WO1993013623A1

WO1993013623A1 - Method and apparatus for providing dual language captioning of a television program

Info

Publication number: WO1993013623A1
Application number: PCT/US1992/004821
Authority: WO
Inventors: Amnon M. Salomon; Anthony M. Faust
Original assignee: National Captioning Institute, Inc.
Priority date: 1991-12-24
Filing date: 1992-06-12
Publication date: 1993-07-08
Also published as: AU2235892A; CA2114771A1; DE4294569T1; US5294982A; US5519443A

Abstract

A method and apparatus of decoding recorded audio data for a language having the Roman alphabet or a language having a syllabic alphabet from a composite video signal comprises the steps of receiving the data in the form of data packets and determining from bit values stored at particular bit positions whether the data is control data or represents printable character data comprising a head code or a tail code. Once it is determined that the data represents either a head code or a tail code of a printable character, the data bytes are valued for parity and, from that determination, a letter component is generated which points to a letter component or complete character for one or the other alphabet. Because characters of a syllabic language may be quite complex, the step of displaying the syllabic language character includes the steps of overlaying (112) two or more letter components to form the syllabic character image. Furthermore, the syllabic language character is displayed having a height of approximately three quarters inch on a standard resolution NTSC television screen.

Description

METHOD AND APPARATUS FOR PROVIDING DUAL LANGUAGE CAPTIONING OF A TELEVISION PROGRAM

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to the field of producing closed captioning for television program viewers who are deaf or hard-of-hearing, and more particularly to a method and apparatus for providing closed captioning in two languages, the first language using the Roman alphabet and the second language using a syllabic alphabet, as will be more particularly defined herein.

2. Description of Relevant Art

Closed captioning is the method by which the audio portion of a television program or home video is processed into recorded words that can be displayed on a television screen with the aid of circuitry contained in an external device known as a captioning decoder or related decoder circuitry built into a television receiver. One known decoder commercially available through the National Captioning Institute of Falls Church, Virginia is the TeleCaption (TM) 4000 decoder.

The purpose of the decoder is to receive encoded captioning data transmitted at a particular line of the vertical blanking interval of a standard television signal which may be used for data transmission. This line may be any of lines 10 through 21 of the vertical blanking interval of a known standard television signal format adapted for use in the United States. In accordance with United States standard National Television Subcommittee (NTSC) format as described at 47 Code of Federal Regulations (CFR) Section 73.682 (a) (22), the chosen data transmission line is line 21, which is immediately adjacent to active video. In one higher resolution European standard television broadcast signal, the chosen line is line 16 or line 329 of the vertical blanking interval, in another, line 22 or line 335. Particular details of specifications for a decoder have been published by the Federal Communications Commission on June 13, 1991 at 47 CFR section 15.119 through the Federal Register, to become effective July 15, 1991. There is provided a transmission and encoding scheme for transmitting special characters such as musical notes, the Roman alphabet, punctuation, attributes, control codes and such in hexadecimal format. The special character set further includes alphabet characters, for example, having a grave accent so that European languages such as French or Spanish 'ay be transmitted. The decoder decodes the captioning and control code data transmitted on line 21 in accordance with the published format. The decoder includes memory for looking up a stored character set and causes a display of closed captioned text on a television screen simultaneously with the image of the person speaking the text.

An overall block schematic diagram for the TeleCaption 4000 decoder is shown as prior art Figure IA. A broadcast television signal is received at a television tuner 101 selectively actuated by a controller 103, preferably a microprocessor, to tune to a selected television channel. In particular, controller 103 may be a Motorola 6805P6 microprocessor, part no. F24K189 or comparable microprocessor known in the art. The tuner 101 is actuated under user control, preferably by channel up and channel down key or other input device input (not shown) . The received television signal is demodulated from the selected channel frequency and the audio and video carriers at baseband separated at the television tuner 101. The audio signal is provided to a volume control circuit 102 and the video to a close-caption processor 104, both under control of the controller circuit 103. Audio preferably may be regulated under user control via a user input device (not shown) , for example, via up and down volume keys. Regulated audio at a desired volume level is provided from the volume control circuit 102 to a channel 3/4 modulator 105. At the same time, the close-caption processor 104 extracts the textual and command control data including caption data representative of the audio transmission and outputs an overlaid video signal including captions to the channel 3/4 modulator 105. The close-caption processor 104 most conveniently comprises a Sierra NC74021 application specific integrated circuit, available from the National Captioning Institute, and a microprocessor, for example, a Motorola 6803 custom mask SC93193P controller, also available from ^■ e National Captioning Institute. Further details of one closed caption processor comprising these two integrated circuits are provided in Figure IB. The channel 3/4 modulator 105, preset to one or the other of channels 3 or 4, modulates the combined video and audio signal to the selected frequency. The output of the channel 3/4 modulator 105 is then provided to an associated television set (not shown), which if tuned to the preset channel 3 or 4, will display the output of the caption decoder of Figure IA.

A schematic circuit diagram of the close-caption processor 104 or decoder section of Figure IA is represented as Figure IB. The received baseband video signal is provided to a close-caption overlay circuit 112, to a close- caption timing circuit 106 and to a data extractor 107. The close-caption timing circuit 106 regards the input video signal to determine the location of the vertical blanking interval, the identity of the received field, be it odd or even, and determines the starting point of the selected line, for example, line 21 for the identified field. The close-caption timing circuit 106, operating at sub-line frequency, also generally clocks all the operations of the principal building block circuits of the decoder circuitry. For example, the close-caption timing circuit 106 clocks and signals the data extractor circuit 107 to extract the data received at the selected line.

Referring briefly to Figure 2A, typically, a clock run in burst is used to obtain a half power value for data slicing and the data extractor 107, clocked by the timing circuit 106 extracts a serial data stream comprising two data bytes at a time and forwards the extracted data to controller 109. At the same time, the close-caption timing circuit 106 clocks and signals the attribute register circuit 108 when to begin to store attribute data for an output caption to be generated and eventually overlaid on the incoming video signal via the close-caption overlay circuit 112. The close-caption timing circuit 106 also clocks and signals the close-caption controller 109, which most conveniently comprises a microprocessor, to accept data from the data extractor circuit 107. Also, the close- caption timing circuit 106 clocks the display RAM circuit 110 as it receives temporary data from the close caption controller 109, outputs attribute data to the attribute register and pointer data to a character ROM ill, also clocked by the close-caption timing circuit 106.

Pointer data output from the display RAM 110 points uniquely to a permanently stored character set stored in the character ROM circuit ill. The attribute register circuit 108 further provides attribute data to the character ROM 111 for characters. In a caption mode of operation, attributes, for example, may be related to style, whether or not the character is to blink or to appear in a particular color. Attribute data provided to the close-caption overlay circuit 112 relates to attributes for an entire overlay or caption. In this manner, an entire caption is generated for display on an associated television set which may be rolled-up (scrolled) , popped-on (displayed all at one time) , or painted-on (displayed in a continuously printing manner) . If a caption is to be printed in italics, the closed caption timing circuit 106 is signalled by the closed caption controller responsive, for example, to receipt of a mid-row italics code to output timing signals to generate pointer data output from display RAM 110. However, closed caption timing circuit 106 outputs clocking signals at a different rate to character ROM 111 in such manner that the output character data of character ROM 111 is intentionally slanted to appear in italics.

