Abstract:
An object detecting apparatus according to the present invention has: an image sensor capturing a plurality of object images in time sequence; a first detection start signal generator generating a signal to start detection of an object, included in a first area, of the object images captured by the image sensor; a first detector detecting a characteristic of the object included in the first area in response to the signal from the first detection start signal generator; and a second detector detecting an object similar to the characteristic detected by the first detector, within a second area larger than the first area. Consequently, even when a moving object is shot, the user can take a picture intended by him only by determining the composition so that the main object is roughly followed.

Description:
[0001]    This application is based on the application No. 2001-195126 filed in Japan, the content of which is thereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an object detecting apparatus for determining a main object to be shot with emphasis, from within the shooting field.  
           [0004]    2. Description of the Related Art  
           [0005]    Conventionally, a camera has been widely known that has a microcomputer and automatically adjusts focus and exposure in order that shooting can be performed with an object constituting part of the shooting field as the reference. This camera generally has a structure as shown in FIG. 13. The camera  80  which has a photometer  81  detecting the brightness of the object and a pair of image detectors  82  calculates the distance to the object and the brightness of the object by a microcomputer  83  based on the signals from the photometer  81  and the image detectors  82 , and adjusts a taking lens  84  based on the result of the calculation so that an image of the object is formed on imaging means  85 .  
           [0006]    A distance measurement frame indicating the distance measurement range is provided in the finder of this camera, and the user performs shooting while framing the picture so that the main object is captured in the frame. In order that the distance to the object captured in the distance measurement frame can be measured by the image detectors  82 , distance measurement points normally disposed so as to be invisible are provided, and shooting can be performed with focus and exposure adjusted with respect to the object overlapping a distance measurement point.  
           [0007]    However, when the distance measurement range of the camera is small, it sometimes occurs that an object behind the object to be shot is in focus. That is, when a picture is taken with the main object  88  not overlapping any of the distance measurement points  87  as shown in FIG. 14, the main object  88  is not in focus, so that a picture intended by the user cannot be taken.  
           [0008]    To solve this problem, it has been proposed to perform focus lock by half depressing the release button as shown in FIG. 15. When the release button is half depressed with the main object  88  overlapping the distance measurement frame  89 , since the main object  88  is present on a distance measurement point in the distance measurement frame  89 , a condition where the main object  88  is in focus is fixed. Then, to obtain the composition intended by the user, the frame is moved with the half-depressed condition of the release button maintained, and then, the release button is fully depressed.  
           [0009]    However, according to the focus lock, when a moving object such as a running child or a person participating in a sport is shot, it is difficult to determine when to half depress the release button. Moreover, the obtained picture is out of focus when the distance to the object which is once captured and on which focus is locked changes before the determination of the composition and shooting are actually performed.  
           [0010]    On the other hand, an improvement has been made that distance measurement points are disposed in a wide range to increase the distance measurement range. This enables shooting to be performed with the main object as the reference even when the composition is such that the main object is not situated in the center. However, since it is difficult to select a main object in a wide distance measurement range, there are cases where an object not desired by the user is in focus.  
           [0011]    Accordingly, to solve these problems, the present invention provides an object detecting apparatus capable of performing shooting with a main object desired by the user as the reference even when the object moves.  
         SUMMARY OF THE INVENTION  
         [0012]    To attain the above-mentioned object, an object detecting apparatus according to the present invention has: an image sensor for capturing a plurality of object images in time sequence; a first detection start signal generator for generating a signal to start detection of an object, included in a first area, of the object images captured by the image sensor; a first detector for detecting a characteristic of the object included in the first area in response to the signal from the first detection start signal generator; a second detector for detecting an object similar to the characteristic detected by the first detector, within a second area larger than the first area; a second detection start signal generator for generating a signal to start detection by the second detector; a detection end signal generator for generating a signal to end the detection by the second detector; and a controller for performing focusing for the object detected by the second detector in response to the signal from the detection end signal generator.  
