Abstract:
An imaging apparatus includes an imaging unit configured to image an object, a gain adjustment unit configured to adjust a gain for an image signal output from the imaging unit, a signal processing unit configured to process the image signal, the signal processing unit including a first noise reduction unit to reduce a particular noise included in the image signal, an image compression unit configured to compress an image signal output from the signal processing unit, the image compression unit including a second noise reduction unit to reduce the particular noise included in the image signal output from the signal processing unit, and a control unit configured to set one of the first and second noise reduction units into an operative state and another unit into an inoperative state according to a gain adjustment by the gain adjustment unit.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an imaging apparatus, and more particularly, to an imaging apparatus including a noise reducing function. 
         [0003]    2. Description of the Related Art 
         [0004]    In recent years, a technique for processing a digital signal has been developed, and thus a large amount of digital information, e.g., a moving image, a still image, sound, or the like, can be easily compressively coded so as to be recorded on a small recording medium or transmitted to a communication medium. More particularly, in the field of compression coding of an image, a standard technique for moving image coding, e.g., MPEG-2 (Moving Picture Experts Group phase 2), has become widely used, and digital video cameras using MPEG-2 has come into practical use. 
         [0005]    An imaging function of a digital video camera includes a function referred to as a gain increase. A photographer can perform high-sensitive shooting by intentionally increasing the gain of an amplifier. However, when the gain-increased image signal is compressed with MPEG-2, image quality may be deteriorated by a random noise component. 
         [0006]    A cause of that problem is as follows. Since random noise components in the image signal caused by the gain increase do not correlate with each other between each frame, each noise component is determined as movement of an image. Thus, a great number of coding bits are allotted to the noise. As a result of this, the number of bits which should be allotted to original image information decreases, and thus, image quality after the compression coding is largely deteriorated. To prevent the deterioration of image quality, a configuration for controlling filter processing characteristics of an image compression unit according to a gain increase is discussed in U.S. Pat. No. 5,926,224 (corresponding to International Publication No. WO/1997/005745). 
         [0007]    Furthermore, a recent multifunction digital video camera includes a noise reduction filter, with which a photographer can set a noise elimination level so as to directly output a noise-reduced image signal to an external. Thus, the digital video camera includes a terminal adapted to directly output an image signal from a camera unit (a camera image signal) to an external image monitor, a video recording apparatus, or the like. 
         [0008]    Since a video camera capable of outputting an image signal from a camera unit to an external includes noise reduction units both in the camera unit and an image compression unit, an excessive amount of noise reduction may be applied at the time of recording an image signal. As a result, a high-frequency component of the image signal may be lost and image quality may be deteriorated. This problem is noticeable when a photographer sets a noise reduction level in the camera unit to high and increases the gain of an amplifier. 
         [0009]    In the configuration discussed in U.S. Pat. No. 5,926,224, a camera unit of the video camera does not include a noise reduction unit. Thus, when a camera image signal is directly output to an external with the gain increased, a noise of the camera image signal cannot be adjusted. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention is directed to an imaging apparatus capable of reducing deterioration of an image even when the gain is increased. 
         [0011]    The present invention is also directed to an imaging apparatus capable of adjusting a noise of a camera image signal output to an external. 
         [0012]    According to an aspect of the present invention, an imaging apparatus includes an imaging unit configured to image an object, a gain adjustment unit configured to adjust a gain for an image signal output from the imaging unit, a signal processing unit configured to process the image signal, the signal processing unit including a first noise reduction unit to reduce a particular noise included in the image signal, an image compression unit configured to compress an image signal output from the signal processing unit, the image compression unit including a second noise reduction unit to reduce the particular noise included in the image signal output from the signal processing unit, and a control unit configured to set one of the first and second noise reduction units into an operative state and another unit into an inoperative state according to a gain adjustment by the gain adjustment unit. 
         [0013]    Further features and aspects of the present invention will become apparent from the following detailed description of exemplary embodiments with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate exemplary embodiments, features, and aspects of the invention and, together with the description, serve to explain the principles of the invention. 
           [0015]      FIG. 1  is a block diagram showing an exemplary configuration of a camcorder according to an aspect of the present invention. 
           [0016]      FIG. 2  a block diagram showing an exemplary configuration of a noise reduction unit according to an aspect of the present invention. 
