JP2008052225A - Camera, focus control method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a camera capable of focusing a subject moving during consecutive photographing, and to provide a focus control method and a program. <P>SOLUTION: Upon an instruction to start consecutive photographing (A), focusing first takes place by contrast control ((C), (B)) using a so-called climbing system. Then, consecutive photographing is started. After the start of consecutive photographing, a contrast and a face area are detected from each photographic image. If it is judged that the contrast has decreased, a change in face area is judged by a motion vector. If it is judged that the face area is enlarged, it is judged that the subject is approaching. Then, the focus of a photographic lens is shifted toward a close distance. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for controlling the focus of a camera during continuous shooting.

  As a photography method, changing the shutter speed or aperture control (manual shooting) changes the effect of the lens or the effect of expressing what is moving, and the image is expressed by the effect of exposure. Methods for adjusting are well known. Continuous shooting is effective for a moving subject or a subject whose timing is difficult to match. Even in continuous shooting, it is desirable that the focus follows a moving subject. Therefore, as a technique for focusing even during continuous shooting, Patent Document 1 describes a camera that can select either phase difference AF (autofocus) or contrast AF.

  In recent years, as an extension of continuous shooting technology, compression methods (interframe compression) using continuous digital screens have been developed, and many cameras with enhanced video functions have appeared. Many of these cameras are not only capable of capturing moving images, but are also equipped with a motion detection circuit that detects the motion (position change) of the subject, for example, to prevent camera shake, for example.

Until now, in order to deal with such a problem of subject movement, as in Patent Documents 2 and 3, proposals have been made to further improve the high-speed performance of the camera by using the above-described motion detection concept and circuit. . For example, in Patent Document 2, the focusing area is switched according to the movement of the subject. Japanese Patent Application Laid-Open No. 2004-228620 proposes to detect a subject using information at the time of inter-frame compression (a numerical value of the magnitude and direction of subject motion) called a motion vector.
Japanese Patent Laid-Open No. 2001-275033 Japanese Patent Application Laid-Open No. 07-23272 JP 2003-189290 A

  In a compact camera, in many cases, a method (so-called hill-climbing AF) is employed in which imaging is performed by moving a focusing lens during focusing and a lens position with high contrast is selected. However, in principle, this requires a plurality of times of image capturing and focusing control, and has the disadvantage that tracking is slow.

  In the case of a camera of a category called single lens reflex, the viewfinder optical path and the imaging optical path are selectively switched. In a single-lens reflex camera, since the focus detection means is installed on the finder optical path side, there is a problem that AF cannot be performed during continuous shooting unless the optical path is switched every time. As described above, the two typical conventional focus detection methods have such limitations, and even if the reading speed of the image sensor increases, the continuous shooting speed is limited in terms of the focusing speed.

  It is desirable to be able to shoot a picture without failure by tracking the moving object or during high-speed continuous shooting when moving while shooting. If the high-speed imaging function and image processing function unique to a digital camera are used effectively for focusing, a high-speed continuous shooting speed may be realized.

  In view of the above problems, the present invention provides a camera capable of focusing on a moving subject during continuous shooting, a focus control method thereof, and a program.

In order to achieve the above object, a camera according to a first aspect of the present invention is a camera that performs continuous shooting, a photographing lens that forms a subject image, and an imaging device that outputs an image signal based on the formed subject image. The focus position control means for controlling the focusing of the photographing lens and the screen of the photographed image based on the image signal are divided into a plurality of blocks, and the photographed images obtained repeatedly are compared in units of blocks to change the position of the subject. The focus position control means predicts a distance change from the subject according to the position change detection result and performs focusing.

  The camera according to the second aspect of the invention includes a first position for reflecting the subject light that has passed through the photographing lens, and a reflecting mirror for moving a second position for allowing the subject light to pass through and forming an image on the image sensor. In a single-lens reflex camera that performs continuous shooting while the reflecting mirror is moved to the second position, the focusing control unit that controls focusing of the photographing lens, and the reflecting mirror is moved to the first position. In this state, the focus control unit includes a focus detection unit that detects focus from the phase difference of the subject light that has passed through the photographic lens, and a motion determination unit that determines the motion of the subject from the captured image. The focus is controlled in accordance with the result of the focus detection unit with the reflecting mirror moved to the first position at the start of shooting, and the reflecting mirror is moved to the second position after starting continuous shooting. The motion judgment unit It controls to focus on the subject distance predicted from the determined subject movement.

  The focus control method according to the third invention is a focus control method for a camera that performs continuous shooting, and at the start of continuous shooting, the contrast of the captured image is determined and the focus of the shooting lens is controlled according to the contrast. After the continuous shooting is started, the movement of the subject is determined from the captured image, and the focusing of the photographing lens is controlled according to the change in the subject distance predicted based on the movement of the subject.

  According to a fourth aspect of the present invention, there is provided a program for causing a computer to execute a focus control method for a camera that performs continuous shooting, wherein the focus control method determines a contrast of a captured image at the start of continuous shooting. The focus of the photographic lens is controlled accordingly.After continuous shooting is started, the movement of the subject is determined from the captured image, and the photographic lens is focused according to the change in the subject distance predicted based on the movement of the subject. It is something to control.

According to the present invention, it is possible to provide a camera capable of focusing on a moving subject during continuous shooting, a shooting control method thereof, and a program.

For cameras that allow the user to switch the shutter speed and control the exposure appropriately by controlling the aperture and sensitivity, if the shutter speed is generally slowed down, for example, when shooting a river flow, the water flow is like a thread. This makes it possible to depict images that have been extended. If you increase the shutter speed, you can capture the same river flow, capture the moment, and make it possible to reproduce the moment when the splashes rise and the state of ripples. Even in sports photos, if the shutter speed is increased, the movement of the subject can be stopped, and the facial expression can be clearly captured.

