JP2010200138A - Photographic subject tracking device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve photographic subject tracking performance under a flicker light source. <P>SOLUTION: Images produced by an image forming optical system are repeatedly imaged. A reference image of a photographic subject for tracking is established from the imaged first image (initial image). Simultaneously in a second image (comparison image) imaged after the first image, the position of a partial image similar to the reference image is searched. When tracking the photographic subject for tracking moving in an imaging screen, an exposure time of imaging means is controlled so that imaging of the first image takes a longer exposure time T0 than imaging of the second image. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a subject tracking device.

  When shooting a moving subject, the subject image of the specified part in the screen is acquired as a template image (reference image), and the position of the subject image similar to the template image is searched (template matching) among images repeatedly shot. A subject tracking device that tracks a subject moving within a screen is known (see, for example, Patent Document 1).

JP 2006-058431 A

By the way, under a flicker light source such as a fluorescent lamp, the color and brightness change under the influence of flicker. Therefore, it is difficult to correctly determine the similarity between the template image (reference image) and the comparison image, and erroneous determination is likely to occur. . In particular, when a template image is acquired, if it is affected by flicker, the template image itself is different from the correct tracking target subject image, making it difficult to track the target subject.
In order to solve this problem, it is conceivable to acquire and average images a plurality of times, or to acquire images with an exposure time longer than the flicker cycle. However, if this is done, the subject tracking cycle becomes longer and the tracking performance decreases. It will be.

According to the present invention, an imaging unit that repeatedly captures an image formed by the imaging optical system, a reference setting unit that sets a reference image of a tracking target subject from the first image captured by the imaging unit, and an imaging unit The present invention is applied to a subject tracking device that includes position search means for searching for the position of a partial image similar to a reference image in a second image captured after one image, and that tracks a tracking target subject that moves within a shooting screen.
An exposure control unit that controls the exposure time of the imaging unit is provided, and the exposure control unit sets a longer exposure time than when the second image is captured when the first image is captured.

  According to the present invention, a reference image (template image) that accurately represents a subject image to be tracked can be obtained, and high accuracy and reliability in subject tracking can be realized using such a reference image. In addition, the tracking cycle when subject tracking control is performed while acquiring the second image (tracking comparison image) is shortened, and high responsiveness of subject tracking can be maintained.

The figure which shows the structure of the imaging device (single-lens reflex digital still camera) provided with the image recognition apparatus and focus adjustment apparatus of one Embodiment The figure which shows the detailed structure of a body drive control apparatus Front view showing a detailed configuration of the second image sensor Front view showing details of each pixel of the second image sensor The figure for demonstrating the to-be-photographed object tracking method of one embodiment. The figure for demonstrating the to-be-photographed object tracking method of one embodiment. The figure for demonstrating the to-be-photographed object tracking method of one embodiment. Flowchart showing subject tracking processing of an embodiment The flowchart which shows the initial process of the tracking control of one embodiment Timing chart showing the acquisition timing of the initial image for tracking the subject and the comparative image by the second image sensor 16 of the embodiment Timing chart showing acquisition timing of tracking initial image and tracking comparison image in conventional subject tracking device Timing chart showing acquisition timing of tracking initial image and tracking comparison image in conventional subject tracking device Timing chart showing the acquisition timing of the tracking initial image and tracking comparison image during continuous shooting in the conventional subject tracking device Timing chart showing the acquisition timing of the tracking initial image and tracking comparison image during continuous shooting in the subject tracking device of the embodiment

  The focus adjustment state of the photographic lens (in this embodiment, the defocus amount) is detected in a plurality of focus detection areas set in the photographic screen, and the photographic lens is focused based on the defocus amount in one of the areas. The automatic focus adjustment (AF) function to be driven and the image of the subject to be tracked in the photographed image are stored as a template image (reference image). A single-lens reflex digital still camera that has an image tracking function that tracks the subject to be tracked while searching for a position (template matching), and that tracks the target while driving the photographic lens with the AF function and the image tracking function. A mounted embodiment will be described.

