Abstract:
An image sensing apparatus includes a selector, an image sensing unit, a memory unit, an image combining unit and a recording unit. The selector is used to select a main object. The image sensing unit senses a plurality of images including the main object. The memory unit stores the plurality of images. The image combining unit combines the plurality of images stored in the memory unit to generate a combined image in which the main object appears to be stopped and an object other than the main object appears to be flowing. The recording unit compresses the combined image and records the compressed combined image on a recording medium.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an image sensing apparatus such as a digital camera. 
     BACKGROUND OF THE INVENTION 
     When an object of a photographing operation is moving at a high speed, a photographer has conventionally performed photographing using a high-speed shutter to obtain an image of the object without blurring, or performed photographing while panning the camera following the motion of the object. When the high-speed shutter is used, as the time to expose image sensing devices is reduced, the blurring of the object is reduced. However, in this case, all of the object is image-sensed without blurring, and therefore the obtained image lacks a realistic sensation that the object is moving. On the other hand, when photographing is performed with a camera panning to keep up with the motion of the object so as to obtain a realistic moving sensation, an image where the blurring of the object is reduced but the background is blurred (an image with follow shot effects) is obtained. However, the blurring of the object cannot be completely prevented due to the difference between the speed of motion of the object and the speed of the camera panning and camera shaking in a direction different from the direction of the motion of the object. 
     Further, upon night photographing to obtain an image where a car tail lamp or the like is flowing, the camera is fixed with a tripod stand or the like and exposure is performed over an extended time period, and an image where only a moving object appears to be flowing (an image with lasting effects) can be obtained. However, when the camera cannot be fixed since the tripod stand cannot be used, the entire image is blurred due to camera shaking. 
     As a method for correcting such blurring, an optical anti-shake system to perform image blur correction by detecting an acceleration, an angular acceleration, an angular velocity, an angular displacement and the like with a laser gyroscope and the like, appropriately performing calculation processing based on the results of detection, and driving a correcting optical device to decenter an photographing optical axis is known. Further, a method for performing image sensing plural times for exposure periods not to cause camera shaking and composition images obtained by the plural times of image sensing while correcting image shifts to obtain an image by long-hour exposure image sensing (composite image) is known (for example, Japanese Patent Application Laid-Open No. 5-7336). 
     Recently, downsizing of digital cameras is promoted in comparison with silver-chloride compact cameras. Especially, a camera having an SXGA-class image sensing device is so downsized that it can be included in a mobile electronic device (for example, a cellular phone). 
     When the above-described optical anti-shake system is incorporated in such a camera, further downsizing of the blur correcting optical device is required or downsizing of the shake detection unit, such as a laser gyroscope, is required. 
     However, downsizing of the blur correcting optical device is limited since it supports a correction lens and drives the lens with high accuracy. Further, as most of currently used shake detection units utilize an inertia force, when such shake detection unit is downsized, its detection sensitivity is lowered, and blur correction with high accuracy cannot be performed. 
     Further, as blurring applied to a camera, angular blurring about a predetermined axis and shift blurring by parallel shaking of the camera are detected. The angular blurring can be corrected by the optical anti-shake system. However, the shift blurring cannot be corrected without difficulty. Especially, as a camera is downsized, the shift blurring is increased. 
     On the other hand, in the anti-shake method as disclosed in the above Japanese Patent Application Laid-Open No. 5-7336, as a high-speed shutter not to cause blur in one image is employed, an image with follow shot effects or lasting effects as described above cannot be obtained by repeating image sensing and performing a composition of obtained images. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to overcome the above-described drawbacks. For example, one object of the present invention is to provide a small image sensing apparatus capable of providing an image with follow shot effects and/of lasting effects (i.e., visible indications that the object is moving). 
     According to an aspect of the present invention, an image sensing apparatus comprises detection means for detecting motion information of plural images; selection means for selecting an object; image moving means for performing position conversion on the plural images in a plain coordinates based on the motion information detected by the detection means; and interpolation means for performing interpolation between the plural images based on the motion information detected by the detection means, wherein the apparatus performs image composition so as to bring the object image selected by the selection means into correspondence by the image moving means and to perform interpolation between the plural images regarding an object other than the object selected by the selection means by the interpolation means. 
     According to another aspect of the present invention, an image sensing apparatus comprises detection means for detecting motion information of plural images; selection means for selecting an object; image moving means for performing position conversion on the plural images in a plain coordinates based on the motion information detected by the detection means; and interpolation means for performing interpolation between the plural images based on the motion information detected by the detection means, wherein the apparatus performs image composition so as to bring an object other than the object image selected by the selection means into correspondence by the image moving means and to perform interpolation between the plural images regarding the object selected by the selection means by the interpolation means. 
     According to another aspect of the present invention, an image sensing apparatus comprises detection means for detecting motion information of plural images; selection means for selecting an object; image moving means for performing position conversion on the plural images in a plain coordinates based on the motion information detected by the detection means; interpolation means for performing interpolation between the plural images based on the motion information detected by the detection means; and selection means for selecting one of a first mode to perform image composition so as to bring the object image selected by the selection means into correspondence by the image moving means and to perform interpolation between the plural images regarding an object other than the object selected by the selection means by the interpolation means, and a second mode to perform image composition so as to bring an object other than the object image selected by the selection means into correspondence by the image moving means, and to perform interpolation between the plural images regarding the object selected by the selection means by the interpolation means. 
