Patent Publication Number: US-2013229506-A1

Title: Imaging Apparatus, Imaging Method, and Endoscope Apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation and is based upon and claims the benefit of priority from U.S. application Ser. No. 13/111,811 and is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-261140, filed on Nov. 24, 2010; the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     Embodiments described herein relate generally to a head separated type imaging apparatus including a head unit and a main unit which are separated, the head unit imaging a subject and the main unit processing an image signal transmitted from the head unit, and to an imaging method and an endoscope apparatus. 
     BACKGROUND 
     Among conventional imaging apparatuses, there is one in which a camera device (head unit) including an image sensor (for example, a CCD (Charge Coupled Device) sensor, a CMOS (Complementary Metal Oxide Semiconductor) sensor, or the like) which images a subject is attached detachably to a host device (main unit). When the camera device is used in a state of being detached from the host device, the image signal of an image captured by the camera device is transmitted to the host device via wireless communication, and when the camera device is used in a state of being attached to the host device, the image signal of an image captured by the camera device is transmitted to the host device via wired communication. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a structural diagram of an endoscope apparatus according to a first embodiment. 
         FIG. 2  is a structural diagram of a head. 
         FIG. 3  is an explanatory diagram of correction data. 
         FIG. 4  is an explanatory diagram of a correcting method. 
         FIG. 5  is a structural diagram of a CCU. 
         FIG. 6  is a flowchart illustrating operation of the endoscope apparatus. 
         FIG. 7  is a structural diagram of an endoscope apparatus according to a second embodiment. 
         FIG. 8  is a structural diagram of a head. 
         FIG. 9  is a structural diagram of a CCU. 
         FIG. 10  is a structural diagram of an endoscope apparatus according to a third embodiment. 
         FIG. 11  is a structural diagram of a head. 
         FIG. 12  is a structural diagram of a CCU. 
         FIG. 13  is a flowchart illustrating operation of the endoscope apparatus. 
     
    
    
     DETAILED DESCRIPTION 
     An imaging apparatus according to an embodiment is a head separated type imaging apparatus including a head unit and a main unit which are separated, the main unit processing an image signal transmitted from the head unit. The main unit includes a first communication unit transmitting/receiving data to/from the head unit via wireless communication, a second communication unit transmitting/receiving data to/from the head unit via wired communication, and a control unit detecting whether the second communication unit is communicable, and continuing, when the first and second communication units are switched based on a detection result therefrom, transmission/reception of the data which is performed before the switching. 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 
     First Embodiment 
     In a first embodiment, the structure of ahead separated type endoscope apparatus as an example of an imaging apparatus will be described. Further, an embodiment using CMOS (Complementary Metal Oxide Semiconductor) sensors as an image sensor (imaging device) will be described. However, any other sensor such as a CCD (Charge Coupled Device) sensor or the like may be used instead of the CMOS sensors. 
       FIG. 1  is a structural diagram of an endoscope apparatus  1  according to the first embodiment. The endoscope apparatus  1  includes a scope  10  provided with an objective lens  10   a  on a leading end and inserted into a subject to be inspected, a head  20  transmitting via wireless communication or wired communication an image signal captured by an image sensor  21  (imaging unit) situated on an imaging plane of the objective lens  10   a , a CCU (camera control unit)  30  processing the image signal transmitted from the head  20 , a light source  40  for exposing an imaging area, and an optical fiber  60  for guiding the light from the light source  40  to a leading end portion of the scope  10 . In addition, the scope  10  is attached detachably to the head  20 . A camera cable  50  is a cable for wired communication between the head  20  and the CCU  30 , and houses signal wires for transmitting/receiving correction data, an image signal, a control signal, and so on. 
     (Structure of the Head  20 ) 
       FIG. 2  is a structural diagram of the head  20 . The head  20  includes the image sensor  21 , a memory  22 , a wired communication unit  23 , a wireless communication unit  24 , an internal antenna  25 , a transfer control unit  26 , a battery  27 , a connection terminal T 1 , and a charging terminal T 2 . The image sensor  21  is a three plate type image sensor, and is made up of a prism  21   a  separating the light from the objective lens  10   a  into three colors of R (red), G (Green), and B (Blue), and CMOS sensors  21   b  to  21   d  converting the light separated into the colors of R, G, B to electric signals. The three plate type image sensor has a characteristic in that it excels in color reproducibility because this sensor retains information of RGB for every pixel. The image sensor  21  is a color image sensor corresponding to full HD (high definition). 
     The image sensor  21  may be a single plate type instead of the three plate type. The single plate type image sensor has a color filter on each pixel of a CMOS sensor, and separates an electric signal outputted from the CMOS sensor into R, G, B signals in a circuit. This sensor has a characteristic in that it can be produced inexpensively because it is unnecessary to adhere the prism and the CMOS sensor to each other. In addition, examples of the array of color filters include color difference line sequential array and Bayer array. However, in the first embodiment it is not limited to the color difference line sequential array and Bayer array, and any one of various array types can be used. 
     The memory  22  is a non-volatile memory which is electrically rewritable (for example, a flash memory or the like) in which correction data (correction information) and setting conditions (for example, frame rate, gain, sensitivity, and so on) of the image sensor  21 , ID (identifier), and so on are stored. In addition, for the memory storing the correction data, the setting conditions, and so on, any memory other than the flash memory may be used as long as it is rewritable. 
     (Correction Data) 
     In the image sensor  21 , there exist two types of noise called fixed pattern noise (FPN) and random noise. In the first embodiment, correction data (correction information) of the fixed pattern noise are stored in advance in the memory  22  of the head  20 . The correction data are transferred from the head  20  to the CCU  30  when the endoscope apparatus  1  is activated, and the image signal transmitted from the image sensor  21  is corrected using the transferred correction data. 