           [0017]      FIG. 3  is a block diagram showing an exemplary configuration of an image compression unit according to an aspect of the present invention. 
           [0018]      FIG. 4  is a schematic view illustrating a processing method of a three-dimensional filter processing according to an aspect of the present invention. 
           [0019]      FIG. 5  is a diagram showing an example of frequency characteristics of a three-dimensional filter according to an aspect of the present invention. 
           [0020]      FIG. 6  is an example of weighting coefficients used for a spatial filter processing according to an aspect of the present invention. 
           [0021]      FIG. 7  is a diagram showing an example of frequency characteristics of a spatial filter according to an aspect of the present invention. 
           [0022]      FIG. 8  is a flowchart illustrating control of a noise reduction unit according to an aspect of the present invention. 
           [0023]      FIG. 9  is a flowchart illustrating control of a noise reduction unit according to an aspect of the present invention. 
           [0024]      FIG. 10  illustrates an example of a setting screen for a camera setting menu according to an aspect of the present invention. 
           [0025]      FIG. 11  illustrates the relationship between a gain increase and a spatial filter or a three-dimensional filter according to an aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0026]    Various exemplary embodiments, features, and aspects of the invention will be described in detail below with reference to the drawings. 
       First Exemplary Embodiment 
       [0027]    A first exemplary embodiment of the present invention will now herein be described.  FIG. 1  is a block diagram showing an exemplary configuration of a camcorder  10  according to the first exemplary embodiment of the present invention. In  FIG. 1 , continuous lines indicate the flow of an image signal and dashed lines indicate the flow of a control signal. 
         [0028]    A camcorder  10  is a digital video camera but may be a digital still camera or the like. The camcorder  10  includes an imaging unit  12 , a camera image signal output terminal  22 , an image compression unit  30 , a recording/reproduction unit  32 , a recording medium  34 , an image expansion unit  36 , a reproduced image signal output terminal  38 , a display unit  40 , an operation unit  42 , and a system control unit  44 . 
         [0029]    The imaging unit  12  includes a lens system  14 , a charge-coupled device (CCD) image sensor  16 , an analog-to-digital conversion unit (A/D)  18 , and a signal processing unit  20 . 
         [0030]    The lens system  14  includes a lens, a zoom mechanism, a focus mechanism, a diaphragm, and the like. The lens system  14  forms an optical image from an object on an imaging plane of the CCD image sensor  16 . The CCD image sensor  16  converts the optical image from the lens system  14  into an electrical signal. 
         [0031]    The A/D conversion unit  18  includes a correlated double sampling (CDS)/auto gain control (AGC)  18 a and an A/D converter. The A/D conversion unit  18  converts the electrical signal from the CCD image sensor  16 , that is, an analog image signal, into a digital image signal. The signal processing unit  20  executes color correction processing, gamma correction, white balance adjustment, and matrix processing on the digital image signal from the A/D conversion unit  18 . Then, the signal processing unit  20  outputs a camera image signal to the image compression unit  30 , the camera image signal output terminal  22 , and the display unit  40 . Further, the signal processing unit  20  includes a noise reduction unit  20   a  including a three-dimensional filter or a spatial filter. 
         [0032]    The image compression unit  30  compresses the camera image signal from the signal processing unit  20  based on an image compression system, e.g., MPEG-2, H.264 (AVC), Motion JPEG, JPEG2000, or the like. The image compression unit  30  includes a noise reduction unit  30   a  including a three-dimensional filter or a spatial filter. In addition, the noise reduction unit  30   a  is used for a smoothing processing of an image to be coded before or after the image compression. 
         [0033]    The recording/reproduction unit  32  records compression image data from the image compression unit  30  on the recording medium  34  as recording data. Further, the recording/reproduction unit  32  reproduces compression image data recorded on the recording medium  34  and transfers the reproduction data to the image expansion unit  36 . The recording medium  34  is a hard disk, an optical disk, a magneto-optical disk, a magnetic tape, or a nonvolatile memory card. 
         [0034]    The image expansion unit  36  expands the compression image data from the recording/reproduction unit  32 . The image signal output from the image expansion signal  36  is a reproduced image signal. The reproduced image signal is output to the reproduced image signal output terminal  38  and the display unit  40 . 
