Patent Publication Number: US-6710807-B1

Title: Image sensing apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image sensing apparatus for sensing a still image and/or moving image. 
     2. Description of the Related Art 
     Conventionally, image sensing apparatuses such as electronic cameras and the like, which record/play back still images and moving images sensed by a solid-state image sensing element such as a CCD or the like using memory cards having solid-state memory elements as recording media, have already been commercially available. 
     In such electronic camera, a single shot mode for sensing images frame by frame every time the shutter button is pressed, and a continuous shot mode for sensing images successively while the shutter button is held down can be switched by selecting either mode. 
     On the other hand, when an image is sensed using a solid-state image sensing element such as a CCD or the like, a dark noise correction process can be done by computations using dark image data which is read out after charge accumulation in the same manner as in actual image sensing while the image sensing element is not exposed, and actually sensed image data which is read out after charge accumulation while the image sensing element is exposed. 
     With this process, sensed image data can be corrected in terms of image quality deterioration such as pixel omission or the like caused by dark current noise produced by the image sensing element and small scratches unique to the image sensing element, thus obtaining a high-quality sensed image. 
     Especially, since dark current noise increases with increasing charge accumulation time and temperature rise of the image sensing element, if exposure for a long period of time (seconds) or at high temperature is done, a great image quality improvement effect can be obtained, and the dark noise correction process is a function effective for the electronic camera users. 
     However, in the conventional image sensing apparatus such as an electronic camera or the like, when actual image sensing is done after dark image data is sensed, the shutter release time lag becomes longer by the dark image sensing time in the single shot mode, thus missing a shutter chance. 
     On the other hand, when dark image data is sensed after actual image sensing, the image sensing interval between the first and second frames is prolonged by the dark image sensing time in the continuous shot mode. As a result, constant image sensing frame intervals cannot be set. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is to provide an apparatus, which comprises an image sensing device, a signal processing device for performing a first image sensing operation for making the image sensing device perform an image sensing operation in an exposure state to obtain a sensed image signal, and a second image sensing operation for making the image sensing device perform an image sensing operation in a non-exposure state to obtain a sensed image signal, and processing the sensed image signal obtained by the first image sensing operation by the sensed image signal obtained by the second image sensing operation, the signal processing device having a first mode for making the image sensing device perform the first image sensing operation and then the second image sensing operation, and a second mode for making the image sensing device perform the second image sensing operation and then the first image sensing operation, and a storage device for storing signals obtained in the first and second modes processed by the signal processing device, thereby preventing a shutter chance from being missed, and setting constant image sensing frame intervals. 
     Another aspect of the present invention is to provide an apparatus, which comprises an image sensing device, a signal processing device for performing a first image sensing operation for making the image sensing device perform an image sensing operation in an exposure state to obtain a sensed image signal, and a second image sensing operation for making the image sensing device perform an image sensing operation in a non-exposure state to obtain a sensed image signal, and processing the sensed image signal obtained by the first image sensing operation by the sensed image signal obtained by the second image sensing operation, the signal processing device having a first mode for making the image sensing device perform the first image sensing operation and then the second image sensing operation, and a second mode for making the image sensing device perform the second image sensing operation and then the first image sensing operation, and a switching device for switching the signal processing device between the first and second modes in accordance with a state of shutter release operation, thereby preventing a shutter chance from being missed, and setting constant image sensing frame intervals. 
     Another aspect of the present invention is to provide an apparatus, which comprises an image sensing device, a signal processing device for performing a first image sensing operation for making the image sensing device perform an image sensing operation in an exposure state to obtain a sensed image signal, and a second image sensing operation for making the image sensing device perform an image sensing operation in a non-exposure state to obtain a sensed image signal, and processing the sensed image signal obtained by the first image sensing operation by the sensed image signal obtained by the second image sensing operation, the signal processing device having a first mode for making the image sensing device perform the first image sensing operation and then the second image sensing operation, and a second mode for making the image sensing device perform the second image sensing operation and then the first image sensing operation, and a switching device for switching the signal processing device to the first mode when the exposure start instruction device issues an exposure start instruction while the signal processing device is executing the second image sensing operation in the second mode, thereby preventing a shutter chance from being missed, and setting constant image sensing frame intervals. 
     Another aspect of the present invention is to provide an apparatus, which comprises an image sensing device, an exposure instruction device for issuing an exposure preparation instruction at a first stroke position of a shutter release member, and issuing an exposure start instruction at a second stroke position of the shutter release member, and a signal processing device for performing a first image sensing operation for making the image sensing device perform an image sensing operation in an exposure state to obtain a sensed image signal, and a second image sensing operation for making the image sensing device perform an image sensing operation in a non-exposure state to obtain a sensed image signal, and processing the sensed image signal obtained by the first image sensing operation by the sensed image signal obtained by the second image sensing operation, the signal processing device performing the second image sensing operation in response to the exposure preparation instruction issued by the exposure instruction device, and performing the first image sensing operation in response to the exposure start instruction issued by the exposure instruction device, thereby preventing a shutter chance from being missed, and setting constant image sensing frame intervals. 
    
    
     Other features and advantages of the present invention will be apparent from the following description 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 
     FIG. 1 is a block diagram showing the arrangement of an image sensing apparatus according to the first embodiment of the present invention; 
     FIG. 2 is a flow chart of a main routine showing the control sequence of the image sensing apparatus; 
     FIG. 3 is a flow chart of the main routine showing the control sequence of the image sensing apparatus and continued from FIG. 2; 
     FIG. 4 is a flow chart of the main routine showing the control sequence of the image sensing apparatus and continued from FIG. 3; 
     FIG. 5 is a flow chart showing the sequence of a distance measurement/photometry process in step S 132  in FIG. 3 in detail; 
     FIG. 6 is a flow chart showing the sequence of an image sensing process in step S 163  in FIG. 4 in detail; 
     FIG. 7 is a flow chart showing the sequence of a dark capture ( 1 ) process in step S 137  in FIG. 3 in detail; 
     FIG. 8 is a flow chart showing the sequence of a dark capture ( 2 ) process in step S 166  in FIG. 4 in detail; 
     FIG. 9 is a timing chart showing the flow of image sensing operation in the first embodiment; 
     FIG. 10 is a flow chart of a main routine showing the control sequence of an image sensing apparatus according to the second embodiment; 
     FIG. 11 is a flow chart of the main routine showing the control sequence of the image sensing apparatus according to the second embodiment and continued from FIG. 10; 
     FIG. 12 is a flow chart of the main routine showing the control sequence of the image sensing apparatus according to the second embodiment and continued from FIG. 11; and 
     FIG. 13 is a timing chart showing the flow of image sensing operation in the second embodiment 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. 
     First Embodiment 
     FIG. 1 is a block diagram showing the arrangement of an image sensing apparatus according to the first embodiment of the present invention. 
     Referring to FIG. 1, reference numeral  100  denotes an image sensing apparatus. 
     Reference numeral  12  denotes a shutter for controlling the exposure amount on an image sensing element; and  14 , an image sensing element such as a CCD, CMOS, or the like for converting an optical image into an electrical signal. 
     Light rays that have entered a lens  310  are guided onto the image sensing element  14  via a stop  312 , lens mounts  306  and  106 , a mirror  130 , and the shutter  12  by a single-lens reflex system, and form an optical image on the image sensing element  14 . 
     Reference numeral  16  denotes an A/D converter for converting an analog signal output into a digital signal. 
     Reference numeral  18  denotes a timing generation circuit for supplying clock signals and control signals to the image sensing element  14 , the A/D converter  16 , and a D/A converter  26 . The timing generation circuit  18  is controlled by a memory control circuit  22  and system control circuit  50 . 
     Reference numeral  20  denotes an image processing circuit for performing a predetermined pixel interpolation process and color conversion process for data from the A/D converter  16  or the memory control circuit  22 . 
     Also, the image processing circuit  20  can execute a TTL (through the lens) AF (auto-focus) process, AE (auto-exposure) process, and EF (flash light control) process. In these processes, the image processing circuit  20  makes predetermined computations using sensed image data as needed, and the system control circuit  50  controls a shutter control circuit  40  and distance measurement circuit  42  on the basis of the obtained computation result. 
     Furthermore, the image processing circuit  20  makes predetermined computations using sensed image data, and executes a TTL AWB (auto white balance) process on the basis of the obtained computation result. 
     Since this embodiment comprises the distance measurement circuit  42  and a photometry circuit  46  dedicated to those processes, the AF, AE, and EF processes may be done using the distance measurement circuit  42  and photometry circuit  46  in place of those using the image processing circuit  20 . 
