Patent Publication Number: US-2023156323-A1

Title: Imaging apparatus, imaging control method, and program

Description:
TECHNICAL FIELD 
     The present technology relates to, for example, an imaging apparatus that is used for a surveillance camera and the like. 
     BACKGROUND ART 
     Conventionally, surveillance cameras have been widely used in fields such as anti-crime and traffic fields. There is a problem in that power consumption increases if surveillance cameras constantly capture images at high-resolution because they needs to be basically constantly driven. 
     Patent Literature 1 below has been disclosed as a technology related to such a problem. In the technology described in Patent Literature 1 below, the shift between a pixel-binning mode and a normal mode is controlled. 
     On the pixel-binning mode, low-resolution images based on the pixel-binning are acquired and a motion (event) of an object to be imaged is detected on the basis of this image. When the motion of the object to be imaged is detected on the pixel-binning mode, the mode is shifted to the normal mode. On the normal mode, images are captured at a high-resolution without the pixel-binning. After a predetermined number of images are captured on the normal mode, the mode is shifted to the pixel-binning mode. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Application Laid-open No. 2018-22935 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     However, in a case of the technology of Patent Literature 1, a shift to the normal mode is performed also when erroneous detection occurs in motion detection, which unnecessarily increases the number of shifts to the normal mode. Therefore, there is a limitation on power consumption reduction. 
     In view of the above-mentioned circumstances, it is an object of the present technology to provide a technology such as an imaging apparatus capable of suitably reducing power consumption. 
     Solution to Problem 
     An imaging apparatus according to the present technology includes a mode control unit.
         The mode control unit   shifts, when a motion is detected on a motion detection mode to detect the motion on the basis of image information, the mode to a feature detection mode to detect features on the basis of image information having a higher resolution than a resolution of the image information that is used for the motion detection, and   shifts, when a specific feature is detected on the feature detection mode, the mode to an imaging mode to acquire image information having a higher resolution than the resolution of the image information that is used for the feature detection.       

     In the present technology, the feature detection mode is provided between the motion detection mode and the imaging mode, and therefore it is possible to prevent unnecessary shifting to the imaging mode, and it is possible to suitably reduce the power consumption of the imaging apparatus. 
     In the imaging apparatus, the mode control unit may shift the mode to the motion detection mode when the specific feature is not detected on the feature detection mode. 
     In the imaging apparatus, the mode control unit may shift the mode to the motion detection mode when a prescribed number of pieces of image information are acquired on the imaging mode. 
     In the imaging apparatus, the feature detection mode may include a first feature detection mode and a second feature detection mode to more specifically perform feature detection than on the first feature detection mode. 
     In the imaging apparatus, the resolution of the image information that is used for the feature detection on the second feature detection mode may be higher than the resolution of the image information that is used for the feature detection on the first feature detection mode. 
     In the imaging apparatus, the image information that is used for the feature detection on the first feature detection mode may be an entire image and the image information that is used for the feature detection on the second feature detection mode may be a partial image corresponding to a portion subjected to the features detection on the first feature detection mode. 
     The partial image may have a resolution higher than a resolution of the entire image. 
     In the imaging apparatus, the mode control unit may shift the mode to the first feature detection mode when the motion is detected on the motion detection mode, shift the mode to the second feature detection mode when a specific feature is detected on the first feature detection mode, and shift the mode to the imaging mode when a specific feature is detected on the second feature detection mode. 
     In the imaging apparatus, the mode control unit may shift the mode to when a specific feature is not detected on the first feature detection mode and shift the mode to the motion detection mode when a specific feature is not detected on the second feature detection mode. 
     The imaging apparatus may further include a motion extraction unit that extracts the motion from the image information on the motion detection mode. 
     In the imaging apparatus, the motion extraction unit may extract the motion from image information of an analog signal. 
     In the imaging apparatus, the motion extraction unit may extract the motion from image information of a digital signal. 
     The imaging apparatus may further include a feature extraction unit that extracts the features from the image information on the feature detection mode. 
     In the imaging apparatus, the feature extraction unit may extract features from image information of an analog signal. 
     In the imaging apparatus, the feature extraction unit may extract features from image information of a digital signal. 
     The imaging apparatus may further include an image sensor including a pixel array portion that obtains the image information, in which
         inside the image sensor, provided may be   the mode control unit,   a motion extraction unit that extracts the motion from the image information on the motion detection mode,   a motion determination unit that determines whether the motion is detected on the basis of the motion extracted by the motion extraction unit on the motion detection mode, and   a feature extraction unit that extracts features from the image information on the feature detection mode.       

     In the imaging apparatus, inside the image sensor, provided may be a feature determination unit that determines whether the specific feature is detected on the basis of features extracted by the feature extraction unit on the feature detection mode. 
     In the imaging apparatus, outside the image sensor, provided may be a feature determination unit that determines whether the specific feature is detected on the basis of features extracted by the feature extraction unit on the feature detection mode. 
     An imaging control method according to the present technology includes:
         shifting, when the motion is detected on the motion detection mode to detect the motion on the basis of the image information, the mode to the feature detection mode to detect features on the basis of the image information having a higher resolution than a resolution of the image information that is used for the motion detection; and   shifting, when a specific feature is detected on the feature detection mode, the mode to the imaging mode to acquire image information having a higher resolution than the resolution of the image information that is used for the feature detection.       

     A program according to the present technology causes a computer to execute processing, including:
         shifting, when a motion is detected on a motion detection mode to detect the motion on the basis of image information, the mode to a feature detection mode to detect features on the basis of image information having a higher resolution than a resolution of the image information that is used for the motion detection; and   shifting, when a specific feature is detected on the feature detection mode, the mode to an imaging mode to acquire image information having a higher resolution than the resolution of the image information that is used for the feature detection.       

    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    A block diagram showing a configuration of an imaging apparatus according to a first embodiment. 
         FIG.  2    A block diagram showing a configuration of an image sensor according to the first embodiment. 
         FIG.  3    A flowchart showing processing of a sensor control unit. 
         FIG.  4    A diagram showing a mode shift example. 
         FIG.  5    A diagram showing a resolution of image information acquired on each mode in a pixel array portion. 
         FIG.  6    A block diagram showing a configuration of an image sensor according to the second embodiment. 
         FIG.  7    A flowchart showing processing of a sensor control unit according to the second embodiment. 
         FIG.  8    A diagram showing a mode shift example. 
         FIG.  9    A block diagram showing a configuration of an image sensor according to a third embodiment. 
         FIG.  10    A block diagram showing a configuration of an image sensor according to a fourth embodiment. 
         FIG.  11    A block diagram showing an image sensor according to a fifth embodiment. 
         FIG.  12    A block diagram showing a configuration of an imaging apparatus according to a sixth embodiment. 
         FIG.  13    A block diagram showing configurations of an image sensor and a DSP circuit. 
     
    
    
     MODE(S) FOR CARRYING OUT THE INVENTION 
     Hereinafter, embodiments according to the present technology will be described with reference to the drawings. 
     First Embodiment 
     &lt;Overall Configuration of Imaging Apparatus  100  and Configurations of Respective Parts&gt; 
       FIG.  1    is a block diagram showing a configuration of an imaging apparatus  100 . The imaging apparatus  100  is, for example, a surveillance camera and installed and used in a constant location. 
     As shown in  FIG.  1   , the imaging apparatus  100  includes an image sensor  10 , a control unit  1 , a storage unit  2 , a display unit  3 , an operation unit  4 , and a communication unit  5 . These respective parts are electrically connected to one another via a bus  6 . 
     The image sensor  10  includes, for example, a solid-state imaging element (pixel array portion  11 ) such as a charge coupled device (CCD) sensor and a complemented metal oxide semiconductor (CMOS) sensor. Further, the image sensor  10  includes an optical system including a plurality of lenses, a diaphragm, a shutter, and the like. The image sensor  10  outputs acquired image information to the storage unit  2  and the display unit  3  as necessary. It should be noted that a detailed configuration of the image sensor  10  will be described later with reference to  FIG.  2   . 
