Abstract:
An apparatus and a method for adjusting the colors of the on-screen display graphics to match the colors of the video with which the OSD graphics are to be combined. In one aspect, a selected one of a plurality of OSD color palettes ( 103, 105 ) is used to produce graphics for a selected one of a plurality of signal sources. As such, the appropriately formatted palette is used to produce graphics for a similarly formatted input signal, i.e., an analog source would be combined with graphics produced from a palette having Y, P I , P Q  formatted signals. Consequently, the color compensation matrices would properly compensate both the graphics and the video from each source. In another aspect, a desired one of a plurality of matrices ( 107, 109 ) operates on the OSD signal source to match the OSD colorimetry with the input signal colorimetry.

Description:
This application claims the benefit under 35 U.S.C. § 365 of International Application PCT/US00//17477, filed Jun. 26, 2000, which was published in accordance with PCT Article 21(2) on Jan. 25, 2001 in English; and which claims benefit of U.S. provisional application Ser. No. 60/144,151 filed Jul. 15, 1999. 

   BACKGROUND OF THE INVENTION 
   1) Field of the Invention 
   The invention relates to an apparatus and a method for processing video signals, and more particularly, to an apparatus and a method for processing on screen display (OSD) signals and video signals from various sources having different colorimetries. 
   2) Description of the Related Art 
   Modern television receivers are designed to receive and process video signals from various sources, for example, analog television signals from a National Television Standards Committee (NTSC) transmission or a video tape, as well as digital video signals transmitted in accordance with the ATSC Digital Television Standard, A/54 (1995). Different signal sources may be encoded according to different colorimetries. “Colorimetry” refers to the combination of color primaries, transfer characteristics, and matrix coefficients associated with generating and processing color representative signals. For example, NTSC signals comply with SMPTE 170M colorimetry and ATSC signals default to comply with ITU-R BT.709 (1990) colorimetry. Additionally, ISO/IEC 13818-2 provides for the broadcaster to specify the input colorimetry to the receiver to allow for other colorimetry combinations. 
   In view of the possible differences in colorimetries between different signals, it is desirable to design television receiver circuitry with colorimetry compensation so that the video display of the signals from the various sources has a uniform colorimetry. Such circuitry compensates the input video signals such that the color of similar objects are substantially similar regardless of the particular colorimetry. For example, a flesh tone from an ATSC source should appear similar to a flesh tone from an NTSC source. 
   Television receivers also produce and display OSD graphics that provide information and enable user interface functions. Typically, the OSDs are generated in response to user input to provide information about a program or the receiver, and to allow the user to control functions such as channel selection, image quality and the like. An OSD system usually comprises a common source of OSD signals, which signals are generated by a processing unit in response to received signals or user input, stored in a memory, and then read out and combined with the received video signals. The signals are combined after colorimetry compensation has been performed on the video signal. The OSD signals are combined with the video signals in a mixer that is controlled by a microprocessor. As the lines of the image are traced on a CRT, or a similar display device, the microprocessor selects either the OSD signal or the video signal for output in response to an output of a counter, thereby selectively inserting the OSD image onto the video program image. 
   BRIEF SUMMARY OF THE INVENTION 
   However, it may be desirable to couple the OSD signal to the video signal prior to the colorimetry compensation. Coupling the signals prior to the colorimetry compensation can reduce memory requirements and reduce processing delays. In this regard, OSD colors may change when colorimetry compensation is applied to a combined signal that includes video program and OSD signals. As such, the OSD graphics colorimetry may change substantially from one video source to another. Therefore, it is also desirable to couple the OSD signal to the video signal prior to the colorimetry compensation in a manner that provides uniform color output of the OSD image regardless of the signal source. 
   The present invention provides a method and apparatus for coupling an OSD signal with a video program signal prior to colorimetry compensation. In particular, the present invention provides a method and apparatus for coupling an OSD signal with a video program signal prior to colorimetry compensation in a manner that the displayed OSD colors are uniform regardless of the signal source. 
   In one aspect, the present invention comprises an OSD unit having an OSD palette, which OSD unit is coupled to a display processor. The output of the display processor is coupled to one of a plurality of matrices to provide colorimetry compensation. The output of the selected matrix is coupled to a display unit, for example a CRT, a flat panel display or the like, for providing an output image. 
   In another aspect, the present invention comprises an OSD unit having a plurality of OSD palettes, each one of the plurality of OSD palettes having OSD data stored in a particular colorimetry format and being associated with a particular one of a plurality of signal sources. A display processor is coupled, via a switch, to a selected one of the OSD palettes in response to the selection of a particular signal source. In this manner, the colorimetry of the OSD signal matches the colorimetry of the video program signal from the signal source. The output of the display processor is coupled to one of a plurality of matrices to provide colorimetry compensation. The output of the selected matrix is coupled to a display unit. 