     Alternatively, the AF, AE, and EF processes may be done using the distance measurement circuit  42  and photometry circuit  46  in addition to those using the image processing circuit  20 . 
     Reference numeral  22  denotes a memory control circuit which controls the A/D converter  16 , the timing generation circuit  18 , the image processing circuit  20 , an image display memory  24 , the D/A converter  26 , a memory  30 , and a compression/expansion circuit  32 . 
     Data output from the A/D converter  16  is written in the image display memory  24  or memory  30  via the image processing circuit  20  and memory control circuit  22  or via the memory control circuit  22  alone. 
     Reference numeral  24  denotes an image display memory;  26 , a D/A converter; and  28 , an image display unit comprising, e.g., a TFT LCT or the like. Display image data written in the image display memory  24  is displayed on the image display unit  28  via the D/A converter  26 . 
     When sensed image data is displayed using the image display unit  28  as needed, an electronic viewfinder function can be implemented. 
     The image display unit  28  can turn on/off its display in accordance with an instruction from the system control circuit  50 . When the display is OFF, great power savings of the image sensing apparatus  100  can be achieved. 
     Reference numeral  30  denotes a memory for storing sensed still or moving images. The memory  30  has a sufficient memory size capable of storing a predetermined number of still images or a moving image for a predetermined period of time. Hence, even in a continuous shot mode or panorama mode for continuously sensing a plurality of still images, a large number of images can be written in the memory  30  at high speed. 
     Also, the memory  30  can be used as a work area of the system control circuit  50 . 
     Reference numeral  32  denotes a compression/expansion circuit for compressing/expanding image data by the adaptive discrete cosine transform (ADCT), wavelet transform, or the like. The compression/expansion circuit  32  loads an image stored in the memory  30 , compresses or expands it, and writes the compressed or expanded data in the memory  30 . 
     Reference numeral  40  denotes a shutter control circuit for controlling the shutter  12  on the basis of photometry information from the photometry circuit  46  in cooperation with a stop control circuit  340  that controls the stop  312 . 
     Reference numeral  42  denotes a distance measurement circuit used to execute the AF process. Light rays that have entered the lens  310  are guided to the distance measurement circuit  42  via the stop  312 , the lens mounts  306  and  106 , the mirror  130 , and a distance measurement sub-mirror (not shown) by the single-lens reflex system, thus measuring the focusing state of an image formed as an optical image. 
     Reference numeral  46  denotes a photometry circuit used to execute the AE process. Light rays that have entered the lens  310  are guided to the photometry circuit  46  via the stop  312 , the lens mounts  306  and  106 , the mirror  130  and a mirror  132 , and a photometry lens (not shown), thus measuring the exposure state of an image formed as an optical image. 
     The photometry circuit  46  also has an EF process function in cooperation with an electronic flash  48 . 
     Reference numeral  48  denotes an electronic flash which has a function of projecting AF assist light, and a flash light control function. 
     Note that the system control circuit  50  can perform exposure control and AF control using a video TTL scheme for the shutter control circuit  40 , stop control circuit  340 , and distance measurement control circuit  342  on the basis of a computation result of image data output from the image sensing element  14  by the image processing circuit  20 . 
     Furthermore, AF control may be done using both the measurement result of the distance measurement circuit  42  and the computation result of image data output from the image sensing element  14  by the image processing circuit  20 . 
     Moreover, exposure control may be done using both the measurement result of the photometry circuit  46  and the computation result of image data output from the image sensing element  14  by the image processing circuit  20 . 
     Reference numeral  50  denotes a system control circuit for controlling the overall image sensing apparatus  100 ; and  52 , a memory for storing constants, variables, programs, and the like required for operating the system control circuit  50 . 
     Reference numeral  54  denotes an indication unit which comprises a liquid crystal display device, loudspeaker, and the like, and indicates the operation state, messages, and the like using characters, images, sound, and the like in accordance with execution of programs in the system control circuit  50 . The indication unit  54  is set at one or a plurality of easy-to-see positions around the console of the image sensing apparatus  100 , and is constructed by a combination of an LCD, LEDs, sound generation element, and the like. Some functions of the indication unit  54  are set within an optical viewfinder  104 . 
     Of the indication contents of the indication unit  54 , those displayed on the LCD or the like include, e.g., a single/continuous shot indication, self timer indication, compression ratio indication, recording pixel count indicating, recorded image count indication, remaining recordable image count indication, shutter speed indication, aperture value indication, exposure correction indication, flash indication, red-eye suppression indication, macro image sensing indication, buzzer setup indication, remaining timepiece battery capacity indication, remaining battery capacity indication, error indication, information indication using numerals of a plurality of digits, attachment/detachment indication of recording media  200  and  210 , attachment/detachment indication of a lens unit  300 , communication I/F operation indication, date/time indication, connection indication with an external computer, and the like. 
     Of the indication contents of the indication unit  54 , those displayed within the optical viewfinder  104  include, e.g., in-focus indication, image sensing ready indication, camera shake alert indication, flash charging indication, flash charging completion indication, shutter speed indication, aperture value indication, exposure correction indication, recording medium write access indication, and the like. 
     Furthermore, of the indication contents of the indication unit  54 , those displayed using the LEDs and the like include, e.g., in-focus indication, image sensing ready indication, camera shake alert indication, flash charging indication, flash charging completion indication, recording medium write access indication, macro image sensing setup notification, secondary battery charging state indication, and the like. 
     Of the indication contents of the indication unit  54 , those indicated by lamps and the like include, e.g., a self timer notification lamp, and the like. The self timer notification lamp may be commonly used as AF assist light. 
     Reference numeral  56  denotes an electrically erasable/programmable nonvolatile memory, which uses, e.g., an EEPROM or the like. 
     Reference numerals  60 ,  62 ,  64 ,  66 ,  68 , and  70  denote operation units for inputting various operation instructions of a system control circuit  118 . These operation units are constructed by one or a plurality of combinations of a switch, a dial, a touch panel, a pointer using line of sight detection, a voice recognition device, and the like. 
     Examples of these operation units will be explained below. 
     Reference numeral  60  denotes a mode dial switch which can selectively set one of various function image sensing modes: an automatic image sensing mode, programmed image sensing mode, shutter speed priority image sensing mode, aperture priority image sensing mode, manual image sensing mode, focal depth priority (depth) image sensing mode, portrait image sensing mode, landscape image sensing mode, macro image sensing mode, sport image sensing mode, night scene image sensing mode, panorama image sensing mode, and the like. 
     Reference numeral  62  denotes a shutter switch SW 1 , which is turned on at the middle (half stroke position) of operation of a shutter button (not shown), and instructs start of the AF process, AE process, AWB process, EF process, and the like. 
     Reference numeral  64  denotes a shutter switch SW 2 , which is turned on upon completion of operation (at the full stroke position) of the shutter button (not shown), and instructs start of a series of processes including an exposure process for writing a signal read out from the image sensing element  14  as image data in the memory  30  via the A/D converter  16  and memory control circuit  22 , a development process using computation results in the image processing circuit  20  and memory control circuit  22 , and a recording process for reading out image data from the memory  30 , compressing the readout data by the compression/expansion circuit  32 , and writing the compressed image data in the recording medium  200  or  210 . 
     Reference numeral  66  denotes a playback switch which instructs to start playback operation for reading out an image sensed in a given image sensing mode from one of the memory  30  and the recording media  200  and  210 , and displaying the readout image on the image display unit  28 . 
     Reference numeral  68  denotes a single/continuous shot switch, which can set one of a single shot mode for sensing one frame of image upon depression of the shutter switch SW 2 , and then setting a standby state, and a continuous shot mode for successively sensing images while the shutter switch SW 2  is held down. 
     Reference numeral  70  denotes a console including various buttons, touch panel, and the like, which include a menu button, set button, macro button, multi-frame playback new page button, flash setup button, single shot/continuous shot/self timer switch button, menu move+(plus) button, menu move−(minus) button, playback image move+(plus) button, playback image move−(minus) button, sensed image quality select button, exposure correct button, date/time setup button, select/change button that can select and change various functions upon executing image sensing and playback in, e.g., the panoramic mode, determine/execute button which can determine and execute various functions upon executing image sensing and playback in, e.g., the panoramic mode, image display ON/OFF switch for turning on/off the image display unit  28 , quick review ON/OFF setup switch for setting a quick review function of automatically playing back sensed image data immediately after image sensing, compression mode switch for selecting a compression ratio of JPEG compression, and selecting a CCDRAW mode for converting directly converting a signal output from the image sensing element into digital data, and recording the digital data in a recording medium, playback mode switch for setting various function modes such as a playback mode, multi-frame playback/delete mode, PC connect mode, and the like, AF mode setup switch which can set a one-shot AE mode for starting auto-focusing upon depression of the shutter switch SW 1 , and maintaining an in-focus state once it is attained, and a servo AF mode for continuously executing auto-focusing while the shutter switch SW 1  is held down, and the like. 
