KR20000068854A - Teletext - Google Patents

Abstract

In order to decode the teletext data of the entire field using a conventional teletext decoder that recognizes only the teletext data contained in the lines of the vertical blanking interval, the data of the entire field is less than or equal to the number of lines in the vertical blanking interval. The channel is divided into a plurality of channels each occupying the number. Data from one selected channel of the plurality of channels is delayed such that the data is generated in the next vertical blanking interval before being applied to the decoder.

Description

Teletext {TELETEXT}

The present invention relates to a method and apparatus for transmitting and / or decoding teletext signals.

Typical teletext signals are transmitted in the vertical blanking interval (VBI) of the video signal, which typically occupies up to 15 lines per field. However, if no video signal is present and the channel is used only for the transmission of teletext data, for 625 lines of PAL television signal, about 300 lines per field may be used. This configuration provides approximately 20 times the capacity of regular teletext transfer capacity, allows more pages to be transferred, and / or reduces access time for each page. However, teletext decoders, such as those typically implemented inside television receivers, cannot receive teletext data of the entire channel. This occurs as a typical teletext television receiver expects, and can only receive teletext data in the VBI. Thus, in the case where a television is connected to a cable channel, for example carrying a teletext of the entire field, access to this data can only be achieved by having a special teletext decoder. This is obviously inconvenient for the user and may mean that there will be much less potential listeners for the channel transmitting teletext over the entire field. Moreover, the potential user base for teletext information of the entire field provided by the cable television, such as data pre-recorded on a record carrier such as video tape, is also reduced.

After all, it is an object of the present invention to enable decoding of teletext transmissions of the entire field using conventional teletext decoders.

The present invention provides a method of transmitting teletext data,

a) transmitting said teletext data during at least some field periods outside of a vertical blanking interval (VBI);

b) dividing the teletext data into m separate data streams each occupying up to n lines, where m and n are integers and n is less than or equal to the number of lines in the VBI. It provides a method characterized by.

This method can be used in particular for cable television having a plurality of channels in which one of the plurality of channels is dedicated to the transmission of data. The data may be formatted in a standard teletext format and transmitted during the VBI as well as during the normal active picture period. By dividing teletext data into a plurality of separate data streams each occupying a number of lines less than or equal to the number of lines in the VBI, a standard teletext decoder can be used in a receiver for receiving teletext data. Obviously, each data stream may contain a different number of lines unless they exceed n, and the number of lines may vary depending on the amount of data to be transmitted.

The teletext data may be recorded on a recording medium. Thus, a recording medium may be provided which may be in the form of a disk or tape and which has been previously recorded with data which is accessible and readable using a standard television receiver. In order to obtain satisfactory reproduction from the teletext data recorded on the VHS videotape, the teletext data can be recorded as a multilevel signal at a data rate lower than the standard teletext data rate. It is well known that standard VHS video recorders cannot satisfactorily record and play back standard teletext data due to limited bandwidth. Apparatus for allowing teletext data to be recorded and reproduced by a VHS video recorder is disclosed in Applicant's co-pending UK patent application No. 9605614.8 (PHB 34056). This co-pending patent application describes a device in which teletext data is recorded as a multilevel signal at a data rate lower than the standard teletext data rate. The recorder also has circuitry for converting the received standard teletext data into a multilevel code and inversely converting the multilevel code into standard teletext data upon reproduction. Since the prerecorded teletext data is already recorded as a multilevel signal, it is of course not necessary to convert the standard teletext into a multilevel signal in the video recorder when the prerecorded tape is played back. In this case, only a device for encoding a multilevel code into a standard teletext code is needed.

Each data stream can occupy 15 lines, which corresponds to the number normally occupied by teletext transmission in the vertical blanking interval. In this case, the number of data streams may be 20. This will occupy a total of 300 lines per field.

Furthermore, the present invention relates to a record carrier having teletext data extending during at least a portion of a field period outside of the VBI, wherein the teletext data is divided into m separate data streams each occupying up to n lines. Where m and n are integers and n is less than or equal to the number of lines in the VBI. The recording medium may be a VHS tape, and the teletext data may be stored as a multilevel code at a data rate lower than that of standard teletext data.