     According to another aspect of the present invention, a control method for an image sensing apparatus have detection means for detecting motion information of plural images; selection means for selecting an object; image moving means for performing position conversion on the plural images in a plain coordinates based on the motion information detected by the detection means; and interpolation means for performing interpolation between the plural images based on the motion information detected by the detection means, for performing image composition so as to bring the object image selected by the selection means into correspondence by the image moving means and to perform interpolation between the plural images regarding an object other than the object selected by the selection means by the interpolation means. 
     According to another aspect of the present invention, a control method for an image sensing apparatus have detection means for detecting motion information of plural images; selection means for selecting an object; image moving means for performing position conversion on the plural images in a plain coordinates based on the motion information detected by the detection means; and interpolation means for performing interpolation between the plural images based on the motion information detected by the detection means, for performing image composition so as to bring an object other than the object image selected by the selection means into correspondence by the image moving means and to perform interpolation between the plural images regarding the object selected by the selection means by the interpolation means. 
     According to another aspect of the present invention, a control method for an image sensing apparatus comprises detection means for detecting motion information of plural images; selection means for selecting an object; image moving means for performing position conversion on the plural images in a plain coordinates based on the motion information detected by the detection means; and interpolation means for performing interpolation between the plural images based on the motion information detected by the detection means, the method comprises a selection step of selecting one of a first mode to perform image composition so as to bring the object image selected by the selection means into correspondence by the image moving means and to perform interpolation between the plural images regarding an object other than the object selected by the selection means by the interpolation means, and a second mode to perform image composition so as to bring an object image other than the object selected by the selection means into correspondence by the image moving means, and to perform interpolation between the plural images regarding the object selected by the selection means by the interpolation means. 
     Other features and advantages of the present invention will be apparent from the following descriptions taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a block diagram showing an example of the construction of an image sensing apparatus according to a first embodiment of the present invention; 
         FIG. 2  is an explanatory view of a selection of an object according to the first embodiment of the present invention; 
         FIGS. 3A and 3B  are explanatory views showing position coordinates of the selected object according to the first embodiment of the present invention; 
         FIG. 4  illustrates a composite image after coordinate conversion according to the first embodiment of the present invention; 
         FIG. 5  is an explanatory view of image interpolation on an object other than the main object according to the first embodiment of the present invention; 
         FIG. 6  is a final composite image according the first embodiment of the present invention; 
         FIG. 7  is a flowchart showing image sensing processing according to the first embodiment of the present invention; 
         FIG. 8  is an explanatory view of the selection of an object according to a second embodiment of the present invention of the present invention; 
         FIGS. 9A and 9B  are explanatory views showing position coordinates of the selected object according to the second embodiment of the present invention; 
         FIG. 10  is a composite image after the coordinate conversion according to the second embodiment of the present invention; 
         FIG. 11  is an explanatory view of the image interpolation on an object other than the main object according to the second embodiment of the present invention; and 
         FIG. 12  is a final composite image according the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings. 
     Note that the following embodiments merely show examples of implementation of the present invention and may be appropriately corrected or changed in accordance with the construction of the apparatus to which the present invention is applied or various conditions. The present invention is not limited to the following embodiments. 
     Further, the object of the present invention can also be achieved by providing a storage medium (or recording medium) holding software program code for performing the functions of the image sensing apparatus to be described later to a system or an apparatus, reading the program code from the storage medium then executing the program by a computer (e.g., CPU, MPU) of the system or apparatus. 
     First Embodiment 
       FIG. 1  is a block diagram showing the construction of a digital camera as an example of an image sensing apparatus according to a first embodiment of the present invention. Note that the image sensing apparatus according to the first embodiment can be realized as a digital video camera, a cellular phone having a camera, a computer having a camera and the like, as well as a digital camera. 
     A light beam (image sensing light) incident from an image sensing lens  11  is light-amount controlled by an aperture  13   a , then passed through a shutter  12   a , and forms an image in an image sensing unit  17 . The image sensing unit  17  converts the received light into an image signal using an image sensing device such as a CMOS image sensor or a CCD image sensor. 
     The photographing lens  11  has plural optical lens groups. A part or all of these lens groups move on an optical axis  10  by a driving force from an AF driving motor  14   a , and stop in a predetermined focusing position, thereby performing focusing adjustment. The AF driving motor  14   a  is driven in accordance with a driving signal from a focusing driver  14   b.    
     Further, a part of optical lens groups of the photographing lens  11  moves on the optical axis  10  by a driving force from a zoom driving motor  15   a  and stops in a predetermined zoom position, thereby changing a photographing view angle. The zoom driving motor  15   a  is driven in accordance with a driving signal from a zoom driver  15   b.    
     The aperture  13   a  has plural aperture blades. These aperture blades operate by a driving force from an aperture driver  13   b  and change an opening area (aperture diameter) as a light passing opening. The shutter  12   a  has plural shutter blades. These shutter blades open/close the opening as the light passing opening by a driving force from a shutter driver  12   b , thereby controlling the light beam to enter the image sensing unit  17 . 
     The focusing driver  14   b , the zoom driver  15   b , the aperture driver  13   b  and the shutter driver  12   b  are controlled by an image sensing controller  18 . 
     The image sensing controller  18  inputs operation signals from a shutter button  12   c , an aperture operation unit  13   c , a zoom operation unit  15   c , an anti-shake effect operation unit  120  and an object selector  121 . The image sensing unit  18  supplies the operation signals to the focusing driver  14   b , the zoom driver  15   b , the aperture driver  13   b  and the shutter driver  12   b  in accordance with the image sensing status of the digital camera, thereby setting image sensing conditions, and performs image sensing. Note that the shutter button  12   c  has a first release switch (SW 1 ) which is turned ON when half-depressed and a second release switch (SW 2 ) which is turned ON when full-depressed. 