By shooting at a high shutter speed, even in a scene where the photographer is moving, the subject can be accurately cut out without blurring the subject. However, if high-speed repeated continuous shooting is assumed, there is a problem that focusing cannot be performed. In the present invention, in order to avoid such a situation as much as possible, an image sensor or an image processing circuit capable of photographing at high speed is used. The best mode for carrying out the present invention will be described below with reference to the drawings.
(First embodiment)
FIG. 1 is an overall block diagram of a camera 1 to which the present invention is applied. The camera 1 includes a photographing lens unit 2, an AF control unit 2a, a diaphragm unit 3, a diaphragm control unit 3a, an imaging element 4, and an analog front end (hereinafter abbreviated as AFE) unit 5 as imaging units.

  The taking lens unit 2 forms an image of the incident subject 20 on the image sensor 4. The taking lens unit 2 has a focus lens inside. The AF (autofocus) control unit 2a detects the focus position, drives the focus lens, and moves the focus lens to the focus position. There are two methods for detecting the in-focus position by the AF control unit 2a. The first method is a method for detecting a focus position (focus position) from a contrast signal peak of a captured image, which is called so-called hill-climbing detection. The second method is a method of detecting a change in a face area as a motion vector and calculating a distance to a subject (details will be described later). The AF control unit 2a is also referred to as a focus position control unit and a focus control unit.

  In or near the photographic lens unit 2, a diaphragm unit 3 that provides a shutter or diaphragm effect is provided. The diaphragm unit 3 opens to a predetermined aperture at the time of photographing, and closes to end the exposure when the exposure ends. The aperture control unit 3a drives the aperture unit 3 to set the aperture diameter.

  The image pickup device 4 is a CCD, a CMOS sensor, or the like including a large number of light receiving surfaces (pixels). The image sensor 4 receives an image from the subject 20 via the photographing lens unit 2 and converts it into an image signal.

  The analog front end (AFE) unit 5 includes AD means, and converts the signal from the image sensor 4 into a digital signal. The AFE unit 5 performs various processes on the image signal output from the image sensor 4. The AFE unit 5 is also provided with a function of reading several pixels of the image sensor 4 in a lump. For example, when the signal level of each pixel is small, such as 4 pixels (2 × 2) and 9 pixels (3 × 3), several pixel signals can be added to improve the S / N. Sensitivity can be increased by such an operation. In this way, S / N can be improved by adding and using several pixel signals of the same color of the image sensor.

  The AFE unit 5 also has a function of selecting image signals output from the image sensor 4 and can extract a limited range of image data from all light receiving surfaces. If an image of only a predetermined area is recorded by this control, an effect similar to so-called trimming can be obtained.

  The camera 1 includes an image processing unit 6, a sensitization unit 6a, a motion determination unit 6b, a contrast determination unit 6c, and a face detection unit 6d. The image processing unit 6 corrects the color, gradation, and sharpness of the input signal. In the image processing unit 6, a sensitizing unit 6a is provided. The sensitizer 6a amplifies the obtained image signal to a predetermined level, and sets the correct gray level and the correct gray level. The sensitizer 6a performs digital operation on the signal so that the digitized signal level becomes a predetermined level.

  The image processing unit 6 is connected to an image determination unit that determines the characteristics of an image input from the image sensor 4 using a signal from the image processing unit 6. The image determination unit includes a motion determination unit 6b, a contrast determination unit 6c, and a face detection unit 6d.

  The motion determination unit 6b compares a plurality of images to detect the position of the subject, thereby calculating a motion vector of the subject and determining in which direction the subject has moved. The motion determination unit 6b is also referred to as motion vector calculation means or position change detection means. The contrast determination unit 6c determines the contrast value of the image signal. The contrast determination unit 6c performs autofocus control in conjunction with the AF control unit 2a of the photographing lens unit 2, which will be described later. The face detection unit 6d examines the characteristics of the image and detects the position of the main subject (face). Then, using the detected face information, the movement determination unit 6b calculates a motion vector from the movement and size change of the face, and determines whether the subject approaches or moves away from the camera.

  In addition, the image processing unit 6 includes resizing means for processing a signal from the image sensor 4 into a size that can be displayed on the display unit so that a live image (monitor image) can be displayed on the display unit in real time. By this function, an image incident on the image sensor can be confirmed prior to shooting, and the timing and photo opportunity at the time of shooting can be determined while looking at this instead of the optical viewfinder.

  Further, the camera 1 includes a compression / expansion unit 7, a recording / reproducing unit 8, a recording medium 9, an output unit 10, a display control unit 11, and a display unit 12. The compression / decompression unit 7 compresses the signal output from the image processing unit 6 during shooting. In the compression / decompression unit 7, MPEG4 and H.264 are stored. A moving image compression unit M 7a including a compression core unit such as H.264 and a still image compression unit S 7b such as a JPEG core unit are provided. This moving image compression is called inter-frame compression or the like. At this time, information such as the movement of the subject calculated by the motion determination unit 6b (motion vector calculation means) is taken into account. The recording / reproducing unit 8 records the image signal compressed here on the recording medium 9. The recording medium 9 is a storage recording medium that can be attached to and detached from the camera.

  The output unit 10 outputs the image data recorded on the recording medium 9 to the outside. As a result, the image data can be uploaded to a service such as a homepage or a blog via a PC or the like. For images premised on such applications, an appropriate photographing method is taken from the time of photographing, and a device is devised so that a predetermined effect can be obtained at the time of posting.

  The display unit 12 is composed of, for example, a liquid crystal or an organic EL, and displays a live (monitor) image at the time of shooting, and displays an expanded recorded image at the time of reproduction. The display control unit 11 controls the display unit 12. The display control unit 11 has a multi-control unit 11a. The multi control unit 11a causes the display unit 12 to display a plurality of images simultaneously. This controls, for example, such that an odd-numbered input image is displayed on the left side of the screen and an even-numbered input image signal is displayed on the right side of the screen. With this multi-screen display function, it is possible to compare and view captured images.

