Patent Publication Number: US-8121473-B2

Title: Imaging apparatus

Description:
CROSS REFERENCE TO THE RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2008-014841, filed on Jan. 25, 2008, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     The present application relates to an imaging apparatus which picks up an image of a subject to generate image data. 
     2. Description of the Related Art 
     Conventionally, various technologies with regard to exposure adjustment of an imaging apparatus have been devised. For example, in inventions of Japanese Unexamined Patent Application Publication No. 2002-84455, an output level is kept constant by switching a target value of exposure control depending on a selected gradation characteristic when a gradation conversion characteristic is switched. 
     In addition, a phenomenon has been known in which dark area gradation of image data is 100% black, totally underexposed by shooting a subject having a large difference in luminance. Therefore, in the inventions of Japanese Patent No. 2663189, gradation is compressed by increasing the gain of dark area gradation to improve blackouts thereof. 
     The inventions of Japanese Unexamined Patent Application Publication No. 2002-84455 employ a constant exposure target value that depends on the gradation conversion characteristic, regardless of a luminance pattern of a subject. Therefore, appropriate exposure adjustment cannot be performed when the optimum exposure adjustment differs in accordance with the luminance pattern of the subject, such as gradation compression of the inventions of the Japanese Patent No. 2663189. 
     SUMMARY 
     A proposition of an imaging apparatus is to perform optimum exposure adjustment and correction of dark area gradation depending on the subject. 
     In order to achieve the above-mentioned proposition, an imaging apparatus includes a photometry unit dividing a subject into a plurality of regions and performing a photometry; a first calculating unit calculating a first exposure control value based on the photometry result of the photometry unit; a comparing unit comparing the first exposure control value with a maximum value of photometry values in the plurality of regions; a second calculating unit correcting the first exposure control value depending on a comparison result by the comparing unit to calculate a second exposure control value; an image pickup unit picking up an image of the subject according to the second exposure control value and generating an image data; and a third calculating unit calculating a lightness improvement amount for a correction of dark area gradation of the image data depending on the comparison result by the comparing unit. 
     Another imaging apparatus includes a photometry unit dividing a subject into a plurality of regions and performing a photometry; a first calculating unit calculating a first exposure control value based on a photometry result of the photometry unit; a first comparing unit comparing the first exposure control value with a maximum value of photometry values in the plurality of regions; a second calculating unit correcting the first exposure control value depending on a comparison result by the first comparing unit to calculate a second exposure control value; an image pickup unit picking up an image of the subject according to the second exposure control value and generating an image data; a second comparing unit comparing the second exposure control value with a minimum value of photometry values in the plurality of regions; and a third calculating unit calculating a lightness improvement amount for a correction of dark are gradation of the image data, depending on the comparison result by the second comparing unit. 
     Another imaging apparatus includes a photometry unit dividing a subject into a plurality of regions and performing a photometry; a first calculating unit calculating a first exposure control value based on a photometry result of the photometry unit; a first comparing unit comparing the first exposure control value with a maximum value of photometry values in the plurality of regions; a second comparing unit comparing the first exposure control value with a minimum value of photometry values in the plurality of regions; a second calculating unit correcting the first exposure control value depending on a comparison result by the first comparing unit and a comparison result by the second comparing unit to calculate a second exposure control value; an image pickup unit picking up an image of the subject according to the second exposure control value and generating an image data; and a third calculating unit calculating a lightness improvement amount for a correction of dark are gradation of the image data, depending on the comparison result by the first comparing unit and the comparison result by the second comparing unit. 
     Here, the imaging apparatus may further includes a correcting unit performing a correction to improve a lightness of dark area gradation of the image data generated in the image pickup unit according to the lightness improvement amount calculated by the third calculating unit, and a recording unit recording the image data after correction by the correcting unit. 
     In addition, the third calculating unit may provide an upper limit to the lightness improvement amount depending on an imaging sensitivity of the image pickup unit. 
     In addition, the imaging apparatus may include a light emission part illuminating a subject, and a luminescence amount calculating unit calculating a luminescence amount for a luminescence by the light emission part, wherein the luminescence amount calculating unit may correct the luminescence amount depending on the lightness improvement amount calculated by the third calculating unit. 
     In addition, the third calculating unit may set the lightness improvement amount as a predefined fixed amount, depending on the shooting condition at time of shooting by the image pickup unit. 
     In addition, the photometry unit may selectively perform any of a plurality of photometry modes including at least one of a center-weighted photometry mode and a spot photometry mode, and the third calculating unit may set the lightness improvement amount as the fixed amount if any of the center-weighted photometry mode and the spot photometry mode is performed at the photometry unit at time of shooting by the image pickup unit. 
     In addition, the imaging apparatus may includes a light emission part illuminating a subject, wherein the third calculating unit may set the lightness improvement amount as the fixed amount if an illumination by the light emission part is performed at time of shooting by the image pickup unit. 
     In addition, the light emission part may selectively perform any of a plurality of luminescence modes including at least one of a daylight synchronous mode and a slow synchronous mode, and the third calculating unit may set the lightness improvement amount as the fixed amount if a luminescence mode other than the center-weighted photometry mode and the spot photometry mode is performed at the light emission part at time of shooting by the image pickup unit. 
     In addition, the photometry value used for a comparison in the first comparing unit and the photometry value used for a comparison in the second comparing unit may be photometry values acquired from different divided regions at the photometry unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a configuration of an electronic camera  1  of a first embodiment. 
         FIG. 2A  is an explanatory diagram illustrating a photometry sensor  12 . 
         FIG. 2B  is an explanatory diagram illustrating the photometry sensor  12 . 
         FIG. 3  is a functional block diagram of the electronic camera  1  of the first embodiment. 