     Note that the aperture operation unit  13   c  is not necessary since generally the opening diameter of the aperture  13   a  is automatically set on the digital camera side upon image sensing. However, the aperture operation unit  13   c  is provided for a photographer to arbitrarily set image sensing conditions. 
     The image sensing controller  18  performs measurement of brightness of an object (photometry) based on a digital image signal inputted in an image processor  111  to be described later, and determines the aperture diameter of the aperture  13   a  and closing timing of the shutter  12   a  (exposure time) based on the result of photometry. Further, the image sensing controller  18  obtains a focusing position of the photographing lens  11  based on an output from the image processor  111  while driving the focusing driver  14   b.    
     An image signal outputted from the image sensing unit  17  is converted to a digital image signal by an A/D converter  110  and inputted into the image processor  111 . The image processor  111  generates image data corresponding to an obtained image from the digital image signal from the A/D converter  110 . 
     The image data generated by the image processor  111  is inputted via an image selector  112  into a display unit  117  and a recording unit  118 . The display unit  117  displays the image data on a display device such as a liquid crystal display. The recording unit  118  compresses the image data and stores the data on a recording medium such as a memory card. 
     In the above-described operations, when follow shot effects without camera shaking is required, a photographer operates the anti-shake effect operation unit  120  to set the anti-shake system to a “follow shot” setting, to perform the following operations. 
     First, when the photographer half-depresses the shutter button  12   c , an image sensing preparatory operations (a focusing adjustment operation, a photometry operation and the like) are started. The closing timing of the shutter  12   a  (exposure period) and the aperture diameter of the aperture  13   a  are set based on a photometry value obtained by the photometry operation. The exposure period is divided into plural short exposure periods, and image sensing is repeated by the number of divided exposure periods. When the exposure period is divided into plural short exposure periods, respective images are obtained in an underexposure state. However, the influence of camera shaking is reduced in these images. 
     Then after the image sensing, the composite image is made by the composition of the plural images, thereby improving exposure. 
     However, when plural images are obtained, even though there is no influence of camera shaking in the respective images obtained by multiple image sensing operations, the composition may be slightly shifted among the images due to camera shaking during the serial image sensing. When the composition of these images are performed, the composite image is blurred in correspondence with the shift of the composition among the respective images. 
     In the present embodiment, plural image signals outputted from the image sensing unit  17  in the serial image sensing operation are converted to digital image signals by the A/D converter  110  and subjected to predetermined image processing by the image processor  111 . 
     On the other hand, when the anti-shake effect operation unit  120  is operated to instruct the image sensing controller  18  to set the anti-shake system to the “follow shot” setting, a display position of a main object on a screen is previously selected using the object selector  121 . As long as the object selector has a cross key, a selection button and an enter key, the display position can be freely selected on the screen. In this example, a central portion on the image screen has been previously selected by the object selector  121 . Further, the object selection by the object selector  121  may be performed by selecting a main object from at least one of the plural images after image sensing. 
     For example, as shown in  FIG. 2 , when a vehicle running on a road  122   a  at the central portion of a frame  121   a  is to be photographed and photographing is to be performed while the digital camera is panned, a frame  125  is drawn by the object selector  121 , thereby designating the selection range. 
     Then image data from the image processor  111  is inputted into the memory  113  via the image selector  112 . 
     The memory  113  holds plural images obtained by serial image sensing. 
     A shift detector  114  extracts a screen feature point in an image stored in the memory  113  within a frame selected by the object selector  121 , and obtains position coordinates of the feature point in the image sensing screen. 
     For example, in  FIGS. 3A and 3B  where a vehicle  123   b  runs on a road  122   b  in a frame  121   b , the photographer tries to perform photographing in the same direction as the traveling direction of the vehicle  123   b  and at the same speed as that of the vehicle  123   b . However, the speed of panning of the digital camera may be different from the speed of the vehicle  123   b , or the camera may be shaken in a direction different from the traveling direction of the vehicle  123   b . As a result of multiple image sensing operations, in the case of the frame  121   c , the composition of the image may be shifted from that of the frame  121   b.    
     The shift detector  114  extracts a high-luminance point, an edge  127   b  of a window  126   b  in the vehicle  123   b  positioned within a frame  125  selected by the object selector  121 , as a feature point, by edge detection, then compares the feature point  127   b  with a feature point  127   c  in the frame  121   c , and corrects the difference (coordinate conversion). 
     In  FIGS. 3A and 3B , the frame  121   c  is subjected to coordinate conversion by moving the feature point  127   b  of the frame  121   b  onto the feature point  127   c  of the frame  121   c  as indicated with an arrow  128 . 
     In this example, the change of feature point is obtained between the first image frame  121   b  and the second image frame  121   c  in the plural images obtained by serial image sensing. Further, the change of feature point is similarly obtained regarding the subsequent images. 
     Note that it may be arranged such that plural points are selected as feature points and a mean value of motion vectors or a minimum scalar value of these points is obtained as the change of feature points. 
     The respective images subjected to the coordinate conversion by the coordinate converter  115  are outputted to an image composition unit  116 , and the composite image is made by the composition of these images as shown in  FIG. 4 . 
     As described above, the main object, the coordinates of which in the respective images are brought into correspondence by the coordinate conversion, appears as the vehicle  123   d  in the composite image in  FIG. 4 . On the other hand, as the digital camera has been panned and the image sensing has been performed at a shutter speed to reduce influence of camera shaking, a tree in the background as an object other than the main object, the coordinates of which in the respective images do not correspond with each other, discretely appears as separate trees  129   b  and  129   c  in the composite image. Next, composition of the discretely composite objects, i.e., the trees  129   b  and  129   c  such that the tree is flowing, will be described with reference to  FIG. 5 . 
