JP2010183145A - Photographing device and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a useless focusing operation, without rebooting a focusing operation if a distance to an object to be tracked does not change, once the object to be tracked is focused. <P>SOLUTION: When focusing operation of a contrast detection system is performed in continuous AF mode, the photographing device 100 moves a tracking block so as to track for a main object M. Once the main object M is focused, the photographing device 100 subsequently computes a correlation value E2 between a tracking block in the newest frame image and a tracking block in a frame image photographed at the last focusing operation point. When it is determined that the correlation value E2 is smaller than a threshold Eth, the photographing device 100 does not reboot the focusing operation. Thereby, a useless focusing operation can be prevented. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a photographing apparatus, and more particularly, to a photographing apparatus for focusing.

  Conventionally, a digital camera generally has an autofocus (hereinafter abbreviated as AF) function for automatically focusing. Conventionally, a contrast detection method has been widely used as an autofocus method. In this contrast detection method, the AF evaluation value is used to determine the in-focus position (the lens position of the focus lens when in focus). This AF evaluation value is an evaluation value indicating the degree of focus. In a digital camera, an AF evaluation value is a high-frequency component of an image obtained from an image sensor or a luminance difference component of adjacent pixels on the image.

  The digital camera sequentially acquires AF evaluation values of images taken when the focus lens is at each lens position while moving the focus lens back and forth in the optical axis direction. Then, the focus lens is stopped at the lens position of the focus lens when the AF evaluation value becomes the largest, and the focusing operation is completed.

  However, even when the digital camera focuses on the subject by the focusing operation, if the subject moves and the distance to the subject changes after that, the subject after the movement cannot be focused.

  Therefore, there is a digital camera capable of setting a continuous autofocus (hereinafter abbreviated as “continuous AF”) mode in which the subject is always focused by continuously restarting the focusing operation. . According to the continuous AF, since the focusing operation is restarted even when the subject moves, it is possible to always focus on the moving subject.

  In this continuous AF mode, as a method of restarting the focusing operation by the contrast detection method, the focusing operation for moving the focus lens is temporarily ended and then unconditionally at a fixed time interval (for example, 1 second). There is a method of restarting the focusing operation and moving the focus lens again.

  However, the conventional method of restarting the focusing operation by the continuous AF method has the following problems. In the conventional method in which the focusing operation is restarted at regular time intervals, focusing is performed unconditionally regardless of whether or not the focusing state (in-focus state) in the previous focusing operation is maintained. The operation is restarted. For this reason, if the focusing operation is restarted when the in-focus state in the previous focusing operation is maintained, useless movement of the focus lens is performed. Furthermore, if the focus lens is moved unnecessarily by driving means such as a motor during the focusing operation, the current consumption increases and the battery life is shortened.

  Therefore, the technique described in Patent Document 1 is based on the correlation value between the latest image obtained every predetermined time for live view display and the previous image that is the immediately preceding image when the continuous AF mode is set. Thus, a change in framing and a movement of a main subject located in a specific area are detected (see FIG. 7 and the like). The technique described in Patent Document 1 once executes a focusing operation when the shutter button is half-pressed. Even if it is determined that the framing has changed, the focus operation is restarted if it is further determined that the in-focus state is maintained because the main subject located in the specific area has not moved. I try not to.

  In the technique described in Patent Document 1, since the focusing operation is restarted only when a change in framing or a movement of a main subject located in a specific area is detected, useless focusing operation in the continuous AF method Can be prevented.

JP 2003-244520 A

  However, in the technique described in Patent Document 1, only the movement of the main subject located in the specific area is determined with respect to the movement of the main subject. That is, with the technique described in Patent Document 1, it cannot be determined whether or not the main subject located in an arbitrary area other than the specific area has moved. Therefore, in the technique described in Patent Document 1, even when the main subject located in an arbitrary area other than the specific area is not moved and the focused state is maintained, the framing is changed. Always restarts the focusing operation, so that there is still a problem that the unnecessary focusing operation cannot be sufficiently prevented.

  Therefore, an object of the present invention is to prevent useless focusing operation.