         FIG. 4  is a flow chart illustrating the operation at the time of shooting by the electronic camera  1  of the first embodiment. 
         FIG. 5  is a flow chart illustrating the operation at the time of shooting by the electronic camera  1  of the first embodiment (continued). 
         FIG. 6  is a flow chart illustrating the operation at the time of shooting by the electronic camera  1  of the first embodiment (continued). 
         FIG. 7  is a graph showing a gain increasing function fg of gradation compression of the first embodiment. 
         FIG. 8  illustrates the characteristic of a low-pass filter. 
         FIG. 9  is a flow chart illustrating the operation at the time of shooting by the electronic camera  1  of a second embodiment. 
         FIG. 10  is a graph showing a gain increasing function fg of gradation compression of the second embodiment. 
         FIG. 11  is a flow chart illustrating the operation at the time of shooting by the electronic camera  1  of a third embodiment. 
         FIG. 12  is a graph showing a gain increasing function fg of gradation compression of the third embodiment. 
         FIG. 13A  illustrates another gain increasing function fg. 
         FIG. 13B  illustrates another gain increasing function fg. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     First Embodiment 
     In the following, a first embodiment will be described referring to the drawings. In the first embodiment, a single-lens reflex type electronic camera is used as an example of an imaging apparatus. 
       FIG. 1  illustrates a configuration of an electronic camera  1  of the first embodiment. As shown in  FIG. 1 , the electronic camera  1  includes a photographic lens  2 , an aperture diaphragm  3 , a quick return mirror  4 , a sub mirror  5 , a diffusing screen  6 , a condenser lens  7 , a pentaprism  8 , a beam splitter  9 , an eyepiece lens  10 , an imaging lens  11 , a photometry sensor  12 , a shutter  13 , an image-capturing sensor  14 , and a focus detecting part  15 . 
     The photometry sensor  12  is a 24-division photometry sensor shown in  FIG. 2A . As for photometry using the photometry sensor  12 , there is a plurality of photometry modes such as “divided photometry mode”, “center-weighted photometry mode”, and “spot photometry mode”, one of which being selectively performed. In addition, the image-capturing sensor  14  is a semiconductor device, such as, for example, a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor). The focus detecting part  15  performs phase-difference focus detection, for example, to detect the focused state of the photographic lens  2 . 
     In addition, the electronic camera  1  further includes a monitor  16  such as a liquid crystal monitor which displays an image generated by image pickup; a light emission part  17  which illuminates a subject; a light emission controlling part  18  which controls the light emission part  17 ; and a controlling part  19  which controls each part. ON/OFF setting of luminescence by the light emission part  17  may be performed manually based on the user&#39;s instruction, or may be performed automatically by the controlling part  19 . In addition, it is preferred that manual setting and automatic setting can be switched, based on the user&#39;s instruction. The controlling part  19  has a memory (not shown) provided therein, on which a program for controlling each part is recorded in advance. 
     At the time of non-shooting, that is, when shooting is not performed, the quick return mirror  4  is positioned at an angle of 45°, as shown in  FIG. 1 . Then, a light flux that passed through the photographic lens  2  and the aperture diaphragm  3  is reflected by the quick return mirror  4  and guided to the eyepiece lens  10  through the diffusing screen  6 , the condenser lens  7 , the pentaprism  8 , and the beam splitter  9 . The user confirms the image composition by viewing the subject image through the eyepiece lens  10 . On the other hand, light flux that is divided upward by the beam splitter  9 , is refocused on the image pickup plane of the photometry sensor  12  through the imaging lens  11 . In addition, the light flux that transmitted through the quick return mirror  4  is guided to the focus detecting part  15  through the sub mirror  5 . 
     At the time of shooting, on the other hand, the quick return mirror  4  is retracted to the position shown by dashed lines to open the shutter  13 , whereby the light flux from the photographic lens  2  is guided to the image-capturing sensor  14 . 
       FIG. 3  is a functional block diagram of the electronic camera  1  of the first embodiment. As shown in  FIG. 3 , in addition to the configuration of  FIG. 1 , the electronic camera  1  further includes the following parts: a timing generator  20 , a signal processing part  21 , an A/D converting part  22 , a buffer memory  23 , a bus  24 , a card interface  25 , a compression/expansion part  26 , and an image displaying part  27 . The timing generator  20  supplies an output pulse to the image-capturing sensor  14 . In addition, image data generated by the image-capturing sensor  14  is temporarily stored in the buffer memory  23  through the signal processing part  21  (including a gain adjusting part corresponding to imaging sensitivity) and the A/D converting part  22 . The buffer memory  23  is coupled to the bus  24 , to which the card interface  25 , the controlling part  19  described in  FIG. 1 , the compression/extension part  26 , and the image displaying part  27  are coupled. The card interface  25  is coupled to a detachable memory card  28  and records image data on the memory card  28 . In addition, switch members  29  (including release buttons and the like which are not shown) of the electronic camera  1 , the timing generator  20 , and the photometry sensor  12  are coupled to the controlling part  19 . Further, the image displaying part  27  displays an image or the like on the monitor  16  disposed on the back surface of the electronic camera  1 . 
     In addition, the electronic camera  1  includes a gradation non-compression mode in which dark area gradation of the image data is not corrected; and a gradation compression mode in which dark area gradation of the image data is corrected. Which mode to be used at the time of shooting is selected in advance by the user via the switch members  29 . 
     Operation of the electronic camera  1 , having the above-described configuration, at the time of shooting will be described with reference to the flow charts shown in  FIGS. 4 to 6 . 
     In Step S 1 , the controlling part  19  performs photometry calculation depending on the photometry result by the photometry sensor  12 . The photometry calculation will be described, referring to the flow chart shown in  FIG. 5 . 
     In Step S 11 , the controlling part  19  acquires the result of 24-division photometry from the photometry sensor  12 . The photometry sensor  12  performs photoelectric conversion of the incident light, and outputs the 24-division luminance values Bv [1,1] to Bv [6,4] corresponding to each of the divided regions, as shown in  FIG. 2A . 
     In Step S 12 , the controlling part  19  acquires, based on the result of 24-division photometry acquired in Step S 11 , the result of the 15-division photometry. The controlling part  19  organizes the 24-division luminance values Bv [1,1] to Bv [6,4] acquired in Step S 11  into groups of four values each, and acquires the 15-division luminance values RBv [1] to RBv [15]. The 15-division luminance values RBv [1] to RBv [15] are calculated by the following formulas 1 to 15. In addition, a part of the 15 divided regions (RBv [1], RBv [3], RBv [5], RBv [11], RBv [13], and RBv [15]) are shown in  FIG. 2B .
 
