Abstract:
A digital camera is provided that includes a first wireless communication module and image data processor. The first wireless communication module transmits image data to a monitor device via wireless communication. The image data processor processes image data before transmitting it to the monitor device via the wireless communication module. The image data processor has a first mode in which the image data are compressed at a predetermined compression ratio when transmitting a through-the-lens image to the monitor device, and a second mode in which the image data are compressed less than the predetermined compression, including zero compression, while carrying out at least one of reducing a frame rate compared to the first mode or extracting part of an image comprising the image data.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a digital camera that is able to represent a through-the-lens image. 
         [0003]    2. Description of the Related Art 
         [0004]    In general, digital cameras are provided with a monitor that is used to display a captured image or a through-the-lens image (a live preview image). In certain such cameras a monitor is configured to be rotatable with respect to the camera body via a rotating mechanism, such as a hinge. Further, a digital camera with a monitor being made detachable from the camera body is also provided in Japanese Unexamined Patent Publication No. 2000-261697. 
       SUMMARY OF THE INVENTION 
       [0005]    It is advantageous if the digital camera disclosed in the above patent document can display a through-the-lens image on the monitor even when the monitor is detached from the camera body. However, the wireless band assigned to such data transmission does not have a sufficient data transfer rate to transmit the above-mentioned moving image, thus representation of the moving image on the monitor device in such a situation is restricted. To resolve this problem, the image data may be compressed prior to data transmission via wireless communication. However, this method is not preferable in focusing image verification because compression artifacts, such as blockiness, mosquito noise and the like, emerge when lossy compression is decoded. For example, a user may not be able to verify whether or not a lens system is properly focused on a subject when using an autofocus (AF) operation of the camera. 
         [0006]    One aspect of the present invention is to provide a digital camera that transmits image data from a camera body to a monitor device via a communication method that is adapted to the purpose of data use. 
         [0007]    According to the present invention, a digital camera is configured with a first wireless communication module and image data processor. The first wireless communication module transmits image data to a monitor device via wireless communication. The image data processor processes the image data before transmitting it to the monitor device via the wireless communication module. The image data processor has a first mode in which the image data are compressed at a predetermined compression ratio when transmitting a through-the-lens image to the monitor device, and a second mode in which the image data are compressed less than the level indicated by the predetermined compression ratio, including zero compression, while carrying out at least one of reducing a frame rate compared to the first mode or extracting part of an image comprising the image data. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The objects and advantages of the present invention will be better understood from the following description, with reference to the accompanying drawings in which: 
           [0009]      FIG. 1  is a block diagram schematically illustrating the general structure of a digital camera of an embodiment of the present invention; 
           [0010]      FIG. 2  is a flowchart of an image data transmission operation; and 
           [0011]      FIG. 3  is a connection diagram of connector terminals of the present embodiment. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0012]    The present invention is described below with reference to the embodiments shown in the drawings. 
         [0013]      FIG. 1  is a block diagram schematically illustrating the general structure of a digital camera to which an embodiment of the present invention is applied. The digital camera  10  includes a camera body  11  and a monitor device  12 . The monitor device is configured to be detachable from the camera body  11 . When the monitor device  12  is attached to the camera body  11 , the camera body  11  and the monitor device  12  are electrically connected to each other via a connector  13 , which is comprised of a pair of connector halves  13 A and  13 B. Namely, moving image data of a through-the-lens image, image data of a still image or control signals are transmitted/received between the camera body  11  and the monitor device  12  via the connector  13 . On the other hand, when the monitor device  12  is detached from the camera body  11 , the above-mentioned data and signals are transmitted/received through wireless communications by wireless communication modules  14  and  15  provided on each side of the camera body  11  and monitor device  12 . 
         [0014]    In the camera body  11 , an image sensor  19  captures an object image through a lens system  16 , an aperture  17  and a shutter  18 . The image captured by the image sensor  19  is fed to a digital signal processor (DSP)  20  where predetermined image processing is performed. Further, the image data is temporarily stored in memory  21  and also fed to a digital signal processor (DSP)  22  of the monitor device via the connector  13  or the wireless communication modules  14  and  15 . The image data received by the digital signal processor (DSP)  22  is stored in memory  23  of the monitor device  12 . At the same time, the received image may also be displayed on an LCD or monitor  24  of the monitor device  12 . Note that the image stored in the memory  21  can also be recorded onto an external recording medium  25 , such as a memory card or the like, if desired. 
         [0015]    Further, the camera body  11  of the present embodiment is configured with an anti-shake mechanism, which is driven by an anti-shake driver  26 , to provide shake reduction or image stabilization functionality. In the example of  FIG. 1 , a sensor-shift type is chosen as the anti-shake mechanism, however, a lens-based type or any other type of image stabilization system or module may also be applied. 