In order to achieve the above object, the first aspect of the present invention provides:
Photographing means for photographing an image of a subject;
Focusing means for repeatedly performing a focusing operation to focus on the subject;
Tracking means for moving the tracking block so as to track the movement of the subject in the image photographed by the photographing means;
Calculating means for calculating a correlation value between the first tracking block on the image captured at the current time point and the second tracking block on the image captured when the focusing operation is performed;
A focusing control unit that does not cause the focusing unit to perform a focusing operation when the correlation value calculated by the calculation unit is smaller than a predetermined threshold;
It is characterized by providing.

In order to achieve the above object, the second aspect of the present invention provides:
Photographing means for photographing an image of a subject;
A focusing means for repeatedly performing a focusing operation to focus on the subject;
Tracking means for moving the tracking block so as to track the movement of the subject in the image photographed by the photographing means;
Calculating means for calculating a correlation value between the first tracking block on the image captured at the current time point and the second tracking block on the image captured when the focusing operation is performed;
A focusing control unit that causes the focusing unit to perform a focusing operation only when the correlation value calculated by the calculating unit is equal to or greater than a predetermined threshold;
It is characterized by providing.

  According to the present invention, useless focusing operation can be prevented.

It is a block diagram which shows the structure of the imaging device which concerns on embodiment of this invention. It is a figure for demonstrating the method of the tracking process which concerns on embodiment of this invention. It is a figure which shows the structure of a storage area in a tracking image memory. It is a figure which shows the flow of operation | movement in the continuous AF mode which concerns on embodiment of this invention. It is a figure which shows the initial state of a tracking block and a search block. It is a figure which shows the movement of a tracking block and a search block accompanying the movement of a main subject.

  Hereinafter, based on the drawings, a photographing apparatus 100 according to an embodiment of the present invention will be described.

<Configuration of photographing apparatus>
FIG. 1 is a block diagram showing a functional configuration of the photographing apparatus 100 according to the present embodiment. The configuration of the photographing apparatus 100 according to the present embodiment will be described with reference to FIG. The photographing apparatus 100 can be configured by a digital camera or the like.

  The photographing apparatus 100 includes a control unit 10, a RAM 11, a ROM 12, an optical lens device 13, an optical system control unit 14, an optical system drive unit 15, a shutter device 16, a shutter control unit 17, and a shutter drive unit. 18, an image sensor 19, an image sensor drive unit 20, a pre-processing unit 21, an image memory 22, an image processing unit 23, a display control unit 24, a display unit 25, an operation unit 26, and a recording medium 27, a subject tracking unit 28, a tracking image memory 29, an AF evaluation unit 30, and a correlation value calculation unit 31.

  The control unit 10 controls the overall operation of the image capturing apparatus 100. The control unit 10 includes a CPU (Central Processing Unit), a real-time clock (Real Time Clock) that is a timing circuit, and the like.

  The RAM 11 functions as a working area when the control unit 10 executes each process. The RAM 11 is composed of a DRAM (Dynamic Random Access Memory) or the like. The ROM 12 stores programs and data necessary for the photographing apparatus 100 to execute each process. The ROM 12 is composed of a flash memory or the like. The control unit 10 uses the RAM 11 as a working area to execute each process in cooperation with a program stored in the ROM 12.

  The optical lens device 13 includes a focus lens, a zoom lens, and the like. The focus lens is a lens for forming a subject image on the light receiving surface of the image sensor 19.

  The optical system control unit 14 controls the optical system driving unit 15 according to the control by the control unit 10 to cause the optical system driving unit 15 to advance and retract the focus lens of the optical lens device 13 in the optical axis direction. Thereby, the position of the focus lens changes to adjust the focus. The optical system driving unit 13 is configured by a stepping motor or the like. The optical system control unit 14 includes a control circuit that controls the optical system driving unit 15.

  The shutter device 16 is a mechanism that functions as a mechanical shutter and also functions as an aperture that adjusts the amount of light of a subject image incident on the image sensor 19. The shutter device 16 includes shutter blades and the like.