  At the time of reproduction, the compression / decompression unit 7 decompresses the compressed data recorded on the recording medium 9, and the image processing unit 6 further performs processing for display of the decompressed image. This image is viewed as a reproduced image on the display unit 12 via the display control unit 11.

  The camera 1 is provided with an auxiliary light emitting unit 13, an MPU 14, a ROM 16, a release switch 15a, a mode switch 15b, and another switch 15c. The auxiliary light emitting unit 13 includes a white LED and a Xe discharge arc tube, and the amount of light can be controlled by the amount of current flowing. Depending on the situation, the subject 20 is irradiated with light to prevent lack of brightness and uneven brightness.

  The MPU 14 is a control unit that controls the entire camera. The release switch 15a, the mode switch 15b, the other switch 15c, and the ROM 16 are connected to the MPU 14. Each switch 15a-15c detects a user's operation, and notifies the result to MPU14 which is a calculation control means which consists of a microcontroller. The MPU 14 switches shooting / playback mode switching, shooting mode switching, and the like in accordance with the operation of these switches. The MPU 14 controls the AF control unit 2a, the aperture control unit 3a, and the like at the time of shooting.

  The ROM 16 is a non-volatile and recordable memory, and is composed of, for example, a flash ROM, and stores a control program for performing control processing of the camera 1. The MPU 14 reads a program from the ROM 16 and executes it. Then, the MPU 14 executes shooting and recording processing as shown in a flowchart of FIG.

  The focusing operation according to the present invention will be specifically described with reference to FIGS. FIG. 2 is a diagram showing the shooting timing of continuous shooting for a subject moving toward the camera and the obtained image in comparison. T1 and T2 (displayed in a low active state) in FIG. 2A indicate photographing timing. The image taken at timing T1 is image 1, and the image taken at timing T2 is image 2. In this case, the subject moves and approaches, so the subject (person) size of the subsequent photographed image becomes larger. In such a scene, since the distance to the subject changes every moment, the following focus control is performed.

  FIG. 3 is a diagram showing face areas detected from the images 1 and 2 photographed in FIG. The face detection unit 6d detects a characteristic part such as an eye nose of the face from the images 1 and 2. The face area where the right face screen is detected is shown. The face screen 1 corresponds to the image 1, and F1 (broken line) indicates the face position detected on the screen. That is, this round area F1 indicates the position and size of the detected face. Similarly, face information detected from the image 2 in FIG. 2 is shown on the face screen 2 as a region F2 (solid line). On the screen of the face screen 2, an area F1 is also displayed for comparison. In this scene, since the subject approaches, the area F2 becomes larger than the area F1.

  In this way, comparing the face areas and calculating the direction and amount of movement of the similar point as a motion vector, the face portion has simply moved up, down, left and right, or moved toward here, and the image is enlarged. Can be determined. The motion determination unit 6b can calculate a motion vector from the result of face detection and estimate the motion of the subject.

  FIG. 4 is a diagram showing a state in which an image area is divided (here, divided into 12), and a motion vector is calculated from changes in the areas F1 and F2. The motion determination unit 6b detects that the face area has changed in the direction and amount indicated by the arrows in the B2 block and the B6 block unit. Then, for each divided block, the motion determination unit 6b determines how the image in the block moves to determine whether the subject is large or small, or simply shifted laterally. judge. In other words, as in this example, when a motion vector is calculated such that the image of the face portion spreads from the center, the subject is determined to be an approaching subject because the portion occupied by the subject has increased.

  As a result, as shown in FIG. 2, it is possible to determine whether or not focus control should be performed on a person who runs toward the person at an athletic meet or the like. Even if the photographer runs and approaches, the same determination is made, but it is better to change the focus position at that time as well.

  Based on the determination result of the movement determination unit 6b, the AF control unit 2a determines the situation and performs focus control. Furthermore, if the AF control unit 2a switches the focus shift amount according to the magnitude of the motion vector, the focusing accuracy is further improved. Further, the AF control unit 2a is adapted to shift the focus more quickly because the method of defocusing is faster when the subject moves quickly.

  FIG. 5 is a timing chart showing a focus position control operation when continuously shooting an approaching subject as shown in FIG. FIG. 5A is a timing chart showing the operation of the release switch 15a for instructing start and end of photographing. The LOW portion corresponds to the shooting period. FIG. 5B is a timing chart showing signal capture (imaging) of the image sensor 4. FIG. 5C shows the position of the focus lens moved by the AF control unit 2a. The upward direction is the short distance direction. FIG. 5D shows the magnitude of the contrast value of the subject determined by the contrast determination unit 6c from the image obtained by imaging. The upper direction is high contrast, and the imaging numbers in FIG. FIG. 5E shows the timing for calculating and determining a motion vector from a captured image by the motion determination unit 6b.

  This will be described in order below. In response to an operation instruction of the release switch 15a, a signal capturing operation of the image sensor 4, that is, imaging is started (FIG. (A)). First, focusing imaging that is not recording imaging is performed a plurality of times (four times in this example) (FIG. 5B). This is because the so-called hill-climbing (contrast) AF (focusing) is performed. In synchronization with this imaging operation, the AF control unit 2a sequentially moves the focus lens in the photographing lens unit 2 from a long distance to a short distance direction ((C) in the figure).

  When the focus position is changed by the movement of the focus lens, the contrast of the main subject of the image changes as shown in FIG. Then, the position of the focus lens is moved to a position where the best (high) contrast is obtained. Here, since the contrast is the highest in the second shooting, this position is determined as the in-focus position. Now that the focus position has been determined, the process proceeds to an imaging operation for photographing. Note that the imaging result at the time of focusing may also be recorded.

  Next, four continuous shootings (Nos. 5, 6, 7, and 8) are performed. This shooting is recorded. During this time, focus control is performed by the motion vector determination method, which is a feature of the present invention. This is because the focus control by the hill-climbing operation as in the first half requires a plurality of shootings, and if such focus control is performed during continuous shooting, the continuous shooting speed is greatly reduced.

