JP5407373B2 - Imaging apparatus and program - Google Patents

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 position of the focus lens when focused). 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 each image data of a subject photographed when the focus lens is at each lens position while moving the focus lens forward and backward 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, 5 seconds). 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 the main subject are detected (see FIG. 7 and the like). The technique described in Patent Document 1 performs a focusing operation when it is determined that the shutter button is in a half-pressed state, and unless a change in framing or movement of the main subject is detected therefrom, the focusing operation is performed. The focus is not restarted.

  In the technique described in Patent Document 1, since the focusing operation is restarted only when a change in framing or a movement of the main subject is detected, it is possible to prevent useless focusing operation in the continuous AF method.

JP 2003-244520 A

  By the way, once the focusing operation is performed and the subject is focused once, if the distance to the subject remains the same before and after the framing change even if the framing changes after that, the focusing operation is restarted Even if not, the in-focus state is maintained.

  However, the technique described in Patent Document 1 has a problem in that a wasteful focus operation cannot be sufficiently prevented because the focus operation is always restarted whenever framing changes.

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

In order to achieve the above object, the present invention is a photographing apparatus, which is photographed by a photographing means for photographing an image of a subject, a focusing means for performing a focusing operation for focusing on the subject, and the photographing means. Similarity calculation means for calculating the difference in brightness between the latest image in the peripheral area of the image and the past image, and the difference in brightness between the latest image in the center area of the image and the brightness of the past image, and the focusing means focuses on the subject. The difference between the brightness of the latest image of the peripheral area and the past image calculated by the similarity calculation unit after being matched is equal to or greater than a first threshold, and the similarity is determined after the focusing unit focuses on the subject. When it is determined that the difference in brightness between the latest image of the central area calculated by the calculation unit and the past image is smaller than a second threshold value, the focusing unit is not restarted . In other cases, the focusing is not performed . Focusing system to restart the means And means, wherein the focusing control means, wherein when it is continuously shot by the imaging means while moving the imaging device, the difference in luminance of the latest image and the past image of the peripheral region is first The photographing apparatus is characterized in that it is determined that the difference in luminance between the latest image and the past image in the central area is smaller than a second threshold value, which is equal to or greater than a threshold value.

  According to the present invention, the first similarity of the peripheral area calculated after focusing on the subject is equal to or greater than the first threshold, and the center calculated after the focusing means focuses on the subject. When the second similarity of the area is smaller than the second threshold, the focusing means is not allowed to perform the focusing operation. As a result, even after the focus is once adjusted on the subject in the central area, the second similarity in the central area is smaller than the second threshold value even if the shooting range is changed. If it is determined that the distance has not changed, the focusing operation is not restarted. Therefore, 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 this embodiment. It is a figure which shows an example of a peripheral area | region and a center area | region. It is a flowchart which shows the flow of the imaging | photography process which concerns on this embodiment. It is a figure which shows the to-be-photographed object image image | photographed in this embodiment.

  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 illustrating a functional configuration of the imaging 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.

  In the photographing apparatus 100, the focus lens 11, the lens control unit 12, the lens driving unit 13, the diaphragm / shutter 14, the diaphragm / shutter control unit 15, the diaphragm / shutter driving unit 16, the image sensor 17, The preprocessing unit 18, the image processing unit 19, the control unit 20, the ROM 22, the operation unit 23, the display unit 24, and the recording medium 25 are electrically connected.

  The focus lens 11 is an optical lens for forming a subject image on the light receiving surface of the image sensor 17. By moving the focus lens 11 in the optical axis direction, the focus of the subject image formed on the light receiving surface of the image sensor 17 is adjusted.

  The lens control unit 12 controls the lens driving unit 13 according to control by the control unit 20. Specifically, the lens control unit 12 controls the lens driving unit 13 to cause the lens driving unit 13 to advance and retract the focus lens 11 in the optical axis direction. Thereby, since the position of the focus lens 11 changes, the focus is adjusted. The lens driving unit 13 is configured by a stepping motor or the like. The lens control unit 12 includes a control circuit that controls the lens driving unit 13.

  The aperture / shutter 14 is a mechanism that functions as a mechanical shutter and also functions as an aperture that adjusts the amount of light of the subject image incident on the image sensor 17.