     Among the fixed pattern noise, there are base noise whose level (intensity) does not change due to external environment (for example, temperature and luminance) and defect noise (for example, white spot and black spot) whose level changes due to the external environment. In the memory  22 , correction data for these two types of noise are stored. The respective correction data for the base noise and the defect noise will be described below. 
     (Correction Data for the Base Noise) 
       FIG. 3  is an explanatory diagram of correction data for the base noise. The base noise generates constant noise irrespective of the external environment. Accordingly, the base noise of the CMOS sensors provided in the image sensor  21  is measured in advance for every pixel, and correction data which cancel out the base noise as illustrated in  FIG. 3  are stored for every pixel in the memory  22 . The correction data of the base noise are stored in the memory  22  in the order of addresses of the pixels. 
     (Correction Data for Defective Pixels) 
     A white spot as defect noise refers to a pixel defect such that pixel data with values higher than those which should be originally outputted are outputted, and the pixel corresponding to the light receiving element thereof appears to be white, and occurs mainly due to a dark current. The dark current refers to a weak current which flows in the CMOS sensors even when no light is radiated, and occurs mainly due to a thermal factor or insulation failure. When the dark current is large, it causes noise in the image. 
     Further, a black spot as defect noise refers to a pixel defect such that pixel data with values lower than those which should be originally outputted are outputted, and the pixel corresponding to the light receiving element thereof appears to be black, and occurs mainly due to dust in the CMOS sensors. It is a failure which occurs when the dust blocks the light to be incident on pixels of the CMOS sensors or when circuits of the CMOS sensors are short circuited. 
     Among all the pixels of the CMOS sensors provided in the image sensor  21 , addresses at which pixel defects such as white spot and black spot have occurred are stored in the memory  22  as correction data for defective pixels.  FIG. 4  is an explanatory diagram of a method for correcting a defective pixel. As illustrated in  FIG. 4 , correction of defective pixels is performed such that image signals of both left and right adjacent pixels of a defective pixel are added and the added value is divided by two, and the resultant value is designated as an image signal of the defective pixel, thereby correcting the image signal of the defective pixel. 
     As described above, the following information is stored as the correction data in the memory  22 . Further, when the correction data stored in this memory  22  are read, they are read in the order of 1→2→3. 
     1: The number of correction data.
 
2: Correction data (plural data) of base noise.
 
3: Correction data (plural data) of defective pixels.
 
     Here, as the correction data of the base noise, correction data of respective pixels of the CMOS sensors of the image sensor  21  are stored together with addresses in the order of addresses of the pixels, and as the correction data of the defective pixels, addresses of the defective pixels are stored in the order of addresses of the pixels. 
     The wired communication unit  23  includes a serializer, an LVDS (low voltage differential signaling) conversion circuit, and so on, and transmits the correction data stored in the memory  22  and the image signal outputted from the image sensor  21  to the CCU  30  via the camera cable  50  connected to the connection terminal T 1 . Further, the communication unit receives initialization data (for example, resolution, clock, mode, and so on) transmitted from the CCU  30 , which will be described later. In addition, the image signal is transmitted as a digital signal as it is to the CCU  30 . 
     The wireless communication unit  24  transmits the correction data stored in the memory  22  and the image signal outputted from the image sensor  21  to the CCU  30  via the internal antenna  25 . Further, the communication unit receives initialization data transmitted from the CCU  30 , which will be described later. In addition, for the wireless communication, for example, methods defined by IEEE802.11a/b/g/n and Wireless HD can be used. 
     A transfer control unit  26  transfers the correction data and data of image signal, and the like to the CCU  30  based on an instruction from the CCU  30 . 
     The battery  27  is a power source supplying power to respective circuits (image sensor  21 , memory  22 , wired communication unit  23 , wireless communication unit  24 , internal antenna  25 , transfer control unit  26 , and so on) provided in the head  20 . The battery  27  is charged by an external power source (for example, a wall outlet) connected to the charging terminal T 2 . In addition, power lines for supplying power to the head  20  may be housed in the camera cable  50 , and the battery  27  may be charged by power supplied via this camera cable  50 . 
     (Structure of the CCU  30 ) 
       FIG. 5  is a diagram illustrating the structure of the CCU  30 . The CCU includes a connection terminal T 3 , a wired communication unit  31 , an internal antenna  32 , a wireless communication unit  33 , an image signal processing circuit  34 , an image output circuit  35 , a system control circuit  36 , a power supply circuit  37 , and a communication establishment determining unit  38 . To the connection terminal T 3 , the camera cable  50  is connected. 
     The wired communication unit  31  includes a deserializer  31   b  and an LVDS conversion circuit  31   b . When power of the CCU  30  is turned on, the wired communication unit  31  starts establishing communication with the wired communication unit  23  of the head  20  and outputs, when the communication is established, the correction signal transmitted from the head  20  via the camera cable  50  to the system control circuit  36  and the image signal to the image signal processing circuit  34 . Further, the wired communication unit  31  transmits a control signal and initialization data, which will be described later, outputted from the system control circuit  36  to the head  20  via the camera cable  50  connected to the connection terminal T 3 . 
     When power of the CCU  30  is turned on, the wireless communication unit  33  starts establishing communication with the wireless communication unit  24  of the head  20  and outputs, when the communication is established, the correction signal received via the internal antenna  32  to the system control circuit  36  and the image signal to the image signal processing circuit  34 . Further, the wireless communication unit  33  transmits the control signal and initialization data outputted from the system control circuit  36  to the head  20  via the internal antenna  32 . Here, when wireless communication is established, the wireless communication unit  33  transmits a signal periodically to the wireless communication unit  24  of the head  20 , and maintains the state that the wireless communication with the wireless communication unit  24  is established. 
