Patent Publication Number: US-2010110291-A1

Title: Wireless image transferring apparatus, wireless image receiving apparatus and wireless image transmitting apparatus, and wireless image transferring method, wireless image receiving method and wireless image transmitting method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the priority benefit of Japanese patent application number 2008-280309 filed Oct. 30, 2009, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1, Field of the Invention 
     The present invention relates to a wireless image transferring apparatus, a wireless image receiving apparatus and the like capable of displaying a highly reliable object image. 
     2. Description of the Related Art 
     Where a camera for picking up images of an object and a liquid crystal display (LCD) device or the like for displaying the images of an object picked up by the camera are separated away from each other, it is necessary that the data of object images captured by the camera be transferred from the camera to the display device within a desired time period. 
     For example, a conventional system implementing such a wireless image transferring method is a camera system where a synchronization signal generated on a display apparatus side is superposed together with a power supply voltage and the synchronization signal thus superposed with the supply voltage is sent to a camera side through a cable such as a coaxial cable. In this camera system, the video signals obtained from the object images picked up in the camera side are synchronized with a received synchronization signal so as to produce composite video signals, and the composite video signals are sent to a display apparatus side through the same coaxial cable. 
     In the display apparatus side, the composite video signals received through the coaxial cable are separated from signals belonging to the coaxial cable itself and the thus separated composite video signals are outputted to the LCD device so as to obtain reproduced images. Since the display apparatus side and the camera side are remotely positioned from each other in a monitoring apparatus or the like using such a camera system, the cable connecting both the display apparatus side and the camera side tends to be longer in general. 
     As a result, the position of video signal outputted to the display apparatus lags the original position for synchronization signal generated on the display apparatus side by a time duration equivalent to the time required for travelling back and forth along the length of coaxial cable. Such a delay causes a deviation in the phase relationship of chrominance subcarriers between color burst signals and video signals, and appears visually on the display apparatus, such as a monitor, as a hue difference. This may adversely affect the color reproducibility. 
     For example, known as a technique for adjusting the phase delay or the like due to the length of a transmission cable is a conventional technique where a marker is superposed and the thus superposed marker is sent from a camera side to a control apparatus side so as to measure the transmission delay time due to the transmission cable. In this conventional method for addressing the concern, a measurement result of transmission delay time is sent from the control apparatus to the camera side as a command. Then in the camera side, the phase of vide signals is advanced, in response to this command, so as to be superposed on the synchronization signal. An example of such a technique may be found in Japanese patent application publication number 2001-103573. 
     Where a transmitting side that wirelessly transmits camera image data or the like and a receiving side that receives the camera image data or the like transmitted wirelessly from the transmitting side are asynchronous and untuned with each other, there is concern that various kinds of inconvenience may be caused. With much deviation in synchronization therebetween, frames or the like that constitute a part of an object image are lost, for example, and the frames are displayed in an overlapped manner, thus causing a great deal of inconvenience such as degradation in the quality of images displayed. 
     For a camera system, such as an automotive rearview apparatus, which is required to display the object image in real time with high reliability, it is desired that such delay is reduced as much as possible. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve the problems as mentioned above, and a purpose thereof is to provide a wireless image transferring apparatus, a wireless image receiving apparatus and the like capable of displaying real-time moving images with high quality and reduced delay. 
     A wireless image transferring apparatus according to an embodiment of the present invention comprises: a free-run transmitter including: a marker appending unit operative to append a vertical synchronization marker to image data; and a nondisplay period adjustment unit operative to adjust the length of nondisplay period of image data according to monitoring information supplied, wherein the free-run transmitter transmits the image data and receives the monitoring information; and a free-run receiver including: a marker extraction unit operative to extract the vertical synchronization marker from the image data received; and a marker position monitoring unit operative to monitor whether the position of a marker in the image data containing the vertical synchronization marker extracted by the marker extraction unit lies within a predetermined range or not and operative to generate the monitoring information containing a synchronization adjustment amount used to expand or contract the nondisplay period of the image data such that the position of a marker lies within the predetermined range in the event that the position of a marker lies outside the predetermined range, wherein the free-run receiver receives the image data and feeds back the monitoring information to the transmitter. 
     A wireless image transferring apparatus according to another embodiment of the present invention comprises: a free-run transmitter including: a marker appending unit operative to append a vertical synchronization marker to image data; and a nondisplay period adjustment unit operative to monitor whether or not the position of a marker in the image data containing the vertical synchronization marker in a receiving side lies within a predetermined range based on monitoring information supplied, and operative to adjust the position of a marker, by expanding or contracting the nondisplay period of the image data, in such a manner that the position of a marker lies within the predetermined range, in the event that the position of a marker lies outside the predetermined range, wherein the free-run transmitter transmits the image data and receives the monitoring information; and a free-run receiver including: a marker extraction unit operative to extract the vertical synchronization marker from the image data received; and a marker position monitoring unit operative to detect the position of a marker in the image data containing the vertical synchronization marker extracted by the marker extraction unit and operative to generate the monitoring information containing positional information indicating the detected position of a marker, wherein the free-run receiver receives the image data and feeds back the monitoring information to the transmitter. 
     In the wireless image transferring apparatus according to the above embodiment of the present invention, the predetermined range may preferably be a predetermined range in a vertical blanking interval. 
     In the wireless image transferring apparatus according to the above embodiment of the present invention, the nondisplay period adjustment unit may preferably adjust the length of nondisplay period by expanding or contracting a horizontal blanking interval in the vertical blanking interval. 
     In the wireless image transferring apparatus according to the above embodiment of the present invention, the nondisplay period adjustment unit may preferably adjust the length of nondisplay period by expanding or contracting termination timing of the nondisplay period of the image data such that the position of a marker lies within the predetermined range. 
     A wireless image receiving apparatus according to an embodiment of the present invention comprises: a marker extraction unit operative to extract a vertical synchronization marker contained in image data received; a marker position monitoring unit operative to monitor whether the position of a marker in the image data containing the vertical synchronization marker extracted by the marker extraction unit lies within a predetermined range or not and operative to generate monitoring information containing a synchronization adjustment amount used to expand or contract the nondisplay period of the image data such that the position of a marker lies within the predetermined range in the event that the position of a marker lies outside the predetermined range; and a free-run transmit-receive unit operative to receive the image data and transmits the monitoring information. 
     A wireless image receiving apparatus according to another embodiment of the present invention comprises: a marker extraction unit operative to extract a vertical synchronization marker contained in image data received; a marker position monitoring unit operative to generate monitoring information, containing positional information indicative of a marker position, by detecting the marker position in the image data containing the vertical synchronization marker extracted by the maker extraction unit; and a free-run transmit-receive unit operative to receive the image data and transmits the monitoring information. 
     In the wireless image receiving apparatus according to the above embodiment of the present invention, the marker position monitoring unit may preferably monitor whether the position of a maker lies within a predetermined range in a vertical blanking interval or not. 
     In the wireless image receiving apparatus according to the above embodiment of the present invention, the marker position monitor unit may preferably monitor whether or not the position of a marker lies within a predetermined period of vertical blanking interval in a manner such that a count value is sequentially counted up in response to a start of the vertical blanking interval and whether a count value corresponding to the marker position lies within a predetermined count value range or not is monitored. 
     A wireless image transmitting apparatus according to an embodiment of the present invention comprises: a marker appending unit operative to append a vertical synchronizing marker to image data; a nondisplay period adjustment unit operative to adjust the length of nondisplay period according to monitoring information supplied; and a free-run transmit-receive unit operative to transmit the image data and receives the monitoring information, wherein the monitoring information contains a synchronization adjustment amount used to expand or contract the nondisplay period of the image data such that the position of a marker lies within a predetermined range in the event that the position of a marker in the image data containing the vertical synchronization marker lies outside the predetermined range at a receiving side. 