According to this, data can be provided on a decodable recording medium using a standard teletext decoder inside a conventional television receiver, where the main requirement is that the television receiver comprises a teletext decoder. Especially in the UK, since most televisions are currently equipped with a teletext decoder, the data can be reproduced by the television from the record carrier and a larger amount of data is available than can be transmitted in a teletext service in the VBI. Do. Of course, it is not essential that the teletext data occupy the entire field or that the teletext data extends out of the VBI interval in all parts of the recording medium. It may be convenient to have the video interspersed with teletext data at the full field rate. In addition, it is not essential that all lines within the data stream are used or that all data streams contain the same number of lines.

Moreover, the present invention relates to a method for decoding teletext data transmitted using a method according to the present invention or reproduced from a recording medium according to the present invention,

a) selecting one of the m data streams of the received teletext data,

b) applying to the teletext decoder teletext data comprising the selected data stream during the VBI. The decoding method according to the invention allows a standard teletext decoder to decode data transmitted or reproduced from a record carrier since one data stream can be selected and time shifted to be generated during VBI. Thus, a standard teletext decoder can recognize a teletext signal and decode the signal to provide an appropriate indication on a TV receiver display.

Moreover, the present invention provides a video reproducing apparatus for reproducing teletext data recorded on a recording medium, comprising: means for selecting one of a plurality of streams of teletext data for reproduction, And a means for making the stream available for output.

Thus, a playback apparatus such as a video cassette recorder has means for encoding teletext data recorded on a video tape in a standard teletext format and delaying its output until the next VBI. According to this, the television receiver clearly receives a standard teletext signal selected from one of a plurality of streams of teletext data generated outside of the VBI during the VBI.

Furthermore, the present invention is directed to a television receiver arranged to receive teletext data transmitted by the method according to the invention, comprising means for selecting one of the m streams of teletext data and the next or subsequent VBI. And means for delaying the application of the selected stream to the teletext decoder until generation.

Thus, by providing selection and delay means in the television receiver, a selected stream of teletext data can be applied to the teletext decoder during VBI. According to this, the standard teletext decoder recognizes the teletext signal and decodes the given teletext signal.

Moreover, the present invention provides a decoder for decoding a television signal comprising teletext data generated by the method according to the present invention, wherein one of m data streams is selected to select a teletext decoder during the VBI. It provides a decoder comprising a means for applying to.

The decoder may, for example, be a so-called set-top box that may be installed to decode digital video broadcasts from satellite or terrestrial transmitters or to decode cable television signals. The decoder may generally include access control and charging means for charging a channel or pay-per-view application, for example.

These and other features and advantages of the present invention will become apparent from the following detailed description of embodiments of the invention given with reference to the accompanying drawings in which:

1 to 3 show teletext data signals of regular and full channels,

4 is a timing diagram illustrating how a selected service is time shifted.

5 is a block diagram showing reproduction of teletext data from a video cassette recorder according to the present invention;

FIG. 6 is a block diagram illustrating a service selector function of the video cassette recorder shown in FIG. 5.

7 shows a combination of a teletext data service and a reduced height television picture,

8 illustrates a process of selecting a specific data stream from a plurality of data streams.

FIG. 1 shows a typical television signal comprising teletext data transmitted in the vertical blanking interval indicated by period A in FIG. 1 and television image information transmitted during the remaining period of the field period indicated by period B in FIG. It represents one field. Typically, the teletext decoder is arranged to retrieve teletext data during lines 6-22 of field 1 and lines 319-335 of field 2. This is for a standard 625 line PAL television signal. In contrast, as shown in FIG. 2, the teletext signal of the entire channel occupies the entire length of the field except for the short field synchronization sequence. Thus, the teletext data replaces the television picture signal during the B periods of the television field. This full channel teletext signal is known, but cannot be decoded by a standard television receiver since the teletext decoder is set to retrieve teletext data only during VBI. One reason for restricting the teletext decoder to retrieve teletext data only during VBI is to prevent false detection of teletext signals by television images similar to teletext data. Thus, certain picture content may produce a signal similar to teletext data, whereby the teletext decoder decodes it as teletext data. However, by having the teletext decoder retrieve only teletext data during VBI, the possibility of such picture content causing false detection of teletext data can be ruled out. In this case, however, there is a corresponding disadvantage that the text data of the entire channel cannot be decoded.