     The image signal processing circuit  34  includes an image signal processing unit  34   a  and a synchronous signal generating unit  34   b . The image signal processing unit  34   a  processes the image signal outputted from the wired communication unit  31  and outputs the processed signal to the image output circuit  35 . The image signal processing unit  34   a  sorts image signals outputted from the wired communication unit  31  in the order of the addresses of pixels, and thereafter corrects the image signals based on the correction data read from the memory  22  of the head  20  and stored in a memory  36   a  by an MPU  36   c , which will be described later. 
     (Correction of the Base Noise) 
     The image signal processing unit  34   a  sorts the image signals in the order of addresses, and thereafter adds the correction data stored in the memory  36   a  to image signals having the same addresses, to thereby correct the image signals. The correction data stored in the memory  36   a  by the MPU  36   c  are created to cancel out the base noise of the CMOS sensors provided in the image sensor  21 , and thus image signals can be corrected by adding the correction data to the image signals having the same addresses. 
     (Correction of the Defective Pixel Noise) 
     The image signal processing unit  34   a  recognizes an image signal of a defective pixel from the addresses of defective pixels stored in the memory  36   a , adds image signals of both left and right adjacent pixels of this defective pixel and divides the added value by two, and designates the resultant value as the image signal of the defective pixel. The image signal of the defective pixel is corrected. 
     The image signal processing unit  34   a  performs enhancement processing such as de-mosaicking processing, knee correction, gamma correction, detail or matrix processing, or the like on the image signal after correction, and inputs the resultant signal to the image output circuit  35 . 
     The synchronous signal generating unit  34   b  generates a synchronous signal used for imaging with the image sensor  21 . The synchronous signal is generated at predetermined intervals corresponding to a set frame rate. The generated synchronous signal is outputted to the MPU  36   c , and is transmitted from the wired communication unit  31  or the wireless communication unit  33  to the head  20 . 
     The image output circuit  35  includes a D/A converter  35   a  and a DVI (digital visual interface) transmitter  35   b , and outputs an image signal processed in the image signal processing circuit  34  to an external monitor (not illustrated) as an analog and digital RGB (red, green, blue) signals. In addition, the image output circuit may include an HD-SDI (high definition serial digital interface) transmitter or an HD-DVI (high definition digital visual interface) instead of the DVI transmitter  35   b.    
     The system control circuit  36  includes the memory  36   a , an OSD (on-screen display) controller  36   b , the MPU (micro processing unit)  36   c , a receiving unit  36   d , and an operation accepting unit  36   e , and controls the entire endoscope apparatus  1 . The memory  36   a  is an EEPROM which is electrically rewritable. The memory  36   a  stores setting conditions (for example, exposure period, gain, and so on) of the CCU  30 , initialization data of the head  20 , and the number of initialization data (hereinafter referred to as initialization data number). 
     The exposure period is a parameter for adjusting the brightness of an image captured by the image sensor  21 , and is equivalent to a shutter speed. As the exposure period, it will suffice to have a few types (for example, 1/240 seconds, 1/120 seconds, and the like). Setting of this exposure period can be changed through an external PC (personal computer) or operation keys, which will be described later. 
     For the memory storing these setting conditions, any memory other than the EEPROM may be used as long as it is rewritable. The OSD controller  36   b  displays text data, bit map, and/or the like in a superposed manner on the image of an image signal processed in the image signal processing unit  34   a.    
     The MPU  36   c  controls the head  20 , the CCU  30 , and the light source  40  based on a remote control signal received in the receiving unit  36   d , a processing content accepted in the operation accepting unit, and set information stored in the memory  36   a.    
     (Transfer of the Correction Data) 
     Further, the MPU  36   c  specifies whether to transmit data via wired communication or via wireless communication, and instructs the transfer control unit  26  of the head  20  to transmit ID and correction data stored in the memory  22  of the head  20 . The MPU  36   c  stores the ID and the correction data transmitted from the transfer control unit  26  of the head  20  in the memory  36   a.    
     First, the MPU  36   c  instructs the transfer control unit  26  to transmit the ID stored in the memory  22  of the head  20 , and stores the transmitted ID in the memory  36   a . Then, the MPU  36   c  instructs the transfer control unit  26  to transmit the correction data number stored in the memory  22  of the head  20 , and stores the transmitted correction data number in the memory  36   a.    
     Furthermore, the MPU  36   c  instructs the transfer control unit  26  to transmit the correction data of base noise and the address of a pixel from the memory  22  of the head  20 , and stores the transmitted correction data of base noise and the transmitted address of a pixel in the memory  36   a.    
     Next, the MPU  36   c  instructs the transfer control unit  26  to transmit correction data (address of a pixel) of a defective pixel from the memory  22  of the head  20 , and stores the transmitted correction data of a defective pixel in the memory  36   a  of the CCU  30 . The MPU  36   c  stores read-out correction data of pixel defect noise (addresses of defective pixels) in the order of reading them out, that is, the order of addresses. 
     Here, the MPU  36   c  increments the value of an internal counter every time the transmitted correction data are stored in the memory  36   a , and at the point the value of this internal counter becomes equal to the correction data number in the memory  22 , the MPU determines that reading of the correction data is finished and resets the value of the internal counter. 
     (Transfer of the Initialization Data) 
     The MPU  36   c  further transmits the initialization data stored in the memory  36   a  to the head  20  via the wired communication unit  31  or the wireless communication unit  33 . The transmitted initialization data are stored in the memory  22  by the transfer control unit  26 . Here, the MPU  36   c  increments the value of an internal counter every time the initialization data are read out and transmitted to the head  20 , and at the point the value of this internal counter becomes equal to the initialization data number stored in the memory  36   a , the MPU determines that transmission of the initialization data is finished and resets the value of the internal counter. 