     In place of the plus and minus buttons, a rotary dial switch may be used to select numerical values and functions more smoothly. 
     Reference numeral  72  denotes a power switch which can selectively set power-ON and power-OFF modes of the image sensing apparatus  100 . Also, the power switch  72  can also selectively set power-ON and power-OFF modes of various accessories such as the lens unit  300 , external electronic flash, recording media  200  and  210 , and the like, which are connected to the image sensing apparatus  100 . 
     Reference numeral  80  denotes a power supply control circuit which is comprised of a battery detection circuit, a DC-DC converter, a switch circuit for switching a block to be energized, and the like. The power supply control circuit  80  detects the presence/absence, type, and remaining battery amount of a battery attached, controls the DC-DC converter on the basis of such detection results and an instruction from the system control circuit  50 , and supplies a required voltage to the respective units including the recording media for a required period of time. 
     Reference numerals  82  and  84  denote connectors; and  86 , a power supply circuit. The power supply circuit  86  includes a primary battery such as an alkali battery, lithium battery, or the like, a secondary battery such as an NiCd battery, NiMH battery, Li battery, or the like, an AC adapter, and the like. 
     Reference numerals  90  and  94  denote interfaces with recording media such as a memory card, hard disk, and the like;  92  and  96 , connectors for connecting recording media such as a memory card, hard disk, and the like; and  98 , a recording medium attachment/detachment detection circuit for detecting whether or not the recording medium  200  or  210  is attached to the connector  92  and/or the connector  96 . 
     Note that this embodiment has two sets of interfaces and connectors that receive the recording media. However, the number of sets of interfaces and connectors that receive the recording media is not particularly limited. Also, combinations of interfaces and connectors of different standards may be used. 
     As the interface and connector, those complying with the standards of a PCMCIA card, CF (compact flash) card, and the like may be used. 
     Furthermore, when the interfaces  90  and  94 , and connectors  92  and  96  use those complying with the standards of a PCMCIA card, CF (compact flash) card, and the like, and various communication cards such as a LAN card, modem card, USB card, IEEE1394 card, P1284 card, SCSI card, PHS, and the like are connected thereto, image data and associated management information can be transferred between the image sensing apparatus and an external computer or its peripheral devices such as a printer and the like. 
     Reference numeral  104  denotes an optical viewfinder which can guide light rays that have entered the lens  310  via the stop  312 , lens mounts  306  and  106 , mirrors  130  and  132  by the single-lens reflex system, and can form and display them as an optical image. In this manner, without using the electronic viewfinder function implemented by the image display unit  28 , image sensing can be done using the optical viewfinder  104  alone. In the optical viewfinder  104 , some functions of the indication unit  54 , e.g., an in-focus indication, camera shake alert indication, flash charging indication, shutter speed indication, aperture value indication, exposure correction indication, and the like are provided. 
     Reference numeral  110  denotes a communication circuit having various communication functions such as RS232C, USB, IEEE1394, P1284, SCSI, modem, LAN, radio communication, and the like. 
     Reference numeral  112  denotes a connector or antenna, which serves as a connector when the image sensing apparatus  100  is connected to another device using the communication means  139 , or serves as an antenna in case of radio communications. 
     Reference numeral  120  denotes an interface for connecting the image sensing apparatus  100  to the lens unit  300  in the lens mount  106 ;  122 , a connector for electrically connecting the image sensing apparatus  100  to the lens unit  300 ; and  124 , a lens attachment/detachment detection circuit for detecting whether or not the lens unit  300  is attached to the lens mount  106  and/or the connector  122 . 
     The connector  122  also has a function of exchanging control signals, status signals, data signals, and the like between the image sensing apparatus  100  and lens unit  300 , and supplying currents of various voltages. The connector  122  may communicate not only electrical signals but also optical signals, audio signals, and the like. 
     Reference numerals  130  and  132  denote mirrors which can guide light rays that have entered the lens  310  to the optical viewfinder  104  by the single-lens reflex system. Note that the mirror  132  may be either a quick return mirror or half mirror. 
     Reference numeral  200  denotes a recording medium such as a memory card, hard disk, or the like. The recording medium  200  comprises a recording unit  202  comprised of a semiconductor memory, magnetic disk, or the like, an interface  204  with the image sensing apparatus  100 , and a connector  206  for connecting the image sensing apparatus  100 . 
     Reference numeral  210  denotes a recording medium such as a memory card, hard disk, or the like. The recording medium  210  comprises a recording unit  212  comprised of a semiconductor memory, magnetic disk, or the like, an interface  214  with the image sensing apparatus  100 , and a connector  216  for connecting the image sensing apparatus  100 . 
     Reference numeral  300  denotes an exchangeable lens type lens unit. 
     Reference numeral  306  denotes a lens mount for mechanically coupling the lens unit  300  to the image sensing apparatus  100 . The lens mount  306  includes various functions of electrically connecting the lens unit  300  and image sensing apparatus  100 . 
     Reference numeral  310  denotes a photographing lens; and  312 , a stop. 
     Reference numeral  320  denotes an interface for connecting the lens unit  300  to the image sensing apparatus  100  in the lens mount  306 ; and  322 , a connector for electrically connecting the lens unit  300  to the image sensing apparatus  100 . The connector  322  also has a function of exchanging control signals, status signals, data signals, and the like between the image sensing apparatus  100  and lens unit  300 , and receiving or supplying currents of various voltages. Note that the connector  322  may communicate not only electrical signals but also optical signals, audio signals, and the like. 
     Reference numeral  340  denotes a stop control circuit for controlling the stop  312  on the basis of photometry information from the photometry circuit  46  in cooperation with the shutter control circuit  40  that controls the shutter  12 . 
     Reference numeral  342  denotes a distance measurement control circuit for controlling focusing of the photographing lens  310 ; and  344 , a zoom control circuit for controlling zooming of the photographing lens  310 . 
     Reference numeral  350  denotes a lens system control circuit for controlling the overall lens unit  300 . The lens system control circuit  350  has a memory function of storing constants, variables, programs, and the like required for operating the lens unit  300 , and a nonvolatile memory function of holding identification information such as a number or the like unique to the lens unit  300 , management information, function information such as a full-aperture value, minimum aperture value, focal length, and the like, current and past setup values, and the like. 
     The operation of the image sensing apparatus with the above arrangement will be explained below with reference to FIGS. 2 to  8 . 
     FIGS. 2 to  4  are flow charts of the main routine showing the control sequence of the image sensing apparatus  100 . Note that these flow charts show an example of the operation of the image sensing apparatus in the one-shot AF mode. 
     Referring to FIG. 2, upon power ON after battery exchange or the like, the system control circuit  50  initializes flags, control variables, and the like and also performs required predetermined initial setups in the respective units of the image sensing apparatus  100  (S 101 ). 
     The system control circuit  50  resets a dark end flag stored in its internal memory or the memory  52  (S 102 ). 
     The system control circuit  50  checks the setup position of the power switch  72  (S 103 ). If the power switch  72  is set at the power-OFF position, the system control circuit  50  executes a predetermined end process (S 104 ). More specifically, the system control circuit  50  changes the indications of the respective indication units to an end state, records required parameters and setup values including flags, control variables, and the like, and the currently selected mode in the nonvolatile memory  56 , cuts off unnecessary power supply to the respective units of the image sensing apparatus  100  including the image display unit  28  by the power supply control circuit  80 , and so forth. After that, the flow returns to step S 102 . 
     If the power switch  72  is set at the power-ON position (S 103 ), the power supply control circuit  80  detects the remaining capacity and operation state of the power supply  86  comprising batteries and the like, and the system control circuit  50  checks based on that detection result if these capacity and operation state pose any problem in the operation of the image sensing apparatus  100  (S 105 ). If any problem is found, a predetermined alert indication is made by means of an image or voice using the indication unit  54  (S 106 ), and the flow then returns to step S 102 . 
     If no problem is found in the power supply  86  (S 105 ), the system control circuit  50  checks the setup position of the mode dial switch  60  (S 107 ). If the mode dial switch  60  is set at one of the image sensing mode positions, the flow advances to step S 109 . 
     If the mode dial switch  60  is set at any of other mode positions (S 107 ), the system control circuit  50  executes a process corresponding to the selected mode (S 108 ), and the flow returns to step S 102  upon completion of the process. 
