Abstract:
An image sensing apparatus comprises an image sensor that senses an image of a subject to obtain a sensed image; an operating frequency setting device that is capable of setting the operating frequency of said image sensing apparatus to at least any of a first operating frequency or a second operating frequency different from said first operating frequency; and a display unit that is capable of electrically displaying the sensed image obtained by the image sensor. The display unit is capable of display operations at any of said first or second operating frequency set by the operating frequency setting device.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an image sensing apparatus, such as a digital camera, and a control method thereof.  
         BACKGROUND OF THE INVENTION  
         [0002]    Conventionally, image sensing apparatus such as digital camera is known which records and reproduce a still picture or an moving picture with a recording medium such as a memory card having a solid state memory device as a recording medium. Some type of such an apparatus is provided with not only an optical finder (OVF) but also an electronic finder composed of a color liquid crystal panel or the like.  
           [0003]    Such image sensing apparatus with an electronic finder often keeps sensed images displayed on the electronic finder successively even when the sensed images are not actually recorded or stored on a storage medium. Under these circumstances, the operations for recording the sensed images, such as focusing and image saving, start only when the shutter is pressed.  
           [0004]    With the above-mentioned conventional image sensing apparatus equipped with an electronic finder, however, keeping sensed images displayed on the electronic finder during image sensing reduces the number of shots that can be taken because a large amount of power is consumed by the electronic finder, resulting in battery drain. On the other hand, lowering the operating frequency of the entire apparatus too much to reduce power consumption is not practical because it will increase the shutter time lag, the time required for the image sensing to be actually carried out after the shutter is pressed.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention has been made to solve the problems of the prior art described above. An object of the present invention, for example, is to achieve power savings without increasing the shutter time lag.  
           [0006]    According to the present invention, there is provided an image sensing apparatus, comprising:  
           [0007]    an image sensor that senses an image of a subject to obtain a sensed image;  
           [0008]    an operating frequency setting device that is capable of setting the operating frequency of said image sensing apparatus to at least any of a first operating frequency or a second operating frequency different from said first operating frequency; and  
           [0009]    a display unit that is capable of electrically displaying the sensed image obtained by said image sensor, the display unit being capable of display operations at any of said first or second operating frequency set by said operating frequency setting device.  
           [0010]    According to the present invention, there is also provided a method for controlling an image sensing apparatus, comprising:  
           [0011]    an image sensing step that senses an image of a subject to obtain a sensed image;  
           [0012]    an operating frequency setting step that sets the operating frequency of said image sensing apparatus to at least any of a first operating frequency or a second operating frequency different from said first operating frequency at least; and  
           [0013]    a display step that electrically displays the sensed image obtained in said image sensing step, in said display step said sensed image being displayed at said first or second operating frequency set in said operating frequency setting step.  
           [0014]    According to the present invention, there is also provided a storage medium that stores a control program of an image sensing apparatus, said control program comprising:  
           [0015]    a code for an image sensing step that senses an image of a subject to obtain a sensed image;  
           [0016]    a code for an operating frequency setting step that sets the operating frequency of said image sensing apparatus to at least any of a first operating frequency or a second operating frequency different from said first operating frequency; and  
           [0017]    a code for a display step that electrically displays the sensed image obtained in said image sensing step, in said display step said sensed image being displayed at said first or second operating frequency set in said operating frequency setting step.  
           [0018]    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  
       [0019]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
         [0020]    [0020]FIG. 1 is a block diagram showing the configuration of the image sensing apparatus according to a first embodiment of the present invention; and  
         [0021]    FIGS.  2  to  5  are flowcharts of image sensing processing. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    Preferred embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.  
         [0023]    [0023]FIG. 1 is a block diagram showing the configuration of the image sensing apparatus according to a first embodiment of the present invention. This device is configured, for example, as a digital camera.  
         [0024]    In the figure, reference numeral  100  denotes an image processing apparatus (image sensing apparatus),  10  denotes a taking lens consisting of a zoom lens and focusing lens,  12  denotes a shutter provided with an aperture adjustment function, and  14  denotes an image sensing device, which converts an optical image into an electrical signal. Reference numeral  16  denotes an A/D converter, which converts the analog signal output of the image sensing device  14  into a digital signal. Reference numeral  18  denotes a timing generator circuit, which supplies clock signals and control signals to the image sensing device  14  and A/D converter  16  and is controlled by a memory control circuit  22  and system control circuit  50 .  