   In another aspect, the present invention comprises an OSD unit having an OSD palette, and a plurality of OSD matrices, each one of the plurality of OSD matrices adapted to provide a particular colorimetry compensation and being associated with a particular one of a plurality of signal sources. The OSD palette is coupled to a selected one of the OSD matrices in response to the selection of a particular signal source. In this manner, the colorimetry of the OSD signal is adjusted to match the colorimetry of the video program signal from the selected signal source. The output of the selected OSD matrix is coupled to a display processor, wherein the OSD signal is combined with a video program signal. The output of the display processor is then coupled, via a switch, to a selected one of a plurality of matrices to provide colorimetry compensation. The output of the selected matrix is coupled to a display unit. 
   Therefore, in accordance with the present invention, the colorimetry of the OSD signal is matched to the colorimetry of the video signal, and the OSD signal is coupled to the video program signal prior to the matrix operation of the combined signal thereby providing uniform OSD colors at the display regardless of the signal source. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The teachings of the present invention are described with reference to the accompanying drawings, wherein: 
       FIG. 1  illustrates a block diagram of an OSD system wherein the OSD signal is coupled to the video signal prior to the colorimetry compensation; 
       FIG. 2  illustrates a block diagram of an OSD system wherein the OSD signal is coupled to the video program signal in a manner to provide uniform colorimetry regardless of the signal source; and 
       FIG. 3  illustrates a block diagram of a another embodiment of an OSD system wherein the OSD signal is coupled to the video program signal in a manner to provide uniform colorimetry regardless of the signal source. 
   

   To facilitate understanding, common reference numerals have been used to designate elements that are common to the figures. 
   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  depicts a simplified block diagram of a video signal processing apparatus  100  in accordance with the present invention. The construction of the elements of apparatus  100  are known to those skilled in the art and will not be discussed in detail here. 
   Apparatus  100  comprises NTSC chroma decoder  104 , which receives an NTSC signal via input  150 . The NTSC signal is received and demodulated and coupled to chroma decoder  104  in the conventionally known manner. Chroma decoder  104  provides a luminance signal Y and two color difference signals I and Q. The color difference signals I and Q comprise R-Y and B-Y components of different magnitude and represent signals on quadrature axes rotated 33 degrees counterclockwise from the R-Y, B-Y axes. 
   The analog output signal Y, I, and Q are applied to digitizer  106  that provides digital representations of the signals, designated Y, P I  and P Q . The digital representations are coupled to a first terminal of switch  122 . Switch  122 , as well as the various other switches illustrated in the figures that couple the various program or OSD signals to the respective processors or matrices, is controlled by microprocessor  165 , which controls the overall operation of the apparatus. Microprocessor  165  may comprise any one of a plurality of control devices known to those skilled in the art for controlling the various elements of the apparatus. Also, although the present invention describes a single microprocessor, those skilled in the art will realize that microprocessor  165  may comprise various dedicated devices to control specific functions, i.e., a memory controller, a microprocessor interface unit, and the like. 
   Digital video signals are coupled to digital video decoder  108  via input  151 . Digital video decoder provides output signals Y, P R  and P B , which are coupled to a second input of switch  122 . The color difference signals P R  and P B  comprise R-Y and B-Y signals that are modified by scale factors. The output of switch  122  is coupled to display processor  110 , which includes a buffer memory for holding video data and/or combined video and OSD data to be read out. The read out of the video data stored in display processor  110  is controlled by microprocessor  165 . 
   The OSD signals are generated using OSD palette  102 , which includes representations of the OSD signals in Y, P R , and P B  format. OSD palette  102  may be embodied in software form, wherein a particular sequence of bits is associated with a particular color. Based on the color information in OSD palette  102 , microprocessor  165  generates an OSD bitstream and transfers the generated OSD bitstream to display processor  110 . The generated OSD bitstream is combined with the video program signal based on the desired location of the OSD image on the output image. Thus, the memory of display processor  110  includes a bit mapped representation of the output signal, which includes the video program image combined with the OSD image. 
   When it is desired to display the bit mapped image stored in display processor  110 , the stored bitstream corresponding to the image is read out to either one of the matrices  112  or  114  via switch  124 . Microprocessor  165  controls switch  124  to couple the output of display processor  110  to the input of matrix  114  if the input signal is an analog signal, and couple the output of display processor  110  to the input of matrix  112  if the input signal is a digital signal. Matrices  112  and  114  operate in the conventionally known manner to provide RGB output signals in response to the input signals. By selecting the appropriate one of the matrices  112  and  114 , proper colorimetry processing is applied to the selected input signal to provide a display having uniform colorimetry regardless of the selected input signal. 