  The aperture / shutter controller 15 drives the aperture / shutter driver 16 in accordance with control by the controller 20. Specifically, the aperture / shutter controller 15 controls the aperture / shutter driver 16 according to the control of the controller 20 to cause the aperture / shutter driver 16 to open and close the aperture / shutter 14. Further, the diaphragm / shutter controller 15 controls the diaphragm / shutter driver 16 according to the control of the controller 20, thereby causing the diaphragm / shutter driver 16 to adjust the diaphragm of the diaphragm / shutter 14.

  The image sensor 17 is an element that photoelectrically converts (photographs) a subject image that is incident from the focus lens 11 and formed on the light receiving surface. Photodiodes as photoelectric conversion elements are arranged in a matrix on the light receiving surface of the image sensor 17, and these photodiodes constitute each pixel of the image sensor 17. The image sensor 17 photoelectrically converts and accumulates subject images at predetermined time intervals under the control of the control unit 20, and sequentially outputs the accumulated electrical signals as analog signals. The image sensor 17 is composed of a CCD (Charge Coupled Device) or the like.

  The preprocessing unit 18 performs various preprocessing such as correlated double sampling processing, gain control processing, A / D (Analog / Digital) conversion processing, etc., on the analog signal supplied from the image pickup device, thereby performing 8-bit digital processing. Generate and output a signal. The digital signal shows luminance (gradation value) in the range of 0 to 255.

  The image processing unit 19 performs image processing such as white balance control processing, γ correction processing, luminance signal processing, and color separation processing on the digital signal supplied from the preprocessing unit 18 to generate a luminance signal and a color difference signal. Generate superimposed image data. A subject image is represented by this image data. In addition, when the shutter button is fully pressed, the image processing unit 19 generates a large amount of image data indicating a relatively high quality image. On the other hand, when displaying the live view image, the image processing unit 20 generates small-capacity image data indicating a relatively low-quality image. The image processing unit 19 includes, for example, a DSP (Digital Signal Processor), a ROM, and a RAM.

  The control unit 20 controls the operation of the entire photographing apparatus 100. The control unit 20 includes, for example, a CPU (Central Processing Unit). The control unit 20 also functions as an image memory 20a, a similarity calculation unit 20b, and an AF evaluation unit 20c.

  The image memory 20a is a buffer memory that cyclically stores image data sequentially supplied from the image processing unit 19 for the latest 60 frames.

The similarity calculation unit 20b calculates the similarity E1 (first similarity) of the peripheral area C in the image expressed by the image data from the live view image expressed by the image data stored in the image memory 20a. Then, the similarity E2 (second similarity) of the central region S is calculated.

  FIG. 2 is a diagram for explaining an example of the peripheral region C and the central region S. FIG. 2 shows an image 30 that is an example of a live view image generated in the present embodiment. In order to facilitate understanding, it is assumed that the main subject is not shown in the image 30.

  As shown in FIG. 2, the control unit 20 sets an upper left region C1, an upper right region C2, a lower left region C3, and a lower right region C4 as the peripheral region C in the live view image (image 30). That is, in the present embodiment, the upper left region C1, the upper right region C2, the lower left region C3, and the lower right region C4 constitute the peripheral region C. The upper left vertex of the upper left area C1 coincides with the upper left vertex of an outer frame (hereinafter simply referred to as “outer frame”) that defines the shooting range of the live view image. Also, the upper right vertex of the upper right region C2 matches the upper right vertex of the outer frame of the live view image. In addition, the lower left vertex of the lower left region C3 matches the lower left vertex of the outer frame of the live view image. Also, the lower right vertex of the lower right region C4 matches the lower right vertex of the outer frame of the live view image.

  In addition, as illustrated in FIG. 2, the control unit 20 sets a central region S1 in the live view image (image 30). The center of the central area S coincides with the center of the live view image.

  In the following description, it is assumed that the size of the live view image (image 30) in the present embodiment is 640 pixels wide × 480 lines vertical. In the image 30, the sizes of the upper left area C1, the upper right area C2, the lower left area C3, the lower right area C4, and the central area S1 are equal to 213 pixels × 160 lines. However, the sizes of these regions may be different from each other. The size of each area is not limited to 213 pixels × 160 lines.

  The similarity calculation unit 20b obtains the similarity E1 of the peripheral areas C1 to C4 and the similarity E2 of the central area S1 between the latest image and the past image. Here, the latest image is an image represented by the newest image data generated by the image processing unit 19 (image data generated last in time). The past image is an image expressed by image data generated by the image processing unit 19 in the past (for example, five frames before) the image data expressing the latest image. That is, the past image is an image taken in the past than the latest image.

