Patent Publication Number: US-10791279-B2

Title: Control device, control method, and exposure control system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a Continuation Application of the U.S. patent application Ser. No. 14/528,181, filed Oct. 30, 2014, to be issued as U.S. Pat. No. 9,736,386 on Aug. 15, 2017, which claims the benefit of Japanese Priority Patent Application No. 2013-266830 filed Dec. 25, 2013, the entire contents of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to control devices, control methods, and exposure control systems. 
     In recent years, an imaging apparatus, such as a digital camera, equipped with an imaging element having a plurality of photo-electric converters and in which the pixels thereof are divided is becoming widely available. By using such an imaging element, a phase-difference-detection autofocus (sometimes referred to as “phase-difference AF” hereinafter) mode that allows for high-speed autofocusing becomes possible. 
     For example, JP 2008-134389A discloses a method for controlling an imaging apparatus that uses an imaging element including phase-difference AF pixels and normal pixels. In JP 2008-134389A, phase-difference AF is performed by using the phase-difference AF pixels, whereas contrast autofocus (AF), live-view display, an automatic exposure (AE) process, and an auto-white-balance (AWB) process are performed by using the normal pixels. 
     JP 2008-300931A discloses a technology that compensates for storage time by performing specific gain correction on each line within an AF frame when the AF frame and a monitor-display frame are alternately read for improving both monitor image quality and focus precision. This avoids a situation where the storage time within the frame becomes uneven, and appropriate exposure is obtained for both the AF frame and the monitor-display frame. 
     SUMMARY 
     However, although JP 2008-134389A and JP 2008-300931A each have a description related to controlling the phase-difference pixels and monitor pixels independently of each other, there is no detailed disclosure of an idea of how control values for the phase-difference pixels and the monitor pixels are to be selected for achieving optimal AE-performance/AF-performance. 
     Therefore, for example, for the monitor pixels, it is difficult to significantly reduce the shutter speed (SS) or to set an international-organization-for-standardization (ISO) value (i.e., gain) to a high value to show a sharp and smooth image to a photographer. In particular, when the shutter speed and the ISO value are set to fixed values, an interlocking range of the monitor pixels becomes narrow. Thus, when the control values for the monitor pixels are identically applied to the phase-difference pixels, it is difficult to obtain sufficient brightness, thus making it difficult to achieve sufficient AF performance. Furthermore, the monitor pixels are smoothed so as not to show, for example, hunting for photographic exposure. Therefore, when autofocusing is performed by using an exposure value identical to that for a monitor image, it takes a long time to reach appropriate exposure. 
     When exposure correction is applied to the monitor pixels, the screen may become too dark or too bright. In this case, when exposure correction applied to the monitor pixels is identically applied to the phase-difference pixels, the AF performance deteriorates. When ultimate control values are set based on the monitor pixels, proper photometry is not achieved if the monitor pixels are not maintained at appropriate values, thus making it difficult to perform control in accordance with an exposure correction value set based on the ultimate control values. 
     Furthermore, in an aperture-value setting process, there is a case where it is difficult to select an aperture value identical to that for capturing when controlling the monitor pixels even during an aperture priority mode (A) or a manual mode (M) due to restrictions of, for example, AF control. When performing a preview, there is a restriction that it is difficult to perform autofocus. 
     Therefore, there is a demand for a control method that realizes more optimal AE-performance/AF-performance when independently controlling a first pixel group and a second pixel group that are disposed in a single imaging surface, like the phase-difference pixels and the monitor pixels. 
     According to an embodiment of the present disclosure, there is provided a control device including a control unit configured to perform exposure control of a first pixel group and exposure control of a second pixel group independently of each other, the first pixel group and the second pixel group being disposed in a single imaging surface. The control unit controls gain or an exposure time of the first pixel group and gain or an exposure time of the second pixel group independently of each other. 
     According to an embodiment of the present disclosure, there is provided a control method including controlling first gain or a first exposure time of a first pixel group, and controlling second gain or a second exposure time of a second pixel group independently of the first pixel group, the first pixel group and the second pixel group being disposed in a single imaging surface. 
     According to an embodiment of the present disclosure, there is provided an exposure control system including a first pixel group and a second pixel group configured to be disposed in a single imaging surface, and a control device having a control unit configured to perform exposure control of a first pixel group and exposure control of a second pixel group independently of each other, the control unit controlling gain or an exposure time of the first pixel group and gain or an exposure time of the second pixel group independently of each other. 
     According to one or more of embodiments of the present disclosure, the gain or the exposure time of the first pixel group and the gain or the exposure time of the second pixel group are controlled independently of each other. Thus, appropriate exposure can be set for each of the first pixel group and the second pixel group. 
     According to one or more of embodiments of the present disclosure described above, with regard to the first pixel group and the second pixel group that are disposed in a single imaging surface, the gain or the exposure time of the first pixel group and the gain or the exposure time of the second pixel group can be controlled independently of each other, thereby allowing for enhanced AF performance. The above-described advantage is not necessarily limitative. In addition to or in place of the above-described advantage, any of advantages described in this specification or another advantage obvious from this specification may be exhibited. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view schematically illustrating a physical configuration of a digital camera including a control device according to an embodiment of the present disclosure; 
         FIG. 2  is a rear view of the digital camera according to the embodiment; 
         FIG. 3  is a plan view of the digital camera according to the embodiment; 
         FIG. 4  is a block diagram schematically illustrating a functional configuration of the control device according to the embodiment; 
         FIG. 5  is a flowchart schematically illustrating an exposure control process performed by the control device according to the embodiment; 
         FIG. 6  is a flowchart illustrating a first-control-value calculation process according to the embodiment; 
         FIG. 7  is a flowchart illustrating a process in an auto mode or a program mode; 
         FIG. 8  is a flowchart illustrating a first-target-luminance calculation process; 
         FIG. 9  is a flowchart illustrating a process in an aperture priority mode; 
         FIG. 10  is a flowchart illustrating a process in a shutter-speed priority mode; 
         FIG. 11  is a flowchart illustrating a process in a manual exposure mode; 
         FIG. 12  is a flowchart illustrating a second-control-value calculation process according to the embodiment; 
         FIG. 13  is a flowchart illustrating a second-target-luminance calculation process; 
         FIG. 14  is a flowchart illustrating a first-control-value correction process based on an aperture value, in accordance with the embodiment; and 
         FIG. 15  illustrates a hardware configuration of the control device according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT(S) 
     Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the appended drawings. Note that, in this specification and the appended drawings, structural elements that have substantially the same function and structure are denoted with the same reference numerals, and repeated explanation of these structural elements is omitted. 
     The description below will proceed in the following order.
     1. Schematic Configuration of Imaging Apparatus   2. Functional Configuration of Control Device   3. Exposure Control Process by Control Device   4. Modifications
       4.1. Exposure Correction by User   4.2. Calculation of Control Values Based on AF/MF Mode   
       5. Hardware Configuration
 