  FIG. 1 shows a configuration of a single-lens reflex digital still camera 1 including a subject tracking device according to an embodiment. In FIG. 1, illustration and description of camera devices and circuits not directly related to the present invention are omitted. In a camera 1 according to an embodiment, an interchangeable lens 3 is attached to a camera body 2 in a replaceable manner. The camera body 2 is provided with a first image sensor 4 for capturing a subject image and recording the image. The first image sensor 4 can be constituted by a CCD, a CMOS, or the like. At the time of photographing, the quick return mirror 5 and the sub mirror 6 are retracted to a position outside the photographing optical path indicated by a solid line, the shutter 7 is opened, and a subject image is formed on the light receiving surface of the first image sensor 4 by the photographing lens 8.

  At the bottom of the camera body 2, a focus detection optical system 9 and a distance measuring element 10 for detecting the focus adjustment state of the photographing lens 8 are provided. In this embodiment, an example is shown in which a focus detection method based on a pupil division type phase difference detection method is employed. The focus detection optical system 9 guides the pair of focus detection light fluxes that have passed through the photographing lens 8 to the light receiving surface of the distance measuring element 10 and forms a pair of optical images. The distance measuring element 10 includes, for example, a pair of CCD line sensors, and outputs a focus detection signal corresponding to the pair of optical images. Before shooting, the quick return mirror 5 and the sub mirror 6 are set at positions in the shooting optical path as indicated by broken lines, and the pair of focus detection light beams from the shooting lens 8 are transmitted through the half mirror portion of the quick return mirror 5. Then, the light is reflected by the sub mirror 6 and guided to the focus detection optical system 9 and the distance measuring element 10.

  A finder optical system is provided on the upper part of the camera body 2. Before shooting, the quick return mirror 5 and the sub mirror 6 are in positions indicated by broken lines, and subject light from the shooting lens 8 is reflected by the quick return mirror 5 and guided to the focusing screen 11, and the subject image is displayed on the focusing screen 11. Form an image. The liquid crystal display element 12 superimposes and displays information such as a focus detection area mark on the subject image formed on the focusing screen 11 and displays various photographing information such as an exposure value at a position outside the subject image. The subject image on the focusing screen 11 is guided to the eyepiece window 15 via the penta roof prism 13 and the eyepiece lens 14 so that the photographer can visually recognize the subject image.

  The finder optical system at the top of the camera body 2 is provided with a second image sensor 16 that captures a subject image for subject tracking and photometry. The subject image formed on the focusing screen 11 is re-imaged on the light receiving surface of the second image sensor 16 via the penta roof prism 13, the prism 17 and the imaging lens 18. The second image sensor 16 outputs an image signal corresponding to the subject image. Although details will be described later, subject tracking control and exposure calculation are performed based on the subject image picked up by the second image sensor 16.

  The camera body 2 is also provided with a body drive control device 19 and an operation member 20. The body drive control device 19 is constituted by peripheral components such as a microcomputer, a memory, and an A / D converter, the details of which will be described later, and performs various controls and calculations of the camera 1. The operation member 20 includes a switch and a selector for operating the camera 1 such as a shutter button, a focus detection area selection switch, and a shooting mode selection switch.

  The interchangeable lens 3 is provided with a zooming lens 8a, a focusing lens 8b, a diaphragm 21, a lens drive control device 22, and the like. In this embodiment, the photographic lens 8 is represented by a zoom lens 8a, a focusing lens 8b, and a diaphragm 21, but the configuration of the photographic lens 8 is not limited to the configuration shown in FIG. The lens drive control device 22 includes a microcomputer (not shown) and peripheral components such as a memory, a drive circuit, and an actuator, and performs drive control of the lenses 8a and 8b and the diaphragm 21 and detection of their set positions. Lens information such as a focal length and an open aperture value of the interchangeable lens 3 is stored in a memory built in the lens drive control device 22.

  The body drive control device 19 and the lens drive control device 22 communicate via the contact 23 of the lens mount, and transmit information such as a lens drive amount and an aperture value from the body drive control device 19 to the lens drive control device 22. Lens information and aperture information are transmitted from the lens drive control device 22 to the body drive control device 19.