     The control unit  1  is constituted by, for example, a central processing unit (CPU) and the like. The control unit  1  executes various arithmetic operations on the basis of various programs stored in the storage unit  2  and comprehensively controls the respective parts of the imaging apparatus  100 . 
     The storage unit  2  includes a nonvolatile memory in which various programs required for processing of the control unit  1  and image information acquired by the image sensor  10  are stored and a volatile memory that is used as a working area for the control unit  1 . It should be noted that the various programs may be read from a portable recording medium such as an optical disc and a semiconductor memory or may be downloaded from a server apparatus over a network. 
     The display unit  3  is constituted by, for example, a liquid-crystal display, an electro-luminescence (EL) display, and the like. On the basis of the control of the control unit  1 , the display unit  3  displays image information acquired by the image sensor  10  on a screen as necessary. 
     The operation unit  4  is various operation units of a press button-type, a proximity-type, and the like, and detects and outputs the user&#39;s operation to the control unit  1 . 
     The communication unit  5  performs communication with external apparatuses in a wired or wireless manner. It should be noted that the external apparatuses that communicates with the imaging apparatus  100  includes, for example, a mobile phone (including a smartphone), a personal computer (PC), a server apparatus over a network, and the like. 
     It should be noted that although the image sensor  10 , the control unit  1 , the storage unit  2 , the display unit  3 , and the operation unit  4  are provided in the same apparatus in the example shown in  FIG.  1   , these respective parts may be separately provided in a plurality of apparatuses. In this case, for example, the image sensor  10  is provided in the imaging apparatus  100  and the other respective parts (the control unit  1 , the storage unit  2 , the operation unit  4 , etc.) are provided in a separate apparatus. 
     That is, it is sufficient that the imaging apparatus  100  at least includes the image sensor  10 . The apparatus separate from the imaging apparatus  100  may be a dedicated apparatus or may be a generally-used apparatus. In a case where the separate apparatus is a generally-used apparatus, the separate apparatus may be a mobile phone (including a smartphone), a PC, a server apparatus over a network, or the like. 
     &lt;Image Sensor  10 &gt; 
       FIG.  2    is a block diagram showing a configuration of the image sensor  10 . As shown in  FIG.  2   , the image sensor  10  includes the pixel array portion  11 , an analog to digital converter (ADC)  12 , a row scanning circuit  13 , a column scanning circuit  14 , and a sensor control unit  15 . The sensor control unit  15  includes a mode control unit  16 , a timing control unit  17 , a motion detection unit  18 , a feature detection unit  19 , an image processing unit  20 , and a switch  21 . 
     Here, in the present embodiment, three modes, i.e., the motion detection mode, the feature detection mode, the imaging mode, are prepared. The three modes are shifted under the control of the mode control unit  16 . 
     The motion detection mode is a mode on which image information having a resolution relatively lower than that of the image information that is used on the feature detection mode and the imaging mode is acquired and is also a mode on which a motion of the object to be imaged is detected on the basis of the image information having this lower resolution. It should be noted that in the description below, the image information acquired on the motion detection mode will be referred to as low-resolution image information for the sake of convenience. 
     The feature detection mode is a mode on which image information having a resolution relatively higher than that of the image information that is used on the motion detection mode and having a resolution relatively lower that of the image information that is used on the imaging mode is acquired and is also a mode on which a feature of the object to be imaged is detected on the basis of the image information having this resolution. It should be noted that in the description below, the image information acquired on the feature detection mode will be referred to as middle-resolution image information for the sake of convenience. 
     The imaging mode is a mode on which image information having a resolution relatively higher than that of the image information that is used on the motion detection mode and the feature detection mode is acquired and imaging is performed. It should be noted that in the description below, the image information acquired on the imaging mode will be referred to as high-resolution image information for the sake of convenience. 
     The pixel array portion  11  includes a plurality of pixels arranged in a two-dimensional grid form. Each pixel photoelectrically converts light entering through an optical system such as lens and generates electric-charge information depending on the light intensity. The pixel array portion  11  generates analog-signal image information by photoelectric conversion using the plurality of pixels and outputs the generated analog-signal image information to the ADC  12 . 
       FIG.  5    is a diagram showing the resolution of the image information acquired on each mode in the pixel array portion  11 . 
     On the motion detection mode, for example, a plurality of pixels (e.g., 16×16=256 pixels, 32×32=1024 pixels, etc.) in the pixel array portion  11  is set as one block. 
     Then, on the motion detection mode, image information is acquired by reding electric-charge information for each block (binning technology). It should be noted that on the motion detection mode, image information may be acquired by reading electric-charge information of an arbitrary pixel of each block from each block (random sampling technology). 
     The resolution of the image information on the motion detection mode is, for example, 40×30 px, 32×20 px, 16×5 px, or the like. 
     Also on the feature detection mode, a plurality of pixels (e.g., 2×2=4 pixels, 4×4=16 pixels, etc.) in the pixel array portion  11  is set as one block as on the motion detection mode. It should be noted that the number of pixels included in the one unit block on the feature detection mode is set to be smaller than the number of pixels included in the one unit block on the motion detection mode. 
     Then, on the feature detection mode, image information is acquired by reading electric-charge information for each block (binning technology). It should be noted that on the feature detection mode, image information may be acquired by reading electric-charge information of an arbitrary pixel of each block from each block (random sampling technology). 
     The resolution of the image information on the feature detection mode corresponds to, for example, video graphics array (VGA) (640×480 px), quarter VGA (QVGA) (320×240 px), quarter QVGA (QQVGA) (160×120 px), or the like. 
     On the imaging mode, for example, image information is acquired by reading electric-charge information for each pixel of the pixel array portion  11 . The resolution of the image information on the imaging mode corresponds to, for example, full high definition (FHD) (1920×1080), high definition (HD) (1280×720), VGA (640×480), or the like. 
     The row scanning circuit  13  drives each pixel of the pixel array portion  11  and causes the pixel array portion  11  to acquire the analog-signal image information. A mode signal indicating which mode of the three modes the current mode is input into the row scanning circuit  13  from the mode control unit  16 . 
     The row scanning circuit  13  controls the pixel array portion  11  on the motion detection mode to generate image information having the resolution for each block (i.e., low-resolution image information). Further, the row scanning circuit  13  controls the pixel array portion  11  to generate image information having the resolution (i.e., middle-resolution image information) for each block (smaller than the number of pixels included in one block on the motion detection mode). Further, on the imaging mode, the row scanning circuit  13  controls the pixel array portion  11  to generate image information having the resolution for each pixel (i.e., high-resolution image information). 
     The ADC  12  converts the analog-signal image information input from the pixel array portion  11  into digital-signal image information in synchronization with a clock signal. Then, the ADC  12  outputs the generated digital-signal image information to the switch  21 . 
     Here, the ADC  12  A/D converts the low-resolution image information on the motion detection mode, and A/D converts the middle-resolution image information on the feature detection mode. Further, the ADC A/D converts the high-resolution image information on the imaging mode. 
     Therefore, as to the amount of data that needs to be A/D converted by the ADC  12 , it is the smallest on the motion detection mode, the second smallest on the feature detection mode, and the largest on the imaging mode. Therefore, as to power consumption in the ADC  12 , it is the smallest on the motion detection mode, the second smallest on the feature detection mode, and the largest on the imaging mode. 
     Therefore, the power consumption in the ADC  12  can be reduced as compared to the case where the pixel array portion  11  acquires constantly high-resolution image information and the ACD A/D converts the high-resolution image information. 
     The column scanning circuit  14  controls the ADC  12  to output the digital-signal image information to the switch  21 . 
     The sensor control unit  15  comprehensively controls the respective parts of the image sensor  10 , for example, on the basis of the program. It should be noted that specific processing of the sensor control unit  15  (in particular, the mode control unit  16 , the motion detection unit  18 , the feature detection unit  19 ) will be described later in detail with reference to  FIG.  3   . 
     The timing control unit  17  controls the operation timings of the row scanning circuit  13 , the ADC  12 , and the column scanning timing. A vertical synchronization signal having a predetermined frequency (e.g., 30 Hz, etc.) is input into the timing control unit  17 . 