         [0035]    The display unit  40  includes a liquid crystal display panel and a drive unit for the panel. The display unit  40  displays the camera image signal or the reproduced image signal as an image. The operation unit  42  includes an imaging switch, a reproduction switch, a recording switch, and the like and is used for operating each operation of imaging, reproducing, and recording. Further, the operation unit  42  is used for operating display of a camera setting menu screen. 
         [0036]    The system control unit  44  is configured to control the camcorder  10 , and especially control an auto gain control in the A/D conversion unit  18 , the noise reduction unit  20   a  in the signal processing unit  20 , and the noise reduction unit  30   a  in the image compression unit  30 . The system control unit  44  produces various control signals for controlling operations of each unit, and control signals S, A 1 , B 1 , C 1 , B 2  and C 2  will be described below. 
         [0037]    Now, an exemplary imaging operation, am exemplary recording operation, and an exemplary reproducing operation of the camcorder  10  will be described. In an imaging mode, the CCD image sensor  16  outputs an image signal representing an object image. The A/D conversion unit  18  converts the image signal from the CCD image sensor  16  into a digital image signal and supplies the digital image signal to the signal processing unit  20 . The signal processing unit  20  executes camera signal processing, e.g., gamma correction, and color correlation processing, on the digital image signal from the A/D conversion unit  18 . At this time, the image signal to be output from the signal processing unit  20  is temporarily stored in a frame memory incorporated in the signal processing unit  20  and is subjected to a noise reduction processing if necessary. Then, the image signal is transferred to the display unit  40  to be displayed on a screen of the display unit  40  in the order of storage. Accordingly, a user can confirm a range and composition of the object. 
         [0038]    In a recording mode, the image signal temporarily stored in the frame memory is also transferred to the image compression unit  30 . The image compression unit  30  compressively codes the camera image signal from the signal processing unit  20  and supplies the compressed image data to the recording/reproduction unit  32 . The recording/reproduction unit  32  records the compressed image data on the recording medium  34 . With this processing, image data including a series of images is stored in the recording medium in a compressed state. 
         [0039]    In a reproduction mode, the recording/reproduction unit  32  reads out compressed image data of a specified image from the recording medium  34  and transfers the compressed image data to the image expansion unit  36 . The image expansion unit  36  expands the compressed image data form the recording/reproduction unit  32  to restore image data. The restored image data, that is, a reproduced image signal, is supplied to the display unit  40 . With this processing, a reproduced image is displayed on the screen of the display unit  40 . 
         [0040]      FIG. 2  a block diagram showing an exemplary configuration of the noise reduction unit  20   a  in the signal processing unit  20 . The signal processing unit  20  is configured to generate a luminance signal (Y) and color-difference signals (Cr, Cb) and executes noise reductions on the luminance signal and the color-difference signals. In order to simplify descriptions, only a portion associated with the luminance signal (Y) is illustrated in  FIG. 2 . Control signals A 1 , B 1  and C 1  are supplied from the system control unit  44 . 
         [0041]    As illustrated in  FIG. 2 , the noise reduction unit  20   a  includes a selector  52 , frame memories  56 ,  58  and  60 , a three-dimensional filter processing unit  62 , a frame memory  64 , and a spatial filter processing unit  66 . 
         [0042]    The selector  52  is cyclically switched to terminals (a), (b) and (c) in the order of frames in an image signal to be processed, based on the control signal A 1  supplied from the system control unit  44 , which indicates switching of frames. More specifically, the selector  52  sequentially operates to store a luminance signal (Y) of the first frame in the frame memory  56 , to store a luminance signal (y) of the second frame in the frame memory  58 , to store a luminance signal (Y) of the third frame in the frame memory  60 , and to store a luminance signal (Y) of the forth frame in the frame memory  56 . The selector  52  repeats this processing in the case of a moving image. 
         [0043]    The three-dimensional filter processing unit  62  enables or disables thee-dimensional filter processing of image data stored in the frame memories  56 ,  58  and  60  according to the control signal B 1  supplied from the system control unit  44 . More specifically, when the control signal B 1  indicates ON (enable), the three-dimensional filter processing unit  62  executes three-dimensional filter processing of image data stored in the frame memories  56 ,  58  and  60  in the above-described order and outputs the processing results to the frame memory  64 . On the other hand, when the control signal B 1  indicates OFF (disable), the three-dimensional filter processing unit  62  directly outputs the present image data in the image data stored in the frame memories  56 ,  58  and  60  to the frame memory  64 . 