     In addition, generally wired communication has a fast transmission speed and high stability of communication compared to wireless communication. Thus, the MPU  36   c  uses wired communication in priority when both wireless communication and wired communication are established. 
     The receiving unit  36   d  receives the control signal for remote control which is transmitted from an external PC or the like, and outputs the received signal to the MPU  36   c . In addition, communication with the external PC is performed via an RS232-C serial port. The operation accepting unit  36   e  accepts processing operated by an external operation key, and outputs the accepted processing to the MPU  36   c . Examples of the operation to be accepted by the operation accepting unit  36   e  include an operation about performing/not performing correction of an image signal (ON/OFF operation of correction), and an operation of a set value of gain. 
     The power supply circuit  37  converts externally supplied power into a predetermined voltage, and supplies the converted voltage to respective circuits in the CCU  30 . Further, the power is also supplied to the head  20  via the camera cable  50  connected to the connection terminal T 3 . 
     The communication establishment determining unit  38  determines whether wired communication and wireless communication are established with the head  20  or not. Various methods can be used for determining this establishment of communication in the communication establishment determining unit  38 . For example, in the first embodiment, LVDS is used when an image signal is transmitted via wired communication. In the LVDS the image signal is transmitted by differential signals, and thus it is possible to determine whether wired communication is established or not between the wired communication unit  31  and the wired communication unit  23  of the head  20  from the presence of voltage between two transmission paths. 
     Upon establishment of wired communication from a state that wired communication is not established, the communication establishment determining unit  38  outputs a “wired communication establishment signal” to the MPU  36   c  of the system control circuit  36 . Further, when changing from the state that the wired communication is established to a state that the wired communication is not established, the communication establishment determining unit  38  outputs a “wired communication disconnection signal” to the MPU  36   c  of the system control circuit  36 . 
     Further, when establishment of communication in wireless communication is to be determined, for example, data transmission for confirming connection defined by IEEE8020.11a/b/g/n or Wireless HD is performed, and then whether wireless communication is established or not between the wireless communication unit  33  and the wireless communication unit  24  of the head  20  can be determined by whether there are response data (Ack) from the wireless communication unit  24  of the head  20  or not. 
     Upon establishment of wireless communication from a state that wireless communication is not established, the communication establishment determining unit  38  outputs a “wireless communication establishment signal” to the MPU  36   c  of the system control circuit  36 . Further, when changing from the state that the wireless communication is established to a state that the wireless communication is not established, the communication establishment determining unit  38  outputs a “wireless communication disconnection signal” to the MPU  36   c  of the system control circuit  36 . 
     The light source  40  includes a lamp and a lens. Further, the optical fiber  60  is connected to the light source  40 . The lamp is, for example, a xenon lamp and emits light for exposing the imaging area of the image sensor  21 . The lens guides the light emitted from the lamp into the optical fiber  60 . The light guided into the optical fiber  60  is led to the leading end portion of the scope  10  for exposing the imaging area of the image sensor  21 . 
     (Operation of the Endoscope Apparatus  1  when Activated) 
       FIG. 6  is a flowchart illustrating operation of the endoscope apparatus  1  according to the first embodiment. Hereinafter, the operation of the endoscope apparatus  1  according to the first embodiment will be described with reference to  FIG. 6 . Note that in the following description, the operation of the endoscope apparatus  1  will be described taking an example that one of wired communication and wireless communication is established. Further, in  FIG. 6 , the initialization data are transferred after transferring the correction data, but the correction data may be transferred after the initialization data are transferred. 
     (Step S 101 ) 
     When power of the CCU  30  is turned on, the MPU  36   c  resets the image signal processing circuit  34  and the image output circuit  35 . The reset mentioned here is, specifically, initialization of image processing setting. Further, the light source  40  turns on the lamp based on a control signal from the MPU  36   c . The light from the lamp is guided into the optical fiber  60  and is radiated via the leading end portion of the scope  10  for exposing the imaging area of the image sensor  21 . 
     (Step S 102 ) 
     The MPU  36   c  reads out the setting conditions (for example, exposure period, gain, and so on) of the CCU  30  from the memory  36   a , and changes the set values of the image signal processing circuit  34  and the image output circuit  35  to the values read from the memory  36   a.    
     (Step S 103 ) 
     The wired communication unit  31  of the CCU  30  starts communication with the wired communication unit  23  of the head  20 . Further, the wireless communication unit  33  of the CCU  30  starts communication with the wireless communication unit  24  of the head  20 . The communication establishment determining unit  38  outputs the “wired communication establishment signal” when the communication between the wired communication unit  31  of the CCU  30  and the wired communication unit  23  of the head  20  is established. Further, the communication establishment determining unit  38  outputs the “wireless communication establishment signal” when the communication between the wireless communication unit  33  of the CCU  30  and the wireless communication unit  24  of the head  20  is established. 
     (Step S 104 ) 
     The MPU  36   c  determines which of wired communication and wireless communication is established based on the “wired communication establishment signal” or the “wireless communication establishment signal” outputted from the communication establishment determining unit  38 . 
     (Step S 105 ) 
     The MPU  36   c  starts obtaining the correction data from the memory  22  of the head  20  when the “wired communication establishment signal” or the “wireless communication establishment signal” is outputted from the communication establishment determining unit  38 . At this time, when the “wired communication establishment signal” is outputted from the communication establishment determining unit  38 , the MPU  36   c  instructs the transfer control unit  26  to transmit the correction data from the memory  22  of the head  20  via wired communication. On the other hand, when the “wireless communication establishment signal” is outputted from the communication establishment determining unit  38 , the MPU  36   c  instructs the transfer control unit  26  to transmit the correction data from the memory  22  of the head  20  via wireless communication. 
     (Step S 106 ) 
     First, the MPU  36   c  instructs the transfer control unit  26  to transmit the ID and the correction data number, and stores the transmitted ID and correction data number in the memory  36   a.    