  The contrast determination unit 6c constantly checks the contrast of the photographed image, and when the contrast of the image starts to change (here, decreases) as shown in FIG. (D) (No. 5 to No. 6), this is detected. When the contrast change is detected, the motion determination unit 6b calculates a motion vector at the timing shown in FIG. If it is to change the size of the subject, particularly when it is determined that the subject will be larger, the AF control unit 2a moves the focus lens so as to shift the focus in the short distance direction. Furthermore, it is estimated that the subject is approaching the camera direction because the contrast is improved by performing a focus shift during the seventh imaging. Therefore, even before the eighth imaging, the motion vector is detected and determined, and the focus shift (focus movement) is again performed in the short distance direction.

  There are two methods for determining the focus shift amount. One is a method of determining the focus shift amount according to the magnitude of the motion vector. The second is a method of determining the shift amount using the relationship between the focus position and contrast change (contrast change / focus change) during the first hill-climbing AF. This is because the larger the contrast reduction amount, the larger the focus shift, and there is a correlation between the contrast decrease amount and the focus shift amount. This contrast change / focus change (shaded dotted line) is added to the figure.

  FIG. 6 is a flowchart showing the sequence of the continuous shooting control process. This process is performed by the AF control unit 2a, the motion determination unit 6b, the contrast determination unit 6c, the face detection unit 6d, and the like, and the MPU 14 that comprehensively controls them.

  First, it is assumed that the camera 1 is set to the shooting mode. Then, it waits for a release operation that is a user's shooting start operation in the shooting mode (step S1). FIG. 7A is a view of the state in which the camera is operated during actual shooting as viewed from the back, and is an example of continuous shooting setting operation. As shown in FIG. 7A, shooting in the high-speed continuous shooting mode is started by pressing the release switch 15a on the upper surface while pressing the mode switch 15b provided on the back surface of the camera 1. When the user views the display unit 12 and thinks that the subject to be photographed and the situation is preferable to the high-speed continuous shooting, the user sets the high-speed continuous shooting mode by such an operation and performs the shooting.

  When a release operation is performed (YES in step S1), exposure (brightness of the subject) is determined, and focus control (AF) is performed (step S2). The focus (focusing) control here is a control based on a contrast method, and corresponds to the processing from No. 1 to No. 4 in FIG. The focus position and contrast change during the focus control process are stored (step S3). This corresponds to the contrast change / focus change slope described with reference to FIG.

  Then, photographing and temporary recording are performed (step S4). It is determined whether the high-speed continuous shooting mode is set (step S5). As described above, for example, as shown in FIG. 7A, the high-speed continuous shooting mode is set by pressing the release switch 15a on the upper surface while pressing the mode switch 15b provided on the back surface of the camera 1. . When it is determined that the high-speed continuous shooting mode is not set (NO in step S5), the image temporarily recorded in step S4 is compressed by the compression / decompression unit 7 (step S6). The compressed image is recorded on the recording medium 9 (step S7).

  When the high-speed continuous shooting mode is set (YES in step S5), in order to prevent the focus from being deviated within a limited time during continuous shooting, in the manner described with reference to FIG. Repeat the flow. The face detection unit 6d performs face detection from the captured image (step S21). The motion determination unit 6b calculates a motion vector from the detected change in the face area (step S22).

  The contrast determination unit 6c determines whether the contrast of the captured image is increased or decreased (step S23). Then, it is determined whether or not the contrast has decreased (step S24). When it is determined that the contrast has decreased (step S24 YES), the motion determination unit 6b determines whether the face area has expanded next (step S25). When it is determined that the face area is enlarged (YES in step S25), the shift amount is determined using the “relationship between contrast and lens position” calculated in step 3 (step S26). According to this shift amount, the AF control unit 2a moves the focus in the forward direction (step S27). As a result, a focused image can be taken even for a moving subject. Note that the order of the contrast reduction determination (step S24) and the facial area enlargement determination (step S25) may be reversed.

  After step S24NO, step S25NO, and step S27, the process returns to step S4 and temporarily records. After the continuous shooting is finished (NO in step S5), the image temporarily recorded in step S4 is compressed by the compression / decompression unit 7 in the same manner as described above (step S6). Further, it is recorded on the recording medium 9 (step S7). In the calculation of the motion vector (step S22), the result of face detection (step S21) is used. However, the present invention is not limited to this. For example, a predetermined area at the center of the screen is substituted. Also good. This is because the face is often placed at the center of the screen during shooting. Further, in the above example, it has been described that the process after step S21 is performed every time shooting is performed, but it is natural that this process is executed once for several shootings in relation to the continuous shooting speed. Good.

  On the other hand, in a situation where the shooting release operation has not yet been performed, the process proceeds from step S1 to step S11. Here, it is determined whether or not there is an operation for switching to the reproduction mode (step S11). When the user gives an instruction to switch to the playback mode (YES in step S11), playback display is performed as the playback mode (step S15). This is a process of reproducing and displaying the image selected by the user from the photographing result on the display unit 12 such as a liquid crystal display.

  Furthermore, the user can compare the results of continuous shooting, which is one of the features of this embodiment. It is determined whether this comparison display is instructed by the user (step S16). When the comparison display is designated (step S16 YES), the comparison display (multi-screen display, see FIG. 4) is performed (step S17). On this comparison screen, the user can also delete images that are not required. It is determined whether or not a deletion instruction is issued by the user (step S18), and the deletion-instructed image is deleted (step S19). Then, it returns to step S1. In addition to the determination of the switching operation to the reproduction mode (NO in step S11), the determination of the power-off operation is also performed (step S12). When the power-off instruction is detected, the termination process is controlled (step S13).

  In other cases (step S11NO, step S12NO), the operation in the imaging mode is performed (step S14). In the imaging mode, real-time live (monitor) image display is continuously performed so that the user can determine the timing and composition of imaging. Although not shown, focusing may be performed at this timing, and the time lag of focusing (mountain climbing AF) after entering the photographing operation may be shortened. You may enable it to control the light emission amount of the auxiliary light emission part 13 in an imaging | photography step from the distance of the obtained to-be-photographed object. In addition, the amount of auxiliary light is not such a distance measurement method, but a so-called direct dimming technology that receives the reflected light from the subject when the auxiliary light is emitted and turns it off after reaching a predetermined level. It may be determined using.

