Patent Publication Number: US-9420181-B2

Title: Electronic camera, computer readable medium recording imaging control program thereon and imaging control method

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a Divisional application of parent application Ser. No. 13/659,013, filed Oct. 24, 2012, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2011-241309, filed Nov. 2, 2011; the entire contents of (all of) which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electronic camera for imaging an object and recording the shot object as a still image, and also relates to a computer readable medium recording an imaging control program thereon and an imaging control method. 
     2. Description of the Related Art 
     The shake correction methods having been applied in cameras are roughly classified into the optical shake correction and the electronic shake correction. The optical shake correction relates to a method of driving a part of an optical system by using an actuator. On the other hand, as the electronic shake correction, there is known a method in which a plurality of continuous images are shot and the corresponding pixels of the respective shot images are added to each other (see JP-A-2001-230965, for example). 
     In the method of adding the pixels of the plurality of continuous shot images, there arises a disadvantage that, depending on the imaging condition, noise is generated at the time of adding the plurality of images. When the imaging is performed under the condition requiring the shake correction, the pixel addition of the plurality of continuous shot images acts as an effective shake correction means. However, when the similar pixel addition is executed in the case where the imaging is performed under the condition of not requiring the shake correction, useless degradation of image quality is caused due to the aforesaid disadvantage. 
     In the aforesaid related art, since the shake correction is executed without determining whether or not the shake correction is necessary, the useless degradation of image quality is caused inevitably. 
     SUMMARY OF THE INVENTION 
     The first mode of an electronic camera according to this invention includes an optical system, an imaging unit, a first imaging processing unit, a second imaging processing unit, a control unit and a zoom detection unit. The optical system has a zoom function and provides an image of an object. The imaging unit performs an exposure to take the image of the object and obtains image data of the object. The first imaging processing unit exposes the imaging unit once with a suitable exposure time being set and outputs the obtained image data. The second imaging processing unit exposes the imaging unit for plural times continuously each with an exposure time which is shorter than the set suitable exposure time and executes an addition processing of adding respective image data obtained sequentially for the plural times of exposures. The control unit operates one of the first imaging processing unit and the second imaging processing unit in accordance with a circumstance at a time of imaging. The zoom detection unit detects a zoom value of the optical system. The control unit makes operable only the first imaging processing unit when the detected zoom value is equal to or smaller than a predetermined reference value. The control unit makes selectively operable one of the first imaging processing unit and the second imaging processing unit when the detected zoom value is larger than the predetermined reference value. 
     The second mode of an electronic camera according to this invention includes an optical system, an imaging unit, a first imaging processing unit, a second imaging processing unit, a parameter detection unit, a memory unit and a control unit. The optical system provides an image of an object. The imaging unit performs an exposure to take the image of the object and obtains image data of the object. The first imaging processing unit exposes the imaging unit once with a suitable exposure time being set and outputs the obtained image data. The second imaging processing unit exposes the imaging unit for plural times continuously each with an exposure time which is shorter than the set suitable exposure time and executes an addition processing of adding respective image data obtained sequentially for the plural times of exposures. The parameter detection unit detects at least two kinds of parameters relating to the image of the object. The memory unit stores a table which is configured by a coordinate plane defined by one parameter axis representing parameter values of one of the at least two kinds of parameters and another parameter axis representing parameter values of another of the at least two kinds of parameters. The coordinate plane is divided by a slanted boundary line into a single imaging area for operating the first imaging processing unit and a continuous imaging area for operating the second imaging processing unit. The control unit determines whether a coordinate position is in the single imaging area or in the continuous imaging area and operates one of the first imaging processing unit and the second imaging processing unit in accordance with a determination of the control unit. The coordinate position in the table corresponds to a value of the one kind of parameter and another value of the said another kind of parameter detected by the parameter detection unit. 
