WO2006003557A1

WO2006003557A1 - Method of decoding a teletext service

Info

Publication number: WO2006003557A1
Application number: PCT/IB2005/052061
Authority: WO
Inventors: Rajendra S. Sisodia; Herman J. R. Schmitz
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-06-28
Filing date: 2005-06-23
Publication date: 2006-01-12

Abstract

A method of decoding a teletext service broadcast to a receiver (1) and structured in pages, includes acquiring at least a part of a page's contents as broadcast at a first instance and acquiring at least a part of the page's contents as broadcast at a second instance. It further includes identifying sections of a displayable part, common to the acquired parts, of the contents of the page differing between the first and the second instance, and generating a signal for displaying at least the displayable part in such a manner that the identified sections are displayed in a distinctive manner.

Description

Method of decoding a teletext service

The invention relates to a method of decoding a teletext service broadcast to a receiver and structured in pages, including: acquiring at least a part of a page's contents as broadcast at a first instance and acquiring at least a part of the page's contents as broadcast at a second instance. The invention also relates to a system for decoding a teletext service broadcast to a receiver and structured in pages, including at least one module arranged to acquire at least a part of a page's contents, and at least one module for generating a signal for displaying a displayable part of a teletext page, wherein the system is configured to acquire at least a part of a page's contents as broadcast at a first instance and at least a part of the page's contents as broadcast at a subsequent instance.

The invention also relates to a broadcast receiver, for example a television set.

The invention also relates to a computer program for controlling a teletext decoder.

Examples of a method, system and receiver of the types mentioned above are known from US 5,729,298. The known television receiver includes a teletext decoder for receiving and displaying teletext page for signalling that a requested teletext has been changed or not changed with respect to the previous consultation of the relevant page. If a requested page has exactly the same contents upon reception as the previously consulted page of the same page number, an On-Screen-Display message is generated. In this message the user is notified of the fact that he has already seen the page before. If a requested page has a different content upon reception than the previously consulted page of the same page number, the page is displayed.

A problem of the known method is that it requires an on-screen-display generator to generate a separate signal and a separate command to be issued in order to view the page. Thus, the time between page request and display is increased and a more complicated broadcast receiver is required, due to the relatively complicated way in which alterations are brought to the attention of the user.

It is an object of the invention to provide a method and system of the types mentioned above that allow a user's attention to be drawn to changed page contents in a more effective manner.

This object is achieved by the method according to the invention, which is characterised by identifying sections of a displayable part, common to the acquired parts, of the contents of the page differing between the first and the second instance, and generating a signal for displaying at least the displayable part in such a manner that the identified sections are displayed in a distinctive manner.

The generated signal is suitable for displaying the changed contents of a page on a Visual Display Unit. Because the or each section is displayed in a distinctive manner, the user is alerted to changed contents. However, no prior interruption of the page selection process is necessary. An additional advantage is that the method is more informative. Because the sections are identified and displayed in a distinctive manner, the page need not be displayed so long, because the user will generally only want to gain knowledge of the changed sections. It is observed that a method of decoding teletext data broadcast to a receiver and structured in pages is also known from Siu, Y.K., Chan, CK. and Ho, K.L., "Rebroadcasting of real-time teletext data", /EEE transactions on Consumer Electronics, 22 (2), May 1993, pp. 131-135. That paper describes the design, implementation and performance analysis of a financial rebroadcasting system suitable for consumer use. It is capable of extracting real time financial data from a high speed full channel teletext data source and rebroadcasting it through the slow data rate telephone network. A PC AT based server is equipped with a teletext decoder. The server stores all available pages in the local memory. The database is regularly updated should there be changes in the teletext page. During normal operation, only new or changed data will be compressed and broadcast to the end user through the telephone network. At the receiving terminal, the receiving software will decode and process the serial data and then update its database for possible retrieval. A signal for displaying at least the displayable part of the page in such a manner that the identified sections are displayed in a distinctive manner is not generated. In a preferred embodiment, the step of identifying sections differing between the first and second instance is preceded by a step of determining whether the contents of the page have changed between the first and second instance, and the step of identifying sections differing between the first and second instance is carried out conditional upon detecting that the contents of the page have changed.