  In the above description, the scene where the subject approaches is described, but the present invention can also be applied to the case where the subject moves away. At this time, since the opposite estimation can be performed by gradually reducing the size of the subject, the focus may be moved in the reverse direction (long-distance direction).

  As described above, according to the present embodiment, focusing is performed using a change in an image obtained by high-speed continuous shooting according to a situation, so that not only a photo opportunity is missed but also good focus control is performed. Can increase the probability of leaving a photo that the user likes. Accordingly, it is possible to provide a camera in which an area where a moving subject can be imaged or an area where an image can be captured while moving is widened.

(Second Embodiment)
The second embodiment is an example in which the present invention is applied to a single-lens reflex camera. FIG. 7B is a view of the state where the single-lens reflex camera 30 is operated at the time of shooting as viewed from the back. A so-called single-lens reflex camera is a camera in which an optical path from a photographing lens is divided into an optical path to an imaging element for photographing and an optical path for a finder. Such a configuration makes it relatively easy to design the lens to be interchangeable. FIG. 8 is a diagram showing an outline of the optical system of the single-lens reflex camera 30. FIG. 8A shows a state where the mirror is lowered, and FIG. 8B shows a state where the mirror is raised. Since the single lens reflex camera 30 has the same electrical configuration as that of the camera 1 shown in FIG. 1, the block diagram is omitted, and the same components as those of the camera 1 are denoted by the same reference numerals for easy understanding.

  The optical system of the single-lens reflex camera 30 includes a photographic lens unit 2, a mirror 31, a pentaprism 32, an eyepiece lens 33, a sub mirror 34, and an AF sensor 35. The taking lens unit 2 forms an image of the subject 20 on the image sensor 4. The mirror 31 moves between two positions, a position for reflecting the light that has passed through the photographing lens unit 2 and a position for allowing the light to pass through. The pentaprism 32 guides the image of the subject 20 reflected by the mirror 31 to the eyepiece lens 33. The eyepiece 33 guides the image of the subject 20 to the photographer's eyes. The sub mirror 34 is rotatably attached to the back surface of the mirror 31, and further reflects light that has passed through a half mirror region provided in a part of the mirror 31. The AF sensor 35 detects the focus position by the phase difference using the light reflected from the sub mirror 34.

  FIG. 8A shows a state in which the mirror 31 is lowered and before photographing. The subject image reflected by the mirror 31 is reflected inside the pentaprism 32 and guided to the eyepiece 33 so that the user can see it. Then, the subject light beam that has passed through a part of the mirror 31 is reflected by the sub mirror 34 and enters the AF sensor 35, and the AF sensor 35 performs focus detection.

  FIG. 8B shows a state at the time of photographing in which the mirror 31 is retracted out of the optical path. The image of the subject 20 is incident on the image sensor 4 through the photographing lens unit 2. The sub mirror 34 is in a position where it is rotated and retracted from the optical path. The image of the subject 20 is converted into an electric signal by the image sensor 4, input to the recording / reproducing unit 8 after various processing, and recorded on a recording medium.

  In the camera as shown in FIG. 7A, an image with a time lag due to the image reproduction process can only be viewed through the display unit 12. However, in the case of a single-lens reflex configuration, an image is taken with an optical viewfinder. The light passing through the lens can be observed in real time. In addition, photometric means and focusing means that are effective in the state of FIG. 8 (A) are provided, and these dedicated sensors enable high-speed exposure control and focusing, and are more excellent in photometry. It has become. Here, an AF sensor 35 is shown as a focusing means.

  FIG. 9 is a diagram for explaining a focus detection method called a phase difference method by the AF sensor 35. The AF sensor 35 includes a lens pair 35a and a sensor 35b. The light beam that has passed through the photographic lens unit 2 and is reflected by the sub-mirror 34 is divided into two images by the lens pair 35a, and the two images are formed on the sensor 35b. FIG. 10 shows signal curves of two images (I1 and I2) formed on the sensor 35b and output from the sensor 35b. It is detected whether or not focusing is achieved by the position of the two images obtained by the sensor 35b.

  For a light beam such as a dotted line that is in focus, a pair of image signals is generated at a fixed position of the sensor 35b. A light beam such as a solid line that is not in focus forms an image at a position different from that of the broken line, so that a pair of image signals are generated at different intervals. Therefore, since the interval between the pair of image signals corresponds to the amount of focus shift, the amount of focus shift is calculated from the detected amount of shift in the interval. Then, the focus lens of the photographic lens unit 2 is moved so as to correct the amount of defocus. Such an AF method is called a phase difference method. In this state, after the photographing lens unit 2 is focused, the mirror 31 is retracted to perform exposure control.

  Thus, in a single-lens reflex camera, it is indispensable to raise and lower the mirror. When the mirror is up, the sub-mirror 34 is also retracted from the optical path as shown in FIG. 8B, so that focusing cannot be performed. Because of such limitations, when performing AF during continuous shooting of a conventional single-lens reflex camera, the mirror is raised and lowered each time shooting is performed, and shooting is performed with focus control each time. After a single mirror up, the down / up control time was a large time lag, which hindered high-speed continuous shooting.

  Therefore, in the present invention, high-speed continuous shooting is performed during one mirror up, the motion vector is determined, and the focus is adjusted. As a result, the instantaneous movement of the moving subject can be cut out by further high-speed continuous shooting of AF tracking, which is a feature of the present invention.

