Abstract:
A method and apparatus provide multiple on-screen displays in a signal processing unit capable of processing terrestrial, cable, and satellite broadcast signals. Also, a method and apparatus, for use in a settop box(STB), can provide quality OSD&#39;s(On-Screen Displays) to be displayed together with analog broadcast signals. The OSD&#39;s are processed at a digital signal processing module in the STB. While the analog broadcast signal is being displayed on the screen, the viewer can use an improved GUI processed by the digital signal processing module. The digital signal processing module includes a digital broadcast signal demodulator, a first and a second detectors, an A/D convertor, a microprocessor, an OSD buffer, an OSD generator, a video decoder, a mixing circuit, an NTSC/PAL encoder, switches, a first and a second AND gate, an inverter, and an OR gate.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an on-screen display method and apparatus therefor; and, more particularly, to a method and apparatus for providing multiple on-screen displays in a signal processing unit capable of processing terrestrial, cable and satellite broadcast signals. 
     DESCRIPTION OF THE PRIOR ART 
     Conventional television receivers (TV&#39;s) are equipped with a graphic user interface(GUI) in the form of an on-screen display(OSD) for displaying OSD data on a screen of a picture reproduction device either in place of a picture represented by video signals or together with the picture. The OSD data can take the form of alphanumeric symbols, pictorial graphics, or both; and can be channel numbers, channel information, teletexts, operating instructions, or the like. However, the conventional TV can process only analog signals such as terrestrial and cable broadcast signals which carry a limited amount of OSD data insertable in a vertical blanking interval thereof, thereby providing a simple OSD of, e.g., a limited color resolution. 
     Recently, a new broadcasting system, utilizing a communication satellite and digitized broadcast signals, has been rapidly gaining popularity worldwide. The satellite broadcasting system, which can provide broadcast signals to a wide area, employs superhigh RF(radio frequency) signals ranging, e.g., from 11.7 GHz to 12.2 GHz, for carrying the digitized broadcast signals. To receive the superhigh RF signals, a satellite broadcast signal receiver is normally equipped with a low noise blockdown converter for converting the superhigh RF signals into RF signals of, e.g., 950 to 2050 MHz. Thereafter, a tuner employed in the satellite broadcast signal receiver is tuned to a channel selected by a user using the converted RF signals. 
     Owing to the superhigh carrier frequencies, a channel bandwidth of the satellite broadcast signals can be wider than that for the terrestrial and cable broadcast signals, enabling a greater amount of OSD data to be carried in the satellite broadcast signals and resulting in an advanced OSD capability of the satellite broadcasting system. 
     In order to process all of such broadcast signals as terrestrial, cable and satellite broadcast signals at a single unit, a composite receiver, i.e., the so-called settop box(STB), has been developed. Referring to FIG. 1, there is shown a signal processing unit  50  for use in a prior art STB, comprising a tuner  100 , an analog signal processing module  10 , a digital signal processing module  20 , a switch  117 , a microprocessor  105 , a RAM  106 , and a key matrix  107 . The analog signal processing module  10  includes an analog broadcast signal demodulator  101 , a first detector  103 , a composite video signal processing circuit  108 , an OSD generator  109 , and a mixing circuit  110 , whereas the digital signal processing module  20  includes a digital broadcast signal demodulator  102 , a second detector  104 , an OSD buffer  111 , an OSD generator  112 , an MPEG block  115  which has therein a video decoder  113  and a mixing circuit  114 , and an NTSC/PAL encoder  116 . 
     The key matrix  107  provides the microprocessor  105  with input signals via a line L 18  for executing certain functions by key inputs of a viewer. The key matrix  107  has, e.g., a mode key for generating a mode selection signal for selecting either an analog mode corresponding to the terrestrial and cable broadcast signals or a digital mode corresponding to the satellite broadcast signal; a channel up/down key and numerical keys for generating a channel selection signal for selecting a desired broadcast channel; and an OSD key for generating an OSD request signal for requesting the OSD data, e.g., carried by the selected channel to be displayed on a screen(not shown). Typically, a remote controller(not shown) can be used instead of the key matrix  107 . 