     The timing control unit  17  generates timing signals indicating the operation timings of the row scanning circuit  13 , the ADC  12  and the column scanning circuit  14  in synchronization with the vertical synchronization signal and outputs the corresponding timing signals to the respective parts. 
     The switch  21  switches the output destination of the image information output from the ADC  12  on the basis of a mode signal input from the mode control unit  16 . 
     On the motion detection mode, the switch  21  outputs the image information from the ADC  12  (low-resolution image information) to the motion detection unit  18 . Further, on the feature detection mode, the switch  21  outputs the image information from the ADC  12  (middle-resolution image information) to the feature detection unit  19 . Further, on the imaging mode, the switch  21  outputs the image information from the ADC  12  (high-resolution image information) to the image processing unit  20 . 
     On the motion detection mode, the motion detection unit  18  determines whether the motion of the object to be imaged is detected on the basis of the low-resolution image information input from the ADC  12  via the switch  21 , and outputs a determination result to the mode control unit  16 . 
     The motion detection unit  18  includes a motion extraction unit  18   a  and a motion determination unit  18   b . The motion extraction unit  18   a  extracts a motion of the object to be imaged on the basis of the low-resolution image information input from the ADC  12  via the switch  21 , and outputs extracted motion information to the motion determination unit  18   b . The motion determination unit  18   b  determines whether the motion is detected on the basis of the motion information, and outputs a determination result to the mode control unit  16 . 
     On the feature detection mode, the feature detection unit  19  determines whether a specific feature is detected on the basis of the middle-resolution image information input from the ADC  12  via the switch  21 , and outputs a determination result to the mode control unit  16 . 
     The feature detection unit  19  includes a feature extraction unit  19   a  and a feature determination unit  19   b . The feature extraction unit  19   a  extracts a feature of the object to be imaged on the basis of the middle-resolution image information input from the ADC  12  via the switch  21 , and outputs the extracted feature information to the feature determination unit  19   b . The feature determination unit  19   b  determines whether a specific feature is detected on the basis of the feature information, and outputs a determination result to the mode control unit  16 . 
     On the imaging mode, the image processing unit  20  performs various types of image processing such as demosaicing processing, white balance processing, and filtering processing on the high-resolution image information input from the ADC  12  via the switch  21 . Then, the image processing unit  20  outputs the high-resolution image information subjected to the image processing to the storage unit  2  and the display unit  3 . 
     On the basis of the determination result input from the motion detection unit  18  and the determination result input from the feature detection unit  19 , the mode control unit  16  controls the shift of the three modes, i.e., the motion detection mode, the feature detection mode, and the imaging mode. Further, when the mode is shifted, the mode control unit  16  outputs a mode signal indicating the mode after the shift (indicating the current mode) to the row scanning circuit  13  and the switch  21 . 
     Referring to  FIG.  4    to be described later, typically, when the motion of the object to be imaged is detected on the motion detection mode, the mode control unit  16  shifts the mode from the motion detection mode to the feature detection mode. Further, when a specific feature (feature corresponding to an imaging target) is detected on the feature detection mode, the mode control unit  16  shifts the mode from the feature detection mode to the imaging mode. On the other hand, when a specific feature is not detected on the feature detection mode, the mode control unit  16  shifts the mode from the feature detection mode to the motion detection mode. Further, the mode control unit  16  shifts the mode from the imaging mode to the motion detection mode when a prescribed number of pieces of image information are acquired on the imaging mode. 
     Here, in the present embodiment, the image sensor  10  is held in the active state irrespective of the mode while the control unit  1 , the storage unit  2 , the display unit  3 , the communication unit  5 , and the like (hereinafter, the control unit  1  and the like) are held in the sleep state on some modes. That is, the control unit  1  and the like are held in the sleep state on the motion detection mode and the feature detection mode and are held in the active state only on the imaging mode. It should be noted that in a case where the user performs input via the operation unit  4 , the control unit  1  and the like are exceptionally held in the active state irrespective of the mode. 
     When the mode is shifted from the feature detection mode to the imaging mode, the mode control unit  16  activates the control unit  1  and the like in the sleep state. Further, at this time, the mode control unit  16  also activates a reference-clock generation circuit (not shown) that supplies the control unit  1  and the like with a reference clock. 
     Further, when the mode is shifted from the imaging mode to the motion detection mode, the mode control unit  16  causes the control unit  1  and the like to enter the sleep state from the active state. Further, at this time, the mode control unit  16  also deactivates the reference-clock generation circuit (not shown) that supplies the control unit  1  and the like with a reference clock. 
     Since in the present embodiment, the control unit  1  and the like and the reference-clock generation circuit are activated only at necessary timings (imaging mode), power saving of the entire imaging apparatus  100  can be achieved. 
     &lt;Operation Description&gt; 
     Next, processing of the sensor control unit  15  (in particular, the mode control unit  16 , the motion detection unit  18 , the feature detection unit  19 ) will be described.  FIG.  3    is a flowchart showing the processing of the sensor control unit  15 .  FIG.  4    is a diagram showing a mode shift example. 
     In the description of  FIG.  3   , it is assumed that the current mode is initially set to be the motion detection mode. On the motion detection mode, the low-resolution image information is output from the pixel array portion  11 , and this image information is A/D converted by the ADC  12  (the power consumption of the ADC is relatively low). Then, the low-resolution image information converted into the digital signal is input into the motion extraction unit  18   a  of the motion detection unit  18  via the switch  21 . 
     When the low-resolution image information is input, the motion extraction unit  18   a  extracts a motion of the object to be imaged from this image information (Step  101 ). At this time, for example, the motion extraction unit  18   a  generates integrated information by adding up electric-charge information (luminance information) of the respective blocks included in the image information. Then, the motion extraction unit  18   a  extracts a difference between integrated information based on the current image information and integrated information based on the previous image information as motion information and outputs this motion information (difference) to the motion determination unit  18   b.    
     When the motion information (difference) is input from the motion extraction unit  18   a , the motion determination unit  18   b  of the motion detection unit  18  determines whether the motion of the object to be imaged is detected on the basis of this motion information (Step  102 ). 
     For example, the motion determination unit  18   b  compares the difference with a predetermined threshold, and determines that a motion of the object to be imaged is detected in a case where the difference is above the threshold (YES in Step  102 ). On the other hand, the motion determination unit  18   b  determines that a motion of the object to be imaged is not detected in a case where the difference is equal to or smaller than the threshold (NO in Step  102 ). Then, the motion determination unit  18   b  outputs a determination result as to whether the motion is detected to the mode control unit  16 . 
     In a case where a motion of the object to be imaged is not detected (NO in Step  102 ), the mode is still the motion detection mode and the processing returns to Step  101 . On the other hand, in a case where a motion of the object to be imaged is detected (YES in Step  102 ), the mode control unit  16  shifts the current mode from the motion detection mode to the feature detection mode (Step  103 ). At this time, the mode control unit  16  outputs a mode signal indicating that the current mode is the feature detection mode to the row scanning circuit  13  and the switch  21 . 
     When the mode signal indicating the feature detection mode is input, the row scanning circuit  13  controls the pixel array portion  11  to cause the pixel array portion  11  to acquire middle-resolution image information. Further, when the mode signal indicating the feature detection mode is input, the switch  21  switches the output destination of the image information from the ADC  12  from the motion detection unit  18  (motion extraction unit  18   a ) to the feature detection unit  19  (feature extraction unit  19   a ). 
     Therefore, on the feature detection mode, the middle-resolution image information is output from the pixel array portion  11 , and this image information is A/D converted by the ADC  12  (the power consumption of the ADC is relatively middle). Then, the middle-resolution image information converted into the digital signal is input into the feature extraction unit  19   a  of the feature detection unit  19  via the switch  21 . 
     When the middle-resolution image information is input, the feature extraction unit  19   a  extracts, from this image information, feature information of the object to be imaged (information about a group of feature points, edge information, distance information, polarization information, spectrum information, etc.) and outputs this feature information to the feature determination unit  19   b  (Step  104 ). 