  FIG. 2 shows a detailed configuration of the body drive control device 19. Note that illustration and description of control functions not directly related to the present invention are omitted. The body drive control device 19 includes an element control circuit 19a, an A / D converter 19b, a microcomputer 19c, a memory 19d, and the like. The element control circuit 19 a controls charge accumulation and reading of the second image sensor 16. The A / D converter 19b converts the analog image signal output from the second image sensor 16 into a digital image signal. The microcomputer 19c constitutes a tracking control unit 19e, an exposure control unit 19f, a focus detection calculation unit 19g, and a lens drive amount calculation unit 19h according to a software form. The memory 19d stores information such as a template image for image tracking and a defocus amount, lens information such as a focal length of the photographing lens 8, an open F value, an aperture value, a conversion coefficient from an image shift amount to a defocus amount, or details. Stores a similarity determination threshold value Dth and a color threshold value MaxTh, which will be described later.

  The tracking control unit 19e generates a template image (reference image) of the subject image captured by the second image sensor 16 and corresponding to the tracking target position manually specified by the photographer or the tracking target position automatically set by the camera 1. Image) is stored in the memory 19d, and the position of the target is recognized by searching for an image area that matches or is similar to the template image from images repeatedly photographed thereafter. The exposure calculation unit 19f calculates an exposure value based on the image signal captured by the second image sensor 16.

  The focus detection calculation unit 19g detects the focus adjustment state of the photographing lens 8, here the defocus amount, based on the focus detection signal corresponding to the pair of optical images output from the distance measuring element 10. Although details will be described later, a plurality of focus detection areas are set in the shooting screen of the shooting lens 8, and the distance measuring element 10 outputs a focus detection signal corresponding to a pair of optical images for each focus detection area. Then, the focus detection calculation unit 19g detects the defocus amount based on the focus detection signal corresponding to the pair of optical images for each focus detection area. The lens driving amount calculation unit 19h converts the detected defocus amount into a lens driving amount. The lens drive control device 22 performs the focus adjustment by driving the focusing lens 8b according to the lens drive amount by the lens drive amount calculation unit 19h.

  FIG. 3 is a front view showing a detailed configuration of the second image sensor 16. The second imaging element 16 includes a plurality of pixels (photoelectric conversion elements) 26 (here, horizontal 16 × vertical 12 = 192) arranged in a matrix. As shown in FIG. 4, each pixel 26 is divided into three portions 26a, 26b, and 26c, and primary color filters of red R, green G, and blue B are provided in these portions 26a, 26b, and 26c, respectively. . Thereby, the RGB signal of the subject image can be output for each pixel 26.

  Next, a subject tracking operation according to an embodiment will be described. 5 to 7 are diagrams for explaining a subject tracking method according to an embodiment, and FIGS. 8 to 9 are flowcharts illustrating subject tracking processing according to the embodiment. 10 to 14 are timing charts showing the acquisition timing of the initial image for tracking the subject and the comparative image by the second image sensor 16.

  The quick return mirror 5 is set in the photographing optical path shown by the broken line in FIG. 1 except when the shutter button is fully pressed to shoot, and the subject light incident from the photographing lens 8 forms an image on the focusing screen 11. Is done. The subject image on the focusing screen 11 is guided to the second image sensor 16 via the penta roof prism 13, the prism 17 and the imaging lens 18, and the subject image signal is repeatedly output from the second image sensor 16.

  A plurality of focus detection areas are set on the shooting screen of the shooting lens 8, and an area mark is superimposed on the subject image on the focusing screen 11 by the liquid crystal display element 12 to display the position of each focus detection area. In this embodiment, as shown in FIG. 5, an example is shown in which focus detection areas 45a to 45g (denoted as a to g in the figure) are set at seven locations in the photographing screen. When an arbitrary area is selected by the focus detection area selection switch of the operation member 20, the mark of the area is lit up.

  As shown in FIG. 5, when the focus detection area 45b is selected by the focus detection area selection switch of the operation member 20, and the shutter button of the operation member 20 is half-pressed in this state, the focus detection area 45b is stored as the first AF area. 19d. Thereby, a tracking symmetrical subject is designated. In this example, the photographer selects the first AF area and manually designates the subject to be tracked. For example, in a camera having a function of automatically recognizing the subject, the first AF is performed based on the subject recognition result. An area and a tracking target subject may be set.