     In response to the mode and the channel selection signals from the key matrix  107 , the microprocessor  105  generates a tuning control signal representing a mode and a channel to be tuned to the tuner  100  via a line L 16  and also provides the switch  117  with a control signal CS 1  for selecting a video signal on a terminal “0” or “1” thereof. 
     The tuner  100  tunes a selected channel of the terrestrial, the cable, or the satellite broadcast signals in response to the tuning control signal fed from the microprocessor  105  and outputs the tuned channel signal to the analog broadcast signal demodulator  101  or the digital broadcast signal demodulator  102  depending on whether the selected channel corresponds to either the terrestrial and the cable broadcast signals or the satellite broadcast signal. 
     When a terrestrial or a cable channel is selected by a viewer through the key matrix  107 , the selected channel is tuned by the tuner  100  and the switch  117  is connected to a terminal “0” in response to the control signal CS 1  issued by the microprocessor  105 . The tuned channel signal is fed to the analog broadcast signal demodulator  101 . The analog broadcast signal demodulator  101  demodulates the tuned channel signal to generate a baseband composite video signal to the first detector  103  and the composite video signal processing circuit  108  via a line L 11 . 
     The composite video signal includes a synchronization signal, an analog video signal and OSD data carried via a vertical blanking interval thereof. Then, the composite video signal processing circuit  108  processes the composite video signal by performing, e.g., a level amplification, noise elimination, gain control, etc, to thereby provide a video image signal representing, e.g., a video image  303  shown in FIG. 3A to be displayed on the screen. The first detector  103  extracts the OSD data included in the baseband composite video signal and provides the extracted OSD data signal to the OSD generator  109  via a line L 19 . 
     When the viewer instructs to generate an OSD on the screen in order to control the STB or to view information, e.g, teletext, channel information, or the like, carried by the selected channel, an OSD generation signal fed from the microprocessor  105  via a line L 12  is inputted to the OSD generator  109 , wherein the OSD generation signal is generated in response to the OSD request signal or the channel selection signal fed thereto from the key matrix  107  via the line L 18 . Responding to the OSD generation signal, the OSD generator  109  creates, e.g., an OSD  301  shown in FIG. 3B corresponding to the OSD data signal fed thereto from the first detector  103 . The OSD data signal includes OSD data to be displayed on the screen  302  and position information thereof within the screen  302 ; and can be, e.g., a newly selected channel number generated on a line L 13  from the microprocessor  105  in case the OSD generation signal is generated by the channel selection signal. Thereafter, the OSD generator  109  transmits the OSD signal representing the OSD  301  to the mixing circuit  110 , wherein the OSD signal includes a video signal corresponding to the OSD  301  and position information thereof within the screen  302 . 
     The mixing circuit  110  mixes the video image signal provided from the composite video signal processing circuit  108  with the OSD signal generated by the OSD generator  109  with reference to the synchronization signal included in the video image signal, to thereby produce a composite video image signal representing a composite video image  304  shown in FIG. 3C, wherein the composite video image  304  includes the OSD  301  and a portion of the video image  303  non-overlapping therewith. The composite video image signal is transmitted, as a video output signal of the signal processing unit  50 , through the terminal “0” of the switch  117  to a display unit(not shown) for the display thereof. 
     When the viewer selects a satellite channel, the selected satellite channel is tuned by the tuner  100  and the switch  117  is connected to a terminal “1” in response to the control signal CS 1  issued by the microprocessor  105 . The selected satellite channel signal is demodulated at the digital broadcast signal demodulator  102  to thereby generate a satellite video signal to be fed to the video decoder  113 , wherein the satellite video signal is an encoded digital signal, compressed based on, e.g., the so-called MPEG(Moving Picture Expert Group)-2 scheme and includes an encoded digital video signal and digitized OSD data. The video decoder  113  decodes the encoded digital video signal to thereby provide the mixing circuit  114  with a reconstructed digital video signal corresponding to, e.g., a reconstructed video image  405  shown in FIG.  4 A. Meantime, the second detector  104  extracts the digitized OSD data from the satellite video signal and provides same on a line L 15  to the microprocessor  105  which in turn stores the extracted OSD data in the RAM  106  via a line L 17 . 