     Next, the MPU  36   c  instructs the transfer control unit  26  to sequentially transmit the correction data, and stores the transmitted correction data in the memory  36   a . At this time, the MPU  36   c  increments the value of the internal counter every time a piece of the correction data is stored in the memory  22 . 
     (Step S 107 ) 
     The MPU  36   c  determines whether the piece of the correction data stored in step S 106  is the last piece of the correction data or not. Specifically, the MPU  36   c  determines whether or not the value of the internal counter is equal to the correction data number stored in the memory  36   a.    
     When the value of the internal counter is not equal to the correction data number stored in the memory  36   a  (No in Step S 107 ), the MPU  36   c  repeats the operation of step S 105  to step S 107  until the value of the internal counter becomes equal to the correction data number stored in the memory  36   a.    
     (Step S 108 ) 
     When the value of the internal counter is equal to the correction data number stored in the memory  36   a  (Yes in Step S 107 ), the MPU  36   c  reads out the initialization data (for example, resolution, clock, mode, and so on) from the memory  36   a  and transmits the read data to the head  20 . The initialization data transmitted to the head  20  are stored in the memory  22  by the transfer control unit  26 . 
     (Step S 109 ) 
     The MPU  36   c  increments the value of the internal counter every time a piece of the initialization data is transferred. 
     (Step S 110 ) 
     The MPU  36   c  determines whether the piece of the initialization data transferred in the step S 108  is the last piece of the initialization data or not. Specifically, the MPU  36   c  determines whether or not the value of the internal counter is equal to the initialization data number stored in the memory  36   a.    
     When the value of the internal counter is not equal to the initialization data number stored in the memory  36   a  (No in Step S 110 ), the MPU  36   c  repeats the operation of step S 108  to step S 110  until the value of the internal counter becomes equal to the initialization data number stored in the memory  36   a.    
     When the value of the internal counter is equal to the initialization data number stored in the memory  36   a  (Yes in Step S 110 ), the MPU  36   c  proceeds to the next step. 
     (Step S 111 ) 
     The synchronous signal generating unit  34   b  generates a synchronous signal and transmits the generated synchronous signal to the head  20  at predetermined time intervals. 
     (Step S 112 ) 
     Upon reception of the synchronous signal transmitted from the synchronous signal generating unit  34   b , the image sensor  21  accumulates a charge in a phototransistor for every scanning line, converts the accumulated charges in respective phototransistors into voltages, and amplifies and reads out the voltages. 
     (Step S 113 ) 
     The charges accumulated in the respective phototransistors of the image sensor  21  are converted into voltages for every scanning line, and thereafter amplified, read out, and transmitted to the CCU  30  as an image signal. 
     (Step S 114 ) 
     The image signal processing unit  34   a  of the image signal processing circuit  34  performs sorting of pixel information in the image signal transmitted from the head  20 , and performs correction on this sorted image signal. The image signal processing unit  34   a  corrects the image signal based on the correction data stored in the memory  36   a . Furthermore, the image signal processing unit  34   a  performs enhancement processing and/or the like on the image signal after correction, and then outputs the processed image signal to the image output circuit  35 . 
     (Step S 115 ) 
     The image output circuit  35  outputs the image signal outputted from the image signal processing unit  34   a  to an external monitor (not illustrated) as an analog and digital RGB (red, green, blue) signals, and a corrected image is displayed on this monitor. 
     (Operation of the Endoscope Apparatus  1  when Transferring Data) 
     Next, operation of the endoscope apparatus  1  when transferring data according to the first embodiment will be described with respect to the following three cases. 
     Case 1: Wireless communication is established, and then wired communication is established.
 
Case 2: Wired communication is established, and then wireless communication is established.
 
Case 3: Wired communication is established and then wireless communication is established, and thereafter the wired communication is disconnected.
 
     (Case 1) 
     The case 1 will be described. As the situation that wireless communication is established and then wired communication is established, for example, it is conceivable that the endoscope apparatus  1  is activated in a state that the camera cable  50  is removed, and thereafter the head  20  and the CCU  30  are connected by the camera cable  50 . 
     When wireless communication is established first in step S 103  of  FIG. 6 , the communication establishment determining unit  38  outputs the “wireless communication establishment signal”. The MPU  36   c  determines that wireless communication is established based on the “wireless communication establishment signal” outputted from the communication establishment determining unit  38 , and instructs the transfer control unit  26  to transmit the ID and the correction data via wireless communication. 
     When wired communication is established and the communication establishment determining unit  38  outputs the “wired communication establishment signal” while the ID and the correction data are obtained via wireless communication, the MPU  36   c  determines that wired communication is established based on the “wired communication establishment signal” outputted from the communication establishment determining unit  38 , and instructs the transfer control unit  26  to switch the communication with the head  20  from wireless communication to wired communication. 
     The MPU  36   c  instructs the transfer control unit  26  to transmit the ID via wired communication. The MPU  36   c  determines whether the ID transmitted from the transfer control unit  26  and the ID obtained when the wired communication is established are the same or not. When the IDs are the same, the MPU  36   c  determines to what point the correction data have been transferred from the value of the internal counter, and instructs the transfer control unit  26  to transfer the rest of the correction data via wired communication. Further, when the IDs are not the same, the MPU  36   c  resets the value of the internal counter, and instructs the transfer control unit  26  to transfer the correction data from the beginning. 
     Although the operation when the correction data are transferred has been described above, note that operation when the initialization data and the image signal are transferred is the same. That is, when wired communication is established while the initialization data are transferred, the MPU  36   c  switches the communication with the head  20  from wireless communication to wired communication, determines to what point the initialization data have been transferred from the value of the internal counter, and transfers the rest of the initialization data via wired communication. Further, when wired communication is established while the image signal is transferred, the MPU  36   c  instructs the transfer control unit  26  to switch the communication with the head  20  from wireless communication to wired communication and transmit the image signal via wired communication. 
