Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1982-11-22
1986-09-09
Groody, James J.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358141, 358142, 358146, 340723, 340728, H04N 7087, H04N 708
Patent
active
046112278
DESCRIPTION:
BRIEF SUMMARY
STATEMENT OF THE INVENTION
The present invention relates to television systems and more particularly to a method of apparatus for decoding digital information processed for inclusion in a wide band T.V. video signal.
BRIEF DESCRIPTION OF THE PRIOR ART
In any normal television system, the transmission of the wide band video signals which are to produce the actual picture elements on the screen of the receiver is interrupted between the scannning periods for line and field synchronization purposes. Consequently, there are periods during which no video signals are being transmitted. It is now possible to use these periods for the transmission of data which is not necessarily concerned with the video transmission itself.
Basically, data representable by standard symbols such as alpha-numeric symbols can be transmitted via a restricted channel provided that the rate of transmission is restricted. It is now possible to use periods as aforesaid especially the line times of the field blanking intervals (i.e. the times of the individual lines occurring between fields which correspond with the times occupied by video signals on active picture lines), for the transmission of pages of data. Typically, using 8-bit digital signals representing alpha-numeric characters (7 bits of data plus 1 bit for protection) at a bit rate of 2.5M bit per second, 50 pages of data each consisting of 22 strips of 40 characters can be transmitted repeatedly in a total cycle time of 90 seconds using only a single line of the field blanking period per field of the 625 lines system as operated in the United Kingdom.
Data transmission as described above is already commercially available in the United Kingdom under the name "Teletext", and transmitters and receivers are described in more detail in our U.K. Pat. Nos. 1,486,771; 1,486,772; 1,486,773 and 1,486,774.
Existing teletext displays consist of 40 characters per row and 24 rows per page. The U.K. teletext transmission standard specifies a data rate of 6.9375 Mbits per second (which has proven to be at the upper reasonable limit of transmission rate for system I, B/G system) so as just to achieve transmission of a complete row of text on one video line of the field blanking time.
The advantage of conveying one row of text on one video line is to achieve maximum economy in requirements for transmission of addressing information needed to correctly position the text information on the displayed page. Since whole rows of text are transmitted on each line, only a row number need be transmitted with each data line of text. Row zero which acts as the page demarcation signal requires additional page numbering information and also incorporates various display and interpretation codes appropriate to the particular page. In order to facilitate parallel magazine working every row of text also incorporates a 3-bit magazine number, being the most significant digit of the page number.
The above structure incorporating as it does one text row on every data line thus results in a very efficient utilization of the transmission facility. However, the existing Teletext transmissions do have limitations in so far as they are less satisfactory when in a "graphics" mode as compared with an "alpha-numeric" mode.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a system of digital transmission which will produce improved pictures when in the "graphics" mode while being compatible with existing U.K. Teletext transmissions. The type of graphics in which we are interested is usually termed alpha-geometrics but in this specification is called high resolution graphics (HRG).
The present invention provides a television receiver system having a parallel binary memory device, an input for receiving a demodulated television signal carrying, during picture-free periods thereof, a set of pages of information represented by serial binary signals provided in a repeated cycle, the form of which is such that the binary signals for the set of pages are received in groups, which groups are received
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Brockhurst David M.
Day Stephen
Dyer Martyn R.
Vivian Roy H.
Groody James J.
Independent Broadcasting Authority
Parker Michael D.
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