1. Schematic Configuration of Imaging Apparatus
   

     First, a schematic configuration of an imaging apparatus equipped with a control device according to an embodiment of the present disclosure will be described. The imaging apparatus according to this embodiment is an imaging apparatus equipped with two imaging elements in a single imaging surface and is, for example, a digital camera  1  as shown in  FIGS. 1 to 3 .  FIG. 1  is a cross-sectional view schematically illustrating a physical configuration of the digital camera  1  including the control device according to this embodiment.  FIG. 2  is a rear view of the digital camera  1 .  FIG. 3  is a plan view of the digital camera  1 . 
     The digital camera  1  is constituted of a lens unit, a main camera unit, and a flash unit. As shown in  FIG. 1 , the lens unit includes a photographic lens  10 , a focusing lens  12 , and a diaphragm  14 . The main camera unit includes a photographic pixel group  16 , a phase-difference detection pixel group  18 , a liquid-crystal display (LCD) monitor  20 , an electronic viewfinder (EVF)  22 , an ocular lens  24 , and a finder  26 . The flash unit includes a light-emitting unit  28  and a light-emission control unit (not shown). Furthermore, as shown in  FIGS. 2 and 3 , the main camera unit includes an exposure correction dial  30 , a photographic mode dial  32 , an LCD-monitor operating dial  34 , a preview button  36 , an autofocus/manual-focus (AF/MF) switch button  38 , and a shutter button  40 . 
     The photographic lens  10  is an optical system that takes in light from a subject and projects a subject image onto the imaging elements. 
     The focusing lens  12  is an optical system that performs focus control of the subject image. For example, the focusing lens  12  is moved in an optical-axis direction (i.e., an X-axis direction) by a focusing-lens driving mechanism (not shown) that moves the focusing lens  12 . The focusing-lens driving mechanism operates based on driving command information from the control device and moves the focusing lens  12 . A focal point of the subject image can be controlled by the focusing lens  12  in this manner. 
     The diaphragm  14  adjusts the quantity of light taken in from the subject through the photographic lens  10  based on a control value set by a control device  100 - 1 . For example, the diaphragm  14  is constituted of a plurality of diaphragm blades and is driven by a diaphragm mechanism (not shown) that moves the diaphragm blades. The diaphragm mechanism moves the diaphragm blades based on an f-number set by the control device  100 - 1  so that the quantity of light taken in from the subject can be adjusted. 
     The photographic pixel group  16  performs photo-electric conversion on the light taken in from the subject through the photographic lens  10 . For example, the photographic pixel group  16  may be a solid-state imaging element, such as a complementary metal oxide semiconductor (CMOS) or a charge-coupled device (CCD). 
     The phase-difference detection pixel group  18  is a pixel group in which an optical-path direction of the light taken in from the subject through the photographic lens  10  is controlled. For example, micro-lenses corresponding to pixels in the phase-difference detection pixel group  18  may be arranged such that the center positions of the micro-lenses are not aligned with the center positions of the pixels. The photographic pixel group  16  and the phase-difference detection pixel group  18  are disposed in a single imaging surface. For example, the pixels in the photographic pixel group  16  may be arranged in odd-numbered rows, whereas the pixels in the phase-difference detection pixel group  18  may be arranged in even-numbered rows. 
     The LCD monitor  20  displays an image acquired by imaging as well as a stored image. Furthermore, the LCD monitor  20  displays an image used for setting, for example, a photographing method of the digital camera  1 . For example, the LCD monitor  20  may be a liquid-crystal panel or an organic electroluminescence (EL) panel. Alternatively, the LCD monitor  20  may be a touch-screen. 
     The EVF  22  shows the image acquired by imaging. Specifically, the EVF  22  sequentially acquires an electric signal photo-electrically converted by the photographic pixel group  16  from the photographic pixel group  16  and projects an image based on the acquired electric signal onto the finder  26  via the ocular lens  24 . For example, the EVF  22  may display the image acquired from the photographic pixel group  16  in real time. 
     The ocular lens  24  expands the image shown by the EVF  22 . 
     The finder  26  is an eyepiece used by a user for checking the image shown by the EVF  22 . The user can check a sequentially-imaged subject by looking into the finder  26 . 
     The light-emitting unit  28  emits light in accordance with a light-emission quantity and a light-emission timing set by the light-emission control unit. 
     The light-emission control unit controls the light-emission quantity and the light-emission timing of the light-emitting unit  28  based on control values set by the control device  100 - 1 . For example, the light-emission control unit controls pre-light emission and main light emission. 
     The exposure correction dial  30  is used for setting the degree of correction of an exposure control value during imaging. For example, if an image acquired by imaging is to be made brighter, the dial is set by being turned toward the positive side, or if the image is to be made darker, the dial is set by being turned toward the negative side. Exposure control related to correction may involve controlling of the gain, the exposure time, the aperture, or a combination thereof. 
     The photographic mode dial  32  is used for setting an exposure control mode. For example, the mode may be an auto mode (Auto), a program mode (P), an aperture priority mode (A), a shutter-speed priority mode (S), and a manual exposure mode (M). The auto mode and the program mode are modes in which the digital camera  1  automatically performs exposure control. The aperture priority mode is a mode in which an aperture value is set by the user and the aperture value is automatically controlled. The shutter-speed priority mode is a mode in which the exposure time is set by the user and the aperture value is automatically controlled. The manual exposure mode is a mode in which the aperture value and the exposure time are set by the user. By rotating the photographic mode dial  32  to set a desired mode to a preset position, the mode can be set. 
     The LCD-monitor operating dial  34  is used for operating an image displayed on the LCD monitor  20 . Specifically, the user manipulates the LCD-monitor operating dial  34  to operate the image displayed on the LCD monitor  20  so as to perform, for example, setting operation of the digital camera  1 . 
     The preview button  36  is used for setting whether or not to execute a preview. Specifically, the digital camera  1  transitions to a preview execution mode when the preview button  36  is pressed, and then transitions to a preview non-execution mode when the preview button  36  is pressed again. A preview in this case is, for example, displaying, on the LCD monitor  20  and the EVF  22 , an image obtained when an image acquired from the photographic pixel group  16  in real time is exposure-controlled based on a set exposure control value. 
     The AF/MF switch button  38  is used for switching a focus setting of the digital camera  1  to autofocus or manual focus. Every time the AF/MF switch button  38  is pressed, the focus setting is switched between autofocus and manual focus. 
     The shutter button  40  is an operable section used for causing the digital camera  1  to execute an autofocusing (AF) process or an imaging process. Specifically, the AF process is executed when the shutter button  40  is half-pressed, and the imaging process is executed when the shutter button  40  is fully pressed. 
     Although not shown in  FIGS. 1 to 3 , the digital camera  1  includes the control device  100 - 1  constituted of, for example, a central processing unit (CPU) and a memory. Although an example in which the control device  100 - 1  is included in the digital camera  1  is described, the control device  100 - 1  may be included in, for example, an electronic apparatus, such as a smartphone, a tablet terminal, or a notebook-type personal computer. 
     2. Functional Configuration of Control Device 
     Next, a functional configuration of the control device  100 - 1  according to this embodiment will be described with reference to  FIG. 4 .  FIG. 4  is a block diagram schematically illustrating the functional configuration of the control device  100 - 1  according to this embodiment. 
     The control device  100 - 1  is a controller that performs exposure control of a photographic pixel group (first pixel group)  102  and exposure control of a phase-difference detection pixel group (second pixel group)  104 , which are disposed in a single imaging surface, independently of each other. The control device  100 - 1  controls the gain or the exposure time of the photographic pixel group (first pixel group)  102  and the gain or the exposure time of the phase-difference detection pixel group (second pixel group)  104  independently of each other. The photographic pixel group  102  corresponds to the photographic pixel group  16  in  FIG. 1 , and the phase-difference detection pixel group  104  corresponds to the phase-difference detection pixel group  18  in  FIG. 1 . 
     An image acquired by the photographic pixel group  102  is also used as a monitor image to be displayed on the LCD monitor  20 . For an actually photographed image, photographic gain and a photographic shutter speed are set automatically or in accordance with user settings. For the monitor image, first control values, such as first gain and a first shutter speed, are set so that a sharp and smooth image can be displayed on the LCD monitor  20 . On the other hand, for the phase-difference detection pixel group  104 , first control values, such as second gain and a second shutter speed, are set independently of the photographic pixel group  102  so as to enhance AF performance. 
     As shown in  FIG. 4 , the control device  100 - 1  includes a first-detection-value acquiring unit  106 , a second-detection-value acquiring unit  108 , a first-gain control unit  110 , a second-gain control unit  112 , a first-timing control unit  114 , a second-timing control unit  116 , a setting unit  118 , and a memory  124 . 
     The first-detection-value acquiring unit  106  detects an imaging signal from the photographic pixel group  102  and outputs a first detection value. The first detection value is output from the first-detection-value acquiring unit  106  to the first-gain control unit  110 . 
