Abstract:
A video combining circuit includes: a video component controller for receiving and processing a first video component signal to output a first video signal including location information; and a video signal controller coupled to the video component controller for receiving the first video signal and a second video signal and choosing one of the first and second signals according to the location information to output a video composite signal; wherein the first and second video signal does not overlap.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to digital TV, and more particularly, to a video combining circuit for a digital TV and method thereof.  
         [0003]     2. Description of the Prior Art  
         [0004]     Compared with conventional CRT-type displays, flat panels such as LCD panels and PDP panels have the property of low thickness, thereby possessing considerable advantage for high-level TV application of large displaying size. As the technique involved in manufacturing LCD and PDP panels advances, TVs equipped with LCD or PDP panels have become more and more popular. Because these modern high-level TVs generally support a picture-in-picture (PIP) function, a user can view two TV programs on the same TV screen at the same time.  
         [0005]     Obviously, however, a main-video signal and a sub-video signal respectively corresponding to two programs need to be decoded, as well as subtitle information of the main-video signal and subtitle information of the sub-video. For example, referring to  FIG. 1 , a conventional video combining circuit first reads a plurality of video component signals from a memory, the signals respectively corresponding to a main-picture  214 , a sub-picture  224 , and a background picture  234 . The video combining circuit then processes these video component signals independently, and combines the above-processed signals to output a composite picture  200 . Therefore, a trade-off between the cost and the efficiency of a conventional digital TV exists because the conventional digital TV consumes a large proportion of the system resource and bandwidth in order to display two TV programs on the same TV screen at the same time.  
       SUMMARY OF THE INVENTION  
       [0006]     It is therefore one of the objectives of the claimed invention to provide a video combining apparatus for a digital TV and method thereof, so as to save the bandwidth needed for accessing memory.  
         [0007]     The claimed invention provides a video combining circuit according to a first embodiment. The video combining circuit includes a first video component controller for receiving and processing a first video component signal to output a first video signal that includes location information; and a video signal controller coupled to the video component controller for receiving the first video signal and a second video signal and choosing the first or second video signal according to the location information for outputting a video composite signal, wherein the first video signal and the second video signal do not overlap.  
         [0008]     The claimed invention further provides a video combining circuit according to a second embodiment. The video combining circuit includes a first video component controller for receiving and processing a first video component signal to output a first video signal that includes a first location information; a second video component controller for receiving and processing a second video component signal to output a second video signal; and a video signal controller coupled to the first and second component controllers for receiving the first video signal and the second video signal, and outputting the first video signal in a first time interval and the second video signal in a second time interval according to the location information.  
         [0009]     The claimed invention also provides a corresponding video combining method. The video combining method includes outputting a first video signal according to a first video component signal, the first video signal containing a location information; outputting a second video signal according to a second video component signal; and combining the first and second video signals according to the location information to output a video composite signal, wherein the first video signal is a first portion of the video composite signal, the second video signal is a second portion of the video composite signal, and the first and second portions of the video composite signal do not overlap.  
         [0010]     An advantage of the claimed invention is that the disclosed apparatus and method will not increase the bandwidth requirement for accessing memory when performing video composition, and therefore capable of improving data processing efficiency of a digital TV.  
         [0011]     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a diagram illustrating a conventional video combining method.  
         [0013]      FIG. 2  is a diagram illustrating the system architecture of a digital TV according to the present invention.  
         [0014]      FIG. 3  is a diagram of a processed composite picture of the digital TV shown in  FIG. 2 .  
         [0015]      FIG. 4  is a diagram of a video combining circuit according to the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0016]      FIG. 2  is a diagram illustrating the system architecture of a digital TV  100  according to an embodiment of the present invention. As shown in  FIG. 2 , the digital TV  100  comprises an antenna  102 , a tuner  104 , a front-end processing circuit  106 , a bus  108 , a memory  110 , a CPU  112 , a scaler  114 , a graphic drawing engine (GDE)  118 , a subtitle controller  120 , a plurality of video mixers  130  and  140 , an on-screen display (OSD) controller  150 , a hardware cursor controller  160 , and a mask window module  170 . The front-end processing circuit  106 , after performing front-end processing on the digital TV signal received from the antenna  102  and the tuner  104 , stores the processed data in the memory  110  through the bus  108 . The CPU  112  can control other devices connected to the bus  108 . The mask window module  170  performs video processing, such as edge enhancing, color changing, etc., upon the pixels within a selected mask window. The video scaler  114  reads an image data  214  of a main-picture  210  and an image data  224  of a sub-picture  220  from the memory  110  and generates a main-video signal S 1  and a sub-video signal S 2  by performing scaling on the image size of the read image data. After processing by the video mixers  130  and  140 , the video signals S 1  and S 2  and other information are mixed together to generate a mixed signal S_mix and an output signal S_out corresponding to a composite picture  200 , successively. The output signal S_out is further transmitted to a monitor, a video output port, or a video output terminal of the digital TV  100 . Users can view the composite picture  200  on the monitor of the digital TV  100 , or on a monitor of an external display unit coupled to the video output port or the video output terminal of the digital TV  100 .  
         [0017]     Please refer to  FIG. 3 . The picture  244  can be divided into at least two parts, a first video signal (i.e., the sub-picture  224 ) and a second video signal (i.e., the background picture  234 ). The video combining circuit according to the embodiment of the present invention is used for processing the first video signal and the second video signal. Since these two video signals do not overlap, the disclosed video combining circuit will not increase the bandwidth requirement for accessing the memory.  