  FIG. 11 is a diagram for explaining the principle of adjusting the focus position by detecting a subject distance change based on the determination based on the motion vector. It is assumed that the subject 20 at the position of the distance L1 approaches the position of the distance L2 after a certain time. In response to this, the size of the face of the subject 20 on the shooting screen also changes from W1 to W2. The motion determination unit 6b determines the change in the size of the face from the motion vector. Then, the AF control unit 2a calculates L2 that is a distance W1 / W2 times as large as L1. Further, the AF control unit 2a controls the photographing lens unit 2 so as to focus on the calculated L2. As a result, accurate focusing can be performed without performing focus detection by the AF sensor 35 as shown in FIG.

  FIG. 12 is a diagram for explaining the principle of detecting a subject distance change by motion vector determination for a subject approaching from an oblique direction. In FIG. 11, the subject approaching straight is described. However, even when the subject does not approach straight, it is possible to focus by calculating the motion vector.

  It is assumed that the subject 20 that was initially at the position of the distance L1 approaches the position of the distance L2 after a certain time. FIGS. 12A and 12B are views of the subject as viewed from directly above. FIG. 12A shows a change in the right side position of the subject, and FIG. 12B shows a change in the left side position. When the subject 20 is at the distance L1, the position of the right portion of the subject 20 on the image sensor 4 is R1. Then, the position of the right part of the subject on the image sensor 4 when the subject 20 approaches the distance L2 is set as R2, and the difference ΔR is detected by the motion determination unit 6b (FIG. 12A).

  Similarly, when the subject 20 is at the distance L1, the position of the left part of the subject 20 is Le1. Then, when the subject 20 approaches the distance L2, the position of the left portion of the subject is set to Le2, and the motion determination unit 6b detects the difference ΔLe (FIG. 12B).

  From (Le1-R1) corresponding to W1 in FIG. 11, it can be seen that the size of the subject has changed to (Le1-ΔLe-R1 + ΔR) corresponding to W2 in FIG. Therefore, the distance L2 can be calculated from (Le1−R1) × L1 / (Le1−R1 + ΔR−ΔLe) by photographing after focusing on the distance L1. The AF control unit 2a calculates L2. By focusing and shooting at the calculated distance, it is possible to achieve good focusing without using hill-climbing (contrast) AF or a single-lens reflex phase difference method. Since this motion vector detection is used when compressing a moving image, it is possible to provide such excellent focus control without adding a special circuit.

  FIG. 13 is a time chart showing the operation of each function during continuous shooting. FIG. 13A shows the timing for instructing the start and end of shooting by pressing the release switch 15a. FIG. 5B shows the timing of up / down of the mirror 31. The mirror 31 is initially in a mirror-down state, and the mirror 31 is rotated halfway, and then enters a mirror-up state. FIG. 4C shows the operation timing of phase difference AF by the AF sensor 35. The focus position of the photographic lens unit 2 is switched so that the interval between the two images is appropriate. FIG. 4D shows imaging timing. Here, it is assumed that continuous shooting is performed four times after the mirror 31 is raised (No 1, 2, 3, 4). FIG. 5E shows the focus position of the taking lens unit 2 controlled by the AF control unit 2a with the upward direction as the short distance direction. FIG. 8F shows the contrast of the captured image determined by the contrast determination unit 6c. FIG. 5G shows the timing of face detection by the face detection unit 6d and the determination of the motion vector by the motion determination unit 6b using the result.

  The operation according to the above will be briefly described. Shooting is started by the operation (A) of the release switch 15a. First, in the mirror-down state (B), the AF sensor 35 detects the focus position by detecting the phase difference (C). The AF control unit 2a moves the photographing lens unit 2 to the detected focus position (E). Waiting for the end of this AF process, the mirror 31 is raised. After the mirror is raised, continuous shooting is started. Shooting is performed a total of four times (D). The contrast curve of the captured image decreases from No1 to No2 (F). The motion determination unit 6b operates by reducing the contrast of the subject from No1 to No2. Then, face detection is performed by the face detection unit 6d, and the motion determination unit 6b calculates a motion vector from the size change of the face and predicts that the subject is approaching. In accordance with this prediction, the AF control unit 2a changes the focus position to the front (E).

  FIG. 14 is a flowchart illustrating a procedure of the focus control process for the continuous shooting described above. This process is performed by the AF control unit 2a, the motion determination unit 6b, the contrast determination unit 6c, the face detection unit 6d, and the like, and the MPU 14 that comprehensively controls them.

  First, it is assumed that the camera 1 is set to the shooting mode. Then, it waits for a release operation that is a user's shooting start operation in the shooting mode (step S51). When a release operation is performed (YES in step S51), exposure (brightness of the subject) is determined, and focus control (AF) is performed (step S52). The focus control here is based on phase difference AF by the AF sensor 35. Then, photographing and temporary recording are performed (step S53).

  Next, it is determined whether a continuous shooting operation is performed (step S54). The continuous shooting operation is an operation similar to, for example, FIG. When it is determined that the continuous shooting operation has not been performed (NO in step S54), the image temporarily recorded in step S53 is compressed by the compression / decompression unit 7 (step S55). The compressed image is recorded on the recording medium 9 (step S56).

  When the continuous shooting operation is being performed (step S54 YES), the flow after step S71 is executed. The MPU 14 initializes the continuous shooting number n to 1 (step S71). For the first photographed image, the face detection unit 6d performs face detection. The face size of the nth image is Wn, and the face size detected first is W1 (step S72). The contrast determination unit 6c determines the contrast from this captured image (step S73).

  Then, the continuous shooting number n is incremented by 1 (step S74), photographed and temporarily recorded (step S75). The motion determination unit 6b calculates a motion vector of the subject compared with the previous captured image (step S76). The face detection unit 6d performs face detection. The detected face size is stored as Wn (step S77). Further, the contrast of this image is determined (step S78). Next, it is determined whether the continuous shooting operation is continued (step S79). If the operation of the release switch 15a is released and the continuous shooting operation is finished (NO in step S79), the process proceeds to step S55. The temporarily recorded image is compressed by the compression / decompression unit 7 (step S55) and recorded on the recording medium 9 (step S56).