     In  FIG. 5 , feature points outside the object selection frame  125  in the frame  121   b  are extracted. Among the objects outside the object selection frame  125 , edges  130   b ,  131   b  and  132   b  of the tree  129   b , having generally high luminance, color hue, chromaticity and brightness, are extracted as feature points by edge detection and stored. Then the object in the background, the tree  129   b  is extracted based on the luminance, color hue, chromaticity and brightness levels obtained by the edge detection. Then, points having the same feature levels as those of the previously stored points are extracted from the whole screen of the frame  121   c  ( 130   c ,  131   c  and  132   c ). The edge loci are obtained by connecting the edges between the respective frames with straight lines, and the amount and the direction of movement of the tree  129   b  are predicted. The locus between the edges  130   b  and  130   c  is indicated as an arrow  133 ; that between the edges  131   b  and  131   c  is indicated as an arrow  134 ; and that between the edges  135   b  and  135   c  is indicated as an arrow  135 . Then image interpolation is performed along the loci with the same luminance, color hue, chromaticity and brightness, thereby performing image drawing such that the tree  129   b  flows to the tree  129   c  as shown in  FIG. 6 . Note that when the tree  129   b  is drawn to the tree  129   c , the vehicle  123   d  as the main object is not interpolated, thereby preventing it from being covered with the background. The range of the vehicle  123   b  as the main object can be determined since plural edges as the same edges have not been detected by the edge detection in the vehicle  123   b  (the object in the respective frames already correspond with each other). 
     The composite image data made by the image composition unit  116  is inputted via the image selector  112  to the display unit  117  and the recording unit  118 . The display unit  117  displays the image data on the display device such as a liquid crystal display. The recording unit  118  compresses the image data and stores the data onto a recording medium such as a memory card. 
       FIG. 7  is a flowchart showing image sensing processing in the digital camera according to the first embodiment. The flow starts when the power of the digital camera is turned ON. 
     At step S 1001 , the camera is in a standby status until the shutter button  12   c  is half-depressed. When the first release switch (SW 1 ) is turned ON, the process proceeds to step S 1002 . 
     At step S 1002 , image sensing is performed by the image sensing unit  17 . The image sensing controller  18  drives the AF driving motor  14   a  to move the photographing lens  11  in an optical axis direction while detecting an image contrast based on an output from the image processor  111 . 
     When a highest contrast is obtained, the driving of the photographing lens  11  is stopped, thereby the image sensing optical system is set to a focusing state (AF by the hill climbing method). Note that the focusing adjustment may be performed by phase difference detection. 
     Further, at this time, the image sensing controller  18  obtains the brightness of an object based on the output from the image sensing unit  17 . 
     At step S 1003 , it is determined whether or not the photographer has set the anti-shake effect operation unit  120  to the “follow shot” setting. When the anti-shake effect operation unit  120  is in the “follow shot” setting, the process proceeds to step S 1004 , otherwise, the process proceeds to step S 1018 . 
     Next, the flow of the case where the anti-shake effect operation unit  120  is set to the “follow shot” setting will be described. 
     At step S 1004 , the number of times of image sensing and exposure periods of the respective times of image sensing are obtained based on the image sensing conditions such as the brightness of the object obtained at step S 1002 . 
     The image sensing conditions include: 
     1. brightness of object; 
     2. focal length of image sensing optical system 
     3. brightness of image sensing optical system (aperture value); and 
     4. sensitivity of image sensing device. 
     For example, assuming that the sensitivity of the image sensing unit  17  is ISO 100, to measure the brightness of an object (photometry) and perform appropriate exposure based on the result of photometry, the aperture  13   a  is full-opened (e.g., f4.0) and the closing timing of the shutter  12   a , i.e., the exposure period, is set to 1/50 sec. 
     When the focal length of the image sensing optical system is equivalent to 100 mm of 35 mm film, image sensing with an exposure period of 1/50 sec may cause image blurring due to camera shaking. To prevent camera shaking from affecting the image, the exposure period is set to 1/100 sec and image sensing is performed twice. 
     On the other hand, when the focal length of the image sensing optical system is 400 mm, the exposure period is set to 1/500 sec and image sensing is performed 10 times so as to prevent camera shaking from affecting the image. 
     In this manner, the exposure period upon multiple image sensing operations is determined in correspondence with image sensing conditions, and the number times of image sensing is performed is set in correspondence with the image sensing conditions. 
     In a case where the same object is image-sensed plural times, it is preferable that exposure conditions of respective times of image sensing are close to an appropriate exposure as much as possible so as to perform image sensing with accurate information by the image sensing unit  17 . 
     For this purpose, when an object is dark or the aperture of the photographing lens is narrowed and the brightness of the lens is low, or when the sensitivity of the image sensing unit  17  is low, the exposure periods of respective times of image sensing are lengthened as much as possible even in plural times of image sensing, to obtain effective exposure conditions. 
     Note that if exposure periods are too long, the influence of camera shaking appears in an image surface. Accordingly, as described above, when the focal length of the image sensing optical system is equivalent to 100 mm of 35 mm film, the exposure period is set to 1/100 sec corresponding to about 1/100 mm (focal length). 
     Further, the number of times of image sensing is set so as to compensate for the underexposure. 