     The second-detection-value acquiring unit  108  detects an imaging signal from the phase-difference detection pixel group  104  and outputs a second detection value. The second detection value is output from the second-detection-value acquiring unit  108  to the second-gain control unit  112 . The phase-difference detection pixel group  104  and the first-detection-value acquiring unit  106  simultaneously read the respective imaging signals. 
     The first-gain control unit  110  performs gain adjustment on the first detection value based on the first gain. After amplifying the first detection value by applying the first gain thereto, the first-gain control unit  110  outputs the first detection value to a first-control-value arithmetic unit  120  in the setting unit  118 . 
     The second-gain control unit  112  performs gain adjustment on the second detection value based on the second gain. The second-gain control unit  112  according to this embodiment functions independently of the first-gain control unit  110 . After amplifying the second detection value by applying the second gain thereto, the second-gain control unit  112  outputs the second detection value to a second-control-value arithmetic unit  122  in the setting unit  118 . 
     The first-timing control unit  114  performs exposure control of the photographic pixel group  102  based on the first shutter speed (i.e., a first exposure time). The first-timing control unit  114  controls the exposure of the photographic pixel group  102  based on the first shutter speed calculated by the first-control-value arithmetic unit  120  in the setting unit  118 , which will be described later. 
     The second-timing control unit  116  performs exposure control of the phase-difference detection pixel group  104  based on a second exposure time (i.e., the second shutter speed). The second-timing control unit  116  functions independently of the first-timing control unit  114  and controls the exposure of the phase-difference detection pixel group  104  based on the second exposure time calculated by the second-control-value arithmetic unit  122  in the setting unit  118 , which will be described later. The first-timing control unit  114  and the second-timing control unit  116  simultaneously expose the respective pixel groups to light. 
     The setting unit  118  is a functional unit that calculates control values used for performing exposure control of the pixel groups  102  and  104  and includes the first-control-value arithmetic unit  120  and the second-control-value arithmetic unit  122 . 
     The first-control-value arithmetic unit  120  calculates the first shutter speed, the first gain for adjusting the first detection value, and a set value (referred to as “aperture value” hereinafter) of the diaphragm  14  based on the first detection value gain-adjusted at the first-gain control unit  110  and information from the lens unit. The information from the lens unit includes, for example, AF information and aperture information. Then, the first-control-value arithmetic unit  120  outputs the first shutter speed to the first-timing control unit  114 , the first gain to the first-gain control unit  110 , and the aperture value to the second-control-value arithmetic unit  122 . 
     Based on the second detection value gain-adjusted at the second-gain control unit  112  and the aperture value calculated by the first-control-value arithmetic unit  120 , the second-control-value arithmetic unit  122  calculates the second shutter speed and the second gain for adjusting the second detection value. Then, the second-control-value arithmetic unit  122  outputs the second shutter speed to the second-timing control unit  116  and the second gain to the second-gain control unit  112 . 
     The memory  124  is a storage unit that stores therein, for example, various kinds of setting information and captured images of the digital camera  1 . The memory  124  is constituted of a storage medium, such as a read-only memory (ROM) or a random access memory (RAM). For example, the various kinds of setting information stored in the memory  124  are read by the first-control-value arithmetic unit  120  and the second-control-value arithmetic unit  122  in the setting unit  118  so as to be used for arithmetic processes. 
     3. Exposure Control Process by Control Device 
     Next, a general outline of an exposure control process performed by the control device  100 - 1  according to this embodiment will be described with reference to  FIG. 5 .  FIG. 5  is a flowchart schematically illustrating the exposure control process performed by the control device  100 - 1  according to this embodiment. 
     S 202 : Initialization 
     First, as shown in  FIG. 5 , the control device  100 - 1  performs initialization when a photographing process is to be performed (step S 202 ). The initialization involves setting an initial aperture value, an initial value of first gain for adjusting a first detection value of the photographic pixel group  102 , an initial value of a first shutter speed, an initial value of second gain for adjusting a detection value of the phase-difference detection pixel group  104 , and an initial value of a second shutter speed. In this case, the second gain is set in correspondence with an exposure value that is lower than the first gain, and the second shutter speed is set in correspondence with an exposure value that is higher than the first shutter speed. 
     Furthermore, the control device  100 - 1  sets an initial value of first target luminance for the photographic pixel group  102  and an initial value of second target luminance for the phase-difference detection pixel group  104 . Target luminance is a target value of each control value, and a subsequent control value is set so as to follow the target value. Target luminance is to be used in a smoothing process for averaging out unevenness of brightness within an image. The initial value of the first target luminance is set to, for example, a value obtained by subtracting the first gain from a sum of the aperture value and a first exposure time, and the initial value of the second target luminance is set to, for example, a value obtained by subtracting the second gain from a sum of the aperture value and a second exposure time. Accordingly, the initial values of the first target luminance and the second target luminance are set to be different from each other. 
     S 204 : AE Activation Process 
     Subsequently, the control device  100 - 1  performs an AE activation process (step S 204 ). In step S 204 , the first detection value of the photographic pixel group  102  and the second detection value of the phase-difference detection pixel group  104  are acquired and gain-adjusted. Then, based on these values, the first target luminance and the second target luminance are calculated. Each target luminance is set in accordance with a magnitude relationship obtained by comparing the corresponding gain-adjusted detection value with a preset threshold value. 
     S 206 : Acquisition of Key Information 
     When the AE activation process is completed, the control device  100 - 1  acquires key information (step S 206 ). As the key information, operation information of, for example, an exposure mode, an exposure correction value, a preview mode, and an AF/MF switch state is acquired. The exposure mode can be acquired from the setting of the photographic mode dial  32 , and the exposure correction value can be acquired from the setting of the exposure correcting dial  30 . The preview mode can be acquired from the setting of the preview button  36 , and the AF/MF switch state can be acquired from the setting of the AF/MF switch button  38 . 
     S 208 : Acquisition of Lens Information 
     The control device  100 - 1  acquires lens information (step S 208 ). As the lens information, for example, AF information and aperture information are acquired. The AF information is acquired from the focusing-lens driving mechanism that drives the focusing lens  12  or from a controller that controls the focusing-lens driving mechanism. The aperture information is acquired from the diaphragm mechanism that opens and closes the diaphragm blades of the diaphragm  14  or from a controller that controls the diaphragm mechanism. 
     S 210 : Calculation of First Control Values 
     Then, the control device  100 - 1  calculates first control values (step S 210 ). In step S 210 , the first-control-value arithmetic unit  120  calculates the first control values, which include a first shutter speed at which the photographic pixel group  102  is exposed to light for a first exposure time, first gain for adjusting the first detection value, and an aperture value. 
     The process in step S 210  will be described in detail with reference to  FIGS. 6 to 12 .  FIG. 6  is a flowchart illustrating a first-control-value calculation process according to this embodiment.  FIG. 7  is a flowchart illustrating a process in the auto mode or the program mode.  FIG. 8  is a flowchart illustrating a first-target-luminance calculation process.  FIG. 9  is a flowchart illustrating a process in the A mode.  FIG. 10  is a flowchart illustrating a process in the S mode.  FIG. 11  is a flowchart illustrating a process in the M mode.  FIG. 12  is a flowchart illustrating a second-control-value calculation process according to this embodiment. 
     As shown in  FIG. 6 , in the process in step S 210 , the exposure mode is first checked (step S 602 ). The exposure mode is acquired in step S 206  in  FIG. 5  based on the setting of the photographic mode dial  32 . The control device  100 - 1  calculates and sets the first target luminance, the aperture value, the first gain, and the first shutter speed in accordance with the exposure mode. 
     If it is determined in step S 602  that the exposure mode is the auto mode (Auto) or the program mode (P), the control device  100 - 1  calculates the first control values based on the flowchart shown in  FIG. 7  (step S 604 ). In this case, an imaging signal of the photographic pixel group  102  is first acquired as the first detection value by the first-detection-value acquiring unit  106  and is gain-adjusted by the first-gain control unit  110  (step S 702 ). Then, the first-control-value arithmetic unit  120  calculates the first target luminance, which is for a smoothing process at the photographic-pixel-group side, by using the first detection value gain-adjusted by the first-gain control unit  110  (step S 316 ). 
       FIG. 8  illustrates the process in step S 316  in detail. As shown in  FIG. 8 , the first-control-value arithmetic unit  120  first calculates current luminance based on the first detection value and second control values (step S 402 ). This luminance indicates the current brightness of a subject. 
     Then, the first-control-value arithmetic unit  120  calculates ultimate first target luminance (step S 404 ). The ultimate first target luminance indicates ultimately aimed brightness and is calculated based on the first detection value, a monitor reference level, and the exposure correction value. The monitor reference level is a fixed value and is a preset reference value. The ultimate first target luminance may be calculated based on, for example, expression (1) shown below.
 