     The system control circuit  50  checks if the recording medium  200  or  210  is attached, acquires management information of image data recorded on the recording medium  200  or  210 , and then checks if the operation state of the recording medium  200  or  210  poses any problem in the operation of the image sensing apparatus  100 , in particular, recording/playback of image data to/from the recording medium  200  or  210  (S 109 ). If any problem is found, a predetermined alert indication is made by means of an image or voice using the indication unit  54  (S 106 ), and the flow then returns to step S 102 . 
     If no problem is found, the flow advances to step S 110 , and the system control circuit  50  checks the setup state of the single/continuous shot switch  68  that sets the single/continuous shot mode (S 110 ). If the single shot mode is selected, the circuit  50  sets a single/continuous shot flag to indicate the single shot mode (S 111 ); if the continuous shot mode is selected, the circuit  50  sets the single/continuous shot flag to indicate the continuous shot mode (S 112 ). Upon completion of flag setups, the flow advances to step S 113 . 
     With the single/continuous shot switch  68 , the one-shot mode for sensing one frame of image upon depression of the shutter switch SW 2 , and then setting a standby state, and the continuous shot mode for successively sensing images while the shutter switch SW 2  is held down can be arbitrarily selectively set. 
     Note that the state of the single/continuous shot flag is stored in the internal memory of the system control circuit  50  or the memory  52 . 
     The system control circuit  50  indicates various setup states of the image display apparatus  100  by means of an image or voice using the indication unit  54  (S 113 ). When the image display of the image display unit  28  is ON, various setup states of the image display apparatus  100  are indicated by means of an image also using the image display unit  28 . 
     Referring to FIG. 3, if the shutter switch SW 1  is OFF (S 131 ), the flow returns to step S 102 . 
     If the shutter switch SW 1  is ON (S 131 ), the system control circuit  50  executes a distance measurement/photometry process (S 132 ). More specifically, the system control circuit  50  executes a distance measurement process for bringing the photographing lens  310  into focus on an object, also executes a photometry process to determine the aperture value and shutter speed, and stores photometry data and/or setup parameters in its internal memory or the memory  52 . In the photometry process, the electronic flash is set if necessary. The distance measurement/photometry process (S 132 ) will be described in detail later with reference to FIG.  5 . 
     The aperture value (Av value) and shutter speed (TV value) are determined on the basis of the stored photometry data and/or setup parameters, and the image sensing mode selected by the mode dial switch  60 , the charge accumulation time is determined in accordance with the determined shutter speed (Tv value), and these determined values are stored in the internal memory of the system control circuit  50  or the memory  52  (S 133 ). After that, the flow advances to step S 134 . 
     The system control circuit  50  checks the state of the single/continuous shot flag stored in its internal memory or the memory  52  (S 134 ). If the single shot mode is set, the flow jumps to step S 139 . 
     In this manner, if it is determined in step S 134  that the single shot mode is selected, the flow jumps to step S 139  without executing a dark capture ( 1 ) process (S 137 ; to be described later). With this control, a release time lag upon depression of the shutter switch SW 2  in step S 139  can be reduced, as will be described later. 
     If the continuous shot mode is selected (S 134 ), the system control circuit  50  checks if the shutter switch SW 2  is ON (S 135 ). If the shutter switch SW 2  is ON, the circuit  50  sets a dark end flag (S 136 ), and the flow then jumps to step S 161 . 
     In this manner, if it is determined in step S 134  that the continuous shot mode is selected, and the shutter switch SW 2  is ON, the dark end flag is set, and the flow jumps to step S 161  without executing dark capture ( 1 ) process (S 137 ; to be described later). With this control, a release time lag upon depression of the shutter switch SW 2  can be reduced by giving priority to an image sensing timing (to be described later) over the dark capture process. 
     In this case, as will be described later, the next frame of image is sensed in step S 163 , and a dark capture ( 2 ) process is done in step S 166 . 
     If the continuous shot mode is selected (S 134 ), and if the shutter switch SW 2  is OFF (S 135 ), the system control circuit  50  executes a dark capture ( 1 ) process (S 137 ). That is, the system control circuit  50  accumulates noise components such as dark current and the like of the image sensing element  14  for the same period of time as that required for actual image sensing, while closing the shutter  12 , and reads out the accumulated noise image signal. After that, the flow advances to step S 138 . 
     By making correction computations using dark image data captured by the dark capture ( 1 ) process, sensed image data can be corrected in terms of image quality deterioration such as pixel omission or the like caused by dark current noise produced by the image sensing element  14  and scratches unique to the image sensing element  14 . The dark capture ( 1 ) process (S 137 ) will be described in detail later using FIG.  7 . 
     In this manner, if it is determined in step S 134  that the continuous shot mode is set, but if continuous shot image sensing is not started as the shutter switch SW 2  has not been pressed yet, the dark capture ( 1 ) process (S 137 ) is executed prior to execution of the continuous shot image sensing, and hence nearly constant continuous-shot frame intervals can be set when continuous shot image sensing is done upon depression of the shutter switch SW 2  in step S 139 , as will be described later. 
     The system control circuit  50  checks the state of the dark end flag stored in its internal memory or the memory  52  (S 138 ), and if the dark end flag is set, the flow jumps to step S 161 . 
     In this manner, if the dark end flag is set in the dark capture ( 1 ) process routine (S 137 ), the flow jumps to step S 161 , and a release time lag upon depression of the shutter switch SW 2  can be reduced by giving priority to an image sensing timing over the dark capture process, as will be described later. 
     In this case, as will be described later, the next frame of image is sensed in step S 163 , and a dark capture ( 2 ) process is then executed in step S 166 . 
     If the dark end flag is reset (S 138 ), the flow advances to step S 139 . 
     In such case, since the dark capture ( 1 ) process (S 137 ) has been executed prior to continuous shot image sensing, nearly constant continuous-shot frame intervals can be set when continuous shot image sensing is done upon depression of the shutter switch SW 2  in step S 139 , as will be described later. 
     If the shutter switch SW 2  is OFF (S 139 ), the system control circuit  50  checks if the shutter switch SW 1  is ON (S 140 ). If the shutter switch SW 1  is ON, the flow returns to step S 139 . 
     If the shutter switch SW 1  is turned off (S 140 ), the flow returns to step S 102 . 
     If the shutter switch SW 1  is turned on (S 139 ), the flow advances to step S 161 . 
     Referring to FIG. 4, the system control circuit  50  checks if an area that can store sensed image data is available on an image storage buffer area on the memory  30  (S 161 ). If no area that can store sensed image data is available on the image storage buffer area on the memory  30 , a predetermined alert indication is made by means of an image or voice using the indication unit  54  (S 162 ), and the flow then returns to step S 102 . 
     For example, the user experiences such state immediately after he or she has executed continuous shot image sensing corresponding to a maximum number of images that can be stored in the image storage buffer area. In this state, the first image to be read out from the memory  30  and written in the recording medium  200  or  210  is not recorded on the recording medium  200  or  210  yet, and a free area even for one image cannot be assured on the image storage buffer area on the memory  30 . 
     When sensed image data is stored in the image storage buffer area on the memory  30  after it is compressed, it is checked in step S 161  if an area that can store sensed image data is available on the image storage buffer area on the memory  30 , in consideration of the fact that the compressed image data size varies depending on the setups of the compression mode. 
     If an area that can store sensed image data is available on the image storage buffer area on the memory  30  (S 161 ), the system control circuit  50  executes an image sensing process (S 163 ). More specifically, the system control circuit  50  reads out a sensed image signal, which has been accumulated for a predetermined period of time upon image sensing, from the image sensing element  14 , and writes the sensed image data on the predetermined area of the memory  30  via the A/D converter  16 , image processing circuit  20 , and memory control circuit  22 , or from the A/D converter  16  directly via the memory control circuit  22 . 
     The image sensing process (S 163 ) will be explained in detail later using FIG.  6 . 
     Upon completion of the image sensing process (S 163 ), the system control circuit  50  checks the state of the single/continuous shot flag stored in its internal memory or the memory  52  (S 164 ). 
     As a result of checking the state of the single/continuous shot flag, if the single shot mode is selected (S 164 ), the flow advances to step S 166 , and the system control circuit  50  executes a dark capture ( 2 ) process. 
     In this manner, if it is determined in step S 164  that the single shot mode is selected, the system control circuit  50  executes the dark capture ( 2 ) process (S 166 ) after the image sensing process (S 163 ). With this control, a release time lag upon depression of the shutter switch SW 2  in step S 139  can be reduced. 
     On the other hand, as a result of checking the state of the single/continuous shot flag, if the continuous shot mode is selected (S 164 ), the system control circuit  50  checks the state of the dark end flag stored in its internal memory or the memory  52  (S 165 ). If the dark end flag is set, the flow advances to step S 166 . 