  If the continuous shooting operation is continued (YES in step S79), it is determined whether the contrast is greatly reduced as compared with the previous image (step S80). If the contrast is greatly reduced (step S80 YES), it is next determined whether the face area is enlarged (step S81). If it is enlarged (YES in step S81), the AF control unit 2a moves the taking lens unit 2 so as to shift the focus forward (step S82). This is because it is estimated that the subject is approaching.

  This shift amount is calculated from Wn corresponding to W2 shown in FIG. 11 and W1. In this calculation, since there is a possibility that the subject is moving from the time when Wn is acquired until the time when the next image is acquired (change in Δt), the correction is made in consideration of the predicted amount until the next shooting. May be. In the case of shooting at a fixed interval, it is sufficient to focus on the position of L3 = L1-2 × ΔL, assuming that the change corresponding to the change of L1 → L2 (ΔL) occurs once again. In general, the focus position is proportional to the reciprocal of the subject distance. Therefore, the correction result k is added to the focus result at L1, and k × (1 / (L1-2 × ΔL) −1 / L1), What is necessary is just to shift a focus position. Instead of using W1 as a reference, the shift amount may be calculated based on the previous face size determination result Wn-1.

  If it is determined that the contrast is not lowered (NO in step S80) or the face area is not enlarged (NO in step S81), the process returns to step S74 without performing a focus shift. Note that the order of the contrast reduction determination (step S80) and the facial area enlargement determination (step S81) may be reversed. In face detection (steps S72 and S77), instead, a plurality of predetermined points may be stored and a change may be detected by a motion vector. Further, the determination of the decrease in contrast (step S73, step S78, step S80) can be omitted, and the focus lens movement may be determined only by the change of the motion vector (step S81).

  If no shooting instruction is given (NO in step S51), the process proceeds to the reproduction process. The procedure of the reproduction process from step 61 to step S69 is the same as that from step S11 to step S19 described with reference to FIG. Similarly, power-off processing and the like (steps S62 to S64) are also omitted. In the above description, the scene where the subject approaches is described, but the present invention can also be applied to the case where the subject moves away. At this time, since the reverse estimation can be performed by reducing the size of the subject, the focus may be moved in the reverse direction (long-distance direction).

  As described above, according to the present embodiment, by using the motion vector of the subject, it is possible to correct the focus from the characteristics of the obtained image at any time without performing extra control or mechanical switching during continuous shooting. Therefore, it is possible to provide a camera that is suitable for moving subjects. Of course, it is also possible to devise such as sequentially performing imaging for focusing and imaging for shooting without performing continuous shooting. In addition, if the change in contrast is taken into account, more reliable focus control can be obtained. In the camera having such a configuration, the present invention is more effective because of the response to the further speed. In particular, in a scene where a long-focus lens is used to capture a photograph of a theme such as sports at a high speed, the present invention makes it possible to prevent failure of photography.

(Other examples)
Part or all of the processing of the MPU 14 described in the above embodiments may be configured by hardware. Conversely, hardware such as the motion determination unit 6b and the face detection unit 6d may be configured by software. The specific configuration is a design matter.

  Each control process by the MPU 14 is realized by a software program stored in the ROM 16 being supplied to the MPU 14 and operating according to the supplied program. Therefore, the software program itself realizes the functions of the MPU 14, and the program itself constitutes the present invention.

  A recording medium for storing the program also constitutes the present invention. As a recording medium, besides a flash memory, an optical recording medium such as a CD-ROM or DVD, a magnetic recording medium such as an MD, a tape medium, a semiconductor memory such as an IC card, or the like can be used. Moreover, although each embodiment demonstrated the example which applied this invention to the digital camera, you may apply not only to this but the camera part of a mobile telephone, for example.

  Furthermore, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is an overall block diagram of a camera 1 to which the present invention is applied in a first embodiment. FIG. 6 is a diagram showing a comparison between shooting timing and an obtained image in a scene in which a subject moving toward the camera is continuously shot in the first embodiment. The figure which shows the face area detected from the image 1 and the image 2 which were image | photographed in FIG. 2 in 1st Embodiment. The figure which shows a mode that a motion vector is detected from the change of a face area in the divided image area in 1st Embodiment. 4 is a timing chart illustrating the operation of each function when performing continuous shooting in the first embodiment. 5 is a flowchart for describing focus control processing during continuous shooting in the first embodiment. The figure which looked at the mode of camera operation at the time of actual imaging | photography from 1st Embodiment in 1st Embodiment. FIG. 6 is a diagram illustrating an outline of an optical system of a single-lens reflex camera in a second embodiment. The figure explaining the focus detection system by AF sensor 35 in a 2nd embodiment. The figure which shows the signal curve of two images (I1, I2) imaged by the sensor 35b and output from the sensor 35b in 2nd Embodiment. FIG. 10 is a diagram for explaining the principle of adjusting a focus position by detecting a change in subject distance by motion vector determination in the second embodiment. The figure explaining the principle which detects a to-be-photographed object distance change by motion vector determination with respect to the to-be-obtained object in 2nd Embodiment. The time chart which shows operation | movement of each function at the time of continuous shooting in 2nd Embodiment. 9 is a flowchart illustrating a procedure of focus control processing for continuous shooting in a single-lens reflex camera in the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Camera, 2 ... Shooting lens part, 2a ... AF control part, 3 ... Diaphragm part, 3a ... Diaphragm control part,
4 ... Image sensor, 5 ... AFE part, 6 ... Image processing part, 6a ... Sensitization part, 6b ... Motion determination part, 6c ... Contrast determination part,
6d: Face detection unit, 7: Compression / decompression unit, 7a ... Compression unit M, 7b ... Compression unit S
DESCRIPTION OF SYMBOLS 8 ... Recording / reproducing part, 9 ... Recording medium, 10 ... Output part, 11 ... Display control part, 11a ... Multi-control part, 12 ... Display part 14 ... MPU, 15a ... Release switch, 15b ... Mode switch, 15c ... Other switch 16 ROM
20 ... Subject, 30 ... Single-lens reflex camera, 31 ... Mirror, 32 ... Pental prism, 33 ... Ocular lens, 34 ... Sub mirror,
35 ... AF sensor, 35a ... Lens pair, 35b ... Sensor