 RBv [ 1]=( Bv [ 1,1 ]+Bv [ 2,1]+ Bv [ 1,2]+ Bv [ 2,2])/4   (formula 1)
 
 RBv [ 2]=( Bv [ 2,1 ]+Bv [ 3,1]+ Bv [ 2,2]+ Bv [ 3,2])/4   (formula 2)
 
 RBv [ 3]=( Bv[ 3,1 ]+Bv[ 4,1]+ Bv[ 3,2]+ Bv [ 4,2])/4   (formula 3)
 
 RBv [ 4]=( Bv[ 4,1 ]+Bv[ 5,1]+ Bv[ 4,2]+ Bv [ 5,2])/4   (formula 4)
 
 RBv [ 5]=( Bv[ 5,1]+ Bv[ 6,1]+ Bv[ 5,2]+ Bv [ 6,2])/4   (formula 5)
 
 RBv [ 6]=( Bv[ 1,2]+ Bv[ 2,2]+ Bv[ 1,3]+ Bv [ 2,3])/4   (formula 6)
 
 RBv [ 7]=( Bv[ 2,2]+ Bv[ 3,2]+ Bv[ 2,3]+ Bv [ 3,3])/4   (formula 7)
 
 RBv [ 8]=( Bv[ 3,2]+ Bv[ 4,2]+ Bv[ 3,3]+ Bv [ 4,3])/4   (formula 8)
 
 RBv [ 9]=( Bv[ 4,2]+ Bv[ 5,2]+ Bv[ 4,3]+ Bv [ 5,3])/4   (formula 9)
 
 RBv [ 10]=( Bv[ 5,2]+ Bv[ 6,2]+ Bv[ 5,3]+ Bv [ 6,3])/4   (formula 10)
 
 RBv [ 11]=( Bv[ 1,3]+ Bv[ 2,3]+ Bv[ 1,4]+ Bv [ 2,4])/4   (formula 11)
 
 RBv [ 12]=( Bv[ 2,3]+ Bv[ 3,3]+ Bv[ 2,4]+ Bv [ 3,4])/4   (formula 12)
 
 RBv [ 13]=( Bv[ 3,3]+ Bv[ 4,3]+ Bv[ 3,4]+ Bv [ 4,4])/4   (formula 13)
 
 RBv [ 14]=( Bv[ 4,3]+ Bv[ 5,3]+ Bv[ 4,4]+ Bv [ 5,4])/4   (formula 14)
 
 RBv [ 15]=( Bv[ 5,3]+ Bv[ 6,3]+ Bv[ 5,4]+ Bv [ 6,4])/4   (formula 15)
 
     In Step S 13 , the controlling part  19  calculates, based on the photometry result acquired in Step S 11  and Step S 12 , the average luminance value BvMean, the maximum luminance value BvMax 15 , the minimum luminance value BvMin 15 , the median luminance value BvC of the 15-division luminance values RBv, and the maximum luminance value BvMax 24  of the 24-division luminance values Bv as the characteristic amount. Each value is acquired by each of the following formulas. 
                   BvMean   =       (       ∑     i   =   1     15     ⁢           ⁢     RBv   ⁡     [   i   ]         )     /   15             (     formula   ⁢           ⁢   16     )                 Bv Max15=MAX( RBv [ 1] to  RBv [ 15])   (formula 17)
 
 Bv Min15=MIN( RBv [ 1] to  RBv [ 15])   (formula 18)
 
 BvC=RBv[ 8]  (formula 19)
 
 Bv Max24=MAX( Bv [ 1,1] to  Bv [ 6,4])   (formula 20)
 
     In Step S 14 , the controlling part  19  calculates, based on each value calculated in Step S 13 , an exposure control value BvCntl 0 . The exposure control value BvCntl 0  is acquired by the next formula.
 
 BvCntl 0 =k 1 ·Bv Mean+ k 2 ·Bv Max15+ k 3 ·Bv Min15 +k 4 ·BvC+k 5   (formula 21)
 
     In formula 21, k 1  to k 4  are coefficients indicating the weight of each term. In addition, k 5  is a constant term. k 1  to k 5  are numbers depending on the average luminance value BvMean, and determined in advance so that a better image can be obtained in various sample scenes. An example of k 1  to k 5  is shown in the following Table 1. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                   
               
               
                   
                 k1 
                 k2 
                 k3 
                 k4 
                 k5 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 BvMean ≦ Bv4 
                 0.4 
                 0.1 
                 0.2 
                 0.3 
                 0.3 
               
               
                   
                 Bv4 &lt; BvMean 
                 0.2 
                 0.2 
                 0.3 
                 0.3 
                 −0.3 
               
               
                   
                   
               
            
           
         
       
     
     In Step S 15 , the controlling part  19  compares the exposure control value BvCntl 0  calculated in Step S 14  with the maximum luminance value BvMax 24  of the 24-division luminance values Bv. Using the next formula, the controlling part  19  acquires dHi, i.e. the value such that the difference between the exposure control value BvCntl 0  and the maximum luminance value BvMax 24  of the 24-division luminance values Bv exceeds a predefined value thHi.
 
 dHi=Bv Max24 −BvCntl 0 −thHi    (formula 22)
 
     In formula 22, the predefined value thHi, an amount at which the highlight part of the image is estimated to saturate, is around 2 Ev to 3Ev, for example. This predefined value thHi is chosen as the optimum value according to the saturation level of the image-capturing sensor  14  which is an image sensor, and the pixel size of the photometry sensor  12 . 
     In Step S 16 , the controlling part  19  calculates, based on the comparison result in Step S 15 , a highlight recovery amount HiRcv. The controlling part  19  finds the highlight recovery amount HiRcv using the next formula. 
     
       
         
           
             
               
                 
                   HiRcv 
                   = 
                   
                     { 
                     
                       
                         
                           0 
                         
                         
                           
                             dHi 
                             &lt; 
                             0 
                           
                         
                       
                       
                         
                           dHi 
                         
                         
                           
                             0 
                             ≦ 
                             dHi 
                             ≦ 
                             thdHi 
                           
                         
                       
                       
                         
                           thdHi 
                         
                         
                           
                             thdHi 
                             &lt; 
                             dHi 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     23 
                   
                   ) 
                 
               
             
           
         
       
     
     In formula 23, thdHi is a predefined threshold value indicating an amount at which highlight recovery is possible, depending on the size of dynamic range of the image-capturing sensor  14  which is an image sensor. 
     As shown in formula 23, the controlling part  19  clips dHi, i.e. the value acquired in Step S 15  such that the difference between the exposure control value BvCntl 0  and the maximum luminance value BvMax 24  of the 24-division luminance values Bv exceeds a predefined value thHi, in between zero and a threshold value thdHi to provide the highlight recovery amount HiRcv. 
     However, when the image-capturing sensor  14  is configured at a high ISO sensitivity, there is a risk that noise increases and a dynamic range becomes insufficient. Therefore, an upper limit may be provided on the highlight recovery amount HiRcv acquired by formula 23 to provide a relatively small correction, when the image-capturing sensor  14  is configured at high ISO sensitivity. Alternatively, the threshold value thdHi may be set smaller when the image-capturing sensor  14  is configured at high ISO sensitivity. 
     Furthermore, it may be arranged such that the predicted amount of noise occurrence at the time of shooting is detected as appropriate, and an upper limit is provided on the highlight recovery amount HiRcv, or the above-mentioned threshold value thdHi is decreased, depending on the detection result. 
     In Step S 17 , the controlling part  19  corrects, based on the highlight recovery amount HiRcv calculated in Step S 16 , the exposure control value BvCntl 0  calculated in Step S 14 . Correction of the exposure control value BvCntl 0  is performed by the next formula.
 
