Patent Publication Number: US-9413979-B2

Title: Imaging apparatus and method for recapturing an image captured in a multiple exposure shooting mode

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an imaging apparatus, and more particularly to an imaging apparatus that can multiple combine a plurality of captured images. 
     2. Description of the Related Art 
     There has conventionally been a technology of performing multiple exposure shooting through addition processing of a plurality of digital image signals. 
     Japanese Patent Application Laid-Open No. 2002-218313 discusses retaining three images in a recording area in the process of image capturing in a multiple exposure shooting mode. The three images to be retained include an image captured immediately before, an addition image (keep image) up to the previous image capturing, and an addition image obtained by adding the addition image up to the previous image capturing and the image captured immediately before. Japanese Patent Application Laid-Open No. 2002-218313 also discusses receiving an instruction to clear the image captured immediately before while the addition image immediately after the image capturing is displayed for a preview. Then, the image to be added to the keep image can be recaptured. 
     Japanese Patent Application Laid-Open No. 2006-340063 discusses providing a preview display after each time an image is captured in a multiple exposure mode. During the preview display, an image preview switch can be pressed each time to switch to display of a multiple exposure image in the captured image in a picture-in-picture fashion, display only the captured image, and display only the multiple exposure image. 
     Consider the case of clearing an image captured immediately before for the sake of recapturing as discussed in Japanese Patent Application Laid-Open No. 2002-218313. In such a case, information for making a decision whether to clear the image captured immediately before (hereinafter, also referred to as immediately-previous image) may be obtained if a comparison can be made between the outcome when the immediately-previous image is added to an existing addition image (multiple combined image) and the outcome when not added. However, according to Japanese Patent Application Laid-Open No. 2002-218313, it is only possible to display a multiple combined image obtained by adding all images captured in a multiple exposure shooting mode (an addition image or a keep image during a through image display), not a multiple combined image without the immediately-previous image added. According to Japanese Patent Application Laid-Open No. 2006-340063 also, it is only possible to display a multiple combined image obtained by adding all images captured in a multiple exposure shooting mode (multiple exposure image) and an immediately-previous image (captured image), but not a multiple combined image without the immediately-previous image. In other words, it has conventionally not been possible to compare the outcome when an immediately-previous image captured immediately before in the multiple exposure shooting mode is added to an existing multiple combined image and the outcome when not added. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an imaging apparatus that enables a comparison between a multiple combined image to which an image captured immediately before is not added and a multiple combined image to which the image captured immediately before is added. 
     According to an aspect of the present invention, an imaging apparatus includes a receiving unit configured to receive an instruction to recapture an image last captured in a multiple exposure shooting mode after a first number of images are acquired in the multiple exposure shooting mode, a generation unit configured to generate an image into which an image that is captured in the multiple exposure shooting mode after the instruction to recapture the image is received by the receiving unit and a second number of images are multiple combined, the second number of images being the first number of images excluding the image last captured, and a display control unit configured to display, on a display unit, a first image obtained by multiple combining the first number of images and a second image obtained by multiple combining the second number of images after the first number of images are acquired in the multiple exposure shooting mode and before the instruction to recapture the image is received by the receiving unit. 
     According to an exemplary embodiment of the present invention, a comparison can be made between a multiple combined image to which an image captured immediately before is not added and a multiple combined image to which the image captured immediately before is added. 
     Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a configuration block diagram illustrating a digital camera according to an exemplary embodiment of the present invention. 
         FIGS. 2A and 2B  are external views of the digital camera. 
         FIGS. 3A and 3B  are diagrams illustrating display examples of a presetting menu screen for multiple exposure shooting. 
         FIGS. 4A, 4B, 4C, 4D, and 4E  are diagrams illustrating image data stored in a buffer memory during multiple exposure shooting. 
         FIG. 5  is a flowchart illustrating multiple exposure shooting mode processing. 
         FIG. 6  is a flowchart illustrating multiple exposure shooting processing. 
         FIGS. 7A and 7B  are diagrams illustrating display examples of a quick review in multiple exposure shooting. 
         FIG. 8  is a flowchart illustrating multiple quick review and playback processing. 
         FIG. 9  is a flowchart illustrating multiple first image quick review and playback processing. 
         FIGS. 10A, 10B, 10C, 10D, 10E, 10F, 10G, and 10H  are diagrams illustrating display examples where a processing select dialog is displayed during a quick review in multiple exposure shooting. 
         FIG. 11  is a flowchart illustrating one image back processing. 
         FIG. 12  is a flowchart illustrating save and exit processing. 
         FIG. 13  is a flowchart illustrating exit without saving processing. 
         FIG. 14  is a diagram illustrating a display example of another presetting menu screen for multiple exposure shooting. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings. 
       FIG. 1  is a block diagram illustrating the configuration of a digital camera  100 , which serves as an imaging apparatus according to an exemplary embodiment of the present invention. 
     In  FIG. 1 , a photographic lens  101  is a detachably-attached interchangeable lens, which includes a zoom lens and a focus lens. 
     An autofocus (AF) drive circuit  102  includes a direct-current (DC) motor or a stepping motor, for example. The AF drive circuit  102  changes the position of a focus lens included in the photographic lens  101  for focusing under control of a microcomputer  123 . 
     A diaphragm drive circuit  104  drives a diaphragm  103 . The microcomputer  123  calculates the amount of driving, and the diaphragm drive circuit  104  changes an optical aperture value. 
     A main mirror  105  is a mirror for switching a light flux incident from the photographic lens  101  to between a finder side and an image sensor  112  side. The main mirror  105  is arranged to reflect the light flux toward a finder unit when in a normal condition. When performing photographing and during a live view display, the main mirror  105  is flipped up and retracted out of the light flux so that the light flux is introduced to the image sensor  112 . The main mirror  105  is configured as a half mirror so that some of the light can be transmitted through a center area. Some of the light flux is thus transmitted and made incident on a sensor for focus detection. 
     A sub mirror  106  is a mirror for reflecting a light flux transmitted through the main mirror  105  toward the sensor intended for focus detection (which is included in a focus detection circuit  109 ). 
     A mirror drive circuit  107  drives the main mirror  105  under control of the microcomputer  123 . 
     A pentagonal prism  108  constitutes a finder. The finder also includes a focusing screen and an eyepiece lens (not illustrated). 
     The focus detection circuit  109  is a block intended for focus detection. A sensor for photoelectric conversion is arranged inside the focus detection circuit  109 . The light flux that is transmitted through the center area of the main mirror  105  and reflected by the sub mirror  106  reaches the sensor for photoelectric conversion. The sensor output can be calculated to determine a defocus amount for use in focus calculation. The microcomputer  123  evaluates the result of calculation and instructs the AF drive circuit  102  to drive the focus lens. 
     A shutter drive circuit  111  drives a focal plane shutter  110 . The microcomputer  123  controls an opening time of the focal plane shutter  110 . 
     Examples of the image sensor  112  include a charge-coupled device (CCD) sensor and a complementary metal oxide semiconductor (CMOS) sensor. The image sensor  112  converts an object image formed by the photographic lens  101  into an electrical signal. 
     An analog-to-digital (A/D) converter  115  converts an analog output signal output from the image sensor  112  into a digital signal. 
     An image signal processing circuit  116  is implemented by logic devices such as a gate array. The image signal processing circuit  116  performs various types of image signal processing. 
     A display drive circuit  117  is a drive circuit that causes a display member  118  to produce a display. 
     The display member  118  is a display such as a thin-film transistor (TFT) liquid crystal display and an organic electroluminescence (EL) display. In the present exemplary embodiment, the display member  118  is implemented as a rear monitor of the digital camera  100 . 
     A memory controller  119  stores unprocessed digital image data input from the image signal processing circuit  116  into a buffer memory  122 , and stores processed digital image data into a recording medium  120 . The memory controller  119  outputs image data from the buffer memory  122  and the recording medium  120  to the image signal processing circuit  116 . The memory control  119  can output an image or images stored in the recording medium  120  through an external interface  121 , which is connectable to a computer. 
     The recording medium  120  is a removable recording medium such as a memory card. The recording medium  120  may be a built-in recording medium of the digital camera  100 . A plurality of recording media may be used. 
     The external interface  121  is an interface for establishing connection with an external device such as a computer by wired or wireless communications. 
     The buffer memory  122  is a memory for temporarily retaining image data. Various images used in the process of multiple exposure shooting are also stored in the buffer memory  122 . 
     The image signal processing circuit  116  performs filter processing, color conversion processing, and gamma processing on a digitized image signal to generate development data. The image signal processing circuit  116  also performs Joint Photographic Experts Group (JPEG) or other compressing processing and outputs the result to the memory controller  119 . 