         [0018]      FIG. 4  is a diagram illustrating a video combining circuit  400  according to an embodiment of the present invention. The video combining circuit  400  includes a first video component controller  410  and a video signal controller  420 . The first video component controller  410  can read an image data  408  (data of an image  222 C,  222 L,  222 B, or  224  shown in  FIG. 3 ) of a sub-picture  220  and output an image data  412  (data of an image  222 C′,  222 L′,  222 B′, or  224 ) of a sub-picture  220 ′ after specific processing, such as video scaling. The video signal controller  420  receives an image data  412  of the sub-picture  220 ′ and a background information  416  corresponding to the background picture  230 ′, combines the image data of the sub-picture  220 ′ and the background information  416  according to a relative location information  418  of the sub-picture  220 ′, and generates an output data  422  corresponding to a combined frame  244 . The video signal controller  420  can be a multiplexer since the image data of the sub-picture  220 ′ and the background information of the background picture  230 ′ in the output data  422  corresponding to the combined frame  244  do not overlap. Please note that the relative location information  418  can be expressed by a start coordinate and an end coordinate, or a start coordinate and a window size. In this embodiment, the first video component controller  410  is a controller for processing a windowed video signal. For example, the first video component controller  410  could be implemented by the video scaler  114 , the subtitle controller  120  or the mask window module  170 . The above-mentioned windowed video signal represents a video signal capable of being displayed by a window. Additionally, the above-mentioned relative location information  418  can be extended in its definition to be information  418  of a reserved region used for determining the display region reserved for the image data of the sub-picture  220 ′. When the size of the reserved region is set to zero, the output data  422  of the video signal controller  420  contains no image data of the sub-picture  220 ′. Please note that although the video signal controller  420  includes an input port for receiving the relative location information  418 , this should not be taken as a limitation of the present invention. The video signal controller  420  can acquire the relative location information  418  in many different ways. For example, the header of the image data  408  of the sub-picture  220 , read by the first video component controller  410  from the memory  110 , contains the relative location information  418 . Therefore, the video signal controller  420  can acquire the relative location information  418  from the first video component controller  410 . In an embodiment of the present invention, the video signal controller  420  includes a location information identifier for acquiring the relative location information from the image data  408 , and a multiplexer coupled to the location information identifier for combining the image data of the sub-picture  220 ′ and the background information  416  according to the relative location information and for outputting the output data  422  corresponding to the combined frame  244 .  
         [0019]     The subtitle controller  120  detailed below is taken as an example and is not meant to be a limitation of the present invention. The subtitle controller  120  is used for processing the image signals SUB_U and SUB_L of the subtitle data in the picture  210  and picture  220 , such as image data of the caption  212 C and  222 C, image data of TV station Logo  212 L and  222 L, and image data of scrolling banner  212 B and  222 B. Then, the subtitle controller  120  outputs the corresponding video signals S 3  and video signal S 4  to the video mixer  130  for video signal mixing. The subtitle controller  120  is further fed with a background information signal BG of a background picture  230 . In this embodiment, the subtitle controller  120  includes a main-picture subtitle processing unit  122  and a sub-picture subtitle processing unit  124 , which respectively output a video signal S 3  corresponding to the image signal SUB_U of the main-picture subtitle information and a video signal S 4  corresponding to the image signal SUB_L of the sub-picture subtitle information and the background information signal BG. Out of these two video signals, the video signal S 3  comprises image data only when a scanned location corresponds to the caption  212 C, TV station Logo  212 L or scrolling banner  212 B of the main-picture  210 . The video signal S 4  comprises image data only when a scanned location corresponds to the slashed area of the background picture  230  of the composite picture  200 , and the TV station Logo  222 L or the scrolling banner  222 B of the sub-picture  220 . The video mixer  130 , after receiving and mixing the signals S 1 , S 2 , S 3  and S 4 , outputs the mixed signal S_mix of the composite picture  200 .  
         [0020]     According to the present embodiment, the CPU  112  is a control unit of the digital TV  100 . In other words, the digital TV  100  is under the control of the CPU  112 . The operation of the subtitle controller  120  is driven according to the control signal generated by the CPU  112 , wherein the CPU  112  determines the control signal according to the properties of the pictures  210 ,  220  and a user command from a user interface (not shown) of the digital TV  100 . For example, the control signal includes an enabling bit for a background picture. The subtitle controller  120  decides whether or not to display the background picture  230  according to the binary value of the enabling bit. If the subtitle controller  120  decides not to display the background picture  230 , the subtitle controller  120  displays the slashed area of the composite picture  200  according to a background parameter in the control signal. According to the present embodiment, the background parameter is a background color parameter.  
         [0021]     Based on the above-mentioned preferred embodiment, the present invention has another embodiment similar to the preferred embodiment. The major difference between these two embodiments is detailed as follows. In this embodiment, a firmware takes the place of the CPU  112  implemented in the above-mentioned preferred embodiment.  
         [0022]     Please note that the same concept of the present invention can not only be applied to a main picture with a sub-picture in a PIP context, but can also be applied to the background with a picture of any size less than the whole screen.  
         [0023]     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.