  The shutter control unit 17 drives the shutter drive unit 18 according to control by the control unit 10. Specifically, the shutter control unit 17 controls the shutter drive unit 18 according to the control by the control unit 10 to cause the shutter drive unit 18 to open and close the shutter blades of the shutter device 16. Further, the shutter control unit 17 controls the shutter drive unit 18 according to the control by the control unit 10, thereby causing the shutter drive unit 18 to adjust the aperture of the shutter device 16. The shutter drive unit 18 includes a lever that kicks the shutter blades. The drive control unit 17 includes a control circuit that controls the shutter drive unit 18.

  The image sensor 19 is an element that photoelectrically converts (shoots) a subject image that is incident from the optical lens device 13 and formed on the light receiving surface. On the light receiving surface of the image sensor 19, photodiodes that are photoelectric conversion elements are arranged in a matrix. These photodiodes constitute each pixel of the image sensor 19. On each photodiode, color filters of R (red), G (green), and B (blue) are arranged according to the Bayer arrangement. The image sensor 19 photoelectrically converts the subject image at predetermined time intervals to store image signals under the control of the image sensor driving unit 20, and sequentially outputs the stored image signals as analog signals. The image sensor 19 is composed of a CCD (Charge Coupled Device) type image sensor or the like.

  The image sensor driving unit 20 drives the image sensor 19 according to the control by the control unit 10. The image sensor driving unit 20 generates various clock pulses and the like according to control by the control unit 10. The image sensor driving unit 20 reads out an analog signal representing the subject image from the image sensor 19 at regular intervals based on the generated various clock pulses and the control signal supplied from the control circuit 10. The image sensor driving unit 20 includes a timing generator that generates various clock pulses, a scanning circuit, and the like.

  The pre-processing unit 21 performs various signal processing such as correlated double sampling processing, gain control processing, and A / D (Analog / Digital) conversion processing on the analog signal supplied from the image sensor 19 to obtain a digital signal. Generate and output Bayer data. The preprocessing unit 21 is configured by an A / D converter or the like.

  The image memory 22 temporarily stores the Bayer data generated by the preprocessing unit 21 and the image data generated by the image processing unit 23. The image memory 21 is also used as a working area when the image processing unit 22 generates image data from Bayer data. The image memory 21 includes a DRAM (Dynamic Random Access Memory) or the like.

  The image processing unit 23 performs image processing such as white balance correction processing, γ correction processing, and YC conversion processing on the Bayer data stored in the image memory 22 to generate image data in which the luminance signal and the color difference signal are superimposed. To do. A subject is expressed by this image data. Further, when the shutter button is fully pressed, the image processing unit 23 generates image data for a captured image with a relatively high image quality and a large capacity. On the other hand, when displaying a live view image, the image processing unit 23 generates image data for a live view image with a relatively low image quality and a small capacity. The image processing unit 23 includes, for example, a DSP (Digital Signal Processor).

  The display control unit 24 converts the image data stored in the image memory 22 into an analog signal and outputs it under the control of the control unit 10. The display control unit 24 includes a VRAM (Video Random Access Memory), a D / A (Digital / Analog) converter, and the like.

  The display unit 25 displays an image represented by an analog signal supplied from the display control unit 24. The display unit 25 includes a liquid crystal display provided on the back surface of the housing of the photographing apparatus 100.

  The operation unit 26 receives various button operations from the user. The operation unit 25 includes a power button, a shutter button, a zoom button, a cursor key, a determination button, a menu button, and the like. The operation unit 26 supplies signals indicating various key operations received from the user to the control unit 10. The shutter button is configured to accept from the user a half-press operation for instructing shooting preparation (focusing operation or the like) and a full-press operation for instructing shooting. When these signals are received from the operation unit 26, the control unit 10 executes processing based on the received signals.

  The recording medium 27 records the image data generated by the image processing unit 23. The recording medium 27 includes a semiconductor memory card that can be attached to and detached from the photographing apparatus 100.

  The subject tracking unit 28 tracks a subject shown in the live view image. Various methods are known as methods for tracking one tracking block. The subject tracking unit 28 can employ any of these methods. The imaging apparatus 100 according to the present embodiment employs a known block matching method as a tracking processing method.