     The image signal processing circuit  116  can add two or more pieces of development data on the buffer memory  122 , generate high-precision data with increased gradation bits from development data, or simultaneously perform both the processes, and write the result back to the buffer memory  122 . The image signal processing circuit  116  can also output an image signal from the image sensor  112  and/or an image signal reversely input from the memory controller  119  to the display member  118  through the display drive circuit  117 . The image signal processing circuit  116  switches such functions based on an instruction from the microcomputer  123 . The image signal processing circuit  116  can output information to the microcomputer  123  if needed. Examples of the information include exposure information on the signal of the image sensor  112  and information on white balance. Based on such pieces of information, the microcomputer  123  issues instructions as to white balance and a gain adjustment. In a continuous shooting operation, shot data is once stored into the buffer memory  122  as unprocessed images. The image signal processing circuit  116  reads the unprocessed image data through the memory controller  119 , and performs image processing and compression processing for continuous shooting. The number of shots in continuous shooting depends on the capacity of the buffer memory  122 . 
     The microcomputer  123  is a main control unit for controlling the entire digital camera  100 . The microcomputer  123  executes various types of programs recorded on a nonvolatile memory  130  by using a system memory  132  as a work memory. 
     An operation detection unit  124  detects that an operation member is operated. If the operation member is operated, the operation detection unit  124  informs the microcomputer  123  of that state. The microcomputer  123  controls various components according to the change of the operation member. The operation detection unit  124  is capable of detecting the open/close state of a lid of a slot where the recording medium  120  is accommodated (hereinafter, referred to as a card lid) and the open/close state of a battery lid. 
     An example of the operation member is a release button  10 . A switch  1  (hereinafter, referred to as SW 1 )  125  is a switch that is turned ON by a half press operation of the release button  10 . If the SW 1   125  is ON, the microcomputer  123  performs shooting preparation processes such as an AF operation and a light metering operation. 
     A switch  2  (hereinafter, referred to as SW 2 )  126  is a switch that is turned ON by a full press operation of the release button  10 . If the SW 2   126  is ON, the microcomputer  123  performs an actual shooting process of capturing an image and recording the captured image on the recording medium  120  as an image file. 
     A continuous shooting operation is performed while the SW 1   125  and the SW 2   126  remain ON. 
     A liquid crystal drive circuit  127  drives an external liquid crystal display member  128  and an in-finder liquid crystal display member  129  according to display contents and commands from the microcomputer  123 . The external liquid crystal display member  128  and the in-finder liquid crystal display member  129  display operation statuses and messages by using characters and/or graphics. The in-finder liquid crystal display member  129  includes a not-illustrated backlight such as a light-emitting diode (LED). The liquid crystal drive circuit  127  also drives the LED. 
     Parameters such as an International Organization for Standardization (ISO) sensitivity, an image size, and image quality are set in advance of shooting. The microcomputer  123  can check the remaining capacity of the recording medium  120  through the memory controller  119 , and calculate the number of shots available based on predicted value data on an image size according to the set parameters. The number of shots available may be displayed on the display member  118 , the external liquid crystal display member  128 , and/or the in-finder liquid crystal display member  129  if needed. 
     Examples of the nonvolatile memory  130  include an electrically erasable programmable read-only memory (EEPROM) and a flash memory. The nonvolatile memory  130  can retain data even when the digital camera  100  is not powered on. A power supply unit  131  provides a necessary power supply to the foregoing blocks and drive systems. 
       FIGS. 2A and 2B  illustrate external views of the digital camera  100 .  FIG. 2A  is a front perspective view of the digital camera  100 .  FIG. 2B  is a rear perspective view of the digital camera  100 . The front perspective view illustrates the digital camera  100  with the photographic lens  101 , an interchangeable lens, dismounted. 
     As illustrated in  FIG. 2A , the digital camera  100  has operation members including the release button  10 , a main electronic dial  11 , an ISO setting button  12 , an exposure compensation button  13 , a shooting mode dial  14 , and an aperture reducing button  15 . The aperture reducing button  15  is a button for reducing the diaphragm  103  to a set aperture stop value (F value). The user can press the aperture reducing button  15  to check the brightness of a captured image through the set aperture during a live view display in a shooting mode. A live view display refers to a continuous display of images being captured by the image sensor  112  on the display member  118  generally in real time, with the main mirror  105  retracted. Such a display, or a through display, makes the display member  118  function as an electronic viewfinder. The main electronic dial  11  is a rotating operation member. The main electronic dial  11  is used for operations such as increasing and decreasing various set values including a photographing condition, changing a selected item when selecting various items, and switching images in units of groups when in a playback mode. 
     As illustrated in  FIG. 2B , the digital camera  100  has operation members including an information display button  16 , a menu button  17 , a playback button  18 , a delete button  19 , a main switch  20 , and a set button  21 . The digital camera  100  also has a sub electronic dial  22 , a zoom-in button  23 , a zoom-out button  24 , and a multi controller  25 . The main switch  20  is an operation member for powering ON/OFF the digital camera  100 . The sub electronic dial  22  is a rotating operation member. The sub electronic dial  22  is used for operations such as changing a selected item when selecting various items, and switching images to display when in a playback mode. An eye-side finder unit  26  is an eyepiece unit through which the user looks into a viewfinder and views an optical image. 
     Next, a method of setting preset items as to multiple exposure shooting will be described. 
       FIGS. 3A and 3B  illustrate display examples of a menu screen for making settings of the digital camera  100  as to multiple exposure shooting. A menu screen  300  as to multiple exposure shooting illustrated in  FIG. 3A  appears on the display member  118  when the user presses the menu button  17  to display a general menu, selects a menu for multiple exposure shooting from the general menu, and confirms the selection. 
     The menu screen  300  displays menu items  301  to  304 . The user can operate the sub electronic dial  22  to select any of the menu items  301  to  304 . When the user presses the set button  21  with any one of the menu items selected, a list of setting candidates for the selected menu item is displayed. The user can operate the sub electronic dial  22  or make other operations to select a desired setting candidate from the displayed list of setting candidates, and press the set button  21  again to confirm and set the selected setting candidate as a set value. 
     The menu item  301  is a menu item for selecting whether to perform multiple exposure shooting. Either one of two setting candidates “on” and “off” can be selected and set. Hereinafter, the setting of the present menu item  301  will be referred to as a multiple exposure shooting necessity setting. The multiple exposure shooting necessity setting is recorded in the system memory  132  or the nonvolatile memory  130 . If the multiple exposure shooting necessity setting is changed from “off” to “on” according to a user operation, the digital camera  100  starts multiple exposure shooting at the next image capturing. The multiple exposure shooting necessity setting is automatically changed from “on” to “off” under several conditions to be described below, such as when multiple exposure shooting has reached a predetermined number of shots and ended. If the menu item  301  is set to “off” according to a user operation in a multiple exposure shooting in-process state to be described below, the digital camera  100  ends the multiple exposure shooting at that point. Here, a multiple combined image file is generated if possible. 
     The menu item  302  is a menu item for selecting the number of images to be superimposed for a set of multiple exposure shots. The number of images can be selected and set from among setting candidates of 2 to 9. If a base image to be described below is not selected, the number of images set by the menu item  302  serves as the number of images predetermined for multiple exposure shooting. If a base image is selected, the number of images predetermined for multiple exposure shooting is the number of images selected by the menu item  302  minus one. The number of images predetermined for multiple exposure shooting is recorded in the system memory  132 . It should be noted that the menu item  302  is not selectable to change if one or more images have been captured by multiple exposure shooting and the multiple exposure shooting is yet to be completed. Such a state will hereinafter be referred to as a multiple exposure shooting in-process state. In the multiple exposure shooting in-process state, a multiple exposure shooting in-process flag to be described below is set to 1. 
     The menu item  303  is a menu item for selecting whether an automatic exposure adjustment function needs to be performed in multiple exposure shooting. Either one of two setting candidates “on” and “off” can be selected and set. The present menu item  303  is not selectable to change in the multiple exposure shooting in-process state. 
