Abstract:
Reduction in power consumption is not considered in the prior art documents. Provided is an encoding method for encoding image information and having: a step in which image information is input; an analysis step in which the characteristics of the input image information are analyzed; a bit depth output step in which the bit depth for video encoding is determined and output; and an encoding step in which the bit depth output in the bit depth output step is used and the input image information is encoded. The encoding method is characterized by the output bit depth being switched in the bit depth output step, on the basis of the analysis results from the analysis step.

Description:
TECHNICAL FIELD 
       [0001]    A technical field relates to video encoding. 
       BACKGROUND ART 
       [0002]    PATENT LITERATURE 1 describes a technique of “assigning an upper bit-plane group as a base layer, and a bit-plane group having the larger number of bits including the upper bit-plane group as an enhancement layer in a plurality of bit-planes that give image data when hierarchically encoding a moving image, and generating encoded data of the enhancement layer by encoding a difference between the layers of a differential picture by prediction in the enhancement layer and a differential picture by prediction in the base layer in the enhancement layer” (see [0007] in PATENT LITERATURE 1) as a solving means for an object of “providing an encoding technique to efficiently performing encoding by imparting a pixel depth different for each moving image” ([0006] in PATENT LITERATURE 1). 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         PATENT LITERATURE 1: JP-A-2007-266749 (FIG. 1) 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0004]    However, the reduction of power consumption is not considered in PATENT LITERATURE 1. 
       Solution To Problem 
       [0005]    In order to solve the above-described problem, a configuration described in, for example, the claims is employed. 
         [0006]    The present application includes a plurality of means to solve the above-described problem, and an example thereof is an encoding method including: a step in which an image information is inputted; an analysis step of analyzing a feature of the inputted image information; a bit-depth output step of determining and outputting a bit-depth with respect to video encoding; and an encoding step of performing an encoding process on the inputted image information using the bit-depth output in the bit-depth output step, wherein, in the bit-depth output step, a bit-depth to be output is switched based on an analysis result in the analysis step. 
       Advantageous Effects of Invention 
       [0007]    According to the present invention, it is possible to reduce power consumption by changing a bit-depth depending on a feature of an image or a remaining amount of power. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1  is an example of a video encoding device according to a first embodiment. 
           [0009]      FIG. 2  is an example illustrating an image feature amount and a range within a feature amount threshold value according to the first embodiment. 
           [0010]      FIG. 3  is another example illustrating the image feature amount and the range within the feature amount threshold value according to the first embodiment. 
           [0011]      FIG. 4  is an example illustrating the image feature amount and the range within the feature amount threshold value according to the first embodiment. 
           [0012]      FIG. 5  is an example illustrating the range within the feature amount threshold value and a range threshold value according to the first embodiment. 
           [0013]      FIG. 6  is an example illustrating a bit-depth for each frame according to the first embodiment. 
           [0014]      FIG. 7  is another example illustrating the bit-depth for each frame according to the first embodiment. 
           [0015]      FIG. 8  is still another example illustrating the bit-depth for each frame according to the first embodiment. 
           [0016]      FIG. 9  is an example of a video encoding device according to a second embodiment. 
           [0017]      FIG. 10  is an example of a system in which the video encoding device according to the first embodiment or the second embodiment is used. 
           [0018]      FIG. 11  is an example of an in-vehicle camera system. 
           [0019]      FIG. 12  is an example of a monitoring camera system. 
           [0020]      FIG. 13  is an example of a teleconference system. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0021]    Recently, a need for high gradation of an image has been increased in a video encoding process so as to realize a high image quality of video content, digitization of an in-vehicle camera, and further improvement of stability in a monitoring system. 
         [0022]    In H.264/AVC standard, which is a typical video encoding method, a profile is defined according to a bit-depth, and it is possible to realize the high gradation by performing video encoding with a high bit-depth. 
         [0023]    In the following embodiments, a description will be made regarding an encoding device that realize high gradation of an image, and further reduce power consumption, and a system using the same. 
         [0024]    First, a description will be made regarding an outline of an in-vehicle camera system, a monitoring system and a teleconference system to which the encoding device of the present embodiments is applied. 
         [0025]      FIG. 11  is a block diagram illustrating an example of the in-vehicle camera system. In this example, network  111  is equipped in vehicle  110 , and camera units  112 ,  113 ,  114  and  115 , ECU (Engine Control Unit)  116  are connected to network  111 . In addition, monitor unit  117  is connected to the ECU. 