     When the viewer requests to generate an OSD on the screen by generating the OSD request signal via the key matrix  107  in order to control STB or to view information, e.g., teletext, channel information, or the like, carried by the selected satellite channel, the microprocessor  105  retrieves the OSD data signal from the RAM  106  via the line L 17  and provides the retrieved OSD data signal to the OSD generator  112  via the line L 13 . Also, as in the case of the analog signal processing module  10 , the OSD data signal can be, e.g., a channel number or volume level generated by the microprocessor  105 , if a channel or volume level is changed by the viewer. The OSD data signal includes OSD data to be displayed and position information thereof within the screen. Responding to the OSD data signal, the OSD generator  112  creates, e.g., a combined OSD  401  shown in FIG. 4B, wherein the combined OSD  401  includes one or more actual OSD&#39;s  402  and  403  and a surplus OSD  404 . The created OSD signal representative of the corresponding combined OSD  401  and position information thereof within the screen are temporarily stored at the OSD buffer  111 , and then transmitted to the mixing circuit  114 , wherein each pixel included in the OSD signal is represented by luminance (Y) data and chrominance (C r , C b ) data as well known in the art. For instance, each pixel of the OSD signal includes Y of 6-bits, C r  of 4-bits and C b  of 4-bits. 
     Among the OSD&#39;s included in the combined OSD  401 , only the actual OSD&#39;s  402  and  403  carry OSD data to be displayed on the screen, while the surplus OSD  404  has dummy data not to be displayed on the screen. A combined OSD is of a rectangular shape and is constructed such that the combined OSD includes therein all the actual OSD&#39;s to be displayed on the screen simultaneously and a surplus OSD corresponding to the remaining portion of the combined OSD not occupied by the actual OSD&#39;s. Such an OSD structure is advantageous in storing and retrieving OSD data in and from a storage, e.g., OSD buffer  111 , especially when there exists a plurality of actual OSD&#39;s to be displayed on the screen at the same time and those OSD&#39;s overlap horizontally, or in other words, share one or more horizontal scanning lines, as shown in FIG.  4 B. 
     Next, the mixing circuit  114  generates a digital video image signal by mixing the reconstructed video signal from the video decoder  113  and the OSD signal from the OSD buffer  111 . For example, as shown in FIG. 4C, the digital video image signal is constructed by the actual OSD&#39;s  402  and  403  replacing a portion of the reconstructed video signal overlapping therewith and the remaining portion of the reconstructed video signal non-overlapping with the actual OSD&#39;s  402  and  403 . 
     In the NTSC/PAL encoder  116 , the digital video image signal is converted to a standard NTSC/PAL analog signal based on, e.g., a 27 MHz synchronization(SYNC) signal applied thereto from an internal oscillator(not shown) and outputted as the video output signal via the terminal “1” of the switch  117 . 
     As described above, analog and digital OSD&#39;s are processed at their respective signal processing modules in a conventional STB, which may deteriorate the quality of the analog OSD&#39;s; and further there exist redundancies of the OSD generators and the mixing circuits in the signal processing modules of the STB. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a method and apparatus, for use in a settop box(STB), capable of providing quality OSD&#39;s(On-Screen Displays) to be displayed together with analog broadcast signals, wherein the OSD&#39;s are processed at a digital signal processing module in the STB. 