     (Case 2) 
     The case 2 will be described. As the situation that wired communication is established and then wireless communication is established, for example, it is conceivable that the endoscope apparatus  1  is activated in a state that the camera cable  50  is attached. Generally, wired communication is faster in communication speed than wireless communication, and thus it is conceivable that the wired communication is established first when the endoscope apparatus  1  is activated in a state that the camera cable  50  is attached. 
     When wired communication is established first in step S 103  of  FIG. 6 , the communication establishment determining unit  38  outputs the “wired communication establishment signal”. The MPU  36   c  determines that wired communication is established based on the “wired communication establishment signal” outputted from the communication establishment determining unit  38 , and instructs the transfer control unit  26  to transmit the ID and the correction data via wired communication. When wireless communication is established while the ID and the correction data are transmitted via wired communication, the communication establishment determining unit  38  outputs the “wireless communication establishment signal”. 
     The MPU  36   c  determines that wireless communication is established based on the “wireless communication establishment signal” outputted from the communication establishment determining unit  38 . However, since the wired communication is faster in communication speed and higher in stability of communication than the wireless communication, the MPU  36   c  continues transmission of the correction data via wired communication without switching the communication. 
     Although the operation when the correction data are transferred has been described above, note that operation when the initialization data and the image signal are transferred is the same. That is, when wireless communication is established while the initialization data or image signal is transferred, the communication is not switched, and transfer of the rest of the initialization data or image signal is continued via wired communication without switching the communication. 
     (Case 3) 
     The case 3 will be described. As the situation that wired communication is established and then wireless communication is established, and thereafter the wired communication is disconnected, for example, it is conceivable that the endoscope apparatus  1  is activated in a state that the camera cable  50  is attached, and thereafter the camera cable  50  is removed. 
     When wired communication is established first in step S 103  of  FIG. 6 , the communication establishment determining unit  38  outputs the “wired communication establishment signal”. The MPU  36   c  determines that wired communication is established based on the “wired communication establishment signal” outputted from the communication establishment determining unit  38 , and instructs the transfer control unit  26  to transmit the ID and the correction data via wired communication. When wireless communication is established while the ID and the correction data are transmitted via wired communication, the communication establishment determining unit  38  outputs the “wireless communication establishment signal”. 
     The MPU  36   c  determines that wireless communication is established based on the “wireless communication establishment signal” outputted from the communication establishment determining unit  38 . However, since the wired communication is faster in communication speed and higher in stability of communication than the wireless communication, the MPU  36   c  continues transfer of the rest of the correction data via wired communication without switching the communication. 
     Thereafter, when the camera cable  50  is removed while the correction data are transferred, the communication establishment determining unit  38  detects the disconnection of wired communication and outputs the “wired communication disconnection signal”. The MPU  36   c  determines that the wired communication is disconnected based on the “wired communication disconnection signal” outputted from the communication establishment determining unit  38 , and switches the communication with the head  20  from wired communication to wireless communication. 
     After the communication is switched, the MPU  36   c  instructs the transfer control unit  26  to transmit the ID via wireless communication. The MPU  36   c  determines whether the ID transmitted from the transfer control unit  26  and the ID obtained when the wired communication is established are the same or not. When the IDs are the same, the MPU  36   c  determines to what point the correction data have been transferred from the value of the internal counter, and instructs the transfer control unit  26  to transfer the rest of the correction data via wireless communication. Further, when the IDs are not the same, the MPU  36   c  resets the value of the internal counter, and instructs the transfer control unit  26  to transfer the correction data from the beginning. 
     Although the operation when the correction data are transferred has been described above, note that operation when the initialization data and the image signal are transferred is the same. That is, when wired communication is disconnected while the initialization data are transferred, the MPU  36   c  switches the communication with the head  20  from wired communication to wireless communication, determines to what point the initialization data have been transferred from the value of the internal counter, and transfers the rest of the initialization data via wireless communication. Further, when wired communication is disconnected while the image signal is transferred, the MPU  36   c  instructs the transfer control unit  26  to switch the communication with the head  20  from wired communication to wireless communication and transmit the image signal via wireless communication. 
     As has been described, since the endoscope apparatus  1  according to the first embodiment stores to what point the correction data and the initialization data are transferred by using the counter, it is unnecessary to start over the transfer of the correction data and the initialization data from the beginning when the communication state is switched from wireless communication to wired communication or switched from wired communication to wireless communication, allowing efficient transfer of data. 
     Further, the endoscope apparatus  1  according to the first embodiment uses wired communication in priority. Generally, wired communication has a fast transmission speed and high stability of communication compared to wireless communication. Thus, by using wired communication in priority, the communication speed and the stability can be secured. 
     Furthermore, since the state that wireless communication is established is maintained even when wired communication is established first, the communication can be switched immediately to the wireless communication to continue transfer of data when the wired communication is disconnected while the data are transmitted. 
     In addition, in the above description, although establishment of wired communication and wireless communication is started from the CCU  30  side, it may be structured such that establishment of wired communication and wireless communication is started from the head  20  side. 
     Second Embodiment 
     In a second embodiment, an embodiment will be described which transfers the correction data and the initialization data in different file formats via wired communication and wireless communication. Note that the same components as those of the endoscope apparatus  1  according to the first embodiment which are described with  FIG. 1 ,  FIG. 2 , and  FIG. 5  are denoted by the same numerals, and duplicated descriptions are omitted. 
       FIG. 7  is a structural diagram illustrating an endoscope apparatus  2  according to the second embodiment. As illustrated in  FIG. 7 , the endoscope apparatus  2  according to the second embodiment is different in structure from the endoscope apparatus  1  according to the first embodiment described with  FIG. 1  in that it includes a head  20 A and a CCU  30 A. 