         [0025]    Reference numeral  20  denotes an image processing circuit, which performs designated pixel interpolation or color conversion on the data from the A/D converter  16  or data from the memory control circuit  22 . The image processing circuit  20  carries out designated computations using sensed image data. Based on the computed results, the system control circuit  50  instructs the exposure controller  40  and focusing controller  42  to perform TTL (through-the-lens) mode AF (autofocusing), AE (automatic exposure), and EF (preflashing) processes. Moreover, the image processing circuit  20  carries out designated computations using sensed image data, and based on the computed results, it performs a TTL mode AWB (automatic white balance) adjustment.  
         [0026]    Reference numeral  22  denotes the memory control circuit, which controls the A/D converter  16 , the timing generator circuit  18 , the image processing circuit  20 , an image display memory  24 , a D/A converter  26 , a memory  30 , and a compression/decompression circuit  32 .  
         [0027]    The data from the A/D converter  16  is written into the image display memory  24  or memory  30  via the image processing circuit  20  and memory control circuit  22  or directly via the memory control circuit  22 .  
         [0028]    Reference numeral  24  denotes the image display memory,  26  denotes the D/A converter, and  28  denotes an image display section constituted by a TFT-LCD (thin film transistor liquid crystal display) and the like. The image data written into the image display memory  24  is displayed by the image display section  28  via the D/A converter  26 . The image display section  28  can achieve the function of an electronic finder if it displays sensed image data successively. Also, it can turn on and off the display at any time in accordance with instructions from the system control circuit  50 . Turning off the display helps reduce the power consumption of the image processing apparatus  100  greatly.  
         [0029]    Reference numeral  30  denotes a memory for storing still pictures or moving pictures as well as voice data. It has enough storage capacity to store a designated number of still pictures or designated minutes of moving pictures. This allows a large volume of image data to be written into the memory  30  at high speed even during sequential photography or panoramic photography which involves taking a series of still pictures successively. The memory  30  can also be used as a working area by the system control circuit  50 .  
         [0030]    Reference numeral  32  denotes a compression/decompression circuit, which compresses and decompresses image data through adaptive discrete cosine transform (ADCT) or the like. The circuit compresses or decompresses image data read from the memory  30  and writes the resulting data back into the memory  30 .  
         [0031]    Reference numeral  40  denotes an exposure controller, which controls the shutter  12  and can have a flash control function if linked with a flash  404 . Reference numeral  42  denotes a focusing controller, which controls the focusing of the taking lens  10 . The exposure controller  40  and focusing controller  42  are controlled by means of a TTL system. The system control circuit  50  controls the exposure controller  40  and focusing controller  42 , based on the results of the computations performed by the image processing circuit  20  on sensed image data.  
         [0032]    Reference numeral  44  denotes a zoom controller, which controls the zooming of the taking lens  10 . Reference numeral  46  denotes a barrier controller, which controls a protector  102  that serves as a barrier. Reference numeral  48  denotes a connector, also known as an accessory shoe, which incorporates an electric contact and mechanical clamp for flash apparatus  400 .  
         [0033]    Reference numeral  50  denotes a system control circuit, which controls the entire image processing apparatus  100 . Reference numeral  52  denotes a memory, which stores the constants, variables, programs, etc. for the operation of the system control circuit  50 .  
         [0034]    Reference numeral  54  denotes a display section, which is constituted by a liquid crystal display, speaker, etc. This section displays operating state, messages, and the like using characters, images, voice, etc. according to the program executed by the system control circuit  50 . The display section  54  is installed at one or more readily visible locations near input devices of the image processing apparatus  100  and constituted by, for example, a combination of an LCD (liquid crystal display), LEDs (light emitting diodes), sound-producing elements and the like.  