     The first mode of a non-transitory computer readable medium according to this invention stores a program causing a computer to execute an imaging control process. The computer includes an optical system, an imaging unit and a zoom detection unit. The optical system has a zoom function and provides an image of an object. The imaging unit performs an exposure to take the image of the object and obtains image data of the object. The zoom detection unit detects a zoom value of the optical system. The imaging control process includes: first imaging processing to expose the imaging unit once with a suitable exposure time being set to thereby output the obtained image data; second imaging processing to expose the imaging unit for plural times continuously each with an exposure time which is shorter than the set suitable exposure time to thereby execute an addition processing of adding respective image data obtained sequentially for the plural times of exposures; and operating one of the first imaging processing and the second imaging processing in accordance with a circumstance at a time of imaging; operating only the first imaging processing when the detected zoom value is equal to or smaller than a predetermined reference value, and operating one of the first imaging processing and the second imaging processing when the detected zoom value is larger than the predetermined reference value. 
     The second mode of a non-transitory computer readable medium according to this invention stores a program causing a computer to execute an imaging control process. The computer includes an optical system, an imaging unit and a memory unit. The optical system provides an image of an object. The imaging unit performs an exposure to take the image of the object and obtains image data of the object. The memory unit stores a table which is configured by a coordinate plane defined by axes respectively representing at least two kinds of parameters relating to the image of the object. The coordinate plane is divided by a slanted boundary line into a single imaging area and a continuous imaging area. The imaging control process includes: first imaging processing to expose the imaging unit once with a suitable exposure time being set to thereby output the obtained image data; second imaging processing to expose the imaging unit for plural times continuously each with an exposure time which is shorter than the set suitable exposure time and to thereby execute an addition processing of adding respective image data obtained sequentially for the plural times of exposures; detecting parameters relating to the respective axes of the table; determining whether a coordinate position is in the single imaging area or in the continuous imaging area, the coordinate position in the table corresponding to the detected values of the respective parameters; and operating one of the first imaging processing and the second imaging processing in accordance with the determining. 
     The first mode of a imaging control method according to this invention is for a imaging apparatus. The imaging apparatus includes an optical system, an imaging unit and a zoom detection unit. The optical system has a zoom function and provides an image of an object. The imaging unit performs an exposure to take the image of the object and obtains image data of the object. The zoom detection unit detects a zoom value of the optical system. The imaging control method includes: first imaging processing to expose the imaging unit once with a suitable exposure time being set to thereby output the obtained image data; second imaging processing to expose the imaging unit for plural times continuously each with an exposure time which is shorter than the set suitable exposure time to thereby execute an addition processing of adding respective image data obtained sequentially for the plural times of exposures; operating one of the first imaging processing and the second imaging processing in accordance with a circumstance at a time of imaging; operating only the first imaging processing when the detected zoom value is equal to or smaller than a predetermined reference value; and operating one of the first imaging processing and the second imaging processing when the detected zoom value is larger than the predetermined reference value. 
     The second mode of a imaging control method according to this invention is for a imaging apparatus. The imaging apparatus includes an optical system, an imaging unit and a memory unit. The optical system provides an image of an object. The imaging unit performs an exposure to take the image of the object and obtains image data of the object. The memory unit stores a table which is configured by a coordinate plane defined by axes respectively representing at least two kinds of parameters relating to the image of the object. The coordinate plane is divided by a slanted boundary line into a single imaging area and a continuous imaging area. The imaging control method includes: first imaging processing to expose the imaging unit once with a suitable exposure time being set to thereby output the obtained image data; second imaging processing to expose the imaging unit for plural times continuously each with an exposure time which is shorter than the set suitable exposure time and to thereby execute an addition processing of adding respective image data obtained sequentially for the plural times of exposures; detecting parameters relating to the respective axes of the table; determining whether a coordinate position is in the single imaging area or in the continuous imaging area, the coordinate position in the table corresponding to the detected values of the respective parameters; and operating one of the first imaging processing and the second imaging processing in accordance with the determining. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing the circuit configuration of a digital camera according to an embodiment of this invention. 
         FIG. 2  is an explanatory diagram showing the summary of a two-dimensional table in this embodiment. 
         FIG. 3  is a flowchart showing the processing procedure of this embodiment. 