         [0026]    Camera units  112 ,  113 ,  114  and  115  transmit photographed ambient video information of vehicle  110  to network  111 . The video information may be transmitted to network  111  as an uncompressed state, or may be transmitted to network  111  after being subjected to compression processing in camera units  112 ,  113 ,  114  and  115 . 
         [0027]    ECU  116  receives the video information transmitted to network  111 , and outputs the video information to monitor  117 . ECU  116  performs decompression processing in a case where the video information to be input is compressed, and outputs the obtained decoded video information to monitor  117 . 
         [0028]    Monitor unit  117  performs video display of the received video information. ECU  116  and camera units  112 ,  113 ,  114  and  115  are capable of exchanging a control signal via network  111 . For example, it is possible to perform instruction of information require for camera processing or the compression processing from ECU  116  to camera units  112 ,  113 ,  114  and  115 . Examples of the information required for the camera processing include photographing start, photographing stop, and the like. Examples of the information required for the compression processing include a bit-depth, a control threshold, and the like. 
         [0029]    According to the configuration, it is possible to watch a video photographed by each camera on monitor  117 , to record in ECU  116 , and the like while controlling camera units  112 ,  113 ,  114  and  115 . 
         [0030]      FIG. 12  is a block diagram illustrating an example of the monitoring system. This example illustrates an exemplary monitoring system in which camera units  122 ,  123  and  124 , and monitoring center  120  are connected to network  121 . 
         [0031]    Camera units  122 ,  123  and  124  photograph ambient video information of each place where the each camera unit is installed, and transmit the information to network  121 . The video information may be transmitted to network  121  in an uncompressed state, or may be transmitted to network  121  after being subjected to compression processing in camera units  122 ,  123  and  124 . 
         [0032]    Monitoring center  120  receives the video information transmitted to network  121 , and analyzes the video information. Monitoring center  120  performs decompression processing in a case where the video information to be input is compressed. The monitoring center may have a monitor that displays the video information. 
         [0033]    Monitoring center  120  and camera units  122 ,  123  and  124  are capable of exchanging a control signal via network  111 . For example, it is possible to indicate information required for camera processing or the compression processing from monitoring center  120  to camera units  122 ,  123  and  124 . Examples of the information required for the camera processing include photographing start, photographing stop, and the like. Examples of the information required for the compression processing include a bit-depth, a control threshold, and the like. 
         [0034]    According to the configuration, it is possible to watch and record a video photographed by each camera by monitoring center  120  while controlling the cameras  122 ,  123  and  124  from monitoring center  120 . 
         [0035]      FIG. 13  is a block diagram illustrating an example of the teleconference system. This example illustrates an exemplary teleconference system in which terminal units  131 ,  134  and  137  are connected to network  130 . Terminal unit  131  has camera unit  133  and monitor unit  132 . 
         [0036]    Camera unit  133  photographs ambient video information of a place where the camera unit is installed, and outputs the information to terminal unit  131 . Terminal unit  131  transmits the received video information to network  130 . The video information may be transmitted to network  130  without compression, or may be transmitted to network  130  after compression processing in camera unit  133  or terminal unit  131 . In addition, terminal unit  131  inputs the video information to be transmitted to network  130 , and outputs the information to monitor unit  132 . 
         [0037]    Monitor unit  132  performs display of the inputted video information. In a case where the video information to be inputted is compressed, the video information is subjected to decompression processing in terminal unit  131  or monitor unit  132 , and the decoded video information is displayed in the monitor unit. 
         [0038]    Terminals  134  and  137  have the equivalent function as terminal  131 , and thus, the description thereof will be omitted. Terminal units  131 ,  134  and  137  are capable of exchanging a control signal among the respective terminal units via network  130 . For example, it is possible to perform instruction of information require for camera processing or compression processing from terminal unit  131  to terminal unit  134 . Examples of the information required for the camera processing include photographing start, photographing stop, and the like. Examples of the information required for the compression processing include a bit-depth, a control threshold, and the like. 
         [0039]    According to the configuration, the exchange of the video information or audio information among terminal units  131 ,  134  and  137 , and thus, the teleconference system can be realized. 
         [0040]    Next, a description will be made regarding an in-vehicle camera, a monitoring camera, and a camera for a teleconference system that are used in  FIGS. 11 to 13 .  FIG. 10  is a block diagram illustrating an example of a camera system. Each block may be configured using hardware, or it may be configured such that a part of or the entire function of each block is realized using software. 