     When the focal length is long, the exposure period is further shortened so as to prevent image degradation due to camera shaking, and the number of times of image sensing is increased to compensate for the underexposure. 
     In this manner, when multiple image sensing operations are performed, as the object or the photographing lens is dark, the exposure period is long. As the sensitivity of the image sensing unit  17  is low, the exposure period is long. Further, as the focal length of the lens is long, the exposure period is short. 
     The number of times of image sensing of serial image sensing is increased as the object becomes darker or aperture of the photographing lens is narrowed. As the sensitivity of the image sensing device decreases, the number of times of image sensing is increased, and further, as the focal length of the lens is lengthened, the number of times of image sensing is increased. 
     After the completion of the above calculation, the setting of anti-shake mode (plural image sensing mode) is displayed on the display unit  117 , and at the same time, the number of times of image sensing is displayed on the display unit  117  for the photographer. 
     At step S 1005 , it is determined whether or not the shutter button  12   c  has been full-depressed. When the shutter button  12   c  has been full-depressed, the second release switch (SW 2 ) is turned ON. 
     At step S 1006 , the obtained images are temporarily stored into the memory  113 . 
     Step S 1006  is repeated until it is determined at step S 1007  that all the image sensing has been completed. 
     When all the image sensing has been completed, the process proceeds to step S 1008 . 
     At step S 1008 , the shift detector  114  extracts a characteristic image (feature point) from an image (e.g., the vehicle  123   b  in  FIGS. 3A and 3B ) in the object selection frame (e.g., the frame  125  in  FIGS. 3A and 3B ) previously set by the object selector  121 , and obtains the coordinates of the image. 
     At step S 1009 , the coordinate converter  115  performs coordinate conversion of respective images. Note that coordinate conversion is not performed only on the first frame image (first image). That is, the first image is used as a reference image upon coordinate conversion. 
     The feature point extraction at step S 1008  and the coordinate conversion at step S 1009  are performed on all the second and subsequent images, and when it is determined at step S 1010  that the coordinate conversion of all the images has been completed, the process proceeds to step S 1011 . 
     At step S 1011 , the shift detector  114  extracts a characteristic image (feature point) from an image (e.g., the tree  129   b  in  FIG. 5 ) outside the object selection frame (e.g., the frame  125  in  FIG. 5 ) previously set by the object selector  121 , and obtains the coordinates of the image. At this time, the luminance, color hue, chromaticity and brightness of the extracted point are stored. Points having the same features are extracted as a group, thereby extracting the image of the tree  129   b . The shift detector  114  extracts points having the same features as those of the stored points from the second image group (the frame  121   c  in  FIG. 5 ), and obtains the loci of the image of the tree  129   b.    
     At step S 1012 , image interpolation is performed using the luminance, color hue, chromaticity and brightness of the respective points along the loci calculated at step S 1011 , thereby generating an image where the tree  129   b  flows to the tree  129   c  in  FIG. 5 . 
     The feature point extraction at step S 1011  and the image interpolation at step S 1012  are repeated until all the second and subsequent images have been processed. When it is determined at step S 1013  that the coordinate conversion of all the images has been completed, the process proceeds to step S 1014 . 
     At step S 1014 , the composition of the first image and the respective image of the coordinate-converted second image group are performed. 
     The image composition is performed by averaging corresponding coordinate values of the respective images, and random noise in the image can be reduced by the averaging. Then, the image with reduced noise is subjected to gain control to increase the level of gain, to optimize the exposure. 
     At step S 1015 , in the composite image, an area where the respective images are not overlaid due to composition shift (an area  140  in  FIG. 5 ) is cut, and the image is subjected to diffusion-interpolation to obtain the initial frame size. 
     At step S 1016 , the image data generated by the image processor  111  or the composite image data made by the image composition unit  116  is displayed on the display unit  117 . 
     At step S 1017 , the image data generated by the image processor  111  or the composite image data made by the image composition unit  116  is stored on a recording medium such as a memory card. 
     At step S 1018 , the process returns to START. 
     Note that in a case where the shutter button  12   c  is still half-depressed and the switch SW 1  is ON at step S 1018 , the process proceeds to steps S 1001  to S 1004  again. 
     Further, in a case where the shutter button  12   c  has been full-depressed and the switch SW 2  is ON at step S 1018 , the process does not return to START but stands by at step S 1017 . 
     Next, the flow of the case where the anti-shake effect operation unit  120  is OFF at step S 1003  will be described. 
     At step S 1003 , if it is determined that the anti-shake effect operation unit  120  is OFF, the process proceeds to step S 1020 . 
     At step S 1020 , the process proceeds from step S 1001  to step S 1020  until the shutter button  12   c  is full-depressed and the switch SW 2  is turned ON. 
     At step S 1021 , the process stands by until normal image sensing (normal image sensing mode under exposure conditions effective in one exposure) has been completed. Upon completion of exposure, the process proceeds to step S 1016 . 
     At step S 1016 , the image data generated by the image processor  111  or the composite image data made by the image composition unit  116  is displayed on the display unit  117 . 
     At step S 1017 , the image data generated by the image processor  111  or the composite image data made by the image composition unit  116  is stored on a recording medium such as a memory card. 
     At step S 1018 , the process returns to START. 
     According to the first embodiment, an image with follow shot effects and without blur due to camera shaking can be obtained by performing image sensing plural times for exposure periods not to cause image blurring while panning a camera, then performing image composition so as to eliminate shifts of a main object while correcting the locus of motion of object(s) other than the main object in images obtained by the multiple image sensing operations. 