3 shows the teletext data of the entire channel divided into a plurality of separate data streams each having a duration less than the length of the VBI. In this case, the teletext data may be divided into 20 separate data streams each occupying 15 lines. Of course, if the number of lines in this data stream is less than or equal to the number of lines in the VBI, then each of these 20 separate data streams need not occupy the same number of lines. Moreover, it is not essential that all lines in any data stream are occupied by teletext data. Each of these 20 separate data streams, for example, provides individual services so that 20 services can be transmitted and the user can select them.

In order to decode the teletext data of the entire channel, one of the 20 separate data streams is selected, and means are provided for moving the occurrence of the selected data channel to a period corresponding to the VBI.

4 shows this process. Assuming that data stream 6 is selected as the enable signal as shown in FIG. 4A, a circuit such as that shown in FIG. 4B is generated that allows data inside data stream 6 to be written to the buffer memory. This is shown in FIG. 4. Thus, data is usually written to the buffer memory in the line occupied by channel 6 of the teletext data when it contains the TV picture signal but the text of the entire channel is conveyed. The buffer memory is then read during the VBI of the next field, as a result of which the standard teletext decoder recognizes this as text data. Thus, by dividing the text data of the entire channel into m streams each occupying n lines, one of these data streams can be selected and applied to the teletext decoder during VBI. In a particular embodiment, m is 20 and n is 15. These numbers are not essential and all that is required is that the number of lines in each data stream is less than or equal to the number of lines in the VBI, or within the number of lines the teletext decoder can contain teletext data. It should be, and the number of streams depends on how many lines are present in the television field and whether you want to fully occupy the television field by teletext data.

The source of teletext data may be conventional television transmissions from terrestrial transmitters, satellite transmitters or cable television services. Alternatively, the source may be a recording medium, for example an optical disc or a magnetic disc. In the case of the proposed digital service from a cable television system or satellite broadcast, or from a cable satellite or terrestrial transmitter, there is a decoder box inserted in front of a standard television receiver. Such a decoder box can be arranged to convert the transmitted signal from one encoding format, for example to a PAL system, or to provide RGB output. In the former case, a teletext decoder can be placed inside the television receiver since the television receiver receives at least one CVBS signal containing encoded teletext data, in the latter case the decoder box is a teletext signal. Because is the place where it can be and can be decoded, the teletext decoder should be placed inside the decoder box. For reproduction from an optical recorder or video tape recorder, the teletext decoder can be present inside the player or television receiver. In the case where the teletext decoder is present inside the television receiver, of course, the connection from the playback apparatus to the television receiver needs to have a CVBS form or inversely modulated to the PAL channel.

It is well known that standard teletext data cannot be successfully recorded and reproduced from a VHS video cassette recorder. This is because the bandwidth of the recorder is insufficient for the bandwidth of the teletext signal. Thus, a non-decoded distorted signal is generated upon reproduction, so that reception of satisfactory teletext cannot be achieved. However, the technique disclosed in UK patent application 9605614.8 (PHB 34056) allows the recording of teletext data on VHS tapes. This patent application describes a VHS video recorder comprising an encoding device that receives teletext data and encodes it into a multilevel signal at a transmission rate of half the standard teletext transmission rate. Thus, each aggregate of two bits is encoded using four level codes, which are recorded on tape. At the time of reproduction, a complementary decoder is used which converts the 4-level code back to standard teletext data and then applies the standard teletext data to the teletext decoder placed inside the VCR or the television receiver to which the VCR is connected. . Details of such encoding and decoding, and details of video cassette recorders capable of performing these functions, are described in Applicant's co-pending patent application No. 9605614.8 (PHB 34056), the contents of which are for reference. It is incorporated within this specification.

