PATENT DOCUMENT

Abstract:
This device includes an image data creator that creates a first type of image data for test shooting and creating a second type of image data for real shooting; a compressor that compresses the image data in a predetermined compression format; and a processor; wherein the compressor has one or plural compression parameters relating to a compression rate; the creator newly supplies files of the first type to the compressor one after another; the compressor compresses at least two files among the continuously supplied first type using values of compression parameters; the processor decides the value of the compression parameter to be used for the second type according to a predetermined standard, based on two and more files of first type image data that are compressed using values of compression parameters; and the processor sets the value of the compression parameter of the compressor at the decided value.

Full Description:
RELATED APPLICATION  
       [0001]     This application is a U.S. Continuation Application under 35 USC 371 of International Application PCT/JP2003/008038 filed 25 Jun. 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a function for optimally controlling a value of a compression parameter when compressing the image data that is photographed by a digital photographic device, and particularly, the present invention relates to the optimum method in the case of mounting a control function of the compression parameter value of such image data in a camera-equipped cellular phone and a camera-equipped PDA or the like and a digital photographic device that is provided with the structure for this method.  
         [0004]     2. Description of the Related Art  
         [0005]     In recent years, there are many occasions that a camera is incorporated in an electric device such as a personal computer, a PDA, and a cellular phone. These devices also can photograph a still image and a moving image as same as a digital camera that is a conventional specialized photographic machine. However, there is a function to estimate number of remaining images to be shot as a function that is mounted in the digital camera that is the specialized photographic machine but that has not mounted yet in a multi-function cellular phone, PDA, or the like such as a camera-equipped cellular phone.  
         [0006]     The remaining shot number predicting function displays the number of images that can still be shot. According to a film camera, since a piece of film is consumed for each shooting, it is possible to clearly know the number of remaining images to be shot. However, according to a digital image pick-up apparatus which saves the photographs as data in a digital format, since it is normal that the portion of a data recording medium consumed by one shot is not fixed, the user cannot clearly know the number of images that can still be shot. If the user cannot know the number of remaining images, it is difficult for the user to form a shooting plan and it is a disadvantage for the user. Therefore, conventionally, in the digital camera that is the specialized photographic machine, a function that makes efforts to maintain a uniform consumption of the data recording by each shooting so as to make it possible to estimate the number of remaining images to be shot is mounted.  
         [0007]     In order to easily estimate the number of remaining images, it is effective to make the data size of the image data file to be generated by each shooting uniform because the number of photographable images can still be shot can be calculated from the remaining capacity of the data recording medium if the data size of the image data file generated for each shot is regular. In the meantime, since more image data are saved in the data recording medium, the image data is normally compressed and then saved in the data recording medium. One or a plurality of parameters is involved in this compression and a parameter called a quality factor is a typical one in the compression of a JPEG format. The sizes of the data of images after compression using the same parameter value are different depending on the content of the photographed image. Accordingly, when all the image data are compressed by the same compression parameter, the size of the generated image data file is different for each shooting. Therefore, as described in JP-A-4-233373, in the conventional specialized photographic machine, the data of different images generated by shooting is compressed at different compression parameter values and when it is compressed into a desired data size, the compressed image data is saved so as to always maintain a set data size of the compression image data file to be generated. Accordingly, the parameter value of the compression parameter for use in the compression of the image data is slightly different for each shooting.  
         [0008]     The structure of the hardware of the conventional specialized photographic machine and a method of deciding a parameter value of a compression parameter will be described with reference to  FIG. 7 .  FIG. 7  typically shows a hardware structure of the conventional specialized photographic machine. A specialized photographic machine  130  is configured by a lens  132 , a solid-state image pickup device  133 , an A/D converter  134 , a DSP  135  for the image processing, a CPU  136 , a temporary storage unit  137 , a main storage device  138 , a display  139 , and a user interface  140  such as a shutter button, and the exchange of a signal among these devices is carried out through a bus  131 . If the shutter button of the user interface  140  is pressed down, the CPU  136  issues an order to start shooting, the light passed through the lens  132  is converted into an electric signal by the solid-state image pickup device  133 , and this electric signal is digitalized by the A/D converter  134  to be temporally stored in the temporary storage unit  137 . Here, all of the signals outputted from all pixels of the solid-state image pickup device are stored in the temporary storage unit  137  as the digital data. Next, the DSP  135  reads the output signal of the solid-state image pickup device  133  that is made into the digital data stored in the temporary storage unit  137  to create the image data for one photographed frame from the data. The image data is in a YUV format. The DSP  135  temporarily saves the created image data for one frame in the temporary storage unit  137  again.  
         [0009]     Continuously, the DSP  135  reads the image data for one frame that was created previously from the temporary storage unit  137  and it JPEG-compresses this image data at a predetermined compression parameter value, and measures the data size after the compression. The compression format is normally JPEG. When the data size after compression is not a desired data size, the image data for one frame from the temporary storage unit  137  is read again, the compression parameter is changed, it is compressed again, and the DSP  135  measures the data size after compression. Then, repeating the above-described operation, the DSP  135  saves the image data that is compressed at a compression parameter value that the data size after compression becomes the desired data size in the main storage device  138 .  
         [0010]     However, trying to execute the above-described conventional method of controlling a parameter value of a compression parameter also in the conventional camera-equipped cellular phone, two disadvantages are generated. This will be described with reference to  FIG. 8 .  