  In step 1 of FIG. 8, an initial image for subject tracking is acquired by the second image sensor 16. This initial tracking image is an image acquired first after starting the image tracking process, and the above-described template image (reference image) is generated from this initial tracking image. After acquiring the tracking initial image, a subject tracking comparison image for comparison with the template image is repeatedly acquired.

  FIG. 10 is a timing chart showing the acquisition timing of the subject tracking initial image and the comparative image by the second image sensor 16 according to the embodiment. In this embodiment, when charge accumulation (exposure) for acquiring a tracking initial image is performed by the second image sensor 16, the charge accumulation time (exposure time) T0 is used, and the tracking comparison image thereafter is obtained. The charge accumulation time T1 is longer than the charge accumulation time T1, and is approximately equal to the flicker period T. As the flicker cycle T, a value obtained by measuring the subject luminance change cycle by the second image sensor 16 may be used, or a cycle of 50 Hz may be used as representative of commercial power supply frequencies of 50 Hz and 60 Hz. .

  Note that a change in subject brightness is measured by the second image sensor 16, and if there is a periodic change in subject brightness, it is determined that the light source at the time of shooting is a flicker light source, and only in that case is shown in FIG. Exposure control may be performed. Alternatively, the exposure control shown in FIG. 10 may be performed only when the flicker light source is selected in the white balance setting. Thereby, the exposure control shown in FIG. 10 is reliably executed under the flicker light source.

  FIG. 11 is a timing chart showing the acquisition timing of the tracking initial image and the tracking comparison image in the conventional subject tracking device. The charge accumulation time T3 for obtaining the tracking initial image and the tracking comparison image is equal and shorter than the flicker cycle T. In general, in charge accumulation for photometry for measuring the luminance of the object scene, accumulation is performed by so-called peak AGC (Auto Gain Control) that adjusts the accumulation gain so that the luminance of the brightest part of the object scene is not saturated. Although the time is determined, since the color information of the subject must be acquired in charge accumulation for subject tracking, the accumulation time is determined by so-called subject-oriented AGC that adjusts the accumulation gain in the vicinity of the average luminance of the object scene. . Usually, the accumulation time determined by subject-oriented AGC is often longer than the accumulation time determined by peak AGC.

  When the tracking initial image and the tracking comparison image are acquired by subject-oriented AGC, it is not possible to determine in which range of the flicker cycle T the charge accumulation is performed. For example, as shown in FIG. If the charge accumulation of the tracking initial image is performed in the range of the luminance valley, the luminance information and the color information of the acquired tracking initial image become scarce, and a template image that accurately represents the subject image to be tracked cannot be obtained. Therefore, even if subject tracking is performed using such a template image, sufficient tracking performance cannot be expected.

  Therefore, as shown in FIG. 12, when the charge accumulation time T4 for acquiring the tracking initial image and the tracking comparison image is set to a time substantially equal to the flicker cycle T, the tracking cycle for acquiring the tracking comparison image and performing subject tracking control is performed. T5 becomes long, and subject tracking responsiveness decreases.

  In one embodiment, as shown in FIG. 10, the charge accumulation time T0 for obtaining the tracking initial image is made substantially equal to the flicker cycle T and is longer than the charge accumulation time T1 for obtaining the tracking comparison image. Since the length is increased, charge accumulation is performed over the entire range of the flicker period T even if the luminance of the object scene changes under the flicker light source, and a tracking initial image that is not affected by the flicker light source can be stably acquired. . Thus, a template image that accurately represents the subject image to be tracked can be obtained, and high accuracy and reliability in subject tracking can be realized using such a template image. Furthermore, since the charge accumulation time T1 for acquiring the tracking comparison image is set to the necessary minimum length that is shorter than the charge accumulation time T0 for acquiring the tracking initial image, subject tracking control is performed while acquiring the tracking comparison image. The tracking cycle T2 (see FIG. 10) when performing is shortened, and high responsiveness of subject tracking can be maintained.