An application specific integrated circuit (ASIC) for performing the decoding of teletext signals transmitted with ^television signal is available from ITT Corporation and is commercially known as the Teletext Processing Unit (TPU) 2740, a 24 pin ASIC. This chip also generates English teletext characters for display as a teletext television image, typically a static image of textual data. Teletext is a service provided, for example, over broadcast television channels, cable television channels or through direct broadcast satellite systems, and while not related specifically to closed captioning, relates to a method of providing textual information which may be superimposed on an action image or a plain background.

Data required for closed captioning requires both textual or captioning data and display command data for, for example, synchronizing the caption data with the spoken dialogue of a television program. Thus, a caption decoder includes circuitry which additionally decodes display command data to display a caption at the bottom of a television image.

Captioned television thus enables viewers to read the dialogue and narration of programs. Closed captioning provides access to the entertainment, educational and informational benefits of television for viewers who are deaf or hard-of-hearing. When the spoken word is in a foreign language and sub-titles in a native tongue are provided, people learning the foreign language can enjoy the benefits of such captioned television as well.

Known decoders generally comprise a character generator as per Figure IB or similar circuitry which causes captions to appear in the lower portion of the television screen, below the video image of the speaker. As already described, the character generator may also be built into an associated television set. The video information appearing on the horizontal lines of the caption image are appropriately _- replaced with character data output by the character generator, for example, via closed caption overlay circuit 112. Character sizes vary proportionately to the size of the television screen. On a nineteen inch screen, for instance, captions appear to be about one half inch high. The captions are easily visible - typically white letters against a black background. Appearing at the bottom of the picture, captions typically do not obstruct one's view of the action portion of the video program image, that is, that portion of the image where the normal viewer, without captioning, would focus their attention in order to enjoy the displayed image.

Closed captioning technology was developed by the Public Broadcasting Service (PBS) during the period 1973- 1979. Numerous over-the-air test transmissions were conducted to test all aspects of the caption generation including encoding, decoding, and the display of captions. Service was launched in"March of 1980 by the then newly created National Captioning Institute in cooperation with the television networks. The original target audience for captioning included people who were deaf or hard-of-hearing (about 20 million people) , but now includes people learning English as a second language and those learning to read, such as students with learning disabilities. Weekly availability in the United States of captioned programs now exceeds 400 hours between network TV, cable television and syndicated programs.

For encoding according to NTSC and Federal Communications Commissions Standards, broadcasters may obtain a model EN230 or smart encoder manufactured by E.E.G. Enterprises, Inc. of Farmingdale, New York. This same company manufactures a model EN210 or simple encoder as well. The encoder inserts caption data into fields one and two at line 21 of the vertical blanking interval. A so- - called smart encoder receives data to be inserted through an RS232 serial data port. The smart encoder, having a built- in decoder, can recognize gaps in caption data and can fill the gaps with additional caption or text service data. For Example, if already existent captioning data appears at line 21 but there exists a capacity to display up to fifteen rows of thirty-two characters, there is spare capacity for additional captions or text services. These text services may comprise emergency announcements such as tornado warnings or other messages to the target audience. The simple encoder is used to create new captions and has no internal decoder.

A means for encoding a character set for certain alphabet characters, namely, the ASCII character code is well known and comprises 96 different hexadecimal codes for pointing to corresponding characters in memory. Thus, two bytes transmitted one byte per field or two bytes per frame uniquely point to an alphabetic, control, punctuation, or other character for display in English. As the NTSC transmission rate provides for the transmission of 30 frames (of two interlaced fields) per second, the data transmission rate for alphabet characters can be as high as sixty characters per second which are stored and displayed, as controlled by display command data, simultaneously with the spoken message in intelligible form, such as in complete sentences. A problem with existing decoders is that they are only capable of receiving captioning data in one language at a time, for example English, French, German, or Spanish, which is based on the Roman alphabet. Nevertheless, the NTSC format is used in other major countries as well such as Korea, Japan, and Taiwan. In such countries therefore, there is an opportunity to provide captioning in the languages of these countries, namely Korean, Japanese and Chinese, consistent with the NTSC standards and known _^methods of caption transmission utilizing the data-carrying capabilities of the vertical blanking interval.

On the other hand, languages, such as Korean, Japanese and Chinese, and for the purposes of the present application, the Korean language will be discussed as exemplary, are unique in their means of recording the spoken word. Notwithstanding a danger of oversimplification, such languages are recorded in the form of pictographic or ideographic communications, rather than on a Roman letter by letter basis as in English to form syllables from a plurality of letters. The Korean alphabetic character set, in particular, provides hints as to how to form one's mouth to speak a syllable represented by a character. Consequently, fewer characters are required to form the same thought or sentence as would be required in English, but the greater variety of characters and their relative complexity make the ability to print the Korean character set difficult.

From the Korean government publication Han'gul. (Korean Alphabet and Language) , Korea Background Series Volume No. 9, available through the Korean Overseas Information Service and published in December, 1981, it is described how the Korean alphabet was developed by King Sejong in relatively modern times to phonetically describe sounds making up syllables of words. The Han'gul alphabet, a syllabic alphabet, comprises twenty-eight letters comprising seventeen consonants and eleven vowels. Consonants and vowels alternate in words to form syllables of words which phonetically describe how to pronounce Korean words.

The Korean language is thus unlike English. In the English language, strings of consonants may be run together such as "str" in "straight" and a combination of vowels and consonants may have to be interpreted together before one may pronounce a word-, such as the combination of letters "aight" in "straight".

For the purposes of the present application and claims, and for want of better terminology, the term "Roman alphabet" will be used to describe a category of alphabets for Latin-based languages, for example, such languages as English, French, Spanish, German, Dutch, Swedish and such. The term "syllabic alphabet" will be used as a term of art to describe a category of alphabets used in various languages such as Korean.

According to the well-known ASCII coding format, two consecutive bytes of data may combine to form a hexadecimal pointer into a Roman alphabetic or other character memory to obtain letters, numbers, or other special characters for display. There is no well-known, published coding scheme for providing captions in a syllabic language such as the Korean, language.

Associated with solving the problem of providing an electronic typewriter for the Korean language, C. H. Yeh in U.S. Patent No. 4,187,031, suggests an encoding scheme whereby sets of hexadecimal numbers be provided for the Bangui character set, one for the alphabetic symbol, and another, called a form code, for defining how to build a Hangul character. Such a coding system, however, has its limitations if adapted for data transmission within a line of a vertical blanking interval. Yet, there is an obvious need to provide captioning for deaf or hard-of-hearing people in countries such as Korea or, more particularly, to provide dual language captioning in any country including the United States. SUMMARY OF THE INVENTION

Thus, it is a general object of the present invention to provide means for recording, encoding, transmitting, receiving, decoding, and displaying recordable sounds of various languages, for example, for providing captioning, text or other services such that alphabetic, numeric and other characters of a syllabic language, consistent with known formats for encoding Roman alphabetic, numeric, musical note and other characters of a language such as English, French, German or Spanish for transmission, may eventually be displayed on a viewer's screen. Thus, it is also a general object to provide both Roman and syllabic alphabet captioning for display on an associated television signal receiver, telecommunications device or other apparatus for displaying the spoken word..

In order to accomplish these general objects, it is a specific object of the present invention to provide a method and apparatus for encoding and decoding the Roman and syllabic alphabets in a manner for transmission and reception on a single line of the vertical blanking interval of a television signal.