         [0011]      FIG. 8  typically shows a conventional camera-equipped cellular phone. A conventional camera-equipped cellular phone  150  is characterized in that it comprises a host module  152  handling functions such as telephone calling and scheduling and an interface  153  is located among the modules. The reason that a conventional camera-equipped cellular phone  150  in particular comprises two modules is that a general versatility is given to the camera module. If a camera part is made into an independent module, it is possible to combine the same camera module with various cellular phones and PDAs.  
         [0012]     Such a camera module is obviously forced to be a compact size and cheap. However, if the conventional method of controlling a parameter value of a compression parameter used in the conventional specialized photographic machine is used, a DSP  135  with a high processing ability and a temporary storage unit  137  must be mounted in the camera module, and this makes the camera module a large size and expensive. Since the temporary storage unit  137  must save the image data configuring one frame, the higher the resolution of the image pickup device is, the more the size and the price of the camera module are increased.  
         [0013]     Therefore, if the conventional method of controlling a parameter value of a compression parameter is mounted on a host module  152  without providing a compression function of the image data to a camera module  151 , the other disadvantage is generated. In this case, at first, the bus width of an interface  153  should be widened so as to be capable of transferring the image data that is not compressed. In order to make the bus width broad, the number of the signal line for this should be increased and this increases the size and the price of the camera module. Accordingly, it is preferable that the image data is compressed by the camera module  151  and then transferred to the interface  153 . In addition, it is preferable that the data processing amount is made as light as possible, because while the host module also has a temporary storage device and a CPU, the host module must perform various processing not done by the specialized photographic machine. Accordingly, a method to decide the parameter value of a compression parameter by exchanging the image data between the temporary storage unit and the CPU many times is not effective.  
         [0014]     Thus, due to a problem with respect to the sizes and the prices of the camera module and the interface and the data processing capability, the conventional camera-equipped cellular phone and camera-equipped PDA or the like cannot make the data size of the image data file uniform by controlling the compression parameter value of the image data.  
       SUMMARY OF THE INVENTION  
       [0015]     The object of the present invention is to provide a digital photographic device for controlling a parameter value of a compression parameter to be used for the compression of the image data without needing a large-size temporary storage unit, a broad bus width, or a high processing capability; and a method of deciding the parameter value of the compression parameter of the image data.  
         [0016]     The first invention of the present application may provide a digital photographic device including: an image data creator that creates first type of image data for test shooting and creating second type of image data for real shooting; a compressor that compresses the image data in a predetermined compression format; and a processor that processes the data; wherein the compressor has one or plural compression parameters determining a compression rate; the image data creator newly supplies the first type of image data to the compressor one after another, newly performing the test shooting one after another; the compressor compresses at least two and more first type of image data among the continuously supplied first type of image data at values of the compression parameters which are different from each other; the processor decides the value of the compression parameter to be used for the second type of image data, based on two and more first type image data files that were compressed with different compression parameters, according to a predetermined standard; and further, the processor sets the value of the compression parameter of the compressor to be the above decided value.  
         [0017]     In the digital photographic device, it is preferable that the first type of data has a lower resolution than that of the second type of image data. In addition, in the digital photographic device, any one of the one or plural compression parameters may be not only a one-dimensional matrix but also a second-dimensional matrix. Further, in the digital photographic device, it is preferable that the predetermined standard relates to a compression rate. In addition, in the digital photographic device, it is preferable that the predetermined standard relates to a compression rate estimation table to estimate the difference between the compression rate in the test shooting image data and the compression rate of the image data for saving, caused chiefly by the difference of the resolution of these two images.  
         [0018]     Further, the digital photographic device is provided with a display unit and it is preferable that the digital photographic device is configured in such a manner that the processor displays the first type of image data that is not compressed by the compressor on the display unit. In addition, the digital photographic device is provided with a main storage unit to store the data and it is preferable that the digital photographic device is configured in such a manner that the data creator supplies the second type of image data to the compressor for the real shooting; the compressor compresses the second type of image data to be supplied with the decided value of the parameter; and the processor saves the compressed second type of image data in the main storage unit. Further, in the digital photographic device, it is preferable that the predetermined compression system is a JPEG format. In addition, in the digital photographic device, it is preferable that the one or plural compression parameters include a quantization table or a quality factor.  
         [0019]     Further, the second invention of the present application may provide a digital photographic device including: a camera module including an image data creator that creates a first type of image data for test shooting and second type of image data having a higher resolution than that of the first type of image data for real shooting, a compressor that compresses the image data at a predetermined compression format, a data output part for transmitting the data to the outside, and a control signal input part for receiving a control signal; and a host module including a processor that processes the data, a data input part for receiving the data, and a control signal output part for transmitting a control signal to the camera module; wherein the compressor has one or plural compression parameters relating to a compression rate, the camera module newly supplies the first type of image data to the compressor one after another, newly performs the test shooting one after another with the image data creator; compresses at least two files of the first type of image data from the repeatedly supplied first type of image data, each with different compression parameters, with the compressor; and transmits the compressed first type of image data to the host module through the data output part one after another; and the host module receives the compressed first type of image data through the data input part one after another, decides with the processor the value of the compression parameter to be used for the second type of image data according to a predetermined standard, based on the two or more first-type image data files that are compressed with values of the compression parameters which are different from each other; and further, transmits a control signal through the control signal output part which has the processor set the value of the compression parameter of the compressor at the value decided.  