     The menu item  304  is a menu item for selecting a base image for multiple exposure shooting. Any one of images recorded on the recording medium  120  can be selected and set as a base image. The present menu item  304  can be set only when the multiple exposure shooting necessity setting is set at “on” and the digital camera  100  is in a state other than the multiple exposure shooting in-process state. More specifically, a base image can be set by the menu item  304  only between when the multiple exposure shooting necessity setting is set at “on” and when the first image is captured. If a base image is set, the screen display changes to that illustrated in  FIG. 3B . An image  306  is an image that is selected as a base image from among images recorded on the recording medium  120 . The image signal processing circuit  116  reads a base image from the recording medium  120 , converts the base image into development data, and loads the resulting development data into the buffer memory  122 . When a base image is selected, the set value of an image size serving as a photographing condition (the image size of an image or images to be captured in the subsequent multiple exposure shooting) is set at the same value as the image size of the base image. The selection of a base image makes it possible to perform multiple exposure shooting with an image captured in the past as the first captured image. In the present exemplary embodiment, images that can be selected as a base image are limited to images previously captured by the digital camera  100  because the image sizes need to be matched. Images other than those captured by the digital camera  100  may be included as candidates for a base image if the images have image sizes that the digital camera  100  can set as a photographing condition. When multiple exposure shooting ends, the setting of a base image is cancelled and the digital camera  100  returns to the state where no base image is selected. A cancel selected image button  305  is a button icon for canceling a selected base image. When the cancel selected image button  305  is selected, the digital camera  100  immediately restores the state where no base image is selected. 
     Referring to  FIGS. 4A to 4E , data retained in the buffer memory  122  during multiple exposure shooting will be described. Each time an image is captured, the buffer memory  122  retains up to five pieces of image data including development data, high-precision data, multiple development data, display-specific multiple data, and previous image capturing time display-specific multiple data. 
     Development data refers to data that is generated by applying development processing such as color processing to an image signal obtained from the image sensor  112  in the image capturing immediately before. The development data can be compressed in the JPEG format to generate an image file of an original image to be recorded on the recording medium  120 . 
     For the purpose of multiple combination, development data obtained by the previous image capturing is subjected to the image signal processing circuit  116  for bit enhancement (hereinafter, precision enhancement). High-precision data refers to the bit-enhanced image data that is added to high-precision data generated before. The precision enhancement can reduce the possibility that gradations may be saturated by multiple combination processing. Other processing that facilitates multiple combination may be applied aside from the precision enhancement. 
     Multiple development data is high-precision data currently generated (multiple-combined with an image or images obtained before) to which development data obtained by the current image capturing is added. The multiple development data can be compressed in the JPEG format to generate an image file of a multiple combined image to be recorded on the recording medium  120 . 
     Display-specific multiple data is data that is generated by reducing and compressing multiple development data for display purpose. Such data is used to perform multiple quick review (hereinafter, also referred to as QR) and playback processing and multiple first image QR and playback processing to be described below. 
     Previous image capturing time display-specific multiple data is display-specific multiple data that has been generated by previous image capturing. A multiple image combination and a multiple image combination result image may refer to an image generated by superimposing, composing, synthesizing, or merging images by way of example and not of limitation. Multiple image combination and multiple image combination result image do not refer to synthesizing a plurality of images that are placed in a tile-arranged configuration such as is done for a panoramic effect. Multiple image combination and multiple image combination result image may be referred to as multiple-synthesize image, multiple-composite image, multiple image combination image, or multiple-composite image. 
       FIGS. 4A to 4E  illustrate data retained in the buffer memory  122  in respective states without a base image. 
       FIG. 4A  illustrates the state of the buffer memory  122  after the first image is captured. An image signal A is obtained by the capturing of the first image. The image signal A is developed into development data A, which is then retained in the buffer memory  122 . Note that none of the high-precision data, multiple development data, display-specific multiple data, and previous image capturing time display-specific multiple data is generated or stored, and as much free area is reserved in the buffer memory  122 . Since as much capacity as needed to store high-precision data, multiple development data, display-specific multiple data, and previous image capturing time display-specific multiple data is left unused, the capacity may be allocated for other processing so that the other processing can be performed at high speed. Examples of the other processing include face detection processing using live view shooting, and contrast AF processing. 
       FIG. 4B  illustrates the state of the buffer memory  122  after the second image is captured. An image signal B is obtained by the capturing of the second image. The image signal B is developed into development data B, which is then retained in the buffer memory  122 . The development data A which has been retained since the capturing of the first image is enhanced in precision and retained as high-precision data A (no addition occurs because there has been no high-precision data retained after the first image). The high-precision data A and the development data B are multiple combined to generate multiple development data A+B, which is then retained in the buffer memory  122 . The multiple development data A+B is reduced and compressed to generate display-specific multiple data A+B, which is then retained in the buffer memory  122 . There is no display-specific multiple data generated when the first image is captured. When the second image is captured, previous image capturing time display-specific multiple data is thus generated from the image file of the first image A recorded on the recording medium  120 . The generated previous image capturing time display-specific multiple data is then retained in the buffer memory  122 . 
       FIG. 4C  illustrates the state of the buffer memory  122  after the third image is captured. An image signal C is obtained by the capturing of the third image. The image signal C is developed into development data C, which is then retained in the buffer memory  122 . The development data B which has been retained since the capturing of the second image is enhanced in precision. The result is added to the high-precision data A, which has been retained since the capturing of the second image, to generate high-precision data A+B. The generated high-precision data A+B is then retained in the buffer memory  122 . The high-precision data A+B and the development data C are multiple combined to generate multiple development data A+B+C, which is then retained in the buffer memory  122 . The multiple development data A+B+C is reduced and compressed to generate display-specific multiple data A+B+C, which is then retained in the buffer memory  122 . The display-specific multiple data A+B, which is generated when the second image is captured, is retained as previous image capturing time display-specific multiple data A+B. 
       FIG. 4D  illustrates the state of the buffer memory  122  when the image obtained by the third image capturing is discarded by multiple QR and playback processing to be described below. When the image obtained by the third image capturing is discarded, then the development data C, the multiple development data A+B+C, and the display-specific multiple data A+B+C are discarded from the buffer memory  122  of the state illustrated in  FIG. 4C . The image data that is retained as the previous image capturing time display-specific multiple data A+B in  FIG. 4C  is retained as display-specific multiple data A+B in  FIG. 4D . 
       FIG. 4E  illustrates the state of the buffer memory  122  when the third image is recaptured after the third captured image is discarded. An image signal D is obtained by the recapturing of the third image (image capturing in a multiple exposure shooting mode after acceptance of a recapturing instruction). The image signal D is developed into development data D, which is then retained in the buffer memory  122 . The high-precision data A+B which has been retained since the discard of the third image is retained unchanged. The high-precision data A+B and the development data D are multiple combined to generate multiple development data A+B+D, which is then retained in the buffer memory  122 . The multiple development data A+B+D is reduced and compressed to generate display-specific multiple data A+B+D, which is then retained in the buffer memory  122 . The display-specific multiple data A+B which has been retained since the discard of the third image is retained as previous image capturing time display-specific multiple data A+B. 
     Next, data used in the processing of multiple exposure shooting will be described. The processing of multiple exposure shooting is executed by using the following variables:
         Multiple exposure shooting necessity setting: Can be set to either “on” or “off.” The set value is recorded in the nonvolatile memory  130  or the system memory  132 . The state “on” indicates a multiple exposure shooting mode.   Multiple exposure shooting in-process flag: A variable that indicates whether multiple exposure shooting is in process. This variable is recorded in the system memory  132 . If the multiple exposure shooting necessity setting is set at “on” and one or more images are captured, the multiple exposure shooting in-process flag is 1 (multiple exposure shooting in-process state). If multiple exposure shooting ends, the multiple exposure shooting in-process flag is “0”. Whether to perform normal quick review processing or multiple quick review processing is determined based on this flag.   Number of images predetermined for multiple exposure shooting: A value that indicates the number of times of multiple exposure shooting to be performed (hereinafter, referred to as a set of multiple exposure shots) for generating a multiple combined image. This value is recorded in the system memory  132 . If no base image is set, the number of images predetermined for multiple exposure shooting is the number of images set via the menu item  302  illustrated in  FIG. 3 . If a base image is set, the number of images predetermined for multiple exposure shooting is the number of images set via the menu item  302  illustrated in  FIG. 3  minus one.   Number of images captured for multiple exposure shooting: A value that indicates the number of images captured so far for a set of multiple exposure shots. This value is recorded in the system memory  132 . If the number of images captured for multiple exposure shooting reaches the number of images predetermined for multiple exposure shooting, a set of multiple exposure shots ends. The multiple exposure shooting processing is thus completed.       

     In the multiple exposure shooting in-process state, information that indicates the storage location of each original image captured so far by a set of multiple exposure shots on the recording medium  120  is recorded in the system memory  132  as written file information. If there is a plurality of recording media to record images on, information that specifies the storing recording medium is also recorded. 