         [0044]    The spatial filter processing unit  66  enables or disables spatial filter processing of image data stored in the frame memory  64  according to the control signal C 1  supplied from the system control unit  44 . More specifically, when the control signal C 1  indicates ON (enable), the spatial filter processing unit  66  executes spatial filter processing of image data stored in the frame memory  64  and outputs the processing result. On the other hand, when the control signal C 1  indicates OFF (disable), the spatial filter processing unit  66  directly outputs the image data stored in the frame memory  64 . 
         [0045]    The camera signal processing unit  20  executes edge enhancement processing, color correction processing, and the like on the image data processed by the noise reduction processing unit  20   a  and outputs the processing result to the image compression unit  30 , the display unit  40 , and the camera output terminal  22 . 
         [0046]      FIG. 3  is a block diagram showing an exemplary configuration of the image compression unit  30 . The image compression unit  30  includes a noise reduction unit  30   a  and an MPEG2 compression coding circuit  30   b.  The noise reduction unit  30   a  has a configuration similar to that of the noise reduction unit  20   a  shown in  FIG. 2 .  FIG. 3  illustrates a three-dimensional filter processing unit  70  and a spatial filter processing unit  72  as typical elements of the noise reduction unit  30   a.  The control signal B 2  supplied from the system control unit  44  is an enable/disable signal which enables or disables the three-dimensional filter processing unit  70 . The control signal C 2  is an enable/disable signal which enables or disables the spatial filter processing unit  72 . Operations according to the control signals B 2  and C 2  are similar to those described with reference to  FIG. 2 . 
         [0047]    The three-dimensional filter processing will be described below.  FIG. 4  is a schematic view illustrating an exemplary processing method of the three-dimensional filter processing.  FIG. 5  is a diagram showing an example of frequency characteristics of a three-dimensional filter. 
         [0048]    In  FIG. 4 , frames F(n−1), F(n), and F(n+1) indicate image data stored in the frame memories  56 ,  58 , and  60 , respectively, in order. An image block  82  of the frame F(n) is compared with each of corresponding image blocks  80  and  84  of the frames F(n−1) and F(n+1) on a block-by-block basis. Then, if both differences are a predetermined value or less, the frame F(n) is determined as a still image and is averaged with corresponding pixels of the frames F(n−1), F(n), and F(n+1). If any one of the differences is greater than the predetermined value, the frame F (n) is determined as a moving image, and pixel values of the frame F(n) are directly output. It is publicly known that averaging processing of a still image reduces noise. 
         [0049]      FIG. 5  is a diagram illustrating an example of characteristics of the three-dimensional filter processing on an image signal of  30  frames/second. The horizontal axis indicates frame frequency and the vertical axis indicates gain. A curve  86  indicates the characteristic of an image block which is not subjected to the three-dimensional filter processing. A curve  88  indicates the characteristic of an image block which is subjected to the three-dimensional filter processing. 
         [0050]    Exemplary spatial filter processing will be described next.  FIG. 6  illustrates an example of weighting coefficients used for the spatial filter processing.  FIG. 7  is a diagram illustrating an example of frequency characteristics of a spatial filter. 
         [0051]    For example, an image block composed of 5 pixels×5 pixels in the horizontal and vertical directions centering on a target pixel in image data is considered. A value of the target pixel is multiplied by a weighting coefficient k 0 , and pixels around the target pixel are respectively multiplied by coefficients k 1  to k 24 . Then, 25 multiplied results are summed. Such a processing is known as a finite impulse response (FIR) filter method. This method properly sets values of the coefficients k 0  to k 24  to obtain a desired characteristic of spatial frequency. 
         [0052]    With such calculations, characteristics of the spatial filter processing as illustrated in  FIG. 7  can be obtained, so that a high-frequency noise component can be reduced. In  FIG. 7 , the horizontal axis indicates spatial frequency and the vertical axis indicates gain. A curve  90  indicates the characteristic of an image block which is not subjected to the spatial filter processing. A curve  92  indicates the characteristic of an image block which is subjected to the spatial filter processing. 