       FIG. 8  is a structural diagram of the head  20 A provided in the endoscope apparatus  2  according to the second embodiment. As illustrated in  FIG. 8 , the head  20 A of the endoscope apparatus  2  according to the second embodiment is different from the head  20  of the endoscope apparatus  1  according to the first embodiment in that it includes a coding/decoding unit  28 . 
     The coding/decoding unit  28  of the head  20 A lossless compresses the correction data and data of the image signal to be transferred from the memory  22  to the CCU  30 A based on an instruction from the transfer control unit  26 . Further, the coding/decoding unit  28  decodes the initialization data transferred from the CCU  30 A to the memory  22  based on an instruction from the transfer control unit  26 . 
     Specifically, when the correction data and data of the image signal are transferred to the CCU  30 A using wireless communication, the transfer control unit  26  instructs the coding/decoding unit  28  to lossless compress (code) the correction data and data of the image signal to be transferred to the CCU  30 A, and the transfer control unit  26  transfers the correction data and data of the image signal which are lossless compressed in the coding/decoding unit  28  to the head  20 A. Further, when the initialization data are transmitted from the CCU  30 A using wireless communication, the transfer control unit  26  instructs the coding/decoding unit  28  to decode the lossless compressed initialization data to return them to the data before being compressed, and stores the decoded initialization data in the memory  22 . 
       FIG. 9  is a structural diagram of the CCU  30 A provided in the endoscope apparatus  2  according to the second embodiment. As illustrated in  FIG. 9 , the CCU is different from the CCU  30  of the endoscope apparatus  1  according to the first embodiment in that a system control circuit  36 A provided in the CCU  30 A of the endoscope apparatus  2  according to the second embodiment includes a coding/decoding unit  36   f.    
     The coding/decoding unit  36   f  of the CCU  30 A lossless compresses the initialization data to be transferred from the memory  36   a  to the head  20 A based on an instruction from the MPU  36   c . Further, the coding/decoding unit  36   f  decodes the lossless compressed correction data and data of the image signal transferred from the head  20 A based on an instruction from the MPU  36   c.    
     Specifically, when transmitting the initialization data to the head  20 A using wireless communication, the MPU  36   c  instructs the coding/decoding unit  36   f  to lossless compress the initialization data to be transmitted, and transmits the initialization data lossless compressed in the coding/decoding unit  36   f  to the head  20 . Further, when the correction data and data of the image signal are transmitted to the CCU  30 A using wireless communication, the MPU instructs the coding/decoding unit  36   f  to decode the correction data and data of the image signal to return them to the data before being compressed, and stores the decoded correction data and data of the image signal in a memory  236   a.    
     As described above, when data (correction data, initialization data, and image signal data) are transferred via wireless communication, the endoscope apparatus  2  according to the second embodiment transfers lossless compressed data. Generally, wireless communication has a slow communication speed compared to wired communication, but while performing wireless communication, the volume of data is reduced by lossless compressing the data to be transferred, and thus the time taken for data transfer can be shortened. 
     Third Embodiment 
       FIG. 10  is a structural diagram of an endoscope apparatus  3  according to a third embodiment. Hereinafter, the endoscope apparatus  3  according to the third embodiment will be described. The same components as those of the endoscope apparatus  1  according to the first embodiment which are described with  FIG. 1 ,  FIG. 2 , and  FIG. 5  are denoted by the same numerals, and duplicated descriptions are omitted. 
     The endoscope apparatus  3  according to the third embodiment includes a plurality of heads  20   a ,  20   b , and a CCU  30 B used in common between the heads  20   a ,  20   b . The CCU  30 B includes a plurality of terminals  30   a ,  30   b  for charging batteries provided in the heads  20   a ,  20   b , and performs transfer of the correction data and the initialization data while the batteries of the heads  20   a ,  20   b  connected to the terminals  30   a ,  30   b  are charged. 
     Here, in the third embodiment, the head in use (head  20   a  in  FIG. 10 ) communicates with the CCU  30 B via wireless communication, and the other head (head  20   b  in  FIG. 10 ) is connected to one of the terminals  30   a ,  30   b  of the CCU  30 B to have the battery charged. 
       FIG. 11  is a structural diagram of the head  20   a . Note that the heads  20   a ,  20   b  have the same structure, and thus only the head  20   a  will be described here. As illustrated in  FIG. 11 , the head  20   a  of the endoscope apparatus  3  according to the third embodiment is different from the head  20  of the endoscope apparatus  1  according to the first embodiment described with  FIG. 2  in that it includes a terminal T 3  combining a connection terminal for the wired communication unit  23  and a charging terminal for the battery  27 . By connecting this terminal T 3  to one of the terminals  30   a ,  30   b  of the CCU  30 B, it becomes possible to perform wired communication with the CCU  30 B and to charge the battery  27 . In addition, IDs (identifiers) different from each other are stored in the memories  22  of the heads  20   a ,  20   b , respectively. 
     Further, the connection terminal for the wired communication unit  23  and the charging terminal for the battery  27  need not necessarily be combined, and can be structured of separate terminals as long as they have shapes such that contacts with both the terminals are made when the head is brought into contact with the CCU  30 B. 
       FIG. 12  is a structural diagram of the CCU  30 B. As illustrated in  FIG. 12 , the CCU  30 B includes the plurality of terminals  30   a ,  30   b  and a connection detecting circuit  39 . Each of the terminals  30   a ,  30   b  is a terminal combining a connection terminal for the wired communication unit  31  and a charging terminal for the battery  27  provided in the head  20   a ,  20   b . Each of the terminals  30   a ,  30   b  is connected to the wired communication unit  31  and the power supply circuit  37 , and when the terminal T 3  of the head  20   a ,  20   b  is connected thereto, it becomes possible to perform wired communication with the head  20   a ,  20   b  and charge the battery  27  of the head  20   a ,  20   b.    