         [0041]    Camera unit  2  is a block that digitizes a taken image, and outputs the digitized image. Video encoding device  1  is a block that encodes the image information output from camera unit  2  and outputs the encoded information. Network interface  3  is a block that outputs the video encoded data outputted from video encoding device  1  to network  5  such as LAN. CPU  4  is a block that controls camera unit  2 , video encoding device  1 , and network interface  3 . 
         [0042]    In the camera system of  FIG. 10 , the image taken in camera unit  2  is encoded by video encoding device  1 , and then, outputs the encoded image to network  5  via network interface  3 . 
         [0043]    Next, a description will be made regarding an operation of video encoding device  1  of  FIG. 10 .  FIG. 1  is a block diagram illustrating an example of a video encoding device according to the present embodiment. Each block may be configured using hardware, or it may be configured such that a part of or the entire function of each block is realized using software. 
         [0044]    Video encoding device  1  is a video encoding device that performs an encoding process on an input image, and outputs encoded video data. Video encoding device  1  is used in, for example, a broadcasting video delivery system, a broadcasting relay system, a portable terminal, a monitoring camera system, an in-vehicle camera system, and the like. 
         [0045]    Input unit  10  is a block that inputs image data to the video encoding device. Examples of the image data which is inputted to the input unit include image data photographed by an external camera, image data recorded in external recording media, and the like. 
         [0046]    Input image analysis unit  11  receives the image data taken by input unit  10 , and extracts one-type or a plurality of types of feature amount of the image data for each feature amount extraction region. An example of the feature amount extraction region is a rectangular pixel block configured of one pixel, or X×Y pixels (X and Y are all positive numbers). An example of the rectangular pixel block is a macroblock configured of 16 pixels×16 pixels, which is a unit of the video encoding. 
         [0047]    Examples of the feature amount of the image data include a luminance value, a chrominance value, a luminance or chroma variance, a luminance or chroma average value, a correlation value of luminance and chrominance, and the like. Examples of the average value include an average value of luminance values in the macroblock, and the like. 
         [0048]    Bit-depth determination unit  12  receives the feature amount of the image data, feature amount threshold value  100 , and range threshold value  101 , and determines a bit-depth, and outputs the result. Bit-depth determination unit  12  extracts the feature amount extraction region in which the feature amount of the image data is equal to or larger than feature amount threshold value  100 , and outputs a higher bit-depth in a case where a region in which the extracted feature amount extraction regions are continuous is equal to or larger than range threshold value  101 , than the other case. Feature amount threshold value  100  and range threshold value  101  are supplied from CPU  4  in  FIG. 10 , for example. Incidentally, bit-depth determination unit  12  is also referred to as a bit-depth output unit. 
         [0049]    An example of a unit of range threshold value  101  is a pixel. For example, when range threshold value  101  is set to 4096 pixels, a higher bit-depth is outputted in a case where the region in which the extracted feature amount extraction regions are continuous is equal to or larger than 4096 pixels, as compared to the case of being smaller than 4096 pixels. 
         [0050]    Another example of the unit of range threshold value  101  is the feature amount extraction region. For example, a case where the feature amount extraction region is the macroblock configured of 16 pixels×16 pixels is assumed. When range threshold value  101  is set to 16 macroblocks, a higher bit-depth is outputted in a case where the region in which the extracted feature amount extraction regions are continuous is equal to or larger than 16 macroblocks, as compared to the case of being smaller than 16 macroblocks. 
         [0051]    Examples of the bit-depth include 8-bit, 10-bit, and 12-bit. For example, 12-bit is outputted in a case where the region in which the extracted feature amount extraction regions are continuous is equal to or larger than range threshold value  101 , and 8-bit is outputted in the other case in bit-depth determination unit  12 . 
         [0052]      FIG. 4  is a diagram illustrating an example in which the unit of range threshold value  101  is set to the feature amount extraction region. In the present embodiment, lower-limit value B 0  is provided as feature amount threshold value  100 , and upper-limit value A 1  is provided as range threshold value  101 . Frame  40  represents an image frame region to be encoded. A feature amount extraction region of a portion painted in black in frame  40  is a feature amount extraction region in which the feature amount of the image data is smaller than lower-limit value B 0 . 