Claims (16)

For cameras that take continuous shots,
A taking lens that forms a subject image;
An image sensor that outputs an image signal based on the imaged subject image;
A focus position control means for controlling the focusing of the photographing lens;
A position change detecting unit that divides a screen of a captured image based on the image signal into a plurality of blocks, compares the repeatedly acquired captured image in units of blocks, and detects a change in the position of the subject. Is a camera that predicts a change in distance from the subject according to the position change detection result and performs focusing. Face detection means for detecting the position of the face of a person as a subject from a captured image based on the image signal,
The camera according to claim 1, wherein the position change detection unit selects a plurality of blocks for detecting the position change in accordance with a detection result of the face detection unit. Face detection means for detecting the position of the face of a person as a subject from a captured image based on the image signal,
The position change detection means detects a position change of the face based on the detected face position as the position change of the subject, and determines whether the face area is in an expanding direction;
2. The camera according to claim 1, wherein the focus position control unit changes the focus position to the near distance side when it is determined that the face area is in an expanding direction. 3. The focus position control means performs focusing based on the contrast detected from the captured image based on the image signal at the start of continuous shooting, and predicts the distance change from the subject during continuous shooting. The camera according to claim 1, wherein: Switching means for switching the optical path of the subject image incident from the photographing lens to one of a first optical path leading to the imaging element and a second optical path leading to the finder optical system;
A focusing sensor disposed in the first optical path;
The camera according to claim 1, wherein the focus position control unit performs focusing by a focusing sensor, and performs focusing by predicting a change in distance from the subject after the switching. For cameras that take continuous shots,
A focus control unit for controlling the focusing of the taking lens;
A movement determination unit that determines the movement of the subject from the captured image;
A contrast determination unit that determines the contrast of the captured image,
The focus control unit controls focusing according to the contrast determined by the contrast determination unit at the start of continuous shooting, and based on the movement of the subject determined by the motion determination unit after the continuous shooting starts. A camera that controls focusing according to a predicted change in subject distance. A face detection unit that detects the position of a person's face from a captured image,
The movement determination unit determines the movement of the subject in the front-rear direction according to the size of the face according to the detection result of the face detection unit,
The camera according to claim 6, wherein the focus control unit controls focusing according to a change in a subject distance predicted from a movement of the subject in the front-rear direction. The focus control unit performs control in consideration of a contrast change of a captured image by the contrast determination unit when controlling focusing based on the movement of the subject by the motion determination unit after the continuous shooting is started. The camera according to claim 6. The camera according to claim 8, wherein the focusing control unit performs focusing control based on the movement of the subject by the motion determination unit when the contrast is lowered. The focus control unit detects the relationship between the contrast change and the focus position change by the focus control operation at the start of continuous shooting, and based on this relationship, changes the focus position from the contrast change of the captured image after the continuous shooting starts. The camera according to claim 8, wherein the focus adjustment control is performed after the determination. A reflection mirror that moves a first position that reflects the subject light that has passed through the photographic lens and a second position that causes the subject light to pass through and is imaged on the image sensor; the reflection mirror moves to the second position; In a single-lens reflex camera that performs continuous shooting in the
A focus control unit for controlling the focusing of the taking lens;
A focus detection unit that detects focus from a phase difference of subject light that has passed through the photographic lens in a state where the reflection mirror has moved to the first position;
A movement determination unit that determines a movement of a subject from a captured image based on a signal of an image sensor. The focus control unit detects the focus when the reflection mirror is moved to the first position at the start of continuous shooting. The focus is controlled according to the result of the unit, and after the continuous shooting is started, the reflection mirror is moved to the second position, and the subject distance predicted from the motion of the subject determined by the motion determination unit is A camera that is controlled to focus. In the focus control method of a camera that performs continuous shooting,
At the start of continuous shooting, the contrast of the captured image is determined and the focus of the photographic lens is controlled according to the contrast.
After continuous shooting is started, the movement of the subject is determined from the photographed image, and the focus of the photographing lens is controlled in accordance with the change in the subject distance predicted based on the movement of the subject. . The in-focus control method according to claim 12, wherein the focus control method controls in consideration of a contrast change of a captured image when controlling the focus based on the movement of the subject after the start of continuous shooting. Control method. A reflection mirror that moves a first position that reflects the subject light that has passed through the photographic lens and a second position that causes the subject light to pass through and is imaged on the image sensor; the reflection mirror moves to the second position; In a focus control method in a single-lens reflex camera that performs continuous shooting in a state where
At the start of continuous shooting, with the reflecting mirror moved to the first position, focus is detected from the phase difference of the subject light that has passed through the photographic lens, and the focus is controlled according to the result. A focus control method comprising: controlling the focus on the distance of a subject predicted from the movement of the subject determined from the captured image in a state where the reflecting mirror is moved to position 2. In a program that causes a computer to execute a focus control method for a camera that performs continuous shooting,
The focus control method is
At the start of continuous shooting, the contrast of the captured image is determined and the focus of the photographic lens is controlled according to the contrast.
A program that determines the movement of a subject from a captured image after the start of continuous shooting, and controls focusing of the photographing lens in accordance with a change in subject distance predicted based on the movement of the subject. A reflection mirror that moves a first position that reflects the subject light that has passed through the photographic lens and a second position that causes the subject light to pass through and is imaged on the image sensor; the reflection mirror moves to the second position; In a program for causing a computer to execute a focusing control method in a single-lens reflex camera that performs continuous shooting in a state where
The focus control method is
At the start of continuous shooting, with the reflecting mirror moved to the first position, focus is detected from the phase difference of the subject light that has passed through the photographic lens, and the focus is controlled according to the result. A program that controls to focus on the distance of the subject predicted from the movement of the subject determined from the captured image in a state where the reflection mirror is moved to the position of 2.

Images