Ultimate Target Luminance=Current Luminance+(log 2 (First Detection Value)−log 2 (Monitor Reference Level))−Exposure Correction Value  (1)
 
     The first-control-value arithmetic unit  120  subtracts the current luminance calculated in step S 402  from the ultimate first target luminance calculated in step S 404  so as to obtain an amount of change in ultimate luminance (step S 406 ). This amount of change in ultimate luminance is an amount of change when the first control values are made to follow target values. 
     Subsequently, the first-control-value arithmetic unit  120  calculates an amount of change in subsequent luminance to be set in a subsequent process based on the amount of change in ultimate luminance calculated in step S 406  (step S 408 ). For example, an amount of change in subsequent luminance ΔEV 1  may be calculated based on expression (2) shown below. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     Then, the first-control-value arithmetic unit  120  adds the current luminance calculated in step S 402  and the amount of change in subsequent luminance ΔEV 1  calculated in step S 408  together so as to obtain subsequent first target luminance (step S 410 ). Specifically, the subsequent first target luminance is expressed by expression (3) shown below.
 
Subsequent First Target Luminance=Current Luminance+Amount of Change in Subsequent Luminance ΔEV 1   (3)
 
     Referring back to  FIG. 7 , when the subsequent first target luminance is calculated in step S 316 , the first-control-value arithmetic unit  120  calculates the aperture value (step S 704 ). Based on the aperture value, the first-control-value arithmetic unit  120  calculates photographic gain (step S 706 ) and then calculates a photographic shutter speed (step S 708 ). The auto mode and the program mode are modes in which the digital camera  1  automatically performs exposure control. The photographic gain and the photographic shutter speed are automatically set based on the aperture value set in accordance with the subsequent first target luminance. 
     Subsequently, the first-control-value arithmetic unit  120  calculates the first gain (step S 710 ) and then calculates the first shutter speed (step S 712 ), which are for monitoring. In order to present to a user an image that is as identical to an actually photographed image as possible, it is desirable that the first gain and the first shutter speed be the same as the photographic gain and the photographic shutter speed, respectively. However, the first gain and the first shutter speed do not have to match the photographic gain and the photographic shutter speed, respectively. 
     The first control values in the auto mode or the program mode are calculated in this manner. 
     If it is determined in step S 602  that the exposure mode is the aperture priority mode (A), the control device  100 - 1  calculates the first control values based on the flowchart shown in  FIG. 9  (step S 606 ). In this case, an imaging signal of the photographic pixel group  102  is first acquired as the first detection value by the first-detection-value acquiring unit  106  and is gain-adjusted by the first-gain control unit  110  (step S 702 ). Then, the first-control-value arithmetic unit  120  calculates the first target luminance, which is for a smoothing process at the photographic-pixel-group side (step S 316 ). Since the processes in step S 702  and step S 316  are the same as those in the auto mode (Auto) or the program mode (P) described above, descriptions thereof will be omitted here. 
     When the first target luminance is calculated in step S 316 , the first-control-value arithmetic unit  120  sets the aperture value to a value set by the user (step S 802 ). The aperture priority mode (A) is a mode in which the diaphragm  14  is set by the user and the aperture value is automatically controlled. As a result of step S 802 , the setting of the diaphragm  14  by the user is reflected on the settings of the digital camera  1 . 
     Subsequently, the first-control-value arithmetic unit  120  calculates the photographic gain (step S 706 ) and then calculates the photographic shutter speed (step S 708 ). The photographic gain and the photographic shutter speed are automatically set based on the aperture value set by the user. 
     Subsequently, the first-control-value arithmetic unit  120  calculates the first gain (step S 710 ) and then calculates the first shutter speed as a first exposure time (step S 712 ), which are for monitoring. Since the processes in step S 710  and step S 712  are the same as those in the auto mode (Auto) or the program mode (P) described above, descriptions thereof will be omitted here. The first control values in the aperture priority mode (A) are calculated in this manner. 
     If it is determined in step S 602  that the exposure mode is the shutter-speed priority mode (S), the control device  100 - 1  calculates the first control values based on the flowchart shown in  FIG. 10  (step S 608 ). In this case, an imaging signal of the photographic pixel group  102  is first acquired as the first detection value by the first-detection-value acquiring unit  106  and is gain-adjusted by the first-gain control unit  110  (step S 702 ). Then, the first-control-value arithmetic unit  120  calculates the first target luminance, which is for a smoothing process at the photographic-pixel-group side (step S 316 ). Since the processes in step S 702  and step S 316  are the same as those in the auto mode (Auto) or the program mode (P) described above, descriptions thereof will be omitted here. 
     When the first target luminance is calculated in step S 316 , the first-control-value arithmetic unit  120  sets the photographic shutter speed to a value set by the user (step S 902 ). The shutter-speed priority mode is a mode in which the exposure time is set by the user and the aperture value is automatically controlled. As a result of step S 902 , the photographic shutter speed set by the user is reflected on the settings of the digital camera  1 . In step S 704  to be described later, the aperture value is automatically controlled such that appropriate exposure is obtained in accordance with the photographic shutter speed. 
     Subsequently, the first-control-value arithmetic unit  120  calculates the first shutter speed (step S 712 ) and then calculates the aperture value (step S 704 ), which are for monitoring. The aperture value is set in accordance with the photographic shutter speed. Then, the first-control-value arithmetic unit  120  calculates the first gain (step S 710 ) and then calculates the photographic gain (step S 706 ). Since the processes in step S 706 , step S 710 , and step S 712  are the same as those in the auto mode (Auto) or the program mode (P) described above, descriptions thereof will be omitted here. The first control values in the shutter-speed priority mode (S) are calculated in this manner. 
     If it is determined in step S 602  that the exposure mode is the manual exposure mode (M), the control device  100 - 1  calculates the first control values based on the flowchart shown in  FIG. 11  (step S 610 ). The manual exposure mode is a mode in which the aperture value and the exposure time are set by the user. Therefore, the photographic shutter speed and the aperture value are set to values set by the user. 
     In this case, an imaging signal of the photographic pixel group  102  is first acquired as the first detection value by the first-detection-value acquiring unit  106  and is gain-adjusted by the first-gain control unit  110  (step S 702 ). Then, the first-control-value arithmetic unit  120  calculates the first target luminance, which is for a smoothing process at the photographic-pixel-group side (step S 316 ). Since the processes in step S 702  and step S 316  are the same as those in the auto mode (Auto) or the program mode (P) described above, descriptions thereof will be omitted here. 
     When the first target luminance is calculated in step S 316 , the first-control-value arithmetic unit  120  sets the photographic shutter speed to a value set by the user (step S 902 ) and then sets the aperture value to a value set by the user (step S 802 ). The process in step S 902  is the same as that in the shutter-speed priority mode (S) described above, and the process in step S 802  is the same as that in the aperture priority mode (A) described above. 
     Subsequently, the first-control-value arithmetic unit  120  calculates the photographic gain based on the photographic shutter speed and the aperture value (step S 706 ). Moreover, the first-control-value arithmetic unit  120  calculates the first shutter speed (step S 712 ) and then calculates the first gain (step S 710 ), which are for monitoring. Since the processes in step S 710  and step S 712  are the same as those in the auto mode (Auto) or the program mode (P) described above, descriptions thereof will be omitted here. The first control values in the manual exposure mode (M) are calculated in this manner. 
     When the first control values are calculated in accordance with each exposure mode in the above-described manner, the first-control-value arithmetic unit  120  determines whether or not the preview mode is set to an on state (step S 612 ). In the preview mode, a predetermined aperture value is temporarily set by user operation. The user can check an image acquired when the aperture value is set to that value by looking into, for example, the LCD monitor  20 . 
     The setting of the preview mode is determined based on an on/off state of the preview button  36 . When the preview button  36  is in an on state, the first-control-value arithmetic unit  120  performs open-close control of the diaphragm  14  to set it to the predetermined aperture value so that a preview is performed (step S 614 ). When the control of the diaphragm  14  is completed, the control device  100 - 1  sets a preview flag, which indicates that the preview mode is in progress, to an on state (step S 616 ) and ends the process shown in  FIG. 6 . On the other hand, when the preview button  36  is in an off state in step S 612 , the first-control-value arithmetic unit  120  sets the preview flag to an off state (step S 618 ) and ends the process shown in  FIG. 6 . 
     S 212 : Calculation of Second Control Values 
     Referring back to  FIG. 5 , when the first control values are calculated in step S 210  in accordance with the flowchart in  FIG. 6 , the control device  100 - 1  subsequently calculates second control values (step S 212 ). In step S 212 , the second-control-value arithmetic unit  122  calculates a second shutter speed and second gain as the second control values. 
     The process in step  5212  will be described in detail with reference to  FIGS. 12 and 13 .  FIG. 12  is a flowchart illustrating a second-control-value calculation process according to this embodiment.  FIG. 13  is a flowchart illustrating a second-target-luminance calculation process. 
     As shown in  FIG. 12 , in order to calculate the second control values, the control device  100 - 1  first causes the second-control-value arithmetic unit  122  to acquire the first control values (step S 1002 ). With regard to the first control values, the values calculated in step S 210  are used. 
     Subsequently, the control device  100 - 1  causes the second-detection-value acquiring unit  108  to acquire the second detection value (step S 1004 ). The second detection value acquired by the second-detection-value acquiring unit  108  is adjusted based on the second gain at the second-gain control unit  112 , and is subsequently output to the second-control-value arithmetic unit  122 . Then, the second-control-value arithmetic unit  122  calculates the second target luminance by using the gain-adjusted second detection value (step S 310 ). 
       FIG. 13  illustrates the process in step S 310  in detail. As shown in  FIG. 13 , the second-control-value arithmetic unit  122  first calculates current luminance based on the second detection value and previous second control values (step S 502 ). Then, the second-control-value arithmetic unit  122  calculates ultimate second target luminance (step S 504 ). The ultimate second target luminance indicates ultimately aimed brightness and is calculated based on the second detection value and a phase-difference reference level. The phase-difference reference level is a fixed value and is a preset reference value. 
     The ultimate second target luminance may be calculated based on, for example, expression (4) shown below. In this case, ΔMF_Offset indicates a photometric-range offset value when performing manual focusing and is set to, for example, an exposure value (EV) of 2. When performing autofocusing, ΔMF_Offset is equal to zero.
 