  With reference to FIG. 2, the tracking processing method in the present embodiment will be briefly described. In FIG. 2A, the symbol F (n-1) indicates the (n-1) th frame image (n is an arbitrary natural number). A symbol P (n−1) indicates a tracking block in the (n−1) -th frame image. In FIG. 2B, the symbol F (n) indicates the nth frame image taken. A symbol C (n) indicates a candidate block in the nth frame image. The code S (n) represents a search block to which the candidate block C (n) can move. In the present embodiment, it is assumed that the size of the search block S (n) in each sequentially captured frame image is equal to the size of one image area of each image area obtained by dividing the frame image into nine.

  The subject tracking unit 28 calculates a correlation value E1 between the tracking block P (n−1) and the candidate block C (n). At this time, the candidate block C (n) is moved one pixel at a time in the horizontal direction or the vertical direction in the search block S (n), and the correlation value E1 is calculated for each movement. The correlation value E1 is, for example, the sum of the absolute values of the luminance differences of the pixels at the same position between the tracking block P (n−1) and the candidate block C (n). This correlation value E1 is generally called SAD (Sum of Absolute Difference). Note that the correlation value may be obtained by the sum of squares of luminance difference (Sum of Squared Difference) or the like.

  The correlation value E1 (such as the luminance difference of each pixel) becomes smaller as the similarity between the tracking block P (n−1) and the candidate block C (n) is higher. Therefore, if the position of the candidate block C (n) having the smallest correlation value E1 is obtained, it can be determined where the tracking block P (n-1) is located in the nth frame image. As a result, a motion vector between P (n−1) of the (n−1) th frame image and the tracking block P (n) of the nth frame image is obtained. The subject tracking unit 28 repeatedly obtains a motion vector between temporally adjacent frame images, and sequentially moves the tracking block according to the motion vector, thereby tracking a subject that falls within the tracking block.

  Returning to FIG. 1, the tracking image memory 29 stores image data representing an image in the tracking block. The tracking image memory 29 is composed of a DRAM (Dynamic Random Access Memory) or the like.

  FIG. 3 is a diagram showing the configuration of the storage area of the tracking image memory 29. As shown in FIG. 3, the storage area of the tracking image memory 29 includes a first tracking image storage area 29a and a second tracking image storage area 29b. The first tracking image storage area 29a is a storage area for storing image data representing the inside of the tracking block in the latest frame image (the frame image taken at the current time point). In the first tracking image storage area 29a, every time new image data is stored, the image data stored immediately before is overwritten and deleted. The second tracking image storage area 29b is a storage area for storing image data representing the inside of the tracking block in the frame image taken at the previous focusing point (when the subject is focused by the previous focusing operation). is there. In the second tracking image storage area 29b, every time new image data is stored, the image data stored immediately before is overwritten and deleted.

  Returning to FIG. 1, the AF evaluation unit 30 extracts an AF evaluation value that is a high-frequency component from the image data stored in the image memory 22, and supplies the extracted AF evaluation value to the control unit 10. During the focusing operation, the control unit 10 drives the optical system driving unit 15 by controlling the optical system control unit 14 to move the focus lens of the optical lens device 13 forward and backward in the optical axis direction. Then, the control unit 10 causes the AF evaluation unit 30 to extract the AF evaluation value from the image data obtained when the focus lens is at each position. Then, the control unit 10 performs a focusing operation to stop the focus lens at the lens position where the AF evaluation value supplied from the AF evaluation unit 30 is the highest.

  The correlation value calculation unit 31 calculates a correlation value E2 between the tracking block in the latest frame image and the tracking block in the frame image taken immediately before the focusing. That is, the correlation value calculation unit 31 calculates the correlation value E2 between the image data stored in the first tracking image storage area 29a and the image data stored in the second tracking image storage area 29b. The correlation value E2 is, for example, the sum of absolute values (SAD) of the luminance differences of the pixels located at the same position between these image data. Note that the correlation value E2 may be obtained by the sum of squares of the luminance difference or the like.