It is a further specific object of the present invention to determine an appropriate character and caption size for display on a standard resolution television set to enable a syllabic alphabet character and caption comprising the characters to be readable on a standard resolution color television screen and to further extend the principles of the present invention to enhanced or high definition television or telecommunications receivers as they become more commercially and widely available.

It is a still further object of the present invention to extend the principles of the present invention to the display of caption, text or other services in ideographic languages such as Japanese and Chinese.

In accordance with the present invention, a method of encoding syllabic alphabetic or numeric characters provides for transmitting four bytes of syllabic language data at a particular line of alternating fields of a standard, enhanced or high resolution NTSC, PAL, SECAM, MUSE or other television or telecommunications signal. The bytes are formed by encoding a syllabic block of language data into the four bytes, preferably in two byte increments to comply with existing standards, in such manner that upon receipt the^' four bytes are decoded into three bytes of pointer data into a master Korean syllabic alphabet including Roman alphabetic characters, number or other special character memory. For the master Korean or syllabic language character set including both the Han'gul and Roman alphabets, the four byte data packet comprises one "head code" and three "tail" codes, as will also be subsequently defined herein in connection with the following discussion of Figure 3. In accordance with the invention, the principles of the present invention may be extended to provide captioning in the Japanese and Chinese languages as well. These ideographic languages will require application of one head code and two tail codes; that is, only sixteen bits or two bytes would be required to identify approximately twenty thousand pictographic characters, a typical vocabulary of one using an ideographic language to communicate.

In particular for the Korean (and English) language, four seven bit data packets are decoded using bit-mapping techniques into one seven bit and two eight bit pointers. These pointers may particularly comprise Korean letter components pointers for pointing to components of Korean (syllabic) and English (Roman alphabet) characters in memory. The Korean letter components stored in memory are, for example, partial images comprising display segments of picture elements at particular locations in a character cell which in combinations of two or more are overlaid to form Korean syllabic characters for display in the cell.

Depending on the syllabic character for display, the two or more display segments of a Han'gul character may be extended in horizontal or vertical dimensions in the character cell. Because of the higher resolution required to read Korean characters, it has been determined that the optimum size of a character cell for Korean characters for display on a nineteen inch television screen be approximately 3/4 inch, slightly larger than the half inch suggested for display of the Roman alphabet. In particular, a", syllabic language character such as a Korean language character may comprise a ten by sixteen picture element character such that it fits wholly within a twelve by twenty picture element display cell. The character may be preferably highlighted, foreground on background, for example, white on black for ease of reading. With a high definition television receiver and as presently contemplated, the syllabic character set may be displayed with a character cell size of 1/2 inch, despite the greater complexity of the Korean syllabic characters.

In particular and to conform with known standards, Korean language closed caption data may be encoded and transmitted on line 21 of field 2 of each frame of an NTSC television signal. Preferably, a display of syllabic characters may comprise nine rows of syllabic alphabet or other characters in twenty columns. With respect to an NTSC television signal, the phonetic language display will begin at line 51 and comprise 180 lines in total, ending toward the bottom of the image at line 230 (of 262 or 263 lines maximum, the even and odd fields respectively) . However, one of ordinary skill in the art may transmit the recorded word at any particular line of other known or contemplated formats following the principles of the present invention.

Consequently, according to the present invention, a method of decoding the caption data transmitted with a composite television signal is characterized by the steps of decoding data packets of printable characters and command codes comprising a plurality of data bytes indicated as to type by value or by particular bit indications appearing in one of the bytes of the data packets, decoding the head code and tail codes of each printable character data packet, storing a plurality of characters and display segments in memory for at least two languages, a first language having the Roman alphabet and a second language having a syllabic alphabet, determining if the data packet represents a non- printable character or command code, and mapping remaining bit positions for a printable character into a number of letter component pointer bytes less than or equal to the number of data bytes comprising the data packet, the letter component pointer for pointing to Roman or special alphabet characters or to one of a plurality of syllabic alphabet letter components in memory. The plurality of syllabic letter components are given by starting coordinates and by dimensions and are overlaid to form a syllabic character for display with a remaining picture signal.

Various methods may be employed for determining if captioning in English or Korean is to be provided. For example, one method is to provide a switch on a decoder for reading either line 21 field one data (language channel one) or line 21 field two data (language channel 2) . Another method is to provide in-channel data within a particular language channel for defining a means for evaluating the letter component pointer bytes and, if they have a certain value, then assume that it or another predetermined byte relate to a particular alphabet type, Roman or syllabic. These and other features of the present invention will be discussed in greater detail in connection with the detailed description of the drawings which follow. BRIEF DESCRIPTION OF THE DRAWINGS

Figure IA is a block schematic drawing of a known caption decoder for decoding caption and command code data transmitted at line 21 of the vertical blanking interval of a television signal;

Figure IB is a block schematic drawing of a .first close-caption processor of the decoder of Figure IA or of a close-caption processor comprising two integrated circuits according to the present invention;

" Figure IC is a block schematic drawing of a second close-caption processor of the decoder of Figure IA comprising four integrated circuits according to the present invention;

Figure 2A is a waveform diagram of the line 21, field 1 data transmission signal for transmitting captioning data for a television signal pursuant to standards promulgated by the United States Federal Communications Commission;

Figure 2B is a standard Latin or Roman alphabet character set including special characters and respective eight bit codes;

Figure 2C is a table providing miscellaneous control codes for data channel 1 or 2 caption transmission;

Figure 2D is a table providing mid-row attribute codes for caption transmission;

Figure 2E provide preamble address codes for caption transmission;

Figure 3 is a bit map for decoding (or, in reverse, encoding) a four byte language data packet into three syllabic or Roman alphabetic or other character component pointers for pointing to character data stored in decoder read only or non-volatile memory (character ROM) shown in Figure 1; Figures 3B through 3E comprises completed bit maps for encoding/decoding Korean syllabic characters and Roman alphabetic characters according to the present invention;

Figure 4 comprises a character font set according to the present invention for displaying the three hundred most common Hangul syllabic characters;

Figure 5A is a table showing Hangul character type, size in display segments, the start coordinates, the number of Hangul syllabic characters, the number of nibbles required for storage in character memory and the total number of bits;

Figure 5B shows an example of Hangul character display requiring 10 x 16 display segments and showing typical beginning coordinates and a display of a type J character element image;

Figures 6A through 6E comprise encoding tables showing Hangul character type, letter components, their size and starting coordinates; in particular. Figure 6A shows encoding of initial consonants of two component component syllabic characters; Figure 6B shows encoding of initial consonants for three part syllables; Figure 6C provides a table of vowels by initial consonant groups for two part syllables; Figure 6D provides a table of vowels by initial consonant groups for three part syllables; and Figure 6E is a table of final consonants by vowel types for three part syllables;

Figures 7A, 7B and 7C comprise letter component tables for encoding or decoding Hangul syllabic character elements for display. Figure 7A relating to the first of three pointers. Figure 7B relating to the second pointer and Figure 7C relating to the third pointer;

Figures 8A through 8D are flow charts of the decoding process for decoding command codes and either Roman alphabetic, numeric or other characters or syllabic alphabetic, numeric or other characters according to the present invention;

Figure 9, by way of example, shows the process of displaying a Hangul character element or letter component according to the present invention; and

Figure 10 comprises typical displays of Latin or Roman alphabet character data represented by the letters USA followed by a display of Hangul and Latin character. data, showing a preferred character display whereby each syllabic language character is approximately 3/4 inch high on a nineteen inch standard resolution television screen and the caption appears between horizontal lines 51 and 230 and preferably toward the bottom of a television image. DETAILED DESCRIPTION OF THE DRAWINGS

In order to better understand the principles and concepts of the present invention, the following definitions are provided for terms of art employed within the specification and claims:

A caption box is a contiguous display region surrounded by a solid border that overlays a variable portion of a video image and contains video image related textual information. The caption box supplements a video image displayed on a television or other display screen by providing an alternative presentation of the audio portion or recorded speech of the associated video image. More than one caption box may be displayed on screen at the same time, for example, when two or more people are speaking in a particular scene of a television program. Examples of caption boxes are shown in Figure 10, for example, caption box 1000.