   Switch  126  couples the output of the selected matrix with the input of display controller  116 . Display controller  116  generally includes circuitry for controlling the output image in response to user input controls, such as brightness and contrast. The output of display controller  116  is then coupled to a display device  120 , which may include a CRT, a flat panel display, or the like. 
   In apparatus  100 , an OSD signal is coupled to display processor  110  prior to matrices  112  and  114 , which convert the input signals to RGB format for display. This is in contrast with prior art devices, wherein the OSD signal is combined with the video program signal in a mixer disposed downstream of display controller  116 . 
   However, apparatus  100  does not match the colorimetry of the OSD signals in response to the selected signal source. This may lead to undesired changes in the colors of the OSD depending on the selected signal source. In other words, the OSD colors will change as the colorimetry compensation is changed. To avoid such changes, it is desirable to modify the OSD colors to complement the compensation provided to the video program signal. 
     FIG. 2  illustrates a second embodiment of the present invention, wherein OSD colors are modified to complement the colorimetry processing applied to the combined video signal. Apparatus  200  includes OSD palettes  103  and  105 , wherein OSD palette  103  provides output signals in the Y, P R , P B  format, and OSD palette  105  provides output signals in the Y, P I , P Q  format. In operation, OSD palette  105  is coupled to display processor  110  when an analog input signal is selected via signal source  150  and OSD palette  103  is coupled to display processor  110  when a digital input signal is selected via signal source  151 . The desired one of palettes and  103  and  105  is selected by switch  140 , which is controlled by microprocessor  165 . 
   When apparatus  200  receives an analog signal via source  150 , switch  122  is coupled to the output of digitizer  106 , switch  140  is coupled to the output of OSD palette  105 , switch  124  is coupled to matrix  114 , and switch  126  is coupled to matrix  114 . In this manner, the input signal and the OSD signal are both in the Y, P I , P Q  format and the colorimetries match. 
   Similarly, when apparatus  200  receives a digital signal via source  151 , switch  122  is coupled to the output of digital video decoder  108 , switch  140  is coupled to the output of OSD palette  103 , switch  124  is coupled to matrix  112 , and switch  126  is coupled to matrix  112 . Here, the input signal and the OSD signal are both in the Y, P R , P B  format and the colorimetries again match. As a result, the colors of the OSD remain uniform regardless of whether the input signal is from signal source  150  or  151 . 
     FIG. 3  illustrates another embodiment of the present invention, wherein OSD colors are modified to complement the colorimetry compensation applied to the video program signal. In apparatus  300 , OSD palette  125  is coupled to display processor  110  via either matrix  107  or matrix  109 . In this case, OSD palette  125  stores the OSD information in RGB format. Matrix  107  operates on the OSD signals from OSD palette  125  to provide Y, P R , P B  formatted signals. Matrix  109  operates on the OSD signals to provide Y, P I , P Q  formatted signals. The outputs of matrices  107  and  109  are coupled to display processor  110  via switch  140 , which is controlled by microprocessor  165 . 
   When source  150  is selected, thereby providing Y, P I , P Q  signals to display processor  110 , switch  122  is coupled to the output of digitizer  106 , switch  142  is coupled to the input of matrix  109 , switch  140  is coupled to the output of matrix  109 , switch  124  is coupled to matrix  114 , and switch  126  is coupled to matrix  114 . In this manner, the input signal and the OSD signal are both in the Y, P I , P Q  format and the colorimetries match. 
   Similarly, when source  151  is selected, thereby providing Y, P R , P B  signals to display processor  110 , switch  122  is coupled to the output of digital video decoder  108 , switch  142  is coupled to matrix  107 , switch  140  is coupled to matrix  107 , switch  124  is coupled to matrix  112 , and switch  126  is coupled to matrix  112 . Here, the video signal and the OSD signal are both in the Y, P R , P B  format and the colorimetries again match. As the colorimetry of the OSD signal match the colorimetry of the input video signal regardless of the signal source, the colors of the OSD on the output image remain uniform regardless of whether the input signal is an analog signal or a digital signal. 
   It will be apparent to those skilled in the art that although the present invention has been described in terms of various exemplary embodiments, modifications and changes may be made to the disclosed embodiment without departing from the essence of the invention. For example, those skilled in the are will realize that various elements for operating on the video or OSD signals, as well as the switches for coupling the signals from one element to another may be implemented in either hardware or software form using conventionally known techniques. Therefore, it is to be understood that the present invention is intended to cover all modifications as would fall within the true scope and spirit of the present invention.