     In this manner, in continuous shot image sensing, when the dark capture ( 1 ) process (S 137 ) is skipped to give priority to the image sensing timing and to reduce any release time lag upon depression of the shutter switch SW 2 , the dark capture ( 2 ) process is done in step S 166  after the image sensing process (S 163 ), as will be described later. If the dark end flag is reset (S 165 ), the flow advances to step S 167 . 
     In this manner, in the continuous shot mode, when the dark capture ( 1 ) process has already been done in step S 137 , another dark capture ( 2 ) process (S 166 ) is skipped. 
     The system control circuit  50  executes the dark capture ( 2 ) process for accumulating noise components such as dark current and the like of the image sensing element  14  for the same period of time as that required for actual image sensing, while closing the shutter  12 , and reading out the accumulated noise image signal (S 166 ). The flow then advances to step S 167 . 
     By making correction computations using-dark image data captured by the dark capture ( 2 ) process, sensed image data can be corrected in terms of image quality deterioration such as pixel omission or the like caused by dark current noise produced by the image sensing element  14  and scratches unique to the image sensing element  14 . 
     The dark capture ( 2 ) process (S 166 ) will be described in detail later using FIG.  8 . 
     Upon completion of the dark capture ( 2 ) process, the system control circuit  50  reads out some of image data written in the predetermined area of the memory  30  via the memory control circuit  22 , executes a WB (white balance) integral computation process and OB (optical black) integral computation process required to execute development processes, and stores the computation results in its internal memory or the memory  52 . 
     The system control circuit  50  reads out sensed image data written in the predetermined area of the memory  30  using the memory control circuit  22  and the image processing circuit  20  as needed, and executes various development processes including AWB (auto white balance) process, gamma conversion, color conversion, and the like using the computation results stored in its internal memory or the memory  52  (S 167 ). 
     Furthermore, in the development processes, the system control circuit  50  also executes a dark correction computation process for canceling dark current noise and the like of the image sensing element  14  by executing a subtraction process using the dark image data captured in the dark capture process. 
     The system control circuit  50  reads out image data written in the predetermined area of the memory  30 , makes the compression/expansion circuit  32  execute an image compression process in accordance with the selected mode (S 168 ), and writes the image data that has sensed and undergone a series of processes in a free image space of the image storage buffer area on the memory  30 . 
     Upon executing a series of processes, the system control circuit  50  starts a recording process for reading out image data stored in the image storage buffer area of the memory  30 , and writing the readout image data in the recording medium  200  or  210  such as a memory card, compact flash card, or the like (S 169 ). 
     This recording process is started for new image data, which has been sensed and undergone a series of processes, every time that image data is written in a free image space of the image storage buffer area on the memory  30 . 
     While a write of image data in the recording medium  200  or  210  is underway, a recording medium write access indication (e.g., flashing an LED of the indication unit  54 ) is made to clearly indicate that write access. 
     The system control circuit  50  checks if the shutter switch SW 1  is ON (S 170 ). 
     If the shutter switch SW 1  is OFF (S 170 ), the flow returns to step S 102 . 
     If the shutter switch SW 1  is ON (S 170 ), the system control circuit  50  checks the state of the single/continuous shot flag stored in its internal memory or the memory  52  (S 171 ), and if the single shot mode is selected, the flow returns to step S 170  to repeat the current process until the shutter switch SW 1  is turned off. 
     If the continuous shot mode is selected (S 171 ), the flow returns to step S 139  to proceed with image sensing, thus repeating a series of processes. 
     FIG. 5 is a flow chart showing the detailed sequence of the distance measurement/photometry process in step S 132  in FIG.  3 . 
     In the distance measurement/photometry process, the system control circuit  50  and the stop control circuit  340  or distance measurement control circuit  342  exchange various signals via the interface  120 , connectors  122  and  322 , interface  320 , and lens control circuit  350 . 
     The system control circuit  50  starts an AF (auto-focusing) process using the image sensing element  14 , distance measurement circuit  42 , and distance measurement control circuit  342  (S 201 ). 
     The system control circuit  50  executes AF control for checking the focusing state of an image formed as an optical image by guiding light rays, which have entered the lens  310 , to the distance measurement circuit  42  via the stop  312 , lens mounts  306  and  106 , mirror  130 , and distance measurement sub-mirror (not shown), and detecting the focusing state using the distance measurement circuit  42  while driving the lens  310  using the distance measurement control circuit  342  (S 202 ), until the distance measurement (AF) result indicates an in-focus (S 203 ). 
     If the distance measurement (AF) result indicates an in-focus (S 203 ), the system control circuit  50  determines an in-focus distance measurement point from those in an image sensing screen (S 204 ), and stores distance measurement data and/or setup parameters in its internal memory or the memory  52  together with the determined distance measurement point data. The flow then advances to step S 205 . 
     Subsequently, the system control circuit  50  starts an AE (auto-exposure) process using the photometry circuit  46  (S 205 ). 
     The system control circuit  50  executes a photometry process using the shutter control circuit  40  (S 206 ) for measuring the exposure state of an image formed as an optical image by guiding light rays, which have entered the lens  310 , to the photometry circuit  46  via the stop  312 , lens mounts  306  and  106 , mirrors  130  and  132 , and photometry lens (not shown), until it is determined that the exposure (AE) value is appropriate (S 207 ). 
     If it is determined that the exposure (AE) value is appropriate (S 207 ), the system control circuit  50  stores photometry data and/or setup parameters in its internal memory or the memory  52 , and the flow advances to step S 208 . 
     Note that the system control circuit  50  determines the aperture value (Av value) and shutter speed (Tv value) in accordance with the exposure (AE) result detected by the photometry process (S 206 ) and the image sensing mode selected by the mode dial switch  60 . 
     The system control circuit  50  determines the charge accumulation time of the image sensing element  14  in accordance with the determined shutter speed (Tv value), and executes the image sensing process and dark capture process using an equal charge accumulation time. 
     The system control circuit  50  checks based on the measurement data obtained by the photometry process (S 206 ) if flash emission is required (S 208 ). If flash emission is required, the circuit  50  sets a flash flag, and charges the electronic flash  48  (S 209 ) until charging of the electronic flash  48  is completed (S 210 ). 
     Upon completion of charging of the electronic flash  48  (S 210 ), the distance measurement/photometry process routine (S 132 ) ends. 
     FIG. 6 is a flow chart showing the detailed sequence of the image sensing process in step S 163  in FIG.  4 . In this image sensing process, the system control circuit  50  and the stop control circuit  340  or distance measurement control circuit  342  exchange various signals via the interface  120 , connectors  122  and  322 , interface  320 , and lens system control circuit  350 . 
     The system control circuit  50  moves the mirror  130  to a mirror up position using a mirror driving circuit (not shown) (S 301 ), and drives the stop  312  to a predetermined aperture value by the stop control circuit  340  in accordance with photometry data stored in its internal memory or the memory  52  (S 302 ). 
     The system control circuit  50  clears charge on the image sensing element  14  (S 303 ), then starts charge accumulation of the image sensing element  14  (S 304 ), opens the shutter  12  by the shutter control circuit  40  (S 305 ), and starts exposure of the image sensing element  14  (S 306 ). 
     The system control circuit  50  checks based on the flash flag if the electronic flash  48  is required (S 307 ), and if the electronic flash  48  is required, the circuit  50  controls the electronic flash  48  to emit light (S 308 ). 
     The system control circuit  50  waits for the end of exposure of the image sensing element  14  in accordance with the photometry data (S 309 ), closes the shutter  12  by the shutter control circuit  40  (S 310 ), and ends exposure of the image sensing element  14 . 
     The system control circuit  50  drives the stop  312  to a full-open aperture value by the stop control circuit  340  (S 311 ), and moves the mirror  130  to a mirror down position by the mirror driving circuit (not shown) ( 312 ). 
     If the determined charge accumulation time has elapsed (S 313 ), the system control circuit  50  reads out a charge signal from the image sensing element  14  upon completion of charge accumulation of the image sensing element  14  (S 314 ), and writes sensed image data in a predetermined area of the memory  30  via the A/D converter  16 , image processing circuit  20 , and memory control circuit  22 , or from the A/D converter  16  directly via the memory control circuit  22  (S 315 ). 
     Upon completion of a series of processes, the image sensing process routine (S 163 ) ends. 
     FIG. 7 is a flow chart showing the detailed sequence of the dark capture ( 1 ) process in step S 137  in FIG.  3 . 
     The system control circuit  50  clears charge on the image sensing element  14  (S 401 ). 