A display cell is a subpart of a caption box which contains an image of a Roman alphabetic, a numeric or a syllabic language alphabetic character, for example, a letter of an English word, a number, or a syllabic (Han'gul) character of the Korean language. This region encompasses an area with a height of one row and a width of one column; yet, the pixel size of the display cell will vary between language types. Referring briefly to Figure 10, the actual pixel dimensions of a display cell are dependent upon the maximum row and column dimensions allotted to the particular display format for a selected language type. Display cell 1001 is an example of a Latin character display cell and display cell 1002 is an example of a syllabic character display cell.

A character cell is wholly within a display cell and comprises the maximum area of a particular character. A border surrounding a character cell plus the character cell is equivalent to the display cell. Referring to Figure 5B, there is shown a 10 x 16 character cell for a Hangul syllabic character, sometimes referred to herein also as a character box.

Han'gul is the name of the Korean language alphabet.

Han'gul syllabic characters comprise Han'gul letter components and display segments used to make up a Hangul syllable. The letter components may comprise partial images of syllabic characters comprising combinations of appropriately placed lines, dots and other such shapes formed of picture elements. Figure 4 provides a font for the three hundred most common syllabic characters. Figures 7A through 7B provide Hangul letter components which comprise the syllabic characters.

Han'gul syllables comprise a group of Han'gul characters displayed in a display cell, the syllables used to form Korean words. Referring to Figure 10, there is shown a Korean caption box in which is displayed a Korean word and its English language counterpart.

The Korean (dual language) syllable comprises a string of four successive printable ASCII compatible codes, for example, from line 21 of the vertical blanking interval defining a Han'gul syllable .or a Roman alphabet based alphanumeric character. The four codes comprise a data packet of one head code and three tail codes, for example, as per one of Figures 3A through 3E.

A letter block is an image enclosed entirely within a display cell that forms either a Han'gul syllable or a Roman alphabet based character. The letter block is equivalent in size to a character cell.

A letter component is one of a collection of character elements that combine to form a letter block. An English alphanumeric character will have one image per letter block. ^~ Han'gul syllable, on the other hand, may comprise two or more letter components or partial images per letter block. According to Figure IA, there is shown a block schematic diagram of a known TeleCaption 4000 caption decoder for decoding caption and command code data transmitted at line 21 of the vertical blanking interval of an NTSC television signal for display on a television screen. Figure IB provides particular details of the closed caption processor of Figure IA. Figures IA and IB are already described in the Background of the Invention section of the present invention in regard to the operation and circuitry of a TeleCaption 4000 decoder. According to the present invention, however, the closed caption processor 104 of Figure IB comprising two integrated circuits, as described above, may be replaced by a processor as described herein for decoding a master Korean language character set. Referring to Figure IC, the block functional elements of Figure IB may be arranged to comprise a four integrated circuit functional chip set. An incoming video signal may be split and a portion provided to six bit analog to digital conversion circuit 116 and a portion provided to synch stripper or processor circuit 113, which may be a conventional synch stripper circuit known in the art. The six bit analog to digital conversion circuit may comprise a UPC 661 integrated circuit available from the National Captioning Institute. Analog to digital converter 116 comprises data extractor block 107 and a portion of closed caption timing block 106 while the remaining duties of closed caption timing block 106 are performed by sych stripper 113. Processor block 115 comprises a custom forty pin proprietary integrated circuit from the same chip family as the TPU 2740 described above, manufactured for the National Captioning Institute by ITT Corporation. This chip • comprises closed caption controller block 109, character ROM 111, and caption overlay block 112. Controller 115 communicates with dynamic random access memory (DRAM) 114 which comprises attribute register block 108 and display RAM block 110. DRAM circuit 114 most conveniently comprises, for example, a UPD484256 128 kbyte memory available from the National Captioning Institute. The analog to digital conversion circuit 116 and the controller circuit 115 are clocked by clock circuit 117 at, for example, 14.3 MHz for data extraction. The data clock is most conveniently a multiple of the horizontal line rate of the incoming video signal. The controller itself is clocked at, for example, 20 MHz by clock circuit 118 for data processing purposes. The software algorithm for controller 115 will be described in detail herein in connection with a discussion of Figures 3 through 9.

Referring to Figure 2A, captions associated with a television program are transmitted as an encoded composite data signal during line 21 of a standard NTSC video signal. The signal consists of a clock run-in signal, a start bit, and sixteen bits of data corresponding to two separate bytes of eight bits each. The eight bit bytes typically each comprise a parity bit and a seven bit ASCII or special character and command code data as per Figures 2B through 2E. Thus, data transmission is at a rate of 480 bits per second calculated as follows: eight bits per field times sixty fields per second amounts to 480 bits per second. According to a frame rate of thirty frames of two fields each, data is transmitted at four bytes per frame. This data stream contains encoded command information which provides instructions for formatting characters as well as the characters to be displayed and other characters. According to the present invention not only are ASCII and other character data transmitted as per Figure 2B but Hangul syllabic data as well, as will be further described herein. Still referring to Figure 2A, there is shown a waveform diagram for the caption data signal of line 21 of the vertical blanking interval. After a horizontal blanking pulse and a color burst, a clock run-in signal is provided consisting of a seven-cycle burst of sinusoidal frequency phase-locked to a caption data run-in signal whose frequency, 32 times the horizontal line rate, is twice that of the data clock, providing synchronization for the data decoder (or encoder) clock. According to the principles of the present invention, the clock run-in is most efficiently evaluated for determining a half power data-slicing value for the following data stream. If one multiplies thirty-two times the horizontal line rate of 15.732 kHz, the decoder clock rate is obtained at 5.034965 MHz. The clock run-in signal is followed by two data bits at a zero logic level, then followed by a logic one start bit. The last two cycles of clock run-in of 5.034965 MHz, these last two logical zeroes, and the logical one start bit together constitute an eight bit frame code signifying the start of data.

The transmitted data following the eight bit frame code is transmitted in non-return-to-zero (NRZ) format. Seven bits of data for each character are followed by a parity bit indicating odd parity for error detection.

Each caption transmission is preceded by a preamble code, which consists of a non-printing character and a printing character to form a row address and display color code. Preamble address codes are shown in Figure 2E. Both characters together form a control code, and all control codes are transmitted within a single field of line 21 and twice in succession to ensure correct reception of the control information contained within the code. Miscellaneous control codes are shown In Figure 2C. These include alarm, roll-up, flash on, resume, and erase commands.

