Abstract:
The optical disc reproducing apparatus includes an optical pick-up, a video decoder and a graphics circuit. The optical pick-up reproduces a signal from an optical disc wherein the reproduced signal includes at least video data and sub-picture data. The video decoder decodes the video data in the reproduced signal. The graphics circuit stores a plurality of text portions, and receives the reproduced signal and character control instructions. The graphics circuit generates first character data representing at least one of the plurality of text portions based on the character control instructions, and generates second character data based on the sub-picture data in the reproduced signal. A digital video signal is then generated by mixing the first and second character data and the decoded video data.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical disc reproducing apparatus and method, and more particularly to an optical disc reproducing apparatus for displaying text such as caption data, program menu data, reproduction information, etc., on a display screen using a single character generating device. 
     2. Description of Related Art 
     A greater demand exits in the industry for techniques which allow large amounts of information to be densely recorded upon recording media. Development has focused on recording media such as compact discs, digital video discs (DVD), etc., to meet this need. 
     A DVD reproducing apparatus has been designed to reproduce data recorded on a DVD (diameter: 12 cm, thickness: 1.2 mm) for about 135 minutes, and to provide better image and sound quality than a laser disc. Accordingly, a DVD device is one of the noticeable multi-media devices in audio/video and computer applications. DVDs are widely used in image processing applications due to their large storage capacity. One of the DVD system formats has system specifications as follows: 
     1. Maximum 9 camera angles reproducible; 
     2. Maximum 8 channels for audio and 32 languages as a caption; 
     3. Storage of a plurality of user selectable programs, selectable via a menu screen; and 
     4. Provision of parental lock function which can prevent children from watching adult programs. 
     According to the above system specification, the structure of the data stream used in DVDs is shown in FIG.  1 . This data stream includes a video stream, an audio stream, and a sub-picture stream. Although not shown, the data stream also includes control data which is used during reproduction to control the reproducing operation. The video stream includes video or image data such as for a moving image, the audio stream includes audio data such as voice and/or sound data, and the sub-picture stream includes caption data to be displayed on a display screen during reproduction. As also shown in FIG. 1, the audio data includes multiple channels. 
     A conventional optical disc reproducing apparatus using the above-described data stream structure will be described with reference to FIG.  2 . As shown in FIG. 2, the optical disc reproducing apparatus for reproducing data from an optical disc  1  includes a motor  11  for rotating the optical disc  1 ; an optical pick-up  3  for reading the data recorded on the optical disc  1 ; a servo circuit  13  for generating drive signals to control the operation of the motor  11  and the optical pick-up  3 ; and microprocessor  15  for controlling the operation of the servo circuit  13 , a signal processing circuit  5 , an error correction circuit  7 , a navigator  17 , and an on screen display (OSD) unit  31  based on key input from a user. 
     In accordance with the instructions received from the microprocessor  15 , the signal processing circuit  5  amplifies the reproduced signal output from the optical pick-up  3 , and performs phase compensation thereon. The microprocessor  15  also obtains management and sub-management data from the reproduced signal processed by the signal processing circuit  5 . The management data includes table of contents (TOC) data such as recorded in the lead-in area of the optical disk  1 . The sub-management data includes characteristic information for the data recorded on the optical disk such as recorded in the headers of logically grouped data. With respect to a DVD, the characteristic information could indicate which camera angle from the plurality of camera angles the data in the following logical group represents, or could indicate that the data in the following logical group is English language caption data. 
     The error correction circuit  7  corrects, under the control of the microprocessor  15 , errors in the bit stream of the reproduced signal output by the signal processing circuit  5 . A variable transfer rate (VBR) buffer  9  temporarily stores the error corrected reproduced signal. The navigator  17  controls the transfer of data from the VBR buffer  9  to a data decoding section  30  in part based on control signals from the microprocessor  15  and in part based on the control data extracted from the bit stream of the reproduction signal output from the VBR buffer  9 . 
     The data decoding section  30  includes a video decoding part  21 , a graphics circuit  24 , and an audio decoding part  27  operating under the control of the navigator  17 . The graphics circuit  24  receives the output of the VBR buffer  9  via the video decoding part  21 , and the audio decoding part  27  receives the output of the VBR buffer  9  via the graphics circuit  24  and the video decoding part  21 . 