     In accordance with one aspect of the invention, there is provided a method, for use in a video equipment, for providing a mixed video image signal, wherein the video equipment has a tuner for selecting an analog or a digital broadcast signal, comprising the steps of: 
     a) generating an analog video signal from the selected analog broadcast signal; 
     b) providing a digital on-screen display(OSD) signal including a combined OSD signal representing a combined OSD, wherein the combined OSD signal has therein an actual OSD signal representing one or more OSD&#39;s to be displayed on a screen; 
     c) producing a digital padding signal; 
     d) replacing a portion of the digital padding signal with the actual OSD signal to thereby provide a mixed digital OSD signal; 
     e) converting the mixed digital OSD signal into an analog OSD signal; and 
     f) substituting a part of the analog video signal with a fraction of the analog OSD signal corresponding to the actual OSD signal to thereby provide the mixed video image signal. 
     In accordance with another aspect of the invention, there is provided an apparatus for providing a mixed video image signal, comprising: a tuner for selecting an analog or a digital broadcast signal; a digital padding signal generator; a composite video signal processing circuit for generating an analog video signal from the selected analog broadcast signal; a video decoder for providing a reconstructed digital video signal from the selected digital broadcast signal; an MPEG block for producing, as a digital image signal, the digital padding signal or the reconstructed digital video signal if the analog or the digital broadcast signal is selected; an OSD generator for obtaining a digital OSD signal including a combined OSD signal, wherein the combined OSD signal has therein an actual OSD signal representing one or more OSD&#39;s to be displayed on a screen; a mixing circuit for replacing a portion of the digital image signal with the actual OSD signal to thereby provide a mixed digital image signal; an NTSC/PAL encoder for converting the mixed digital image signal into a mixed analog image signal; a transparency indicator for generating a first control signal if the digital broadcast signal is selected, and if the analog broadcast signal is selected, determining whether each pixel included in the mixed digital image signal belongs to the actual OSD signal to thereby generate the first control signal if each pixel belongs to the actual OSD signal and a second control signal if otherwise; and a switch for selecting, on a pixel-by-pixel basis, the mixed analog image signal and the analog video signal in response to the first and the second control signals, respectively, to thereby provide the mixed video image signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which: 
     FIG. 1 shows a conventional signal processing unit for use in a STB; 
     FIG. 2 represents a signal processing unit for use in a STB in accordance with the present invention; 
     FIGS. 3A to  3 C depict typical analog OSD&#39;s; and 
     FIGS. 4A to  4 C illustrate exemplary digital OSD&#39;s. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 2, there is shown a signal processing unit  250  for use in a STB in accordance with the present invention. For the sake of simplicity, like elements are represented by like reference numerals in FIGS. 1 and 2; and the tuner  100 , the analog broadcast signal demodulator  101 , the digital broadcast signal demodulator  102 , the second detector  104 , and the key matrix  107  shown in FIG. 1, are omitted in FIG. 2 since those elements function in identical manners as described in FIG.  1 . 
     The signal processing unit  250  includes those omitted elements  100 ,  101 ,  102 ,  104  and  107  and further includes a composite video signal processing circuit  108 , a synchronization signal separator  201 , a switch  117 , a digital signal processing module  30 , an A/D converter  230 , and a microprocessor  105 . 
     The digital signal processing module  30  includes an OSD buffer  111 , an OSD generator  112 , a video decoder  113 , a mixing circuit  114 , and an NTSC/PAL encoder  116  as in FIG.  1  and further includes switches  202  and  203 , a first and a second AND gate  204  and  206 , an inverter  205 , and an OR gate  207 . The first and second AND gates  204  and  206 , the inverter  205 , and the OR gate  207  form a transparency indicator  40  which will be described later in more detail and the video decoder  113 , the switch  202  and the mixing circuit  114  constitute an MPEG block  115 . Comparing with the prior art signal processing unit  50  shown in FIG. 1, only one OSD generator  112  and one mixing circuit  114  exist in the signal processing unit  250  of the present invention, and the first detector  103  is coupled to the A/D convertor  230  via the line L 19  instead of the OSD generator  109 . 