Ultimate Second Target Luminance=Current Luminance+(log 2 (Second Detection Value)−log 2 (Phase-Difference Reference Level))−ΔMF_Offset  (4)
 
     Alternatively, the ultimate second target luminance may be calculated based on expression (5) shown below in view of a second-luminance correction amount. In this case, the second-luminance correction amount is set to a value in which the upper and lower limits for the luminance correction amount are limited to ±1 EV.
 
Ultimate Second Target Luminance=Current Luminance+(log 2 (Second Detection Value)−log 2 (Phase-Difference Reference Level))−Second-Luminance Correction Amount+ΔMF_Offset  (5)
 
     Then, the second-control-value arithmetic unit  122  subtracts the current luminance calculated in step S 502  from the ultimate second target luminance calculated in step S 504  so as to obtain an amount of change in ultimate luminance (step S 506 ). This amount of change in ultimate luminance is an amount of change when the second control values are made to follow target values. 
     Subsequently, the second-control-value arithmetic unit  122  calculates an amount of change in subsequent luminance to be set in a subsequent process based on the amount of change in ultimate luminance calculated in step S 506  (step S 508 ). For example, an amount of change in subsequent luminance ΔEV 2  may be calculated based on expression (6) shown below. 
     
       
         
           
             
               
                 
                   
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     In this case, ΔEV 2_ p for the phase-difference detection pixel group  104  is set to be larger than or equal to ΔEV  1_ p for the photographic pixel group  102 . Alternatively, ΔEV 2_ p may be an infinite value that is set such that the target luminance can be reached as quickly as possible. Likewise, ΔEV 2_ m for the phase-difference detection pixel group  104  is set to be smaller than or equal to ΔEV 1_ m for the photographic pixel group  102 . Alternatively, ΔEV 2_ m may be a negative infinite value that is set such that the target luminance can be reached as quickly as possible. Accordingly, high-speed smoothing of the phase-difference detection pixel group  104  can be achieved, whereby the time it takes to reach appropriate exposure in phase-difference AF can be shortened. Thus, AF response can be enhanced. 
     Then, the second-control-value arithmetic unit  122  adds the current luminance calculated in step S 502  and the amount of change in subsequent luminance calculated in step S 508  together so as to obtain subsequent second target luminance (step S 510 ). Specifically, the subsequent second target luminance is expressed by expression (7) shown below. The subsequent second target luminance is used as a phase-difference control value in a subsequent cycle.
 
Subsequent Second Target Luminance=Current Luminance+Amount of Change in Subsequent Luminance ΔEV 2   (7)
 