         [0053]    An exemplary control operation of the system control unit  44  will be described in detail with reference to  FIGS. 8 to 11 .  FIGS. 8 and 9  are flowcharts illustrating exemplary control of the noise reduction units  20   a  and  30   a  by the system control unit  44 .  FIG. 10  illustrates an example of a setting screen for a camera setting menu to set the gain increase, the spatial filter, and the three-dimensional filter.  FIG. 11  is a table showing the relationship among the gain increase, the spatial filter, and the three-dimensional filter. The setting screen for the camera setting menu in  FIG. 10  is a graphic user interface obtained by combining a screen image displayed on the display unit  40  and an operation instruction by the operation unit  42 . 
         [0054]    In the present embodiment, with the setting screen for a camera setting menu as illustrated in  FIG. 10 , a user can set the gain increase, the spatial filter, and the three-dimensional filter to ON or OFF. However, as for a default setting of the camera setting menu, each of the gain increase, the spatial filter, and the three-dimensional filter are set to ON. 
         [0055]    When an imaging start switch in the operation unit  42  is pushed, the system control unit  44  reads each setting information of the gain increase, the spatial filter, and the three-dimensional filter from a memory (not shown) (step S 10 ). In this case, when the gain increase is set to OFF, the spatial filter is set to ON, and the three-dimensional filter is set to OFF with the camera setting menu as illustrated in  FIG. 10 , the system control unit  44  reads information indicating the setting contents. 
         [0056]    The system control unit  44  determines whether the gain increase is set to ON or OFF based on the setting information read in step S 10  (step S 11 ). If the gain increase is set to OFF (OFF in step S 11 ), the system control unit  44  outputs a control signal S to the CDS/AGC  18 , which turns off the gain increase. Further, the system control unit  44  outputs control signals B 2  and C 2  to the image compression unit  30 , which turn off the three-dimensional filter processing and spatial filter processing in the image compression unit  30  (step S 12 ). 
         [0057]    The system control unit  44  determines whether the spatial filter is set to ON or OFF based on the setting information read in step S 10  (step S 13 ). If the spatial filter is set to ON (ON in step S 13 ), the system control unit  44  outputs a control signal C 1  to the signal processing unit  20 , which turns on the spatial filter processing in the signal processing unit  20  (step S 14 ). On the other hand, if the spatial filter is set to OFF (OFF in step S 13 ), the system control unit  44  outputs a control signal C 1  to the signal processing unit  20 , which turns off the spatial filter processing in the signal processing unit  20  (step S 15 ). 
         [0058]    The system control unit  44  determines whether the three-dimensional filter is set to ON or OFF based on the setting information read in step S 10  (step S 16 ). If the three-dimensional filter is set to ON (ON in step S 16 ), the system control unit  44  outputs a control signal B 1  to the signal processing unit  20 , which turns on the three-dimensional filter processing in the signal processing unit  20  (step S 17 ). On the other hand, if the three-dimensional filter is set to OFF (OFF in step S 16 ), the system control unit  44  outputs a control signal B 1  to the signal processing unit  20 , which turns off the three-dimensional filter processing in the signal processing unit  20  (step S 18 ). 
         [0059]    Accordingly, in the present embodiment, when the gain increase is set to OFF, the spatial filter processing and three-dimensional filter processing in the image compression unit  30  are forcibly stopped, and the system control unit  44  can operate the spatial filter processing and three-dimensional filter processing in the signal processing unit  20  according to setting by a user. 
         [0060]    On the other hand, when the gain increase is set to ON (ON in step S 11 ), the system control unit  44  outputs a control signal S to the CDS/AGC  18   a,  which turns on the gain increase. The system control unit  44  determines whether the spatial filter is set to ON or OFF based on the setting information read in step S 10  (step S 20 ). If the spatial filter is set to ON (ON in step S 20 ), the system control unit  44  outputs a control signal C 1  to the signal processing unit  20 , which turns on the spatial filter processing in the signal processing unit  20  (step S 21 ). Further, the system control unit  44  outputs a control signal C 2  to the image compression unit  30 , which turns off the spatial filter processing in the image compression unit  30  (step S 22 ). 
         [0061]    On the other hand, if the spatial filter is set to OFF (OFF in step S 20 ), the system control unit  44  outputs a control signal C 1  to the signal processing unit  20 , which turns off the spatial filter processing in the signal processing unit  20  (step S 23 ). Further, the system control unit  44  outputs a control signal C 2  to the image compression unit  30 , which turns on the spatial filter processing in the image compression unit  30  (step S 24 ). 