         [0035]    Reference numeral  56  denotes an electrically erasable programmable non-volatile memory such as an EEPRO (electrically erasable and programmable read only memory) Reference numerals  60 ,  61 ,  62 ,  64 ,  66 , and  70  denote input devices, via which various instructions for the system control circuit  50  are entered and which are constituted by one or more switches, dials, touch panels, pointing devices employing line-of-sight detection, speech recognition devices, etc. or their combinations.  
         [0036]    Now the input devices  60 ,  61 ,  62 ,  64 ,  66 , and  70  will be described concretely.  
         [0037]    Reference numeral  60  denotes a power switch that turns on and off the image processing apparatus  100 . Reference numeral  61  denotes a mode dial switch, which allows selection among various modes such as automatic shooting mode, manual shooting mode, panoramic photography mode, playback mode.  
         [0038]    Reference numeral  62  denotes a shutter switch (SW 1 ), which turns on halfway through the release operation of a shutter button (not shown) and gives the command to start AF (autofocusing), AE (automatic exposure), AWB (automatic white balance), EF (preflashing), and other processes.  
         [0039]    Reference numeral  64  denotes a shutter switch (SW 2 ), which turns on when the release operation of the shutter button (not shown) is completed and triggers a sequence of processes: an exposure process of writing the signals read out of the image sensing device  12  into the memory  30  as image data through the A/D converter  16  and memory control circuit  22 ; developing process using the computations carried out in the image processing circuit  20  and memory control circuit  22 ; and recording process of reading image data out of the memory  30 , compressing it in the compression/decompression circuit  32 , and writing it in a recording medium  200  or recording medium  210 .  
         [0040]    Reference numeral  66  denotes an image display ON/OFF switch, which allows the image display section  28  to be set to ON or OFF. This function makes it possible to shut off the current to the image display section constituted by an TFT-LCD, etc. during photography by the use of an optical finder  104 , and thereby save power. The ON/OFF setting of the image display section  28  is stored as an image display flag (ON/OFF) in a memory  52 . The user can set the image display flag at will using the input device  70 . The setting may also be stored in an internal memory of the system control circuit  50 .  
         [0041]    A zoom switch (not shown) instructs zooming of the taking lens  10 .  
         [0042]    Reference numeral  70  denotes the input device, which consists of various buttons, a touch panel, etc., including a menu button, set button, macro button, multi-screen playback/page-break button, flash setting button, single-shot/multi-shot self-timer switchover button, menu forward (+) button, menu backward (−) button, image forward (+) button, image backward (−) button, menu up button, menu down button, picture quality selection button, exposure compensation button, date/time setting button, etc.  
         [0043]    Reference numeral  80  denotes a power supply controller, which is constituted by a battery detector circuit, DC/DC converter, and switching circuit for switching the block to turn on. This controller detects the presence or absence of a battery, type of battery, and remaining battery capacity, and supplies required voltages for required periods of time to various parts of the system, including the recording media  200  and  210 , by controlling the DC/DC converter, based on the results of the detection and instructions from the system control circuit  50 .  
         [0044]    Reference numerals  82  and  84  denote connectors while reference numeral  86  denotes a power supply, which is constituted by a primary battery such as an alkaline or lithium cell, secondary battery such as an NiCd, NiMH, or Li cell, AC adaptor, etc.  
         [0045]    Reference numerals  90  and  94  denote interfaces (I/F) to the recording media  200  and  210  such as memory cards or hard disks while reference numerals  92  and  96  denote connectors for connecting to the recording media  200  and  210  such as memory cards or hard disks.  
         [0046]    Reference numeral  98  denotes a media detector, which detects whether the recording medium  200  or  210  has been inserted in the connectors  92  and/or  96 .  
         [0047]    This embodiment has two sets of an interface and connector for connecting storage media. Of course, the present invention may be configured to have either one set or multiple sets of an interface and connector for connecting recording media. Also, it may be configured to have a combination of interfaces and connectors of different standards.  
         [0048]    Cards that comply with PCMCIA, CF (compact flash), or other similar standards may be used as the interfaces and connectors. When cards that comply with PCMCIA, CF (compact flash), or other similar standards are used for the interfaces  90  and  94  and connectors  92  and  96 , if communications cards such as a LAN card, modem card, USB card, IEEE1394 card, P1284 card, SCSI card, and/or telecommunication card for PHS are connected, image data and accompanying management information can be exchanged with other computers or peripherals such as printers.  