     First, when a terrestrial or a cable channel is selected by a viewer, the switches  202  and  203  are connected terminals “0” thereof in response to a control signal CS 1  issued by the microprocessor  105  and also the switch  117  is connected terminal “0” thereof in response to a control signal CS 3  issued by the transparency indicator  40 , and a composite video signal is inputted to the composite video signal processing circuit  108  via a line L 11  as in FIG.  1 . In the preferred embodiment of the invention, the control signal CS 1  is of a first logic level, e.g., 0, when an analog channel, i.e., a terrestrial or a cable channel, is selected. An output control signal CS 3  of the OR gate  207  is set as “0” if no OSD is generated while an analog channel is selected, as will be described in detail hereinafter. 
     As described in FIG. 1, the composite video signal includes a synchronization signal, an analog video signal, and analog OSD data carried via the selected channel. The composite video signal processing circuit  108  operates the same way as described with respect to FIG.  1  and generates a video image signal corresponding to the video image, e.g.,  405  shown FIG.  4 A. Then, the generated video image signal is transmitted to the terminal “0” of the switch  117  and the synchronization signal separator  201 , which serves to generate an analog synchronization signal from the video image signal. Meanwhile, the analog OSD data extracted by the first detector  103  is provided to the A/D convertor  230  via a line L 19  and converted to digital OSD data. The converted digital OSD data is then stored by the microprocessor  105  in the RAM  106  via a line L 17 . 
     When the viewer requests to generate an OSD on a screen(not shown) in order to control the STB or to view information, e.g., teletext or viewdata, or the like, carried by the selected analog channel, an OSD data is retrieved by the microprocessor  105  from the RAM  106  via the line L 17  and provided to the OSD generator  112  through the line L 13 . Responding to the OSD data signal, the OSD generator  112  generates, e.g., the OSD  401  shown in FIG.  4 B. The OSD data signal includes OSD data to be displayed on the screen and position information thereof within the screen; and can be either generated from the microprocessor  105  or provided via the selected analog channel. The OSD generated from the OSD generator  112  can be either a normal or a combined OSD, e.g., shown in FIGS. 3B and 4B. Thereafter, the OSD generator  112  provides an OSD signal to the OSD buffer  111 . The OSD signal includes data for all the pixels within the screen and position information of the OSD, wherein each pixel in the generated OSD signal is represented by N-bits of binary numbers, e.g., Y of 6-bits, C r  of 4-bits, and C b  of 4-bits as described above. In the preferred embodiment of the invention, N-bits for each of the pixels corresponding to a surplus OSD, e.g.,  404  shown in FIG. 4B, are all “1” bits and each pixel included in the remaining part of the OSD, i.e., the actual OSD&#39;s  402  and  403  carrying OSD data to be displayed, is expressed by N-bits having one or more “0” bits. Further, each pixel residing outside the OSD  301  or  401  is also expressed by N-bits of binary numbers having therein one or more “0” bits. The position information included in the OSD signal represents position data for the OSD&#39;s  402 - 404  in case the OSD generated by the OSD generator  112  corresponds to the combined OSD  401  and position data for, e.g., the OSD  301  if the OSD generated by the OSD generator  112  corresponds to the normal OSD. 
     The OSD buffer  111  stores therein the generated OSD signal and transmits same to the mixing circuit  114  and the pixel data included in the OSD signal to the AND gate  204 . 
     The mixing circuit  114  receives the generated OSD signal and a digital padding signal fed from the switch  202 , wherein the black level signal is generated by a padding signal generator(not shown). Thereafter, the mixing circuit  114  mixes the pixel data from the OSD buffer  111  with the digital padding signal based on the position information included in the OSD signal. The mixing circuit  114  functions in a similar fashion as in FIG. 1 to thereby generate a mixed OSD signal representing a video image, similar to the one, e.g., shown in FIG. 4C excepting that all the pixels residing outside the actual OSD&#39;s  402  and  403  are represented by the digital padding signal of, e.g., a black level having all “0” bits in lieu of decoded pixel values from the video decoder  113 . The mixing circuit  114  transmits the mixed OSD signal to the NTSC/PAL encoder  116  via a line L 25 . Also, the mixing circuit  114  transmits an OSD indication signal to the second AND gate  206  through a line L 26 . The OSD indication signal represents whether a pixel is included in the combined OSD, wherein the OSD indication signal has a first logic level, e.g., 0, if a pixel is outside the combined OSD and a second logic level, e.g., 1, if otherwise. 