5 is a block diagram schematically illustrating the playback function of a VCR in which a teletext signal is encoded according to the configuration outlined in the co-pending patent application described above and a full channel teletext service is provided. Since the actual source of the data on the tape is not important in the present invention, only the playback function is shown in this block diagram and the long function function is not shown. Therefore, this may be for a pre-recorded tape marketed by a service provider or recorded by a user directly, which recording process is not directly related to the present invention. As shown in Fig. 5, the reproducing function includes a tape reproducing head 1 for supplying a signal to the luminance processor 2. The luminance processor is simply a standard VCR luminance processor. The output of the luminance processor is given to the decoder 3 and the control and timing circuit 4 and the multiplexer 5. The output of the decoder 3 is supplied to the buffer memory 6, and the output of the buffer memory is supplied to the teletext encoder 7 which converts the output of the buffer RAM into standard teletext data form. The control and timing circuit 4 takes timing information from the signal generated by the luminance processor 2 and controls the operation of the decoder 3. Accordingly, the decoder 3 decodes the data output from the luminance processor at an appropriate time during each line period under the control of the control and timing circuit 4. For simplicity, the decoder can be set to decode such data every line, and the output of the decoder is read into the buffer memory 6 under the control of the service selector 8. Thus, the service selector 8 allows data to be written into the buffer memory 6 only when the selected service is output by the luminance processor 2. The output generated from the control and timing circuit 4 is directly connected to the buffer memory 6 as a read enable signal that causes the data in the buffer RAM 6 to be read by the teletext encoder at regular VBI time. Thus, data written to the buffer RAM during the normal video period of the field is stored in the buffer memory 6 and read out during the subsequent VBI. In order to be able to select a particular service, the recorder is provided with a remote control receiver 15 which receives a signal from the remote control handset 9. Accordingly, the command input to the remote control handset 9 is detected by the receiver 15 and supplied to the control and timing circuit 4. This allows the service selector 8 to generate a write enable signal to the buffer memory 6 at an appropriate time, so that the selected data stream can be written to the buffer memory 6. The multiplexer 5 is controlled by another output from the control and timing circuit 4 so that the teletext encoder 7 depends on whether the teletext or mixed teletext and video signals of the entire channel are recorded on the tape. Data from or video from the luminance processor 2 is selected. The output of the multiplexer is a CBVS signal supplied to the output 10 and connected to a television via a SCART connector, or supplied to the modulator 11, where the output of the multiplexer is modulated on the UHF carrier to output 12 Is given to the antenna output of the associated television receiver.

6 is a schematic block diagram of one embodiment of a service selector 8 as shown inside the VCR of FIG. The service selector has an input 80 given to a register 81, which stores the service number requested by the user. The output of the register 81 is supplied to the first input of the comparator 82, and the second input of the comparator is connected to the output of the service counter 83. Input 84 of service selector 8 receives a plurality of pulses at a line frequency, which is fed to line counter 85. The line counter also receives a reset signal from the input 86 and resets the line counter at the end of each field. The line counter has an output connected to the service counter 83. Thus, in the illustrated embodiment, the line counter increments the service counter every 15 lines. The output of the comparator 82 is given to the first input of the multiplexer 82, and the second input of the multiplexer receives a timing signal via the input 88. A control signal is supplied to the input 89 which controls which input of the multiplexer 87 is given to the output 90. This control signal 89 indicates whether a typical mixed teletext and video signal is present or whether teletext data of the entire channel is present. The timing signal at input 88 corresponds to the normal VBI timing that is selected when a mixed teletext / video signal is present. In the case where there is teletext of the entire channel, the output of the comparator is fed to the output 90 as a write enable signal to the buffer memory 6, which means that the decoded data is present if the required service stream is present. Read into the buffer memory 6. In other words, the output of the comparator causes a write enable signal to exist for 15 lines, during which the selected service is decoded.