         [0049]    Reference numeral  102  denotes the barrier or protector  102 , which covers an image sensing section including the taking lens  10  of the image processing apparatus  100  to protect the image sensing section from contamination and damage. Reference numeral  104  denotes the optical finder, which allows the user to take photographs only by using the optical finder  104  without using the electronic finder function of the image display section  28 . Besides, the optical finder  104  incorporates some of the functions of the display section  54 : for example, an in-focus indicator function, blur warning function, flash charge indicator function, shutter speed indicator function, f-number indicator function, exposure compensation indicator function.  
         [0050]    Reference numeral  110  denotes a communications section, which has various communications functions such as RS232C, USB, IEEE1394, P1284, SCSI, modem, LAN, and wireless communications functions. Reference numeral  112  denotes either a connector used to connect the image processing apparatus  100  to other equipment through the communications section  110  or an antenna used for wireless communications.  
         [0051]    Reference numeral  200  denotes the storage medium such as a memory card or hard disk. The storage medium  200  has a recording section  202  constituted by a semiconductor memory, magnetic disk, or the like; an interface (I/F)  204  to the image processing apparatus  100 ; and a connector  206  for connecting to the image processing apparatus  100 .  
         [0052]    Reference numeral  210  denotes the storage medium such as a memory card or hard disk. The storage medium  210  has a recording section  212  constituted by a semiconductor memory, magnetic disk, or the like; an interface (I/F)  214  to the image processing apparatus  100 ; and a connector  216  for connecting to the image processing apparatus  100 .  
         [0053]    Reference numeral  400  denotes the flash apparatus and  402  denotes a connector for connecting to the accessory shoe of the image processing apparatus  100 . Reference numeral  404  denotes a flash, which is provided with an AF fill-flash function and flash control function.  
         [0054]    With the above configuration, if the mode dial switch  61  is set at image sensing mode, the image sensing can be carried out with the shutter switch (SW 1 )  62  and shutter switch (SW 2 )  64 . The system control circuit  50  is normally ready for photography. If a press of the shutter switch (SW 1 )  62  is detected, the exposure controller  40  controls exposure and the focusing controller  42  controls focusing. When these control operations are completed, the system gets ready to start exposure. When a press of the shutter switch (SW 2 )  64  is detected, the exposure is started. The sensed image acquired by photography is stored in the memory  30  via the image sensing device  14 , A/D converter  16 , image processing circuit  20 , and memory control circuit  22 . The recorded image stored in the memory  30  are compressed by the compression/decompression circuit  32  as required, and stored again in the memory  30 . The system control circuit  50  finishes photography in this state.  
         [0055]    FIGS.  2  to  5  are drawings showing flowcharts of the image sensing processing according to this embodiment.  
         [0056]    First, during initialization, i.e., upon power-up after a battery replacement or the like, the system control circuit  50  initializes flags and control variables (Step S 101 ). Next, the system control circuit  50  checks the state of the power switch  60  to see if it is set at ON (Step S 102 ). If the power switch  60  is set at OFF, the system control circuit  50  performs finishing processes (Step S 105 ). Specifically, it finishes the display in the display sections, closes the barrier of the protector  102  to protect the image sensing section, stores necessary set values and mode settings as well as the settings of necessary parameters including flags and control variables in the non-volatile memory  56 , shuts off unnecessary power to individual sections of the image processing apparatus  100  including the image display section  28  by means of the power supply controller  80 , and performs other designated finishing processes. Then the flow returns to the Step S 102 .  
         [0057]    On the other hand, if it is found in the Step S 102  that the power switch  60  is set at ON, the system control circuit  50  checks the setting position (either photo mode or playback mode) of the mode dial switch  61  to see if it is set at photo mode (Step S 103 ). If it is found that the mode dial switch  61  is set at playback mode, the system control circuit  50  runs the playback process (Step S 104 ) and returns to the Step S 102 .  