         [0062]    The system control unit  44  determines whether the three-dimensional filter is set to ON or OFF based on the setting information read in step S 10  (step S 25 ). If the three-dimensional filter is set to On (ON in step S 25 ), the system control unit  44  outputs a control signal B 1  to the signal processing unit  20 , which turns on the three-dimensional filter processing in the signal processing unit  20  (step S 26 ). Further, the system control unit  44  outputs a control signal B 2  to the image compression unit  30 , which turns off the three-dimensional filter processing in the image compression unit  30  (step S 27 ). 
         [0063]    On the other hand, if the three-dimensional filter is set to OFF (OFF in step S 25 ), the system control unit  44  outputs the control signal B 1  to the signal processing unit  20 , which turns off the three-dimensional filter processing in the signal processing unit  20  (step S 28 ). Further, the system control unit  44  outputs a control signal B 2  to the image compression unit  30 , which turns on the three-dimensional filter processing in the image compression unit  30  (step S 29 ) 
         [0064]    Accordingly, in the present embodiment, when the gain increase is set to ON, the spatial filter processing and three-dimensional filter processing in the signal processing unit  20  is operated according to setting by a user, and the image compression unit  30  operates only the noise reduction processing which is not operated in the signal processing unit  20 . Thus, overlapping of the noise reduction processing can be prevented. 
         [0065]      FIG. 11  illustrates the relationship among the gain increase, the three-dimensional filter processing and spatial filter processing in the signal processing unit  20 , and the three-dimensional filter processing and spatial filter processing in the image compression unit  30 . 
         [0066]    In the present embodiment, operating any one of the noise reduction unit  20   a  in the signal processing unit  20  and the noise reduction unit  30   a  in the image compression unit  30  facilitates preventing double noise reduction filter processing, thus reducing the deterioration of a recording image. Further, providing the noise reduction units  20   a  and  30   a  in the signal processing unit  20  and the image compression unit  30  facilitates applying optimum noise reduction processing to the camera image signal and the reproduced image signal. 
         [0067]    Accordingly, for example, when a photographer wishes to output the gain-increased camera image signal with clear image to an external from the camera image signal output terminal  22 , the noise reduction processing in the signal processing unit  20  can be set to ON. Further, when the photographer wishes to output a camera image signal intentionally keeping a feeling of noise to an external, the noise reduction processing in the signal processing unit  20  can be set to OFF. 
         [0068]    In the present embodiment, the noise reduction processing includes the three-dimensional filter and the spatial filter. However, the present invention is not limited to those filters, and a filter may be one type. In this case, for example, an operation state of the noise reduction unit  30 a in the image compression unit  30  can be switched according to an operation state of the noise reduction unit  20   a  in the signal processing unit  20 . 
         [0069]    Furthermore, the present embodiment exemplarily describes the three-dimensional filter and the spatial filter as the noise reduction filter. However, another filter capable of reducing noise, e.g., a median filter, can be used. 
         [0070]    Moreover, in the present embodiment, the noise processing unit  20   a  has a similar configuration as the noise processing unit  30   a.  However, those units can have different configurations to execute the noise reduction processing. 
         [0071]    Furthermore, in the present embodiment, the noise reduction filter processing is controlled by two steps of ON and OFF. However, the intensity of the filter processing can be gradually or continuously controlled. 
         [0072]    Additionally, the image compression unit  30  and the image expansion unit  36  can be configured with a single integrated circuit. A single output terminal can be used for outputting of the camera image signal and outputting of the reproduced image signal. 
         [0073]    Moreover, in the above-described embodiment, a photographer can manually set the gain, spatial filter, and three-dimensional filter in the imaging unit  12 . However, the present invention can also be applied to a case where the gain, spatial filter, and three-dimensional filter in the imaging unit  12  are automatically set according to the amount of exposure for an object. In this case, for example, the system control unit  44  controls the noise reduction unit  20   a  in the signal processing unit  20  and the noise reduction unit  30   a  in the image compression unit  30  based on the relationship as illustrated in  FIG. 11  according to the gain that is automatically determined by the CDS/AGC  18   a.    
         [0074]    While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures, and functions. 
         [0075]    This application claims priority from Japanese Patent Application No. 2006-035925 filed Feb. 14, 2006, which is hereby incorporated by reference herein in its entirety.