     A mixer  43  mixes the output of the video decoding part  21  and the graphics circuit  24  to produce a digital video signal. A first digital/analog converter  23  digital-to-analog converts the digital video signal, while a second digital/analog converter  29  digital-to-analog converts the output of the audio decoding part  27 . 
     The OSD unit  31 , under the control of the microprocessor  15 , adds character data representing reproduction information to the analog video signal output by the first digital/analog converter  23  to produce an output video signal. 
     Next, the operation of the conventional optical disc reproducing apparatus will be described. After mounting the optical disc  1  on a turntable (not shown), the user selects a specific system function and options associated therewith using a plurality of input keys (not shown). For instance, after selecting a basic reproduction operation, the user can select the reproduction characteristics. The reproduction characteristics include, for example, the camera angle to be reproduced, that a caption should be displayed, and the language of the caption. If the user does not elect to select the reproduction characteristics, then the basic reproduction operation will proceed according to predetermined default reproduction characteristics. 
     When the user selects a reproduction operation, the microprocessor  15  controls the servo circuit  13  to drive the motor  11  and the optical pick-up  3 . According to the drive signals from the servo circuit  13 , the optical pick-up  3  reproduces data recorded on the optical disc  1 . The reproduced data is converted into an electrical signal and output to the signal processing circuit  5 . The signal processing circuit  5  performs a predetermined signal processing operation such as noise amplification, phase compensation, etc., on the electrical signal (i.e., the reproduced signal) in accordance with the instructions received from the microprocessor  15 , and the microprocessor  15  extracts the management and sub-management data from the processed reproduced signal. 
     The processed reproduced signal is output to the error correction circuit  7 . The error correction circuit  7  corrects errors generated in the reproduced signal in a predetermined manner as instructed by the microprocessor  15 . The error corrected reproduced signal is then output to and temporarily stored by the VBR buffer  9 . Based on the reproduction characteristics and the management and sub-management data, the navigator  17  controls the transfer of data from the VBR buffer  9  to the data decoding section  30 . Because frames of video data are compressed to different sizes according to the characteristics of the images in the frame, the quantity of data input by the VBR buffer  9  varies. In order to store variably transferred data, yet output a continuous and seamless stream of data, the VBR buffer  9 , under the control of the navigator  17 , is used. 
     As discussed above with respect to FIG. 1, the data output from the VBR buffer  9  includes system related control data, video data, sub-picture data, (e.g, caption and menu selection data), and audio data. The navigator  17  extracts the control data, and controls the operation of the data decoding section based in part thereon. 
     The data output from the VBR buffer  9  is received by the video decoding part  21  of the data decoding section  30 . The video decoding part  21  extracts, decompresses, and decodes the video data in the bit stream output from the VBR buffer  9  under the control of the navigator  17 . The video decoding part  21  then outputs the processed video data to the mixer  43 . The video decoding part  21  also passes the bit stream from the VBR buffer  9  to the graphics circuit  24 . 
     The graphics circuit  24  extracts and decodes the sub-picture data in the bit stream from the VBR buffer  9 , and outputs the decoded sub-picture data to the mixer  43 . FIG. 3 is a detailed block diagram of the conventional graphics circuit  24 . As shown in FIG. 3, the graphics circuit  24  includes a data extracting part  33  for extracting the sub-picture data in the bit stream output from the VBR buffer  9 . A timing circuit  35  also receives the bit stream output by the VBR buffer  9 , and detects a sync signal from the video data included in the bit stream. Based on the detected sync signal, the timing circuit  25  generates a clock signal. 
     The graphics circuit  24  further includes a decoder  37  and a first character memory  39 . The decoder  37  receives the sub-picture data output by the data extracting part  33 , and decodes the sub-picture data. The decoded sub-picture data is then stored in the first character memory  39 . In accordance with the clock signal output by the timing circuit  35 , the first character memory  39  outputs the decoded sub-picture data for display at a predetermined position on the display screen. The decoded sub-picture data output by the first character memory  39  is amplified by a level controller  41 , and output to the mixer  43 . The mixer  43  mixes the processed video data output by the video decoding part  21  with the amplified decoded sub-picture data to produce a digital video signal. 