     It should be noted that the feature extraction unit  19   a  may extract the feature information from the entire image information or may extract the feature information from a specific portion of the image information. That is, on the feature detection mode, a point where the motion had been made has been determined in the motion detection, and therefore it is also possible to partially extract feature information from a portion corresponding to the point where this motion had been made. In this case, the power consumption in the image sensor  10  can be further reduced. 
     When the feature information is input from the feature extraction unit  19   a , the feature determination unit  19   b  of the feature detection unit  19  determines whether a specific feature is detected on the basis of this feature information (Step  105 ). 
     In this case, for example, the feature determination unit  19   b  compares the extracted feature information with the cognitive model, and determines that a specific feature is detected in a case where the feature information matches the cognitive model (YES in Step  105 ). On the other hand, the feature determination unit  19   b  determines that a specific feature is not detected in a case where the feature information does not match the cognitive model (NO in Step  105 ). Then, the feature determination unit  19   b  outputs a determination result as to whether a specific feature is detected to the mode control unit  16 . 
     The cognitive model is a model corresponding to an object to be imaged (e.g., a person, an animal, a car, etc.) assumed as the imaging target and stored in the feature determination unit  19   b  in advance. 
     Here, for example, in a case where a person is assumed as the imaging target, the feature determination unit  19   b  compares the extracted feature information with a cognitive model indicating the person&#39;s entire body, a cognitive model indicating the person&#39;s face and determines whether a specific feature is detected (human detection, facial detection). 
     Further, in a case where an animal such as a cat or dog is set as the imaging target, the feature determination unit  19   b  compares the extracted feature information with a cognitive model indicating the animal&#39;s entire body, a cognitive model indicating the animal&#39;s face and determines whether a specific feature is detected (animal detection, animal&#39;s face detection). Further, in a case where a car is assumed as the imaging target, the feature determination unit  19   b  compares the extracted feature information with a cognitive model indicating the entire car, a cognitive model indicating parts of the car and determines whether a specific feature is detected (car detection, portion detection). 
     It should be noted that in a case where a plurality of kinds of objects to be imaged is set as the imaging targets, the feature determination unit  19   b  compares the feature information with the corresponding cognitive models and determines whether a specific feature is detected. For example, in a case where a person and a car are set as the imaging targets, the feature determination unit  19   b  compares the extracted feature information with the cognitive model indicating the person&#39;s entire body, the cognitive model indicating the person&#39;s face, the cognitive model indicating the entire car, the cognitive model indicating the respective parts of the car and determines whether a specific feature is detected. 
     It should be noted that required imaging targets may be selectable among the plurality of kinds of imaging targets prepared in advance by the user via the operation unit  4 . For example, it is assumed that respective kinds of imaging targets such as a person, an animal, and a car are prepared in advance, and the user has selected the person among them as a required imaging target. In this case, the feature determination unit  19   b  compares the feature information with the cognitive model indicating the person&#39;s entire body, the cognitive model indicating the person&#39;s face and determines whether a specific feature is detected. 
     On the feature detection mode, in a case where a specific feature is not detected (NO in Step  105 ), the mode control unit  16  shifts the current mode from the feature detection mode to the motion detection mode (Step  107 ). 
     On the left-hand side of  FIG.  4   , a state when a specific feature is detected on the feature detection mode and the mode is returned to the motion detection mode after the motion is detected on the motion detection mode and the mode is shifted to the feature detection mode is shown. 
     When shifting the mode from the feature detection mode to the motion detection mode, the mode control unit  16  outputs a mode signal indicating that the current mode is the motion detection mode to the row scanning circuit  13  and the switch  21 . 
     When the mode signal indicating the motion detection mode is input, the row scanning circuit  13  controls the pixel array portion  11  to cause the pixel array portion  11  to acquire the low-resolution image information. Further, when the mode signal indicating the motion detection mode is input, the switch  21  switches the output destination of the image information from the ADC  12  from the feature detection unit  19  (feature extraction unit  19   a ) to the motion detection unit  18  (motion extraction unit  18   a ). 
     When the mode is shifted to the motion detection mode, the processing returns to Step  101 . 
     On the feature detection mode, in a case where a specific feature is detected (YES in Step  105 ), the mode control unit  16  shifts the current mode from the feature detection mode to the imaging mode (Step  106 ). 
     On the right-hand side of  FIG.  4   , a state when a specific feature is detected on the feature detection mode and the mode is shifted to the imaging mode after the motion is detected on the motion detection mode and the mode is shifted to the feature detection mode is shown. 
     When shifting the mode to the imaging mode, the mode control unit  16  outputs a mode signal indicating that the current mode is the imaging mode to the row scanning circuit  13  and the switch  21 . Further, at this time, the mode control unit  16  activates the control unit  1  and the like in the sleep state and also activates the reference-clock generation circuit that supplies the control unit  1  and the like with a reference clock. 
     When the mode signal indicating the imaging mode is input, the row scanning circuit  13  controls the pixel array portion  11  to cause the pixel array portion  11  to acquire the high-resolution image information. Further, when the mode signal indicating the imaging mode is input, the switch  21  switches the output destination of the image information from the ADC  12  from the feature detection unit  19  (feature extraction unit  19   a ) to the image processing unit  20 . 
     Therefore, on the imaging mode, the high-resolution image information is output from the pixel array portion  11 , and this image information is A/D converted by the ADC  12  (the power consumption of the ADC is relatively higher). Then, the high-resolution image information converted into the digital signal is input into the image processing unit  20  via the switch  21 . The image processing unit  20  performs various types of image processing such as demosaicing processing on the high-resolution image information and outputs the high-resolution image information subjected to the image processing to the storage unit  2  and the display unit  3  (Step  108 ). With this, the high-resolution image information on the imaging mode is output from the image sensor  10 , stored in the storage unit  2 , and displayed on the display unit  3 . 
     It should be noted that in the present embodiment, the low-resolution image information on the motion detection mode is used only for the motion detection and is not used for storage or for display. Similarly, the middle-resolution image information on the feature detection mode is used only for the feature detection and is not used for storage or for display. With this, it is possible to prevent the storage unit  2  from storing unnecessary information. 
     It should be noted that the low-resolution image information on the motion detection mode and the middle-resolution image information on the feature detection mode can also be used for storage or for display (in particular, as to the middle-resolution image information). 
     When the acquisition of the high-resolution image information is started on the imaging mode, the mode control unit  16  determines whether the number of pieces of image information acquired on the imaging mode reaches the prescribed number (Step  109 ). In a case where the number of pieces of image information acquired does not reach the prescribed number (NO in Step  109 ), the mode control unit  16  outputs the high-resolution image information from the image sensor  10  while maintaining the imaging mode as the mode (Step  108 ). 
     On the other hand, in a case where the number of pieces of image information acquired reaches the prescribed number (YES in Step  109 ), the mode control unit  16  shifts the current mode from the imaging mode to the motion detection mode (Step  110 ). 
     It should be noted that it is sufficient that the number of pieces of image information acquired on the imaging mode is set as appropriate, for example, 1, 2, 3, and so on. Further, the number of pieces of image information acquired on the imaging mode may be variable by the user in accordance with the user&#39;s input via the operation unit  4 . 
     When shifting the mode to the motion detection mode, the mode control unit  16  outputs a mode signal indicating that the current mode is the motion detection mode to the row scanning circuit  13  and the switch  21 . Further, at this time, the mode control unit  16  causes the control unit  1  and the like to enter the sleep state from the active state and also deactivates the reference-clock generation circuit that supplies the control unit  1  and the like with a reference clock. 
     When the mode signal indicating the motion detection mode is input, the row scanning circuit  13  controls the pixel array portion  11  to cause the pixel array portion  11  to acquire the low-resolution image information. Further, when the mode signal indicating the motion detection mode is input, the switch  21  switches the output destination of the image information from the ADC  12  from the image processing unit  20  to the motion detection unit  18  (motion extraction unit  18   a ). 
     When the mode is shifted to the motion detection mode, the processing returns to Step  101 . 