Exposure control value  BvCntl 1 after correction= BvCntl 0 +HiRcv    (formula 24)
 
     Here, the normal exposure control value is employed when the photometry mode is the “center-weighted photometry mode” or the “spot photometry mode”, other than the “divided photometry mode”, while using a fixed value HiRcvConst with regard to the highlight recovery amount HiRcv. 
     Having performed the photometry calculation described above, the controlling part  19  proceeds to Step S 2  of  FIG. 4 . 
     In Step S 2 , the controlling part  19  determines whether or not start of shooting is instructed by the user through the switch members  29 . The controlling part  19  repeats the photometry calculation described at Step S 1  until determining that the start of shooting is instructed and, upon determining that the start of shooting is instructed, proceeds to Step S 3 . 
     In Step S 3 , the controlling part  19  determines whether or not luminescence by the light emission part  17  is ON. Upon determining that luminescence by the light emission part  17  is ON, the controlling part  19  proceeds to Step S 4 . On the other hand, upon determining that luminescence by the light emission part  17  is not ON (luminescence by the light emission part  17  is OFF), the controlling part  19  proceeds to Step S 5  described below. 
     In Step S 4 , the controlling part  19  calculates the luminescence amount. Calculation of the luminescence amount will be described using the flow chart shown in  FIG. 6 . 
     In Step S 21 , the controlling part  19  controls the light emission controlling part  18  to perform monitor luminescence by the light emission part  17 . The luminescence amount in this occasion is a predefined small luminescence amount. 
     In Step S 22 , the controlling part  19  acquires photometry result from the photometry sensor  12 . The photometry result contains fixed light components. The photometry sensor  12  performs photoelectric conversion on the incident light and outputs 24-division luminance values Bv [1,1] to Bv [6,4] corresponding to each of the divided regions as shown in  FIG. 2A . Here, the controlling part  19  may acquire 15-division luminance values RBv [1] to RBv [15], in place of the 24-division luminance values Bv [1,1] to Bv [6,4]. 
     In Step S 23 , the controlling part  19  calculates, based on the luminance values Bv [1,1] to Bv [6,4] acquired in Step S 22 , the amount of received reflected light other than the above-mentioned fixed light components. 
     In Step S 24 , the controlling part  19  calculates, based on the amount of received reflected light calculated in Step S 23 , the luminescence amount IL in the light emission part  17 . A specific method of calculating the luminescence amount IL is similar to that of a known technology. 
     In Step S 25 , the controlling part  19  determines whether or not a gradation compression mode has been entered. Upon determining that the gradation compression mode has been entered, the controlling part  19  proceeds to Step S 26 . On the other hand, upon determining that the gradation compression mode has not been entered (gradation non-compression mode has been entered), the controlling part  19  terminates the processing of luminescence amount calculation and proceeds to Step S 5  in  FIG. 4 . 
     In Step S 26 , the controlling part  19  corrects, based on the highlight recovery amount HiRcv (see Step S 16  of  FIG. 5 ) acquired in the photometry calculation, the luminescence amount IL calculated in Step S 24 . Correction of the luminescence amount IL is performed by the next formula.
 
 IL  after correction= IL ·2 −HiRcv    (formula 25)
 
     In other words, correction to decrease the luminescence amount IL based on the highlight recovery amount HiRcv is performed by correcting, according to formula 25, the luminescence amount IL calculated in Step S 24 . 
     However, there may be a case in which an actual exposure control value is different from the exposure control value BvCntl 1  acquired by the above-mentioned photometry calculation (see Step S 17  of  FIG. 5 ) when shutter speed is automatically limited in order to prevent camera shake. Therefore, in such a case, a fixed value HiRcvConst is used in place of the highlight recovery amount HiRcv in formula 25. In addition, it is similar to cases such as limitation by camera shake, or strobe X contact point limitation by strobe speed of the light emission part  17 . 
     Having performed the luminescence amount calculation described above, the controlling part  19  proceeds to Step S 5  of  FIG. 4 . Here, if it is determined in Step S 25  that the gradation compression mode has not been entered (gradation non-compression mode has been entered), the luminescence amount IL calculated in Step S 24  is used in subsequent processings without any correction. 
     Having completed the calculation of luminescence amount, the controlling part  19  controls each part in Step S 5  to capture an image of the subject by the image-capturing sensor  14  and generate image data, based on the result of photometry calculation performed in Step S 1 . Here, the controlling part  19  controls the light emission controlling part  18  and causes the light emission part  17  to emit light in synchronization with the image capturing, if it is determined in Step S 3  that luminescence is ON. The luminescence is performed based on the result of calculation of the luminescence amount performed in Step S 4 . Then, the image data generated by the image-capturing sensor  14  is temporarily stored in the buffer memory  23  via the signal processing part  21  and A/D converting part  22 . 
     In Step S 6 , the controlling part  19  reads out image data from the buffer memory  23  to perform a normal image processing. The normal image processing includes, white balance adjustment, interpolation, hue correction, gradation conversion, or the like. Since a specific method of the processing is similar to that of known technology, description thereof is omitted. 
     In Step S 7 , the controlling part  19  determines whether or not the gradation compression mode has been entered. Upon determining that the gradation compression mode has been entered, the controlling part  19  proceeds to Step S 8 . On the other hand, upon determining that the gradation compression mode has not been entered (gradation non-compression mode has been entered), the controlling part  19  proceeds to Step S 9  described below. 
     In Step S 8 , the controlling part  19  performs gradation compression processing on the image data which has gone through the normal image processing in Step S 6 . 
       FIG. 7  is a graph showing a gain increasing function fg of gradation compression. The gain increasing function fg has a gain that depends on the luminance Y of the image, as shown in  FIG. 7 . The smaller the luminance Y becomes (the darker the neighboring range including the pixel to be processed is), the larger the gain increasing function fg will grow. On the contrary, the larger the luminance Y becomes (the lighter the neighboring range including the pixel to be processed is), the closer to one the gain increasing function fg approaches. 
     The controlling part  19  acquires, based on the highlight recovery amount HiRcv (see Step S 16  of  FIG. 5 ) acquired in the photometry calculation described above, the gain increasing function fg and increases the gain of the dark area region according to the lightness of the vicinity of pixels of interest x and y in a manner described below. 
     In  FIG. 7 , the gain increasing function fg is illustrated for cases in which the highlight recovery amount HiRcv is large and the highlight recovery amount HiRcv is small. A plurality of gain increasing functions fg may be prepared in advance, depending on the highlight recovery amount HiRcv, or only the gain increasing function fg having the largest gain increase may be prepared to calculate appropriate gain increasing function in the range between the gain increasing function fg having the largest gain increase and the gain of one. 
     In addition, when it is determined in Step S 7  that the gradation compression mode has not been entered (gradation non-compression mode has been entered), the gain increasing function fg of  FIG. 7  indicating HiRcv=0 is used if the gradation compression processing cannot be skipped due to configuration of the processing circuit within the controlling part  19 . 
     Gradation compression calculation in each of the pixels R [x,y], G [x,y], and B [x,y] is performed by the following formulas 26 to 29. 
     