     If the shutter switch SW 2  is turned on (S 403 ) before the charge clear operation of the image sensing element  14  comes to an end (S 402 ), the flow jumps to step S 412 . If the shutter switch SW 2  is OFF (S 403 ), the flow returns to step S 401  to proceed with the charge clear operation of the image sensing element  14 . 
     Upon completion of the charge clear operation of the image sensing element  14  (S 402 ), the system control circuit  50  starts charge accumulation of the image sensing element  14  while the shutter  12  is closed (S 404 ). 
     If the shutter switch SW 2  is turned on (S 406 ) before a predetermined charge accumulation time elapses (S 405 ), the flow jumps to step S 412 . If the shutter switch SW 2  remains OFF (S 406 ), the flow returns to step S 405 . 
     If the predetermined charge accumulation time has elapsed (S 405 ), the system control circuit  50  executes a dark image read process (S 407 ). More specifically, the system control circuit  50  reads out a charge signal from the image sensing element  14  upon completion of charge accumulation of the image sensing element  14  (S 407 ), and writes image data (dark image data) in a predetermined area of the memory  30  via the A/D converter  16 , image processing circuit  20 , and memory control circuit  22 , or from the A/D converter  16  directly via the memory control circuit  22 . 
     If the shutter switch SW 2  stays OFF (S 410 ) until a read of the dark image is completed (S 409 ), the flow returns to step S 408  to proceed with the dark image read process. 
     By executing the development process using this dark capture data, sensed image data can be corrected for image quality deterioration such as pixel omission or the like caused by dark current noise produced by the image sensing element  14  and scratches unique to the image sensing element  14 . 
     Note that this dark image data is held on the predetermined area of the memory  30  until a new distance measurement/photometry process is done or the power switch of the image sensing apparatus  100  is turned off. This dark image data is used when the next image sensing process is done, and image data sensed by that process is read out to execute the development process. Or when image data sensed by the image sensing process and read out from the image sensing element  14  has already been written in the memory  30 , the development process is executed using dark image data. 
     If the shutter switch SW 2  is turned on (S 410 ) before a read of dark image data is completed (S 409 ), the flow advances to step S 412 . 
     Upon completion of a read of dark image data (S 409 ), the system control circuit  50  resets the dark end flag (S 411 ), and then ends the dark capture ( 1 ) process routine (S 137 ). 
     Or the system control circuit  50  sets the dark end flag (S 412 ), and then ends the dark capture ( 1 ) process routine (S 137 ). 
     In this manner, if the shutter switch SW 2  is turned on during the dark capture ( 1 ) process, the dark end flag is set to forcibly end the dark capture process, thus giving priority to image sensing timing, and reducing any release time lag upon depression of the shutter switch SW 2 . 
     FIG. 8 is a flow chart showing the detailed sequence of the dark capture ( 2 ) process in step S 166  in FIG.  4 . 
     The system control circuit  50  clears charge on the image sensing element  14  (S 501 ). Upon completion of the charge clear operation of the image sensing element  14  (S 502 ), the system control circuit  50  starts charge accumulation of the image sensing element  14  while the shutter  12  is closed (S 503 ). 
     If a predetermined charge accumulation time has elapsed (S 504 ), the system control circuit  50  executes a dark image read process (S 506 ). More specifically, the system control circuit  50  reads out a charge signal from the image sensing element  14  upon completion of charge accumulation of the image sensing element  14  (S 505 ), and writes image data (dark image data) in a predetermined area of the memory  30  via the A/D converter  16 , image processing circuit  20 , and memory control circuit  22 , or from the A/D converter  16  directly via the memory control circuit  22 . 
     The flow returns to step S 506  to proceed with the dark image read process until a read of dark image data is completed (S 507 ). 
     By executing the development process using this dark capture data, sensed image data can be corrected for image quality deterioration such as pixel omission or the like caused by dark current noise produced by the image sensing element  14  and scratches unique to the image sensing element  14 . 
     Note that this dark image data is held on the predetermined area of the memory  30  until a new distance measurement/photometry process is done or the power switch of the image sensing apparatus  100  is turned off. This dark image data is used when the image sensing process is done later, and image data sensed by that process is read out to execute the development process. Or when image data sensed by the image sensing process and read out from the image sensing element  14  has already been written in the memory  30 , the development process is executed using dark image data. 
     Upon completion of a read of dark image data (S 507 ), the dark capture ( 2 ) process routine (S 166 ) ends. 
     FIG. 9 is a timing chart showing the flow of image sensing operation in the first embodiment. 
     As can be seen from FIG. 9, in the continuous shot mode, the dark capture process is executed after the shutter switch SW 1  is turned on. If the shutter switch SW 2  stays OFF during execution of this dark capture process, the dark capture process comes to an end. As a result, even when continuous shot image sensing is done by turning on the shutter switch SW 2  after that process, since the dark capture process is complete, nearly constant continuous shot frame intervals can be set. 
     On the other hand, in the continuous shot mode, the dark capture process is executed after the shutter switch SW 1  is turned on. If the shutter switch SW 2  is turned on before completion of the dark capture process, the dark capture process is forcibly ended, and image sensing is started. In this manner, priority is given to image sensing timing, and any release time lag upon depression of the shutter switch SW 2  can be reduced. In this case, the dark capture process must be done after the first image sensing, and constant continuous shot frame intervals cannot always be set. 
     In case of the single shot mode, the dark capture process is done after image sensing, thus reducing any release time lag upon depression of the shutter switch SW 2 . 
     Second Embodiment 
     The second embodiment will be described below. 
     Since the arrangement of the second embodiment is basically the same as that of the first embodiment, the arrangement of the first embodiment will be used in the description of the second embodiment. 
     In the second embodiment, the contents of the control processes done by the image sensing apparatus are different from those of the first embodiment. 
     FIGS. 10 to  12  are flow charts of the main routine showing the control sequence of the image sensing apparatus according to the second embodiment. Note that the operation example of the image sensing apparatus in the one-shot AF mode has been explained in the first embodiment, but an operation example of the image sensing apparatus in a servo AF mode will be explained in the second embodiment. 
     Referring to FIG. 10, upon power ON after battery exchange or the like, the system control circuit  50  initializes flags, control variables, and the like and also performs required predetermined initial setups in the respective units of the image sensing apparatus  100  (S 601 ). 
     The system control circuit  50  resets a dark end flag stored in its internal memory or the memory  52  (S 602 ). 
     The system control circuit  50  checks the setup position of the power switch  72  (S 603 ). If the power switch  72  is set at the power-OFF position, the system control circuit  50  executes a predetermined end process (S 604 ). More specifically, the system control circuit  50  changes the indications of the respective indication units to an end state, records required parameters and setup values including flags, control variables, and the like, and the currently selected mode in the nonvolatile memory  56 , cuts off unnecessary power supply to the respective units of the image sensing apparatus  100  including the image display unit  28  by the power supply control circuit  80 , and so forth. After that, the flow returns to step S 602 . 
     If the power switch  72  is set at the power-ON position (S 603 ), the power supply control circuit  80  detects the remaining capacity and operation state of the power supply  86  comprising batteries and the like, and the system control circuit  50  checks based on that detection result if these capacity and operation state pose any problem in the operation of the image sensing apparatus  100  (S 605 ). If any problem is found, a predetermined alert indication is made by means of an image or voice using the indication unit  54  (S 606 ), and the flow then returns to step S 602 . 
     If no problem is found in the power supply  86  (S 605 ), the system control circuit  50  checks the setup position of the mode dial switch  60  (S 607 ). If the mode dial switch  60  is set at one of the image sensing mode positions, the flow advances to step S 609 . 
     If the mode dial switch  60  is set at any of other mode positions (S 607 ), the system control circuit  50  executes a process corresponding to the selected mode (S 608 ), and the flow returns to step S 602  upon completion of the process. 
     The system control circuit  50  checks if the recording medium  200  or  210  is attached, acquires management information of image data recorded on the recording medium  200  or  210 , and then checks if the operation state of the recording medium  200  or  210  poses any problem in the operation of the image sensing apparatus  100 , in particular, recording/playback of image data to/from the recording medium  200  or  210  (S 609 ). If any problem is found, a predetermined alert indication is made by means of an image or voice using the indication unit  54  (S 606 ), and the flow then returns to step S 602 . 
     If no problem is found, the flow advances to step S 610 , and the system control circuit  50  checks the setup state of the single/continuous shot switch  68  that sets the single/continuous shot mode (S 610 ). If the single shot mode is selected, the circuit  50  sets a single/continuous shot flag to indicate the single shot mode (S 611 ); if the continuous shot mode is selected, the circuit  50  sets the single/continuous shot flag to indicate the continuous shot mode (S 612 ). Upon completion of flag setups, the flow advances to step S 613 . 