Transmitted captions may be interrupted by mid-caption control codes between two words in order to change display conditions such as color, underline or italics, for example, used for emphasis. Mid-row control codes are shown in Figure 2D. At the completion of a caption transmission, an end-of-caption control code is sent as per Figure 2C.

' The first character of a control code is a non-printing ASCII character, 0000000 through 0011111, but codes 0000000 through 0010000 are not used. Thus, non-printing control codes are easily distinguishable from printable characters. This is followed by printing characters which have the code series 0100000 through 1111110. All characters that are received after a set of valid control codes are interpreted and loaded into memory as characters or letter components to be printed. Character codes with bad parity result in ones code being written into memory; this normally causes display of a blank background box (a delete symbol) . This delete symbol is typically displayed in place of a desired character transmitted in error. Spelling and context error correction algorithms are known, however, which can make a high probability guess at the identity of the character transmitted in error.

For Roman alphabetic character display on a television screen, the caption display typically consists of fifteen rows of characters with up to a maximum of 32 characters per row. A switch of the known decoder allows services to be provided to be switched between captioning services and text services. In a captioning mode of operation, a maximum of four rows of characters are utilized during the encoding process for a typical caption, the purpose being to synchronize a caption with a typical scene of a movie or other entertainment event and not to interfere significantly with enjoyment of the event. These four rows comprising a caption can appear anywhere in the allocated fifteen rows, but typically appear in the bottommost rows so as to not interfere with the action portion of a television image. Each character row occupies 26 out of 525 horizontal lines of a two field frame. The first row of the fifteen possible rows starts at line 43 in each successive field, be it the even or odd field (262 or 263 line field) of a standard resolution NTSC display. Thirteen lines of each, odd and ven, field make up a twenty-six line high character.

Each row is displayed with a black or other surround for a, for example, white character in order to enhance its readability against a normal video picture background. The black box surrounding the row extends one character to the left of the first character and one character to the right of the last character to be displayed in a row.

Each letter block of a Han'gul language character is represented in a caption display by a combination of two or more letter components. The number and placement restrictions upon the letter components in a character cell allows all possible Han'gul letter blocks to be represented by a combination of one 8 bit head code and three 8 bit tail codes as per Figure 3A. This represents a requirement for transmitting 23 bits of usable data to represent all possible Han'gul letter blocks, as represented by the five empty head code bit positions and eighteen empty bit positions in the three tail codes of Figure 3A.

The well-known line 21 data transmission protocol requires a seven data bit word length, with an eighth bit as a parity bit. The transmission of four of these seven bit words will be more than adequate to meet the requirement of transmitting at least 23 bits of usable data to represent all possible Han'gul letter blocks. The resulting data rate of fifteen letter blocks per second is more than adequate for Korean closed captioning calculated as follows: sixty bytes per second maximum data rate divided by four bytes per letter block. Furthermore, the four bytes per letter block may be most conveniently transmitted two bytes per field in the same manner as English language captions.

Referring to Figure 3A, there is shown a bit map for detecting and translating the four 8 bit packets of Korean language data, i.e. a head code and three tail codes into one 7 bit (pointer 2) and two 8 bit pointers (pointers 0 and 1) to Han'gul or Roman letter components stored in a decoder character ROM or non-volatile memory. Only one representative bit-mapping scheme is shown, but the principles therein indicated may be modified to create other bit-mapping schemes without violating the principles of the invention. In the reverse, it likewise shows a method of encoding Korean characters for transmission. The seventh bit position of a head code or any tail code may be, to be consistent with the prior art ASCII caption transmission scheme, the parity bit and is denoted P. In a typical decoder, this bit is used for error detection and a delete or nul character displayed. Bits 5 and 6 of byte 0 are set to l and 0 respectively to indicate the first or head code of four bytes forming the Korean (dual language) data packet. Bit positions 0 through 5 of tail code bytes 0, 1 and 2 may conveniently become bits 0 through 5 of related pointer bytes as described below. Otherwise, the bits shown are mapped from the respective head code data byte to corresponding bit positions 6 and 7 of the three letter component pointer bytes as shown.

Now the encoding process of the present invention will be described in considerable detail in connection with the following discussion of Figures 3B through 3E. Encoding apparatus is not shown for the present invention but preferably comprises a standard personal computer with appropriate input and output devices selected for the intended application. For example, a live news broadcast may be simulcast with recorded audio captioning by means of voice recognition and encoding circuitry applied for data input. The personal computer of the encoder may comprise encoding tables and algorithms as decribed herein in connection with encoding table Figures 6A through 6E.

Firstly, an encoding of the Korean character "ha" will be described according to Figure 3B with reference to Figures 4, 5A, 6A through 6E, and 7A, 7B, and 7C as appropriate. The Hangul character "ha" is one of the three hundred plus most common syllabic characters and is shown at coordinates (1,1) of Figure 4. Rather than store entire syllabic characters according to Figure 4 in decoder character ROM, only letter components are stored as per Figures 7A, 7B, and 7C which are overlaid as appropriate to form the entire syllable. In particular, the Korean character "ha" comprises two such letter components or partial images.

A Korean syllable may comprise as many as three components, an example of which will be described in connection with the following discussion of Figure 3C. Nevertheless, the first step of encoding the present example, "ha", comprises identifying the two letter components and a null component of the syllabic character. Referring to Figure 7A, pointer 0, the first pointer to the initial consonant, is defined to comprise code 000E (14 in decimal) . The reader will note that there are other similarly portrayed letter components such as those represented by codes 20 01, 20 OF, 40 02, 50 05, 60 03, 70 06, 80 09, 90 07, A0 0A, B0 0D and CO 0B. It is a principle of the present invention to decrease the cost of a decoder in relation to the cost of an encoder. In this regard, encoding software and related processing may allowably be hundreds of times more expensive in view of the relative relationship between the expected number of encoders and decoders. In other words, only one encoder need be required, for example, for each transmitting station while the expected number of decoders may be on the order of millions. Nevertheless, according to the present invention, encoding is relatively simple and determined per Figures 6A through 6E as will be subsequently explained. Consequently, encoding software may most conveniently make a determination as to which among these several codes for each letter component pointer is appropriate based on the entire syllabic character to be transmitted. The determination is Related to the relative dimensions of the letter component compared with the entire syllable to be transmitted. In particular, Figures 6A through 6E are referred to to first identify an initial consonant (Figures 6A and 6B) , a middle vowel (Figures 6C and 6D) and a final consonant (Figure 6E) of a syllable, if a final consonant is required (i.e., a three letter component syllable) . Thus, decoder software, on the other hand, may be comparatively unsophisticated and simply be actuated to overlay partial image upon partial image based on the order of letter components transmitted until a character block is filled.

Figure 6A provides the initial consonant for a two part syllable, such as "ha", while Figure 6B provides the initial consonant for a three part syllable. When followed by a simple A or vertical type vowel, the consonant is shown by table position decimal 14, a 6 x 16 dimension image (hexadecimal image 00 0E) . In binary, most significant bit first, the pointer 0 register of Figure 3B comprises 0111 0000. The consonant will be displayed beginning at coordinates (0,0) of the character cell.