       FIG. 5  is a flowchart illustrating multiple exposure shooting mode processing. The processing illustrated in  FIG. 5  is implemented by a program recorded in the nonvolatile memory  130  being loaded into the system memory  132  and executed by the microcomputer  123 . The processing illustrated in  FIG. 5  starts when the multiple exposure shooting necessity setting is set to “on.” 
     In step S 501 , the microcomputer  123  determines whether the SW 2  is ON. If the SW 2  is ON (YES in step S 501 ), the microcomputer  123  proceeds to step S 502 . If the SW 2  is not ON (NO in step S 501 ), the microcomputer  123  proceeds to step S 507 . 
     In step S 502 , the microcomputer  123  performs multiple exposure shooting processing. The multiple exposure shooting processing will be described in detail below with reference to  FIG. 6 . 
     In step S 503 , the microcomputer  123  refers to the system memory  132  and determines whether the number of images captured for multiple exposure shooting is “1”. In other words, the microcomputer  123  determines whether the first image for a set of multiple exposure shots is captured by the multiple exposure shooting processing performed in step S 502 . If the number of images captured for multiple exposure shooting is “1” (YES in step S 503 ), the microcomputer  123  proceeds to step S 504 . In step S 504 , the microcomputer  123  sets a multiple exposure shooting in-process flag of “1” in the system memory  132 . If in step S 503  the number of images captured for multiple exposure shooting is determined to be not “1” (NO in step S 503 ) or after the multiple exposure shooting in-process flag is set to “1” in step S 504 , the microcomputer  123  proceeds to step S 505 . 
     In step S 505 , the microcomputer  123  determines whether the number of images captured for multiple exposure shooting retained in the system memory  132  is equal to the number of images predetermined for multiple exposure shooting. If the two numbers are equal (YES in step S 505 ), a set of multiple exposure shots has been completed. In step S 506 , the microcomputer  123  performs save and exit processing, and then ends the multiple exposure shooting mode processing. The save and exit processing will be described below with reference to  FIG. 12 . 
     In step S 507 , the microcomputer  123  determines whether the playback button  18  is pressed (whether there is an instruction to enter a playback mode). If the playback button  18  is pressed (YES in step S 507 ), the microcomputer  123  proceeds to step S 508 . If the playback button  18  is not pressed (NO in step S 507 ), the microcomputer  123  proceeds to step S 514 . 
     In step S 508 , the microcomputer  123  refers to the system memory  132  and determines whether the multiple exposure shooting in-process flag is “1” (whether in the multiple exposure shooting in-process state). If the multiple exposure shooting in-process flag is “1” (YES in step S 508 ), the microcomputer  123  proceeds to step S 510 . If the multiple exposure shooting in-process flag is not “1” (NO in step S 508 ), the microcomputer  123  proceeds to step S 509 . 
     In step S 509 , the microcomputer  123  performs normal playback mode processing. In the normal playback mode processing, the microcomputer  123  performs playback processing including a single image display, a multiple display, image advancing, delete, and attaching an attribute. The playback mode processing is targeted for all images that are recorded on the recording medium  120  and reproducible by the digital camera  100 . 
     In step S 510 , the microcomputer  123  determines whether a base image is set. If no base image is set (NO in step S 510 ), the microcomputer  123  proceeds to step S 511 . If a base image is set (YES in step S 510 ), the microcomputer  123  proceeds to step S 513 . 
     In step S 511 , the microcomputer  123  determines whether the number of images captured for multiple exposure shooting recorded in the system memory  132  is greater than or equal to “2”. If the number is determined to be greater than or equal to “2” (YES in step S 511 ), the microcomputer  123  proceeds to step S 513 . If the number is less than “2” (NO in step S 511 ), the microcomputer  123  proceeds to step S 512 . Since the multiple exposure shooting in-process flag is “1”, that the number of images captured for multiple exposure shooting is less than “2” means that the number of images captured for multiple exposure shooting is “1”. 
     In step S 512 , the microcomputer  123  performs multiple first image QR and playback processing. The multiple first image QR and playback processing is display processing intended to check an image that has been acquired after entry to a multiple exposure shooting mode, and to check how the image is multiple combined. None of the images captured before the entry to the multiple exposure shooting mode is displayed, except a base image. The multiple first image QR and playback processing will be described below with reference to  FIG. 9 . 
     In step S 513 , the microcomputer  123  performs multiple QR and playback processing. The multiple QR and playback processing is display processing to check images that have been acquired after entry to the multiple exposure shooting mode, and to check how the images are multiple combined. None of images captured before the entry to the multiple exposure shooting mode is displayed, except a base image. The multiple QR and playback processing will be described below with reference to  FIG. 8 . 
     In step S 514 , the microcomputer  123  refers to the system memory  132  and determines whether the multiple exposure shooting in-process flag is “1”. If the multiple exposure shooting in-process flag is “1” (YES in step S 514 ), the microcomputer  123  proceeds to step S 515 . If the multiple exposure shooting in-process flag is not “1” (NO in step S 514 ), the microcomputer  123  proceeds to step S 517 . 
     In step S 515 , the microcomputer  123  determines whether an interruptive event has occurred. The interruptive event refers to an event on which the multiple exposure shooting mode is to be interrupted. Examples include the following:
         An event that changes the multiple exposure shooting necessity setting to “off” according to a user operation.   A user operation on the main switch  20 , opening of the card lid, and opening of the battery lid. An event that turns off the power, such as expiration of an automatic power-off time.   An event that prevents continuation of multiple exposure shooting depending on conditions of shooting settings.
 
If an interruptive event has occurred (YES in step S 515 ), the microcomputer  123  proceeds to step S 516 . If no such event has occurred (NO in step S 515 ), the microcomputer  123  proceeds to step S 517 .
       

     In step S 516 , the microcomputer  123  performs the save and exit processing. The save and exit processing will be described below with reference to  FIG. 12 . 
     In step S 517 , the microcomputer  123  refers to the multiple exposure shooting necessity setting stored in the system memory  132  or the nonvolatile memory  130 , and determines whether the multiple exposure shooting is set at “on.” If the multiple exposure shooting is set at “on” (YES in step S 517 ), the microcomputer  123  proceeds to step S 501  to repeat the multiple exposure shooting mode processing. If the multiple exposure shooting is set at “off” (NO in step S 517 ), the microcomputer  123  ends the multiple exposure shooting mode processing. 
       FIG. 6  is a flowchart illustrating the multiple exposure shooting processing in step S 502  illustrated in  FIG. 5  described above. The processing illustrated in  FIG. 6  is implemented by a program recorded in the nonvolatile memory  130  being loaded into the system memory  132  and executed by the microcomputer  123 . 
     In step S 601 , the microcomputer  123  controls exposure. When the exposure is completed, then in step S 602 , the microcomputer  123  performs control to read an image signal accumulated in the image sensor  112 . 
     In step S 603 , the microcomputer  123  instructs the image signal generation circuit  116  to generate development data from the image signal read in step S 602 . As illustrated in  FIGS. 4A to 4E , the generated development data is stored in the buffer memory  122 . 
     In step S 604 , the microcomputer  123  causes the image signal processing circuit  116  to compress the development data generated in step S 603 . In step S 605 , the microcomputer  123  records the result on the recording medium  120  as an image file (first recording control). The image file contains a single original image, not a combined one. In step S 606 , the microcomputer  123  adds information indicating the storage location of the image file recorded in step S 605  to written file information retained in the system memory  132 . Instead of or in addition to the information indicating the storage location of the image file, the microcomputer  123  may record information that identifies the image file (such as a file name). The microcomputer  123  adds “1” to the number of images captured for multiple exposure shooting retained in the system memory  132 . 
     In step S 607 , the microcomputer  123  determines whether a base image is set. If there is a base image (YES in step S 607 ), the microcomputer  123  proceeds to step S 608 . If no base image is set (NO in step S 607 ), the microcomputer  123  proceeds to step S 611 . 
     In step S 608 , the microcomputer  123  refers to the system memory  132  and determines whether the number of images captured for multiple exposure shooting is greater than or equal to “2”. If the number is less than “2”, i.e., the number of captured images is only one which results from the current image capturing (NO in step S 608 ), the microcomputer  123  proceeds to step S 609 . If the number is greater than or equal to “2” (YES in step S 608 ), the microcomputer  123  proceeds to step S 610 . 
     In step S 609 , the microcomputer  123  reads the base image from the recording medium  120  and acquires development data of the base image. The microcomputer  123  enhances the precision of the development data of the base image by using the image signal processing circuit  116 , and stores the resulting high-precision data into the buffer memory  122 . In other words, the processing is performed with the base image as an image signal A obtained by the capturing of the first image in  FIG. 4B  and with the image data acquired by the current image capturing in step S 602  as an image signal B obtained by the capturing of the second image in  FIG. 4B . 