  Here, the correlation value E2 (luminance difference of each pixel) is small between the tracking block in the latest frame image and the tracking block in the frame image taken immediately before focusing. It shows that there is. That is, in the above calculation method, the smaller the value of the correlation value E2, the greater the similarity between the tracking block in the latest frame image and the tracking block in the frame image taken immediately before the focusing.

  When the correlation value E2 is equal to or greater than the predetermined threshold Eth, the size of the subject in the tracking block has changed between the time when the frame image at the time of focusing was taken and the time when the latest frame image was taken. Conceivable. In this case, it is considered that the distance to the subject existing in the tracking block of the frame image shot at the time of focusing has changed between the shooting time of the frame image at the focusing time and the shooting time of the latest frame image. . On the other hand, when the correlation value E2 is smaller than the predetermined threshold Eth, the size of the subject shown in the tracking block changes between the time when the frame image at the time of focusing is taken and the time when the latest frame image is taken. It is thought that it is not. In this case, the distance to the subject existing in the tracking block of the frame image captured at the time of focusing is not changed between the time of capturing the frame image at the time of focusing and the time of capturing the latest frame image. Conceivable. Note that the predetermined threshold Eth is a value (experimental value or the like) at which the reactivation of the focusing operation actually works well.

<Operation of the photographing device>
FIG. 4 is a flowchart showing an operation in the continuous AF mode of the photographing apparatus 100 according to the present embodiment. The operation in the continuous AF mode performed by the image capturing apparatus 100 will be described with reference to FIG.

  Also in the continuous AF mode according to the present embodiment, the focusing operation is automatically executed repeatedly as in the normal continuous AF mode. Here, when the distance to the subject once focused has not changed, it is not necessary to restart the focusing operation. Therefore, in the continuous AF mode according to the present embodiment, the imaging apparatus 100 considers that the distance to the tracked subject has not changed once the subject tracked by the focusing operation is focused. In such a case, the focusing operation is not restarted. Thereby, useless focusing operation can be prevented. Moreover, since useless focusing operation can be prevented, the power required for the focusing operation can be reduced and the battery life can be extended.

  When the continuous AF mode is set by a predetermined operation on the operation unit 26 by the user, the photographing apparatus 100 reads out the program stored in the ROM 12 and shows it by the flowchart of FIG. 4 in cooperation with this program. Start processing.

  First, in step S1, the control unit 10 starts live view display. Specifically, the control unit 10 sequentially supplies frame images sequentially generated by the image processing unit 23 to the display control unit 24, thereby causing the display control unit 24 to display the frame image as a live view image on the display unit 25. Display.

  Next, in step S2, the control unit 10 determines whether or not the shutter button is half-pressed by the user. Specifically, the control unit 10 determines whether the shutter button is half-pressed by the user by monitoring a signal corresponding to the half-press operation of the shutter button from the operation unit 26. When determining that the shutter button is not half-pressed (step S2: NO), the control unit 10 continues the live view display until a signal corresponding to the half-press operation of the shutter button is detected. On the other hand, when it is determined that the shutter button is half-pressed (step S2: YES), the control unit 10 advances the process to step S3.

  Next, in step S <b> 3, the control unit 10 performs an initial setting of the tracking process. Specifically, the control unit 10 causes the subject tracking unit 28 to cut out an image within an AF frame located in a predetermined central area on the frame image taken at the time of step S3, and expresses the cut out image. The image data to be stored is stored in the first tracking image storage area 29a as the image data of the tracking block in the initial state. Further, the control unit 10 causes the subject tracking unit 28 to set the image region located at the center among the image regions obtained by dividing the frame image captured at the time of step S3 into nine as search blocks in the initial state.

  FIG. 5 is a diagram illustrating the tracking block P (1) in the initial state and the search block S (2) in the initial state. The tracking block P (1) is a tracking block in the first frame image taken after the control unit 10 detects a half-press operation of the shutter button. The search block S (2) is a search block in the second frame image photographed after the first frame image.