     &lt;Actions, Etc.&gt; 
     Next, actions, etc. in the present embodiment will be described. First of all, in the present embodiment, a case where a motion of an animal that is not the imaging target is detected on the motion detection mode in the situation where the imaging target is a person will be assumed. In this case, due to the detection of the motion of the animal, the mode is shifted from the motion detection mode to the feature detection mode. 
     On the feature detection mode, feature information of the animal is extracted and the feature information of the animal is compared to the cognitive model of the person that is the imaging target. In this case, since the feature information does not match the cognitive model, the mode is returned to the motion detection mode from the feature detection mode (see the left-hand side of  FIG.  4   ). 
     In contrast, a case where a motion of the person that is the imaging target is detected on the motion detection mode in a case where the imaging target is a person will be assumed. In this case, due to the detection of the motion of the person, the mode is shifted from the motion detection mode to the feature detection mode. 
     On the feature detection mode, feature information of the person is extracted and the feature information of the person is compared to the cognitive model of the person that is the imaging target. In this case, since the feature information matches the cognitive model, the mode is shifted from the feature detection mode to the imaging mode (see the right-hand side of  FIG.  4   ). Then, after a prescribed number of pieces of high-resolution image information in which the person is shown are acquired on the imaging mode, the mode is returned to the motion detection mode from the imaging mode. 
     As described above, in the present embodiment, the mode is not shifted to the imaging mode when the object to be imaged the motion of which has been detected is not the imaging target in a case where a motion of the object to be imaged is detected on the motion detection mode. Then, in a case where a motion of the object to be imaged is detected on the motion detection mode, the mode is shifted to the imaging mode as long as the object to be imaged the motion of which has been detected is the imaging target. 
     Here, a case where the mode is two modes, i.e., the motion detection mode and the imaging mode will be assumed as a comparative example. In this case, in a case where erroneous detection (detection of a motion that is not the imaging target) occurs in the motion detection, shifting to the imaging mode is immediately performed, and therefore the number of shifts to the imaging mode unnecessarily increases, and there is a limitation on reduction of power consumption (in particular, the power consumption of the ADC). 
     In contrast, in the present embodiment, as described above, in a case where a motion of the object to be imaged is detected on the motion detection mode, the mode is shifted to the imaging mode as long as the object to be imaged the motion of which has been detected is the imaging target. 
     As described above, in the present embodiment, since the mode can be shifted to the imaging mode only as it is necessary, it is possible to prevent unnecessary shifting to the imaging mode due to erroneous detection. 
     Further, in the present embodiment, since the image information acquired on the feature detection mode has a resolution lower than that of the image information acquired on the imaging mode, the power consumption in the image sensor  10  (in particular, power consumption during A/D conversion by the ADC  12 ) can be reduced. Further, since the image information acquired on the feature detection mode has a resolution higher than that of the image information acquired on the motion detection mode, it is possible to suitably determine whether the object to be imaged the motion of which has been detected is the imaging target. 
     Further, in the present embodiment, the control unit  1  and the like are held in the sleep state on the motion detection mode and the feature detection mode and are held in the active state only on the imaging mode. Further, in the present embodiment, the reference-clock generation circuit that supplies the control unit  1  and the like with a reference clock is held in an inactive state on the motion detection mode and the feature detection mode and is held in the active state only on the imaging mode. With this, the power consumption of the entire imaging apparatus  100  can be further reduced. 
     &lt;Modified Example of First Embodiment&gt; 
     Here, in a case where the imaging target is an object that moves at high speed such as a car and the imaging target passes near the imaging apparatus  100 , imaging on the imaging mode cannot be in time. In view of this, in a case where the imaging target is an object that moves at high speed such as a car (e.g., in a case where a car is selected by the user as the imaging target), the middle-resolution image information acquired on the feature detection mode may be stored in the storage unit  2 . 
     That is, since the feature detection mode is a mode on which shifting is immediately performed once a motion of the object to be imaged is detected on the motion detection mode and the resolution of the image information acquired is not so high, time until the image information is acquired is also short. Further, on the feature detection mode, it is unnecessary to wait for activation of the control unit and the like unlike the imaging mode. Therefore, image information (resolution of which is not so high) of a high-speed moving object such as a car can be suitably saved by storing the image information used for the feature detection on the feature detection mode in the storage unit  2 . 
     In the description of the first embodiment, the case where the resolution of the image information acquired by the pixel array portion  11  is different has been described as an example in a case where the resolution of the image information on each mode is different. On the other hand, on each mode, a bit resolution (ADC resolution) during the A/D conversion at the ADC  12  may be different. Alternatively, on each mode, the resolution of the image information acquired by the pixel array portion  11  and the bit resolution during the A/D conversion at the ADC  12  may be different. That is, the “resolution of the image information” means the resolution of the image information output from the pixel array portion  11  and/or the bit resolution (ADC resolution) of the image information output from the ADC  12 . 
     In a case where the bit resolution is different, for example, image information having the same resolution (it may be different) is output from the pixel array portion  11  on each mode. In this case, on the motion detection mode, the ADC  12  A/D converts and outputs the image information at a bit resolution lower than that of the feature detection mode and the imaging mode. Further, on the feature detection mode, the ADC  12  A/D converts and outputs the image information at a bit resolution higher than that of the motion detection mode and lower than that of the imaging mode. Further, on the imaging mode, the ADC  12  A/D converts and outputs the image information at a bit resolution higher than that of the motion detection mode and the feature detection mode. 
     In this case, as to the power consumption in the ADC  12 , it is the smallest on the motion detection mode, the second smallest on the feature detection mode, and the largest on the imaging mode. Therefore, in this case, the power consumption in the ADC  12  can be reduced as compared to a case of A/D converting the image information from the pixel array portion  11  constantly at a high bit resolution. 
     It should be noted that also in the respective embodiments to be described below, a case where the resolution of the image information acquired by the pixel array portion  11  is different will be described as an example in a case where the resolution of the image information on each mode is different. On the other hand, also in the respective embodiments to be described below, on each mode, the bit resolution during the A/D conversion at the ADC  12  (ADC resolution) may be different 
     Second Embodiment 
     Next, a second embodiment of the present technology will be described. It should be noted that the second embodiment in the description below, portions having functions and configurations identical to those of the first embodiment will be denoted by the same reference signs and the descriptions will be omitted or simplified. 
     In the second embodiment, the feature detection mode is divided into two modes, i.e., a first feature detection mode and a second feature detection mode. The second feature detection mode is a mode to more specifically perform feature detection than on the first feature detection mode. 
     The first feature detection mode is a mode on which image information having a resolution relatively higher than that of the image information that is used on the motion detection mode and having a resolution relatively lower than that of the image information that is used on the second feature detection mode and the imaging mode is acquired and is also a mode on which a feature of the object to be imaged is detected on the basis of the image information having this resolution. It should be noted that in the description below, the image information acquired on the first feature detection mode will be referred to as image information having a lower-middle resolution for the sake of convenience. 
     The second feature detection mode is a mode on which the image information having a resolution relatively higher than that of the image information that is used on the motion detection mode and the first feature detection mode and having a resolution relatively lower than that of the image information that is used on the imaging mode is acquired and is also a mode on which a feature of the object to be imaged is detected on the basis of the image information having this resolution. It should be noted that in the description below, the image information acquired on the second feature detection mode will be referred to as information having an upper-middle resolution for the sake of convenience image. 
     It should be noted that on the second feature detection mode, the feature detection is performed on the basis of the image information having the higher resolution than that of the image information that is used on the first feature detection mode, and therefore the accuracy of the feature detection is higher than on the first feature detection mode. 
       FIG.  6    is a block diagram showing a configuration of the image sensor  31  according to the second embodiment. 
     Although the image sensor  31  according to the second embodiment basically has configuration similar to that of the image sensor  10  according to the first embodiment, for the feature detection unit, two feature detection units, i.e., a first feature detection unit  22  and a second feature detection unit  23  are provided. Further, in the second embodiment, four output destinations of a switch  24  are set. 