This increases processing efficiency, since detection of a change of contents can be carried out more quickly than a complete analysis to identify the differing sections of the contents. This embodiment is suitable for use when a teletext service with multiple pages with contents varying at different rates is broadcast. It is also suitable for decreasing the processing load on the system carrying out the method, when the rate of updates to a specific page varies.

In a preferred variant, the step of detecting a change in contents of the page includes deriving a characteristic from at least the contents of the page as broadcast at the second instance. The characteristic is thus derived by decoding the data in the teletext signal to analyse the contents. The characteristic may be derived by a calculation using the contents as input. An example would be the calculation of a digest of the displayable part of the contents. The characteristic could also be a flag in one of the (non-displayable) packets of the page. In another variant, a change in contents of the page is detected by detecting arrival at the receiver of a unit of teletext data encoding a section of a page of which the contents have changed relative to the section as broadcast at a previous instance.

This is a very efficient variant, since it narrows down the size of the contents within which the differing sections have to be identified. Indeed, the identification and detection will generally be combined into one process step if the data of which the arrival is detected encodes only the differing sections of the displayable part.

In a preferred embodiment of the method, at least the step of identifying sections differing between the first and second instance is preceded by a step of receiving instructions from a user input device, including a representation of a page address, selecting at least a part of the page for display, by a step of storing data representative of the contents of at least a part of the selected part in memory, and by a step of generating a signal for displaying the selected part a first time, wherein the page's contents as broadcast at the first instance are taken from the stored data. The effect is that sections differing relative to an earlier consultation (viewing) of the page are highlighted. Any versions of the page's contents broadcast between that time of consultation and the time of identification of differences may be ignored. The effect is that the required amount of data processing is limited. In a preferred variant of the method, the part of a page's contents as broadcast at a first instance is stored in memory and the step of generating a signal for displaying at least the display able part of the page includes combining only the identified sections of the page's contents as broadcast at a second instance with a remainder of the displayable part of the page's contents as broadcast at the first instance, wherein the remainder is retrieved from memory.

In a preferred embodiment, the displayable part constitutes a part smaller than the totality of displayable contents of the page and the method includes retrieving selection criteria and selecting the displayable part for identifying the differing sections in accordance with the retrieved selection criteria. The effect is that the data size of the contents within which the differing sections are to be identified is smaller. Processing is thus simplified. An additional effect is that the criteria can be adapted so as to highlight only a few types of displayable content. Thus, highlighting of a field showing the date and/or current time can be avoided.

A favourable variant of this embodiment includes receiving instructions representative of the selection criteria from a user input device and storing the instructions in memory for retrieval.

The effect is that only sections of interest to the user are identified. This again reduces the amount of data processing, as less of the contents have to be analysed to identify differing sections. Additionally, a more informative display can be generated from the signal for displaying the identified differing sections in a distinctive manner.

According to another aspect of the invention, the system for decoding teletext data is characterised in that the system further comprises at least one module adapted to identify sections of a displayable part of the contents of the page differing between the first and the second instance, and in that the system is configured to generate a signal for displaying the displayable part of the page in such a manner that the identified sections are displayed in a distinctive manner.

A module may be formed by a plurality of co-operating discrete devices or device components. The above-defined system provides an informative display of the contents of a page with dynamically changing contents. It allows a viewer to be made aware of updates in an effective manner.

According to another aspect, the invention provides a broadcast receiver, for example a television set, provided with a system according to the invention. The broadcast receiver is equipped with the tuning and demodulation functions to receive the broadcast teletext data. It is provided with the functionality providing the above-mentioned advantages of the system for decoding the teletext data according to the invention.

According to another aspect of the invention, there is provided a computer program for controlling a teletext decoder, adapted, when run on a programmable processing device, to enable the system including the programmable processing device and the teletext decoder to carry out a method according to the invention.

The computer may be a processor integrated with the teletext decoder on a single chip, or it may be a processor providing instructions for controlling a teletext decoder chip via a bus, for instance. Thus, the teletext decoder is adapted to provide the above- mentioned effects of the method according to the invention.