         FIG. 4  is a flowchart showing the procedure of a shake correction ON/OFF determination processing. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, an embodiment of this invention will be explained with reference to drawings.  FIG. 1  is a block diagram showing the circuit configuration of a digital camera  1  according to the embodiment. The digital camera  1  includes a control circuit  102 . The control circuit  102  is provided with a CPU  103 , and is further provided with an interface  105 , an input circuit  107 , a memory card•IF  108  and input/output ports  112 ,  113  each of which is coupled to the CPU  103  via a data bus  104 . An operation input unit  122 , provided with various kinds of operation keys such as a shutter button and a zoom key and a power supply switch etc., is coupled to the input circuit  107 . An image memory medium  125  provided so as to be detachable freely is coupled to the memory card•IF  108 . The shutter button has a half shutter function capable of performing a half-pressing and a full-pressing. 
     To the input/output port  112 , a focus lens driving unit  132 , a zoom lens driving unit  133 , a stop driving unit  135  and a shutter driving unit  136  are coupled, and a strobe  137  is coupled via a strobe driving circuit  138 , and further a photometric/ranging sensor  139  is connected via a detecting circuit  140 . To the input/output port  113 , an angular velocity sensor (Y/Pitch)  141  for detecting the shake in the elevational direction of the digital camera  1  and an angular velocity sensor (X/Yaw)  143  for detecting the shake in the transversal direction are coupled via detecting circuits  142 ,  144 , respectively. 
     A battery  145  is coupled to the control circuit  102  via a power supply control unit  146 . The power supply control unit  146  supplies electric power supplied from the battery  145  to the respective units under the control of the control circuit  102 . Further, a program memory  123  and a data memory  124  are coupled to the data bus  104 . The program memory  123  stores a program for controlling the control circuit  102  so as to perform the operation shown in a flow chart described later. The data memory  124  stores various kinds of data in advance and also stores data other than image data. 
     On the other hand, an imaging device  157  is disposed on an optical axis on the rear side of an imaging optical system  156  including a zoom lens. Within the imaging optical system  156 , a stop  158  driven by the stop driving unit  135  and a shutter  159  driven by the shutter driving unit  136  are disposed. The focus lens driving unit  132  drives a focus lens within the imaging optical system  156 , and the zoom lens driving unit  133  is configured to be controlled in accordance with the operation of the zoom key provided at the operation input unit  122  so as to drive the zoom lens. 
     The imaging device  157  can perform the high-speed reading such as the parallel reading and includes an image sensor unit  160 , a horizontal scanning unit  161 , a vertical scanning unit  162  and a parallel/serial (P/S) conversion unit  163 . A digital signal processor (DSP) unit  164  is coupled to the imaging device  157 . The DSP unit  164  includes a serial/parallel (S/P) conversion unit  165  for processing an image signal taken from the P/S conversion unit  163  of the imaging device  157 , a buffer memory (A)  166 , a multi-plane adding unit  167 , a color interpolation unit  168 , a gradation conversion unit  169 , a gamma correction unit  170 , a matrix  171 , a resolution conversion unit  172 . The DSP unit  164  further includes a controller  173  for controlling the period of the vertical scanning unit  162 , an image feature extraction processing/image recognition processing unit  174  and a photometric processing/auto-focus (AF) detection/automatic white-balance (WB) etc. processing unit  175 . 
     Each of the resolution conversion unit  172 , the image feature extraction processing/image recognition processing unit  174  and the photometric processing/AF detection/automatic WB etc. processing unit  175  is coupled to a buffer memory (B)  177 , an image coder and decoder (CODEC)  178  and a display driving circuit  180  via an image data bus  176 . The image data bus  176  is coupled to the interface  105  of the control circuit  102 . The buffer memory (B)  177  temporarily stores image data used when the image CODEC  178  performs the coding/decoding processing. The display driving circuit  180  drives a display unit  181 . 
       FIG. 2  is an explanatory diagram showing the summary of a two-dimensional table  2  stored in advance in the data memory  124 . As the abscissa of the two-dimensional table  2 , the degree of luminance detected by the photometric/ranging sensor  139  and the detecting circuit  140 , that is, the degree of luminance of the image of a shot object imaged on the imaging device  157  by the imaging optical system  156  is set, whilst a zoom value is set as the ordinate. As additionally described in the abscissa, the shutter speed is set to be lower as the degree of the luminance becomes lower and set to be higher as the degree of the luminance becomes higher. 