     A wireless image transmitting apparatus according to another embodiment of the present invention comprises: a marker appending unit operative to append a vertical synchronizing marker to image data; a nondisplay period adjustment unit operative to monitor whether or not the position of a marker in the image data containing the vertical synchronization marker in a receiving side of the image data lies within a predetermined range based on monitoring information supplied, and operative to adjust the position of a marker, by expanding or contracting the nondisplay period of the image data, in such a manner that the position of a marker lies within the predetermined range in the event that the position of a marker lies outside the predetermined range; and a free-run transmit-receive unit operative to transmit the image data and receives the monitoring information, wherein the monitoring information contains positional information indicative of the position of a marker in the image data containing the vertical synchronization marker detected in the receiving side of the image data. 
     In the wireless image transmitting apparatus according to the above embodiment of the present invention, the nondisplay period adjustment unit may preferably adjust the length of nondisplay period by expanding or contracting a horizontal blanking interval in a vertical blanking interval. 
     In the wireless image transmitting apparatus according to the above embodiment of the present invention, the nondisplay period adjustment unit may preferably adjust the length of nondisplay period of the image data by expanding or contracting termination timing of nondisplay period of the image data in such a manner that the position of a marker lies within the predetermined range. 
     A wireless image transferring method according to an embodiment of the present invention includes: appending a vertical synchronization marker to image data to be transmitted by a free-run transmitter; extracting the vertical synchronization marker from the image data received by a free-run receiver; monitoring, by the receiver, whether the position of a marker in the image data containing the vertical synchronization marker extracted by the receiver in the extracting lies within a predetermined range or not; generating monitoring information, by the receiver, containing a synchronization adjustment amount used to expand or contract the nondisplay period of the image data such that the position of a marker lies within the predetermined range in the event that the position of a marker lies outside the predetermined range; feeding back the monitoring information, by the receiver, to the transmitter; and adjusting the length of nondisplay period of the image data, by the transmitter, according to the fed-back monitoring information. 
     A wireless image transferring method according to another embodiment of the present invention includes: appending a vertical synchronization marker to image data to be transmitted by a free-run transmitter; extracting the vertical synchronization marker from the image data received by a free-run receiver; generating monitoring information, by the receiver, containing marker positional information in the image data containing the vertical synchronization marker extracted in the extracting; feeding back the monitoring information generated in the generating, by the receiver, to the transmitter; and monitoring, by the transmitter, whether the position of a marker in the image data containing the vertical synchronization marker in the receiver lies within a predetermined range or not, based on the fed-back monitoring information, and adjusting the length of nondisplay period of the image data by expanding or contracting the nondisplay period of the image data, in such a manner that the position of a marker lies within the predetermined range, in the event that the position of a marker lies outside the predetermined range. 
     A wireless image receiving method according to an embodiment of the present invention includes: extracting a vertical synchronization marker contained in image data received; monitoring whether the position of a marker in the image data containing the vertical synchronization marker extracted in the extracting lies within a predetermined range or not; generating monitoring information containing a synchronization adjustment amount used to expand or contract the nondisplay period of the image data such that the position of a marker lies within the predetermined range, in the event that the position of a marker lies outside the predetermined range; and transmitting the monitoring information generated in the generating. 
     A wireless image receiving method according to another embodiment of the present invention includes: extracting a vertical synchronization marker contained in image data received; generating monitoring information containing marker positional information in the image data that contains the vertical synchronization marker extracted in the extracting; transmitting the monitoring information generated in the generating. 
     A wireless image transmitting method according to an embodiment of the present invention includes: appending a vertical synchronization marker to image data to be transmitted; and adjusting the length of nondisplay period of the image data according to monitoring information supplied, wherein the monitoring information contains a synchronization adjustment amount used to expand or contract the nondisplay period of the image data such that the position of a marker lies within a predetermined range, in the event that the position of a marker in the image data containing the vertical synchronization marker lies outside the predetermined range at a receiving side of the image data. 
     A wireless image transmitting method according to another embodiment of the present invention includes: appending a vertical synchronization marker to image data to be transmitted; and monitoring whether or not the position of a marker in the image data containing the vertical synchronization marker in a receiving side of the image data lies within a predetermined range, based on monitoring information supplied; and adjusting the position of a marker, by expanding or contracting the nondisplay period of the image data, in such a manner that the position of a marker lies within the predetermined range in the event that the position of a marker lies outside the predetermined range, wherein the monitoring information contains positional information indicative of the position of a marker, detected in the receiving side of the image data, in the image data containing the vertical synchronization marker. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a system structure of an automotive wireless image transferring apparatus; 
         FIG. 1B  is a conceptual block diagram showing an exemplary structure of a marker position monitoring unit; 
         FIGS. 2A to 2D  are timing charts conceptually showing a processing of image data carried out by a received signal processing unit; 
         FIGS. 3A to 3D  illustrate cases where a marker is positioned outside a lower-limit-side range of a marker allowable range; 
         FIGS. 4A to 4D  illustrate cases where a marker is positioned outside an upper-limit-side range of a marker allowable range; 
         FIG. 5  conceptually illustrates a frame structure of image data; 
         FIGS. 6A and 6B  are conceptual diagrams schematically showing a deviation in synchronization between a transit-side vertical synchronization signal and a receive-side vertical synchronization signal; 
         FIG. 7  is a conceptual diagram showing an exemplary structure of a marker appending unit; 
         FIG. 8  is a flowchart conceptually showing a typical example of a counting operation of a marker position detection counter; 
         FIG. 9  is a flowchart showing a detailed operation of an automotive wireless image transferring apparatus; 
         FIG. 10  is a block diagram conceptually showing an exemplary structure of a blanking interval adjustment unit, in a transmitting side, according to a second embodiment of the present invention; and 
         FIG. 11  is a flowchart conceptually showing operations processed by an automotive wireless image transferring apparatus according to a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     An automotive wireless image transferring apparatus exemplified in each of embodiments described herein is of free-run type where an image pickup apparatus and a display apparatus operate based on their independent clocks. It is not necessary for the image pickup apparatus and the display apparatus exemplified herein to have dedicated microcomputers, dedicated memories and the like for synchronizing each other. 
     In this automotive wireless image transferring apparatus, an adjustment of taking or adjusting a predetermined synchronization between the image pickup apparatus and the display apparatus is made at an image pickup apparatus side by using a synchronization marker appended at the image pickup apparatus side and by carrying out a detection processing at a display apparatus side. Thus, even if a slight displacement occurs in the frequency or phase of each clock, the adjustment can be made such that the image pickup apparatus and the display apparatus are promptly synchronized with each other and their frequencies and/or clocks are aligned properly. 
     As a result, the signal delay where the image data fail to arrive in time for image display or the occurrence of overflow where the delay of image display relative to the image data can be reduced. Hence, the image degradation due to a so-called “frame loss” or “frame overlapping” is prevented, so that the images can be displayed with high quality. A detailed description is now given of embodiments with reference to the drawings. 
     It is to be noted that, in the description of the following embodiments, the image data may be not only data of practically effective images of an object but also those that include appended data, which accompany the image data, required for the transfer, communication, display and the like of other data. 
     First Embodiment 
       FIG. 1A  illustrates a system structure of an automotive wireless image transferring apparatus  100 . The automotive wireless image transferring apparatus  100  includes a rearview camera  10  provided at the back of a vehicle. 
     The image data of an object picked up by the camera  10  are inputted to a transmit-side unit  20  wherein the object is located in the back of the vehicle. The image data, which are subjected to a predetermined transmission processing and the like in the transmit-side unit  20 , are temporarily stored in a transmit-receive buffer  30  and are wirelessly sent from a radio TX module  40 . 