ただし、上記式において、Ａ（ｉ，ｊ）（１≦ｉ≦２１３,１≦ｊ≦１６０）は、最新画像における左上領域Ｃ１を構成する各画素の輝度である。Ｂ（ｉ，ｊ）（１≦ｉ≦２１３,１≦ｊ≦１６０）は、過去画像における左上領域Ｃ１を構成する各画素の輝度である。なお、ライブビュー画像の左上の頂点に位置する画素の座標を（１，１）とし、ライブビュー画像の右下の頂点に位置する画素の座標を（６４０，４８０）とした。変数ｉと変数ｊとの組合せが、ライブビュー画像上の画素の座標を定める。 The similarity calculation unit 20b can calculate the similarity Ec1 of the upper left region C1 by, for example, the following formula (1).

In the above equation, A (i, j) (1 ≦ i ≦ 213, 1 ≦ j ≦ 160) is the luminance of each pixel constituting the upper left region C1 in the latest image. B (i, j) (1 ≦ i ≦ 213, 1 ≦ j ≦ 160) is the luminance of each pixel constituting the upper left region C1 in the past image. The coordinates of the pixel located at the upper left vertex of the live view image are (1, 1), and the coordinates of the pixel located at the lower right vertex of the live view image are (640, 480). The combination of the variable i and the variable j determines the coordinates of the pixel on the live view image.

ただし、上記式において、Ａ（ｉ，ｊ）（４２７≦ｉ≦６４０,１≦ｊ≦１６０）は、最新画像における右上領域Ｃ２を構成する各画素の輝度である。Ｂ（ｉ，ｊ）（４２７≦ｉ≦６４０,１≦ｊ≦１６０）は、過去画像における右上領域Ｃ２を構成する各画素の輝度である。 The similarity calculation unit 20b can calculate the similarity Ec2 of the upper right region C2 by, for example, the following equation (2).

In the above expression, A (i, j) (427 ≦ i ≦ 640, 1 ≦ j ≦ 160) is the luminance of each pixel constituting the upper right region C2 in the latest image. B (i, j) (427 ≦ i ≦ 640, 1 ≦ j ≦ 160) is the luminance of each pixel constituting the upper right region C2 in the past image.

ただし、上記式において、Ａ（ｉ，ｊ）（１≦ｉ≦２１３,３２１≦ｊ≦４８０）は、最新画像における左下領域Ｃ３を構成する各画素の輝度である。Ｂ（ｉ，ｊ）（１≦ｉ≦２１３,３２１≦ｊ≦４８０）は、過去画像における左下領域Ｃ３を構成する各画素の輝度である。 The similarity calculation unit 20b can calculate the similarity Ec3 of the lower left region C3 by, for example, the following formula (3).

In the above expression, A (i, j) (1 ≦ i ≦ 213, 321 ≦ j ≦ 480) is the luminance of each pixel constituting the lower left region C3 in the latest image. B (i, j) (1 ≦ i ≦ 213, 321 ≦ j ≦ 480) is the luminance of each pixel constituting the lower left region C3 in the past image.

ただし、上記式において、Ａ（ｉ，ｊ）（１≦ｉ≦２１３,１≦ｊ≦１６０）は、最新画像における右下領域Ｃ４を構成する各画素の輝度である。Ｂ（ｉ，ｊ）（１≦ｉ≦２１３,１≦ｊ≦１６０）は、過去画像における右下領域Ｃ４を構成する各画素の輝度である。 The similarity calculation unit 20b can calculate the similarity Ec4 of the lower right region C4 by, for example, the following formula (4).

In the above expression, A (i, j) (1 ≦ i ≦ 213, 1 ≦ j ≦ 160) is the luminance of each pixel constituting the lower right region C4 in the latest image. B (i, j) (1 ≦ i ≦ 213, 1 ≦ j ≦ 160) is the luminance of each pixel constituting the lower right region C4 in the past image.

The similarity calculation unit 20b calculates the average value of the similarities of the regions C1 to C4 as the similarity E1 of the peripheral region C. The similarity calculation unit 20b can calculate the similarity E1 of the peripheral region C by, for example, the following formula (5).
E1 = (Ec1 + Ec2 + Ec3 + Ec4) / 4 (5)

ただし、上記式において、Ａ（ｉ，ｊ）（２１４≦ｉ≦４２６,１６１≦ｊ≦３２０）は、最新画像における中央領域Ｓを構成する各画像の輝度である。Ｂ（ｉ，ｊ）（２１４≦ｉ≦４２６,１６１≦ｊ≦３２０）は、過去画像における中央領域Ｓを構成する各画素の輝度である。 The similarity calculation unit 20b can calculate the similarity E2 of the central region S by, for example, the following formula (6).