  In the present embodiment, as shown in FIG. 5, the face of the main subject M is positioned in the central region of the live view image by first changing the posture of the photographing apparatus 100 that the user holds in his / her hand. The composition is adjusted so as to be within the AF frame. In this state, when the user presses the shutter button halfway, the image data representing the face of the main subject M in the AF frame is the first tracking image memory 29a as the image data of the tracking block P (1) in the initial state. Is remembered. At this time, the image area located in the center among the image areas obtained by dividing the live view image (first frame image) into nine is set as the search block S (2) in the initial state.

  In step S3, the control unit 10 performs a first focusing operation according to the contrast detection method as an initial setting of the tracking process. During the focusing operation, the control unit 10 causes the AF evaluation unit 30 to calculate the AF evaluation value from the image area within the AF frame in the frame images sequentially captured at the time of step S3. Then, the control unit 10 controls the optical system driving unit 15 via the optical system control unit 14 to cause the optical system driving unit 15 to advance and retract the focus lens in the optical axis direction, and is supplied from the AF evaluation unit 30. The focus lens is stopped at the lens position with the highest AF evaluation value. As a result, the face of the main subject M in the AF frame is focused.

  Returning to FIG. 4, in step S <b> 4, the control unit 10 executes a tracking process. Specifically, the control unit 10 causes the subject tracking unit 28 to select a candidate block C (n) in the search block S (n) in the nth frame image that is the latest frame image at the time of step S4. Move one pixel at a time in the horizontal or vertical direction. The subject tracking unit 28 calculates a correlation value E1 between the tracking block P (n−1) and the candidate block C (n) in the (n−1) th frame image each time this movement is performed. The subject tracking unit 28 sets the position of the candidate block C (n) when the correlation value E1 is the smallest as the position of the tracking block P (n) in the nth frame image. Thus, the main subject M is tracked by setting the position of the tracking block in accordance with the movement of the main subject M. The control unit 10 causes the subject tracking unit 28 to cut out image data representing the tracking block P (n) from the n-th frame image, and stores the cut-out image data in the first tracking image storage area 29a. As a result, the image data stored in the first tracking image storage area 29a is updated from the image data of the tracking block P (n-1) to the image data of the tracking block P (n).

  In addition, the subject tracking unit 28 searches the (n + 1) th frame image so that the center of the search block S (n + 1) in the (n + 1) th frame image coincides with the center of the tracking block P (n). The position of block S (n + 1) is set.

  FIG. 6 is a diagram illustrating a state of the main subject M tracked by the tracking process. When the main subject M moves in the live view image, the tracking block P moves following the movement of the main subject M, and the search block S also moves so as to follow the movement of the tracking block P. Further, as illustrated in FIG. 6, the control unit 10 moves the AF frame displayed in the live view image in accordance with the movement of the main subject M.

  Returning to FIG. 4, in step S <b> 5, the control unit 10 determines whether or not a predetermined time (for example, 1 second) has elapsed. Specifically, the control unit 10 determines whether or not the elapsed time from when the determination in step S5 immediately before indicated by the timing circuit in the control unit 10 is YES has reached a predetermined time. Judging. When it is determined that the predetermined time has not elapsed (step S5: NO), the control unit 10 advances the process to step S10. On the other hand, when the control unit 10 determines that the predetermined time has elapsed (step S5: YES), the control unit 10 proceeds to step S6.

  Next, in step S6, the control unit 10 calculates a correlation value of the tracking block. Specifically, the control unit 10 causes the correlation value calculation unit 31 to acquire the image data of the tracking block in the latest frame image and the image data of the tracking block in the frame image captured immediately before the focusing. . That is, the subject tracking unit 28 reads out the image data stored in the first tracking image storage area 29a and the image data stored in the second tracking image storage area 29b at the time of step S6. Then, the control unit 10 causes the correlation value calculation unit 31 to calculate a correlation value E2 between the read image data.