     The image data transmitted from the radio TX module  40  of the automotive wireless image transferring apparatus  100  are received by a radio RX module  50 . The image data received by the radio RX module  50  are stored temporarily in a transmit-receive buffer  60  and are subjected to a predetermined receiving processing in a receive-side unit  70 . 
     The image data processed by the receive-side unit  70  are displayed on a monitor  80  which is a display device such as a liquid crystal display (LCD), so that those image data can be viewed by a vehicle driver and the like. Viewing the monitor  80  allows the vehicle driver and the like to verify the safety and know the exact situation in the back of the vehicle. 
     The transmit-side unit  20  includes an input interface  21  for receiving the input of the image data sent from the camera. The transmit-side unit  20  also includes an input buffer  22  for temporarily storing the image data acquired via the input interface  21 . The transmit-side unit  20  also includes a transmitting signal processing unit  23  for subjecting the image data, stored temporarily in the input buffer  22 , to a signal processing such that the image data can be transmitted wirelessly. 
     The transmitting signal processing unit  23  includes a transmit-side clock generator  24  for generating a reference clock used to synchronize each device in the transmit-side unit  20 . The transmitting signal processing unit  23  also includes a marker appending unit  25  for appending a vertical synchronization marker to the frame header of image data transmitted from the transmit-side unit  20 . The transmitting signal processing unit  23  also includes a blanking interval adjustment  26  unit for adjusting a vertical blanking interval of the image data, based on the position of marker detected by a marker position monitoring unit  72 , such that the marker is positioned within a predetermined range. 
     The receive-side unit  70  includes an output interface  76  for outputting the image data in order to display an object image on the monitor  80 . The receive-side unit  70  also includes an output buffer  75  for temporarily storing the image data which are to be outputted to the output interface  76 . The receive-side unit  70  also includes a received signal processing unit  77  for performing a predetermined processing on the received image data. 
     The received signal processing unit  77  includes a receive-side clock generator  73  for generating a reference clock used to synchronize each device in the receive-side unit  70 . The received signal processing unit  77  also includes a marker extraction unit  71  for extracting the vertical synchronization marker affixed by the transmit-side unit  20 , from the image data received. 
     The received signal processing unit  77  also includes a marker position monitoring unit  72  which detects where the vertical synchronization marker extracted by the marker extraction unit  71  is positioned in a series of serial image data including a receive-side vertical blanking interval. Monitoring information, which is information typically related to the positions of markers, detected by the marker monitoring unit  72  are fed back from the radio RX module  50  to the transmit-side unit  20  by way of the transmit-receiver buffer  60 . The monitoring information to be fed back is received by the radio TX module  40  and inputted to the blanking interval adjustment unit  26  in the transmit-side unit  20  by way of the transmit-receive buffer  30 . Note that the automotive wireless image transferring apparatus  100  may additionally include other structural components or functions in each unit and each device or between them, in addition to the above-described structural components. 
     In the above-described automotive wireless image transferring apparatus  100 , the marker extraction unit  71  extracts the marker which has been appended to the header of image frame data by the marker appending unit  25 . The marker position monitoring unit  72  monitors whether the marker extracted by the marker extraction unit  71  is positioned in a predetermined range or not. 
     If the marker does not lie in the predetermined range, the blanking interval adjustment unit  26  will adjust the length of only horizontal blanking interval in the vertical blanking interval of image data. As a result, the clock phase and the like of the entire image data processed by the receive-side unit  70  are adjusted and a clock synchronized with a clock in the transmit-side unit  20  is generated, thereby achieving synchronization between transmitting and receiving sides. 
     Also, there may be a plurality of cameras  10 . If more than a single camera  10  are used, the clock phase and the like are adjusted according to a present relationship between the receiving-side unit  70  and one or more cameras  10  that transmit and receive the image data. 
     Referring to  FIGS. 2A to 2D , a detailed description is now given of marker detection, monitoring processing and so forth performed by the maker position monitoring unit  72 .  FIGS. 2A to 2D  are timing charts conceptually showing a processing of image data carried out by the received signal processing unit  77 . 
       FIG. 2A  is a timing chart showing a vertical synchronization signal (TV sync ) of image data transmitted from the radio TX module  40 . As shown in  FIG. 2A , in the transmit-side unit  20 , the marker appending unit  25  appends a marker to the header of image frame data having a transmit-side vertical blanking interval  2   a,  based on the reference clock generated by the transmit-side clock generator  24 . The marker appended by the marker appending unit  25  may be any marker-like signal as long as it can be recognized and extracted by the marker extraction unit  71 . 
     As shown in  FIG. 2B , in the receive-side unit  70 , the marker extraction unit  71  sets a marker detection flag M 0  by detecting the marker from the image data received by the radio RX module  50 . For example, the marker detection flag M 0  corresponding to the marker position may be a flag or the like that detects a rising edge or the like of the received image data. In such a case, as the transmit-side vertical blanking interval  2   a  ends, the rising edge itself of the image data may be thought of as a marker. 
       FIG. 2C  is a timing chart showing a receive-side vertical synchronization signal (RVs sync ) based on the reference clock generated by the receive-side clock generator  73 . As shown in  FIG. 2C , the receive-side unit  70  has a receive-side vertical blanking interval  2   c  based on a reference clock which is different from and independent of the transmit-side vertical blanking interval  2   a.    
     In other words, the transmit-side unit  20  and the receive-side unit  70  are each a free-running unit. As a result, the phase and frequency of the synchronization signals in the transmit-side unit  20  and those in the receive-side unit  70  do not coincide completely with each other and therefore a subtle displacement (nonalignment) is caused therebetween. Particularly when the transmit-side unit  20  and the receive-side unit  70  are installed in different temperature environments, the frequency response thereof may differ in between the transmit-side unit  20  and the receive-side unit  70  due to the temperature-dependent characteristics of crystal oscillators. Suppose that the transmit-side unit  20  and the receive-side  70  are installed in different positions. For example, suppose that the transmit-side unit  20  is installed outside a vehicle and the receive-side unit  70  is installed inside the vehicle. Then there may be cases where the temperature environments for them differ greatly. 
     The marker position monitoring unit  72  is provided with a marker position detection counter  721  as shown in  FIG. 1B  for example so that the marker position can be detected as shown in  FIG. 2D .  FIG. 1B  is a conceptual block diagram showing an exemplary structure of the marker position monitoring unit  72 . The marker position detection counter  721  in the marker position monitoring unit  72  is reset to an initial value in synchronism with the start of receive-side blanking interval  2   c,  and counts up starting from “0”, for instance. 
     If there is a marker detection flag M 0  extracted and set by the marker extraction unit  71 , the marker position monitoring unit  72  will detect a count value N of the marker position detection counter  721  and thereby can verify the marker position. The marker position detection counter  721  is reset to the initial value at a falling edge of the vertical synchronization signal and can measure the marker position by counting up sequentially from the initial value “0” within the receive-side blanking interval  2   c  only. 
     That is, the marker position monitoring unit  72  has a comparison calculator  723  compare the count value N of the marker position detection counter  721  with a predetermined count value range  2   d  stored beforehand in a marker position preset range storage  722 , and verifies that the marker detection flag M 0  lies within a marker allowable range T of the receive-side blanking interval  2   c.  In other words, the marker position monitoring unit  72  monitors whether or not the marker detection flag M 0  lies within the predetermined count value range  2   d  corresponding to within the marker allowable range T. The predetermined count value range  2   d  is a count value range between a count value NL, which corresponds to the lower limit of the marker allowable range T, and a count value Nu, which corresponds to the upper limit of the marker allowable range T. The marker position preset range storage  722  may comprise memory, such as flash memory, which is rewritable and erasable from outside. Also, the marker position preset range storage  722  may be such that the predetermined count value range  2   d  which is stored beforehand can be updated or upgraded as appropriate according to its usage environment, at the time of maintenance or the like. 