In a similar manner, pointer 1, for the final vowel of the two part syllable "ha", is determined from Figures 6C or 6D and 7B. Referring first to Figure 6C, Figure 6C shows desired vowels down the left hand column and initial consonants across the top. The initial vowel is shown at position 209, the first vowel in the first row, as a 5 x 16 dimension image beginning at coordinates (5,0). Referring to Figure 7B, the possible encoding choices comprise 0001, 000A, 200B, and 3004. Again, because the example "ha" is represented by only two letter components and its dimensions may be large, the code chosen for the vowel component of "ha" by encoding software is 00 01, the first or 209th letter component after the 208 letter components of table Figure 7A. In binary, most significant bit first, the pointer 1 register of Figure 3B comprises 1000 0000. ^' _v Lastly, since this is only a two letter component character, the last pointer code for transmission is a reserved nul character code or 00 00. The pointer 2 register of Figure 3B shows 0000 0000.

Now referring to Figure 3B, pointer 0 represents the hexadecimal code 0E, most significant bit first, as 0111 0000 filling bit positions 0 through 7. Pointer 1 is represented as 1000 0000 for hexadecimal 01, most significant bit first. Lastly, the nul pointer 00 is represented by a string of zeros. The binary data contents of these three pointer registers are translated or bit mapped into contents of one head code register and three tail code registers for eventual data transmission.

Bit positions 0 through 5 of each pointer byte 0 through 2 map directly into bit positions 0 through 5 of each tail code byte 0 through 2 for transmission as shown. Tail code bit position 6 is always a 1 so parity bit P at bit position 7 may now be calculated, as shown, for odd parity. Thus, in tail code 0, parity bit "P" is a "1"; in tail code 1, parity bit "P" is a "1"; and in tail code 2, parity bit "P" is a "0". The head code byte is comprised of data from bit positions 6 and 7 as shown from pointer bytes 0, 1, and 2. Bit positions 6 and 7 of pointer 0 become bit positions 0 and 1 of the head code byte. Bit positions 6 and 7 of pointer 1 become bit positions 2 and 3 of the head code byte. Lastly, bit position 6 of pointer 2 becomes bit position 4 of the head code byte while dues to the limited number of rows of letter component codes for pointer 2 from the table of Figure 7C, it is assumed that the seventh bit position of pointer 2 is a "0" which is mapped as a "1" to bit position 5 of the head code byte. Furthermore, as a head code signal, bit position 6 is assumed to always be a "0" and as a tail code signal, bit position 6 is assumed to always be a "1". Parity for the head code byte is calculated, and for the present head code byte of Figure 3B, the seventh parity bit position is set at "0" for odd parity.

Lastly, according to Figure 3B, the data packets are serially transmitted over time preferably in two successive transmissions of line 21 two byte data. With odd parity, these are shown as data packets 20, CE, Cl and 40. Thus, with time increasing shown, the head code 20 is received first, determined to be a printing character, and the first partial image decoded per tail code CE. The first step of decoding is to remove parity from the head and tail code data and thus restore, for the head code and first tail code, the data 20 4E. Then, as per Figure 3A in reverse, the head code bit positions 0 through 5 are mapped to the various bit positions of tail code registers and tail code 0 mapped into pointer 0 completing pointer 0 to the consonant portion of "ha" as per Figure 7A stored in decoder character ROM 111.

Following with the next line 21 transmission of data are tail codes 1 and 2. These are first decoded as to parity and then mapped into pointer 1 and pointer 2. The decoder then according to the present invention overlays the images for the two (or more) meaningful letter components over one another and displays their full image or letter block as defined above as clocked by the closed caption timing circuit 106 of Figure IB and in accordance with control code (non-printing) data of Figures 2C, 2D and 2E sent at some other time as described above.

Now, referring to Figure 3C, the encoding of a three letter component Korean character "han" will be described in connection with Figures 6A through 6E. The first step for encoding "han" for transmission are to assemble the letter components in appropriate, predetermined order, for example, left to right, and bottom-most letter component last. The syllabic character "han" is found in the table of Figure 4 at coordinates (7,5) . The initial consonant is found by referring to Figure 6B for three part syllables. Still at column 14 of the initial consonants, one goes down the column to find an appropriate vowel/consonant combination in the row data at the left. In this manner, the initial consonant is found to comprise decimal position 118, corresponding to hex 70 06 of the table of Figure 7A. Referring to Figure 7A again, now the encoder will choose hexadecimal code 70 06 for pointer 0 because there will be three letter components or partial images and the dimensions of each letter component must be smaller for all three images to be overlaid in a letter block. Hexadecimal code 70 06, most significant bit first, is represented as binary 0110 1110.

The vowel for the three part syllable "han" is found on table 6D, where the vowel for a three part syllable is given by rows J, K and L. For a simple consonant and still being in the first column for the given vowel, the particular decimal vowel code is found to be decimal 251. There are 13 x 16 or 208 letter components in Figure 7A; thus, the required vowel is the 43rd (251-208) letter component of Figure 7B. Referring to Figure 7B for pointer l, the encoder will choose code 20 OB, the llth letter component of the third row, in stead of the other possible choices because of the position and dimensions of the respective partial image. Hexadecimal 20 OB is represented in binary, most significant bit first, as 1101 0100.

Lastly, for pointer 2, and referring to Figure 7C, there are two possible choices for the final consonant of the syllable "han", namely 00 01 and 10 0C. The final consonants of a three component syllable are found in Figure 6E. The vowel that has been chosen is in the first column (vertical) , thus the final consonant is found in the first M row. Because this is not the first consonant of the ^syllable, the encoder will select decimal pointer code 286. If Figure 7C immediately follows Figure 7B in memory, there are a total of 208 + 77 or 285 letter components represented by the two tables of Figures 7A and 7B. Consequently and in decimal notation, the 286th letter component is the first letter component of table Figure 7C or hex code 01 or binary 1000 0000, most significant bit first.

Using the bit map of Figure 3C, an encoder will map pointer codes 76, 2B and IC into head code 21 and tail codes 0, 1 and 2 become 76, 6B and 5C without parity. With parity added, head code 21 becomes Al and tail code 2 becomes DC; tail codes 0 and 1 remain unchanged. The transmitted head code for "Han" is 1000 0101. Tail code 0 is 0110 1110. Tail code 1 is 1101 1010. Lastly, tail code 2 becomes 0011 1011.

Now, encoding of a Roman alphabetic character according to the present invention will be described according to Figure 3D and together with Figure 3E, a Roman alphabetic syllable "ha" discussed. It is noted that the well-known ASCII encoding scheme of Figure 2B is employed, wherein "h", for example, becomes 09 (in upper case) . Thus, pointer byte 0 is 09 or, most significant bit first, 1001 0000. In one embodiment of the present invention, pointer bytes 1 and 2 are nul pointers. In accordance with another embodiment of the present invention, pointer byte 2 represents a second Latin alphabet or special character. Other alternative arrangements for improving Latin alphabet data throughput will become obvious to one of ordinary skill in the art according to various variations in the data transmission arrangement of Korean and Latin alphabetic characters.

Following through with the first embodiment, the bit positions of pointers 0, 1 and 2 are mapped as in the preceding example for a Korean syllable into respective head and tail code bytes. With and without parity, "h" becomes translated into head code 20 and tail codes 49, 40 and 40. TJlαe reader will note that in either embodiment pointer 1 is always a nul pointer which, together with identification of the head code, identifies the data pointer data upon receipt as Roman alphabetic data. Similar alternative rules can be fashioned for separating Latin from Korean characters.