In the above expression, A (i, j) (214 ≦ i ≦ 426, 161 ≦ j ≦ 320) is the luminance of each image constituting the central region S in the latest image. B (i, j) (214 ≦ i ≦ 426, 161 ≦ j ≦ 320) is the luminance of each pixel constituting the central region S in the past image.

各領域の類似度Ｅ（第１の類似度、並びに第２の類似度）は、Ａ（ｉ，ｊ）とＢ（ｉ，ｊ）の差分に相当する値の総和であれば何でもよい。 Further, the similarity calculation unit 20b can also calculate the similarity E 1 (first similarity and second similarity) of each region by the following equation (7).

The similarity E (first similarity and second similarity) of each region may be anything as long as it is the sum of values corresponding to the difference between A (i, j) and B (i, j).

Here, the difference between A (i, j) and B (i, j) is small, that is, the difference in luminance between the pixels at the same position in the latest image and the past image is small. It shows that there is. That is, in the above calculation method, the smaller the value of the similarity E 1 (the first similarity and the second similarity) , the greater the similarity between the regions in the latest image and the past image. On the other hand, a large difference between A (i, j) and B (i, j) indicates that they are not similar. That is, in the above calculation method, as the similarity E 1 (the first similarity and the second similarity) increases, the similarity between the regions in the latest image and the past image decreases.

  When the similarity E1 of the peripheral area C is equal to or greater than the predetermined threshold Eth1, it is considered that a subject different from the subject that was captured in the peripheral area C of the past image is captured in the peripheral area C of the latest image. In this case, the control unit 20 determines that the shooting range that is framing has changed between the shooting time of the past image and the shooting time of the latest image. On the other hand, when the similarity E1 of the peripheral region C is smaller than the predetermined threshold Eth1, it is considered that the same subject as the subject shown in the peripheral region C of the past image is captured in the peripheral region C of the latest image. . In this case, the control unit 20 determines that the shooting range has not changed between the shooting time of the past image and the shooting time of the latest image. Note that the predetermined threshold Eth1 is a value (such as an experimental value) that can be satisfactorily determined that the subject in the peripheral area C has changed.

  When the similarity E2 of the central region S is equal to or greater than the predetermined threshold Eth2, the subject that was captured in the central region S of the past image has moved out of the central region S at the time of shooting the latest image, or It is considered that the size of the subject shown in the central area S of the past image has not changed between the time of shooting the past image and the time of shooting the latest image. In this case, the control unit 20 determines that the distance to the subject existing in the central region S of the past image has changed between the time when the past image was taken and the time when the latest image was taken. On the other hand, when the similarity E2 of the central region S is smaller than the predetermined threshold Eth2, the same subject is shown in the same size in the central region S of the past image and the central region S of the latest image. Conceivable. In this case, the control unit 20 determines that the distance to the subject existing in the central region S of the past image has not changed from the time when the past image was taken to the time when the latest image was taken. The predetermined threshold Eth2 is a value (such as an experimental value) at which the reactivation of the focusing operation actually works well.

  Here, if the in-focus state is executed and the in-focus state is once secured, even if the shooting range is changed after that, the distance to the subject once in focus has not changed. There is no need to restart the focusing operation. In many cases including the continuous AF mode, the subject that is first focused is the subject that appears in the center of the shooting range. Therefore, in the present embodiment, when the focus operation is performed and the subject in the central area S is focused, the control unit 20 can determine whether the shooting range has changed afterwards. When it is determined that the distance to the subject in the region S has not changed, the focusing operation is not restarted. Thereby, even when the shooting range changes, it is possible to prevent useless focusing operation. 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.

  Returning to FIG. 1, the AF evaluation unit 20c performs a focusing operation by a contrast detection method. In this focusing operation, the AF evaluation unit 20c calculates an AF evaluation value that is a high-frequency component from the luminance signal of the image data stored in the image memory 20a. Then, the AF evaluation unit 20c controls the lens driving unit 13 via the lens control unit 12 to cause the lens driving unit 13 to advance and retract the focus lens 11 in the optical axis direction, and the calculated AF evaluation value is the highest. The focus lens 11 is stopped at the higher lens position.