     In step S 610 , the microcomputer  123  enhances the precision of the development data obtained by the previous image capturing by using the image signal processing circuit  116 . The microcomputer  123  adds the result to high-precision data generated before to generate high-precision data, and stores the high-precision data into the buffer memory  122 . In terms of the example illustrated in  FIGS. 4A to 4E , such an operation translates as follows: When the third image is captured in  FIG. 4C , development data B obtained by the capturing of the second image is enhanced in precision. The result is added to high-precision data A that is generated when the second image is captured, whereby high-precision data A+B is generated. The high-precision data A+B is stored into the buffer memory  122 . 
     In step S 611 , the microcomputer  123  refers to the system memory  132  and determines whether the number of images captured for multiple exposure shooting is greater than or equal to “2”. If the number is determined to be greater than or equal to “2” (YES in step S 611 ), the microcomputer  123  proceeds to step S 612 . If the number is less than “2”, i.e., the number of captured images is only one, which results from the current image capturing (NO in step S 611 ), the microcomputer  123  proceeds to step S 618 . If in step S 611  the number of images captured for multiple exposure shooting is determined to be only one, which results from the current image shooting (NO in step S 611 ), the buffer memory  122  is in the state illustrated in  FIG. 4A . 
     In step S 612 , the microcomputer  123  determines whether the number of images captured for multiple exposure shooting is “2”. If the number is not “2”, i.e., is three or greater (NO in step S 612 ), the microcomputer  123  proceeds to step S 610 . If the number is “2” (YES in step S 612 ), the microcomputer  123  proceeds to step S 613 . 
     In step S 613 , the microcomputer  123  enhances the precision of the development data obtained by the previous image capturing by using the image signal processing circuit  116 , thereby generating high-precision data. The microcomputer  123  stores the high-precision data into the buffer memory  122 . In terms of the example illustrated in  FIGS. 4A to 4E , such an operation translates as follows. Development data A obtained by the capturing of the first image is enhanced in precision when the second image is captured in  FIG. 4B . The result is stored into the buffer memory  122  as high-precision data A. 
     In step S 614 , the microcomputer  123  multiple combines high-precision data generated in any one of steps S 609 , S 610 , and S 613  with the development data of the current captured image, generated in step S 603 , by using the image signal processing circuit  116 . The microcomputer  123  stores the generated multiple combined image into the buffer memory  122  as multiple development data. 
     In step S 615 , the microcomputer  123  reduces and compresses the high-precision data generated in step S 614  by using the image signal processing circuit  116 . The microcomputer  123  stores the result into the buffer memory  122  as display-specific multiple data. 
     In step S 616 , the microcomputer  123  determines whether a quick review (QR) is set to be made. Whether to make a QR immediately after image capturing may be set in advance according to a user operation. If a QR is set to be made (YES in step S 616 ), the microcomputer  123  proceeds to step S 617 . In step S 617 , the microcomputer  123  performs the multiple QR and playback processing. The multiple QR and playback processing will be described below with reference to  FIG. 8 . If in step S 616  a QR is set not to be made (NO in step S 616 ) or after the processing in step S 617  is completed, the microcomputer  123  ends the multiple exposure shooting processing. The microcomputer  123  then proceeds to step S 503  illustrated in  FIG. 5  described above. 
     In step S 618 , the microcomputer  123  determines whether a quick review (QR) is set to be made. If a QR is set to be made (YES in step S 618 ), the microcomputer  123  proceeds to step S 619 . In step S 619 , the microcomputer  123  performs the multiple first image QR and playback processing. The multiple first image QR and playback processing will be described below with reference to  FIG. 9 . If in step S 618  a QR is set not to be made (NO in step S 618 ) or after the processing in step S 619  is completed, the microcomputer  123  ends the multiple exposure shooting processing. The microcomputer  123  then proceeds to step S 503  illustrated in  FIG. 5  described above. 
       FIGS. 7A and 7B  illustrate display examples of an initial display screen to be displayed on the display member  118  for a quick review in multiple exposure shooting (display control).  FIGS. 7A and 7B  each illustrate a display example where the number of images to be superimposed for multiple exposure shooting is set at “3” via the menu item  302  illustrated in  FIG. 3  described above, and no base image is set via the menu item  304 . 
       FIG. 7A  illustrates an initial display screen that is displayed for a quick review immediately after the capturing of the first image for a set of multiple exposure shots. Such a screen is initially displayed in the multiple first image QR and playback processing illustrated in  FIG. 9  to be described below. A display item  701  includes an icon that indicates that the image is the one obtained by multiple exposure shooting. The display item  701  also includes an indication that there are two images left to reach the number of images predetermined for multiple exposure shooting. A display item  702  is a guide display indicating that the delete button  19  can be pressed to display a processing select dialog to be described below. An image  703  is the one that is not multiple combined because only one image has been captured. The image  703  is based on an image file read from the recording medium  120 . 
       FIG. 7B  illustrates an initial display screen that is displayed for a quick review immediately after the capturing of the second image for a set of multiple exposure shots. Such a screen is initially displayed in the multiple QR and playback processing illustrated in  FIG. 8  to be described below. A display item  704  expresses a meaning similar to that of the display item  701  in  FIG. 7A . The display item  704  indicates that there is one image left, one fewer, to reach the number of images predetermined for multiple exposure shooting. An image  705  is a multiple combined image of the first image and the currently-captured, second, image. The image  705  displays the display-specific multiple data A+B in  FIG. 4B   
       FIG. 8  is a flowchart illustrating the multiple QR and playback processing in step S 513  illustrated in  FIG. 5  and step S 617  illustrated in  FIG. 6  described above. The processing illustrated in  FIG. 8  is implemented by a program recorded in the nonvolatile memory  130  being loaded into the system memory  132  and executed by the microcomputer  123 . 
     In step S 801 , the microcomputer  123  starts counting (starts a timer) the time of a quick review (for example, two seconds). Such processing is not performed if a quick review time is set at HOLD (no automatic cancellation) or if the playback button  18  has been pressed to enter the processing illustrated in  FIG. 8  (i.e., when in the playback mode processing). 
     In step S 802 , the microcomputer  123  displays display-specific multiple data illustrated in  FIGS. 4A to 4E  on the display member  118 . A display example is illustrated in  FIG. 7B  described above. The user can view the display-specific multiple data to check a multiple combined image that is to be generated from images obtained by image capturing so far. More specifically, the user can check a multiple combined image (first image) made of a number (first number) of images including an image or images as many as the number of images captured for multiple exposure shooting at this point in time and a base image if any. 
     In step S 803 , the microcomputer  123  determines whether a predetermined quick view time has elapsed from the clocking of step S 801 . If the predetermined time has elapsed (YES in step S 803 ), the microcomputer  123  ends the multiple QR and playback processing and returns to the multiple exposure shooting mode processing illustrated in  FIG. 5 . If the predetermined time has not elapsed yet (NO in step S 803 ), the microcomputer  123  proceeds to step S 804 . The processing in step S 803  is not performed if the quick review time is set to HOLD (no automatic cancellation) or if the playback button  18  has been pressed to enter the processing illustrated in  FIG. 8  (i.e., when in the playback mode processing). 
     In step S 804 , the microcomputer  123  determines whether the SW 1  is ON and whether the playback button  18  is pressed. If the SW 1  is determined to be ON or the playback button  18  is determined to be pressed (YES in step S 804 ), the microcomputer  123  ends the multiple QR and playback processing and returns to the multiple exposure shooting mode processing illustrated in  FIG. 5 . If not (NO in step S 804 ), the microcomputer  123  proceeds to step S 805 . 
     In step S 805 , the microcomputer  123  determines whether the delete button  19  is pressed. If the delete button  19  is determined to be pressed (YES in step S 805 ), the microcomputer  123  proceeds to step S 806 . If the delete button  19  is determined to be not pressed (NO in step S 805 ), the microcomputer  123  returns to step S 803  and repeats the foregoing processing. 
     In step S 806 , the microcomputer  123  ends counting time and clears the timer if the quick review time has started being counted in step S 801 . 
     In step S 807 , the microcomputer  123  displays a processing select dialog on the display member  118 .  FIG. 10A  illustrates a display example of the processing select dialog. A processing select dialog  1005  is displayed as superimposed on a display of display-specific multiple data  705 . A return to previous screen icon  1001 , a one image back icon  1002 , a save and exit icon  1003 , and an exit without saving icon  1004  are displayed in a lower part of the processing select dialog  1005 . A description text on one of the icons  1001  to  1004  that is currently selected by a select frame is displayed in an upper part of the processing select dialog  1005 . The select frame can be moved to an arbitrary icon according to an operation on the sub electronic dial  22 . For an initial state, in step S 807 , the microcomputer  123  displays the processing select dialog  1005  with the return to previous screen icon  1001  selected by the select frame. Having displayed the processing select dialog  1005 , the microcomputer  123  proceeds to step S 810 . 