     Referring back to  FIG. 12 , when the subsequent second target luminance is calculated in step S 310 , the second-control-value arithmetic unit  122  calculates the second gain (step S 1006 ). The second gain is set to an interlocking range that is wider than that of the first gain. Thus, the second gain can correspond to high sensitivity, whereby appropriate exposure can be obtained in phase-difference AF. Alternatively, the second gain may be a fixed value. By making the second gain a fixed value, stable AF performance can be realized during phase-difference AF. 
     Then, the second-control-value arithmetic unit  122  calculates the second shutter speed (step S 1008 ). The second shutter speed is also set to an interlocking range that is wider than that of the first gain. Thus, the second shutter speed can be set to a low value, whereby appropriate exposure can be obtained in phase-difference AF. Alternatively, the second shutter speed may be a fixed value. By making the second shutter speed a fixed value, stable AF performance can be realized during phase-difference AF. 
     In this embodiment, the interlocking range of the second gain is set to be wider than the interlocking range of the first gain in step S 1006 , and the interlocking range of the second shutter speed is set to be wider than the interlocking range of the first shutter speed in step S 1008 . However, the present technology is not limited to this example. Appropriate exposure in phase-difference AF can be obtained by executing at least one of step S 1006  and step S 1008 . 
     Subsequently, the second-control-value arithmetic unit  122  determines whether or not the preview flag is in an on state (step S 612 ). The second-control-value arithmetic unit  122  performs this determination process based on the on/off state of the preview flag set in step S 616  or S 618  in  FIG. 6 . When the preview flag is in an off state, the second-control-value arithmetic unit  122  ends the process shown in  FIG. 12 . On the other hand, when the preview flag is in an on state, the second-control-value arithmetic unit  122  changes the settings of the second control values (step S 1010  to step S 1020 ). 
     Specifically, the second-control-value arithmetic unit  122  first determines whether or not the aperture value is set to be brighter than a threshold value B and darker than a threshold value A (step S 1010 ). When the aperture value is set to be brighter than the threshold value B and darker than the threshold value A, the second-control-value arithmetic unit  122  changes the second shutter speed by reducing it by a predetermined value A 1  (step S 1012 ). Moreover, the second-control-value arithmetic unit  122  changes the second gain by increasing it by a predetermined value A 2  (step S 1014 ). 
     For example, it is assumed that the threshold value A is F 8  and the threshold value B is F 5 . 6 . In this case, if the aperture value is set to be brighter than F 5 . 6  and darker than F 8 , the second shutter speed is reduced by the predetermined value A 1  (e.g., 0.5 EV). Moreover, the second gain is increased in sensitivity by the predetermined value A 2  (e.g., 0.5 EV). 
     On the other hand, when it is determined that the aperture value is set to be darker than the threshold value B or is set to be brighter than the threshold value A in step S 1010 , the second-control-value arithmetic unit  122  determines whether the aperture value is set to be darker than the threshold value B (step S 1016 ). When the aperture value is set to be darker than the threshold value B, the second-control-value arithmetic unit  122  changes the second shutter speed by reducing it by a predetermined value B 1  (step S 1018 ). Moreover, the second-control-value arithmetic unit  122  changes the second gain by increasing it by a predetermined value B 2  (step S 1020 ). 
     For example, when the threshold value A is F 8  and the threshold value B is F 5 . 6 , if the aperture value is set to be darker than F 5 . 6 , the second shutter speed is reduced by the predetermined value B 1  (e.g., 1.0 EV). Moreover, the second gain is increased in sensitivity by the predetermined value B 2  (e.g., 1.0 EV). In this case, the predetermined values B 1  and B 2  are set to be higher than the predetermined values A 1  and A 2 , respectively. 
     After step S 1010  to step S 1020 , the second-control-value arithmetic unit  122  ends the process shown in  FIG. 12 . If it is determined in step S 1016  that the aperture value is set to be brighter than the threshold value A, the second-control-value arithmetic unit  122  ends the process shown in  FIG. 12  without changing the second gain and the second shutter speed. 
     Accordingly, in the control device  100 - 1  according to this embodiment, exposure control of the photographic pixel group  102  and exposure control of the phase-difference detection pixel group  104  are performed independently of each other. The control device  100 - 1  controls the gain or the exposure time of the photographic pixel group  102  and the gain or the exposure time of the phase-difference detection pixel group  104  independently of each other. Thus, with regard to the photographic pixel group  102 , an image desired by the user can be acquired, and the gain and the shutter speed are set such that a sharp and smooth monitor image can be presented to the user. With regard to the phase-difference detection pixel group  104 , in order to achieve sufficient brightness for enhanced AF performance, the gain and the shutter speed are set such that the interlocking ranges thereof are wider than those for the photographic pixel group  102 . 
     Furthermore, unlike the first control values, the second control values are set automatically regardless of the exposure mode. Thus, the second gain and the second shutter speed can be set such that appropriate exposure is constantly obtained for the phase-difference detection pixel group  104  regardless of the exposure mode, thereby allowing for enhanced AF performance. Alternatively, depending on conditions, the second control values may be set to fixed values regardless of the exposure mode. Thus, phase-difference AF can be performed stably, thereby allowing for enhanced AF performance. 
     For example, it is assumed that the interlocking range of the first gain set in step S 210  is between ISO 100 and ISO 3200, and the interlocking range of the first shutter speed is between 1/15 and 1/8000. In this case, in step S 212 , for example, the interlocking range of the second gain is set to a range between ISO 50 and ISO 12800, and the interlocking range of the second shutter speed is set to a range between 1 and 1/16000. Alternatively, for example, the second gain may be fixed at ISO 400, and the second shutter speed may be fixed at 1/60. 
     S 214 : Correction of First Control Values Based on Aperture Value 
     Referring back to  FIG. 5 , when the second control values are calculated in step S 212 , the control device  100 - 1  subsequently performs a first-control-value correction process, where appropriate (step S 214 ). In step S 214 , when the user reduces the aperture of the diaphragm  14  during controlling of a monitor image in the AF/MF mode or the preview mode, brightness with which sufficient AF performance can be achieved in exposure control of the phase-difference detection pixel group  104  is maintained. 
     Specifically, in a state where the aperture of the diaphragm  14  is reduced, the first control values for the photographic pixel group  102  are corrected in accordance with the aperture value set by the user by performing a process in  FIG. 14 . On the other hand, with regard to the phase-difference detection pixel group  104 , the second shutter speed is set to a low value and the second gain is set to high sensitivity even in the state where the aperture of the diaphragm  14  is reduced, so that brightness sufficient for AF performance is obtained. 
     The first-control-value correction process will be described with reference to  FIG. 14 . As shown in  FIG. 14 , the first-control-value arithmetic unit  120  first determines whether the focus mode is set to manual focus (step S 1102 ). The determination of whether the focus mode is set to manual focus can be performed based on the setting of the AF/MF switch button  38 . When the focus mode is set to manual focus, the first-control-value arithmetic unit  120  determines whether or not the aperture value is set to be darker than a threshold value D (step S 1104 ). The threshold value D may be, for example, F 11 . When the aperture value is set to be brighter than or equal to the threshold value D in step S 1104 , the first-control-value arithmetic unit  120  ends the process in  FIG. 14  without changing the first control values. 
     On the other hand, when it is determined in step S 1104  that the aperture value is set to be darker than the threshold value D, the first-control-value arithmetic unit  120  sets an ultimate aperture value to a value corresponding to the threshold value D (step S 1106 ). Then, the first-control-value arithmetic unit  120  calculates an amount of change in ultimate aperture value for achieving the ultimate aperture value set in step S 1106  (step S 1108 ). Specifically, an amount of change in ultimate aperture value ΔAV is a difference between the aperture value set in step S 210  and the ultimate aperture value set in step S 1106  and is expressed by expression (8) shown below.
 
Amount of Change in Ultimate Aperture Value ΔAV=(Aperture Value)−(Ultimate Aperture Value)  (8)
 