The invention will now be explained in further detail with reference to the accompanying drawing showing an example of a broadcast receiver suitable for implementing the invention.

The figure represents components of a television set 1 as an example of a broadcast receiver for implementing the invention. It is observed that the methods presented in the following could also be carried out in a separate data processing device arranged to receive the contents of teletext page broadcast to a dedicated receiver device. Such a data processing device would acquire a certain page's contents from the receiver device in the form of a data file containing character codes. The exact format of the data encoding the page's contents need not be the same as broadcast and received by the broadcast receiver in this, or in any other embodiment of the method.

In the television set 1 schematically shown in the figure, a radio-frequency signal is received at an input 2 of the television set 1. The received signal passes through an RF amplifier 3 to a tuning circuit 4. The tuning circuit 4 tunes to a specific carrier frequency, associated with a television channel. The output signal of the tuning circuit 4 is passed to a demodulation circuit 5. The demodulation circuit 5 separates video, audio and teletext components from the carrier signal. A colour decoder 6 retrieves and processes the video component. A teletext data acquisition circuit 7 retrieves teletext page data. It is noted that the method as presented herein is not limited to a particular kind of broadcast. In the present example, a signal carrying the data of the teletext service is carried in the vertical blanking interval of an analogue television broadcast signal. Several embodiments of the method presented herein are also suitable for digital television or Internet-based television broadcasts. In the former, the teletext service is, for example, broadcast in a separate MPEG transport stream by satellite, or through a cable network link. In the latter, the teletext service is broadcast in MPEG packets carried in (Internet Protocol) IP packets. The present example will focus on teletext services broadcast in the vertical blanking interval of an analogue television transmission, for example in accordance with European Telecommunication Standard (ETS) 300 706. Teletext data packets according to the above-mentioned standard each comprise forty- five bytes of data, of which the fourth and fifth byte define the packet address. The first part of the packet address encodes a magazine number, the second part a packet number. Packets with number zero are referred to as page headers. Packets with packet numbers one to twenty- five are normal packets, intended for direct display. Packets with numbers twenty-six to thirty-one are non-displayable packets. Following a page header packet, all subsequent packets up to a next page header packet in the same magazine relate to the same page. The page header packet comprises a page address, consisting of a page number and a page sub-code. In this manner, each packet in the service 'belongs' to a page, i.e. the service is structured in pages. A teletext service is broadcast in a carrousel. Some time after the packets grouped together under a certain page address have been broadcast, a new set of packets is transmitted under the same page address. The contents of a certain page or sub-page can be updated. Some pages have extremely dynamically varying contents, so that different data is broadcast under a certain page address at each instance of broadcasting packets addressable under that address. Other pages are relatively static, meaning that the same contents are broadcast every time packets of a certain page address are broadcast.

The television set 1 shown as an example is controlled by a microcontroller 8, which executes instructions stored in a Read Only Memory (ROM) 9 of a known type. These instructions control the operation of the television set so that the entire system is adapted to execute an embodiment of the method as set out in the present application. The microcontroller 8 further has access to a non- volatile memory 10, for storing data that must not be erased when the television set's power is turned off. Commands and data are transferred between the microcontroller 8 and the various components operating under its control via a bus 11, for example an I²C bus.

A user of the television set enters commands via a remote control unit 12, which exchanges data with a remote control interface circuit 13. The commands are passed to the microcontroller 8 via the bus 11. One command the viewer may enter is a command to change channels. This command results in a command from the microcontroller 8 to the tuner 4 directing it to tune to a different frequency.

When teletext is not being viewed, the output of the colour decoder 6 is passed to a multiplexer 14, which passes it unaltered to a video amplifier 15 driving a video display unit 16. The latter may be a cathode ray tube or a plasma display for instance. When a viewer elects to view teletext pages, an appropriate signal is generated by a display section 17 decoding teletext page data loaded into a teletext memory 18. The output generated by the display section is used by the multiplexer 14 to replace part (in the case of subtitles) or all of the video signal provided by the colour decoder 7.