     Second Embodiment 
     In the first embodiment, a feature point of an object within an object selection frame set by the object selector  121  is extracted by the shift detector  114  and image composition is performed, and interpolation processing is performed on object(s) outside the frame such that it flows (i.e., “follow shot” effects photographing to obtain an image where a main object is stopped and the background is flowing). 
     In the second embodiment, feature points of object(s) outside the object selection frame set by the object selector  121  are extracted by the shift detector  114  and image composition is performed, and interpolation processing is performed on an object within the frame such that it flows (i.e., “lasting” effects photographing to obtain an image where a main object is flowing and the background is stopped). 
     As the digital camera according to the second embodiment has the same structure as that according to the first embodiment. In the present embodiment, a method for obtaining the “lasting” effects different from the “follow shot” effects in the first embodiment will be described. 
     In the image sensing apparatus having the same units as those of the first embodiment, to obtain the lasting effects without camera shaking, the photographer sets the anti-shake effect operation unit  120  to set the anti-shake system to the “lasting” setting, to perform the following operations. 
     First, when the photographer half-depresses the shutter button  12   c , image sensing preparatory operations (a focusing adjustment operation, a photometry operation and the like) are started. The closing timing of the shutter  12   a  (exposure period) and the aperture diameter of the aperture  13   a  are set based on a photometry value obtained by the photometry operation. The exposure period is divided into plural short exposure periods, and image sensing is repeated by the number of divided exposure periods. When the exposure period is divided into plural short exposure periods, respective images are obtained in an underexposure state. However, the influence of camera shaking is reduced in these images. 
     Then after the image sensing, the composite image is made by the composition of the plural images, thereby improving exposure. 
     However, when plural images are obtained, even though there is no influence of camera shaking in the respective images obtained by multiple image sensing operations, the composition may be slightly shifted among the images due to camera shaking during the serial image sensing. When the composition of these images is performed, the composite image is blurred in correspondence with the shift of the composition among the respective images. 
     In the present embodiment, plural image signals outputted from the image sensing unit  17  in the serial image sensing are converted to digital image signals by the A/D converter  110  and subjected to predetermined image processing by the image processor  111 . 
     On the other hand, when the anti-shake effect operation unit  120  is operated to instruct the image sensing controller  18  to set the anti-shake system to the “lasting” setting, a display position of a main object on a screen is previously selected using the object selector  121 . As long as the object selector has a cross key, a selection button and an enter key, the display position can be freely selected on the screen. In this example, a central portion on the image screen has been previously selected by the object selector  121 . Further, the object selection by the object selector  121  may be performed by selecting a main object from at least one of the plural images after image sensing. 
     For example, when a vehicle running on a road  142   a  in a lower half portion of the screen in a frame  141   a  is to be taken by fixed-point photographing to obtain lasting effects, a frame  145  is drawn by the object selector  121 , thereby designating the selection range. 
     Then image data from the image processor  111  is inputted into the memory  113  via the image selector  112 . 
     The memory  113  holds plural images obtained by serial image sensing. 
     The shift detector  114  extracts a screen feature point in an image stored in the memory  113  within a frame selected by the object selector  121 , and obtains position coordinates of the feature point in the image sensing screen. 
     For example, when the photographer performs fixed-point photographing to take a scene where a vehicle  143   b  runs on a road  142   b  in a frame  141   b  as shown in  FIGS. 9A and 9B , in an environment where the digital camera cannot be fixed with a tripod stand or the like, the photographer tries to perform image sensing without shaking the digital camera. However, the plural times of image sensing in a hand-hold state may produce an image as in the case of the frame  141   c  where the composition of the image is shifted from that of the frame  141   b.    
     The shift detector  114  extracts a high-luminance point, an edge  147   b  of a window  146   b  in a house  144   b  positioned outside the frame  145  selected by the object selector  121 , as a feature point, by edge detection, then compares the feature point  147   b  with a feature point  147   c  in the frame  141   c , and corrects the difference (coordinate conversion). 
     In  FIGS. 9A and 9B , the frame  141   c  is subjected to the coordinate conversion by moving the feature point  147   b  of the frame  141   b  onto the feature point  147   c  of the frame  141   c  as indicated with an arrow  148 . 
     In this example, the change of feature point is obtained between the first image frame  141   b  and the second image frame  141   c  in the plural images obtained by serial image sensing. Further, the change of feature point is similarly obtained regarding the subsequent images. 
     Note that it may be arranged such that plural points are selected as feature points and a mean value of motion vectors or a minimum scalar value of these points is obtained as the change of feature points. 
     The respective images subjected to the coordinate conversion by the coordinate converter  115  are outputted to the image composition unit  116 , and the composite image is made by the composition of these images as shown in  FIG. 10 . 
     As described above, as the object which is not a main object, the coordinates of which in the respective images are brought into correspondence by the coordinate conversion, appears as the house  144  in the composite image. On the other hand, as the image sensing has been performed at a shutter speed to reduce influence of camera shaking and the object in motion (vehicle) is on the image screen, the vehicle as the main object, the coordinates of which in the respective images do not correspond with each other, discretely appears as separate vehicles  143   b  and  143   c  in the composite image. Next, composition of the discretely composite objects, i.e., the vehicles  143   b  and  143   c  such that the vehicle moves, will be described with reference to  FIG. 11 . 