     Subsequently, the first-control-value arithmetic unit  120  determines whether or not to correct the first gain or the first shutter speed (step S 1110 ). This determination of whether or not to perform the correction is performed by determining whether or not a value obtained by subtracting the amount of change in ultimate aperture value ΔAV from the first gain is larger than or equal to a minimum value of the first gain. Specifically, in step S 1110 , it is determined whether or not the corrected first gain is larger than the minimum value of the first gain. 
     When the value obtained by subtracting the amount of change in ultimate aperture value ΔAV from the first gain is larger than or equal to the minimum value of the first gain, the first-control-value arithmetic unit  120  corrects the first gain to the value obtained by subtracting the amount of change in ultimate aperture value ΔAV from the first gain (step S 1112 ). On the other hand, when the value obtained by subtracting the amount of change in ultimate aperture value ΔAV from the first gain is smaller than the minimum value of the first gain, the first-control-value arithmetic unit  120  corrects the first shutter speed to a value obtained by adding the amount of change in ultimate aperture value ΔAV to the first shutter speed (step S 1114 ). 
     Referring back to step S 1102 , if the focus mode is not set to manual focus in step S 1102 , the first-control-value arithmetic unit  120  determines whether or not aperture correction is set in an on state (step S 1116 ). The setting of the aperture correction can be confirmed from a backup value or menu settings. When it is determined in step S 1116  that the aperture correction is set in an off state, the first-control-value arithmetic unit  120  ends the process in  FIG. 14  without changing the first control values. 
     On the other hand, when it is determined in step S 1116  that the aperture correction is set in an on state, the first-control-value arithmetic unit  120  determines whether or not the aperture value is set to be darker than a threshold value C (step S 1118 ). The threshold value C is set to a value smaller than the threshold value D and may be, for example, F 5 . 6 . When the aperture value is set to be brighter than or equal to the threshold value C in step S 1118 , the first-control-value arithmetic unit  120  ends the process in  FIG. 14  without changing the first control values. 
     On the other hand, when it is determined in step S 1118  that the aperture value is set to be darker than the threshold value C, the first-control-value arithmetic unit  120  sets the ultimate aperture value to a value corresponding to the threshold value C (step S 1120 ). Then, the first-control-value arithmetic unit  120  calculates an amount of change in ultimate aperture value for achieving the ultimate aperture value set in step S 1120  (step S 1108 ). 
     The amount of change in ultimate aperture value is calculated similarly to the above description based on expression (8) shown above. Similar to the above description, when the amount of change in ultimate aperture value is calculated, it is determined whether or not to correct the first gain or the first shutter speed (step S 1110 ). When a value obtained by subtracting the amount of change in ultimate aperture value ΔAV from the first gain is larger than or equal to the minimum value of the first gain, the first-control-value arithmetic unit  120  corrects the first gain to the value obtained by subtracting the amount of change in ultimate aperture value ΔAV from the first gain (step S 1112 ). On the other hand, when the value obtained by subtracting the amount of change in ultimate aperture value ΔAV from the first gain is smaller than the minimum value of the first gain, the first-control-value arithmetic unit  120  corrects the first shutter speed to a value obtained by adding the amount of change in ultimate aperture value ΔAV to the first shutter speed (step S 1114 ). 
     Accordingly, the first control values are corrected in accordance with the aperture value based on the processing flow shown in  FIG. 14 . 
     S 216 : Gain Control 
     When the first control values and the second control values are calculated, the control device  100 - 1  performs setting for gain control (step S 216 ). The first-control-value arithmetic unit  120  outputs the calculated first gain to the first-gain control unit  110  so as to update the first gain. The second-control-value arithmetic unit  122  outputs the calculated second gain to the second-gain control unit  112  so as to update the second gain. 
     S 218 : Timing Control 
     Subsequently, the control device  100 - 1  performs setting for timing control (step S 218 ). The first-control-value arithmetic unit  120  outputs the calculated first shutter speed to the first-timing control unit  114  where exposure control is performed such that the photographic pixel group  102  is exposed to light for a first exposure time. The second-control-value arithmetic unit  122  outputs the calculated second shutter speed to the second-timing control unit  116  where exposure control is performed such that the phase-difference detection pixel group  104  is exposed to light for a second exposure time. 
     S 220 : Diaphragm Control 
     Then, the control device  100 - 1  performs setting for diaphragm control (step S 220 ). The first-control-value arithmetic unit  120  outputs the set aperture value to a diaphragm drive controller (not shown) that drives the diaphragm mechanism. The diaphragm drive controller drives the diaphragm mechanism to open and close the diaphragm  14  so that the diaphragm  14  is set to the aperture value. 
     S 222 : Monitoring Ongoing-State Determination 
     Subsequently, the control device  100 - 1  determines whether monitoring is ongoing (step S 222 ). If monitoring through the LCD monitor  20  is ongoing, the control device  100 - 1  returns to step S 206  so as to repeat the process from step S 206 . If monitoring is finished, the process shown in  FIG. 5  ends. 
     The control device  100 - 1  according to this embodiment and the exposure control method performed by this control device  100 - 1  have been described above. According to this embodiment, the first control values for controlling the exposure of the photographic pixel group  102  and the second control values for controlling the exposure of the phase-difference detection pixel group  104  are set independently of each other. Thus, with regard to the photographic pixel group  102 , an image desired by the user can be acquired, and the gain and the shutter speed are set such that a sharp and smooth monitor image can be presented to the user. With regard to the phase-difference detection pixel group  104 , in order to achieve sufficient brightness for enhanced AF performance, the gain and the shutter speed are set such that the interlocking ranges thereof are wider than those for the photographic pixel group  102 . 
     4. Modifications 
     4.1. Exposure Correction by User 
     Although appropriate exposure is set in the digital camera  1  by automatically measuring the brightness of the overall picture, there may be a case where the image is not that desired by the user. In such a case, the user may perform exposure correction so that an image photographed to be brighter or darker than the appropriate exposure can be acquired. 
     In this case, if exposure correction is also performed on the phase-difference detection pixel group  104 , the AF performance may possibly deteriorate. Furthermore, if the monitor image is not appropriately maintained when ultimate control values are set based on the monitor image, proper photometry may be not performed due to principle restrictions of imager photometry, possibly making it difficult to perform control according to an exposure correction value set based on the ultimate control values. If exposure correction is to be performed by the user in the above-described control process, the exposure correction set by the user may be not applied to the phase-difference detection pixel group  104 . 
     Specifically, when the user performs exposure correction, a process is performed similarly to step S 212  described above so as to acquire second control values for the phase-difference detection pixel group  104  without applying the exposure correction thereto. Then, the first-control-value arithmetic unit  120  applies the exposure correction set by the user to the calculated second control values so as to set photographic control values for the photographic pixel group  102 . When the user performs the exposure correction in this manner, ultimate control values are set based on the control values for the phase-difference detection pixel group  104 , so that deterioration of photometric performance occurring in the related art can be prevented. Thus, constantly stable AF performance and AE performance can be achieved, regardless of the exposure correction set by the user. 
     In the case where the user performs exposure correction, instead of not applying the exposure correction to the phase-difference detection pixel group  104 , for example, the exposure correction may be applied to the phase-difference detection pixel group  104  in a range in which it is not affected by deterioration of photometric performance. 
     4.2. Calculation of Control Values Based on AF/MF Mode 
     In the exposure control method according to this embodiment, AF information is acquired as lens information in step S 208  shown in  FIG. 5 . By using the AF information, the calculation process of the first control values for the photographic pixel group  102  and the calculation process of the second control values for the phase-difference detection pixel group  104  may be switched. 
     For example, when in the autofocus mode based on the AF information, the first-control-value arithmetic unit  120  may set the aperture value based on the second control values calculated by the second-control-value arithmetic unit  122 . 
     Furthermore, when in the manual focus mode based on the AF information, the first-control-value arithmetic unit  120  may set the first gain, the first shutter speed, and the aperture value based on conditions different from those of the autofocus mode. Moreover, the second-control-value arithmetic unit  122  may set a target value for each of the values included in the second control values to a value deviated from the corresponding first control value by a predetermined amount. 
     Thus, control values suitable for the focus modes can be set. 
     5. Hardware Configuration 
     The process performed by the control device  100 - 1  according to the above-described embodiment is achieved in accordance with cooperation between software and hardware of the control device  100 - 1  to be described below. 
       FIG. 15  illustrates a hardware configuration of the control device  100 - 1  according to the embodiment of the present disclosure. As shown in  FIG. 15 , the control device  100 - 1  includes a central processing unit (CPU)  142 , a read-only memory (ROM)  144 , a random access memory (RAM)  146 , a bridge  148 , a bus  150 , an interface  152 , an input device  154 , an output device  156 , a storage device  158 , a connection port  160 , and a communication device  162 . 
     The CPU  142  functions as an arithmetic processor and a controller and realizes the operation of the setting unit  118 , the first-control-value arithmetic unit  120 , the second-control-value arithmetic unit  122 , a light control unit  130 , a selecting unit  132 , a main-light-emission-quantity arithmetic unit  134 , and a light-emission control unit  136  within the control device  100 - 1  by operating in cooperation with various kinds of programs. Alternatively, the CPU  142  may be a micro-processor. The ROM  144  stores therein, for example, a program or an arithmetic parameter to be used by the CPU  142 . The RAM  146  temporarily stores therein, for example, a program to be used in execution of the CPU  142  or a parameter that appropriately changes in the execution. The ROM  144  and the RAM  146  realize a part of the memory  124  within the control device  100 - 1 . The CPU  142 , the ROM  144 , and the RAM  146  are connected to one another by an internal bus constituted of, for example, a CPU bus. 
     The input device  154  includes, for example, an input section, such as a touch-screen, a button, a microphone, a switch, and a lever, configured to be used by a user for inputting information, and an input control circuit that generates an input signal based on input from the user and that outputs the signal to the CPU  142 . The user of the control device  100 - 1  operates the input device  154  so as to input various kinds of data to the control device  100 - 1  or to command execution of processing. 
     The output device  156  performs, for example, output to a device, such as a liquid-crystal display (LCD) device, an organic light emitting diode (OLED) device, or a lamp. Furthermore, the output device  156  may perform audio output to, for example, a speaker and a headphone. 
     The storage device  158  is a device for storing data therein. The storage device  158  may include, for example, a storage medium, a storage unit that stores data into a storage medium, a reading unit that reads data from a storage medium, and a deleting unit that deletes data stored in a storage medium. The storage device  158  stores therein a program to be executed by the CPU  142  as well as various kinds of data. 
     The communication device  160  is, for example, a bus for connecting to an external device or a peripheral device of the control device  100 - 1 . The communication device  160  may be a universal serial bus (USB). 
     The communication device  162  is, for example, a communication interface constituted of a communication unit for connecting to a network. The communication device  162  may be an infrared-communication-compliant device, a wireless local-area-network (LAN) compliant communication device, a long-term-evolution (LTE) compliant communication device, or a wired communication device that performs wired communication. 
     Although a preferred embodiment of the present disclosure has been described above in detail with reference to the appended drawings, the technical scope of the present disclosure is not limited to the above example. It should be understood by those with a general knowledge of the technical field of the present disclosure that various modifications or alterations may occur insofar as they are within the technical scope of the appended claims, and that these modifications or alterations are included in the technical scope of the present disclosure. 
     For example, although the control device  100 - 1  is included in the digital camera  1  in the above embodiment, the present technology is not limited to this example. For example, at least a part of the function included in the control device  100 - 1  may be provided in, for example, a server connected in a communicable manner to the imaging apparatus via a network. For example, in the control device  100 - 1  shown in  FIG. 4 , the functional units excluding the first-detection-value acquiring unit  106  and the second-detection-value acquiring unit  108  may be included in the server. 
     In this case, the first detection value acquired from the photographic pixel group  102  and the second detection value acquired from the phase-difference detection pixel group  104  are output to the server via the network and are gain-adjusted. Subsequently, first control values and second control values are calculated at the setting unit  118 . The calculated control values are output to the imaging apparatus, and the focusing lens  12  and the diaphragm  14  are driven based on these control values. 
     Furthermore, although the above embodiment relates to an example in which the phase-difference detection pixel group  18  is used as a second pixel group, the present technology is not limited to this example. For example, the second pixel group may be a pixel group that captures an image with a depth of field that is different from that of an image captured by the first pixel group. Specifically, micro-lenses with different focal lengths may be provided respectively for the first pixel group and the second pixel group, so that images with different depths of field can be acquired by the first pixel group and the second pixel group. Accordingly, pixel groups for various purposes can be employed as the second pixel group, so that the versatility of the second pixel group can be enhanced. 
     The advantages discussed in this specification are strictly for descriptive or exemplary purposes and are not to be limitative. In other words, in addition to or in place of the above-described advantages, the technology according to the present disclosure may exhibit other advantages that are obvious to those skilled in the art from this specification. 
     Additionally, the present technology may also be configured as below.
     (1) A control device including   