           [0013]    According to this structure, since the main object is first selected from the smaller first area, the control to select the optimum object can be easily performed, so that misdetection can be reduced. Moreover, after the main object is once selected, for the succeeding object image, a similar object is selected from the larger second area, and the following of the main object is performed. Consequently, even when a moving object is shot, the user can take a picture intended by him only by determining the composition so that the main object is roughly followed.  
           [0014]    In the following description, like parts are designated by like reference members throughout the several drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a block diagram of a camera according to an embodiment of the present invention;  
         [0016]    [0016]FIG. 2 is a view showing the structure of a distance measurement portion of the camera of FIG. 1;  
         [0017]    [0017]FIG. 3 is a view showing the structure of an eye sensor of the camera of FIG. 1;  
         [0018]    [0018]FIG. 4 is an explanatory view of a display provided in a finder of the camera of FIG. 1;  
         [0019]    [0019]FIG. 5 is an explanatory view of a positional relationship between a distance measurement frame and a first area of the camera of FIG. 1;  
         [0020]    [0020]FIG. 6 is a view showing the arrangement of distance measurement points in the shooting field;  
         [0021]    [0021]FIG. 7 is an explanatory view of a positional relationship between the first area and the distance measurement points of the camera of FIG. 1;  
         [0022]    [0022]FIG. 8 is a flowchart of the shooting processing in a target mode;  
         [0023]    [0023]FIG. 9 is an explanatory view of a display provided in the finder when shooting is started;  
         [0024]    [0024]FIG. 10 is an explanatory view of a distance image;  
         [0025]    [0025]FIG. 11 is a view explaining the processing to divide an object image and select a main object;  
         [0026]    [0026]FIG. 12 is a view showing a succeeding object image;  
         [0027]    [0027]FIG. 13 is a block diagram showing the structure of the conventional camera;  
         [0028]    [0028]FIG. 14 is a view showing the composition in which the object does not overlap any of the distance measurement points; and  
         [0029]    [0029]FIG. 15 is an explanatory view of an operation example of the focus lock. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0030]    A camera according to an embodiment of the present invention will be described with reference to the drawings.  
         [0031]    Referring to FIG. 1, the camera  10  has: a taking lens  12 ; a finder  14  including a display  19 ; a photometry portion  15  measuring the brightness of the object; a distance measurement portion  16  measuring the distance to the object for each of a plurality of divisional areas by use of an image sensing apparatus outputting image information in time sequence at regular intervals; a release button  17 ; an eye sensor  18 ; and a selector  13 . The release button  17  and the eye sensor  18  are used also as signal transmitting means for detecting and following the main object in the present embodiment. While the distance measurement portion  16  has a pair of two-dimensional sensors (area sensors)  16   a  and  16   b  as shown in FIG. 2, it may have a pair of line sensors. Moreover, one element may be used both as the photometry portion  15  and the distance measurement portion  16 . The selector  13  is used for selecting a shooting mode as described later.  
         [0032]    [0032]FIG. 3 is a view showing the concrete structure of the eye sensor  18 . The eye sensor  18  detects whether or not the user is assuming a posture of shooting and is looking through the finder  14 . The eye sensor  18  comprises an LED light emitting portion  18   a  and a light receiving sensor  18   b  disposed side by side below the finder  14 . When the user brings his head close to the finder to look through the finder, light emitted from the LED light emitting portion  18   a  at predetermined intervals is reflected at the user&#39;s face to be incident on the light receiving sensor  18   b , so that it is detected that the user is preparing for shooting. In the present embodiment, the signal from the eye sensor  18  is used as a signal to start the detection of the main object.  