     First, feature points within the object selection frame  145   b  in the frame  141   b  used upon generation of the composite image from the images  144   b  and  144   c  are extracted. Within the object selection frame  145   b , a window edge  150   b  and a tail lamp  151   b  of the vehicle  143   b  and another feature point (not shown), having generally high luminance, color hue, chromaticity and brightness, are extracted as feature points by edge detection and stored. Then the main object, the vehicle  143   b  is extracted based on the luminance, color hue, chromaticity and brightness levels obtained by the edge detection. Then, points having the same feature levels as those of previously stored points are extracted from the whole screen of the frame  141   c  ( 150   c  and  151   c ). The edge loci are obtained by connecting the edges between the respective frames with straight lines, and the amount and the direction of movement of the vehicle  143   b  are predicted. The locus between the edges  150   b  and  150   c  is indicated as an arrow  153 ; and that between the edges  151   b  and  151   c  is indicated as an arrow  154 . Then image interpolation is performed along the loci with the same luminance, color hue, chromaticity and brightness, thereby performing image drawing such that the vehicle  143   b  flows to the vehicle  143   c  as shown in  FIG. 12 . 
     The composite image data made by the image composition unit  116  is inputted via the image selector  112  to the display unit  117  and the recording unit  118 . The display unit  117  displays the image data on the display device such as a liquid crystal display. The recording unit  118  compresses the image data and stores the data onto a recording medium such as a memory card. 
     Next, the image sensing processing in the digital camera according to the present embodiment will be described with reference to  FIG. 7 . 
     The flowchart showing the image sensing processing in the digital camera according to the present embodiment is the same as that shown in  FIG. 7 , but the difference is that object(s) outside the object selection frame (for example, the frame  145   b  in  FIGS. 9A and 9B ) selected by the object selector  121  (in the first embodiment, within the object selection frame) in the respective images is brought into correspondence, and object(s) within the object selection frame (in the first embodiment, without the object selection frame) is interpolated such that the object(s) flows. The image composition to bring objects into correspondence and the interpolation to obtain an image where an object flows are the same as those described in the first embodiment. 
     At step S 1001 , when the first release switch (SW 1 ) is turned ON, the process proceeds to step S 1002 . 
     At step S 1002 , image sensing is performed by the image sensing unit  17 . The image sensing controller  18  drives the AF driving motor  14   a  to move the photographing lens  11  in the optical axis direction while detecting an image contrast based on an output from the image processor  111 . 
     When a highest contrast is obtained, the driving of the photographing lens  11  is stopped, thereby the image sensing optical system is set to a focusing state (AF by hill climbing method). Note that the focusing adjustment may be performed by phase difference detection. 
     Further, at this time, the image sensing controller  18  obtains the brightness of an object based on the output from the image sensing unit  17 . 
     At step S 1003 , it is determined whether or not the photographer sets the anti-shake effect operation unit  120  to the “lasting” setting. When the anti-shake effect operation unit  120  is set to the “lasting” setting, the process proceeds to step S 1004 , and otherwise, the process proceeds to step S 1018 . 
     Next, the flow of the case where the anti-shake effect operation unit  120  is set to the “lasting” setting will be described. 
     At step S 1004 , the number of times of image sensing and exposure periods of the respective times of image sensing are obtained based on the image sensing conditions such as the brightness of the object obtained at step S 1002 . 
     The image sensing conditions include: 
     1. brightness of object; 
     2. focal length of image sensing optical system; 
     3. brightness of image sensing optical system (aperture value); and 
     4. sensitivity of image sensing device. 
     For example, assuming that the sensitivity of the image sensing unit  17  is ISO 100, to measure the brightness of an object (photometry) and perform appropriate exposure based on the result of photometry, the aperture  13   a  is full-opened (e.g., f2.8) and the closing timing of the shutter  12   a , i.e., the exposure period, is set to 1/50 sec. 
     When the focal length of the image sensing optical system is equivalent to 100 mm of 35 mm film, image sensing with an exposure period of 1/50 sec may cause image blurring due to camera shake. To prevent camera shake, the exposure period is set to 1/100 sec and image sensing is performed twice. 
     On the other hand, when the focal length of the image sensing optical system is 400 mm, the exposure period is set to 1/500 sec and image sensing is performed 10 times so as to prevent camera shaking. 
     In this manner, the exposure period upon plural times of image sensing is determined in correspondence with image sensing conditions, and the number of times of image sensing is set in correspondence with the image sensing conditions. 
     In a case where the same object is image-sensed plural times, it is preferable that exposure conditions of respective times of image sensing are close to an appropriate exposure as much as possible so as to perform image sensing with accurate information by the image sensing unit  17 . 
     For this purpose, when an object is dark or the aperture of the photographing lens is narrowed and the brightness of the lens is low, or when the sensitivity of the image sensing unit  17  is low, the exposure periods of respective times of image sensing are lengthened as much as possible even in plural times of image sensing, to obtain effective exposure conditions. 
     Note that if exposure periods are too long, the influence of camera shaking appears in an image surface. Accordingly, as described above, when the focal length of the image sensing optical system is equivalent to 100 mm of 35 mm film, the exposure period is set to 1/100 sec corresponding to about 1/100 mm (focal length). 
     Further, the number of times of image sensing is controlled so as to compensate for the underexposure. 
     When the focal length is lengthened, the exposure period is further shortened so as to prevent image degradation due to camera shaking, and the number of times of image sensing is increased to compensate for the underexposure. 
     In this manner, in plural times of image sensing, as the object becomes darker or the aperture of the photographing lens is narrowed, the exposure period is lengthened. As the sensitivity of the image sensing unit  17  is decreased, the exposure period is lengthened. Further, as the focal length of the lens is lengthened, the exposure period is shortened. 