     On the motion detection mode, the pixel array portion  11  outputs image information having the resolution such as 40×30 px, 32×20 px, and 16×5 px (low-resolution image information). Further, on the first feature detection mode, the pixel array portion  11  outputs image information having the resolution such as quarter VGA (QVGA) (320×240 px) and QQVGA (Quarter QVGA) (160×120 px) (image information having the lower-middle resolution). 
     Further, on the second feature detection mode, the pixel array portion  11  outputs image information having the resolution such as video graphics array (VGA) (640×480 px) and quarter VGA (QVGA) (320×240 px) (image information having the upper-middle resolution). Further, on the imaging mode, the pixel array portion  11  outputs image information having the resolution such as full high definition (FHD) (1920×1080), HD (high definition) (1280×720), and VGA (640×480) (high-resolution image information). 
     The ADC  12  A/D converts the low-resolution image information (low power consumption) on the motion detection mode, and A/D converts the image information having the lower-middle resolution (lower-middle power consumption) on the first feature detection mode. Further, the ACD A/D converts the image information having the upper-middle resolution (upper-middle power consumption) on the second feature detection mode, and A/D converts the high-resolution image information (high power consumption) on the imaging mode. 
     On the motion detection mode, the switch  24  outputs the image information from the ADC  12  (low-resolution image information) to the motion detection unit  18 . Further, on the first feature detection mode, the switch  24  outputs the image information from the ADC  12  (image information having the lower-middle resolution) to the first feature detection unit  22 . 
     Further, on the second feature detection mode, the switch  24  outputs the image information from the ADC  12  (image information having the upper-middle resolution) to the second feature detection unit  23 . Further, on the imaging mode, the switch  24  outputs the image information from the ADC  12  (high-resolution image information) to the image processing unit  20 . 
     On the first feature detection mode, the first feature detection unit  22  determines whether a specific feature is detected on the basis of the image information having the lower-middle resolution that is input from the ADC  12  via the switch  24 , and outputs a determination result to the mode control unit  16 . 
     The first feature detection unit  22  includes a first feature extraction unit  22   a  and a first feature determination unit  22   b . The first feature extraction unit  22   a  extracts a feature of the object to be imaged on the basis of the image information having the lower-middle resolution that is input from the ADC  12  via the switch  24 , and outputs the extracted feature information to the first feature determination unit  22   b . The first feature determination unit  22   b  determines whether a specific feature is detected on the basis of the feature information, and outputs a determination result to the mode control unit  16 . 
     On the second feature detection mode, the second feature detection unit  23  determines whether a specific feature is detected on the basis of the image information having the upper-middle resolution that is input from the ADC  12  via the switch  24 , and outputs a determination result to the mode control unit  16 . 
     The second feature detection unit  23  includes a second feature extraction unit  23   a  and a second feature determination unit  23   b . The second feature extraction unit  23   a  extracts a feature of the object to be imaged on the basis of the image information having the upper-middle resolution that is input from the ADC  12  via the switch  24 , and outputs the extracted feature information to the second feature determination unit  23   b . The second feature determination unit  23   b  determines whether a specific feature is detected on the basis of the feature information, and outputs a determination result to the mode control unit  16 . 
     &lt;Operation Description&gt; 
     Next, processing of the sensor control unit  15  (in particular, the mode control unit  16 , the motion detection unit  18 , the first feature detection unit  22 , the second feature detection unit  23 ) will be described.  FIG.  7    is a flowchart showing the processing of the sensor control unit  15  according to the second embodiment.  FIG.  8    is a diagram showing a mode shift example. 
     On the motion detection mode, the motion extraction unit  18   a  extracts a motion of the object to be imaged from the low-resolution image information (Step  201 ). The motion determination unit  18   b  determines whether the motion of the object to be imaged is detected on the basis of the motion information from the motion extraction unit  18   a  (Step  202 ). 
     In a case where a motion of the object to be imaged is detected (YES in Step  202 ), the mode control unit  16  shifts the current mode from the motion detection mode to the first feature detection mode (Step  203 ). 
     On a first feature extraction mode, the first feature extraction unit  22   a  extracts feature information of the object to be imaged from the image information having the lower-middle resolution and outputs this feature information to the first feature determination unit  22   b  (Step  204 ). 
     On the basis of the feature information, the first feature determination unit  22   b  determines whether a specific feature is detected (Step  205 ). 
     In this case, for example, the first feature determination unit  22   b  compares the extracted feature information with the cognitive model (e.g., the cognitive model corresponding to the person), and determines that a specific feature is detected in a case where the feature information matches the cognitive model (YES in Step  205 ). On the other hand, the first feature determination unit  22   b  determines that a specific feature is not detected in a case where the feature information does not match the cognitive model (NO in Step  205 ). 
     On the first feature detection mode, in a case where a specific feature is not detected (NO in Step  205 ), the mode control unit  16  shifts the current mode from the first feature detection mode to the motion detection mode (Step  207 ). 
     On the other hand, in a case where a specific feature is detected on the first feature detection mode (YES in Step  205 ), the mode control unit  16  shifts the current mode from the first feature detection mode to the second feature detection mode (Step  206 ). 
     On the second feature detection mode, the second feature extraction unit  23   a  extracts feature information of the object to be imaged from the image information having the upper-middle resolution and outputs this feature information to the second feature determination unit  23   b  (Step  208 ). 
     On the basis of the feature information, the second feature determination unit  23   b  determines whether a specific feature is detected (Step  209 ). 
     In this case, for example, the second feature determination unit  23   b  compares the extracted feature information with the cognitive model (e.g., the cognitive model corresponding to the person), and determines that a specific feature is detected in a case where the feature information matches the cognitive model (YES in Step  209 ). On the other hand, the second feature determination unit  23   b  determines that a specific feature is not detected in a case where the feature information does not match the cognitive model (NO in Step  209 ). 
     Here, the cognitive model may be the same or different between the first feature detection mode and the second feature detection mode. In a case where the cognitive model is different between the two modes, for example, the cognitive model of the person&#39;s entire body may be used on the first feature detection mode (human detection) or the cognitive model of the person&#39;s face may be used on the second feature detection mode (facial detection). 
     On the second feature detection mode, in a case where a specific feature is not detected (NO in Step  209 ), the mode control unit  16  shifts the current mode from the second feature detection mode to the motion detection mode (Step  211 ). 
     On the left-hand side of  FIG.  8   , a state when a motion is detected on the motion detection mode, a specific feature is detected on the first feature detection mode, a specific feature is not detected on the second feature detection mode, and the mode is returned to the motion detection mode is shown. 
     On the other hand, on the second feature detection mode, in a case where a specific feature is detected (YES in Step  209 ), the mode control unit  16  shifts the current mode from the second feature detection mode to the imaging mode (Step  210 ). 
     On the right-hand side of  FIG.  8   , a state when a motion is detected on the motion detection mode, a specific feature is detected on the first feature detection mode, a specific feature is detected on the second feature detection mode, and the mode is shifted to the imaging mode is shown. 
     On the imaging mode, the image processing unit  20  performs various types of image processing such as demosaicing processing on the high-resolution image information input from the ADC  12  via the switch  24 , and outputs the high-resolution image information subjected to the image processing to the storage unit  2  and the display unit  3  (Step  212 ). 
     When the acquisition of the high-resolution image information is started on the imaging mode, the mode control unit  16  determines whether the number of pieces of image information acquired on the imaging mode reaches the prescribed number (Step  213 ). 
     In a case where the number of pieces of image information acquired on the imaging mode reaches the prescribed number (YES in Step  213 ), the mode control unit  16  shifts the current mode from the imaging mode to the motion detection mode (Step  214 ). 
     In the second embodiment, since the feature detection mode has multiple stages, it is possible to more suitably prevent unnecessary shifting to the imaging mode due to erroneous detection. 
     &lt;Modified Example of Second Embodiment&gt; 
     In the description of the second embodiment, the case where the feature detection mode has two stages has been described. On the other hand, the feature detection mode may have three or more stages. In this case, the feature detection mode in the subsequent stage is configured to be capable of detecting a feature more specifically than the feature detection mode in the previous stage. 