     Referring to  FIGS. 3A to 3D , a description is now given of adjustment processing performed, during a vertical blanking interval, based on the monitoring information which has been fed back.  FIGS. 3A to 3D  illustrate cases where a marker appended by the marker appending unit  25  in the transmit-side unit  20  is positioned outside the lower limit range of the predetermined marker allowable range T. 
     As shown in  FIG. 3A , the marker appending unit  25  appends a marker to the end of a transmit-side vertical blanking interval  3   a,  namely the position corresponding to the header of image data having substantial information on the object image. The marker extraction unit  71  decodes and extracts a marker appended to the image data received by the receive-side unit  70 , and sets a marker detection flag M 1 . 
     In the example shown in  FIG. 3C , the marker detection flag M 1  lies within a receive-side vertical blanking interval  3   c  but does not lie within the marker allowable range T and therefore it lies outside the lower limit NL. That is, the marker detection flag M 1  does not lie within a count value range  3   d  (a range between NL and Nu) corresponding to within the marker allowable range T, and indicates a count value N 1  which is less than the lower limit NL. 
     In this case, the blanking interval adjustment unit  26  expands the termination timing of the transmit-side vertical blanking interval  3   a  such that the termination of the receive-side vertical blanking interval  3   c  becomes relatively earlier. In other words, the blanking interval adjustment unit  26  expands the termination timing of the transmit-side vertical blanking interval  3   a  such that the termination timing of the receive-side vertical blanking terminal  3   c  is shifted to the left in  FIG. 3C . This processing of expanding the termination timing of the transmit-side vertical blanking interval  3   a  delays the termination timing of the transmit-side vertical blanking interval  3   a.  As a result, the termination timing of the transmit-side vertical blanking interval  3   a  shown in  FIG. 3A  is shifted to the right. 
     Thus the synchronization between the transmit-side vertical blanking interval  3   a,  which has been expanded as above, and the receive-side vertical blanking interval  3   c  is adjusted, so that both the intervals  3   a  and  3   c  can be positioned within a deviation range in the predetermined marker allowable range T as shown in  FIGS. 2C and 2D . Hence, the frame loss or frame overlapping can be suppressed at low cost without the use of a dedicated microcomputer for adjusting the synchronization, a dedicated buffer ring memory, a high-precision oscillator and the like. 
     Since the processing can be done without the use of a frame memory and the like, the delay otherwise caused due to the storage time of the frame memory can be reduced. Further, control is performed using the vertical blanking part only or more preferably the only horizontal blanking part thereof, on a clock-by-clock basis. As a result, no substantial image data is affected by this control. Also, the occurrence of color shift or the like is suppressed, thus achieving an advantageous effect of reducing the possibility of an adverse effect on the image quality. 
     Referring to  FIGS. 4A to 4D , a description is now given of another processing where the blanking interval adjustment unit  26  adjusts the vertical blanking interval.  FIGS. 4A to 4D  illustrate cases where a marker appended by the marker appending unit  25  in the transmit-side unit  20  is positioned outside the upper limit range of a predetermined marker allowable range T. 
     As shown in  FIG. 4A , the marker appending unit  25  appends a marker to the end of a transmit-side vertical blanking interval  4   a,  namely the position corresponding to the header of image data having substantial information on the object image. The marker extraction unit  71  decodes and extracts a marker appended by the marker extraction unit  71 , from the image data received by the receive-side unit  70 , and sets a marker detection flag M 2 . 
     In the example shown in  FIG. 4C , the marker detection flag M 2  lies within a receive-side vertical blanking interval  4   c  but does not lie within the marker allowable range T and therefore it lies outside the upper limit Nu. That is, the marker detection flag M 2  does not lie within a count value range  4   d  (a range between NL and Nu) corresponding to within the marker allowable range T, and indicates a count value N 2  which exceeds the upper limit Nu. 
     In this case, the blanking interval adjustment unit  26  shortens the termination timing of the transmit-side vertical blanking interval  4   a  so that the termination of the receive-side vertical blanking interval  4   c  is relatively delayed. In other words, the blanking interval adjustment unit  26  shortens the termination timing of the transmit-side vertical blanking interval  4   a  so that the termination of the receive-side vertical blanking interval  4   c  is shifted to the right in  FIG. 4C . 
     Thus, both the transmit-side vertical blanking interval  4   a  and the receive-side vertical blanking interval  4   c  can be positioned within the deviation range in the predetermined marker allowable range T as shown in  FIGS. 2C and 2D . Also, the processing is executed without the use of the frame memory and the like, so that the delay caused otherwise can be reduced. Further, control is performed using a blanking part only on a clock-by-clock basis. As a result, the effect of this control on the substantial image data is minimized. Also, the occurrence of color shift or the like is suppressed, thus achieving an advantageous effect of reducing the possibility of an adverse effect on the image quality. 
     In the above explanation in conjunction with  FIG. 2A  to  FIG. 4D , the marker allowable range T is preferably set narrower in consideration of the time required for feedback communication between a transmitting side and a receiving side such that the synchronization is adjusted before the deviation in synchronization becomes too large. For example, if the time required for feedback communication between a transmitting side and a receiving side is long, it is preferable that the marker allowable range T is set to a significantly narrow range; if the time required for feedback communication therebetween is not long, it is preferable that the marker allowable range T is not set to too narrow a range. 
     As a result, even in the cases where the time required for feedback communication between the transmitting side and the receiving side is long, the synchronization can be adjusted at an earlier stage on the assumption that the deviation in synchronization increases further during this time period required for communication. Hence, the image data can be communicated in real time with a reduced delay in synchronization. Also, in the cases where the time required for feedback communication therebetween is not long, the image data can be communicated in real time with a reduced delay in synchronization even if the marker allowable range T is not much narrowed. In this case, the transmitting side and the receiving side are synchronized within a desired delay range even if the frequency at which the synchronization is adjusted is reduced. This is desirable in that power is saved and synchronization adjustment is achieved with a reduced computational load. 
     A brief description is now given of a structure of image frames (or image field) processed by the automotive wireless image transferring apparatus  100 .  FIG. 5  conceptually illustrates a frame  51  structure of image data. 
     As shown in  FIG. 5 , a vertical synchronization signal  58  in the receive-side unit  70  has about 260 lines. The vertical synchronization signal  58  includes an active part  54  composed of 240 lines and a vertical blanking part  53  composed of about 20 lines. 
     A horizontal synchronization signal  57  in the receive-side unit  70 , which is equivalent to about 1,720 clocks, includes a vertical blanking part  55  composed of about 276 clocks and an active part  56  composed of about 1,440 clocks. The active part  54  and the active part  56  constitute an active region  52  of an image frame. Image data associated with the active region  52  practically have information on an object image and practically correspond to a display period of an image. 
     Also, the vertical blanking part  53  has a horizontal synchronization signal  57  of about 20 lines, so that the vertical blanking part  53  includes a horizontal blanking part  55  of about 20 lines and an active part of about 20 lines. 
     The blanking interval adjustment unit  26  adjusts only the horizontal blanking interval within a vertical blanking interval. That is, the blanking interval adjustment unit  26  advances or delays, clock by clock, the rearmost part of the vertical blanking part  53  (i.e., the transmit-side blanking interval) for only the horizontal blanking part  55  within a vertical blanking part  53 . 
     Specifically, at the transmitting side, the blanking interval adjustment unit  26  expands or contracts the termination timing of the vertical blanking part  53  for a blanking interval associated with a blanking area  59  as shown in  FIG. 5  in such a manner that approximately 3 to 5 is added to or subtracted from the count value measured and counted by the clock count. 