  Note that the charge accumulation time T0 at the time of initial tracking image acquisition is desirably substantially equal to the flicker cycle T, but the longest time allowable in the dynamic range of the second image sensor 16 according to the subject brightness at the time of initial tracking image acquisition. It is necessary to limit to.

  By the way, there are cases where continuous shooting (continuous shooting) is performed while tracking a target subject by subject tracking control. During continuous shooting, the quick return mirror 5 and the sub mirror 6 are repeatedly raised (withdrawn from the photographing optical path) and down (in the photographing optical path) each time an image is taken, and subject light is not guided to the viewfinder optical system in the up state. Therefore, the charge accumulation time for acquiring the tracking image is restricted.

  FIG. 13 is a timing chart showing the acquisition timing of the tracking initial image and tracking comparison image during continuous shooting in the conventional subject tracking device. In order to avoid the influence of the flicker light source, if the charge accumulation time for acquiring the tracking initial image and the tracking comparison image is lengthened, the charge accumulation for acquiring the tracking comparison image has to be interrupted for mirror up, and the interruption Sometimes complex interruptions must be performed each time.

  On the other hand, in this embodiment, the charge accumulation time T0 for obtaining the tracking initial image is made substantially equal to the flicker cycle T and longer than the charge accumulation time T1 for obtaining the tracking comparison image. As shown in FIG. 14, it is not necessary to interrupt the charge accumulation for acquiring the tracking comparison image for the mirror up, and a complicated interruption process at the time of interruption is not necessary. That is, according to this embodiment, it is possible to stably acquire a tracking initial image that is not affected by a flicker light source even during high-speed continuous shooting, and generate a template image that accurately represents the subject image to be tracked. In addition to realizing high accuracy and reliability of subject tracking, it is possible to shorten the tracking cycle when performing subject tracking control while acquiring a tracking comparison image, and maintain high responsiveness of subject tracking.

Returning to step 1 of FIG. 8, the description of the operation of the embodiment will be continued. The initial tracking image acquired in step 1 is represented by RGB values for each pixel.
R [x, y], G [x, y], B [x, y] (1)
Based on the RGB values, color information and luminance information of each pixel are calculated. In this embodiment, RG and BG, which are values indicating the degree of color deviation, are used as color information, and exposure time T, gain Gain, and color composition coefficients Kr and Kg when an image is acquired are used as luminance information. , L calculated by Kb is used.
RG [x, y] = Log ₂ (R [x, y]) − Log ₂ (G [x, y]),
BG [x, y] = Log 2 (B [x, y]) - Log 2 (G [x, y]),
L [x, y] = Log ₂ (Kr × R [x, y] + Kg × G [x, y] + Kb × B [x, y]) − Log ₂ (T) −Log ₂ (Gain) (2)

  Here, as is apparent from the equation (2), RG and BG, which are values indicating the degree of color deviation, have a strong reddish image if the RG value is large, and a strong blue color if the BG value is large. It shows that. Here, an example is shown in which the color information of the color deviations RG and BG to red and blue based on green is used, but the reference color and the color to be compared with the reference color are the colors of this embodiment. It is not limited. When colors other than RG and BG are used as color information, it is necessary to change the color of the filter used for the pixel 26 of the second image sensor 16 shown in FIG. 4 according to the color used as the color information. is there.

  In the subsequent step 2, the tracking control initial process shown in FIG. 9 is executed. In step 101 of FIG. 9, an image at a position corresponding to the position of the focus detection area 45b in the tracking initial image acquired by the second image sensor 16 is stored as subject color information (color information and luminance information). In step 102, as shown in FIG. 6A, the same color information area showing the same color information as the subject color information is detected in the position peripheral portion of the focus detection area 45b (see FIG. 5) in the tracking initial image. In step 103, the same color information area is set as the initial tracking subject area 47.

  Here, an example in which the tracking subject area 47 is determined based on the subject color information is shown, but in order to simplify the processing, the size of the tracking subject area is uniformly set to 3 × 3 pixels, The size of the subject area may be determined according to the distance information of the photographing lens 8.