     A critical line  3  is set within a two-dimensional coordinate plane in which these degrees of luminance and the zoom values are set. The coordinate plane is divided into a continuous imaging area  4  and a single imaging area  5  by the critical line  3 . The critical line  3  may include a boundary line. The continuous imaging area  4  is defined as an area that a shake correction flag is determined to be set (ON) when a coordinate position corresponding to the combination of the degree of luminance and the zoom value belongs to the continuous imaging area  4 . In contrast, the single imaging area  5  is defined as an area that the shake correction flag is determined to be reset (OFF) when a coordinate position corresponding to the combination of the degree of luminance and the zoom value belongs to the single imaging area  5 . As shown in  FIG. 2 , the critical line  3  is provided in a stepwise manner at positions where increase and decrease of parameter values of the abscissa change in accordance with changes of increase and decrease of parameter value of the ordinate. 
     That is, as shown in the figure, supposing a point Pa where the degree of luminance is “x 1 ” and the zoom value is “y 1 ” and a point Pb where the degree of luminance is “x 2 ” and the zoom value is the same value of “y 1 ”, the point Pa (x 1 , y 1 ) belongs to the continuous imaging area  4 . However, as to the point Pb (x 2 , y 1 ), although the zoom value is the same value of y 1 , the degree of luminous is higher, so that this point belongs to the single imaging area  5 . Further, as shown in the figure, supposing a point Pc where the degree of luminance is “x 3 ” and the zoom value is “y 3 ” and a point Pd where the degree of luminance is the same value of “x 3 ” and the zoom value is a different value of “y 4 ”, the point Pc (x 3 , y 3 ) belongs to the continuous imaging area  4 . However, as to the point Pd (x 3 , y 4 ), although the degree of luminous is the same degree of x 3 , the zoom value is smaller, so that this point belongs to the single imaging area  5 . 
     Thus, this two-dimensional table  2  has the characteristics that coordinate position within this table is determined to belong to the continuous imaging area  4  according to the increase of the zoom value thereof and also according to the reduction of the degree of luminance thereof (that is, according to the increase of provability of shake occurrence thereof), whilst determined to belong to the single imaging area  5  according to the reduction of the zoom value thereof and also according to the increase of the degree of luminance thereof (that is, according to the reduction of provability of shake occurrence thereof) 
       FIG. 3  is a flowchart showing the processing procedure of this embodiment. When the power supply switch provided in the operation input unit  122  is turned on, the control circuit  102  having the CPU  103  operates and executes the processing as shown in this flowchart based on the program stored in the program memory  123 . This control circuit  102  operates as a first imaging processing unit, a second imaging processing unit, a zoom detection unit, an operation detection unit and a parameter detection unit. First, the control circuit executes an initializing processing to thereby clear the contents of the buffer memories  166 ,  167  etc. (step S 1 ). Next, the control circuit executes an automatic exposure (AE) processing to thereby obtain the degrees of luminance detected by the photometric/ranging sensor  139  and the detecting circuit  140  (step S 2 ), and displays the live-view image of a shot object on the display unit  181  (step S 3 ). 
     Then, the control circuit executes a zooming processing to thereby control the zoom lens driving unit  133  so as to drive the zoom lens in accordance with the operation of zoom key provided at the operation input unit  122  (step S 4 ). Further, the control circuit executes other processings. That is, the control circuit executes a processing of determining whether or not the strobe  137  is to be operated at the time of imaging based on the degree of luminance obtained in the step S 2 , and further execute a processing of obtaining the detected values of the angular velocity sensor (Y/Pitch)  141  and the angular velocity sensor (X/Yaw)  143  inputted via the detecting circuits  142 ,  144 , respectively, and so on (step S 5 ). Succeedingly, the control circuit executes a shake correction ON/OFF determination processing (step S 6 ). 