  The RAM 21 functions as a working area when the CPU 20 executes each process. The RAM 21 is composed of a DRAM (Dynamic Random Access Memory) or the like.

  The ROM 22 stores programs and data necessary for the photographing apparatus 100 to execute each process and AF process shown in FIG. The ROM 22 is composed of a flash memory or the like. The control unit 20 executes each process in cooperation with a program stored in the ROM 22 using the RAM 21 as a working area.

  The operation unit 23 receives various key operations from the user. The operation unit 23 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 23 supplies signals indicating various key operations received from the user to the control unit 20. The shutter button has a configuration capable of receiving from the user a half-press operation for instructing a focusing operation and a full-press operation for instructing shooting (recording of image data). When the control unit 20 receives these signals from the operation unit 23, the control unit 20 executes processing based on the received signals.

  The display unit 24 displays an image represented by the image data generated by the image processing unit 19. The display unit 24 includes a liquid crystal display and a drive circuit thereof.

  The recording medium 25 records the image data generated by the image processing unit 19. The recording medium 24 includes a semiconductor memory card that can be attached to and detached from the photographing apparatus 100.

<Operation of the photographing device>
FIG. 3 is a flowchart showing an operation in the photographing process of the photographing apparatus 100 according to the present embodiment. A photographing process executed by the photographing apparatus 100 will be described with reference to FIG.

  FIG. 4 is a diagram illustrating an example of a state of the subject image 40 that appears in the shooting range of the shooting apparatus 100 in the present embodiment. In the present embodiment, it is assumed that the user performs photographing while holding the photographing apparatus 100 with his / her hand. Then, it is assumed that the subject M that the user desires to shoot (hereinafter referred to as the main subject M) may move. For this reason, for example, when the user moves the photographing apparatus 100 so as to follow the movement of the main subject M, the state of the subject image 40 in the photographing range changes.

  Returning to FIG. 3, when the photographing apparatus 100 is turned on by the user operating the power button, the photographing apparatus 100 reads the program stored in the ROM 22 into the RAM 21 and cooperates with this program in FIG. 3. The imaging process shown by the flowchart of FIG.

  First, in step S1, the control unit 20 starts live view display. Specifically, the control unit 20 controls the image sensor 14 to capture the subject image 40 that appears in the imaging range. Then, the control unit 20 controls the image processing unit 19 to generate a live view image, and starts processing to display the generated live view image on the display unit 24. Thereafter, the control unit 20 displays the live view image by sequentially supplying the image data sequentially supplied from the image processing unit 19 to the display unit 24. As described above, the size of the live view image generated by the image processing unit 19 is 640 pixels × 480 lines.

  Next, in step S2, the control unit 20 determines whether or not the shutter button is half-pressed by the user. Specifically, the control unit 20 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 23. When it is determined that the shutter button has not been pressed halfway (step S2: NO), the control unit 20 returns the process to step SA2 and continues the live view display. On the other hand, when it is determined that the shutter button is half-pressed (step S2: YES), the control unit 20 advances the process to step SA3.

  Next, in step S3, the control unit 20 performs a focusing operation (AF operation) of a contrast detection method. In the present embodiment, it is assumed that the main subject M exists in the area of the AF frame F at the time of the first processing in step S3. During the focusing operation, the AF evaluation unit 20c in the control unit 20 calculates an AF evaluation value from an area in the AF frame F in the image data stored in the image memory 20a. Then, the AF evaluation unit 20c controls the lens driving unit 13 via the lens control unit 12 to cause the lens driving unit 13 to advance and retract the focus lens 11 in the optical axis direction, and the calculated AF evaluation value is the highest. The focus lens 11 is stopped at the higher lens position. Thus, the main subject M is brought into focus by the first focusing operation. In the present embodiment, as shown in FIG. 4, the position of the AF frame F and the size of the area are the same as the position and size of the central area S.

  Next, in step S4, the control unit 20 acquires the latest image and the past image. Specifically, the control unit 20 acquires the latest image and the past image stored in the image memory 20a, and supplies the acquired latest image and the past image to the similarity calculation unit 21b.