In step 104, the image of the tracking subject area 47 in the tracking initial image is stored in the memory 19d as a template image 48 (see FIG. 6B) used for the image tracking process. For example, when the starting point position of the tracking subject region 47 is (x, y) = (4, 5) as shown in FIG. 6A, the color information RGref, BGref and luminance information Lref of the template image 48 are the following. It is expressed as In FIG. 6A, the horizontal axis is x, the vertical axis is y, and in FIG. 6B, the horizontal axis is rx and the vertical axis is ry.
RGref [rx, ry] = RG [x, y],
BGref [rx, ry] = BG [x, y],
Lref [rx, ry] = L [x, y] (rx, ry = 1 to 3, x = 4 to 6, y = 5 to 7) (3)

  Next, in step 105, an area enlarged by predetermined pixels (here, two pixels) around the tracking subject area 47 is set as the search area 49. In the example shown in FIG. 6A, the search area 49 is an area where x = 2 to 8 and y = 3 to 9.

  When the initial processing of the tracking control is completed, the process proceeds to step 3 in FIG. 8 to check whether or not the shutter button of the operation member 20 has been fully pressed, that is, whether or not the shutter release operation has been performed. If there is no shutter release operation, the process proceeds to step 4 where a tracking comparison image is acquired from the second image sensor 16, and color information RG [x, y], BG [x, y] and luminance information are acquired in the same manner as in step 1. L [x, y] is calculated and stored in the memory 19d. At the same time, the focus detection signal corresponding to the pair of optical images for focus detection is acquired by the distance measuring element 10 for each of the focus detection areas 45a to 45g.

  As shown in FIG. 10, the charge accumulation time T1 for acquiring the tracking comparison image is a necessary minimum time shorter than the charge accumulation time T0 for acquiring the tracking initial image.

  In step 5, regions having the same size as the template image 48 are sequentially cut out from the search region 49 in the tracking comparison image, and a color information difference Diff is calculated for each corresponding pixel of the cut-out image and the template image 48. As shown by a thick broken line in FIG. 7A, a color information difference Diff from the template image 48 is calculated while shifting the region by one pixel in the search region 49.

Now, assuming that the starting point position of the search area 49 is (scx, scy) = (2, 3) as shown in FIG. 7A, the calculation of the difference Diff is performed as follows.
Diff [dx, dy] = ΣΣ {ABS (RG [scx + dx-1 + rx, scy + dy-1 + ry] −RGref [rx, ry]) + ABS (BG [scx + dx−1 + rx, scy + dy−1 + ry] −BGref [rx, ry]) + ABS (L [scx + dx-1 + rx, scy + dy-1 + ry] -Lref [rx, ry])} (4)
In the equation (4), dx, dy = 1 to 5, rx, ry = 1 to 3, scx = 2, scy = 3, and ΣΣ is a sum operation of rx = 1 to 3 and ry = 1 to 3.

  Next, among all the differences Diff calculated by the equation (4), the difference having the smallest value is set as the minimum difference MinDiff. In the example shown in FIG. 7A, the position (minx, miny) that is the minimum difference MinDiff is (4, 4) in the search area 49. The smaller the value of the minimum difference MinDiff, the higher the similarity to the template image 48.

  In step 6, the minimum difference MinDiff obtained in step 5 is compared with the similarity determination threshold value Dth. If the minimum difference MinDiff is larger than the similarity determination threshold value Dth, it is determined that the image of the area for which the minimum difference value MinDiff has been obtained is not similar to the template image 48, and the process proceeds to step 10. On the other hand, if the minimum difference value MinDiff is equal to or smaller than the similarity determination threshold value Dth, it is determined that the image of the area for which the minimum difference value MinDiff is obtained is similar to the template image 48, and the process proceeds to step 7.