       FIG. 4  is a flowchart showing the details of this shake correction ON/OFF determination processing (step S 6 ). That is, it is determined whether or not the turning-on of the strobe  137  upon imaging is decided in the other processings of the step S 5  (step S 601 ). In the case of performing a imaging under the turning-on state of the strobe  137 , since the sufficient degree of luminance is secured and the shutter speed is high, the provability of shake occurrence is low. Thus, in the case where the turning-on of the strobe  137  upon imaging is decided (YES in step S 601 ), the shake correction flag representing the execution of the shake correction is reset (step S 607 ). Further, as described later, the control circuit eliminates an advance notice that “a multiplane addition composition imaging is performed” displayed on the display unit  181  (step S 608 ). 
     However, in the case where the turning-off of the strobe  137  upon imaging is decided (NO in step S 601 ) as a result of the determination in the step S 601 , since the shutter speed is low, the provability of shake occurrence is high. Thus, it is further determined whether or not a imaging of the digital cameral  1  is performed by using a tripod stand (step S 602 ). To be concrete, it is determined that the tripod stand is used when the detected values of the angular velocity sensor (Y/Pitch)  141  and the angular velocity sensor (X/Yaw)  143  each obtained in the other processings of the step S 5  are lower than predetermined values, respectively. In contrast, it is determined that a user performs a imaging by holding this digital camera  1  by hands when at least one of the detected values of the angular velocity sensor (Y/Pitch)  141  and the angular velocity sensor (X/Yaw)  143  is equal to or larger than the predetermined value thereof. When it is determined that the tripod stand is used, since the provability of shake occurrence is low, the processings of the aforesaid steps S 607  and S 608  are executed. 
     In contrast, when it is determined that the tripod stand is not used as a result of the determination in the step S 602 , since the provability of shake occurrence is high, it is determined whether or not the zoom lens is driven to a position other than the position of the zoom value (zoom)=0 (wide end) in  FIG. 2  by the zooming processing in the aforesaid step S 4  (step S 603 ). When the zoom value (zoom) is 0 (wide end) and hence the digital camera is not in a zoom mode (NO in the step S 603 ), since the provability of shake occurrence is low, the processings of the aforesaid steps S 607  and S 608  are executed. 
     When the zoom value (zoom) is not 0 (not at the wide end) and hence the digital camera is in a zoom mode (YES in the step S 603 ), since the provability of shake occurrence is high, it is further determined whether or not the coordinate of a cross point between the zoom value and the luminance degree locates in the continuous imaging area  4  (step S 604 ). In other words, the two-dimensional table  2  shown in  FIG. 2  is referred by using the luminance degree obtained in the step S 2  and the zoom value obtained in the step S 4 . Then, it is determined whether or not the cross point coordinate between the zoom value and the luminance degree locates in the continuous imaging area  4  in the two-dimensional table  2 . 
     As a result of this determination, like the cross point coordinate Pb (x 2 , y 1 ) or Pd (x 3 , y 4 ) exemplarily shown in  FIG. 2 , when the cross point coordinate belongs to the single imaging area  5  (NO in step S 604 ), since the provability of shake occurrence is low, the processings of the aforesaid steps S 607  and S 608  are executed. 
     In contrast, like the cross point coordinate Pa (x 1 , y 1 ) or Pc (x 3 , y 3 ), when the cross point coordinate belongs to the continuous imaging area  4  (YES in step S 604 ), since the shake occurs surely, the shake correction flag representing the execution of the shake correction is set (step S 605 ). 
     In this manner, according to this invention, since the determination as to whether or not the shake correction is to be executed is performed by using the two-dimensional table  2  stored in advance, this determination can be made surely, quickly and simply. 
     Succeedingly, the control circuit displays the advance notice that “multiplane addition composition imaging is performed” on the display unit  181  (step S 606 ). Thus, at the time of performing a imaging by fully pressing the shutter button, since a user can visually recognize the existence or non-existence of the advance notice that “multiplane addition composition imaging is performed” on the display unit  181 , the user can perform a imaging while usually recognizing in advance whether the multiplane addition composition imaging is performed or the normal imaging is performed. 