     In response to the analog synchronization signal, the NTSC/PAL encoder  116  converts the mixed OSD signal into the standard NTSC/PAL analog signal based on the synchronization signal from the switch  203 , in a similar manner as in FIG.  1  and then transmits the converted OSD signal to a terminal “1” of the switch  117 . 
     Meanwhile, it is determined at the transparency indicator  40  whether a pixel included in the converted OSD signal belongs to an actual OSD or not. The transparency indicator  40  issues the control signal CS 3  of the second logic level, i.e., 1, if a pixel is determined to be one of the pixels constituting an actual OSD, and the control signal CS 3  of the first logic level, i.e., 0, if otherwise. Specifically, each pixel positioning outside the surplus OSD has at least one “0” bit and each pixel corresponding to the surplus OSD is represented by N-bits of “1” as described above. As a consequence, the output signal processed by the first AND gate  204  and the inverter  205  is the logic “0” for each pixel belonging to the surplus OSD and the logic “1” for each pixel residing outside the surplus OSD. 
     The second AND gate  206  receives the inverter output and the OSD indication signal from the mixing circuit  108 . As described above, the OSD indication signal is set to the logic “0” for the pixels outside the combined OSD and the logic “1” for the pixels belonging to the combined OSD. The resultant output signal from the second AND gate  206  to the OR gate  207  is the logic “1” for each pixel belong to an actual OSD and the logic “0” for each pixel not included in an actual OSD. The OR gate  207  also receives the control signal CS 1 , which is set to the logic “0” when an analog channel is selected. As a result, the control signal CS 3  outputted from the transparency indicator  40  is determined as the logic “1” for each pixel residing inside an actual OSD and the logic “0” for each pixel not belonging to an actual OSD. 
     At the switch  117 , the video image signal from the composite video signal processing circuit  108  and the converted OSD signal from the NTSC/PAL encoder  116  are selectively chosen on a pixel basis depending on the control signal CS 3 . That is, the switch  117  outputs the video image signal on the terminal “0” thereof if the control signal CS 3  is the logic “0” and the converted OSD signal on the terminal “1” if otherwise, resulting in a video output, e.g., shown in FIG.  4 C. The video output signal is transmitted to a display unit (not shown) and processed therein for the display thereof. It should be apparent to the one skilled in the art that in case an OSD is of the form shown in FIG. 3B having no surplus OSD therein, the OSD can be regarded as a combined OSD having actual OSD&#39;s only and can be processed in a similar manner as described above. 
     As can be seen from the foregoing descriptions, in accordance with the present invention, while the analog broadcast signal is being displayed on the screen, the viewer can use an improved GUI processed by the digital signal processing module  30  shown in FIG.  2 . 
     When the viewer selects a satellite channel, a satellite video signal transmitted via the selected satellite channel and demodulated at the digital broadcast signal demodulator  102 (not shown), is applied to the video decoder  113  and the control signal CS 1  is set to “1” as in FIG. 1, causing an output signal from the video decoder  113  and the 27 MHz SYNC to be selected by the switches  202  and  203 . Consequently, the OSD buffer  111 , the OSD generator  112 , the MPEG block  115  and the NTSC/PAL encoder  116  function in identical manners as in the digital signal processing module  20  shown in FIG.  1 . Further, the control signal CS 3  is set to “1” regardless of the output from the AND gate  206  because the control signal CS 1  inputted to the OR gate  207  is set to “1”, enabling the output signal from the NTSC/PAL encoder  116  to be selected as the video output at the switch  117 . 
     While the present invention has been shown and described with reference to those skilled in the art that many changes and modifications may be without departing from the spirit and scope of the invention as defined in the appended claims.