         [0020]     In the digital photographic device according to the second invention, any one of the one or plural compression parameters may be a matrix. In addition, in the digital photographic device according to the second invention, it is preferable that the predetermined standard relates to a compression rate.  
         [0021]     Further, in the digital photographic device according to the second invention, it is preferable that the host module is provided with a display unit and a main storage unit for storing the data; the camera module transmits the first type of image data that is not compressed by the compressor to the host module through the data output part one after another; the host module receives the first type of image data that is not compressed through the data input part one after another and displays the first type of image data that is not compressed by the compressor on the display unit; further, the camera module supplies the second type of image data to the compressor for the real shooting by the image data creator; compresses the supplied second type of image data with the compressor, using the decided value of the compression parameter; and transmits the compressed second type of image data to the host module through the data output part; and the host module receives the compressed second type of image data through the data input part and saves the compressed second type of image data in the main storage unit by the processor.  
         [0022]     Further, the third invention of the present application may provide a digital photographic device including: a camera module including an image data creator that creates a first type of image data for test shooting and a second type of image data having a higher resolution than that of the first type of image data for real shooting, a first compressor that compresses the image data in a predetermined compression format, a data output part for transmitting the data to the outside, and a control signal input part for receiving a control signal; and a host module including a processor that processes the data, a data input part for receiving the data, and a control signal output part for transmitting a control signal to the camera module; wherein the host module is provided with a second compressor; the compressor has one or plural compression parameters relating to a compression rate; the camera module newly creates the first type of image data one after another, the image data creator newly performing the test shooting one after another, and transmits the continuously created first type of image data to the host module through the data output part one after another; the host module receives the created first type of image data through the data input part one after another; compresses at least two and more files of the first type image data among the continuously received first type image data using the values of compression parameters which are different from each other, with the second compressor; decides with the processor the value of the compression parameter to be used for the second type of image data according to a predetermined standard, based on the two and more files of first type image data that are compressed using the values of the compression parameters which are different from each other; and further, transmits a control signal through the control signal output part in order to set the value of the compression parameter of the first compressor at the value decided by the processor.  
         [0023]     In the digital photographic device according to the third invention of the present application, any one of the one or plural compression parameters may be a matrix. In addition, in the digital photographic device according to the third invention of the present application, it is preferable that the predetermined standard relates to a compression rate. Further, in the digital photographic device according to the third invention of the present application, it is preferable that the second compressor is realized by the same hardware as that of the processor.  
         [0024]     Further, in the digital photographic device according to the third invention of the present application, it is preferable that the host module is provided with a display unit and a main storage unit for storing the data and displays on the display unit, from among the continuously received first type of image data, that which is not compressed by the compressor; further, the camera module supplies the second type of image data for the real shooting generated by the image data creator to the first compressor; compresses the second type of image data to be supplied, using the decided value of the compression parameter, with the first compressor; and transmits the compressed second type of image data to the host module through the data output part; and the host module receives the compressed second type of image data through the data input part and saves the compressed second type of image data in the main storage unit by the processor.  
         [0025]     In addition, the fourth invention of the present application may provide a digital photographic device including: a camera module including an image data creator that creates a first type of image data for test shooting and second type of image data for real shooting, having a higher resolution than that of the first type of image data, a compressor that compresses the image data in a predetermined compression format, and a data output part for transmitting the data to the outside; and a host module including a first processor that processes the data and a data input part for receiving the data; wherein the camera module is provided with a second processor that processes the data; the compressor has one or plural compression parameters relating to a compression rate; the camera module newly supplies the first type of image data to the compressor one after another upon new test shooting one after another by the image data creator; compresses with the compressor at least two files from among the continuously supplied first type of image data, using values of the compression parameters which are different from each other; decides with the second processor the value of the compression parameter to be used for the second type of image data according to a predetermined standard based on the two and more files of the first type of image data that are compressed using values of the compression parameters which are different from each other; and further, sets the value of the compression parameter of the compressor to be the value decided by the second processor.  
         [0026]     Further, in the digital photographic device according to the fourth invention of the present application, any one of the one or plural compression parameters may be a matrix. In addition, in the digital photographic device according to the fourth invention of the present application, it is preferable that the. predetermined standard relates to a compression rate.  
         [0027]     Further, in the digital photographic device according to the fourth invention of the present application, it is preferable that the host module is provided with a display unit and a main storage unit for storing the data; the camera module transmits the first type of image data that is not compressed by the compressor to the host module through the data output part one after another; the host module receives the first type of image data that is not compressed through the data input part one after another and displays the first type of image data that is not compressed by the first compressor on the display unit; further, the camera module supplies the second type of image data for the real shooting which is created by the image data creator to the compressor; compresses the second type of image data to be supplied using the value of the compression parameter decided by the compressor; and transmits the compressed second type of image data to the host module through the data output part; and the host module receives the second type of image data compressed by the first processor through the data input part and saves the compressed second type of image data in the main storage unit.  
         [0028]     In addition, the fifth invention of the present application may provide a method of deciding a value of a compression parameter in the case of compressing second type image data in a digital photographic device, which creates first type of image data for test shooting; creates the second type of image data for real shooting; compresses the created second type of image data; and saves the compressed second type of image data; including: newly creating the first type of image data one after another by newly performing the test shooting one after another; compressing at least two and more files from among the continuously created first type of image data, using the values of compression parameters which are different from each other; and deciding the value of the compression parameter to be used for the second type of image data according to a predetermined standard, based on two and more files of first type image data that are compressed using values of the compression parameters which are different from each other.  