       
         
           
             
               
                 
                   
                     Y 
                     ⁡ 
                     
                       [ 
                       
                         x 
                         , 
                         y 
                       
                       ] 
                     
                   
                   = 
                   
                     
                       kr 
                       · 
                       
                         R 
                         ⁡ 
                         
                           [ 
                           
                             x 
                             , 
                             y 
                           
                           ] 
                         
                       
                     
                     + 
                     
                       kg 
                       · 
                       
                         G 
                         ⁡ 
                         
                           [ 
                           
                             x 
                             , 
                             y 
                           
                           ] 
                         
                       
                     
                     + 
                     
                       kb 
                       · 
                       
                         B 
                         ⁡ 
                         
                           [ 
                           
                             x 
                             , 
                             y 
                           
                           ] 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     26 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     Rc 
                     ⁡ 
                     
                       [ 
                       
                         x 
                         , 
                         y 
                       
                       ] 
                     
                   
                   = 
                   
                     
                       
                         R 
                         ⁡ 
                         
                           [ 
                           
                             x 
                             , 
                             y 
                           
                           ] 
                         
                       
                       · 
                       fg 
                     
                     ⁢ 
                     
                       { 
                       
                         
                           ∑ 
                           
                             i 
                             = 
                             
                               - 
                               d 
                             
                           
                           d 
                         
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                             ∑ 
                             
                               j 
                               = 
                               
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                           ⁢ 
                           
                             ( 
                             
                               
                                 Y 
                                 ⁡ 
                                 
                                   [ 
                                   
                                     
                                       x 
                                       + 
                                       i 
                                     
                                     , 
                                     
                                       y 
                                       + 
                                       j 
                                     
                                   
                                   ] 
                                 
                               
                               · 
                               
                                 Lpw 
                                 ⁡ 
                                 
                                   [ 
                                   
                                     
                                       ( 
                                       
                                         
                                           i 
                                           2 
                                         
                                         + 
                                         
                                           j 
                                           2 
                                         
                                       
                                       ) 
                                     
                                     
                                       1 
                                       / 
                                       2 
                                     
                                   
                                   ] 
                                 
                               
                             
                             ) 
                           
                         
                       
                       } 
                     
                   
                 
               
               
                 
                   ( 
                   
                     formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     27 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     Gc 
                     ⁡ 
                     
                       [ 
                       
                         x 
                         , 
                         y 
                       
                       ] 
                     
                   
                   = 
                   
                     
                       
                         G 
                         ⁡ 
                         
                           [ 
                           
                             x 
                             , 
                             y 
                           
                           ] 
                         
                       
                       · 
                       fg 
                     
                     ⁢ 
                     
                       { 
                       
                         
                           ∑ 
                           
                             i 
                             = 
                             
                               - 
                               d 
                             
                           
                           d 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           
                             ∑ 
                             
                               j 
                               = 
                               
                                 - 
                                 d 
                               
                             
                             d 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             ( 
                             
                               
                                 Y 
                                 ⁡ 
                                 
                                   [ 
                                   
                                     
                                       x 
                                       + 
                                       i 
                                     
                                     , 
                                     
                                       y 
                                       + 
                                       j 
                                     
                                   
                                   ] 
                                 
                               
                               · 
                               
                                 Lpw 
                                 ⁡ 
                                 
                                   [ 
                                   
                                     
                                       ( 
                                       
                                         
                                           i 
                                           2 
                                         
                                         + 
                                         
                                           j 
                                           2 
                                         
                                       
                                       ) 
                                     
                                     
                                       1 
                                       / 
                                       2 
                                     
                                   
                                   ] 
                                 
                               
                             
                             ) 
                           
                         
                       
                       } 
                     
                   
                 
               
               
                 
                   ( 
                   
                     formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     28 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     Bc 
                     ⁡ 
                     
                       [ 
                       
                         x 
                         , 
                         y 
                       
                       ] 
                     
                   
                   = 
                   
                     
                       
                         B 
                         ⁡ 
                         
                           [ 
                           
                             x 
                             , 
                             y 
                           
                           ] 
                         
                       
                       · 
                       fg 
                     
                     ⁢ 
                     
                       { 
                       
                         
                           ∑ 
                           
                             i 
                             = 
                             
                               - 
                               d 
                             
                           
                           d 
                         
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           
                             ∑ 
                             
                               j 
                               = 
                               
                                 - 
                                 d 
                               
                             
                             d 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             ( 
                             
                               
                                 Y 
                                 ⁡ 
                                 
                                   [ 
                                   
                                     
                                       x 
                                       + 
                                       i 
                                     
                                     , 
                                     
                                       y 
                                       + 
                                       j 
                                     
                                   
                                   ] 
                                 
                               
                               · 
                               
                                 Lpw 
                                 ⁡ 
                                 
                                   [ 
                                   
                                     
                                       ( 
                                       
                                         
                                           i 
                                           2 
                                         
                                         + 
                                         
                                           j 
                                           2 
                                         
                                       
                                       ) 
                                     
                                     
                                       1 
                                       / 
                                       2 
                                     
                                   
                                   ] 
                                 
                               
                             
                             ) 
                           
                         
                       
                       } 
                     
                   
                 
               
               
                 
                   ( 
                   
                     formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     29 
                   
                   ) 
                 
               
             
           
         
       
     