     Here, any method can be used for the feature detection on these modes as long as the second feature detection mode (in the subsequent stage) is a mode to perform feature detection more specifically than the first feature detection mode (in the previous stage). For example, an example of a difference between the first feature detection mode and the second feature detection mode is as follows. It should be noted that the second embodiment corresponds to the following example 1. 
     1. The resolution of the image information (entire image) that is used for the feature detection on the second feature detection mode (in the subsequent stage) is higher than the resolution of the image information (entire image) that is used for the feature detection on the first feature detection mode (in the previous stage). 
     2. The image information that is used for the feature detection on the first feature detection mode (in the previous stage) is the entire image and the image information that is used for the feature detection on the second feature detection mode (in the subsequent stage) is a partial image (ROI: region of interest) corresponding to the portion subjected to the feature detection on the first feature detection mode (in the previous stage). In this case, the partial image on the second feature detection mode (in the subsequent stage) may be have a resolution higher than that of the corresponding point of the entire image on the first feature detection mode (in the previous stage). 
     3. The image information that is used for the feature detection on the first feature detection mode (in the previous stage) is a black and white image and the image information that is used for the feature detection on the second feature detection mode (in the subsequent stage) is a color image. It should be noted that this 3 can be combined with 1 and 2. 
     Third Embodiment 
     Next, a third embodiment of the present technology will be described. 
       FIG.  9    is a block diagram showing a configuration of an image sensor  32  according to the third embodiment. In the third embodiment, although the feature detection unit  19  (feature detection mode) has a single stage as in the first embodiment, the feature detection unit  19  (feature detection mode) may have multiple stages as in the second embodiment. The same applies to a fourth embodiment, etc. to be described later. 
     In the first embodiment or the second embodiment, the motion extraction unit  18   a  of the motion detection unit  18  extracts a motion of the object to be imaged from the converted digital-signal image information. In contrast, in the third embodiment, the motion extraction unit  18   a  of the motion detection unit  18  is provided in the ADC  12 , and the motion extraction unit  18   a  extracts a motion of the object to be imaged from analog-signal image information from the pixel array portion  11  on the motion detection mode. 
     A mode signal from the mode control unit  16  is input into the motion extraction unit  18   a , and the motion extraction unit  18   a  operates only in a case where the current mode is the motion detection mode. On the motion detection mode, the motion extraction unit  18   a  extracts a motion from the low-resolution image information (analog signal) output from the pixel array portion  11  and outputs the motion information (analog signal) to the ADC  12 . 
     On the motion detection mode, the ADC  12  converts the analog-signal motion information input from the motion extraction unit  18   a  into a digital signal and outputs the digital-signal motion information to the motion determination unit  18   b  via the switch  21 . The motion determination unit  18   b  determines whether the motion is detected on the basis of the digital-signal motion information. 
     Other processing is basically similar to that of the first embodiment. 
     Here, in the first embodiment and the like, on the motion detection mode, the image information itself is A/D converted by the ADC  12 . On the other hand, in the third embodiment, the motion information, not the image information itself, is A/D converted on the motion detection mode. For this reason, since the amount of data A/D converted by the ADC  12  is smaller as compared to the first embodiment and the like, the power consumption in the ADC  12  can be further reduced. Further, in a case of A/D converting the motion information, A/D conversion at a lower bit resolution is possible as compared to a case of A/D converting the entire image information, and the power consumption in the ADC  12  can be reduced also in this point. 
     It should be noted that in the first embodiment and the like, a motion of the object to be imaged is extracted on the basis of the digital-signal image information on the motion detection mode, and in this case, there is an advantage that the accuracy of motion extraction (motion detection) is higher as compared to the third embodiment where a motion of the object to be imaged is extracted on the basis of the analog-signal image information. 
     That is, in a case of performing motion extraction from the analog-signal image information as in the third embodiment, the accuracy of the motion extraction (motion detection) is lower while the power consumption in the ADC  12  can be reduced as compared to the first embodiment and the like. On the other hand, as in the first embodiment, in a case of performing motion extraction from the digital-signal image information, the power consumption in the ADC  12  is higher while the accuracy of the motion extraction (motion detection) can be improved as compared to the third embodiment. 
     Therefore, the power consumption and the accuracy of the motion extraction (motion detection) are trade-off and in a case where the power consumption reduction is prioritized, a configuration like the configuration described in the third embodiment is employed. On the other hand, in a case where the accuracy of the motion extraction (motion detection) is prioritized, a configuration like the configuration described in the first embodiment or the like is employed. 
     Fourth Embodiment 
     Next, a fourth embodiment of the present technology will be described.  FIG.  10    is a block diagram showing a configuration of an image sensor  33  according to the fourth embodiment. 
     In the fourth embodiment, the feature extraction unit  19   a  of the feature detection unit  19  is provided in the ADC  12 , and the feature extraction unit  19   a  extracts a feature of the object to be imaged from the analog-signal image information from the pixel array portion  11  on the feature detection mode. 
     A mode signal from the mode control unit  16  is input into the feature extraction unit  19   a , and the feature extraction unit  19   a  operates only in a case where the current mode is the feature extraction mode. On the feature extraction mode, the feature extraction unit  19   a  extracts a feature of the object to be imaged from the middle-resolution image information (analog signal) output from the pixel array portion  11  and outputs the feature information (analog signal) to the ADC  12 . 
     On the feature extraction mode, the ADC  12  converts the analog-signal feature information input from the feature extraction unit  19   a  into the digital signal and outputs this digital-signal feature information to the feature determination unit  19   b  via the switch  21 . The feature determination unit  19   b  determines whether the motion is detected on the basis of the digital-signal feature information. 
     In the fourth embodiment, the feature information, not the image information itself, is A/D converted on the feature detection mode. For this reason, since the amount of data A/D converted by the ADC  12  is smaller as compared to the first embodiment and the like, the power consumption in the ADC  12  can be further reduced. Further, in a case of A/D converting the feature information, A/D conversion at a lower bit resolution is possible as compared to a case of A/D converting the entire image information, and the power consumption in the ADC  12  can be reduced also in this point. 
     In a case of performing feature extraction from the analog-signal image information as in the fourth embodiment, the accuracy of the feature extraction (feature detection) is lower while the power consumption in the ADC  12  can be reduced as compared to the first embodiment and the like. On the other hand, as in the first embodiment, in a case of performing feature extraction from the digital-signal image information, the power consumption in the ADC  12  is higher while the accuracy of the feature extraction (feature detection) can be improved as compared to the fourth embodiment. 
     Therefore, in a case where the power consumption reduction is prioritized, a configuration like the configuration described in the fourth embodiment is employed. On the other hand, in a case where the accuracy of the feature extraction (feature detection) is prioritized, a configuration like the configuration described in the first embodiment or the like is employed. 
     Fifth Embodiment 
     Next, a fifth embodiment of the present technology will be described.  FIG.  11    is a block diagram showing an image sensor  34  according to the fifth embodiment. 
     It can be said that the fifth embodiment is a combination of the third embodiment and the fourth embodiment. That is, in the fifth embodiment, the motion extraction unit  18   a  of the motion detection unit  18  and the feature extraction unit  19   a  of the feature detection unit  19  are both provided in the ADC  12 . 
     In the fifth embodiment, since the motion information and the feature information, not the image information itself, are A/D converted by the ADC  12 , the power consumption in the ADC can further reduced. 
     Sixth Embodiment 
     Next, a sixth embodiment of the present technology will be described.  FIG.  12    is a block diagram showing a configuration of an imaging apparatus  101  according to the sixth embodiment. As shown in  FIG.  12   , in the sixth embodiment, as compared to the imaging apparatus according to each of the above-mentioned embodiments, a digital signal processor (DSP) circuit  7  is added. It should be noted that image signal processor (ISP) circuit and the like may be used instead of the DSP circuit  7 . 
       FIG.  13    is a block diagram showing a configuration of an image sensor  35  and the DSP circuit  7 . As shown in  FIG.  13   , in the sixth embodiment, the feature determination unit  19   b  of the feature detection unit  19  is provided inside the DSP circuit  7 . That is, in the sixth embodiment, the feature determination unit  19   b  is provided outside the image sensor  35 . 