     As shown in FIG. 2, the first digital/analog converter  23  converts the digital video signal output by the mixer  43  into an analog video signal. The OSD unit  31  receives the analog video signal, and mixes a character signal with the analog video signal under the control of the microprocessor  15 . 
     FIG. 4 is a detailed block diagram of the conventional OSD unit  31 . As shown in FIG. 4, a timing circuit  45  receives the analog video signal, detects a sync signal in the video signal portion of the analog video signal, and generates a clock signal according to the detected sync signal and instructions from a controller  47 . The controller  47  receives clock data and character control instructions from the microprocessor  15 . The clock data indicates when the clock signal should be output from the timing circuit  45 . In accordance with the clock data, the controller  47  outputs instructions to the timing circuit  45 . The controller  47  also converts the character control instructions into memory addresses, and outputs the memory addresses to a second character memory  49 . The second character memory  49  stores the text of, for example, reproduction information such as time information and operation information (e.g., play, rewind, fast forward, camera angle, etc.). The character control instructions specify the reproduction information the second character memory  49  is to output. 
     Based on the clock signal, the second character memory  49  outputs the text or character data addressed by the memory addresses from the controller  47  to a level controller  51 . Accordingly, the clock signal (i.e., the clock data from the microprocessor  15 ) specifies the position on the display where this character data will appear. The level controller  51  amplifies the character data output from the second character memory  49 , and converts the amplified data into an analog character signal. This analog character signal is then mixed by a mixer  53  with the analog video signal output from the mixer  43  to produce an output video signal. 
     As shown in FIG. 3, the bit stream output by the VBR buffer  9  is transferred from the video decoding part  21  and the graphics circuit  24  to the audio decoding part  27 . Based on instructions from the navigator  17 , the audio decoding part  27  extracts and decodes the audio data in this bit stream. The second analog converter  29  converts the audio data into an output audio signal. 
     As discussed above, both the graphics circuit  24  and the OSD unit  31  output data, which is mixed with video data, to display text on a display screen. As such, elements forming the graphics circuit  24  are duplicated in the OSD unit  31 . As a result, the conventional optical disc reproducing apparatus is large, complex, and costly. 
     Furthermore, the video data in the bit stream output by the VBR buffer  9  undergoes several processes (e.g., extraction, decoding, conversion, mixing). Each signal processing procedure degrades the signal-to-noise ratio of the resulting output video signal such that image quality is deteriorated and the display of characters can become distorted. 
     SUMMARY OF THE INVENTION 
     One object of the present invention is to provide an optical disc reproducing apparatus and method which overcome the problems and disadvantages discussed above. 
     Another object of the present invention is to provide an optical disc reproducing apparatus which is smaller, less complex, and less costly than conventional optical reproducing apparatuses. 
     A further object of the present invention is to provide an optical disc reproducing apparatus which uses a single character generating device to display sub-picture data and reproduction information. 
     Another object of the present invention is to provide an optical disc reproducing apparatus which digitally processes sub-picture data and reproduction information to be displayed on a display screen. 
     These and other objectives are achieved by providing an optical disc reproducing apparatus, comprising: an optical pick-up for reproducing a digital signal from an optical disc, said reproduced digital signal including at least video data and sub-picture data; and processing means for storing a plurality of text portions, for receiving character control instructions, for receiving said reproduced digital signal, for generating first character data representing at least one of said plurality of text portions based on said character control instructions, for generating second character data based on said sub-picture data in said reproduced digital signal, and for generating a digital video signal based on said first and second character data and said video data in said reproduced digital signal. 
     These and other objectives are further achieved by providing an optical disc reproducing apparatus, comprising: an optical pick-up for reproducing a signal from an optical disc, said reproduced signal including at least video data and sub-picture data; a video decoder decoding said video data in said reproduced signal; and a graphics circuit storing a plurality of text portions, receiving character control instructions, receiving said reproduced signal, generating first character data representing at least one of said plurality of text portions based on said character control instructions, and generating second character data based on said sub-picture data in said reproduced signal. 