         [0016]    In the present embodiment, the optical system including the lens system  16 , aperture  17 , shutter  18  and so on, is controlled by a lens driver  27 . Further, the anti-shake driver  26  and the lens driver  27  are controlled by the digital signal processor  20 . Incidentally, an autofocus (AF) operation of the present embodiment may be carried out by the digital signal processor (DSP)  20  by measuring the contrast between images captured by the image sensor  19 , and driving the lens system  16 , accordingly. 
         [0017]    Further, manipulation switch groups  28  and  29  provided on each of the camera body  11  and the monitor device  12  are connected to the digital signal processors (DSPs) and  22 , respectively. Each of the digital signal processors (DSPs)  20  and  22  performs various types of processes based on the manipulation of switches in the manipulation switch groups  28  and  29 . Note that instead of, or in addition to, the manipulation switch group  29 , a touchscreen may be applied to the LCD  24 . 
         [0018]    With reference to the flowchart of  FIG. 2 , a moving-image data transmission operation carried out in the digital camera  10  of the present embodiment will be explained. Note that the moving-image data transmission operation of  FIG. 2  is repeatedly carried out by the digital signal processor (DSP)  20  of the camera body  11  at a predetermined time interval. 
         [0019]    Recently, the number of pixels on the image sensors of digital cameras has been increasing. The resolution of a through-the-lens image (a live preview image) obtained by the image sensor  19  of the digital camera  10  may employ the VGA computer display standard (640*480 pixels). However, since the frequency band for the radio communication (wireless communication) is limited, the data transfer rate is also limited. For example, an effective data transfer rate for a wireless local network employing IEEE802.11n standards is below 3 MB/s while VGA images of 30 fps requires 9.2 MB/s. Consequently, in the present embodiment the image data is compressed to a level in which the effective data transfer rate is below 3 MB/s at 30 fps when through-the-lens images are transferred via wireless communication. 
         [0020]    However, when data are lossy compressed, a decoded image includes compression artifacts, such as blockiness, mosquito noise and the like, which cause the image quality to deteriorate. The compression artifacts become prominent as the compression level increases. When through-the-lens images are merely viewed for checking the composition of the frame, the image quality effects caused by the lossy compression of image data do not cause a problem. However, when verifying focusing conditions of an image, blockiness and/or mosquito noise in a decoded image impede the verification because details of the image must be inspected. 
         [0021]    Accordingly, in the image data transmission portion of the autofocus (AF) operation of the present embodiment, priority is given to image quality that is dissimilar to the case when the normal through-the-lens image or preview image data are transferred. 
         [0022]    In Step S 100 , whether or not the moving-image data transmission has been requested is determined. When it is determined that the data transmission has been requested, whether or not the monitor device (the LCD unit)  12  is attached to the camera body  11  is determined in Step S 102 . Namely, whether the data transmission will be carried out via the wired communication or the wireless communication is determined. Incidentally, the method for detecting the attachment of the monitor device  12  to the camera body  11  will be detailed later with reference to  FIG. 3 . 
         [0023]    When the monitor device  12  is attached to the camera body  11  and thus it is determined in Step S 102  that the data transmission will be carried out via wired communication, in Step S 104  the data of the images being captured by the image sensor are transferred to the monitor device  12  via wires connected through the connector  13  until this moving-image data transmission operation terminates. In this situation, for example, VGA images are transferred from the digital signal processor (DSP)  20  of the camera body  11  at 30 fps via the wires to the digital signal processor (DSP)  22  of the monitor device  12  to be displayed on the LCD  24 . 
         [0024]    On the other hand, when the monitor device  12  is detached from the camera body  11  and thus it is determined that the data transmission will be carried out by radio communication in Step S 102 , whether or not the autofocus operation (AF) is underway is determined in Step S 106 . When the autofocus operation (AF) is inactive, the moving-image data obtained by the image sensor  19  are subjected to predetermined data compression at a predetermined data compression ratio in Step S 108  (a normal mode). Further, the moving-image data compressed in Step S 110  are transmitted to the monitor device  12  via wireless communication using modules  14  and  15 , accordingly. Thereby, this moving-image data transmission operation terminates. 
         [0025]    On the other hand, when it is determined in Step  106  that the autofocus operation (AF) is being executed, data processing particular to the autofocus operation (referred to as quality priority data processing) is carried out using the moving-image data obtained by the image sensor  19  in Step S 112  (an image-quality priority mode). Further, the moving-image data compressed in Step S 110  are transmitted to the monitor device  12  via wireless communication using the wireless modules  14  and  15 , accordingly. Thereby, this moving-image data transmission operation terminates. Note that the autofocus (AF) operation may be repeated while the release button (not shown) is depressed halfway and the release switch (not shown) is maintained ON state. 