         [0053]    Image regions  41  and  42  are enlarged views of partial image regions in frame  40  each of which is configured of 6×6 feature amount extraction regions. Each feature amount extraction region is configured of 16 pixels×16 pixels. Image regions  43  and  44  painted in black are the feature amount extraction region in which the feature amount of the image data is smaller than lower-limit value B 0 . The number of the extracted continuous feature amount extraction regions in image region  41  is 5 regions. The number of the extracted continuous feature amount extraction regions in image region  42  is 23 regions. 
         [0054]    In a case where upper-limit value A 1  of range threshold value  101  is set to 4, the 5 regions and the 23 regions of the number of the extracted continuous feature amount extraction regions in frame  40  are all equal to or larger than upper-limit value A 1 , and thus, a bit-depth, which is higher than a bit-depth with respect to a frame configured only of an image region in which the number of the extracted continuous feature amount extraction regions is smaller than upper-limit value A 1 , is outputted as a bit-depth with respect to frame  40 . 
         [0055]    In addition, in a case where upper-limit value A 1  of range threshold value  101  is set to 10, one of the 5 regions and 23 regions of the number of the extracted continuous feature amount extraction regions in frame  40  is equal to or larger than upper-limit value A 1 , and thus, a bit-depth, which is higher than a bit-depth with respect to the frame configured only of the image region in which the number of the extracted continuous feature amount extraction regions is smaller than upper-limit value A 1 , is output as the bit-depth with respect to frame  40 . 
         [0056]    In addition, in a case where upper-limit value A 1  of range threshold value  101  is set to 100, the number of the extracted continuous feature amount extraction regions in frame  40  is smaller than upper-limit value A 1 , and thus, a bit-depth, which is lower than a bit-depth with respect to a frame including an image region in which the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 , is output as the bit-depth with respect to frame  40 . 
         [0057]      FIG. 2  is an example of an image photographed by the in-vehicle camera. In  FIG. 2 , lower-limit value B 0  is provided as feature amount threshold value  100 , and upper-limit value A 1  is provided as range threshold value  101 , and a feature amount extraction region in which the feature amount of the image data is smaller than lower-limit value B 0  is indicated by being-painted in black. Region  22  in frame  20  represents the feature amount extraction region in which the feature amount of the image data is smaller than lower-limit value B 0 . In addition, other region  21  represents a feature amount extraction region in which the feature amount of the image data is equal to or larger than lower-limit value B 0 . 
         [0058]    For example, a case where a vehicle equipped with the in-vehicle camera system gets approaching a tunnel is assumed. In a case where region  22  corresponds to a tunnel portion, a range of region  22  increases as the vehicle approaches the tunnel. In a case where upper-limit value A 1  of range threshold value  101  is set to N, bit-depth determination unit  12  outputs a lower bit-depth during a period until region  22  becomes N, than a case where region  22  is equal to or larger than N. 
         [0059]    When the car approaches the tunnel as much as region  22  becomes equal to or larger than N, bit-depth determination unit  12  switches the bit-depth to be outputted, and outputs a higher bit-depth than the case in which region  22  is smaller than N. In this example, it is possible to average and reduce loads of the encoding process by outputting a lower bit-depth in a case where the car gets away from the tunnel than in a case where the car approaches the tunnel within a predetermined distance and enters the tunnel and switching to a bit-depth higher than the bit-depth that has been outputted until then at a point in time at which the car approaches the tunnel and there occurs a need to view the inside of the tunnel in detail. 
         [0060]      FIG. 3  is an example of the image photographed by the in-vehicle camera. In  FIG. 3 , upper-limit value A 0  and lower-limit value B 0  are provided as the feature amount threshold value, upper-limit value A 1  is provided as range threshold value  101 , the feature amount extraction region in which the feature amount of the image data is smaller than lower-limit value B 0  is indicated by being-painted in black, and a feature amount extraction region in which the feature amount of the image data is equal to or larger than upper-limit value A 0  is indicated by oblique lines. Among image regions in frame  30 , region  32  represents a region in which the feature amount of the image data is smaller than lower-limit value B 0 . Region  31  represents a region in which the feature amount of the image data is equal to or larger than upper-limit value A 0 . Region  33  represents a region in which the feature amount of the image data is equal to or larger than lower-limit value B 0 , and further, is smaller than upper-limit value A 0 . 