The display section 17 is thus one type of module for generating a signal for displaying a displayable part of the contents of a teletext page. In this case, the signal is formed by the driving signals for the video display unit 16. In other implementations of the method illustrated herein, the module is a module for generating an analogue or digital video signal for transmission over a cable connection to a separate display device, for example a VGA or DVI signal. In yet another implementation, the signal is a modified set of teletext characters, in which the display format of certain characters or page elements has been changed by means of a method as set out below.

As noted, teletext page data is transmitted in a carrousel, implying that a certain amount of time elapses between the receipt of teletext page data encoding a first page and that encoding a further page. Even more time may pass between receipt of a particular page's contents as broadcast at a first instance and the same page's contents as updated and broadcast at a second instance. In order to be able to provide a faster response to a viewer- initiated command selecting a specific page, the television system comprises a teletext data cache 19. If a request for a specific page is received through the remote control interface circuit 13, the teletext data cache 19 is searched for the page. If it is found, it is transferred to the teletext memory 18. If not, the teletext page data encoding the requested page will have to be provided from the teletext data acquisition circuit 7, as soon as it has been provided by the tuning circuit 4 and demodulation circuit 5.

What is displayed to the viewer upon receipt of instructions including a representation of a specific page address, are the contents of the displayable part of the selected page or sub-page. According to the invention, certain sections of that part that have changed relative to an earlier, or first, instance of broadcast are displayed in a distinctive manner. This means that the display format of those sections is modified by the display section 15, so that the changed sections are identifiable as such. Examples of possible modification include use of a particular background colour, foreground colour, italic lettering, bold lettering and/or underlining. Combinations are, of course, possible. Different manners of emphasis for different sections within the same page are also possible, i.e. two or more differing sections within the same page need not be highlighted in a uniform manner. Depending on the method used, identification of sections of a selected page differing between a first and subsequent instance of broadcast may involve a relatively lengthy analysis of the page's contents. For this reason, the step of identifying sections differing between the first and second instance of broadcast is preferably preceded by a step of determining whether the contents of the page have changed at all between the first and second instance. Execution of the identification step is then only carried out if a change is detected. In one favourable embodiment, the television set is configured to receive and decode a special variant of teletext service. In this variant, contents of specific pages are updated dynamically by the provider of the teletext service. The teletext data is broadcast in order of page number, but rapidly varying fields within certain pages are transmitted more often in a specific data format and interleaved with the data broadcast in normal order. This may be done by inserting the page sections concerned into so-called extension packets belonging to a page with a different page address. The page address of the page to which the page section actually belongs in terms of its contents is included in the data following the packet number of the extension packet. Information allowing it to be correctly positioned within the page is also included. This information advantageously includes a reference to a keyword, rather than a particular screen position. The remainder of the page that is transmitted in the normal order then also includes a tag with a corresponding keyword allowing identification of the position of the field with rapidly varying contents. This facilitates combination of the updated section with the (static) remainder of the page. A priority indication is preferably included in the extension packet to ensure that the contents of the extension packet are acquired and decoded before packets belonging to pages with static contents.

The teletext data acquisition circuit 7 acquires the extension packet. The contents of the differing page section are retrieved from the acquired packet and combined with the remainder of the displayable part of the page as stored in the teletext data cache 19 or teletext memory 18. Thus, it is not necessary to acquire all the packets of the page when only the contents of a specific section have changed.

Receipt and subsequent retrieval of the differing page section also serve as a trigger, enabling detection of a change in contents of the page. Furthermore, the identification of the differing page sections merely includes decoding the contents of the extension packet(s) carrying the update.

Where the special variant of teletext service is not used, detection and identification of differing sections of the contents of a page or sub-page will be carried out by comparison of cached information representative of a part of the page's contents as broadcast and received at a first instance of broadcast with the subsequently broadcast and received version. A fast manner of detection is disclosed in US 5,729,298. This method is suitable for quickly determining the necessity of actually comparing the encoded contents of the two versions of the displayable part of the page. According to this method, a checkword is derived from the displayable contents of the page as broadcast at a first and at a second instance. Different checkwords are indicative of a change in contents.