     a control unit configured to perform exposure control of a first pixel group and exposure control of a second pixel group independently of each other, the first pixel group and the second pixel group being disposed in a single imaging surface, 
     wherein the control unit controls gain or an exposure time of the first pixel group and gain or an exposure time of the second pixel group independently of each other.
     (2) The control device according to (1),   

     wherein the first pixel group is a photographic pixel group, and the second pixel group is a phase-difference detection pixel group.
     (3) The control device according to (1) or (2),   

     wherein the control unit sets at least one of an interlocking range of second gain and an interlocking range of a second exposure time of the second pixel group to be wider than an interlocking range of first gain or a first exposure time of the first pixel group.
     (4) The control device according to (3),   

     wherein the control unit sets the second gain or the second exposure time independently of an exposure mode set for an image acquired by the first pixel group.
     (5) The control device according to any one of (1) to (4),   

     wherein when an exposure correction value set by a user is input, the control unit corrects first gain or a first exposure time of the first pixel group based on the exposure correction value, and corrects only a correctable value of second gain or a second exposure time of the second pixel group based on the exposure correction value.
     (6) The control device according to any one of (3) to (5),   

     wherein the control unit corrects the second gain or the second exposure time based on a predetermined set value of a diaphragm set by a user.
     (7) The control device according to (6),   

     wherein when the set value of the diaphragm is temporarily set in a reducing direction by the user, the control unit extends the second gain or increases the second exposure time.
     (8) The control device according to any one of (1) to (7),   

     wherein the control unit sets an amount of change in first luminance and an amount of change in second luminance, the amount of change in first luminance causing first gain or a first exposure time of the first pixel group to follow a target value for the first gain or the first exposure time, the amount of change in second luminance causing second gain or a second exposure time of the second pixel group to follow a target value for the second gain or the second exposure time, and 
     wherein the amount of change in second luminance is set to be larger than the amount of change in first luminance.
     (9) The control device according to (8),   

     wherein an upper limit value is not set for the amount of change in second luminance.
     (10) The control device according to any one of (3) to (9), further including:   

     a first-gain control unit configured to perform gain control of a detection value of the first pixel group based on the first gain and to output a first detection value; 
     a second-gain control unit configured to perform gain control of a detection value of the second pixel group based on the second gain independently of the first-gain control unit and to output a second detection value; 
     a first-timing control unit configured to perform exposure control of the first pixel group based on the first exposure time; and 
     a second-timing control unit configured to perform exposure control of the second pixel group based on the second exposure time independently of the first-timing control unit, 
     wherein the control unit includes 
     a first-control-value arithmetic unit configured to calculate the first gain and the first exposure time, and 
     a second-control-value arithmetic unit configured to calculate the second gain and the second exposure time, 
     wherein the first-control-value arithmetic unit calculates the first gain, the first exposure time, and a set value of a diaphragm based on the first detection value and lens information, and 
     wherein the second-control-value arithmetic unit calculates the second gain and the second exposure time based on the second detection value and the set value of the diaphragm calculated by the first-control-value arithmetic unit.
     (11) The control device according to (10),   

     wherein the control unit calculates gain and an exposure time of the first pixel group and gain and an exposure time of the second pixel group in accordance with a focus mode included in the lens information, 
     wherein when the focus mode is an autofocus mode, the set value of the diaphragm is set based on a calculation result obtained by the second-control-value arithmetic unit, and 
     wherein when the focus mode is a manual focus mode, the first gain, the first exposure time, and the set value of the diaphragm are set based on a condition different from a condition of the autofocus mode, and target values for the second gain and the second exposure time are set to values deviated from the corresponding first gain and the corresponding first exposure time by predetermined amounts.
     (12) A control method including:   

     controlling first gain or a first exposure time of a first pixel group; and 
     controlling second gain or a second exposure time of a second pixel group independently of the first pixel group, the first pixel group and the second pixel group being disposed in a single imaging surface.
     (13) An exposure control system including:   

     a first pixel group and a second pixel group configured to be disposed in a single imaging surface; and 
     a control device having a control unit configured to perform exposure control of a first pixel group and exposure control of a second pixel group independently of each other, the control unit controlling gain or an exposure time of the first pixel group and gain or an exposure time of the second pixel group independently of each other.