         [0058]    If the mode dial switch  61  is set at photo mode, the system control circuit  50  checks the remaining capacity and operating state of the power supply  86  by using the power supply controller  80  to see if the operation of the image processing apparatus  100  will not be hampered (Step S 106 ). If it is judged that the operation of the image processing apparatus  100  will be hampered, the system control circuit  50  goes to Step S 109 . If it is judged that the operation of the image processing apparatus  100  will not be hampered, the system control circuit  50  checks the operating state of the recording medium  200  or  210  to see if the operation of the image processing apparatus  100 , especially the recording and playback operations of image data with respect to the recording medium  200  or  210 , will not be hampered (Step S 107 ). If it is judged that the operation of the image processing apparatus  100  will be hampered, the system control circuit  50  goes to Step S 109 . If it is judged that the operation of the image processing apparatus  100  will not be hampered, the system control circuit  50  initializes the taking lens  10  and checks if it operates normally (Step S 108 ). If it is judged that the taking lens  10  does not operate normally, the system control circuit  50  goes to Step S 109 .  
         [0059]    In Step S 109 , the system control circuit  50  displays warnings in the display section  54 , etc. using images or voice. Then the flow returns to the Step S 102 .  
         [0060]    On the other hand, if it is judged in the Step S 108  that the taking lens  10  operates normally, the system control circuit  50  checks if the image display flag is ON (Step S 110  in FIG. 3). If it is found that the image display flag is ON, the system control circuit  50  switches the operating frequency W of the present apparatus as a whole to a first operating frequency W 1  (Step S 118 ).  
         [0061]    The operating frequency W of the present apparatus is set either at the first operating frequency W 1  or at a second operating frequency W 2  higher than it. At the start of processing (initialization) in FIG. 2, it is set at the second operating frequency W 2 . Therefore, in the Step S 118 , the operating frequency W is switched from the second operating frequency W 2  to the first operating frequency W 1 , the lower frequency. This reduces power consumption. The switching of the operating frequency W is controlled by the system control circuit  50 .  
         [0062]    Next, the system control circuit  50  checks the state of image display in the image display section  28  to see if the image display in the image display section  28  is ON (Step S 119 ). If it is found that the image display in the image display section  28  is not ON, the system control circuit  50  turns on the image display in the image display section  28  (Step S 120 ), puts it in through-display mode so that sensed image data will be displayed successively (Step S 121 ), and goes to Step S 122 . On the other hand, if it is found that the image display in the image display section  28  is ON, the system control circuit  50  goes to the Step S 122  immediately. In the through-display mode described above, the data written successively into the image display memory  24  via the image sensing device  14 , A/D converter  16 , image processing circuit  20 , and memory control circuit  22  is displayed successively in the image display section  28  via the memory control circuit  22  and the D/A converter  26  to implement the function of an electronic finder.  
         [0063]    In the following Step S 122 , the system control circuit  50  checks to see if a setting state indicator flag is ON. If it is ON, the system control circuit  50  displays the setting state in the image display section  28  (Step S 123 ) and goes to Step S 131  in FIG. 4. On the other hand, if the setting state indicator flag is not ON, the system control circuit  50  goes to the Step S 131  immediately.  
         [0064]    If it is found in the Step S 110  that the image display flag is not ON (i.e., the flag is OFF), the system control circuit  50  checks to see if the setting state indicator flag is ON (Step S 111 ). If the setting state indicator flag is not ON, the system control circuit  50  goes to the Step S 131  immediately. If the setting state indicator flag is ON, the system control circuit  50  turns on the image display in the image display section  28  (Step S 112 ), displays the setting state in the image display section  28  (Step S 113 ), and checks to see if a preset setting state display time has expired (Step S 114 ). The system control circuit  50  continues the checking until the setting state display time expires. When the setting state display time expires, the system control circuit  50  turns off the setting state indicator flag (Step S 115 ), clears the setting state display in the image display section  28  (Step S 116 ), turns off the image display in the image display section  28  (Step S 117 ), and goes to the Step S 131 .  
         [0065]    In the following Step S 131  in FIG. 4, the system control circuit  50  checks to see if the shutter switch (SW 1 )  62  is ON. If it is found that SW 1  is not ON, the system control circuit  50  checks to see if the image display flag is ON (Step S 152 ). If it is found that the image display flag is ON, the system control circuit  50  performs metering (Step S 153 ) and AWB adjustment (Step S 154 ) and returns to the Step S 102  in FIG. 2. On the other hand, if it is found that the image display flag is not ON, the system control circuit  50  returns to the Step S 102  immediately.  