     In step S 810 , the microcomputer  123  determines whether the set button  21  is pressed to make a confirmation operation with the return to previous screen icon  1001  selected. If a confirmation operation is determined to be made with the return to previous screen icon  1001  selected (YES in step S 810 ), then in step S 811 , the microcomputer  123  dismisses the processing select dialog to restore the display illustrated in  FIG. 7B . The microcomputer  123  then returns to step S 803  to repeat the processing. If no such confirmation operation is determined to be made (NO in step S 810 ), the microcomputer  123  proceeds to step S 812 . 
     In step S 812 , the microcomputer  123  determines whether the one image back icon  1002  is selected by the select frame. If the one image back icon  1002  is selected (YES in step S 812 ), the microcomputer  123  proceeds to step S 813 . If not (NO in step S 812 ), the microcomputer  123  proceeds to step S 816 . In step S 813 , the microcomputer  123  displays previous image capturing time display-specific multiple data stored in the buffer memory  122 , illustrated in  FIGS. 4A to 4E , on the display member  118 . A display example is illustrated in  FIG. 10B . An image  706  represents previous image capturing time display-specific multiple data. In the example illustrated in  FIG. 10B , two images have been captured for a set of multiple exposure shots when the display is moved one image back. The image  706  thus shows a non-multiple image including only the first image. If three or more images have been captured when a display is moved one image back, then the user can check a multiple combined image excluding the image captured immediately before (last captured image). More specifically, the user can check a multiple combined image (second image) made of a number (second number) of images including images as many as the number of images captured for multiple exposure shooting at this point in time and a base image if any (first number), excluding the last captured image. In such a way, according to an exemplary embodiment of the present invention, a multiple combined image (image  706 ) excluding the last captured image and a multiple combined image (image  705 ) including the last captured image can be switched for display during a quick review or in a playback mode. Such a switched display allows the user to easily compare the two images and determine whether the immediately previous image is a satisfactory one as an image to be multiple combined. If the immediately previous image is not satisfactory, the user can discard the immediately previous image and continue multiple exposure processing from one image back. 
     In step S 814 , the microcomputer  123  determines whether the set button  21  is pressed to make a confirmation operation with the one image back icon  1002  selected (in other words, whether a recapturing instruction is given). If a confirmation operation is determined to be made with the one image back icon  1002  selected (YES in step S 814 ), the microcomputer  123  proceeds to step S 815 . If not (NO in step S 814 ), the microcomputer  123  proceeds to step S 816 . 
     In step S 815 , the microcomputer  123  performs one image back processing. The one image back processing will be described below with reference to  FIG. 11 . Completing the one image back processing, the microcomputer  123  ends the multiple QR and playback processing and returns to the multiple exposure shooting mode processing illustrated in  FIG. 5 . 
     In step S 816 , the microcomputer  123  determines whether the save and exit icon  1003  is selected by the select frame. If the save and exit icon  1003  is selected (YES in step S 816 ), the microcomputer  123  proceeds to step S 817 . If not (NO in step S 816 ), the microcomputer  123  proceeds to step S 820 . In step S 817 , the microcomputer  123  displays display-specific multiple data stored in the buffer memory  122 , illustrated in  FIGS. 4A to 4E , on the display member  118 . A display example is illustrated in  FIG. 10C . The image  705  displays the display-specific multiple data. The user views the image  705 . If the multiple combined image generated from the images obtained by multiple exposure shooting so far is satisfactory, the microcomputer  123  may generate and save a multiple combined image and end the multiple exposure shooting. 
     In step S 818 , the microcomputer  123  determines whether the set button  21  is pressed to make a confirmation operation with the save and exit icon  1003  selected. If a confirmation operation is determined to be made with the save and exit icon  1003  selected (YES in step S 818 ), the microcomputer  123  proceeds to step S 819 . If not (NO in step S 818 ), the microcomputer  123  proceeds to step S 820 . 
     In step S 819 , the microcomputer  123  performs the save and exit processing. The save and exit processing will be described below with reference to  FIG. 12 . Completing the save and exit processing, the microcomputer  123  ends the multiple QR and playback processing. The microcomputer  123  ends the processing in the multiple exposure shooting mode without returning to the multiple exposure shooting mode processing illustrated in  FIG. 5 , and enters a normal shooting mode. 
     In step S 820 , the microcomputer  123  determines whether the exit without saving icon  1004  is selected by the select frame. If the exit without saving icon  1004  is selected (YES in step S 820 ), the microcomputer  123  proceeds to step S 821 . If not (NO in step S 820 ), the microcomputer  123  proceeds to step S 808 . In step S 821 , the microcomputer  123  displays display-specific multiple data stored in the buffer memory  122 , illustrated in  FIGS. 4A to 4E , on the display member  118 . A display example is illustrated in  FIG. 10D . The image  705  displays display-specific multiple data. The user views the image  705 . If the multiple combined image generated from images obtained by multiple exposure shooting so far is not satisfactory on the whole, the user may discard all the images captured so far for the set of multiple exposure shots and end the multiple exposure shooting. 
     In step S 822 , the microcomputer  123  determines whether the set button  21  is pressed to make a confirmation operation with the exit without saving icon  1004  selected. If a confirmation operation is determined to be made with the exit without saving icon  1004  selected (YES in step S 822 ), the microcomputer  123  proceeds to step S 823 . If not (NO in step S 822 ), the microcomputer  123  proceeds to step S 808 . 
     In step S 823 , the microcomputer  123  performs exit without saving processing. The exit without saving processing will be described below with reference to  FIG. 13 . Completing the exit without saving processing, the microcomputer  123  ends the multiple QR and playback processing. The microcomputer  123  ends the processing in the multiple exposure shooting mode without returning to the multiple exposure shooting mode processing illustrated in  FIG. 5 , and enters the normal shooting mode. 
     In step S 808 , the microcomputer  123  determines whether the return to previous screen icon  1001  is selected by the select frame. If the return to previous screen icon  1001  is selected (YES in step S 808 ), the microcomputer  123  proceeds to step S 809 . If not (NO in step S 808 ), the microcomputer  123  proceeds to step S 812 . In step S 809 , the microcomputer  123  displays display-specific multiple data stored in the buffer memory  122 , illustrated in  FIGS. 4A to 4E , on the display member  118 . A display example is illustrated in  FIG. 10A  described above. 
     Note that in the initial display in step S 802  illustrated in  FIG. 8 , the display member  118  displays display-specific multiple data. Instead, the display member  118  may display a non-multiple captured image that is captured immediately before. Processing of selecting and switching to display display-specific multiple data and a non-multiple captured image may be added. 
       FIG. 9  is a flowchart illustrating the multiple first image QR and playback processing in step S 512  illustrated in  FIG. 5  and step S 619  illustrated in  FIG. 6  described above. The processing illustrated in  FIG. 9  is implemented by a program recorded in the nonvolatile memory  130  being loaded into the system memory  132  and executed by the microcomputer  123 . 
     Step S 901  is similar to step S 801  illustrated in  FIG. 8  described above. Description thereof will thus be omitted. 
     In step S 902 , the microcomputer  123  decodes compressed data on the image file of an image that is captured immediately before, recorded on the recording medium  120 , and displays the resultant on the display member  118 . A display example is illustrated in  FIG. 7A  described above. The multiple first image QR and playback processing illustrated in  FIG. 9  deals with a situation where there is no base image and only one image has been captured by multiple exposure shooting. The buffer memory  122  stores no display-specific multiple data. The microcomputer  123  then displays the image  703  based on an image file read from the recording medium  120 . 
     The processing in steps S 903  to S 907  and S 910  to S 912  is similar to the processing in steps S 803  to S 807  and S 810  to S 812  illustrated in  FIG. 8  described above, respectively. Description thereof will thus be omitted.  FIG. 10E  illustrates a display example in step S 907 . 
     In step S 913 , the microcomputer  123  causes the display member  118  to display a black image since the buffer memory  122  stores no previous image capturing time display-specific multiple data. A display example is illustrated in  FIG. 10F . Such a display can inform the user that, after one image back, there is no image obtained by multiple exposure shooting. Other displays may be used instead of a black image. A warning such as “No image to display” may be displayed. An alternative image to the black image may be a monotone image in order to indicate that the image is not a captured one. 