  Next, in step S5, the control unit 20 calculates the similarity E1 of the peripheral region C and the similarity E2 of the central region S. Specifically, the similarity calculation unit 20b in the control unit 20 uses the latest image and the past image acquired in the immediately preceding step S4, and the similarity E1 of the peripheral region C according to the above formulas (1) to (6). And the similarity E2 of the central region S are calculated. In the live view image representing the subject image 40 shown in FIG. 4, the sizes of the peripheral areas C1 to C4 and the central area S are 213 pixels × 160 lines, which are the same as those on the image 30, respectively. .

  Next, in step S6, the control unit 20 determines whether or not the shooting range has changed. Specifically, the control unit 20 determines whether or not the shooting range has changed by determining the magnitude relationship between the similarity E1 of the surrounding area C calculated by the process of the immediately preceding step S5 and the threshold Eth1. . When the similarity E1 of the peripheral area C calculated by the process of immediately preceding step S5 is smaller than the threshold Eth1, the control unit 20 determines that the shooting range has not changed (step S6: NO), and proceeds to step S7. Proceed with the process. On the other hand, when the similarity E1 of the peripheral area C calculated by the process of immediately preceding step S5 is equal to or greater than the threshold Eth1, the control unit 20 determines that the shooting range has changed (step S6: YES), and step S8. Proceed with the process.

  In step S <b> 7, the control unit 20 determines whether or not the distance in the optical axis direction from the imaging device 100 to the main subject M has changed. Specifically, the control unit 20 determines the magnitude relationship between the similarity E2 of the central region S calculated by the process of the immediately preceding step S5 and the threshold Eth2, and thereby the optical axis from the imaging device 100 to the main subject M is determined. It is determined whether the direction distance has changed. The control unit 20 determines that the distance in the optical axis direction from the imaging device 100 to the main subject M has not changed when the similarity E2 of the central region S calculated by the processing in the previous step S5 is smaller than the threshold Eth2. (Step S7: NO), the process proceeds to Step S9 without performing the focusing operation again. On the other hand, when the similarity E2 of the central region S calculated by the process of immediately preceding step S5 is equal to or greater than the threshold Eth2, the control unit 20 determines that the distance in the optical axis direction from the imaging device 100 to the main subject M has changed. Judgment is made (step S7: YES), and the process returns to step S2.

  In step S8, the control unit 20 determines whether or not the distance in the optical axis direction from the imaging device 100 to the main subject M has changed. Specifically, the control unit 20 determines the magnitude relationship between the similarity E2 of the central region S calculated by the process of the immediately preceding step S5 and the threshold Eth2, and thereby the optical axis from the imaging device 100 to the main subject M is determined. It is determined whether the direction distance has changed. The control unit 20 determines that the distance in the optical axis direction from the imaging device 100 to the main subject M has not changed when the similarity E2 of the central region S calculated by the processing in the previous step S5 is smaller than the threshold Eth2. (Step S8: NO), the process proceeds to Step S9 without performing the focusing operation again. On the other hand, when the similarity E2 of the central region S calculated by the process of immediately preceding step S5 is equal to or greater than the threshold Eth2, the control unit 20 determines that the distance in the optical axis direction from the imaging device 100 to the main subject M has changed. Judgment is made (step S8: YES), and the process is returned to step S2.

  When the process returns from step S7 or step S8 to step S2, as long as the user continues to press the shutter button halfway (step S2: YES), the control unit 20 performs the focusing operation again by the process of step S3. Execute again to focus on the subject area within the AF frame F again.

  On the other hand, in step S9, the control unit 20 determines whether or not the shutter button is fully pressed by the user. Specifically, the control unit 20 determines whether or not the shutter button is fully pressed by the user by monitoring a signal corresponding to the shutter button full press operation from the operation unit 23. When it is determined that the shutter button has not been fully pressed (step S9: NO), the control unit 20 returns the process to step S4. On the other hand, when it is determined that the shutter button has been fully pressed (step S9: YES), the control unit 20 advances the process to step S10.

  Next, in step S10, the control unit 20 executes photographing. Specifically, the control unit 20 controls the aperture / shutter control unit 15 to cause the aperture / shutter drive unit 16 to open and close the aperture / shutter 14. As a result, the image sensor 17 captures a subject image and accumulates an electrical signal, and the preprocessing unit 18 generates a digital signal from the electrical signal. Then, the control unit 20 causes the image processing unit 19 to generate image data from the digital signal, and compresses the generated image data using the JPEG method. Then, the control unit 20 records the compressed image data on the recording medium 25.

  After the process of step S10, the control unit 20 ends the process shown in the flowchart of FIG.