In step 7, the area for which the minimum difference value MinDiff has been obtained is determined as a new tracking subject area 47. In the example shown in FIG. 7B, an area indicated by a broken line frame whose starting point position is (x, y) = (5, 6) is a new tracking subject area 47. In the following step 8, the template image is updated using the image information of the new tracking subject area 47. In this embodiment, for example, as shown in the following equation, 20% of the image information of the new tracking subject region 47 is added to 80% of the image information of the current template image 48, and the color information RGref of the new template image 48 is added. BGref and luminance information Lref are generated and stored again in the memory 19d.
RGref [rx, ry] = 0.8 · RGref [rx, ry] + 0.2 · RG [x, y],
BGref [rx, ry] = 0.8 · BGref [rx, ry] + 0.2 · BG [x, y],
Lref [rx, ry] = 0.8 · Lref [rx, ry] + 0.2 · L [x, y],
(Rx, ry = 1-3, x = 5-7, y = 6-8) (5)

  Note that the ratio of the image information in the template image so far and the image information of the new tracking subject area 47 when the template image 48 is updated may be a fixed value as described above, or may be variable according to the minimum difference MinDiff. Also good.

  In step 9, an area enlarged by predetermined pixels (here, two pixels) around the new tracking subject area 47 is set as a new search area 49. Here, as shown in FIG. 7B, an area of x = 3 to 9 and y = 4 to 10 is set as a new search area 49.

  In the subsequent step 10, the focus detection areas 45 a to 45 g shown in FIG. 5 acquired in step 4 in the focus detection area in the new tracking subject area 47 or in the vicinity of the new tracking subject area 47. A known focus detection calculation is performed based on the focus detection signal, and the defocus amount of the focus detection area is calculated. Then, a defocus amount detected in the focus detection area in or near the new tracking subject region 47 is converted into a lens drive amount, and the lens driving control device 22 drives the focusing lens 8b to perform focus adjustment. Then, it returns to step 3 and repeats the process mentioned above.

  Confirm that the release button is fully pressed in step 3 after adjusting the focus. While the shutter button is half-pressed, the processes of steps 4 to 10 are repeatedly executed. When the shutter button is fully pressed, the process proceeds to step 11 to execute a photographing process. In the imaging process, an exposure calculation is performed based on the luminance information of the new tracking subject area 47 determined in step 7, and an aperture value and a shutter speed are calculated. The shutter 7 and the aperture 21 are driven and controlled in accordance with these exposure values, and the first image sensor 4 captures an image.

  In the above-described embodiment, an example in which the subject tracking device of the present invention is mounted on a single-lens reflex digital camera has been described. However, the subject tracking device of the present invention is not limited to a single-lens reflex digital camera, for example, a compact digital camera It can also be installed.

  In the above-described embodiment, the example in which the second image sensor 16 originally provided for photometry is also used for subject tracking control has been described. However, the first image sensor 4 for imaging may also be used for subject tracking control. Good.

  In the above-described embodiments and their modifications, all combinations of the embodiments and the modifications are possible.

DESCRIPTION OF SYMBOLS 1; Camera, 8; Shooting lens, 16; 2nd image pick-up element, 19; Body drive control apparatus, 19a; Element control circuit, 19e;

Claims (5)

Imaging means for repeatedly imaging an image formed by the imaging optical system;
Reference setting means for setting a reference image of the tracking target subject from the first image picked up by the image pickup means;
Position search means for searching for a position of a partial image similar to the reference image in a second image taken after the first image by the imaging means;
In a subject tracking device that tracks a subject to be tracked that moves within the shooting screen,
Exposure control means for controlling the exposure time of the imaging means;
The subject tracking device, wherein the exposure control means sets a longer exposure time when capturing the first image than when capturing the second image. The subject tracking device according to claim 1,
The subject tracking device, wherein the exposure control means sets an exposure time substantially equal to a flicker cycle of a light source when taking the first image. In the subject tracking device according to claim 1 or 2,
The subject tracking device, wherein when the first image is captured, the exposure control means sets the longest time allowable in a dynamic range according to the subject brightness of the image sensor. In the subject tracking device according to any one of claims 1 to 3,
Light source determination means for determining whether the light source at the time of imaging is a flicker light source,
The exposure control means makes the exposure time for capturing the first image longer than the exposure time for capturing the second image when the light source determination means determines that the light source is a flicker light source. A subject tracking device. In the subject tracking device according to any one of claims 1 to 3,
The exposure control means is characterized in that when a flicker light source is selected in a white balance setting, an exposure time for capturing the first image is longer than an exposure time for capturing the second image. Subject tracking device.

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