         [0029]     Further, in the method to decide the parameter value of a compression parameter, it is preferable that the first type of image data has a lower resolution than that of the second type of image data. In addition, in the method to decide a parameter value of a compression parameter, it is preferable that the digital photographic device has the plural compression parameters that are different from each other. Further, in the method of deciding a value of a compression parameter, any one of the one or plural compression parameters may be a matrix. In addition, in the method of deciding a value of a compression parameter, the predetermined standard may relate to a compression rate. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0030]      FIG. 1  is an external view of a camera-equipped cellular phone to which the present invention is applied.  
         [0031]      FIG. 2  is a block diagram of hardware of the camera-equipped cellular phone to which the present invention is applied.  
         [0032]      FIG. 3  is a detailed view of a JPEG compression part of the camera-equipped cellular phone to which the present invention is applied.  
         [0033]      FIG. 4  is a flow chart with respect to decision of a compression parameter value for saving according to the present invention.  
         [0034]      FIG. 5  is a flow chart of photograph mode according to the present invention.  
         [0035]      FIG. 6  is the other embodiment of the present invention.  
         [0036]      FIG. 7  is a block diagram of hardware of a conventional specialized photographic machine.  
         [0037]      FIG. 8  is a block diagram of a conventional camera-equipped cellular phone. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0038]     Hereinafter, an embodiment that the present invention is applied to a camera-equipped cellular phone will be described below with reference to the drawings.  
       Embodiment 1  
       [0039]      FIG. 1  is an external view of a camera-equipped cellular phone to which the present invention is applied. A camera-equipped cellular phone  1  is provided with a display  2 , a numeric keypad  3 , a function button  4 , and an antenna  5  or the like on its front surface; the camera-equipped cellular phone  1  is provided with a camera portion  11  and a battery cover  9  or the like on its rear surface; and further, the camera-equipped cellular phone  1  is provided with a chassis  6  for integrally holding these parts. As well known, the size and the weight of the camera-equipped cellular phone  1  are very small, so that it is not inconvenient to hold the camera-equipped cellular phone  1  by one hand or to carry it in the handbag. The camera portion  11  comprises a camera module provided with a lens  7 , an LED light  8 , and an independent chassis  10 . The camera portion is here made an independent module because a general versatility is given to the camera module so as to be easily combined with other cellular phone models and PDAs. As a result, the camera-equipped cellular phone  1  can be divided into the camera module  11  and the remaining portion (a host module).  
         [0040]     The function button  4  is used a shutter button or the like upon sending and receiving the telephone call and upon taking a picture. In the case of making a call by using the camera-equipped cellular phone  1 , a user may input a telephone number from the numeric keypad  3  and press the functional button  4 . In addition, in the case of taking a picture, the user may have the camera-equipped cellular phone  1  with the lens  7  directed to the target and may check a preview image that is photographed by the camera module  11  on the display  2 . Therefore, if the user presses the function button  4 , the shooting is carried out and the image data created by the shooting is saved in a recording part provided in the camera-equipped cellular phone  1 .  
         [0041]     With reference to  FIG. 2 , the configuration and the operation of the hardware of the camera-equipped cellular phone to which the present invention is applied will be described below. As described above, the camera-equipped cellular phone  1  comprises the camera module  1  and a host module  12 , the camera module  11  may handle the shooting and creation of the image data, and the host module  12  may handle the PDA functions such as the telephone function and the scheduling, as well as saving and display of the created image data.  
         [0042]     The camera module  11  is provided with the lens  7 , the LED light  8 , a solid-state image pickup device  13 , an A/D converter  14 , an image data creator  16 , a JPEG compressor  17 , a bus  18 , a data interface  19 , and a control interface  20  and the like. Among these devices, the image data creator  16 , the JPEG compressor  17 , the bus  18 , the data interface  19 , and the control interface  20  are provided in one chip as a camera LSI  116 .  
         [0043]     As the solid-state image pickup device, for example, a CCD and a CMOS sensor or the like can be used. The solid-state image pickup device  13  may carry out the shooting by converting the light passed through the lens  7  into an electric signal. The output signal of the solid-state image pickup device  13  is converted into the digital data by the A/D converter  14 . This digital data, called RAW data, is not yet image data which can be displayed by a computer or printed by a printer. The image data is created by the image data creator  16 . First, the image data creator  16  performs initial image processing on the RAW data such as a lens shading correction and a white balance or the like. Next, extracting the components such as red (R), green (G), and blue (B) from the RAW data to which the original image processing is applied and applying the CFA (Color Filter Array) interpolation processing, the image data of an RGB formation composed of an RGB  3  plane is created. Further, with respect to this image data, the processing such as intensification of the outline and a gamma correction or the like is carried out. Finally, the format of the image data is converted from the RGB format into a YUV format. The image data composing one frame is created one line or several lines at a time and outputted to the JPEG compressor  17  as it is created. Finally, from the output signal of the solid-state image pickup device  13  acquired by the one shooting, the image data of one entire frame are created.  