         [0026]    Here, the quality priority data processing performed during the autofocus (AF) operation places priority on the image quality, at least for an area (a target area) used in the autofocus (AF) operation. In this data processing procedure, the data compression level may be reduced from the amount indicated by the above-predetermined ratio for the normal mode; the frame rate may be reduced instead of compressing the moving-image data; a partial image around the AF area may be extracted from the original image; or any combination of these methods may be employed. Namely, the quality priority data processing procedure in the autofocus operation of the present embodiment suppresses the data transfer rate to a rate that is available in the assigned wireless band (e.g., 3 MB/s or below) while reducing the amount of data compression (in mathematical terms increasing the data compression ratio, which is defined as compressed size/uncompressed size) including zero compression. 
         [0027]      FIG. 3  schematically shows the connection of terminals in the connector  13 , which is used for detection of the attachment status of the monitor device  12 . Although there are a number of terminals provided in the connector  13 , only three of them are described in  FIG. 3  in this example. In  FIG. 3 , the connector half  13 B of the monitor device  12  is connected to the connector half  13 A of the camera body  11 . 
         [0028]      FIG. 3  schematically shows the connection of terminals in the connector  13 , which is used for detection of the monitor device  12 &#39;s attachment. Although there are a number of terminals provided to the connector  13 , only three of them are described in  FIG. 3  as an example. In  FIG. 3 , the connector half  13 B of the monitor device  12  is connected to the connector half  13 A of the camera body  11 . 
         [0029]    A terminal of the connector half  13 B that is used to detect the attachment of the monitor device  12  to the camera body  11  is connected to the ground while the voltage of the complementary terminal of the connector half  13 A of the camera body  11  is pulled up via a pull-up resistor R connected to a terminal of the digital signal processor (DSP)  20  that is assigned to the above detection. Namely, when the monitor device  12  is detached from the camera body  11  and the connector halves  13 A and  13 B are disconnected, the voltage of the detection terminal of the digital signal processor (DSP)  20  is kept high. On the other hand, when the monitor device  12  is attached to the camera body  11  and the connector halves  13 A and  13 B are connected, the detection terminal of the digital signal processor (DSP)  20  is connected to the ground and the voltage level of the detection terminal is changed to low. Namely, the digital signal processor (DSP)  20  determines the attachment status of the monitor device  12  by determining whether the voltage of the detection terminal is high or low. 
         [0030]    As described above, according to the present embodiment, in which the digital camera with the detachable monitor device, the moving image data can be transferred from the camera body to the monitor device even when the monitor device is detached from the camera body. Further, in the present embodiment, image data can be transferred from the camera body to the monitor device in a suitable format in accordance to particular situations. Namely, in the transmission of moving-image data via wireless communication, through-the-lens images are compressed at a predetermined data compression ratio prior to the data transmission in the normal mode, while the image data are transmitted under a reduced compression level or without compression in the image quality priority mode during the autofocus (AF) operation. Thereby, an image displayed on the monitor is accommodated to the situations that correspond to either of the framing situation or the auto-focusing situation by modifying the above data transmission conditions. 
         [0031]    Further, although the monitor device in the present embodiment is detachable from the camera body, the present invention may also be applied to a system that transmits moving image data by wireless communication (e.g. radio communication) from a digital camera to a monitor or display device that may also be used independently from the digital camera configured with radio communication ability and an integrated monitor. In such case the digital camera may be provided with a monitor integrated with the camera body, and the transmission of the moving image data via radio communication to the remote monitor device may be chosen by a user selecting such mode. Further, during the wireless communication, the image data are subjected to a similar process as described in Step S 106 -S 112  of  FIG. 2  and then transferred to the monitor device. 
         [0032]    Further, in the present embodiment the quality priority data processing procedure is carried out continuously during the autofocus operation using the moving-image data, and the processed data is transferred accordingly via wireless communication to the monitor device. However, only the image data obtained upon completion of an autofocus operation may be subjected to the quality priority data processing and transferred via wireless communication, while images obtained during the autofocus operation must be compressed in the same way as the through-the-lens image (or in the normal mode) before the data is transmitted via the wireless communication. 
         [0033]    Furthermore, in the present embodiment, the autofocus (AF) operation is adopted as an example to explain the invention. However, similar data transmission may also be performed during an auto exposure (AE) operation. 
         [0034]    Although the embodiment of the present invention has been described herein with reference to the accompanying drawings, obviously many modifications and changes may be made by those skilled in this art without departing from the scope of the invention. 
         [0035]    The present disclosure relates to subject matter contained in Japanese Patent Application No. 2010-227388 (filed on Oct. 7, 2010), which is expressly incorporated herein, by reference, in its entirety.