     The number of times of image sensing of serial image sensing is increased as the object becomes darker or aperture of the photographing lens is narrowed. As the sensitivity of the image sensing device is lowered, the number of times of image sensing is increased, and further, as the focal length of the lens is lengthened, the number of times of image sensing is increased. 
     After the completion of the above calculation, the setting of anti-shake mode (plural image sensing mode) is displayed on a display provided in a finder of the digital camera or a liquid crystal display as an extension unit of the digital camera, and at the same time, the number of times of image sensing is displayed on the display unit  117  for the photographer. 
     At step S 1005 , it is determined whether or not the shutter button  12   c  has been full-depressed. When the shutter button  12   c  has been full-depressed, the second release switch (SW 2 ) is turned ON. In this case, the process proceeds to step S 1006 . 
     At step S 1006 , the obtained images are temporarily stored into the memory  113 . 
     Step S 1006  is repeated until it is determined at step S 1007  that all the image sensing has been completed. 
     When all the image sensing has been completed, the process proceeds to step S 1008 . 
     At step S 1008 , the shift detector  114  extracts a characteristic image (feature point) from an image (e.g., the house  144   b  in  FIGS. 9A and 9B ) outside the object selection frame (e.g., the frame  145  in  FIGS. 9A and 9B ) previously set by the object selector  121 , and obtains the coordinates of the image. 
     At step S 1009 , the coordinate converter  115  performs coordinate conversion of respective images. Note that coordinate conversion is not performed only on the first frame image (first image). That is, the first image is used as a reference image upon coordinate conversion. 
     The feature point extraction at step S 1008  and the coordinate conversion at step S 1009  are performed on all the second and subsequent images, and when it is determined at step S 1010  that the coordinate conversion of all the images has been completed, the process proceeds to step S 1011 . 
     At step S 1011 , the shift detector  114  extracts a characteristic image (feature point) from an image (e.g., the vehicle  143   b  in  FIG. 11 ) in the object selection frame (e.g., the frame  145  in  FIG. 11 ) previously set by the object selector  121  in the first-obtained image (first image (the frame  141   b  in FIG.  11 )), and obtains the coordinates of the image. At this time, the luminance, color hue, chromaticity and brightness of the extracted point are stored. Points having the same features are extracted as a group, thereby extracting the image of the vehicle  143   b . The shift detector  114  extracts points having the same features as those of the stored points from the second image group (the second image) (the frame  141   c  in  FIG. 11 ), and obtains the loci of the image of the vehicle  143   b.    
     At step S 1012 , image interpolation is performed using the luminance, color hue, chromaticity and brightness of the respective points along the loci calculated at step S 1011 , thereby generating an image where the vehicle  143   b  flows to the tree  143   c  in  FIG. 11 . 
     The feature point extraction at step S 1011  and the image interpolation at step S 1012  are repeated until all the second and subsequent images have been processed. When it is determined at step S 1013  that the coordinate conversion of all the images has been completed, the process proceeds to step S 1014 . 
     At step S 1014 , the composition of the first image and the respective images of the coordinate-converted second image group is performed. 
     The image composition is performed by averaging corresponding coordinate values of the respective images, and random noise in the image can be reduced by the averaging. Then, the image with reduced noise is subjected to gain control to increase the level of gain, to optimize the exposure. 
     At step S 1015 , in the composite image, an area where the respective images are not overlaid due to composition shift (an area  160  in  FIG. 11 ) is cut, and the image is subjected to diffusion-interpolation to obtain the initial frame size. 
     At step S 1016 , the image data generated by the image processor  111  or the composite image data made by the image composition unit  116  is displayed on the display unit  117 . 
     At step S 1017 , the image data generated by the image processor  111  or the composite image data made by the image composition unit  116  is stored on a recording medium such as a memory card. 
     At step S 1018 , the process returns to START. 
     Note that in a case where the shutter button  12   c  is still half-depressed and the switch SW 1  is ON at step S 1018 , the process proceeds to steps S 1001  to S 1004  again. 
     Further, in a case where the shutter button  12   c  has been full-depressed and the switch SW 2  is ON at step S 1018 , the process does not return to START but stands by at step S 1017 . 
     Next, the flow of the case where the anti-shake effect operation unit  120  is OFF at step S 1003  will be described. 
     At step S 1003 , if it is determined that the anti-shake effect operation unit  120  is OFF, the process proceeds to step S 1020 . 
     At step S 1020 , it is determined whether or not the shutter button  12   c  has been full-depressed. When the shutter button  12   c  has been full-depressed, the second release switch (SW 2 ) is turned ON. In this case, the process proceeds to step S 1021 . 
     At step S 1021 , the process stands by until normal image sensing (normal image sensing mode under exposure conditions effective in one exposure) has been completed. Upon completion of exposure, the process proceeds to step S 1016 . 
     At step S 1016 , the image data generated by the image processor  111  or the composite image data made by the image composition unit  116  is displayed on the display unit  117 . 
     At step S 1017 , the image data generated by the image processor  111  or the composite image data made by the image composition unit  116  is stored on a recording medium such as a memory card. 
     At step S 1018 , the process returns to START. 
     According to the second embodiment, an image with lasting effects and an image without blur due to camera shaking can be obtained by performing image sensing plural times for exposure periods not to cause camera shaking, then performing image composition so as to eliminate shifts of object(s) other than a main object while to correct the locus of motion of the main object in images obtained by the plural times of image sensing. 
     The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, to appraise the public of the scope of the present invention, the following claims are made. 
     CLAIM OF PRIORITY 
     This application claims priority from Japanese Patent Application No. 2004-271009 filed on Sep. 17, 2004, the entire contents of which are incorporated by reference herein.