  Next, in step S7, the control unit 10 determines whether or not the correlation value E2 calculated by the process of immediately preceding step S6 is equal to or greater than the threshold value Eth. If the control unit 10 determines that the correlation value E2 is smaller than the threshold value Eth (step S7: NO), the control unit 10 proceeds to step S10 without performing the focusing operation. On the other hand, when the control unit 10 determines that the correlation value E2 is equal to or greater than the threshold value Eth (step S7: YES), the control unit 10 proceeds to step S8. As described above, when the correlation value E2 is equal to or greater than the predetermined threshold Eth, the distance to the subject existing in the tracking block of the frame image shot at the time of focusing is the latest from the shooting time of the frame image at the focusing time. It is considered that the frame image changed until the time when the frame image was taken. On the other hand, when the correlation value E2 is smaller than the predetermined threshold Eth, the distance to the subject existing in the tracking block of the frame image shot at the time of focusing is the latest frame from the shooting time of the frame image at the focusing time. It is considered that there has been no change until the time of image capture.

  Next, in step S8, the control unit 10 performs a focus detection type focusing operation. During the focusing operation, the control unit 10 causes the AF evaluation unit 30 to calculate an AF evaluation value from the image area in the tracking block in the frame images sequentially captured at the time of step S8. Then, the control unit 10 controls the optical system driving unit 15 via the optical system control unit 14 to cause the optical system driving unit 15 to advance and retract the focus lens in the optical axis direction, and is supplied from the AF evaluation unit 30. The focus lens is stopped at the lens position with the highest AF evaluation value. As a result, the face of the main subject M in the tracking block is focused.

  Next, in step S9, the control unit 10 causes the subject tracking unit 28 to cut out the image of the tracking block in the frame image photographed at the time of focusing in the immediately preceding step S8, and represents the cut-out image. Data is stored in the second tracking image storage area 29b. As a result, the image data stored in the second tracking image storage area 29b is changed from the image data of the tracking block on the frame image taken at the time of focusing in the previous step S9 to the focus in the current step S9. It is updated to the image data of the tracking block on the frame image taken at the time.

  In step S10, the control unit 10 determines whether or not the shutter button is fully pressed by the user. Specifically, the control unit 10 determines whether or not the user has fully pressed the shutter button by monitoring a signal corresponding to the full pressing operation of the shutter button from the operation unit 26. When it is determined that the shutter button has not been fully pressed (step S10: NO), the control unit 10 returns the process to step S4. On the other hand, when it is determined that the shutter button is fully pressed (step S10: YES), the control unit 10 advances the process to step S11.

  Next, in step S11, the control unit 10 performs shooting. Specifically, the control unit 10 controls the shutter control unit 17 to cause the shutter drive unit 18 to open and close the shutter device 16. As a result, the image sensor 19 captures the subject image and accumulates the electrical signal, and the preprocessing unit 21 generates a digital signal from the electrical signal. Then, the control unit 10 causes the image processing unit 23 to generate image data from the digital signal, and compresses the generated image data using a JPEG (Joint Photographic Experts Group) method. Then, the control unit 10 records the compressed image data on the recording medium 27.

  After the process of step S11, the control unit 10 ends the process shown in the flowchart of FIG.

  As described above, when the correlation value E2 is smaller than the threshold Eth, the distance to the subject existing in the tracking block of the frame image shot at the time of focusing is the latest from the shooting time of the frame image at the focusing time. Since it is considered that there has been no change until the time point when the frame image is captured, there is no need to restart the focusing operation. On the contrary, when the correlation value E2 is equal to or greater than the threshold value Eth, the distance to the subject existing in the tracking block of the frame image captured at the time of focusing is determined from the time of capturing the frame image at the time of focusing. Since it is considered that it has changed between the time of shooting the latest frame image, it is necessary to restart the focusing operation.

  Therefore, in the continuous AF mode in which the focusing operation is repeatedly performed, the imaging device 100 according to the present embodiment and the tracking block in the latest frame image (the frame image captured at the current time point) and the immediately previous focusing time point The correlation value E2 with the tracking block in the frame image photographed in is calculated. The imaging apparatus 100 is configured not to restart the focusing operation when it is determined that the calculated correlation value E2 is smaller than the threshold value Eth. In other words, the imaging apparatus 100 restarts the focusing operation only when it is determined that the calculated correlation value E2 is greater than or equal to the threshold Eth. For this reason, according to the imaging device 100 according to the present embodiment, a wasteful focusing operation can be prevented. Moreover, since useless focusing operation can be prevented, the power required for the focusing operation can be reduced and the battery life can be extended.