     The connection detecting circuit  39  detects connection of the head  20   a ,  20   b  to the terminal  30   a ,  30   b . When the terminal T 3  of the head  20   a ,  20   b  is connected to the terminal  30   a ,  30   b , the connection detecting circuit  39  notifies the MPU  36   c  and the power supply circuit  37  of the terminal to which the head  20   a ,  20   b  is connected. 
     Next, operation while the head  20   a ,  20   b  provided in the endoscope apparatus  3  according to the third embodiment is charged will be described.  FIG. 13  is a flowchart illustrating the operation of the endoscope apparatus  3  according to the third embodiment. Note that in the following, operation in the case where the head  20   a  is in use and the head  20   b  is connected to the terminal  30   b  of the CCU  30 B will be described. 
     (Step S 201 ) 
     When the terminal T 3  of the head  20   b  is connected to the terminal  30   b  provided in the CCU  30 B, the connection detecting circuit  39  detects that one of the head  20   a  and the head  20   b  is connected to the terminal  30   b . The connection detecting circuit  39  notifies the MPU  36   c  and the power supply circuit  37  of the connection of the head to the terminal  30   b.    
     (Step S 202 ) 
     Based on the notification from the connection detecting circuit  39 , the power supply circuit  37  supplies power to the terminal  30   b  which is notified, thereby starting charging of the battery  27  of the head  20   b.    
     (Step S 203 ) 
     The MPU  36   c  instructs the wired communication unit  31  to establish wired communication with the head  20   b  based on the notification from the connection detecting circuit  39 . The wired communication unit  31  establishes wired communication with the wired communication unit  23  of the head  20   b  via the terminal  30   b  based on the instruction from the MPU  36   c.    
     (Step S 204 ) 
     Once the wired communication is established, the MPU  36   c  instructs the transfer control unit  26  to transmit the ID from the memory  22  of the head  20   b , and stores the transmitted ID in the memory  36   a.    
     (Step S 205 ) 
     Once the ID is stored, the MPU  36   c  instructs the transfer control unit  26  to transmit the correction data from the memory  22  of the head  20   b , and stores the transmitted correction data in the memory  36   a  in association with the ID which is read in advance. 
     (Step S 206 ) 
     First, the MPU  36   c  instructs the transfer control unit  26  to transmit the number of correction data, and stores the transmitted correction data number in the memory  36   a . Next, the MPU  36   c  instructs the transfer control unit  26  to sequentially transmit the correction data stored in the memory  22 , and stores the transmitted correction data in the memory  36   a . At this time, the MPU  36   c  increments the value of the internal counter every time a piece of the correction data is stored in the memory  36   a.    
     (Step S 207 ) 
     The MPU  36   c  determines whether the piece of the correction data stored in the memory  36   a  in step S 106  is the last piece of the correction data or not. Specifically, the MPU  36   c  determines whether or not the value of the internal counter is equal to the correction data number stored in the memory  36   a.    
     When the value of the internal counter is not equal to the correction data number stored in the memory  36   a  (No in step S 207 ), the MPU  36   c  repeats the operation of step S 205  to step S 207  until the value of the internal counter becomes equal to the correction data number stored in the memory  36   a.    
     (Step S 208 ) 
     When the value of the internal counter is equal to the correction data number stored in the memory  36   a  (Yes in step S 207 ), the MPU  36   c  reads out the initialization data (for example, resolution, clock, mode, and so on) from the memory  36   a  and transmits the read data to the head  20 . The initialization data transmitted to the head  20  are stored in the memory  22  by the transfer control unit  26 . 
     (Step S 209 ) 
     The MPU  36   c  increments the value of the internal counter every time a piece of the initialization data is transferred. 
     (Step S 210 ) 
     The MPU  36   c  determines whether the piece of the initialization data transferred in the step S 208  is the last piece of the initialization data or not. Specifically, the MPU  36   c  determines whether or not the value of the internal counter is equal to the initialization data number stored in the memory  36   a.    
     When the value of the internal counter is not equal to the initialization data number stored in the memory  36   a  (No in Step S 210 ), the MPU  36   c  repeats the operation of step S 208  to step S 210  until the value of the internal counter becomes equal to the correction data number stored in the memory  36   a.    
     When the value of the internal counter is equal to the initialization data number stored in the memory  36   a  (Yes in Step S 110 ), the MPU  36   c  finishes the transfer of initialization data. 
     As described above, the endoscope apparatus  3  according to the third embodiment includes the plurality of heads  20   a ,  20   b , and the CCU  30 B used in common between the heads  20   a ,  20   b , and performs transfer of the correction data and the initialization data while the batteries in the head  20   a ,  20   b  connected to the terminals  30   a ,  30   b  of the CCU  30  are charged. Thus, it is unnecessary to transfer the correction data and the initialization data via wireless communication, which has slow communication speed compared to wired communication, when the heads  20   a ,  20   b  are used, and the image signal transferred from the heads  20   a ,  20   b  can be corrected immediately to obtain a clear image. Accordingly, convenience for the user improves. 
     In the imaging apparatus or the endoscope apparatus according to at least one of the above-described embodiments, a main unit (CCU) includes a first communication unit (wireless communication unit) transmitting/receiving data to/from the head unit via wireless communication, a second communication unit (wired communication unit) transmitting/receiving data to/from the head unit via wired communication, and a control unit (MPU) detecting whether the second communication unit is communicable, and continuing, when the first and second communication units are switched based on a detection result therefrom, transmission/reception of the data which is performed before the switching. Thus, even when the communication state changes, transfer of data can be performed continuing from the data which have been transferred. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodiment in a variety of other forms; furthermore, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.