         [0061]    In a case where the number of the extracted continuous feature amount extraction regions in frame  30  is equal to or larger than range threshold value  101 , a higher bit-depth is outputted. In a case where the macroblock is exemplified as the feature amount extraction region and an average luminance value per macroblock is exemplified as the feature amount, region  31  becomes a high luminance region and region  32  becomes a low luminance region. It is possible to perform the encoding process with a higher bit-depth with respect to a frame in which the high luminance region or the low luminance region equal to or larger than a predetermined region is present, as compared to a bit-depth with respect to the other frame, by applying the present embodiment. Accordingly, it is possible to suppress a blown out highlight in the high luminance region, and improve visibility of a dark portion in the low luminance region. 
         [0062]      FIG. 5  illustrates an example in which image frames are arranged in time order. In  FIG. 5 , lower-limit value B 0  is provided as feature amount threshold value  100 , and upper-limit value A 1  is provided as range threshold value  101 . 
         [0063]    Frames  50 ,  51 ,  52 ,  53 ,  54  and  55  represent the image frames arranged in time order. A portion painted in black in each of the frames represents a region in which the feature amount of the image data is smaller than lower-limit value B 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 . 
         [0064]    Frames  50  and  51  include the region in which the feature amount of the image data is smaller than lower-limit value B 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 . 
         [0065]    On the other hand, frames  52 ,  53 ,  54  and  55  do not include the region in which the feature amount of the image data is smaller than lower-limit value B 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 . 
         [0066]    Here, when bit-depth A is assumed to be lower than bit-depth B, bit-depth B is outputted in a case where the region in which the feature amount of the image data is smaller than lower-limit value A 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1  is present, and bit-depth A is outputted in the other case. 
         [0067]    In the example of  FIG. 5 , bit-depth B is outputted with respect to frames  50  and  51 , and bit-depth A is outputted with respect to frames  52 ,  53 ,  54  and  55 . Accordingly, it is possible to reduce the loads of the encoding process and the power consumption as compared to a case in which a high bit-depth is outputted with respect to the entire frame. 
         [0068]      FIG. 6  illustrates another example in which the image frames are arranged in time order. In  FIG. 6 , lower-limit value B 0  is provided as feature amount threshold value  100  and upper-limit value A 1  and dead zone information C 1  are provided as range threshold value  101 . 
         [0069]    The dead zone information is information for maintaining an existing bit-depth for a designated number of frames without changing the bit-depth in the case that corresponds to a condition under which the bit-depth is changed. A unit of dead zone information C 1  is the number of frames, and a value of dead zone information C 1  is set to 2 in  FIG. 6 . 
         [0070]    Frames  60 ,  61 ,  62 ,  63 ,  64  and  65  represent image frames arranged in time order. A portion painted in black in each of the frames represents a region in which the feature amount of the image data is smaller than lower-limit value B 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 . 
         [0071]    Frames  60  and  61  include the region in which the feature amount of the image data is smaller than lower-limit value B 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 . 
         [0072]    On the other hand, frames  62 ,  63 ,  64  and  65  do not include the region in which the feature amount of the image data is smaller than lower-limit value B 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 . 
         [0073]    Here, when bit-depth A is assumed to be lower than bit-depth B as similarly to  FIG. 5 , bit-depth B is outputted with respect to frames  60  and  61  that include the region in which the feature amount of the image data is smaller than lower-limit value A 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 . 
         [0074]    With respect to frames  62 ,  63 ,  64  and  65  that do not include the region in which the feature amount of the image data is smaller than lower-limit value A 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 , bit-depth B, which is the immediately preceding bit-depth, is maintained for the number of frames indicated by dead zone information C 1 , that is, two frames, that is, frames  62  and  63 . Further, bit-depth A is output for following frames after the number of frames indicated by dead zone information C 1 , that is, two frames, that is, frames  64  and  65 . 
         [0075]    It is possible to avoid a frequent switching of the bit-depth, or a wrong switching of the bit-depth through the process illustrated in  FIG. 6 . 
         [0076]      FIG. 7  illustrates still another example in which the image frames are arranged in time order. In  FIG. 7 , lower-limit value B 0  is provided as feature amount threshold value  100 , and upper-limit value A 1  and dead zone information D 1  are provided as range threshold value  101 . The unit of dead zone information D 1  is the number of frames. In  FIG. 7 , a value of dead zone information D 1  is set to 2. 
         [0077]    Frames  70 ,  71 ,  72 ,  73 ,  74  and  75  represent image frames arranged in time order. A portion painted in black in each of the frames represents a region in which the feature amount of the image data is smaller than lower-limit value B 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 . 
         [0078]    Frames  70  and  71  do not include the region in which the feature amount of the image data is smaller than lower-limit value B 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 . 