Now, referring to Figure 3E, the English alphabet character "a" is encoded, per Figure 2B, as 18, (in upper case). Thus, pointers 0, 1, and 2 become respectively 18, 0 and 0 in the first embodiment (and in a second embodiment, pointer 2 may represent a second Roman alphabetic character) . Either -with or without parity, the four byte data packet becomes 20, 58, 40 and 40, where the head code byte is 20 or 0000 0100, most significant bit first.

The process of displaying a Korean character will now be described in more particular detail in connection with a discussion of Figures 5A through 6B, 7A and especially in view of Figure 9. By way of example, the first consonant of a Korean syllable may be the letter component that looks like an upside down "L". The possibilities for drawing this letter component are shown in decimal in Figure 6A, represented by decimal code 138. In hexadecimal in Figure 7A, they are shown as 20 02, 30 05, 40 08, 50 06, 70 0C, 80 OA, 90 OD, AO 10, and BO OE. Let us further assume, that of these choices, it is predetermined by the selected pointer code, that the letter component is of the type E variety as per Figure 5A and 6A, wherein, this consonant is the first of a three component syllable and begins at coordinate (0,0) of a character or letter block. Now, Figure 5B shows a typical character block with certain starting coordinates indicated. Character type E being a 10 x 8 letter component will subsume the entire top half of the character block. For examples of syllables including this consonant, see Figure 4 at coordinates (1,19) and (1,20). Other examples of type E letter components are shown in Figure 6A, where 10 x 8 represents partial character cell overall dimensions. The table of letter component types of Figure 6A is continued in Figure 6B also showing size in picture elements and starting coordinates for each of letter component types A through M. And as already described, now that a ^' three component character is assumed, the vowel and final consonant will be given by table Figure 6B.

Figure 9 represents nibbles read in order from character ROM 111, which may be a non-volatile memory of the decoder of Figure IB wherein characters are formed from top to bottom and from left to right. Thus, nibbles 0 through 3 represent no image. The first bit of image is represented by the first bit read from nibble 4. The produced image shown is X . . . shown from the top to halfway down the third column of the produced partial image.

This partial image is then stored for display with another partial image filling the bottom half of the character block, for example, a type M letter component of an upside down "T" or horizontal line beginning at (0,10) per Figure 5A.

For another example of character drawing, refer to Figure 5B in which it is shown that a type J letter component or character comprises a 6 x 10 image beginning at (4,0) as per Figure 5A. The bottom portion of the page shows that nibbles are read from character ROM 111 from top to bottom and from left to right. The third nibble, nibble 2,0 to 2,3, runs from the bottom of the first column to the top of the second column. In succession, the first printed nibble is nibble 5 at the top of the third column. Since (6,0) is a 1, the respective picture element is filled, as is (6,2) and so on, depending on the type J letter component or syllable portion to be displayed and the status of the bit for the picture element stored in character ROM 111.

Referring to Figure 5B, three hundred twenty-seven characters may require a character or letter component ROM less than 32k in size. In particular, referring to Figures ^A, 7B and 7C, there are 327 different letter components shown for display which are the same 327 letter components used for calculating character ROM size as per Figure 5A. There are 208 letter components in Figure 7A, 77 in Figure 7B and 42 shown in Figure 7C. These letter components may be selectively displayed to generate the three hundred most common Korean syllabic characters shown in Figure 4.

Many methods may be employed for providing simultaneous English and Korean captioning. One method is to allocate first and second language channels to line 21 field one and line 21 field two respectively. A decoder may be equipped with a simple switch to decode either the first or second language. Another method is to apply a single language channel for both languages. For example, the decoder may determine if the pointer is to point to Hangul or Roman alphabet components by evaluating the bytes of the data packet or the resultant pointer bytes. For example, if a letter component byte 0 and byte 1 are equal to 0, then byte 2 of the three pointer bytes may be a 7 bit English character pointer.

In regard to one embodiment of the present invention, bit positions 5 and six may signal the corresponding decoder as follows. If a 0,0 is transmitted in bit positions 5,6, the character is not-printable and the data represents a control code. If 0,1 are transmitted, the 1 in bit position 5 means that a 1 is placed in the corresponding bit position 5 of the pointer. Similarly, a 0 in bit position 5 if 1,0 are transmitted means that a 0 is mapped into pointer byte bit position 5. In this manner the evaluation of a particular pointer byte may be predetermined, and, consequently, the determination of Roman or phonetic alphabet pointer. A 1,1 in positions 5,6 is reserved to indicate the first byte of a Korean (dual language) data packet of four bytes. Whether English is transmitted or Korean, either a Han'gul syllable or an English alphabetic or numeric character will require four successive printable ASCII characters. As defined above, these four ASCII characters comprise a Korean (Roman alphabet or Han'gul phonetic alphabet) syllable block. The resulting data rate is, for Han'gul alphabetic characters, fifteen syllables per second. In English, the character rate is thirty characters per second. Either is more than sufficient data throughput for closed captioning in either language.

Referring now to Figure 8A through 8D, there is shown a flowchart for a decoding process employed at a decoder or television receiver incorporating the closed caption processor 109 of Figure IB according to the present invention. The algorithm thereby represented is most conveniently adapted for inclusion in integrated circuit form, preferably, for example, as control software for an I.T.T. 40 pin ASIC integrated circuit as per controller 115 of Figure IC. The algorithm described by the flowchart is similar to the algorithm employed in the prior art decoder of Figure IA. Nevertheless, the present invention, as further described by the bitmapping diagram of Figure 3, further may include the steps of determining if the data packet comprises Han'gul or other syllabic language caption data and English or other language caption data employing the Roman alphabet and forms letter component pointer bytes for pointing to respective letter components in Korean character (letter component) ROM memory 111.

Referring first to Figure 8A and Figure 8B, being a continuation of Figure 8A, and then to Figures 8C and 8D, there is shown a flow chart of a decoder processor algorithm for receiving the two bytes of character data via a particular line, such as line 21, of a television signal's vertical blanking interval. From a cold start of the decoder according to Figure 8B at box 810, the decoder controller 109 proceeds to run initialization software. Any pending Korean syllable is cleared and any error flag is cleared. Then, at box 811, the controller 109 of Figure IB awaits data received from data extractor circuit 107. The first decision is whether the first byte received represents a non-printing character. For example, a head code or tail code is first distinguished from a non-printing command code from its value. If the answer is "no", then the byte is assumed to be either a head code or a tail code of a printable character. Figures 8C and 8D are then entered. Referring first to Figure 8C, decision boxes comprising the path 801 through 804 show an error-free path for receiving the two printable character bytes comprising a head code and a first tail code 0. In this scenario, the decoder processor first checks parity and having determined that parity is passed, decodes the received data bytes by stripping parity from the received data. Having passed parity, the first byte is regarded for the characteristics of a head code. Once it is determined that the received data relates to printable characters, the head code is distinguished from the tail codes, for example, by predetermined bit position determination as per Figure 3 (a 10 in respective bit positions 6 and 7, for example, where a tail code has a 1 in bit position 7) . Assuming the first byte of the two bytes received is determined to be a head code of a printable character or letter component, the flowchart moves from box 802 to box 803. Box 803 asks if there is a pending partial syllable. If this is a head code, tail code 0 transmission, there should be no pending partial syllable condition, therefore box 804 should be entered. Appropriate pointer registers of display random access memory 110 can then be loaded, following Figure 3, with received data. At this point in time, a partial syllable is received in a register for pointer 0 of display RAM 110 and a partial syllable pending flag is set for reading, for example, at the next entry of box 803. Also the sixth and seventh bit positions of registers for pointers 1 and 2 respectively are set in display RAM 110 at this time.