     Y in formulas 26 to 29 indicates the luminance value of a pixel of interest. In addition, kr, kg and kb in formula 26 are predefined coefficients. Additionally, Lpw in formulas 27 to 29 is the low-pass filter around a pixel of interest, the low-pass filter having the characteristic shown in  FIG. 8 . Moreover, fg in formulas 27 to 29 corresponds to the above-mentioned gain increasing function fg. 
     In Step S 9 , the controlling part  19  records image data that has gone through the gradation compression processing in Step S 8 , or image data that has gone through the normal image processing in Step S 6  into the memory card  28  via the card interface  25 , and terminates the series of processings. Here, the image data may be subjected to image compression processing (JPEG compression processing or the like), if necessary, before recording the image data into the memory card  28  via the compression/expansion part  26 . 
     As thus described, according to the first embodiment, photometry is performed with the subject being divided into a plurality of regions and a first exposure control value is calculated, based on the photometry result. Then, the first exposure control value is compared with the maximum value of the photometry values in the plurality of regions, and the first exposure control value is corrected according to the comparison result to calculate a second exposure control value. Furthermore, an image of the subject is captured according to the second exposure control value to generate image data and, depending on the above-mentioned comparison result, the lightness improvement amount when correcting the dark area gradation of the image data generated by the image capturing is calculated. Therefore, exposure can be optimally adjusted depending on the subject, and the lightness improvement amount can be acquired to perform the optimum correction of the dark area gradation. 
     In addition, according to the first embodiment, lightness of dark area gradation of the image data generated by image capturing is improved according to the calculated lightness improvement amount, and the image data after correction is recorded. Therefore, dark area gradation can be optimally corrected, depending on the subject. 
     In addition, according to the first embodiment, an upper limit is provided to the above-mentioned lightness improvement amount, depending on the imaging sensitivity in the image pickup unit. Therefore, over-correction of the dark area gradation such that degradation of image quality occurs can be prevented. 
     In addition, according to the first embodiment, the electronic camera includes a light emission part which illuminates a subject and a luminescence amount calculating unit which calculates luminescence amount for luminescence by the light emission part to correct the luminescence amount calculated by the luminescence amount calculating unit, depending on the lightness improvement amount. Therefore, image capturing can be performed with the optimum luminescence amount according to correction of dark area gradation, at the time of luminescence by the light emission part. 
     In addition, according to the first embodiment, the lightness improvement amount is set as a predefined fixed amount, depending on the shooting condition at the time of shooting. Therefore, an appropriate lightness improvement amount can be acquired, depending on the shooting condition. 
     In addition, according to the first embodiment, the lightness improvement amount is provided as a fixed amount if any of the center-weighted photometry mode or the spot photometry mode is performed in photometry unit at the time of shooting. Therefore, an appropriate lightness improvement amount can be acquired, according to the photometry mode. 
     In addition, according to the first embodiment, an appropriate lightness improvement amount is provided as a fixed amount if illumination is performed by the light emission part at the time of shooting. Therefore, an appropriate lightness improvement amount can be acquired, depending on the presence or absence of luminescence by the light emission part. 
     Here, in the first embodiment, it may be arranged such that a fixed value HiRcvConst is used as the highlight recovery amount HiRcv, if luminescence ON (YES in Step S 3  of  FIG. 4 ). If, however, the luminescence mode is “daylight synchronous mode” or “slow synchronous mode”, it is preferred that the highlight recovery amount HiRcv is calculated in the above-mentioned manner. As thus described, an appropriate lightness improvement amount can be acquired according to the luminescence mode, by providing the lightness improvement amount as a fixed amount depending on presence/absence of luminescence or the luminescence mode. 
     Second Embodiment 
     In the following, a second embodiment will be described referring to the drawings. The second embodiment is a variation of the first embodiment. Additionally, in the second embodiment, only the elements that are different from the first embodiment will be described, while elements similar to those of the first embodiment will be described using similar symbols or the like as with the first embodiment. 
     The electronic camera of the second embodiment includes a similar configuration (see  FIGS. 1 to 3 ) as with the electronic camera  1  described in the first embodiment. 
     Operation of the electronic camera  1  of the second embodiment at the time of shooting is basically similar to that of the first embodiment. In the following, only the different points will be described. 
       FIG. 9  is a flow chart illustrating the operation at the time of photometry calculation. 
     Through Steps S 31  to S 37 , the controlling part  19  performs a processing similar to that in Steps S 11  to S 17  of  FIG. 5 . 
     In Step S 38 , the controlling part  19  compares the exposure control value BvCntl 1  calculated in Step S 37  with the minimum luminance value BvMin 15  of the 15-division luminance values Bv. Using the next formula, the controlling part  19  acquires dLo, i.e. the value such that the difference between the exposure control value BvCntl 1  and the minimum luminance value BvMin 15  of the 15-division luminance values Bv exceeds a predefined value thLo.
 
 dLo=BvCntl 1 −Bv Min15 −thLo    (formula 30)
 
     In formula 30, the predefined value thLo, an amount at which the shadow part of the image is estimated to be blurred, is around 2 Ev to 3 Ev, for example. The predefined value thLo is chosen as the optimum value according to the level of the image-capturing sensor  14  which is an image sensor, and the pixel size of the photometry sensor  12 . 
     In Step S 39 , the controlling part  19  calculates the shadow reproduction amount LoRcv, based on the comparison result in Step S 38 . The controlling part  19  acquires the shadow reproduction amount LoRcv using the next formula. 
     
       
         
           
             
               
                 
                   LoRcv 
                   = 
                   
                     { 
                     
                       
                         
                           0 
                         
                         
                           
                             dLo 
                             &lt; 
                             0 
                           
                         
                       
                       
                         
                           dLo 
                         
                         
                           
                             0 
                             ≦ 
                             dLo 
                             ≦ 
                             thdLo 
                           
                         
                       
                       
                         
                           thdLo 
                         
                         
                           
                             thdLo 
                             &lt; 
                             dLo 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     31 
                   
                   ) 
                 
               
             
           
         
       
     
     In formula 31, thdLo is a predefined threshold value indicating an amount at which shadow reproduction is possible, depending on the magnitude of the noise of the image-capturing sensor  14  which is an image sensor. 
     As shown in formula 31, the controlling part  19  clips dLo, i.e. the value acquired in Step S 38  such that the difference between the exposure control value BvCntl 1  and the minimum luminance value BvMin 15  of the 15-division luminance values Bv exceeds a predefined value thLo, in between zero and a threshold value thdLo to provide the shadow reproduction amount LoRcv. 
     However, when the image-capturing sensor  14  is configured at a high ISO sensitivity, there is a risk that noise increases and a dynamic range becomes insufficient. Therefore, an upper limit may be provided on the shadow reproduction amount LoRcv acquired by formula 31 to provide a relatively small correction, when the image-capturing sensor  14  is configured at high ISO sensitivity. Alternatively, the threshold value thdLo may be set smaller when the image-capturing sensor  14  is configured at high ISO sensitivity. 
     In addition, when the photometry mode is the “center-weighted photometry mode” or the “spot photometry mode”, other than the “divided photometry mode”, a fixed value LoRcvConst is used as the shadow reproduction amount LoRcv. 
     Having performed the photometry calculation described above, the controlling part  19  performs a processing that is similar to Steps S 2  and S 3  of  FIG. 4  of the first embodiment, and then performs calculation of the luminescence amount described in Step S 4  (flow chart of  FIG. 6 ). 
     In the luminescence amount calculation, the controlling part  19  performs a processing that is similar to Steps S 1  to S 25  of  FIG. 6  of the first embodiment, and subsequently performs the following processing in place of the processing of Step S 26 . 
     The controlling part  19  corrects the luminescence amount IL calculated in Step S 24 , based on the shadow reproduction amount LoRcv (see Step S 29  of  FIG. 9 ) acquired in the above-mentioned photometry calculation. Correction of the luminescence amount IL is performed by the next formula.
 