     With the single/continuous shot switch  68 , the one-shot mode for sensing one frame of image upon depression of the shutter switch SW 2 , and then setting a standby state, and the continuous shot mode for successively sensing images while the shutter switch SW 2  is held down can be arbitrarily selectively set. 
     Note that the state of the single/continuous shot flag is stored in the internal memory of the system control circuit  50  or the memory  52 . 
     The system control circuit  50  indicates various setup states of the image display apparatus  100  by means of an image or voice using the indication unit  54  (S 613 ). When the image display of the image display unit  28  is ON, various setup states of the image display apparatus  100  are indicated by means of an image also using the image display unit  28 . 
     If the shutter switch SW 1  is OFF in step S 631  in FIG. 11, the flow returns to step S 602 . 
     If the shutter switch SW 1  is ON (S 631 ), the system control circuit  50  executes a distance measurement/photometry process (S 632 ). More specifically, the system control circuit  50  executes a distance measurement process for bringing the photographing lens  310  into focus on an object, also executes a photometry process to determine the aperture value and shutter speed, and stores photometry data and/or setup parameters in its internal memory or the memory  52  (S 632 ). In the photometry process, the electronic flash is set if necessary. 
     Since the detailed contents of the distance measurement/photometry process (S 632 ) are the same as those in the first embodiment shown in FIG. 5, a detailed description thereof will be omitted. 
     The aperture value (Av value) and shutter speed (TV value) are determined on the basis of the stored photometry data and/or setup parameters, and the image sensing mode selected by the mode dial switch  60 , the charge accumulation time is determined in accordance with the determined shutter speed (Tv value), and these determined values are stored in the internal memory of the system control circuit  50  or the memory  52  (S 633 ). After that, the flow advances to step S 634 . 
     The system control circuit  50  checks the state of the single/continuous shot flag stored in its internal memory or the memory  52  (S 634 ). If the single shot mode is set, the flow jumps to step S 639 . 
     In this manner, if it is determined in step S 634  that the single shot mode is selected, the flow jumps to step S 639  without executing a dark capture ( 1 ) process (S 637 ). With this control, the release time lag upon depression of the shutter switch SW 2  in step S 639  can be reduced, as will be described later. 
     If the continuous shot mode is selected (S 634 ), the system control circuit  50  checks if the shutter switch SW 2  is ON (S 635 ). If the shutter switch SW 2  is ON, the circuit  50  sets a dark end flag (S 636 ), and the flow then jumps to step S 661 . 
     In this manner, if it is determined in step S 634  that the continuous shot mode is selected, and the shutter switch SW 2  is ON, the dark end flag is set, and the flow jumps to step S 661  without executing dark capture ( 1 ) process (S 637 ). With this control, any release time lag upon depression of the shutter switch SW 2  can be reduced by giving priority to image sensing timing (to be described later) over the dark capture process. 
     In this case, as will be described later, the next frame of image is sensed in step S 663 , and a dark capture ( 2 ) process is done in step S 666 . 
     If the continuous shot mode is selected (S 634 ), and if the shutter switch SW 2  is OFF (S 635 ), the system control circuit  50  executes a dark capture ( 1 ) process (S 637 ). That is, the system control circuit  50  accumulates noise components such as dark current and the like of the image sensing element  14  for the same period of time as that required for actual image sensing, while closing the shutter  12 , and reads out the accumulated noise image signal. After that, the flow advances to step S 638 . 
     By making correction computations using dark image data captured by the dark capture ( 1 ) process, sensed image data can be corrected for image quality deterioration such as pixel omission or the like caused by dark current noise produced by the image sensing element  14  and scratches unique to the image sensing element  14 . 
     Since the detailed contents of this dark capture ( 1 ) process (S 637 ) are the same as those in the first embodiment shown in FIG. 7, a detailed description thereof will be omitted. 
     In this manner, if it is determined in step S 634  that the continuous shot mode is set, but if continuous shot image sensing is not started as the shutter switch SW 2  has not been pressed yet, the dark capture ( 1 ) process (S 637 ) is executed prior to continuous shot image sensing, and hence nearly constant continuous-shot frame intervals can be set when continuous shot image sensing is done upon depression of the shutter switch SW 2  in step S 639 , as will be described later. 
     The system control circuit  50  checks the state of the dark end flag stored in its internal memory or the memory  52  (S 638 ), and if the dark end flag is set, the flow jumps to step S 661 . 
     In this manner, if the dark end flag is set in the dark capture ( 1 ) process routine (S 637 ), the flow jumps to step S 661 , and any release time lag upon depression of the shutter switch SW 2  can be reduced by giving priority to image sensing timing over the dark capture process, as will be described later. 
     In this case, as will be described later, the next frame of image is sensed in step S 663 , and a dark capture ( 2 ) process is then executed in step S 666 . 
     If the dark end flag is reset (S 638 ), the flow advances to step S 639 . 
     In such case, since the dark capture ( 1 ) process (S 637 ) has been executed prior to continuous shot image sensing, nearly constant continuous-shot frame intervals can be set when continuous shot image sensing is done upon depression of the shutter switch SW 2  in step S 639 , as will be described later. 
     If the shutter switch SW 2  is OFF (S 639 ), the system control circuit  50  checks if the shutter switch SW 1  is ON (S 640 ). If the shutter switch SW 1  is ON, the flow returns to step S 632  to repeat a series of processes. 
     If the shutter switch SW 1  is turned off (S 640 ), the flow returns to step S 602 . If the shutter switch SW 1  is turned on (S 639 ), the flow advances to step S 661 . 
     Referring to FIG. 12, the system control circuit  50  checks if an area that can store sensed image data is available on an image storage buffer area on the memory  30  (S 661 ). If no area that can store sensed image data is available on the image storage buffer area on the memory  30 , a predetermined alert indication is made by means of an image or voice using the indication unit  54  (S 662 ), and the flow then returns to step S 602 . 
     For example, the user experiences such state immediately after he or she has executed continuous shot image sensing corresponding to a maximum number of images that can be stored in the image storage buffer area. In this state, the first image to be read out from the memory  30  and written in the recording medium  200  or  210  is not recorded on the recording medium  200  or  210  yet, and a free area even for one image cannot be assured on the image storage buffer area on the memory  30 . 
     When sensed image data is stored in the image storage buffer area on the memory  30  after it is compressed, it is checked in step S 661  if an area that can store sensed image data is available on the image storage buffer area on the memory  30 , in consideration of the fact that the compressed image data size varies depending on the setups of the compression mode. 
     If an area that can store sensed image data is available on the image storage buffer area on the memory  30  (S 661 ), the system control circuit  50  executes an image sensing process (S 663 ). More specifically, the system control circuit  50  reads out a sensed image signal, which has been accumulated for a predetermined period of time upon image sensing, from the image sensing element  14 , and writes the sensed image data on the predetermined area of the memory  30  via the A/D converter  16 , image processing circuit  20 , and memory control circuit  22 , or from the A/D converter  16  directly via the memory control circuit  22 . 
     Since the detailed contents of the image sensing process (S 663 ) are the same as those in the first embodiment shown in FIG. 6, a detailed description thereof will be omitted. 
     Upon completion of the image sensing process (S 663 ), the system control circuit  50  checks the state of the single/continuous shot flag stored in its internal memory or the memory  52  (S 664 ). 
     As a result of checking the state of the single/continuous shot flag, if the single shot mode is selected (S 664 ), the flow advances to step S 666 , and the system control circuit  50  executes a dark capture ( 2 ) process. 
     In this manner, if it is determined in step S 664  that the single shot mode is selected, the system control circuit  50  executes the dark capture ( 2 ) process (S 666 ) to be described later after the image sensing process (S 663 ). With this control, the release time lag upon depression of the shutter switch SW 2  in step S 639  can be reduced. 
     On the other hand, as a result of checking the state of the single/continuous shot flag, if the continuous shot mode is selected (S 664 ), the system control circuit  50  checks the state of the dark end flag stored in its internal memory or the memory  52  (S 665 ). If the dark end flag is set, the flow advances to step S 666 . 
     In this manner, in continuous shot image sensing, when the dark capture ( 1 ) process (S 637 ) is skipped to give priority to image sensing timing and to reduce the release time lag upon depression of the shutter switch SW 2 , the dark capture ( 2 ) process is done in step S 666  after the image sensing process (S 663 ), as will be described later. If the dark end flag is reset (S 665 ), the flow advances to step S 667 . 
     In this manner, in the continuous shot mode, when the dark capture ( 1 ) process has already been done in step S 637 , another dark capture ( 2 ) process (S 666 ) is skipped. 