Assuming that at box 803 there is a pending partial syllable flag stored in memory, then an error block is put up, the pending partial syllable is dumped because it is presumed to have been received in error and then the error cleared. An error block display most conveniently comprises a character that appears as a square subsuming the character cell.

Now, if the first data byte received is not a head code of a printable character, then it is assumed that it must be tail code 1. Also, the second received data byte must be tail code 2. Consequently, box 805 is entered from the "no" output path of box 802. Now, there should be a pending partial syllable stored in display RAM 110, i.e. pointer 0 should be complete. Consequently, following the "yes" path from box 805 to Figure 8D, the next question at box 806 asks if there was an error. Of course, if there was no error flag set, then, the pointers 1 and 2 can be completed in display RAM 110. On the other hand, if there was an error, the same actions are taken as before, namely, put up an error block, dump the pending partial syllable and clear the error. Once the three pointers are generated and stored in display RAM 110, they are appropriately clocked out of display RAM 110 to uniquely point to a Korean letter component or Latin alphabet based character of character ROM 111 by timing circuit 106.

Now, if in Figure 8C, from box 801, the bytes do not pass parity, they are deemed unusable. At box 807, the question is asked if .there was a pending partial syllable, and if there was, the same action is taken, i.e., to put up an error block, dump the pending partial syllable and clear the error. If there is no pending partial syllable, the error flag is set and a null partial syllable is generated for display. Similarly, at the output of box 805, if there is no pending partial syllable, the error flag is set and a null partial syllable generated for display. ^'

Now, referring again to Figure 8A, if at box 812, the received byte is determined to be a non-printing character, the path follows to box 813. There should be no pending partial syllable preceding transmission of a non-printing character, even a mid-row code. Thus, if the answer at box 813 is yes, the action is taken to put up an error block, dump the pending syllable and clear the error, if set. If there is no pending partial syllable at box 813, the second byte is examined for parity at box 814, the first byte at 815, and, if they both pass parity, the data, stripped of parity, comprising the non-printing character is further examined at box 816 to fall within the range lOh to lFh. If the data is not in the prohibited range, then a valid control pair exists. If byte two fails parity, both bytes are ignored. If byte two passes but byte one does not, an error block is put up. The circle A of Figure 8B represents a return to circle A of Figure 8A and to box 811, awaiting the next data byte pair from data extractor 107.

Figure 10 shows representative examples of captioning in English and Korean on a typical television display according to the present invention. The English characters are displayed in smaller size, typically 1/2 inch per the prior art, while Korean characters may be as large as 3/4 inch, because of the standard resolution presumed for today's television sets. With the advent of so-called enhanced and especially high definition television, it will be possible to somewhat reduce the size of Korean captions, for example, back to 1/2 inch in height. Furthermore, .while the present invention has been described in terms of television transmission, the principles of the present invention are likewise applicable to video telecommunications transmission and associated display devices. Furthermore, the present invention may comprise a portion of a separate decoder device such as the caption decoder of Figure IA or be built into a television or audio/video telecommunications device.

Thus, there has been shown and described a method and apparatus for providing closed captioning, text and other services in two languages which meets the objectives of the invention which should only be deemed to be limited by the scope of the claims which follow.

Claims

1. In decoder apparatus for decoding recorded audio data received on particular horizontal lines of a vertical blanking interval of a composite video signal, a method for decoding the recorded audio data characterized by the steps of decoding data packets, each data packet comprising a plurality of data bytes, the data packets indicated by particular bit indications appearing in one of the plurality of bytes of each data packet, storing a plurality of letter components in memory for at least two languages, a first language having the Roman alphabet and a second language having a syllabic alphabet, determining if the data packet represents a non- v printable character, and mapping remaining bit positions of the data packet for a printable character into a number of letter component pointer bytes less than or equal to the number of bytes comprising the data packets, the letter component pointer bytes for pointing to a Roman alphabet letter or a syllabic alphabet letter component in memory for display.

2. A method according to claim 1 wherein the number of bytes of each data packet is four.

3. A method according to claim 1 wherein the number of bytes of each data packet is three.

4. A method according to claim 1 wherein each data packet comprises one head code and three tail codes.

5. A method according to claim 1 wherein each data packet comprises one head code and two tail codes.

6. A method according to claim 2 wherein the number of letter component bytes is three.

7. A method according to claim 1 further comprising the step of generating a letter block for display.

8. A method according to claim 7 further comprising the step of displaying a syllabic language syllable approximately three quarter inch in height on a standard resolution television screen.

9. A method according to claim 7 wherein the letter block comprises two or more letter components.

10. A method according to claim 1 further comprising the step of evaluating at least two predetermined bit positions of each byte of the data packet.

11. A method according to claim 10 wherein the predetermined bit positions of each byte of the data packet comprise no more than two predetermined bit positions.

12. A method according to claim 10 wherein each byte of each data packet comprises eight bits and the predetermined bit positions comprise at least bit position 6.

13. A method according to claim 1 further comprising the steps of determining whether a letter component pointer byte is equal to a particular value and retrieving a Roman alphabetic letter component or a syllabic language letter component from memory.

14. A method according to claim 1 further comprising the initial step of counting lines to determine one of two fields, each field representing a particular language channel.

15. Apparatus for decoding recorded audio data received on particular horizontal lines of a vertical blanking interval of a composite video signal, the apparatus comprising a data extractor for extracting the recorded data from the particular horizontal lines of the vertical blanking interval and outputing the extracted data, a closed caption data controller, responsive to the data extractor, for stripping parity from the received data, for determining if the data comprises a printable character, and for outputing pointer data, a display random access memory having a plurality of pointer registers responsive to the closed caption data controller, and a character memory, responsive to the display random access memory, for outputing selected character data, the apparatus characterized in that the closed caption data processor further determines the identity of a head code or a tail code of printable character data from predetermined bit positions of the received printable character data, the printable character - data representing a syllabic character or a Latin alphabet character and comprising a first plurality of bytes, the first plurality of bytes of printable character data being translated into a lesser number of letter component pointer bytes and the display random access memory stores letter component pointer data for uniquely pointing to a syllabic character letter component in the character memory.

16. The apparatus according to claim 15 further characterized by a closed caption overlay circuit for overlaying a plurality of letter components output from the character memory to replace input video picture data, the remaining video picture data and the overlaid letter components being output for display on an associated screen.

17. The apparatus according to claim 16 further characterized in that a plurality of overlaid letter components output from the closed caption overlay circuit comprise a syllabic character for display.

18. The apparatus according to claim 15 further characterized in that the character memory comprises memory for storing display data for approximately three hundred twenty-seven letter components.

19. The apparatus according to claim 17 further characterized in that the overlaid letter components comprise a letter block having a size of 10 x 16, each letter component being identified by predetermined starting coordinates and predetermined dimensions within the letter block.

20. The apparatus according to claim 15 wherein the first plurality of printable character data bytes comprise a head code and three tail codes.