 IL  after correction= IL· 2 −LoRcv    (formula 32)
 
     In other words, correction to decrease the luminescence amount IL based on the shadow reproduction amount LoRcv is performed by correcting, according to formula 32, the luminescence amount IL calculated in Step S 24 . 
     However, there may be a case in which an actual exposure control value is different from the exposure control value BvCntl 1  acquired by the above-mentioned photometry calculation (see Step S 37  of  FIG. 9 ) when shutter speed is automatically limited in order to prevent camera shake. In such a case, therefore, a fixed value LoRcvConst is used in place of the shadow reproduction amount LoRcv in formula 32. In addition, it is similar for cases such as limitation by camera shake, or strobe X contact point limitation by strobe speed of the light emission part  17 . 
     Having performed the luminescence amount calculation described above, the controlling part  19  performs a processing similar to Steps S 5  to S 9  of  FIG. 4  of the first embodiment. 
     In the gradation compression processing of Step S 8 , however, the gain increasing function fg shown in  FIG. 10  is used in place of the gain increasing function fg shown in  FIG. 7 . 
     In  FIG. 10 , the gain increasing functions fg are shown for cases in which the shadow reproduction amount LoRcv is large and the shadow reproduction amount LoRcv is small. A plurality of gain increasing functions fg may be prepared in advance, depending on the shadow reproduction amount LoRcv, or only the gain increasing function fg having the largest gain increase may be prepared to remove steps, by appropriate interpolation, in the range between the gain increasing function fg having the largest gain increase and the gain of one. 
     In addition, if it is determined in Step S 7  that the gradation compression mode has not been entered (gradation non-compression mode has been entered), the gain increasing function fg of  FIG. 10  indicating LoRcv=0 is used if the gradation compression processing cannot be skipped due to configuration of the processing circuit within the controlling part  19 . 
     As thus described, according to the second embodiment, photometry is performed with the subject being divided into a plurality of regions and a first exposure control value is calculated, based on the photometry result. Then, the first exposure control value is compared with the maximum value of the photometry values in the plurality of regions, and the first exposure control value is corrected according to the comparison result to calculate a second exposure control value. Furthermore, an image of the subject is captured depending on the second exposure control value to generate image data. Then, the second exposure control value is compared with the minimum value of photometry values in the plurality of regions and, according to the above-mentioned comparison result, the lightness improvement amount when correcting the dark area gradation of the image data generated by image capturing is calculated. Therefore, a similar effect as that of the first embodiment can be acquired. 
     In addition, according to the second embodiment, the photometry value to be used for comparing the first exposure control value with the maximum photometry value in a plurality of regions, and the photometry value to be used for comparing the second exposure control value with the minimum photometry value in a plurality of regions are photometry values acquired from different divided regions in the photometry unit. Therefore, a processing can be implemented assuming 100% white, totally overexposed in relatively narrow regions, whereas a processing can be implemented assuming 100% black, totally underexposed in a relatively wide regions. 
     Third Embodiment 
     In the following, a third embodiment will be described, referring to the drawings. The third embodiment is a variation of the first embodiment. Additionally, in the third embodiment, only the elements that are different from the first embodiment are described, while elements similar to those of the first embodiment will be described using similar symbols or the like as with the first embodiment. 
     The electronic camera of the third embodiment includes a similar configuration (see  FIGS. 1 to 3 ) as with the electronic camera  1  described in the first embodiment. 
     Operation of the electronic camera  1  of the third embodiment a the time of shooting is basically similar to that of the first embodiment. In the following, only the different points will be described. 
       FIG. 11  is a flow chart illustrating the operation at the time of photometry calculation. 
     Through Steps S 41  to S 45 , the controlling part  19  performs a processing similar to that in Steps S 11  to S 17  of  FIG. 5 . 
     In Step S 46 , the controlling part  19  compares the exposure control value BvCntl 0  calculated in Step S 44  with the minimum luminance value BvMin 15  of the 15-division luminance values Bv. Using the next formula, the controlling part  19  acquires dLo, i.e. the value such that the difference between the exposure control value BvCntl 0  and the minimum luminance value BvMin 15  of the 15-division luminance values Bv exceeds a predefined value thLo.
 
 dLo=BvCntl 1 −Bv Min15 −thLo    (formula 33)
 
     In formula 33, the predefined value thLo, an amount at which the shadow part of the image is estimated to be blurred, is around 2 Ev to 3 Ev, for example. The predefined value thLo is chosen as the optimum value according to the level of the image-capturing sensor  14  which is an image sensor, and the pixel size of the photometry sensor  12 . 
     In Step S 47 , the controlling part  19  calculates the dynamic range expansion amount DrRcv, based on the comparison result in Step S 46 . The controlling part  19  first compares dHi acquired in Step S 45  with dLo acquired in Step S 46  and sets the larger one as dDr. 
     Then, using the dDr, the controlling part  19  acquires the dynamic range expansion amount by the next formula. 
     
       
         
           
             
               
                 
                   DrRcv 
                   = 
                   
                     { 
                     
                       
                         
                           0 
                         
                         
                           
                             dDr 
                             &lt; 
                             0 
                           
                         
                       
                       
                         
                           dDr 
                         
                         
                           
                             0 
                             ≦ 
                             dDr 
                             ≦ 
                             thdDr 
                           
                         
                       
                       
                         
                           thdDr 
                         
                         
                           
                             thdDr 
                             &lt; 
                             dDr 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     formula 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     34 
                   
                   ) 
                 
               
             
           
         
       
     
     In formula 34, thdDr is a predefined threshold value indicating an amount which dynamic range expansion is possible, depending on the magnitude of the dynamic range of the image-capturing sensor  14  which is an image sensor. 
     As shown in formula 34, the controlling part  19  clips dDr, i.e. the value mentioned above in between zero and the threshold value thdDr to provide the dynamic range expansion amount DrRcv. 
     However, when the image-capturing sensor  14  is configured at a high ISO sensitivity, there is a risk that noise increases and a dynamic range becomes insufficient. Therefore, an upper limit may be provided on the dynamic range expansion amount DrRcv acquired by formula 34 to provide a relatively small correction, when the image-capturing sensor  14  is configured at high ISO sensitivity. Alternatively, the threshold value thdDr may be set smaller when the image-capturing sensor  14  is configured at high ISO sensitivity. 
     In addition, when the photometry mode is the “center-weighted photometry mode” or the “spot photometry mode”, other than the “divided photometry mode”, a fixed value DrRcvConst is used as the dynamic range expansion amount DrRcv. 
     In Step S 48 , the controlling part  19  corrects, based on the dynamic range expansion amount DrRcv calculated in Step S 47 , the exposure control value BvCntl 0  calculated in Step S 44 . Correction of the exposure control value BvCntl 0  is performed by the next formula.
 