         [0033]    A CPU  20  has a distance measurement information calculator  21 , a photometry information calculator  22 , an image processor  23 , a taking lens controller  24 , a display controller  25 , and a memory  26 . The distance measurement information calculator  21  processes the output from the distance measurement portion  16 , and outputs distance measurement information with respect to each of the divisional distance measurement areas to the taking lens controller  24  and the display controller  25 . The photometry information calculator  22  processes the outputs from the photometry portion  15  and the distance measurement portion  16 , and transmits photometry information to the taking lens controller  24  and the memory  26 . The image processor  23  processes the output from the distance measurement portion  16  at the timing when the signals from the release button  17  and the eye sensor  18  are received. Further, the image processor  23  detects a main following area from a predetermined area based on the result of the processing as described later, and transits the information to the display controller  25  and the memory  26 . The taking lens controller  24  controls the taking lens  12  based on the information from the distance measurement information calculator  21  and the photometry information calculator  22 . The display controller  25  controls the display  19  of the finder  14  based on the information from the distance measurement information calculator  21  and the image processor  23  to display an in-focus indicator mark within the field frame. The memory  26  stores the information from the photometry information calculator  22 , the image calculator  23  and the taking lens controller  24 .  
         [0034]    On the display  19  of the finder  14 , the field frame is displayed as shown in FIG. 4. That is, in the finder, the in-focus indicator mark  40  is displayed outside the field frame, and distance measurement frames  30  to  34  which are arranged in five lines are selectively displayed as appropriate within the field frame  41 . Appropriate combinations of distance measurement frames  30  to  34  enable distance measurement frames of various sizes to be displayed in given positions within a finder field  14   a . The distance measurement frames  30  to  34  are arranged so as to overlap a first area  51  as an object detection area as shown in FIG. 5. The first area  51  is not necessarily displayed within the field. The distance measurement frames  30  to  34  are displayed by a liquid crystal display (LCD) panel, and the in-focus indicator mark  40  is displayed by a light emitting diode (LED). While a distance measurement frame of a predetermined shape is selected as appropriate and displayed in a predetermined position on the display  19  in the present embodiment, as a modification, for example, a mark of a given shape may be displayed in a given position by use of a dot-matrix liquid crystal display panel.  
         [0035]    In the first area  51  as the object detection area, a plurality of distance measurement points  42  is provided as shown in FIGS. 6 and 7, and the distances to objects  61  and  62  displayed so as to overlap the first area  51  can be measured for each of the distance measurement points. A second area  52  is provided in a central part of the first area  51 . While the second area  52  may be variable in size, it is desirable that it be an area comprising a combination of a plurality of distance measurement points  42  and distance measurement can be performed for all the positions in the area. It is desirable for the second area  52  to be displayed within the field frame so that the range thereof is clearly shown to the user. In the present embodiment, the second area  52  is shown with distance frames  32   d  and  32   g  in normal times.  
         [0036]    Next, the flow of the shooting processing of the camera according to the present embodiment will be described. The camera according to the present embodiment has three shooting modes, and is capable of switching among these modes as required. One of the modes that is for selecting and following a main object and will be described below will be called a target mode. FIG. 8 is a flowchart of the shooting processing in the target mode. In the target mode, the CPU  20  determines the condition of a switch S0 (not shown) for determining whether the user is looking through the finder  14  or not by the eye sensor  18  at predetermined intervals (step  81 ). When the user is not looking through the finder  14 , that is, when the switch S0 is not on, the condition of the switch S0 is continuously determined at predetermined intervals. When the user is looking through the finder  14 , that is, when the switch S0 is on, the process shifts to capture of the data of the shot image.  
         [0037]    When the switch S0 becomes on, the data of the shot image is captured by the area sensors provided in the distance measurement portion  16 . Now, for convenience of explanation, a case will be described where a subject including the objects  61  and  62  as shown in FIG. 6 is displayed in the field frame. When the user looks through the finder, a display as shown in FIG. 9 is provided in the field frame  14   a  of the finder. That is, the distance measurement frames  32   d  and  32   g  are displayed in the field frame  14   a , and the user can recognize the second area  52  as described above. The range of the first area  51  is not indicated in the field frame  14   a.    