     The system control circuit  50  executes the dark capture ( 2 ) process for accumulating noise components such as dark current and the like of the image sensing element  14  for the same period of time as that required for actual image sensing, while closing the shutter  12 , and reading out the accumulated noise image signal (S 666 ). The flow then advances to step S 667 . 
     By making correction computations using dark image data captured by the dark capture ( 2 ) process, sensed image data can be corrected for image quality deterioration such as pixel omission or the like caused by dark current noise produced by the image sensing element  14  and scratches unique to the image sensing element  14 . 
     Since the detailed contents of this dark capture ( 2 ) process (S 666 ) are the same as those in the first embodiment shown in FIG. 8, a detailed description thereof will be omitted. 
     Upon completion of the dark capture ( 2 ) process, the system control circuit  50  reads out some of image data written in the predetermined area of the memory  30  via the memory control circuit  22 , executes a WB (white balance) integral computation process and OB (optical black) integral computation process required to execute development processes, and stores the computation results in its internal memory or the memory  52 . 
     The system control circuit  50  reads out sensed image data written in the predetermined area of the memory  30  using the memory control circuit  22  and the image processing circuit  20  as needed, and executes various development processes including AWB (auto white balance) process, gamma conversion, color conversion, and the like using the computation results stored in its internal memory or the memory  52  (S 667 ). 
     Furthermore, in the development processes, the system control circuit  50  also executes a dark correction computation process for canceling dark current noise and the like of the image sensing element  14  by executing a subtraction process using the dark image data captured in the dark capture process. 
     The system control circuit  50  reads out image data written in the predetermined area of the memory  30 , makes the compression/expansion circuit  32  execute an image compression process in accordance with the selected mode (S 668 ), and writes the image data that has sensed and undergone a series of processes in a free image space of the image storage buffer area on the memory  30 . 
     Upon executing a series of processes, the system control circuit  50  starts a recording process for reading out image data stored in the image storage buffer area of the memory  30 , and writing the readout image data in the recording medium  200  or  210  such as a memory card, compact flash card, or the like (S 669 ). 
     This recording process is started for new image data, which has been sensed and undergone a series of processes, every time that image data is written in a free image space of the image storage buffer area on the memory  30 . 
     While a write of image data in the recording medium  200  or  210  is underway, a recording medium write access indication (e.g., flashing an LED of the indication unit  54 ) is made to clearly indicate that write access. 
     The system control circuit  50  checks if the shutter switch SW 1  is ON (S 670 ). 
     If the shutter switch SW 1  is OFF (S 670 ), the flow returns to step S 602 . 
     If the shutter switch SW 1  is ON (S 670 ), the system control circuit  50  checks the state of the single/continuous shot flag stored in its internal memory or the memory  52  (S 671 ), and if the single shot mode is selected, the flow returns to step S 670  to repeat the current process until the shutter switch SW 1  is turned off. 
     If the continuous shot mode is selected (S 671 ), the flow returns to step S 632  to proceed with image sensing, thus repeating a series of processes. 
     FIG. 13 is a timing chart showing the flow of image sensing operation in the second embodiment. 
     As can be seen from FIG. 13, in the second embodiment, after the shutter switch SW 1  is turned on, the auto-focusing (AF) process, auto-exposure (AE) process, and dark capture ( 1 ) process are repeated in the continuous shot mode, or the auto-focusing (AF) process and auto-exposure (AE) process are repeated in the single shot mode until the shutter switch SW 2  is turned on. In the first embodiment, the processes are not repeated in such way. 
     By repeating the processes, in the second embodiment, even when the time interval between the ON timings of the shutter switches SW 1  and SW 2  is long, and the focusing state, exposure data, and dark image data have changed over time, the image sensing process can be done based on the latest data. 
     In the first and second embodiments, the single or continuous shot mode is selected using the single/continuous shot switch  68 . Alternatively, the single or continuous shot mode may be selected in correspondence with the operation mode selected by the mode dial switch  60 . 
     In each of the above embodiments, the charge accumulation time of the actual image sensing process is set to be equal to that of the dark capture process. However, different charge accumulation times may be set as long as sufficient data that can be used to correct dark current noise and the like can be obtained. 
     During execution of the dark capture ( 2 ) process in step S 166  or S 666 , since image sensing cannot be done, a visual or audio message indicating that the dark capture process of the image sensing apparatus  100  cannot be canceled may be made using the indication unit  54  and/or image display unit  28 . 
     On the other hand, during execution of the dark capture ( 1 ) process in step S 137  or S 637 , since the dark capture process can be canceled by pressing the shutter switch SW 2  and actual image sensing can be done preferentially, a visual or audio message indicating that the dark capture process of the image sensing apparatus  100  can be canceled may be made using the indication unit  54  and/or image display unit  28 . For example, if the dark capture process cannot be canceled, a red LED may be turned on; if the dark capture process can be canceled, a green LED may be turned on, so as to indicate different messages. Or if the dark capture process cannot be canceled, an LED may flicker quickly; if the dark capture process can be canceled, a green LED may flicker slowly, so as to indicate different messages. 
     Furthermore, the first embodiment has exemplified the operation in the one-shot AF mode, and the second embodiment has exemplified the operation in the servo AF mode. The operation may be switched by an AF mode (one-shot AF mode or servo AF mode) selected by an AF mode setup switch. 
     In the description of each embodiment, image sensing is done by moving the mirror  130  between the mirror up and down positions. However, the mirror  130  may comprise a half mirror, and image sensing may be done without moving the mirror. 
     Note that the recording media  200  and  210  are not limited to memory cards such as PCMCIA cards, compact flash cards, or the like, hard disks, and the like, but may use micro DATs (digital audio tapes), magneto-optical disks, optical disks such as CD-Rs, CD-WRs, or the like, phase change optical disks such as DVDs, and the like. 
     Also, the recording media  200  and  210  may use hybrid media that integrate memory cards, hard disks, and the like. Furthermore, such hybrid media may include detachable media. 
     In the description of the embodiment, the recording media  200  and  210  are independent from the image sensing apparatus  100  and are arbitrarily connectable. One or both the recording media  200  and  210  may be permanently connected to the image sensing apparatus  100 . 
     An arbitrary number (one or a plurality) of image recording media  200  or  210  may be connectable to the image sensing apparatus  100 . 
     In the above description, the recording media  200  and  210  are attached to the image sensing apparatus. However, one or a combination of a plurality of recording media may be used. 
     In each of the above embodiments, an explanation has been given using the CCD as an example of the image sensing element  14 . Also, when the image sensing element uses a CMOS, the above effects can be obtained. 
     The embodiments of the present invention have been described. However, the present invention is not limited to the arrangements of such embodiments, but may be applied to any other arrangements as long as they may achieve functions defined in the appended claims or functions of the arrangements of the embodiments. 
     For example, in each of the above embodiments, the dark image capture process prior to image sensing is done in the continuous shot mode. However, the present invention is not limited to such specific mode. For example, the dark image capture process prior to image sensing may be done in a servo auto-focusing mode. Furthermore, the present invention can be applied to any other systems that can switch whether the dark image capture process is done before or after image sensing as needed. 
     The software and hardware arrangements of the above embodiments can be appropriately replaced. 
     The present invention may be achieved by combining the above embodiments or their technical components as needed. 
     The present invention may be applied even when all or some of claims or the arrangements of the embodiments form a single apparatus, are combined with another apparatus, or are building components of the apparatus. 
     The present invention can be applied to various types of cameras such as an electronic still camera, video movie camera, a camera using a silver halide film, and the like, image sensing apparatuses other than cameras, devices applied to such cameras and image sensing apparatuses, and building components of those devices. 
     Note that the present invention may be applied to either a system constituted by a plurality of devices, or an apparatus consisting of a single equipment. 
     The objects of the present invention are also achieved by supplying a storage medium, which records a program code of a software program that can implement the functions of the above-mentioned embodiments to the system or apparatus, and reading out and executing the program code stored in the storage medium by a computer (or a CPU or MPU) of the system or apparatus. 
     In this case, the program code itself read out from the storage medium implements the functions of the above-mentioned embodiments, and the storage medium which stores the program code constitutes the present invention. 
     As the storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magnetooptical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM, and the like may be used. 
     The functions of the above-mentioned embodiments may be implemented not only by executing the readout program code by the computer but also by some or all of actual processing operations executed by an OS (operating system) running on the computer on the basis of an instruction of the program code. 
     Furthermore, the functions of the above-mentioned embodiments may be implemented by some or all of actual processing operations executed by a CPU or the like arranged in a function extension board or a function extension unit, which is inserted in or connected to the computer, after the program code read out from the storage medium is written in a memory of the extension board or unit.