         [0044]     The camera-equipped cellular phone  1  is provided with a photograph mode and a preview mode. The photograph mode is a mode to acquire the image data used as a photograph, namely, the so-called picture taking mode. In the photograph mode, the camera module  11  may create the image data at the maximum resolution that is photographable by the solid-state image pickup device  13 . In addition, in order to save the capacity of a main storage unit  34  to be described later, sometimes shooting is carried out with the resolution decreased to half of the maximum resolution of the solid-state image pickup device  13  or ¼ thereof. The image data created in the photograph mode is saved in the data recording medium in order to use this image data afterward. Hereinafter, this image data is called the image data for saving. The preview mode is a mode to check the image to be photographed, using the display  2  for the purpose of deciding the structural outline of the actual photograph. In the preview mode, the image data with the resolution greatly decreased in comparison with the image data to be created in the photograph mode. This image data is used by a display unit  36  that is provided in the host module  12  and it is mainly used for displaying the preview, so that this image data is hereinafter called as the image data for display. Since the display unit  36  only has a small display screen, the resolution of the image data for display may also be small and typically, the resolution is about QQVGA (160 pixels×120 lines). In the preview mode, not by acquiring the output signal from the all pixels of the solid-state image pickup device  13  but by acquiring the output signal only from partial pixels, the image data for display with a small resolution is created. In order to create the image data for display, there are well-known methods such as the above-described CFA interpolation processing.  
         [0045]     With reference to  FIG. 3 , the structure and the operation of the JPEG compressor  17  will be described below. The JPEG compressor  17  is provided with a buffer memory  40 , a DCT part  41 , a quantization part  42 , and a Huffman coding part  43 . This buffer memory  30  may store plural lines, for example 8 lines, of the image data  47  sequentially constructed by an image construction part  16  one line or several lines at a time. The DCT part  41  may apply a discrete cosine transformation to each data block  46  composed of 8×8 units of the image data  47  from the eight lines stored in the buffer memory, and may convert this data into the information of a frequency domain. The quantization part  42  may smooth the data block that has been converted into the frequency information. The quantity of data used for smoothing may be that of a quality factor  44  or a quantization table  45 . The quantization table  45  is a quantization matrix of 8×8 and it is divided by the block converted into the frequency information. The quality factor  44  is a coefficient and by multiplying this with the quantization table  45 , each element of the quantization table  45  is increased or decreased at the same rate. Depending on a degree of this smoothing in the quantization part  42 , the compression rate is changed. Accordingly, by using the different quality factor  44  or the different quantization table  45 , the compression rate can be changed. According to the camera-equipped cellular phone of the present invention, the host module  12  can, by controlling the quantization part  42  through the control interface  20 , change the quality factor  44  and the quantization table  45 . The Huffman coding part  43  may perform compression by converting the data block, which is a two-dimensional data row of 8×8, into a one-dimensional data row by zigzag scan and allocating a short code to a bit pattern with a high frequency of appearance. Thus, the JPEG-compressed image data  48  is sequentially created for each data block.  
         [0046]     In this way, since the JPEG compressor  17  according to the present embodiment sequentially compresses the image data every time the image data of eight lines is created by the image data creator  16 , the JPEG compressor  17  does not need a buffer memory that temporarily saves the entire image data of one piece and it only needs the buffer memory for saving the image data of eight lines. Obviously, the embodiment that the number of lines to be stored in the buffer memory  40  is increased or deceased to 16 lines or 32 liens is also available. In addition, since the compression data  48  created by the JPEG compressor  17  is continuously outputted to the host module  12  as it is generated through the data interface  19 , a buffer memory that temporarily saves the entire image data of one shot is not needed.  
         [0047]     In addition, the JPEG compressor  17  can select whether to carry out the compression processing. This selection is carried out when the CPU  30  of the host module  12  controls the JPEG compressor  17  through the control interface  20 . In the case that the compression processing is not carried out, the JPEG compressor  17  outputs the image data transmitted from the image data creator  16  to the host module  12  through the data interface  19  without performing any processing.  
         [0048]     Returning to  FIG. 2 , the hardware structure and the operation of the host module  12  will be described below. The host module  12  comprises a data interface  25 , a control interface  26 , the CPU  30 , a bus  24 , the interface for a temporary storage unit  31 , a temporary storage unit  32 , a interface for a main storage unit  33 , the main storage unit  34 , the interface for a display unit  35 , the display unit  36 , an interface for a keyboard  37 , a keyboard  38  or the like, a base band control part  22 , and an antenna part  23  or the like. Among these devices, the CPU  30 , the bus  24 , and the interfaces  25 ,  26 ,  31 ,  33 ,  35 , and  37  are provided in one chip as the application engine  21 . The base band control part  22  handles the function for sending and receiving of the telephone call and has the specialized CPU. The application engine  21  may handle the function other than that for sending and receiving of the telephone call and may also handle the function of control of the keyboard  38 , a game, reproduction of music, and preparing a schedule or the like in addition to the processing of the image data transmitted from the camera module  11 . In the meantime, the keyboard  38  may include the data keys  3  and the functional button  4  or the like.  
         [0049]     The image data outputted from the camera module  11  or the compressed image data are inputted in the host module  12  through the data interface  25  and then, it is temporarily saved in the temporary storage unit  32 . A typical storage unit used as the temporary storage unit  32  is a SDRAM.  
         [0050]     In the preview mode, the camera module  11  may newly collect the data by the solid-state image pickup device  13  at predetermined time intervals, for example each 1/10 second, to create new image data for display from this data. Accordingly, in this example, the image data for display of a new frame is created for each 1/10 second. When the image data for display that is not compressed is inputted in the host module  12 , the CPU  30  may read this image data for saving from the temporary storage unit  32  and may display it on the display screen of the display unit  36  by carrying out predetermined processing.  