7 illustrates a situation in which increased teletext data may be transmitted while a TV image of reduced height is being transmitted. This is the case, for example, when the transmission of an image in the form of a mailbox occurs, so that part of the active image line becomes available for teletext data. Thus, an image with an aspect ratio of 16 x 9 displayed on a television of 4 x 3 aspect ratio leaves some lines available for further teletext data service at the top and bottom of the image. The teletext data included in these lines can be time shifted in the same way that teletext data of the entire channel is time shifted to VBI.

8 illustrates a process of selecting a specific data stream from a plurality of data streams transmitted as teletext signals of all channels according to the present invention. Box 90 shows the process of reading data from the tape indicating whether data of the entire channel is available. After reading this data from the tape, an on-screen display at box 91 is initiated, prompting the user to select which channel to display. This is accomplished by the user pressing a numbered key on the remote control. This step is shown in box 92 where the user enters a number from the remote control. Then, as shown in box 93, the on-screen display confirms which service is selected. Accordingly, the on-screen display informs that the user has selected service 6, for example. Then, in box 92, this number is entered into the service number register 81, so that the service selector selects this particular data stream.

From the context of the present invention, further modifications can be made by those skilled in the art. Such modifications may, in addition to, or in addition to, other features already known in the design and use of television receivers and / or video recorders, including teletext decoders and components thereof, as already mentioned herein. It may include other features that may be used. Although the claims are formulated in this application for specific combinations of features, regardless of whether they relate to the same invention as the one currently claimed in any claim, some or all of the same technical problems as the present invention solved. Irrespective of whether or not a solution is made, the scope of the present invention is expressly or implicitly disclosed with the novel features or novel combinations of the features, and one or more obvious to those skilled in the art to which the present invention belongs. It should be interpreted as including the general description of the above features. Accordingly, new claims may be drawn up for such features and / or combinations of these features during the review process of this application or another application derived from this application.

Claims (16)

In a method of transmitting teletext data, a) transmitting said teletext data during at least some field periods outside of a vertical blanking interval (VBI); b) dividing the teletext data into m separate data streams each occupying up to n lines, where m and n are integers and n is less than or equal to the number of lines in the VBI. How to feature. The method of claim 1, The teletext data is transmitted via a cable television channel. The method of claim 1, The teletext data is recorded on a record carrier. The method of claim 3, wherein And the recording medium is a VHS video tape. The method of claim 4, wherein And said teletext data is recorded as a multilevel signal at a data rate lower than a standard teletext data rate. The method according to any of the preceding claims, n = 15. The method according to any of the preceding claims, m = 20. A record carrier having teletext data extending during at least a portion of a field period outside of the VBI, wherein the teletext data is divided into m separate data streams each occupying up to n lines, where m and n is an integer and n is less than or equal to the number of lines in the VBI. The method of claim 8, The recording medium is a recording medium, characterized in that the VHS tape. The method of claim 9, And said teletext data is stored as a multilevel code at a data rate lower than the standard teletext data rate. A method for decoding teletext data transmitted by a method according to any one of claims 1 to 7 or reproduced from a recording medium according to any one of claims 8 to 10, a) selecting one of the m data streams of the received teletext data, b) applying to the teletext decoder teletext data comprising the selected data stream during the VBI. A video reproducing apparatus for reproducing teletext data recorded on a recording medium according to claim 8 or 9, comprising: means for selecting one of a plurality of streams of teletext data for reproduction and teletext data selected during VBI; Means for making a stream of video available for output. The method according to claim 12, wherein And a VHS video recorder, said video recorder comprising means for encoding the multilevel code read from the tape into standard teletext data. A television receiver connected to receive teletext data from the video reproducing apparatus according to claim 12. A television receiver arranged to receive teletext data transmitted by the method of any of claims 1 to 7, wherein the television receiver comprises: means for selecting one of the m streams of teletext data and the next or subsequent VBI; Means for delaying the application of the selected stream to the teletext decoder until generation of the television receiver. A decoder for decoding a television signal comprising teletext data generated by the method according to any one of claims 1 to 7, wherein the decoder selects one of m data streams to teletext the selected data stream during VBI. And a means for applying to the decoder.