         [0066]    If it is found in the Step S 131  that the shutter switch (SW 1 )  62  is ON, the system control circuit  50  checks to see if the image display flag is ON (Step S 132 ). If it is found that the image display flag is ON, the system control circuit  50  goes to Step S 134 . If it is found that the image display flag is not ON, the system control circuit  50  switches the operating frequency W (Step S 133 ) before going to the Step S 134 .  
         [0067]    This process of switching the operating frequency W changes the operating frequency W of the present apparatus as a whole from the first operating frequency W 1  to the second operating frequency W 2 . Thus, the operating frequency W returns to its normal rate. This ensures that subsequent recording operations of sensed images, including metering, focusing control, and recording/saving operations, will be carried out at high speed.  
         [0068]    Next, in Step S 134 , metering is performed. During metering, flash settings are made as required. In the following Step S 135 , focusing control is performed to focus the taking lens on the subject.  
         [0069]    In the following Step S 138 , the system control circuit  50  checks to see if the shutter switch (SW 2 )  64  is ON. If it is found that SW 2  is not ON, the system control circuit  50  checks to see if the shutter switch (SW 1 )  62  is ON (Step S 139 ). If it is found that SW 1  is not ON (has been turned off), the system control circuit  50  returns to the Step S 102 . If it is found that SW 1  is ON (remains ON), the system control circuit  50  returns to the Step S 138 . If it is found in the Step S 138  that the shutter switch (SW 2 )  64  is ON, the system control circuit  50  checks to see if the image display flag is ON (Step S 140  in FIG. 5).  
         [0070]    If it is found that the image display flag is ON, the system control circuit  50  sets the display mode in the image display section  28  to fixed color display mode (Step S 141 ) and goes to Step S 142 . If it is found that the image display flag is not ON, the system control circuit  50  goes to the Step S 142  immediately. In the fixed color display mode, instead of the sensed image data written into the image display memory  24  via the image sensing device  14 , A/D converter  16 , image processing circuit  20 , and memory control circuit  22 ; fixed-color image data is received by the image display section  28  via the memory control circuit  22  and D/A converter  26  to display a fixed-color picture.  
         [0071]    In the following Step S 142 , photographic processing is carried out. Specifically, the system control circuit  50  carries out exposure processing which involves writing photographic image data into the memory  30  via the image sensing device  14 , A/D converter  16 , image processing circuit  20 , and memory control circuit  22  or directly from the A/D converter  16  via the memory control circuit  22  and performs developing which involves reading the image data from the memory  30  using the memory control circuit  22  and, as required, image processing circuit  20  to perform various processing.  
         [0072]    Next, the system control circuit  50  checks to see if the image display flag is ON (Step S 143 ). If it is found that the image display flag is not ON, the system control circuit  50  turns on the image display in the image display section  28  (Step S 144 ) and goes to Step S 145 . If it is found that the image display flag is ON, the system control circuit  50  goes to Step S 145  immediately.  
         [0073]    In Step S 145 , the system control circuit  50  displays a quick review. If the Step S 144  is skipped, the image display section  28  continues to display the sensed image, serving the function of an electronic finder, and the quick review is also displayed immediately after shooting. On the other hand, if the Step S 144  is performed, the sensed image is not displayed for a quick review until just after shooting.  
         [0074]    Next, the recording process of the sensed image data is carried out (Step S 146 ). Specifically, this process involves reading the sensed image data from the memory  30 , performing various image processing on it using the memory control circuit  22  and, as required, image processing circuit  20 , compressing it by the compression/decompression circuit  32  according to the mode setting, and then writing it into the recording medium  200  or  210 .  
         [0075]    Next, the system control circuit  50  checks to see if the image display flag is ON (Step S 147 ). If it is found that the image display flag is ON, the system control circuit  50  sets the display mode to through-display (Step S 148 ) and goes to Step S 149 . In the through-display mode, the sensed image data for the next shot is displayed successively after a quick review of the sensed image.  