         [0079]    On the other hand, frames  72 ,  73 ,  74  and  75  include the region in which the feature amount of the image data is smaller than lower-limit value B 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 . 
         [0080]    Here, when bit-depth A is assumed to be lower than bit-depth B as similarly to  FIG. 5 , bit-depth A is output with respect to frames  70  and  71  that include the region in which the feature amount of the image data is smaller than lower-limit value A 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 . With respect to frames  72 ,  73 ,  74  and  75  that do not include the region in which the feature amount of the image data is smaller than lower-limit value A 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 , bit-depth A, which is the immediately preceding bit-depth, is maintained for the number of frames indicated by dead zone information D 1 , that is, two frames, that is, frames  72  and  73 . Further, the high bit-depth A is output for following frames after the number of frames indicated by dead zone information D 1 , that is, two frames, that is, frames  74  and  75 . 
         [0081]    It is possible to avoid the frequent switching of the bit-depth, or the wrong switching of the bit-depth through the process illustrated in  FIG. 7 . 
         [0082]      FIG. 8  illustrates further still another example in which the image frames are arranged in time order. In  FIG. 8 , lower-limit value B 0  is provided as feature amount threshold value  100 , and upper-limit value A 1  and high bit-depth insertion interval information E 1  are provided as range threshold value  101 . 
         [0083]    The high bit-depth insertion interval information is information that indicates a frame interval at which high bit-depth B is inserted. A unit of bit-depth insertion interval information E 1  is the number of frames. In  FIG. 8 , a value of bit-depth insertion interval E 1  is set to 2. 
         [0084]    Frames  80 ,  81 ,  82 ,  83 ,  84  and  85  represent image frames arranged in time order. A portion painted in black in each of the frames represents a region in which the feature amount of the image data is smaller than lower-limit value B 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 . 
         [0085]    Frames  80  and  81  do not include the region in which the feature amount of the image data is smaller than lower-limit value B 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 . 
         [0086]    On the other hand, frames  82 ,  83 ,  84  and  85  include the region in which the feature amount of the image data is smaller than lower-limit value B 0 , and further, the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1 . 
         [0087]    In  FIG. 8 , high bit-depth B is outputted for each frame interval indicated by high bit-depth insertion interval E 1  regardless of the feature amount of the image data, and a low bit-depth is output with respect to the other frames. 
         [0088]    It is possible to avoid the frequent switching of the bit-depth, or the wrong switching of the bit-depth through the process illustrated in  FIG. 8 . 
         [0089]    In the above-described embodiment, the switching of the bit-depth has been performed depending on whether the region in which the feature amount of the image data is smaller than lower-limit value B 0 , and the number of the extracted continuous feature amount extraction regions is equal to or larger than upper-limit value A 1  is present, but the switching of the bit-depth may be controlled in another method based on the feature amount of the image data. For example, a higher bit-depth is outputted in a case where an area or a ratio of a region in which the feature amount is smaller than a predetermined lower-limit value (for example, a ratio that accounts for one frame) is equal to or larger than a predetermined threshold value, than the case of being smaller than the predetermined value. 
         [0090]      FIG. 9  is a block diagram illustrating another example of the video encoding device. Each block may be configured using hardware, or it may be configured such that a part of or the entire function of each block is realized using software. 
         [0091]    A video encoding device of  FIG. 9  is configured such that external environment information  900  is further inputted to bit-depth determination unit  90  in the video encoding device illustrated in  FIG. 1 . External environment information  900  is supplied from CPU  4  of  FIG. 10 , for example, as similarly to feature amount threshold value  100  and range threshold value  101 . Incidentally, bit-depth determination unit  90  is also referred to as a bit-depth output unit. 
         [0092]    When a remaining amount of power of a battery to which the present video encoding device is connected is exemplified as external environment information  900  and a power amount threshold value is exemplified as feature amount threshold value  100 , a lower bit-depth is outputted in a case where the remaining amount of power of the battery to which the present video encoding device is connected is smaller than the power amount threshold value, as compared to the other case. Accordingly, in a case where the remaining amount of power of the battery to which the present video encoding device is connected decreases, it is possible to save power of the video encoding device. 
         [0093]    According to the above-described embodiments, it is possible to reduce the power consumption by changing the bit-depth depending on the image feature or the remaining amount of power. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  Video encoding device 
           10  Input unit 
           11  Input image analysis unit 
           12  Bit-depth determination unit 
           13  Video encoding unit 
           100  Feature amount threshold value 
           101  Range threshold value