         [0051]     In addition, the CPU  30  may issue the order to the JPEG compressor  17  of the camera module  11  through the control interfaces  26  and  20  and the CPU  30  may control the JPEG compressor  17  so as to compress one file of the image data for display every time the predetermined amount of the image data for display is created. As a result, for example, if three files of the image data for display are created, one file among these is compressed by the JPEG compressor  17 . In this case, the CPU  30  may control the JPEG compressor  17  so as to compress the image data for display by using a different quality factor  44  or a different quantization table  45  every time the image data for display of a new frame is compressed. In this way, a plurality of image data for display respectively compressed by different compressing parameters is created. Then, the CPU  30  reads the data from the temporary storage unit  32 , measures the data size, and stores the quality factor  44  and the quantization table  45  used for compression every time the compressed image data for display is inputted to the CPU through the data interface  25 . When the size of the data is completely measured, the compressed image data for display is discarded and the quality factor and the quantization table used for the compression and the measured data size are temporarily stored in the temporary storage unit  32 . Thus, the CPU  30  measures the data size after each compression using different quality factors and different quantization tables, may compare these combinations, and decides on the compression parameter, namely, the quality factor and the quantization table to attain the desired data size. The CPU  30  can decide the quality factor and the QW to attain the desired data size from the following equation using data size S 1  resulting from using a certain quality factor Q 1  and data size S 2  from using Q 2 . 
 
 QW=Q 1+( Q 1− Q 2)/( S 1− S 2)×( SW−S 1)   equation 1 
 
         [0052]     Here, the SW is the desired data size. The compression rate is defined by (SW/the data size of the image before compression).  
         [0053]     In the photograph mode, the CPU  30  may control the JPEG compressor  17  so as to compress the image data for saving by using the quality factor and the quantization table to attain the desired data size decided in the preview mode. In other words, the CPU  30  may decide the compression rate of the image data for use for the photographing by deciding the quality factor and the quantization table used for photographing. This compression rate of the image data used for photographing is called the compression rate for saving. The camera module  11  in photographing may create the image data for saving and may compress this data by using the previously decided quality factor and quantization table. The compressed image data for saving is inputted in the host module  12  through the data interface  25  to be saved in the temporary storage unit  32  temporarily. The CPU  30  may read the compressed image data for saving from the temporary storage unit  32  and may save it in the main storage unit  34 . The main storage unit  34  is provided with a recording medium that continuously stores the data even when the power source of the camera-equipped cellular phone  1  is turned off. For example, the flash memory, the CF card, and the SD card can be used. In the meantime, according to the above-described description, both of the quality factor  44  and the quantization table  45  of the JPEG compressor  17  are controlled, however, depending on the embodiment, it may be that either the quality factor  44  or the quantization table  45  only is controlled.  
         [0054]     In the meantime, not the compressed image data for display but rather the uncompressed image data for display is displayed on the display unit  36 , so that the user of the camera-equipped cellular phone  1  can check the image on the display screen even if the camera-equipped cellular phone  1  is performing the estimation processing of the parameter value of the compression parameter. In addition, according to the present embodiment, since the compression processing is carried out with respect to the image for display with a lower resolution than that of the image data for saving, it is possible to suppress the amount of processing done by the JPEG compressor  17 .  
         [0055]     Other than this, the CPU  30  not only can control the JPEG compressor  17  of the camera module  11  through the control interfaces  26 ,  20  and the bus  18  but also can control each processing in the image data image data creator  16 , can turn on and off the LED light  8 , can change the data collection mode of the solid-state image pickup device, and further, can control the parameter of the A/D converter  14  or the like.  
         [0056]     Next, with reference to  FIG. 4 , a flow of the processing in order to decide the value of the compression parameter for use in the compression of the image data for saving will be described below. At first, in step  51 , the estimation of the compression parameter value will be started. The preview mode to create and display the image data for display may be started before the estimation of the parameter value is started. The estimation of the parameter value is started, for example, by pressing the function button  4  halfway. In step  52 , in order to create the image data for preview, the data collection due to the solid-state image pickup device  13 , namely, the conversion into an optical electric signal due to the solid-state image pickup device  13 , is carried out. In step  53 , the image data for display is created from the output signal of the solid-state image pickup device  13 . The image data for display composing one frame is sequentially created one line or several lines at a time. The steps of the sequence of operations from the conversion into the optical electric signal due to the solid-state image pickup device  13  until creation of the image data for display are carried out at predetermined time intervals, for example, each 1/10 second (step  54 ). Every time the step  52  and the step  53  are repeated, the image data for display of one frame is created. Sometimes the created image data for display is compressed after that, and other times the created image data for display is not compressed after that. For example, every time three files of image data for display are created, one file among them is compressed. In step  55 , the uncompressed image data for display is displayed on the display unit. In steps  56  to  58 , one file among them is JPEG-compressed. At first, in the step  56 , the discrete cosine transformation is performed for each data block  63  composed of 8×8 image data, and the data describing brightness and color is converted into the data of the frequency band. Next, in the step  57 , quantization is performed and the data block  63  converted into the frequency information is smoothed by the quality factor  64  and the quantization table  65 . Every time the image data for display of a new frame reaches the step  57 , a different quality factor  64  or a different quantization table  65  are used. In other words, every time the image data for display of a new frame reaches the steps  56  to  58 , this image data is compressed at different compression rates. In this example, the description is provided assuming that the quantization table  65  is fixed and the quality factor  64  only is changed. In the last step  58  of the compression process, the Huffman coding is carried out and the JPEG compression is completed. In the step  59 , the sizes of the display data files resulting from the use of the different quality factors are compared with each other with and the quality factor which gives the desired data size is decided upon. In step  60 , the compressor is set at the estimated quality factor.  