     As a result, the state as shown in  FIG. 6  can be prevented where the deviation in synchronization accumulates sequentially and the amount of deviation in synchronization gradually increases in the automotive wireless image transferring apparatus  100 .  FIGS. 6A and 6B  are conceptual diagrams schematically showing a deviation in synchronization between a transit-side vertical synchronization signal and a receive-side vertical synchronization signal. As shown in  FIG. 6 , although the synchronization does not suffer from any deviation at first (Δ S=0), the synchronization differs by Δ A at the next rising edge because the properties of oscillation clocks differ due to the temperature difference and other factors. 
     This deviation in synchronization increases to Δ B (Δ B=2×Δ A) at the next falling edge and further increases to Δ C (Δ C=3×Δ A) at the next falling edge. 
     Generally, the synchronization deviation arising from clock phase difference and other factors accumulates and increases with time, as described above, if left uncontrolled. 
     However, when the synchronization deviation lies outside a predetermined range, the automotive wireless image transferring apparatus  100  adjusts, at the transmitting side, the clock count of the counter that counts the vertical blanking interval. As a result, the automotive wireless image transferring apparatus  100  can eliminate or reduce the synchronization deviation by expanding or contracting the vertical blanking interval. 
     Note that the blanking region  59  corresponds to the blanking intervals for both the vertical direction and the horizontal direction. Thus, the blanking region  59 , which practically does not contain information on the object image, corresponds to the nondisplay period of images. 
     A detailed description is now given of a processing performed by the marker appending unit  25 .  FIG. 7  is a conceptual diagram showing an exemplary structure of the marker appending unit  25 . Referring to  FIG. 7 , the marker appending unit  25 , including an image compression processing unit  254 , may append a vertical synchronization marker as an image compression processing has been performed. An optimum marker selector  252  in the marker appending unit  25  selects an optimum maker from among a plurality of markers stored beforehand in a marker storage  251 . 
     An optimum marker insertion unit  253  inserts the thus selected optimum marker into data. The optimum marker may be, for instance, FFFF_FF or the like which is identifiable by the marker extraction unit  71 . An image compression processing unit  254  in the marker appending unit  25  performs compression processing using quantization information that the image compression processing unit  254  stores beforehand in a quantization table storage  255  per macroblock. 
     In so doing, the quantization table selector  256  selects a quantization table applied to a color-difference block of the macroblock. The optimum marker insertion unit  253  combines the image compression information of the image compression processing unit  254  and the marker selected by the optimum marker selector  252  so as to be inserted into the data. 
     As described above, the vertical synchronization marker may be structured by including an identifier field such as FFFF_FF, a quantization table selection information field and an ancillary data field containing other arbitrary information. 
     Subsequently, referring to  FIG. 8  a detailed description is given of an exemplary counting operation of the marker position detection counter  721  included in the marker position monitoring unit  72 .  FIG. 8  is a flowchart conceptually showing a typical example of a counting operation outline of the marker position detection counter  721 . 
     In step S 81 , The marker position monitoring unit  72  determines if a vertical blanking interval has started or not. The marker position monitoring unit  72  may detect the start of the vertical blanking interval by detecting a falling edge of vertical synchronization signal caused by the start of the vertical blanking interval, for instance. Once the vertical blanking interval starts, proceed to Step S 82 . If the vertical blanking interval does not start, proceed to Step S 88 . 
     In step S 82 , the marker position detection counter  721  initializes the counter value (typically to the count value of “0”) by a reset signal generated as a result of detection of the start of a vertical blanking interval. 
     In step S 83 , the marker position monitoring unit  72  determines whether the marker extraction unit  71  has extracted a marker or not. For instance, the marker monitoring unit  72  determines whether or not there has been an input of detection signal indicating that the marker extraction unit  71  has extracted a marker. If the marker is not extracted, proceed to step S 84 . If the marker is extracted, proceed to step S 89 . 
     In step S 84 , the marker position detection counter  721  adds “ 1 ” to the current count value and then sets this count value added with “1” as a new count value. In other words, the marker position detection counter  721  counts up sequentially by adding “1” to the current count value. 
     In step S 85 , the marker position monitoring unit  72  determines whether the vertical blanking interval has ended or not. The marker position monitoring unit  72  may detect, for example, a rising edge of vertical synchronization signal resulting from the termination of a vertical blanking interval and thereby may detect the termination of the vertical blanking interval. If the vertical blanking interval ends, proceed to step S 86 . If the vertical blanking interval does not end, return to step S 83 . 
     In step S 86 , the marker position detection counter  721  holds the counter value. 
     In step S 87 , the received signal processing unit  77  determines whether the receiving of image data has terminated or not. If the receiving of image data terminates, the flow of count-up operation of the marker position detection counter  721  during the vertical blanking interval will be terminated. If the receiving of image data does not terminate, return to step S 81 . 
     In step S 88 , the marker position monitoring unit  72  determines whether or not the image data is in a blanking interval at the receiving side. If the image data is in a blanking interval, proceed to step S 83 . If not in a blanking interval, proceed to step S 86 . 
     In step S 89 , the comparison calculator  723  in the marker position monitoring unit  72  determines whether or not the counter value is within the count value range  2   d  corresponding to the marker allowable range T. Assume herein that the count value range  2   d  is stored beforehand in the marker position preset storage  722  of the marker position monitoring unit  72 . The same holds true for the cases of predetermined count value range  3   d  and  4   d,  and the predetermined count value ranges  2   d,    3   d  and  4   d  may be identical to each other. 
     If whether the marker position lies within a predetermined range or not is to be determined in the receiving side, the marker position monitoring unit  72  will execute the above-described processing and feed back the deviation amount from the marker allowable range T, to the transmitting side as the monitoring information. 
     If whether the marker position lies within a predetermined range or not is not determined in the receiving side, the receive-side unit  70  will feed back the counter value to the transmitting side. That is, the receive-side unit  70  feeds back the information on a marker position (hereinafter referred to as “marker positional information” also) to the transmitting side as the monitoring information. In such a case, the counter value is a typical example of marker positional information. That is, if whether the marker position lies within a predetermined range or not is determined in the transmitting side, the receive-side unit  70  will feed back the marker positional information to the transmitting side as the monitoring information. This processing will be described in detail later, so that the description thereof is omitted here. 
     As has already been described in Step S 89 , the receive-side unit  70  in the automotive wireless image transferring apparatus  100  may calculate the deviation amount from the marker allowable range T and the required adjustment amount associated with this deviation amount. As has already been described in Step S 89 , the receive-side unit  70  in the automotive wireless image transferring apparatus  100  may detect the marker position only. Then it may feed back the marker positional information (typically the counter value) to the transmit-side unit  20 , and the transmit-side unit  20  may calculate the deviation amount from the marker allowable range T and the required adjustment amount associated with this deviation amount. 
     Next, using  FIG. 9  a detailed description is given of a case where the deviation amount from the marker allowable range T and the necessary adjustment amount associated therewith are calculated by the receive-side unit  70 .  FIG. 9  is a flowchart showing a detailed operation of the automotive wireless image transferring apparatus  100 . The operation thereof will be described following each step in  FIG. 9 . 
     In step S 91 , the transmit-side unit  20  acquires the picked-up images of an object from the camera  10  through the input I/F  21  and the input buffer  22 . The camera  10 , which is comprised of solid-state image sensing devices such as CCD (Charge-Coupled Device) or CMOS (Complementary Metal-Oxide Semiconductor) image sensors, performs photoelectric conversion of light from the object so as to output electric signals. The transmit-side unit  20 , which is provided with the transmit-side clock generator  24 , free-runs responsive to a clock that depends on crystal temperature characteristics according to an installation environment of the transmit-side unit  20 . Assume that a crystal has a temperature dependency of oscillation frequency on the order of ppm or so. 
     In step S 92 , the marker appending unit  25  appends a vertical synchronization marker to image data to be sent. The marker appending unit  25  may append the vertical synchronization marker at the termination timing of a vertical blanking interval and at the timing corresponding to a rising edge of image data. That is, the marker appending unit  25  in the transmitting signal processing unit  23  assigns the vertical synchronization marker to a header portion of active data which is practically effective object image data. 