     The processing in steps S 914  to S 916  is similar to the processing in steps S 814  to S 816  illustrated in  FIG. 8  described above, respectively. Description thereof will thus be omitted. 
     In step S 917 , the buffer memory  122  stores no display-specific multiple data. The microcomputer  123  then decodes compressed data on an image file of an image that is captured immediately before, recorded on the recording medium  120 , and displays the result on the display member  118 . A display example is illustrated in  FIG. 10G . 
     The processing in steps S 918  to S 920  is similar to the processing in steps S 818  to S 820  illustrated in  FIG. 8  described above, respectively. Description thereof will thus be omitted. 
     In step S 921 , the buffer memory  122  stores no display-specific multiple data. The microcomputer  123  then decodes compressed data on an image file of an image that is captured immediately before, recorded on the recording medium  120 , and displays the result on the display member  118 . A display example is illustrated in  FIG. 10H . 
     The processing in steps S 922 , S 923 , and S 908  is similar to the processing in steps S 822 , S 823 , and S 808  illustrated in  FIG. 8  described above, respectively. Description thereof will thus be omitted. 
     In step S 921 , the buffer memory  122  stores no display-specific multiple data. The microcomputer  123  then decodes compressed data on an image file of an image that is captured immediately before, recorded on the recording medium  120 , and displays the result on the display member  118 . 
       FIG. 11  is a flowchart illustrating the one image back processing in step S 815  illustrated in  FIG. 8  and step S 915  illustrated in  FIG. 9  described above. The processing illustrated in  FIG. 11  is implemented by a program recorded in the nonvolatile memory  130  being loaded into the system memory  132  and executed by the microcomputer  123 . 
     In step S 1101 , the microcomputer  123  refers to written file information stored in the system memory  132 . The microcomputer  123  searches for an image file of an image captured immediately before, recorded on the recording medium  120 , and deletes the image file. 
     In step S 1102 , the microcomputer  123  deletes information on the image file deleted in step S 1101  from the written file information stored in the system memory  132 , thereby updating the written file information. 
     In step S 1103 , the microcomputer  123  subtracts “1” from the number of images captured for multiple exposure shooting retained in the system memory  132 . 
     In step S 1104 , the microcomputer  123  determines whether the number of images captured for multiple exposure shooting retained in the system memory  132  is “0”. If the number is determined to be not “0” (NO in step S 1104 ), the microcomputer  123  proceeds to step S 1105 . If the number is determined to be “0” (YES in step S 1104 ), the microcomputer  123  proceeds to step S 1106 . 
     In step S 1105 , the microcomputer  123  discards development data, multiple development data, and previous image capturing time display-specific multiple data from the buffer memory  122 , and ends the one image back processing. Such an operation corresponds to changing the state of the buffer memory  122  from the state illustrated in  FIG. 4C  to that illustrated in  FIG. 4D  described above. In the state illustrated in  FIG. 4D , high-precision data A+B remains in the buffer memory  122 . A third image can thus be recaptured to continue multiple exposure shooting from the previous result of multiple exposure shooting. Display-specific multiple data A+B also remains in the buffer memory  122 . After the recapturing of the third image, the display-specific multiple data A+B is retained as previous image capturing time display-specific multiple data A+B, so that the “one image back” processing can be performed again. 
     In step S 1106 , the microcomputer  123  discards development data from the buffer memory  122 . Such an operation corresponds to discarding the development data in the state illustrated in  FIG. 4A . 
     In step S 1107 , the microcomputer  123  resets the multiple exposure shooting in-process flag retained in the system memory  132  to “0”, and ends the one image back processing. Although the buffer memory  122  contains no image data, the multiple exposure shooting mode processing itself is not terminated here. Multiple exposure shooting can thus be continued from the first image without performing presetting for multiple exposure shooting again. 
       FIG. 12  is a flowchart illustrating the save and exit processing in step S 819  illustrated in  FIG. 8  and step S 919  illustrated in  FIG. 9  described above. The processing illustrated in  FIG. 12  is implemented by a program recorded in the nonvolatile memory  130  being loaded into the system memory  132  and executed by the microcomputer  123 . 
     In step S 1201 , the microcomputer  123  determines whether the number of images captured for multiple exposure shooting retained in the system memory  132  is greater than or equal to “2”. If the number is greater than or equal to “2” (YES in step S 1201 ), the microcomputer  123  proceeds to step S 1202 . If the number is less than “2” (NO in step S 1201 ), the microcomputer  123  proceeds to step S 1206 . 
     In step S 1202 , the microcomputer  123  compresses multiple development data stored in the buffer memory  122  to generate an image file. 
     In step S 1203 , the microcomputer  123  generates an image file of a multiple combined image from the multiple development data compressed in step S 1202 . An example of the generated image file is a JPEG file. The microcomputer  123  may refer to written file information retained in the system memory  132 , and record information that identifies the original images of the multiple combined image into a header of the image file of the multiple combined image as attribute information. The microcomputer  123  may store such information into a different area in association with the image file. 
     In step S 1204 , the microcomputer  123  records the image file of the multiple combined image generated in step S 1203  on the recording medium  120  (second recording control). 
     In step S 1205 , the microcomputer  123  performs multiple exposure shooting initialization processing. In the initialization processing, the microcomputer  123  discards all pieces of image data recorded in the buffer memory  122 . The microcomputer  123  resets the number of images predetermined for multiple exposure shooting and the number of images captured for multiple exposure shooting recorded in the system memory  132 . The microcomputer  123  changes the multiple exposure shooting necessity setting to “off.” The microcomputer  123  resets the multiple exposure shooting in-process flag retained in the system memory  132  to “0”. The microcomputer  123  deletes all the contents of written file information retained in the system memory  132 . Completing the processing in step S 1205 , the microcomputer  123  ends the save and exit processing. 
     In step S 1206 , the microcomputer  123  determines whether the number of images captured for multiple exposure shooting retained in the system memory  132  is “1”. If the number is “1” (YES in step S 1206 ), the microcomputer  123  proceeds to step S 1207 . If the number is not “1”, i.e., is “0” (NO in step S 1206 ), the microcomputer  123  proceeds to step S 1205 . 
     In step S 1207 , the microcomputer  123  determines whether a base image is set. If a base image is set (YES in step S 1207 ), the microcomputer  123  proceeds to step S 1202 . In step S 1202 , the microcomputer  123  generates an image file of a multiple combined image and records the image file on the recording medium  120 . If no base image is set (NO in step S 1207 ), the microcomputer proceeds to step S 1208 . 
     In step S 1208 , only one image has been captured for a set of multiple exposure shots and there is no base image. In such a situation, the generation of a multiple combined image produces substantially no superimposition and results in substantially the same image as the only one image. The microcomputer  123 , therefore, displays a warning that no multiple combined image is generated in the absence of superimposition. The microcomputer  123  also displays on the display member  118  a user interface (UI) for accepting a selection whether to delete the written original image file. 
     In step S 1209 , the microcomputer  123  determines whether the UI displayed in step S 1208  has accepted an instruction from the user via an operation member, the instruction instructing to delete the written original image. If the delete instruction has been received (YES in step S 1209 ), the microcomputer  123  proceeds to step S 1210 . If no such delete instruction has been received (NO in step S 1209 ), the microcomputer  123  proceeds to step S 1211 . 
     In step S 1210 , the microcomputer  123  refers to written file information retained in the system memory  132 , and deletes the image file of the original image that is captured in the multiple exposure shooting mode and recorded on the recording medium  120 . The microcomputer  123  also deletes information on the deleted image file from the written file information. 
     In step S 1211 , the microcomputer  123  displays a screen for receiving a selection whether to register the written original image as the first image to be displayed on a base image select screen when performing presetting for multiple exposure shooting next time (selection acceptance). The microcomputer  123  then determines whether an instruction to register the written original image as the first image to be displayed on the base image select screen next time is received from the user via an operation member. If the instruction is determined to be received (YES in step S 1211 ), the microcomputer  123  proceeds to step S 1212 . If the instruction is determined to be not received (NO in step S 1211 ), the microcomputer  123  proceeds to step S 1205 . 
     In step S 1212 , the microcomputer  123  registers the written original image as the first image to be displayed on the base image select screen when performing presetting for multiple exposure shooting next time. As a result, the only image captured in the multiple exposure shooting that is interrupted by the present processing is displayed as the first candidate for a base image when setting a base image from the menu item  304  illustrated in  FIG. 3  next time. For example, suppose that multiple exposure shooting is started, an image is captured, and the multiple exposure shooting is once ended for the purpose of image capturing other than the multiple exposure shooting. The processing in step S 1212  can reduce the user&#39;s operation burden when resuming the multiple exposure shooting at where it ended the last time. 