     These and other objectives are also achieved by providing an optical disc reproducing method, comprising: reproducing a digital signal from an optical disc, said reproduced digital signal including at least video data and sub-picture data; storing a plurality of text portions; receiving character control instructions; generating first and second character data based on said character control instructions and said sub-picture data in said reproduced digital video signal, said first character data representing at least one of said plurality of text portions; and generating a digital video signal based on said first and second character data and said video data. 
     These and other objectives are additionally achieved by providing an optical disc reproducing apparatus, comprising: an optical pick-up for reproducing a signal from an optical disc, said reproduced signal including at least video data and sub-picture data; and processing means for storing a plurality of text portions in a single memory, for receiving character control instructions, for receiving said reproduced digital signal, for generating, using said single memory, first character data representing at least one of said plurality of text portions based on said character control instructions, and for generating, using said single memory, second character data based on said sub-picture data in said reproduced signal. 
     Other objects, features, and characteristics of the present invention; methods, operation, and functions of the related elements of the structure; combination of parts; and economies of manufacture will become apparent from the following detailed description of the preferred embodiments and accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
     FIG. 1 shows the structure of a data stream in a DVD; 
     FIG. 2 is a schematic block diagram of a conventional optical disc reproducing apparatus; 
     FIG. 3 is a detailed block diagram of the graphics circuit shown in FIG. 2; 
     FIG. 4 is a detailed block diagram of the OSD unit shown in FIG. 2; 
     FIG. 5 is a schematic block diagram of an optical disc reproducing apparatus according to the present invention; 
     FIG. 6 is a detailed block diagram of the digital OSD unit shown in FIG. 5; and 
     FIG. 7 is a detailed block diagram of another embodiment of the digital OSD unit shown in FIG.  5   
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIG. 5, the optical disc reproducing apparatus according to the present invention is the same as the conventional optical disc apparatus shown in FIG. 2 except that the graphics circuit  24  has been replaced by a digital OSD unit  125  and no OSD unit is connected to the output of the first digital/analog converter  23 . In view of the foregoing, only the differences between the present invention and the conventional art will be discussed. 
     FIG. 6 illustrates one embodiment of the digital OSD unit  125 . As shown in FIG. 6, the digital OSD unit  125  includes a single character memory  139  connected to a timing circuit  135 , a decoder  137 , a level controller  141 , and a controller  145 . The character memory  139  includes a first and second portion (not shown). The first portion of the character memory  139  is, for example, a random access memory RAM, while the second portion of the character memory  139  is, for example, a read only memory ROM. The second portion of the character memory  139  stores the text of, for example, reproduction information such as time information and operation information (e.g., play, rewind, fast forward, camera angle, etc.) at predetermined memory addresses. 
     As further shown, a data extracting part  133  receives the bit stream output by the VBR buffer  9  from the video decoding part  21 , and sends output to the decoder  137 . The controller  145  receives the clock data and the character control instructions from the microprocessor  15 , and sends output to the timing circuit  135  and the character memory  139 . 
     The level controller  141  amplifies the character data received from the character memory  139 , and sends the amplified character data to the mixer  43 . As also shown in FIG. 6, the digital OSD unit  125  transfers the bit stream output from the VBR buffer  9  to the audio decoding part  27 . 
     The operation of the digital OSD unit  125  shown in FIG. 6 will now be described. The data extracting part  133  extracts the sub-picture data in the bit stream output from the VBR buffer  9 . The sub-picture data includes menu selection data (e.g., camera angle selection, audio and language selection, etc.), caption data, etc. The decoder  137  decodes this sub-picture data, and the decoded sub-picture data is stored in the first portion of the character memory  139 . 
     The controller  145  receives clock data and character control instructions from the microprocessor  15 . The controller  145  converts the character control instructions into memory addresses of reproduction information stored in the character memory  139 , and outputs the memory addresses to the character memory  139 . Based on the clock data, the controller  145  generates timing instructions, and outputs these timing instructions to the timing circuit  135 . The timing circuit  135  detects the sync signal from the video data in the bit stream output from the VBR buffer  9 , and based on the timing instructions and the sync signal, generates a clock signal. 