         [0038]    Returning to FIG. 8, at step  82 , the incident object light is integrated by the area sensors, and an image signal is captured from each of the pair of area sensors. The partial areas extracted from the image signals from the pair of area sensors  16   a  and  16   b  correspond to each other. The distance to the object can be calculated for each partial area (distance measurement point  42 ) based on the principle of the triangulation by use of the image signals of the corresponding partial areas of the area sensors  16   a  and  16   b  (AF calculation). The object distance distribution (hereinafter, referred to as distance image) is detected from the object distance information obtained for each of the distance measurement points. An example of the distance image is shown in FIG. 10. The distance image comprises the distances to the objects  61  and  62  in the field  14   a  arranged for each partial area (distance measurement point  42 ). In FIG. 10, it is apparent that the objects  61  and  62  are at shorter distances than the background and the object  62  is closer to the camera than the object  61 . While the partial areas (distance measurement points  42 ) do not overlap each other in FIGS. 6 and 7, they may overlap each other. Moreover, it may be performed to calculate a distance measurement value for each of areas smaller than the partial areas by use of the distance measurement value obtained for each partial area and obtain the distance image from the distance information obtained for each of the smaller areas.  
         [0039]    Then, the image processor  23  divides the image information into a plurality of areas by use of the distance image. In the above-described example, as shown in FIG. 11, the image information is divided into areas  53 ,  54  and  55  corresponding to the background, the object  61  and the object  62 , respectively, by use of the distance image shown in FIG. 10.  
         [0040]    Then, at step  83 , a target object as the main object is selected from the divisional areas. Of the areas  53 ,  54  and  55  obtained by the division at the previous step, an area at least part of which is present in the second area  52 , that is, the area  54  corresponding to the object  61  is selected as the target object. When a plurality of divisional areas is present in the second area  52 , for example, the area corresponding to the object at the shortest distance is selected as the target object. The target object may be selected based on the color information, the size and the shape of the divisional areas as well as the distance. Hereinafter, the explanation will be continued on the assumption that the object  61  is selected as the target object as the main object.  
         [0041]    When the target object is selected, photometry calculation is performed for the target object, and which object is the target object is indicated in the finder. The indication is provided by the display controller  25  controlling the display  19  so that distance measurement frames are displayed. When these processings are finished for the target object as the main object, the CPU  20  stores characteristics of the main object into the memory  26 . The characteristics of the main object include the distance to the object, the width of the object, the brightness of the object, and the position of the object on the screen for the divisional area  54 .  
         [0042]    Then, at step  85 , it is determined whether the switch S1 is off or not. In the present embodiment, the switch S1 is turned on when the release button  17  is half depressed. When the release button  17  is not half depressed (the switch S1 is off), the process returns to step  81  to repeat the above-described loop for the image information on the object captured in time sequence.  
         [0043]    When the release button  17  is half depressed, the process shifts to step  86  to perform the processing to follow the main object selected in the previous preprocessing. Assuming now that the object  61  moves leftward while the processing from step  86  is being performed, a case will be considered where the captured succeeding object image information is as shown in FIG. 12. A processing similar to that at step  82  of the main object selecting processing is performed on the succeeding object image information captured in time sequence, and the object image is divided based on the created distance image (step  86 ).  
         [0044]    The CPU  20  selects an object to be followed which is the most appropriate object from the image divided at step  86  (step  87 ). In the present embodiment, the selection is made by making a comparison between the previously detected image of the area of the main object and the object image captured this time for each of the divisional areas. The succeeding object image information to be compared is information within the range of the first area  51 . An area similar to the area  54  corresponding to the object  61  as the target object stored in the memory  26  is selected from among the divisional areas  53   a ,  54   a  and  55   a . In the selection, the previously captured information on the area  54  stored in the memory  26  as described above is compared, for example, with the distance to the object, the width of the object, the brightness of the object and the position of the object on the screen in the succeeding divisional areas  53   a ,  54   a  and  55   a . For example, the area  54   a  corresponding to the object  61  is selected as a result.  