     It should be noted that in the sixth embodiment, why the feature determination unit  19   b  is provided inside the DSP circuit  7  specially provided in the imaging apparatus  101  is that the processing of the feature determination is complicated than the other processing. 
     On the feature detection mode, the feature extraction unit  19   a  of the feature detection unit  19  extracts a feature of the object to be imaged from the middle-resolution image information input from the ADC  12 . Then, the feature extraction unit  19   a  outputs the feature information to the feature determination unit  19   b  in the DSP circuit  7 . It should be noted that the DSP circuit  7  is, for example, held in the active state only on the feature detection mode. 
     The feature determination unit  19   b  in the DSP circuit  7  determines whether a specific feature is detected on the basis of the feature information, and outputs a determination result to the mode control unit  16  in the image sensor  35 . 
     The other processing is basically similar to that of the first embodiment. 
     In the sixth embodiment, since the feature determination unit  19   b  is provided inside the DSP circuit  7  specially provided outside the image sensor  35 , the accuracy of the feature determination (feature detection) can be improved as compared to the first embodiment and the like. On the other hand, in a case where the feature determination unit  19   b  is provided inside the image sensor  10  as in the first embodiment and the like, there is an advantage that the time for the feature determination (feature detection) is shorter than in the sixth embodiment (e.g., because of unnecessity to activate the DPS circuit, no communication time between the DSP circuit  7  and the image sensor  35 , and the like). Further, in a case where the feature determination unit  19   b  is provided inside the image sensor  10  as in the first embodiment and the like, there is an advantage that the power consumption is reduced (because it is unnecessary to supply the DSP circuit  7  with power) as compared to the sixth embodiment. 
     That is, in a case where the feature determination unit  19   b  is provided inside the DSP circuit  7  as in the sixth embodiment, the time for the feature determination (feature detection) is longer and the power consumption increases while the accuracy of the feature determination (feature detection) can be increased as compared to the first embodiment and the like. On the other hand, in a case where the feature determination unit  19   b  is provided inside the image sensor  10  as in the first embodiment and the like, the accuracy of the feature determination (feature detection) is lower while the time for the feature determination (feature detection) can be shortened and the power consumption can be reduced as compared to the sixth embodiment. 
     Therefore, a configuration like the configuration described in the sixth embodiment is employed in a case where the accuracy of the feature determination (feature detection) is prioritized, and a configuration like the configuration described in the first embodiment is employed in a case where the time reduction for the feature determination and the power consumption reduction are prioritized. 
     It should be noted that in a case where the DSP circuit  7  is added in the imaging apparatus  101  as in the sixth embodiment, the image processing unit  20  may be provided inside the DSP circuit  7 . 
     In the sixth embodiment, the motion extraction unit  18   a  and the feature extraction unit  19   a  performs the motion extraction and the feature extraction from the digital-signal image information. However, as in the third embodiment to the fifth embodiment, at least one of the motion extraction unit  18   a  or the feature extraction unit  19   a  may perform the motion extraction and the feature extraction from the analog-signal image information. 
     Various Modified Examples 
     The present technology can also take the following configurations.
     (1) An imaging apparatus, including
       a mode control unit that   shifts, when a motion is detected on a motion detection mode to detect the motion on the basis of image information, the mode to a feature detection mode to detect features on the basis of image information having a higher resolution than a resolution of the image information that is used for the motion detection, and   shifts, when a specific feature is detected on the feature detection mode, the mode to an imaging mode to acquire image information having a higher resolution than the resolution of the image information that is used for the feature detection.   
       (2) The imaging apparatus according to (1), in which the mode control unit shifts the mode to the motion detection mode when the specific feature is not detected on the feature detection mode.   (3) The imaging apparatus according to (1) or (2), in which
       the mode control unit shifts the mode to the motion detection mode when a prescribed number of pieces of image information are acquired on the imaging mode.   
       (4) The imaging apparatus according to (1), in which
       the feature detection mode include a first feature detection mode and a second feature detection mode to more specifically perform feature detection than on the first feature detection mode.   
       (5) The imaging apparatus according to (4), in which
       the resolution of the image information that is used for the feature detection on the second feature detection mode is higher than the resolution of the image information that is used for the feature detection on the first feature detection mode.   
       (6) The imaging apparatus according to (4), in which
       the image information that is used for the feature detection on the first feature detection mode is an entire image and the image information that is used for the feature detection on the second feature detection mode is a partial image corresponding to a portion subjected to the features detection on the first feature detection mode.   
       (7) The imaging apparatus according to (6), in which
       the partial image has a resolution higher than a resolution of the entire image.   
       (8) The imaging apparatus according to any one of (4) to (7), in which
       the mode control unit shifts the mode to the first feature detection mode when the motion is detected on the motion detection mode, shifts the mode to the second feature detection mode when a specific feature is detected on the first feature detection mode, and shifts the mode to the imaging mode when a specific feature is detected on the second feature detection mode.   
       (9) The imaging apparatus according to (8), in which
       the mode control unit shifts the mode to when a specific feature is not detected on the first feature detection mode and shifts the mode to the motion detection mode when a specific feature is not detected on the second feature detection mode.   
       (10) The imaging apparatus according to any one of (1) to (9), further including
       a motion extraction unit that extracts the motion from the image information on the motion detection mode.   
       (11) The imaging apparatus according to (10), in which
       the motion extraction unit extracts the motion from image information of an analog signal.   
       (12) The imaging apparatus according to (10), in which
       the motion extraction unit extracts the motion from image information of a digital signal.   
       (13) The imaging apparatus according to any one of (1) to (12), further including
       a feature extraction unit that extracts the features from the image information on the feature detection mode.   
       (14) The imaging apparatus according to (13), in which
       the feature extraction unit extracts features from image information of an analog signal.   
       (15) The imaging apparatus according to (13), in which
       the feature extraction unit extracts features from image information of a digital signal.   
       (16) The imaging apparatus according to any one of (1) to (15), further including
       an image sensor including a pixel array portion that obtains the image information, in which   inside the image sensor, provided are   the mode control unit,   a motion extraction unit that extracts the motion from the image information on the motion detection mode,   a motion determination unit that determines whether the motion is detected on the basis of the motion extracted by the motion extraction unit on the motion detection mode, and   a feature extraction unit that extracts features from the image information on the feature detection mode.   
       (17) The imaging apparatus according to (16), in which
       inside the image sensor, provided is a feature determination unit that determines whether the specific feature is detected on the basis of features extracted by the feature extraction unit on the feature detection mode.   
       (18) The imaging apparatus according to (16), in which
       outside the image sensor, provided is a feature determination unit that determines whether the specific feature is detected on the basis of features extracted by the feature extraction unit on the feature detection mode.   
       (19) An imaging control method, including:
       shifting, when the motion is detected on the motion detection mode to detect the motion on the basis of the image information, the mode to the feature detection mode to detect features on the basis of the image information having a higher resolution than a resolution of the image information that is used for the motion detection; and   shifting, when a specific feature is detected on the feature detection mode, the mode to the imaging mode to acquire image information having a higher resolution than the resolution of the image information that is used for the feature detection.   
       (20) A program that causes a computer to execute processing, including:
       shifting, when a motion is detected on a motion detection mode to detect the motion on the basis of image information, the mode to a feature detection mode to detect features on the basis of image information having a higher resolution than a resolution of the image information that is used for the motion detection; and   shifting, when a specific feature is detected on the feature detection mode, the mode to an imaging mode to acquire image information having a higher resolution than the resolution of the image information that is used for the feature detection.   
       

     REFERENCE SIGNS LIST 
     
         
           10 ,  31  to  35  image sensor 
           11  pixel array portion 
           12  ADC 
           13  row scanning circuit 
           14  column scanning circuit 
           15  sensor control unit 
           16  mode control unit 
           17  timing control unit 
           18  motion detection unit 
           19  feature detection unit 
           20  image processing unit 
           100 ,  101  imaging apparatus