  In addition, the imaging apparatus 100 according to the present embodiment has a tracking block in which the main subject M is positioned on the latest frame image and a tracking in which the main subject M is positioned on the frame image captured immediately before the focusing. The correlation value E2 with the block is calculated. As a result, the imaging apparatus 100 also uses the correlation value between the latest frame image and the frame image captured at the previous in-focus point for the main subject M located in an arbitrary region on the latest frame image. E2 can be calculated. That is, the imaging apparatus 100 can determine whether or not the main subject M has moved from the previous in-focus point for the main subject M located in an arbitrary area on the latest frame image.

  The above-described embodiments are merely examples of the present invention and are not intended to limit the present invention. Accordingly, all modifications that can be made to the present embodiment are included in the present invention.

  DESCRIPTION OF SYMBOLS 100 ... Imaging device, 10 ... Control part, 11 ... RAM, 12 ... ROM, 13 ... Optical lens apparatus, 14 ... Optical system control part, 15 ... Optical system drive , 16 ... shutter device, 17 ... shutter control unit, 18 ... shutter drive unit, 19 ... image sensor, 20 ... image sensor drive unit, 21 ... pre-processing unit, 22 ... Image memory, 23 ... Image processing unit, 24 ... Display control unit, 25 ... Display unit, 26 ... Operation unit, 27 ... Recording medium, 28 ... Subject tracking unit 29 ... Tracking image memory, 30 ... AF evaluation unit, 31 ... Correlation value calculation unit.

Claims (5)

Photographing means for photographing an image of a subject;
A focusing means for repeatedly performing a focusing operation to focus on the subject;
Tracking means for moving the tracking block so as to track the movement of the subject in the image photographed by the photographing means;
Calculating means for calculating a correlation value between the first tracking block on the image captured at the current time point and the second tracking block on the image captured when the focusing operation is performed;
A focusing control unit that does not cause the focusing unit to perform a focusing operation when the correlation value calculated by the calculation unit is smaller than a predetermined threshold;
An imaging apparatus comprising: A tracking image memory having a first storage area for storing the image data of the first tracking block and a second storage area for storing the image data of the second tracking block;
2. The calculation unit according to claim 1, wherein the calculation unit calculates a correlation value between the image data stored in the first storage area and the image data stored in the second storage area. Shooting device. Photographing means for photographing an image of a subject;
Focusing means for repeatedly performing a focusing operation to focus on the subject;
Tracking means for moving the tracking block so as to track the movement of the subject in the image photographed by the photographing means;
Calculating means for calculating a correlation value between the first tracking block on the image captured at the current time point and the second tracking block on the image captured when the focusing operation is performed;
A focusing control unit that causes the focusing unit to perform a focusing operation only when the correlation value calculated by the calculating unit is equal to or greater than a predetermined threshold;
An imaging apparatus comprising: A computer comprising photographing means for photographing an image of a subject and focusing means for repeatedly performing a focusing operation for focusing on the subject;
Tracking means for moving the tracking block so as to track the movement of the subject in the image photographed by the photographing means;
Calculating means for calculating a correlation value between the first tracking block on the image captured at the current time point and the second tracking block on the image captured when the focusing operation is executed;
A focusing control unit that does not cause the focusing unit to perform a focusing operation when the correlation value calculated by the calculating unit is smaller than a predetermined threshold;
Program to function as. A computer comprising photographing means for photographing an image of a subject and focusing means for repeatedly performing a focusing operation for focusing on the subject;
Tracking means for moving the tracking block so as to track the movement of the subject in the image photographed by the photographing means;
Calculating means for calculating a correlation value between the first tracking block on the image captured at the current time point and the second tracking block on the image captured when the focusing operation is executed;
A focusing control unit that causes the focusing unit to perform a focusing operation when the correlation value calculated by the calculating unit is equal to or greater than a predetermined threshold;
Program to function as.

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