         [0045]    When the object to be followed is selected from the first area, the display controller  25  displays distance measurement frames  33   b  and  33   c  so that the object to be followed is surrounded by the frames  33   b  and  33   c , and displays the object to be followed so that it is visually recognized by the user with ease (step  88 ). Then, the information on the object to be followed which is the main object is stored into the memory  26 . The characteristics of the main object include, like the previously captured information on the area  54 , the distance to the object, the width of the object, the brightness of the object and the position of the object on the screen with respect to the divisional area  54   a . Moreover, a characteristic newly serving as a reference such as the direction of movement of the object  61  as the main object may be obtained based on the previously captured information on the area  54 .  
         [0046]    Then, the CPU  20  determines whether a switch S2 is off or not (step  89 ). The switch S2 is for determining whether the release button  17  is fully depressed or not. When the switch S2 is not off, that is, when the release button  17  is fully depressed, the CPU  20  stops the selection of the object to be followed, and performs shooting.  
         [0047]    When the switch S2 is off, that is, when the release button  17  is not fully depressed, the process shifts to step  90  to determine whether the switch S1 is off or not. When the switch S1 is not off, that is, when the release button is kept half depressed, the process shifts to step  86  to continue the detection of the object to be followed by performing a processing similar to the above-described one based on the previously captured object image information. When the switch S1 is off, that is, when the release button  17  is released from the half-depressed condition, the process returns to step  81  to perform the target object selection processing from the beginning.  
         [0048]    In the camera according to the present embodiment, the signals from the distance measurement information calculator  21  and the photometry information calculator  22  are transmitted to the taking lens controller  24  at regular intervals. Every time an object to be followed is selected while the release button  17  is half depressed, focus and exposure of the taking lens are adjusted in accordance with the object to be followed. The adjustment may be performed only at the time of shooting instead of every time an object to be followed is selected. In the case of digital cameras and movie cameras having a liquid crystal display, when the preview function and the moving image shooting are considered, it is desirable to perform the adjustment of the taking lens every time an object to be followed is selected.  
         [0049]    The camera according to the present embodiment has a wide mode and a spot mode as well as the above-described target mode, and is capable of switching among the three shooting modes by the selector  13 . In the wide mode, the main object is selected from the image information included in the first area  51  in response to a half depression of the release button  17 , and the lens adjustment is performed with the selected main object as the reference. That is, after the main object is selected, the following of the main object is not performed. In this mode, the focus lock to determine the focus and the aperture with the selected object as the reference is performed in the comparatively large range of the first area.  
         [0050]    In the spot mode, in response to a half depression of the release button  17 , the main object is selected with the image information included in the second area being divided into a plurality of areas, and the lens adjustment is performed with the selected main object as the reference. That is, after the main object is selected, the following of the main object is not performed. In this mode, the focus lock to determine the focus and the aperture with the selected object as the reference is performed in the small range of the second area. This mode ensures the selection of the main object, and reduces the misdetection that an object not desired by the user is in focus.  
         [0051]    As described above, according to the present embodiment, after a main object is selected in a small area, the camera follows the main object by capturing it in a large area, and focus adjustment can be performed with the object as the reference. Consequently, the out-of-focus condition caused when a moving object is shot with the focus lock and the misdetection of the object when the object is not present in the center can be prevented.  
         [0052]    The present invention is not limited to the above-described embodiment, but may be embodied in various forms. For example, the present invention is also applicable to digital cameras and movie cameras.  
         [0053]    Although the present invention has been fully described by way of examples with reference to the accompanying drawings, it is to be noted that various change and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention, they should be construed as being including therein.