     In step S 93 , the transmit-side unit  20  transmits the image data to which the vertical synchronization marker has been appended, to the radio TX module  40  via the transmit-receive buffer  30 . 
     In step S 94 , the receive-side unit  70  receives the vertical-synchronization-marker-appended image data transmitted from the transmit-side unit  20 , via the radio RX module  50 . The image data received are temporarily stored in the transmit-receive buffer  60  of the receive-side unit  70  and then are processed by the received signal processing unit  77 . The receiver-side unit  70  and the transmit-side unit  20  are each configured to free-run independently, so that they operate based on different reference clocks generated by the different clock generators. 
     In step S 95 , the marker extraction unit  71  in the received signal processing unit  77  extracts the vertical synchronization marker from the image data. As the marker extraction unit  71  extracts the vertical synchronization marker, it sets the marker detection flag M 0  as shown in  FIG. 2B , for instance. 
     In step S 96 , the marker position monitoring unit  72  detects the position of the marker extracted by the marker extraction unit  71 . For example, the marker position monitoring unit  72  monitors the marker position in such a manner that the correspondence is detected between the marker detection flag M 0  set by the marker extraction unit  71  and a proper count value of the marker position detection counter  721 , which is reset at the start of a receive-side blanking interval and counts up starting from there. Specifically, the monitoring unit  72  detects which count value of the marker position detection counter  721  corresponds to the marker detection flag M 0 . 
     In step S 97 , the marker position monitoring unit  72  determines whether the marker position is within a predetermined range or not. If the marker position is within the predetermined range, proceed to Step S 98 . If the marker position is not within the predetermined range, proceed to Step S 9   c.  For example, the comparison calculator  723  compares the predetermined count value range  2   d  corresponding to the marker allowable range T stored in the marker position preset range storage  722  with the counter value of the marker position detection counter  721  corresponding to the marker detection flag M 0 . As a result of comparison made by the comparison calculator  723 , if the counter value corresponding to the marker detection flag M 0  is within the predetermined count value range  2   d,  proceed to Step S 98 . As a result of comparison made by the comparison calculator  723 , if the counter value corresponding to the marker detection flag M 0  is not within the predetermined count value range  2   d,  proceed to Step S 9   c.    
     In step S 98 , the comparison calculator  723  generates data, as monitoring information, indicating that there is no phase lag and then sends the thus generated data to the transmit-receive buffer  60 . 
     In step S 99 , the receive-side unit  70  transmits the monitoring information generated in the above-described S 98  to the transmit-side unit  20  through the radio RX module  50  in a feedback manner. 
     In step S 9   a,  the blanking interval adjustment unit  26  adjusts a horizontal blanking interval in the vertical blanking interval of the transmit-side vertical synchronization signal, based on the fed-back monitoring information. Typically, the blanking interval adjustment unit  26  advances or delays the termination timing of the transmit-side horizontal blanking interval in such a manner that  3  or so is added to or subtracted from the count value measured and counted by the clock count. Advancing or delaying the termination timing of the horizontal blanking interval by the blanking interval adjustment unit  26  allows advancing or delaying the termination timing of the vertical blanking interval. The vertical blanking interval is a period during which there is practically no image data. Hence, the above-described processing reduces adverse effects on the image data itself and enables the adjustment of synchronizing the timing between the transmitting side and the receiving side. It is to be noted here that a counter for measuring the time of a blanking interval and the like includes an up-count terminal and a down-count terminal which forcibly count up and count down the count value, respectively, in addition to a clock terminal to which the clock signal to be counted is inputted. The blanking interval adjustment unit  26  can count up or down the count value by inputting a trigger to the up-count terminal or down-count terminal of the counter. As a result, at the transmitting side, the blanking interval adjustment unit  26  can extend or shorten the blanking interval. Note that the adjustment made by the blanking interval adjustment unit  26  continues to be done until the marker detection flag is contained within a predetermined range. For this reason, a process for verifying and monitoring whether the marker detection flag is positioned within the predetermined range or not may be further implemented. The received signal processing unit  77  performs processing on the image data which have been received and decoded so that a desired image display can be achieved. Then image data suitable for image display are obtained as a result of the processing. The receive-side unit  70  has the monitor  80  display the image data via the output interface  76 . As described above, the timing of the image data is adjusted by the transmit-side unit  20  so that the timing thereof in the receive-side unit  70  becomes approximately synchronized with the transmit-side clocks within a predetermined allowable range. Hence, high-quality real-time display can be achieved without delay. 
     In step  96   b,  if the real-time display of an object image is done with high image quality and then the image pickup of the object is terminated, this processing flow on synchronization adjustment will be terminated. If the image pickup thereof is not terminated, return to Step S 91 . Note that the aforementioned each processing of synchronization adjustments can be performed in parallel while the image is being displayed on the monitor  80 . 
     In step S 9 C, the comparison calculator  723  determines whether or not the counter value N of the marker position detection counter  721  corresponding to the marker detection flag M 0  set by the marker extraction unit  71  is larger than the upper limit Nu of the predetermined count value range  2   d  corresponding to the marker allowable range T stored in the marker position preset range storage  722 . If the comparison calculator  723  determines that the counter value N of the marker position detection counter  721  corresponding to the marker detection flag M 0  set by the marker extraction unit  71  is larger than the upper limit Nu of the predetermined count value range  2   d  corresponding to the marker allowable range T stored in the marker position preset range storage  722 , proceed to Step S 9   d.  If, on the other hand, the comparison calculator  723  determines that the counter value N of the marker position detection counter  721  corresponding to the marker detection flag M 0  set by the marker extraction unit  71  is not larger than the upper limit Nu of the predetermined count value range  2   d  corresponding to the marker allowable range T stored in the marker position preset range storage  722 , proceed to Step S 9   e.    
     In step S 9   d,  the comparison calculator  723  calculates the difference between the counter value N of the marker position detection counter  721  corresponding to the marker detection flag M 0  set by the marker extraction unit  71  and the upper limit Nu of the predetermined count value range  2   d,  and generates transmit data with its difference value as the monitoring information. 
     In step S 93 , the comparison calculator  723  calculates the difference between the counter value N of the marker position detection counter  721  corresponding to the marker detection flag M 0  set by the marker extraction unit  71  and the lower limit NL of the predetermined count value range  2   d,  and generates transmit data with its difference value as the monitoring information. 
     The automotive wireless image transferring apparatus  100  exemplified in this first embodiment uses the vertical synchronization marker received together with the image data by the receive-side unit  70  to calculate an amount of deviation in synchronization from the transmitting side. Then the thus calculated amount of deviation in synchronization or the like is fed back to the transmit-side unit  20 . Thus the transmit-side unit  20  can adjust the vertical blanking interval at the transmitting side by counting it up or counting it down by the count corresponding strictly to the thus fed-back amount of deviation in synchronization. 
     Thus the receive-side unit  70  can maintain the synchronization in real time with the transmit-side unit  20  within a desired range. Hence the receive-side unit  70  no longer needs to have storage devices therein, used to adjust the phase, such as a high-capacity buffer ring memory. As a result, the apparatus can be lighter in weight and smaller in size. 
     Also, if the monitoring information fed back from the receive-side unit  70  in the aforementioned Step S 9   a  is information indicating that the phase lag is within a predetermined range, there will be no need for the transmitting side to adjust the deviation in synchronization. If, on the other hand, the monitoring information fed back from the receive-side unit  70  in the aforementioned Step S 9   a  is information indicating a deviation amount, for example, where the counter value N exceeds the upper limit Nu of the predetermined count value range  2   d,  the blanking interval adjustment unit  26  may adjust the synchronization in a manner such that the marker detection flag M 0  is within the predetermined count value range  2   d  and is in the neighborhood of the lower limit NL of the predetermined count value range  2   d  after the predetermined count value range  2   d  is added to the deviation amount. 