         [0076]    On the other hand, if it is found in the Step S 147  that the image display flag is not ON, the system control circuit  50  turns off the image display in the image display section  28  (Step S 150 ), turns on the setting state indicator flag (Step S 151 ), and goes to the Step S 149 .  
         [0077]    In the following Step S 149 , the system control circuit  50  checks to see if the shutter switch (SW 1 )  62  is ON. If it is found that SW 1  is ON, the system control circuit  50  returns to the Step S 138  to get ready for shooting. If it is found that SW 1  is not ON (has been turned off), this means that the sequence of photographic operations is finished and the system control circuit  50  returns to the Step S 102 .  
         [0078]    According to this processing, if the image display flag is ON, the operating frequency W of the apparatus is set at the lower, first operating frequency W 1  until the shutter switch (SW 1 )  62  is pressed, and when the SW 1  is pressed, the operating frequency W of the apparatus is switched to the second operating frequency W 2 , the normal frequency, before metering, focusing control, etc. On the other hand, if the image display flag is OFF, the operating frequency W of the apparatus is constantly set at the normal, second operating frequency W 2 .  
         [0079]    According to this embodiment, when a sensed image is displayed for image sensing, the apparatus operates at the lower, first operating frequency W 1  until the shutter switch (SW 1 )  62  is pressed triggering the operations (metering, focusing control, saving, etc.) for recording the sensed image. This effectively reduces power consumption, which tends to be increased by the image display in the image display section  28 . Besides, during the recording of sensed images, the apparatus operates at the normal, second operating frequency W 2  to increase the processing speed and reduce the shutter time lag. Thus, power savings can be achieved without increasing the shutter time lag.  
         [0080]    When the image sensing is carried out without sensed image display, since the image display section  28  consumes less power from the beginning, the decrease in the operating frequency is less effective in power savings. Therefore, the apparatus is always made to operate at the normal, second operating frequency W 2  to give priority to the processing speed and avoid increasing the shutter time lag more reliably.  
         [0081]    Although in this embodiment, the process of lowering the operating frequency W to the first operating frequency W 1  is applied to the entire apparatus, it is also possible to apply this process only to the operations (image sensing operation by the image sensing device  14 , display operation by the image display section  28 , etc.) directly relevant to the image display in the image display section  28 .  
         [0082]    Although in this embodiment, the timing of switching the operating frequency W from the first operating frequency W 1  back to the second operating frequency W 2  is provided after SW 1  is pressed but before the metering (Step S 134 ) to reduce the shutter time lag effectively, this timing is not limited to this time interval. It may be provided before the metering (Step S 134 ), or after the shutter switch (SW 2 )  64  is pressed (Step S 138 ) but before the photographic processing (Step S 142 ).  
         [0083]    As described above, when carrying out the image sensing while displaying an image, this embodiment can achieve power savings without increasing the shutter time lag, by using the low operating frequency before the recording operation is started or except during the recording operation.  
         [0084]    When the sensed image is not displayed and thus less power saving effect is available, this embodiment can give priority to the processing speed and avoid increasing the shutter time lag more reliably.  
         [0085]    Needless to say, the object of the present invention can also be achieved by a storage medium containing the software program code that implements the functions of the above embodiments: it is supplied to an image sensing apparatus (image sensing apparatus  100 ), whose computer (or a CPU or MPU) (system control circuit  50 ) then reads the program code out of the storage medium and executes it.  
         [0086]    In that case, the program code itself read out from the storage medium will implement the new functions of the above embodiments, and the storage medium which stores the program code will constitute the present invention.  
         [0087]    As the storage medium for supplying the program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape, non-volatile memory card, ROM, or the like may be used.  
         [0088]    The functions of the above embodiments may be implemented not only by the program code read out and executed by the computer, but also by part or all of the actual processing executed, in accordance with instructions from the program code, by an OS (operating system) running on the computer.  
         [0089]    Furthermore, the functions of the above embodiments may also be implemented by part or all of the actual processing executed by a CPU or the like contained in a function expansion card inserted in the computer or a function expansion unit connected to the computer if the processing is performed in accordance with instructions from the program code that has been read out of the storage medium and written into memory on the function expansion card or unit.  
         [0090]    As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the claims.