Exposure control value  BvCntl 1 after correction= BvCntl 0 +DrRcv    (formula 35)
 
     However, when the photometry mode is the “center-weighted photometry mode” or the “spot photometry mode”, other than the “divided photometry mode”, a normal exposure control value is employed and a fixed value DrRcvConst is used as the dynamic range expansion amount DrRcv. 
     Having performed the photometry calculation described above, the controlling part  19  performs a processing that is similar to Steps S 2  and S 3  of  FIG. 4  of the first embodiment, then performs calculation of the luminescence amount described in Step S 4  (flow chart of  FIG. 6 ). 
     In the luminescence amount calculation, the controlling part  19  performs a processing that is similar to Steps S 1  to S 25  of  FIG. 6  of the first embodiment, and subsequently performs the following processing in place of the processing of Step S 26 . 
     The controlling part  19  corrects the luminescence amount IL calculated in Step S 24 , based on the dynamic range expansion amount DrRcv (see Step S 47  of  FIG. 10 ) acquired in the above-mentioned photometry calculation. Correction of the luminescence amount IL is performed by the next formula.
 
 IL  after correction= IL· 2 −DrRcv    (formula 36)
 
     In other words, correction to decrease the luminescence amount IL based on the dynamic range expansion amount DrRcv is performed by correcting, according to formula 36, the luminescence amount IL calculated in Step S 24 . 
     However, there may be a case in which an actual exposure control value is different from the exposure control value BvCntl 1  acquired by the above-mentioned photometry calculation (see Step S 48  of  FIG. 10 ) when shutter speed is automatically limited in order to prevent camera shake. Therefore, in such a case, a fixed value DrRcvConst is used in place of the dynamic range expansion amount DrRcv in formula 32. In addition, it is similar for cases such as limitation by camera shake, or strobe X contact point limitation by strobe speed of the light emission part  17 . 
     Having performed the luminescence amount calculation described above, the controlling part  19  performs a processing that is similar to Steps S 5  to S 9  of  FIG. 4  of the first embodiment. 
     In the gradation compression processing of Step S 8 , however, the gain increasing function fg shown in  FIG. 10  is used in place of the gain increasing function fg shown in  FIG. 7 . 
     In  FIG. 12 , the gain increasing functions fg are illustrate for cases in which the dynamic range expansion amount DrRcv is large and the dynamic range expansion amount DrRcv is small. A plurality of gain increasing functions fg may be prepared in advance, depending on the dynamic range expansion amount DrRcv, or only the gain increasing function fg having the largest gain increase may be prepared to remove steps, by appropriate interpolation, in the range between the gain increasing function fg having the largest gain increase and the gain of one. 
     In addition, when it is determined in Step S 7  that the gradation compression mode has not been entered (gradation non-compression mode has been entered), the gain increasing function fg of  FIG. 12  indicating DrRcv=0 is used if the gradation compression processing cannot be skipped due to configuration of the processing circuit within the controlling part  19 . 
     As thus described, according to the third embodiment, photometry is performed with the subject being divided into a plurality of regions and a first exposure control value is calculated, based on the photometry result. Then, the first exposure control value is compared with the maximum value of the photometry values in the plurality of regions, and the first exposure control value is compared with the minimum value of photometry values in the plurality of regions. Furthermore, the first exposure control value is corrected to calculate a second exposure control value, according to the two comparison results, and an image of the subject is captured according to the second exposure control value to generate image data. Then, depending on the above-mentioned two comparison results, the lightness improvement amount when correcting the dark area gradation of the image data generated by image capturing is calculated. Therefore, a similar effect as that of the first embodiment can be acquired. 
     In addition, according to the third embodiment, the photometry value to be used for comparing the first exposure control value with the maximum photometry in a plurality of regions, and the photometry value to be used for comparing the second exposure control value with the minimum photometry value in a plurality of regions are photometry values acquired from different divided regions in the photometry unit. Therefore, a processing can be implemented assuming 100% white, totally overexposed in relatively narrow regions. whereas a processing can be implemented assuming 100% black, totally underexposed in a relatively wide regions. 
     Here, in the third embodiment, it may be arranged such that different gain increasing functions fg are used for the case in which dHi acquired in Step S 45  is larger and the case in which dLo acquired in Step S 46  is larger, when acquiring the dynamic range expansion amount DrRcv in Step S 47  of the flow chart of  FIG. 11 . For example, it may be arranged such that a gain increasing function fg having a different trend along the horizontal axis is used as shown in  FIG. 13A , or a gain increasing function fg having a different trend along the vertical axis is used as shown in  FIG. 13B . 
     Additionally, in the second and third embodiments, the threshold value thdLo relating to the highlighted side, and the threshold value thdHi relating to the shadow side does not necessarily have to be the same. For example, the threshold value thdLo relating to the highlighted side may be set somewhat larger than the threshold value thdHi relating to the shadow side. 
     Additionally, in each of the above-mentioned embodiments, although 24-division photometry sensors shown in  FIG. 2  have been presented in the description as an example of the photometry sensor  12 , the present application is not limited to this example. For example, in each of the above-mentioned embodiments, although an example of switching the number of divisions to between 24 and 15 has been presented, a fixed number of divisions may also suffice. Additionally, in each of the above-mentioned embodiments, although an example of dividing the region evenly has been presented, the region may be divided unevenly. For example, sensitivity with regard to the central portion may be increased by dividing the vicinity of the center into relatively narrow regions, while dividing the peripheral area into relatively wide regions. 
     Additionally, in each of the above-mentioned embodiments, an example of realizing the technology of the present application in the electronic camera  1  has been described. However, the present application is by no means limited to this example. For example, the present application can also be applied to a compact type electronic camera or a movie camera that picks up motion pictures. 
     In addition, the image processing described in each of the above-mentioned embodiments may be implemented as software by a computer and an image processing program. In this case, a part or all of the processing of the flow chart described in each of the above-mentioned embodiments may be implemented with a computer. In order to implement the processing with a computer, it suffices to provide the computer with information indicating whether or not the gradation compression mode has been entered or information indicating the gradation compression amount is provided, together with image data. Such information can be provided using EXIF information of image data or the like. By such an arrangement, it becomes possible to perform a processing similar to those in each of the above-mentioned embodiments. 
     The many features and advantages of the embodiments are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the embodiments that fall within the true spirit and scope thereof. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the inventive embodiments to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope thereof.