of the subject detected from the captured image. The imaging apparatus according to claim 1, wherein the acquisition unit acquires the detected distance to the subject based on an adjustment position of the focus lens. The imaging apparatus according to claim 1, wherein the determining unit determines an upper limit value in a close direction of a driving speed of the focus lens to a value larger than an upper limit value in a far direction. The said estimation means determines the feature of the detected said subject, and estimates the moving speed of the said subject by referring the determined said feature of the said subject with the table prepared previously. Imaging device. Detection means for detecting a subject from the captured image;
Focus control means for driving a focus lens to focus on the detected subject,
In an imaging method of an imaging apparatus having an autofocus function,
Estimating the moving speed of the detected subject,
Get the distance to the detected subject,
An imaging method including a step of determining an upper limit value of the driving speed of the focus lens based on the estimated moving speed of the subject and the acquired distance to the subject.

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