         [0057]     Here, since the estimated compression parameter is acquired by compressing image data for display with a low resolution, sometime it is not proper to use the estimated parameter as it is for the image data for photographing with a high resolution. It is known that the image with the higher resolution is generally compressed more effectively in the case of using the same compression parameter. Accordingly, sometimes it is preferable that a parameter QW′ which gives a compression rate higher than the quality factor QW estimated as the equation 1 is used. In addition, the smaller the value of the quality factor, the lower the image quality and thus the higher the compression rate. Therefore, QW′=QW×S (S&lt;1.0) may be decided on the basis of the difference of the resolution between the display image and the photographed image and judgment gained from experience. In the step  59 , by using a compression rate estimation table indicating a relation between such a correction amount S and a corrected quality factor, a desired quality factor may be decided. An example of the compression rate estimation table is indicated in Table 1 as follows.  
                                       TABLE 1                           Compression rate estimation table                Quality factor            Value of quality factor   Correction Quantity   after correction               th1 &lt; = QW &lt; th2   s1   QQW = s1 × QW       th2 &lt; = QW &lt; th3   s2   QQW = s2 × QW       th3 &lt; = QW &lt; th4   s3   QQW = s3 × QW                 QW is a quality factor estimated by the equation 1.            QQW is a quality factor after correction.            s1, s2, and s3 are quantities determined by the experiment.            th1, th2, the3, and th4 are threshold values determined by the experiment.            (Example 1) s1 = s2 = s3 = 0.75            (Example 2) s1 = 0.8, s2 = 0.75, s3 = 0.7             
 
         [0058]     Next, with reference to  FIG. 5 , the flow of the processing in the photograph mode of the digital photographic device according to the present invention will be described below. At first, in step  71 , the photograph mode is started. The photograph mode is started, for example, by completely pressing the functional button  4  in  FIG. 1 . In step  72 , the data collection due to the solid-state image pickup device  13  is carried out and the conversion into the optical electric signal is performed by the solid-state image pickup device  13 . In step  73 , the image data for saving is sequentially created one line or several lines at a time. In step  74 , the discrete cosine transformation is performed for each data block composed of the image data of 8×8 and the data describing brightness and a color is converted into the data of the frequency band. Next, in step  75 , quantization is performed using the quality factor  80  the quantization table  81  decided by the flow of the processing shown in  FIG. 4 . In step  76 , the Huffman coding is carried out and the JPEG-compressed image data for saving is sequentially created for each data block composed of the image data of 8×8. In step  77 , the compressed image data for saving is saved in the recording medium. At last, in step  78 , the calculation and the display of the number of images which still can be shot are carried out based on the remaining capacity of the recording medium and the data size per image data (one frame).  
       Embodiment 2  
       [0059]     According to the embodiment 1, the camera-equipped cellular phone  1  compresses the image data for display in the preview mode by using the JPEG compressor  17  of the camera module  11 . However, when the processing capability of the host module  12  is abundant, it is also possible to compress the image data for display in the preview mode with the host module  12 . Such an embodiment will be described with reference to  FIG. 2 .  
         [0060]     In the preview mode, the camera module  11  may take a picture at predetermined time intervals to create the image data for display. Since the operation of the camera module  11  is the same as the embodiment 1 except when the compression is not performed, the explanation thereof is herein omitted. In the host module  12 , the image data for display of a new frame is inputted through the data interface  25 . The inputted image data for display is temporarily saved in the temporary storage unit  32 . The CPU  30  may compress one file of the image data for display every time a predetermined amount of the image data for display is inputted. For example, if the three files of image data for display are inputted, one file of the image data for display among them is JPEG-compressed. The uncompressed image data for display is displayed by the display unit  36 . With respect to the image data for display to be compressed, the CPU  30  may perform the compression processing such as the discrete cosine transformation, the quantization, and the Huffman coding. In other words, the compression processing is carried out by the software processing using the CPU  30 .  
         [0061]     Also according to the present embodiment, every time the image data for display of a new frame is compressed, a different quality factor or a different quantization table are used. In this way, the CPU  30  may measure the data size after compressing in each case and may decide the quality factor and the quantization table to attain the desired data size.  
         [0062]     In the photograph mode, the CPU  30  may control the JPEG compressor  17  of the camera module  11  so as to compress the image data for saving by using the quality factor and the quantization table to attain the desired data size, decided by operation in the preview mode.  
         [0063]     In the photograph mode, as same as the embodiment 1, the JPEG compressor  17  of the camera module  11  compresses the image data for saving. In this case, the CPU  30  of the host module  20  does not compress the data because the data interfaces  19  and  25  must be provided with broad bus width in order to transfer uncompressed image data for saving, and this leads to increase of the cost. In addition, the temporary storage unit  32  also must be made larger and this also leads to increase of the cost.  
       Embodiment 3  
       [0064]     According to the embodiment 1, in the camera-equipped cellular phone  1 , the CPU  30  of the host module  12  decides the parameter value of the compression parameter to be used for the compression of the image data for saving in the previous mode. However, in the case that the camera module is provided with an independent CPU, the parameter value can be decided in the camera module. Such an embodiment will be described below with reference to  FIG. 6 .  