     The deviation in synchronization is typically caused by the phase misalignment of each clock between the transmit-side unit  20  and the receive-unit  70 , and this misalignment tends to be almost constant under a constant temperature environment. Accordingly, if the counter value N exceeds the upper limit Nu of the predetermined count value range  2   d  and therefore the deviation amount is detected by the marker position monitoring unit  72 , the similar misalignment pattern is likely to continue for at least a certain period of time. 
     Thus the comparison calculator  723  may feed back a count value, which is derived by adding the predetermined count value range  2   d  to the difference (deviation amount) between the predetermined count value range  2   d  and the counter value N exceeding the upper limit Nu thereof, as the monitoring information. Also, in this case, the blanking interval adjustment unit  26  may adjust the blanking interval by an amount corresponding to the monitoring information fed back. Hence, no adjustment will be required until the next synchronization adjustment becomes necessary, so that the frequency of adjustment of blanking interval can be reduced. Since the frequency of adjustment of blanking interval can be reduced, the computational load and communication load can be reduced, which in turn saves the power of the automotive wireless image transferring apparatus  100 . 
     Second embodiment 
     A description is next given of a case, according to a second embodiment, where the synchronization adjustment amount is calculated based on the marker position and so forth by a transmit-side unit  20 . That is, in the second embodiment, a receive-side unit  70  detects the marker position only and feeds back the marker positional information (typically the counter value) to the transit-side unit  20 , and the transmit-side unit  20  calculates a deviation amount from a marker allowable range T and a necessary adjustment amount associated with the deviation amount. A description is hereinbelow given of the second embodiment centering around differences from the automotive wireless image transferring apparatus  100  exemplified in the first embodiment. And components identical to or equivalent to those of the first embodiment are given the same reference numerals and the repeated explanation thereof is omitted here. 
     In an automotive wireless image transferring apparatus  100  according to the second embodiment, a marker position monitoring unit  72  needs to feed back only a count value N of a marker position detection counter  721  corresponding to the position of the marker detection flag M 0  of the vertical synchronization maker. Thus the automotive wireless image transferring apparatus  100  according to the second embodiment may not be provided with the two structural components, namely, a marker position preset range storage  722  and a comparison calculator  723  in the marker position monitoring unit  72  as shown in  FIG. 1B . As a result, the computational load in a monitor  80  side is reduced and the signals in the transmitting side and those in the receiving side can be synchronized even in a multi-camera system comprising a single monitor  80  for a plurality of cameras, for instance. A description is now given of a blanking interval adjustment unit  26  in the transmitting side that calculates the deviation amount from the marker allowable range T and the required adjustment amount associated with this deviation amount. 
       FIG. 10  is a block diagram conceptually showing an exemplary structure of the blanking interval adjustment unit  26 , in the transmitting side, according to the second embodiment. As shown in  FIG. 10 , the blanking interval adjustment unit  26  includes a marker position preset range storage  262  that stores a predetermined count value range  2   d  corresponding to the marker allowable range T. Here, the same applies to predetermined count value ranges  3   d  and  4   d.  The blanking interval adjustment unit  26  also includes a comparison calculator  263  that compares the count value N fed back through a transmit-receive buffer  30  with the count value range  2   d  stored in the marker position preset range storage  262 . 
     A vertical blanking interval counter  261  includes a reset terminal which is reset-inputted in response to the start of a transmit-side vertical blanking interval, an up-count terminal which advances the count, and a down-count terminal which delays the count. The comparison calculator  263  determines whether the count is to be advanced or delayed, based on the above comparison result, and calculates the extent to which the adjustment amount is expanded or contracted. In accordance with the thus calculated expansion/contraction adjustment amount, the comparison calculator  263  outputs a trigger to the up-count terminal or down-count terminal. Then the comparison calculator  263  adjusts the count value of the vertical blanking interval counter  261  so as to adjust preferably the horizontal blanking interval in a transmit-side vertical blanking interval. 
       FIG. 11  is a flowchart conceptually showing operations processed by the automotive wireless image transferring apparatus  100  according to the second embodiment. Based on each step shown in  FIG. 11 , a description is now given hereinbelow of operations processed by the automotive wireless image transferring apparatus  100  according to the second embodiment. As for the processings identical or equivalent to those of the first embodiment, the explanation thereof will be simplified using the description in conjunction with  FIG. 9 . 
     The description of Step S 111  is the same as that of Step S 91 , so that the repeated explanation thereof is omitted here. The description of Step S 112  is the same as that of Step S 92 , so that the repeated explanation thereof is omitted here. The description of Step S 113  is the same as that of Step S 93 , so that the repeated explanation thereof is omitted here. The description of Step S 114  is the same as that of Step S 94 , so that the repeated explanation thereof is omitted here. The description of Step S 115  is the same as that of Step S 95 , so that the repeated explanation thereof is omitted here. The description of Step S 116  is the same as that of Step S 96 , so that the repeated explanation thereof is omitted here. 
     In step S 117 , the marker position monitoring unit  72  regards the count value N corresponding to the position of the marker detection flag M 0  extracted and set by the marker extraction unit  71 , as the monitoring information. That is, the marker position detection counter  721  in the marker position monitoring unit  72  counts up sequentially in response to the start of the vertical blanking interval  2   c,  and detects the count value N corresponding to the marker detection flag M 0 . Note that in the second embodiment the same processing is carried out for both the count value N 1  corresponding to the marker detection flag M 1  and the count value N 2  corresponding to the marker detection flag M 2 . 
     In step S 118 , the receive-side unit  70  feeds back the monitoring information generated in the above-described Step S 117 , to the transmit-side unit  20  via the radio RX module  50 . Here, the monitoring information fed back to the transmit-side unit  20  by the receive-side unit  70  is the count value N corresponding to the marker detection flag M 0 . This is the marker positional information that does not require heavy calculation and therefore the computational load of the receive-side unit  70  is minimized. 
     In step S 119 , the comparison calculator  263  determines whether the fed-back marker positional information (typically the count value N) is within a predetermined range (typically the predetermined count value range  2   d ) or not. If the marker position is within the predetermined range, proceed to Step S 11   f.  If the marker position is not within the predetermined range, proceed to Step S 11   a.    
     For example, the comparison calculator  263  compares the predetermined count value range  2   d  corresponding to the marker allowable range T stored beforehand in the marker position preset range storage  262  with the counter value N of the marker position detection counter  721 , which has been sent by a feedback, corresponding to the marker detection flag M 0  set by the marker extraction unit  71 . As a result of comparison made by the comparison calculator  263 , if the counter value N corresponding to the marker detection flag M 0  is within the predetermined count value range  2   d,  proceed to Step S 11   f.  As a result of comparison made by the comparison calculator  263 , if the counter value N corresponding to the marker detection flag M 0  is not within the predetermined count value range  2   d,  proceed to Step S 11   a.    
     In step S 11   a,  the comparison calculator  263  determines whether or not the fed-back counter value N is greater than the upper limit Nu of the predetermined count value range  2   d  corresponding to the marker allowable range T stored in the marker position preset range storage  262 . 
     If the comparison calculator  263  determines that the fed-back counter value N is greater than the upper limit Nu of the predetermined count value range  2   d  corresponding to the marker allowable range T stored in the marker position preset range storage  262 , proceed to Step S 11   b.  If, on the other hand, the comparison calculator  263  determines that the fed-back counter value N is not greater than the upper limit Nu of the predetermined count value range  2   d  corresponding to the marker allowable range T stored in the marker position preset range storage  262 , proceed to Step S 11   d.    