  As described above, in the imaging apparatus 100 according to the present embodiment, once the main subject M in the central area S (AF frame F) is focused once the focusing operation is performed, the imaging range changes thereafter. If it is determined that the distance to the main subject M in the central area S (AF frame F) has not changed even if it is determined that the focus operation has been performed, the focusing operation is not restarted. Yes. Thereby, even when the shooting range changes, it is possible to prevent useless focusing operation. 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 the present embodiment, the change in luminance between the latest image and the past image is calculated as the similarity. However, the motion of the subject between the latest image and the past image may be detected as a motion vector, and the detected motion vector may be calculated as the similarity. In this case, a known detection method may be used as the motion vector detection method.

In this embodiment, the four corner areas (C1 to C4) of the captured image are defined as the peripheral area C. However, for example, in the captured image, the remaining area excluding the central area S may be set as the peripheral area C. Further, only one area (for example, the peripheral area C1) of the four corner areas (C1 to C4) of the captured image may be set as the peripheral area C. Further, only two or three of the four corner regions (C1 to C4) of the captured image may be used as the peripheral region C.

  In the present embodiment, the sum of the luminance differences for each pixel constituting each region (C1 to C4, S) between the latest image and the past image is calculated as the similarity of each region. However, the average value of the luminance of each pixel constituting each region (C1 to C4, S) in the latest image and the average value of the luminance of each pixel constituting each region (C1 to C4, S) in the past image The difference may be calculated as the similarity of each region.

  In the present embodiment, the size of the area in the AF frame F is the same as the size of the central area S. However, the size of the area in the AF frame F may be different from the size of the central area S.

  Each of the above embodiments is merely an example of the present invention, and is 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 Image pick-up device 11 Focus lens 12 Lens control part 13 Lens drive part 14 Aperture and shutter 15 Aperture and shutter control part 16 Aperture and shutter drive part 17 Image sensor 18 Preprocessing part 19 Image processing part 20 Control part 20a Image memory 20b Similarity Calculation unit 20c AF evaluation unit 21 RAM
22 ROM
23 Operation unit 24 Display unit 25 Recording medium

Claims (4)

A photographing device,
Photographing means for photographing an image of a subject;
A focusing means for performing a focusing operation to focus on the subject;
Similarity calculation means for calculating the difference between the brightness of the latest image and the past image in the peripheral area of the image taken by the shooting means, and the brightness difference between the latest image and the past image in the center area of the image ;
The difference in luminance between the latest image of the peripheral area and the past image calculated by the similarity calculation unit after the focusing unit focuses on the subject is equal to or more than a first threshold, and the focusing unit is the subject. When it is determined that the brightness difference between the latest image of the central area and the past image calculated by the similarity calculation unit after focusing on is smaller than a second threshold value, the focusing unit is restarted. In other cases, focusing control means for restarting the focusing means, and
With
The focus control means has a brightness difference between the latest image and the past image in the peripheral area equal to or greater than a first threshold when the photographing means is continuously photographed while moving the photographing apparatus; and The photographing apparatus according to claim 1, wherein the difference in luminance between the latest image in the central region and the past image is determined to be smaller than a second threshold value. The imaging apparatus according to claim 1, wherein each of the peripheral areas includes at least one area including any one vertex of an outer frame of an image captured by the imaging unit. The imaging apparatus according to claim 1, wherein a center of the central area coincides with a center of an image captured by the imaging unit. A computer comprising photographing means for photographing an image of a subject and focusing means for performing a focusing operation for focusing on the subject;
Similarity calculation means for calculating the difference in brightness between the latest image and the past image in the peripheral area of the image captured by the imaging means, and the difference in brightness between the latest image and the past image in the center area of the image ;
The difference in luminance between the latest image of the peripheral area and the past image calculated by the similarity calculation unit after the focusing unit focuses on the subject is equal to or more than a first threshold, and the focusing unit is the subject. When it is determined that the brightness difference between the latest image of the central area and the past image calculated by the similarity calculation unit after focusing on is smaller than a second threshold value, the focusing unit is restarted. In other cases, focusing control means for restarting the focusing means,
Function as
The focus control means has a brightness difference between the latest image and the past image in the peripheral area equal to or greater than a first threshold when the photographing means is continuously photographed while moving the photographing apparatus; and The program characterized in that it is determined that the difference in luminance between the latest image and the past image in the central area is smaller than a second threshold value.

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