     In accordance with the clock signal, the character memory  139  outputs the decoded sub-picture data as first character data. In accordance with the clock signal and the memory addresses, the character memory  139  outputs the addressed reproduction information as second character data. 
     The first character data output from the character memory  139  represents the text of a caption and/or menu selection, and the position of this caption and/or menu selection on the display screen is predetermined with respect to the sync signal. The second character data output by the character memory  139  represents the text of reproduction information, and is positioned on the display screen in accordance with the timing instructions output by the controller  145  to the timing circuit  135 . 
     The character data output of the character memory  139  is amplified by the level controller  141 . The mixer  43  mixes the amplified character data with the processed video signal output by the video decoding part  21  to generate a digital video signal. Also, the bit stream output from the VBR buffer  9  is transferred to the audio decoding part  27 . 
     Unlike the conventional optical disc reproducing apparatus, the optical disc reproducing apparatus according to the present invention, which incorporates the digital OSD unit  125 , includes a single character generating device for both the sub-picture data and the reproduction information. Because a single extracting, decoding, and mixing operation are performed, the signal-to-noise ratio is improved compared to the conventional optical disc reproducing apparatuses. Furthermore, the processing performed by the OSD unit  125  takes place entirely in the digital domain. This further benefits the signal-to-noise ratio by eliminating the number of digital-to-analog conversions to produce an output video signal. 
     Another embodiment of the digital OSD unit  125  is illustrated in FIG.  7 . As shown in FIG. 7, the digital OSD unit  125  includes a first character memory  239  and a second character memory  247 . The first character memory  239  is connected to a timing circuit  235 , a decoder  237 , and a level controller  241 . The first character memory  239  is, for example, a RAM. The second character memory  247  is connected to the timing circuit  235 , the level controller  241 , and a controller  245 . The second character memory  247  is, for example, a ROM, and stores the text of, for example, reproduction information such as time information and operation information (e.g., play, rewind, fast forward, camera angle, etc.). 
     As further shown, a data extracting part  233  receives the bit stream output by the VBR buffer  9  from the video decoding part  21 , and sends output to the decoder  237 . The controller  245  receives the clock data and the character control instructions from the microprocessor  15 , and sends output to the timing circuit  235  and the second character memory  247 . 
     The level controller  241  amplifies the character data output by the first and second character memories  239  and  247 , and outputs the amplified character data to the mixer  43 . As also shown in FIG. 6, the digital OSD unit  125  transfers the bit stream output from the VBR buffer  9  to the audio decoding part  27 . 
     The operation of the digital OSD unit  125  according to the second embodiment will now be described. The data extracting part  233  extracts sub-picture data from the bit stream output by the VBR buffer  9 . A decoder  237  decodes the sub-picture data, and the decoded sub-picture data is stored in the first character memory  239 . 
     The controller  245  receives the clock data and character control instructions from the microprocessor  15 . The controller  245  converts the character control instructions into memory addresses of reproduction information stored in the second character memory  247 , and outputs the memory addresses to the second character memory  247 . The controller  245  also generates timing instructions based on the clock data, and outputs the timing instructions to the timing circuit  235 . The timing circuit  235  detects the sync signal in the video data of the bit stream output from the VBR buffer  9 , and generates a clock signal based on the detected sync signal and the timing instructions received from the controller  245 . 
     In accordance with the clock signal, the first character memory  239  outputs the decoded sub-picture data as the first character data such that a caption and/or menu selection is displayed at a first predetermined position on a display screen. Based on the clock signal and the memory addresses, the second character memory  247  outputs the addressed reproduction information as second character data such that reproduction information is displayed at a position specified by the clock data on the display screen. 
     The level controller  241  amplifies the character data output from the first and second character memories  239  and  247 , and the mixer  43  mixes the amplified character data with the processed video data output from the video decoding part  21  to produce a digital video signal. Also, the bit stream output from the VBR buffer  9  is transferred-to the audio decoding part  27 . 
     Like the first embodiment discussed above with respect to FIG. 6, the number of processing steps is reduced such that the signal-to-noise ratio is improved. Additionally, all processing is performed in the digital domain. 
     It should be understood that the optical disc reproducing apparatus according to the present invention is not limited to use with DVDs, but can be used with any optical disc recording media. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.