     In step S 11   b,  the comparison calculator  263  calculates the difference between the counter value N and the upper limit Nu. In such a case, the comparison calculator  263  may add the predetermined count value range  2   d  stored in the marker position preset range storage  262 , to this calculated difference value between the counter value N and the upper limit Nu. These values calculated in this Step S 11   b  by the comparison calculator  263  are equivalent to the adjustment amount, in the next Step S 11   c,  for the vertical blanking interval in the blanking interval adjustment unit  26 . 
     In step S 11   c,  the blanking interval adjustment unit  26  shortens preferably the horizontal blanking interval in a vertical blanking interval by the amount equivalent to the value calculated in Step S 11   b.  More specifically, the vertical blanking interval counter  261  advances the count based on the signal corresponding to an adjustment amount of vertical blanking interval inputted to the up-count terminal from the comparison calculator  263  so as to practically perform adjustment processing of shortening the measurement period of a vertical blanking interval. This adjustment processing adjusts the synchronization of the marker detection flag M 0  within the marker allowable range T, so that the desired synchronization can be achieved between the transmitting side and the receiving side. 
     In step S 11   d,  the comparison calculator  263  calculates the difference between the counter value N of the marker position detection counter  721 , which has been fed back from the receive-side unit  70 , corresponding to the marker detection flag M 0  set by the marker extraction unit  71  and the lower limit NL of the predetermined count value range  2   d  stored in the marker position preset range storage  262 . The value of difference calculated by the comparison calculator  263  in this Step S 11   d  is equivalent to the adjustment amount of vertical blanking interval, in the blanking interval adjustment unit  26 , used in the next Step S 11   e.    
     In step S 11   e,  the blanking interval adjustment unit  26  expands the vertical blanking interval by the amount equivalent to the value calculated in Step S 11   d.  More specifically, the vertical blanking interval counter  261  delays the count based on the signal corresponding to an adjustment amount of vertical blanking interval inputted to the down-count terminal from the comparison calculator  263  so as to practically perform adjustment processing of extending the measurement period of a vertical blanking interval. This adjustment processing adjusts the synchronization of the marker detection flag M 0  within the marker allowable range T, so that the desired synchronization can be achieved between the transmitting side and the receiving side. 
     In step S 11   f,  if the real-time display of the object image is done with a reduced delay and high image quality and then the image pickup of the object is terminated, this processing flow on synchronization adjustment will be terminated. If the image pickup thereof is not terminated, return to Step S 111 . Note that the aforementioned each processing of synchronization adjustments can be performed in parallel while the image is being displayed on the monitor  80 . 
     The automotive wireless image transferring apparatus  100  exemplified in the second embodiment detects the position of a vertical synchronization marker sent together with the image data, in the receive-side unit  70 , and then feeds back the detected position thereof to the transmit-side unit  20 . The transmit-side unit  20  uses the fed-back marker position to calculate an amount of deviation in synchronization from the receiving side. And the transmit-side unit  20  can adjust the vertical blanking interval by counting it up or counting it down by the count corresponding to the thus calculated amount of deviation in synchronization. 
     Thus, while the receive-side unit  70  communicates with the transmit-side unit  20 , the receive-side unit  70  can maintain the synchronization in real time with the transmit-side unit  20  within a desired range. Hence the receive-side unit  70  no longer needs to have storage devices therein, used to adjust the phase, such as a high-capacity buffer ring memory. As a result, the apparatus can be lighter in weight and smaller in size. 
     Also, if the monitoring information fed back from the receive-side unit  70  in the aforementioned Step S 118  indicates that the phase lag is within a predetermined range, there will be no need for the transmitting side to adjust the deviation in synchronization. If, on the other hand, the monitoring information fed back from the receive-side unit  70  in the aforementioned Step S 118  indicates a difference, for example, where the counter value N exceeds the upper limit Nu of the predetermined count value range  2   d,  the blanking interval adjustment unit  26  may adjust the synchronization in a manner such that the marker detection position is within the predetermined count value range  2   d  and is in the neighborhood of the lower limit NL of the predetermined count value range  2   d  after the predetermined count value range  2   d  is added to the difference. 
     The deviation in synchronization is typically caused by the phase misalignment of each clock between the transmit-side unit  20  and the receive-unit  70 , and this misalignment tends to be almost constant under a constant temperature environment. Accordingly, if the counter value N exceeds the upper limit Nu of the predetermined count value range  2   d  and therefore a deviation is detected by the comparison calculator  263 , the similar misalignment pattern is likely to continue for at least a certain period of time. 
     Thus the comparison calculator  263  calculates a count value in a manner such that the predetermined count value range  2   d  is added to a deviation amount, where the counter value N exceeds the upper limit Nu of the predetermined count value range  2   d,  and may supply a count-up trigger, corresponding to the value thus calculated, to the vertical blanking interval counter  261 . That is, based on the fed-back counter value N, the blanking interval adjustment unit  26  may adjust the blanking interval by an amount derived by adding the predetermined count value range  2   d  to the difference between the predetermined count value range  2   d  and the counter value N exceeding the upper limit Nu thereof. This can permit a longer length of time until the next time when the synchronization adjustment needs to be made, so that the frequency of adjustment of blanking interval can be reduced. Since the frequency of adjustment of blanking interval can be reduced, the computational load and communication load can be reduced, thereby achieving a power-saving automotive wireless image transferring apparatus  100 . 
     As described above, the automotive wireless image transferring apparatus  100  provides the image transfer and display at low cost and with reduced frame loss, frame overlapping and the like. Also, the automotive wireless image transferring apparatus  100  directly adjusts the length of horizontal blanking interval of image data without the use of a dedicated buffer memory for adjusting the phase and timing. Thus the delay of display images relative to the camera images can be reduced. 
     Also, the automotive wireless image transferring apparatus  100  adjusts the horizontal blanking interval only, on a clock-by-clock basis. Thus an adverse effect on the practically effective part of an object image in the image data is reduced. 
     Also, the blanking interval adjustment unit  26  adjusts the length of horizontal synchronization signal by adjusting the blanking interval, in a vertical synchronization signal composed on the basis of a horizontal synchronization signal corresponding to the number of lines. Accordingly, the automotive wireless image transferring apparatus  100  can adjust the cycle of vertical synchronization signal without changing the number of lines in each image frame. 
     As a result, the automotive wireless image transferring apparatus  100  can display the received images without causing pixels to be deviated in the horizontal direction at the time of image display. 
     Also, in each of a free-run transmitter and a free-run receiver of the automotive wireless image transferring apparatus  100 , the phase difference and the frequency difference can be contained as appropriate within predetermined ranges. Thus the occurrence of failures can be reduced. The failures include a problem where the transmitted data arrive earlier than the display timing and a problem where conversely the transmitted data don&#39;t arrive in time for the display timing. 
     In the conventional practice, the phase difference in transmit-receive image synchronization signal cumulatively accumulates with time and an asynchronous state continues. This undesired state is prevented in the automotive wireless image transferring apparatus  100  according to the present embodiments. Since the asynchronous state does not continue, the display caused by the pixel skipping of image data in units of frame can be significantly reduced and the overlapped display, such as a repeated display of frame data stored in a buffer, and other undesired displays can be significantly reduced. 
     Hence the automotive wireless image transferring apparatus  100  reduces the occurrence of discontinuous moving images, so that a so-called “frame skip” or “frame jump” can be reduced and at the same time the moving images of an object that moves fast can be displayed with high reliability 
     While the embodiments of the present invention have been described using specific terms, such description is for illustrative purposes only. The automotive wireless image transferring apparatus  100  according to the present invention is not limited to those of the above-described embodiments only, and it is to be understood that changes and variations in structure and/or operations may be made without departing from the spirit or scope of the appended claims. The technical ideas or concepts, underlying the present invention, which are exemplified and disclosed in the present embodiments are not limited to the transferring (transmission and receiving) realized by the wireless connection and may be applied to the transferring of image data through a wired connection.