     Completing the processing in step S 1212 , the microcomputer  123  proceeds to step S 1205 . In step S 1205 , the microcomputer  123  performs the multiple exposure shooting initialization processing, and ends the save and exit processing. 
     According to the processing illustrated in  FIG. 12 , multiple exposure shooting may be ended without a base image and with only one image captured by the multiple exposure shooting, or with a base image and without an image captured by the multiple exposure shooting. In such cases, the microcomputer  123  does not generate or record an image file of a multiple combined image. More specifically, if there is only one image to be multiple combined, the microcomputer  123  does not generate or record an image file of such a multiple combined image. This can prevent substantially the same image files from being redundantly recorded to waste a storage capacity when a multiple combined image generated ends up being substantially the same as its original image. If there is only one image to be multiple combined, the microcomputer  123  may perform up to the generation of a multiple combined image but not the recording of the multiple combined image. This can provide the same effect in terms of preventing the recording capacity from being wasted. The foregoing description has dealt with the case where the written original image is registered in step S 1212  as a first image to be displayed on the base image select screen next time. Instead, a base image may simply be set to be used next time and the written original image may be set as the base image next time. 
       FIG. 13  is a flowchart illustrating the exit without saving processing in step S 823  illustrated in  FIG. 8  and step S 923  illustrated in  FIG. 9  described above. The processing illustrated in  FIG. 13  is implemented by a program recorded in the nonvolatile memory  130  being loaded into the system memory  132  and executed by the microcomputer  123 . 
     In step S 1301 , the microcomputer  123  refers to written file information retained in the system memory  132 , and searches the recording medium  120  for a written image file of an image that is captured for the current set of multiple exposure shots. 
     In step S 1302 , the microcomputer  123  deletes the written image file searched for and found in step S 1301  from the recording medium  120 . 
     In step S 1303 , the microcomputer  123  refers to the written file information retained in the system memory  132 , and determines whether there is any written image file that is captured for the current set of multiple exposure shots and recorded on the recording medium  120 . If it is determined that there is such a file (YES in step S 1303 ), the microcomputer  123  returns to step S 1301  and repeats processing to delete the remaining image(s). If it is determined that there is no such file, i.e., all images captured for the current set of multiple exposure shots are determined to have been deleted (NO in step S 1303 ), the microcomputer  123  proceeds to step S 1304 . 
     In step S 1304 , the microcomputer  123  performs multiple exposure shooting initialization processing, and ends the exit without saving processing. The multiple exposure shooting initialization processing is the same processing as that in step S 1205  illustrated in  FIG. 12 . 
     Instead of the multiple exposure shooting setting menu illustrated in  FIG. 3  described in the foregoing exemplary embodiment, more detailed presetting may be performed as to multiple exposure shooting. 
       FIG. 14  illustrates another display example of the menu screen for making settings of the digital camera  100  as to the multiple exposure shooting.  FIG. 14  illustrates a menu screen  1300  for multiple exposure shooting. The menu screen  1300  is displayed on the display member  118  when the user presses the menu button  17  to display a general menu and selects a multiple exposure shooting menu from the general menu. 
     The menu screen  1300  displays menu items  1301  to  1306 . The method of selecting a menu item and the method of setting a set value from a list of setting candidates for each menu item are similar to those illustrated in  FIGS. 3A and 3B . 
     The menu item  1301  is a menu item for selecting how multiple exposure shooting is performed. Any one of setting candidates “off,” “function and operation priority mode,” and “continuous shooting priority mode” can be selected and set. “Off” is the same as “off” illustrated in  FIGS. 3A and 3B  described above. “Function and operation priority mode” is the same as “on” illustrated in  FIGS. 3A and 3B  described above. “Continuous shooting priority mode” is a mode intended for faster continuous shooting speed. The continuous shooting priority mode includes saving the usage of the buffer memory  122  and omitting the generation and recording of image files of original images. When the continuous shooting priority mode is selected, the microcomputer  123  does not generate display-specific multiple data after each image capturing. The microcomputer  123  does not store display-specific multiple data or previous image capturing time display-specific multiple data into the buffer memory  122 . The microcomputer  123  does not perform the multiple QR and playback processing ( FIG. 8 ) or the multiple first image QR and playback processing ( FIG. 9 ). Nothing happens when the playback button  18  is pressed while the multiple exposure shooting in-process flag is “1”. The microcomputer  123  thus does not perform the exit without saving processing ( FIG. 13 ). In such a way, the continuous shooting speed in multiple exposure shooting can be improved. 
     The menu item  1302  is a menu item for selecting a method of combination when generating a multiple combined image. Any one of setting candidates “add,” “arithmetic average,” “compare (lighten),” and “compare (darken)” can be selected and set. “Add” is the same as the automatic exposure control function “off” illustrated in  FIGS. 3A and 3B  described above. “Arithmetic average” is the same as the automatic exposure control function “on” illustrated in  FIGS. 3A and 3B  described above. “Compare (lighten)” refers to a method in which multiple development data of captured images is compared with an image captured immediately before, and only portions where the image captured immediately before is brighter are extracted for combination. On the other hand, “compare (darken)” refers to a method in which only portions where the image captured immediately before is darker are extracted for combination. 
     The menu item  1303  is a menu item for selecting the number of images to be superimposed for a set of multiple exposure shots. The menu item  1303  is the same as the menu item  302  illustrated in  FIGS. 3A and 3B  described above. 
     The menu item  1304  is a menu item for selecting whether to record an original image or images on the recording medium  120 . Either one of setting candidates “all images” and “multiple image only” can be selected and set. “All images” is selected to record the original image (s) as well. “Multiple image only” is selected not to record the original image(s). When “multiple image only” is set, the microcomputer  123  does not record a captured non-multiple image file (original image file) in step S 605  illustrated in  FIG. 6  described above. 
     The menu item  1305  is a menu item for selecting whether to continue performing multiple exposure shooting under the same condition as set in  FIG. 14  after the number of images captured for multiple exposure shooting reaches the number of images predetermined for multiple exposure shooting and a set of multiple exposure shots is completed. Either one of “once-off” and “repeat” can be set. “Once-off” applies to the procedure illustrated in  FIG. 5  described above. When the number of images captured for multiple exposure shooting reaches the number of images predetermined for multiple exposure shooting, the microcomputer  123  performs the save and exit processing (S 506 ) and changes the multiple exposure shooting necessity setting to “off.” The microcomputer  123  ends the multiple exposure shooting mode processing and enters another shooting mode. In the case of “repeat,” when the number of images captured for multiple exposure shooting reaches the number of images predetermined for multiple exposure shooting and a set of multiple exposure shots is completed (S 505 ) in  FIG. 5  described above, the microcomputer  123  does not change the multiple exposure shooting necessity setting to “off” in the save and exit processing (S 506 ). After the processing in step S 505 , the microcomputer  123  returns to step S 501  with the condition set in  FIG. 14 , and repeats the multiple exposure shooting mode processing from the first image. 
     The present exemplary embodiment has dealt with the case of using development data for multiple combination. However, undeveloped raw image data may be used for multiple combination. 
     The control of the microcomputer  123  may be performed by a single piece of hardware. The entire apparatus may be controlled by distributing processing among a plurality of pieces of hardware. 
     The present invention has been described in detail based on exemplary embodiments thereof. The present invention is not limited to such particular exemplary embodiments, and various aspects are also included in the present invention without departing from the gist of the invention. The foregoing exemplary embodiments are just a few exemplary embodiments of the present invention. The exemplary embodiments may be combined as appropriate. 
     The foregoing embodiments have dealt with the cases where the present invention is applied to a digital camera. This is not restrictive, and exemplary embodiments of the present invention may be applied to any imaging apparatus that includes an imaging unit. More specifically, exemplary embodiments of the present invention may be applied to a digital camera, a digital video camera, a camera-equipped personal computer, a camera-equipped personal digital assistant (PDA), a camera-equipped cellular phone terminal, a camera-equipped music player, a camera-equipped game machine, and a camera-equipped electronic book reader. 
     An exemplary embodiment of the present invention may be implemented by executing the following processing. The processing includes supplying software (program) that implements the functions of the foregoing exemplary embodiments to a system or an apparatus via a network or via various types of storage media, and a computer (or a central processing unit (CPU) or micro processing unit (MPU)) of the system or apparatus reading and executing the program code. In such a case, the program and the storage media containing the program constitute exemplary embodiments of the present invention. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures, and functions. 
     This application claims priority from Japanese Patent Application No. 2011-101315 filed Apr. 28, 2011, which is hereby incorporated by reference herein in its entirety.