     On the other hand, in the flowchart of  FIG. 3 , in a step S 7  succeeding to the shake correction ON/OFF determination processing (step S 6 ), the state of the shutter button is detected. When the shutter button is in an OFF state without being pressed, the processings is repeated from the step S 2 . On the other hand, when the shutter button is pressed halfway, an AF processing is executed to thereby drive the focus lens within the imaging optical system  156  by the focus lens driving unit  132  (step S 8 ). Thus, a live-view image in a focused state is displayed on the display unit  181 . Further, a stop value and the shutter speed are determined based on the detected degree of luminance (step S 9 ), and the processings is repeated from the step S 2 . 
     Thus, in the state where the shutter button is not pressed or the shutter button is pressed halfway, that is, until the imaging operation is performed by fully pressing the shutter button, the shake correction ON/OFF determination processing (step S 6 ) is repeatedly executed. That is, the determination whether or not the shake correction is to be performed (whether or not the multiplane addition composition imaging is to be performed) is made in advance before the start of a imaging while updating the determination. Accordingly, as compared with the case where the determination whether or not the shake correction is to be performed (whether or not the multiplane addition composition imaging is to be performed) is made at the time of a imaging after executing the imaging operation by fully pressing the shutter, the processing at the time of a imaging can be simplified. Therefore, the processing at the time of a imaging can be performed quickly. As a result, since the next imaging can also be performed quickly, a imaging can be performed continuously without missing a shot. 
     When the imaging operation is performed by fully pressing the shutter button, the CPU  103  proceeds the processing to a step S 10  from the step S 7  to thereby determine whether or not the shake correction flag is set. As a result of this determination, when the shake correction flag is not set but reset, the normal imaging is executed (step S 11 ). 
     That is, the stop driving circuit  135  drives the stop  158  so as to be the stop value determined by the step S 9 . Similarly, the shutter driving circuit  136  drives the shutter  159  once so as to be the shutter speed determined by the step S 9  to thereby perform a single imaging. Image data obtained by this single imaging is compressed and encoded to obtain a shot image, and this shot image is stored in the image memory medium  125 . 
     Thus, the multiplane addition composition imaging is not performed uselessly under the imaging condition where the provability of shake occurrence is low. As a result, since the multiplane addition composition imaging is not performed without inevitability, it is possible to avoid a disadvantage that a useless addition processing is executed to thereby generate noise in a shot image stored in the image memory medium  125 . 
     Further, when it is determined that the shake correction flag is set as the result of the determination performed in the step S 10 , the multiplane addition composition imaging is executed (step S 12 ). That is, each of the imaging device  157  and the DSP unit  164  is set in a continuous imaging mode and a multiplane addition mode to thereby determine the shutter speed again based on the shutter speed determined in the step S 9 . To be more concrete, supposing that the shutter speed determined in the step S 9  is “T” and the number of images to be added is “n”, the shutter speed is set again as “T/n”. For example, in the case where the numbers “n” of images to be added is 2, 4, 8, 16, . . . , the shutter speeds T are set again as “T/n”, that is, T/2, T/4, T/8, T/16, . . . , respectively. Then, the imaging device  157  is driven sequentially with the shutter speed “T/n” to thereby sequentially subject n image data thus obtained to the multiplane addition composition processing. Thereafter, single shot image data obtained by this multiplane addition composition processing is compressed and encoded to obtain a shot image, and this shot image is stored in the image memory medium  125 . 
     In this manner, since the multiplane addition composition imaging is performed inevitably under the imaging condition where the provability of shake occurrence is high, it is possible to prevent in advance the occurrence of the disadvantage that a shaken shot image is recorded. Thus, it is possible to avoid the disadvantage that noise is generated in a shot image without inevitability when the aforesaid processing of the step S 11  is performed. Further, the shake correction of a shot image can be performed effectively by suitably performing the addition processing in the step S 12 . 
     In the aforesaid embodiment, although the multiplane addition processing is performed simply, the multiplane addition processing may be performed in a manner of positioning the feature amounts of a main object of continuously-shot images based on the feature amount of a background area. 
     As described above, although this invention is explained as to the particular embodiment, this invention is not limited thereto and contains the invention claimed in claims and invention equivalent thereto.