         [0065]      FIG. 6  is a hardware block diagram showing a third embodiment of a camera-equipped cellular phone to which the present invention is applied. The camera-equipped cellular phone of the present embodiment is also configured by a camera module  90  and a host module  91 .  
         [0066]     The camera module  90  is provided with an LED light  92 , a lens  93 , a solid-state image pickup device  94 , an A/D converter  95 , an image data creator  97 , a JPEG compressor  98 , a data interface  103 , and a control interface  104  or the like. In addition, the camera module  90  is provided with a CPU  100  connected to the image data creator  97  and the JPEG compressor  98  through a bus  101 . To the bus  101 , a buffer memory  99  is also connected. The CPU  100  is further connected to the LED light  92 , the solid-state image pickup device  94 , and the A/D converter  95  through the bus  102 . The image data creator  97 , the JPEG compressor  98 , the buffer memory  99 , the CPU  100 , the buses  101  and  102 , and the interfaces  103  and  104  are provided in one chip as a camera LSI  96 .  
         [0067]     The operations of the solid-state image pickup device  94 , the A/D converter  95 , the image data creator  97 , and the JPEG compressor  98  with respect to the creation and the compression of the image data are the same as those of the embodiment 1. In addition, it is also the same that the camera-equipped cellular phone  1  is provided with the photograph mode and the preview mode. In the preview mode, the camera module  90  newly performs the data collection by the solid-state image pickup device  94  at each passage of a predetermined time interval, for example, every 1/10 second, namely, perform the conversion of light into electric signals by the solid-state image pickup device  94  to create new image data for display. The uncompressed image data for display among them is transmitted to the camera module  91  through the data interface  103 . However, in the preview mode, the CPU  100  may issue an order to the JPEG compressor  98  through the bus  101  and may control the JPEG compressor  98  so as to compress one file of the image data for display every time the predetermined amount of the image data for display is created. For example, if three files of the image data for display is created, one file among them is compressed by the JPEG compressor  98 . The CPU  100  may measure the data size of the compressed image data for display and may save it in the buffer memory  99  together with the quality factor and the quantization table used for the compression. The compressed image data for display is discarded when the size of the data is completely measured, so that the compressed image data for display is not outputted from the camera module to the outside. The CPU  100  may control the JPEG compressor  98  so as to compress the image data for display of a new frame by using a different quality factor or a different quantization table, respectively. Thus, the data size after each case of compression using a plurality of different quality factor and quantization table is measured, and comparing these combinations, the CPU  100  decides the quality factor and the quantization table to attain the desired data size. In addition, can be inferred from the above descriptions, since the size of the buffer memory  99  is sufficient if it can store a plurality of quality factors, quantization tables, and data sizes, large size is not necessary.  
         [0068]     In the photograph mode, the CPU  100  may control the JPEG compressor  98  so as to compress the image data for saving by using the quality factor and the quantization table to attain the desired data size which was determined in the preview mode. In other words, the CPU  100  may decide the compression rate of the image data to be used for the photographing, namely, the compression rate for saving by deciding the quality factor and the quantization table that are used for photographing.  
         [0069]     The CPU  100  may receive a message based order from a CPU  111  of the host module  91  to be described later through the control interface  104 , and interpreting this message based order, the CPU  100  may control the component parts of the camera module  90  such as the solid-state image pickup device  94  and the image data creator  97  or the like. Thus, if the independent CPU  100  is provided to the camera module  90  and the CPU  100  controls the component parts of the camera module  90  by interpreting the message based order received by the CPU from the outside, the control software of the camera module can be independent from the control software of the host module. Thus, the present embodiment has the advantages such that the control software of the host module and the camera module can be independently developed and the control software can be easily updated.  
         [0070]     Next, the hardware structure and the operation of the host module  91  will be described. The host module  91  is configured by a data interface  109 , a control interface  110 , a CPU  111 , a bus  108 , an interface  112  for a temporal storage unit, a temporal storage unit  113 , an interface  114  for a main storage unit, a main storage unit  115 , an interface  116  for a display unit, a display unit  117 , an interface  118  for a keyboard, a keyboard  119 , a base band control part  106 , and an antenna part  107  or the like. Among these devices, the CPU  111 , the bus  108 , and the interfaces  109 ,  110 ,  112 ,  114 ,  116  and  118  are provided in one chip as the application engine  105 . The base band control part  106  handles the function for sending and receiving of the telephone call and has the specialized CPU. The application engine  105  handles the functions other than that for sending and receiving of the telephone call and may also handle the function of control of the keyboard  119 , a game, reproduction of music, and preparing a schedule or the like in addition to the processing of the image data to be transmitted from the camera module  90 .  
         [0071]     In the preview mode, the only data transmitted from the camera module  90  is uncompressed image data for display. The data inputted in the host module  91  through the data interface  109  is temporarily saved in the temporal storage unit  113 . The CPU  111  may read this data from the temporal storage unit  113  and may perform predetermined processing to display it on the display screen of the display unit  117 . When in the photograph mode, the data transmitted from the camera module  90  is the compressed image data for saving. The image data for saving is saved in the temporal storage unit  113  temporarily, and then it is saved in the main storage unit  115 .  
         [0072]     The above-described embodiments are merely examples of putting the present invention in practice, and of course various embodiments not exceeding the scope of the present invention are conceivable.