A teletext service provider may also include a flag in the packets belonging to a page of which the contents have changed relative to a previous instance of broadcasting. The television set will then preferably use this flag as an even faster method of detecting a change in the contents of a certain page in the teletext service. Other detection methods are conceivable.

In a first variant of the method presented herein, sections of a selected, displayable, part of the contents of a page that differ relative to the last instance of broadcast and receipt of the page, or of the section concerned, are identified and displayed in a distinctive manner. This variant is easily and efficiently implemented, since the last received contents of the page are generally available in the teletext data cache 19 anyway. This variant thus requires little or no additional memory. It also leads to the identification of a limited number of page sections, since the number of changes between subsequent instances of broadcast is relatively small. In a second variant of the method presented herein, the contents of a displayable part of a selected page are compared with the contents of the selected page as selected and viewed on a previous occasion by means of the television set. In this variant, instructions are received through the remote control interface unit 13. The instructions include a representation of a page address, by which the page or a sub-page is selected for display. Data representative of at least a part of the page or sub-page is stored in memory. This part generally includes at least the part displayed on the video display unit 16. In the variant of the teletext service in which tagged page section updates are transmitted, only the value of the changing field at the time of display need be stored specially, as the remainder of the page is cached anyway. Thus, little additional storage capacity is required.

It is noted that the part of a selected page's contents that is included in the comparison with a previously broadcast version is generally smaller than the totality of the page's displayable contents. In particular, it is advantageous to exclude the displayable contents of the header packets, since these often comprise a real-time clock, changing continuously with each instance of broadcast.

The television set 1 may include a utility for personalising the display of the contents of a teletext page. This is of special advantage where rapidly varying sections are transmitted with a tag including a keyword. Sections in tags including keywords corresponding to a user's preset criteria are compared with a view to detecting and identifying changes, whereas others are not processed. Similar mechanisms may be used to allow a user to enter a particular page location as a criterion, for example a certain line in a page containing a table or Scoreboard. In that case, the broadcast contents need not be tagged.

It should be noted that the above-mentioned embodiments illustrate, rather than limit, the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "comprising" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several components, several of these components can be embodied by one and the same item of hardware. Conversely, the term module refers generally to a functional unit, which may be implemented in one or a combination of pieces of hardware, conceivably augmented by software. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. Method of decoding a teletext service broadcast to a receiver (1) and structured in pages, including: acquiring at least a part of a page's contents as broadcast at a first instance and acquiring at least a part of the page's contents as broadcast at a second instance, characterised by identifying sections of a displayable part, common to the acquired parts, of the contents of the page differing between the first and the second instance, and generating a signal for displaying at least the displayable part in such a manner that the identified sections are displayed in a distinctive manner.

2. Method according to claim 1, wherein the step of identifying sections differing between the first and second instance is preceded by a step of determining whether the contents of the page have changed between the first and second instance, wherein the step of identifying sections differing between the first and second instance is carried out conditional upon detecting that the contents of the page have changed.

3. Method according to claim 2, wherein the step of detecting a change in contents of the page includes deriving a characteristic from at least the contents of the page as broadcast at the second instance.

4. Method according to claim 2 wherein a change in contents of the page is detected by detecting arrival at the receiver of a unit of teletext data encoding a section of a page of which the contents have changed relative to the section as broadcast at a previous instance.

5. Method according to any one of the preceding claims, wherein at least the step of identifying sections differing between the first and second instance is preceded by a step of receiving instructions from a user input device, including a representation of a page address, selecting at least a part of the page for display, by a step of storing data representative of the contents of at least a part of the selected part in memory, and by a step of generating a signal for displaying the selected part a first time, wherein the page's contents as broadcast at the first instance are taken from the stored data.

6. Method according to any one of the preceding claims, wherein the part of a page's contents as broadcast at a first instance is stored in memory (10,17,19) and the step of generating a signal for displaying at least the displayable part of the page includes combining only the identified sections of the page's contents as broadcast at a second instance with a remainder of the displayable part of the page's contents as broadcast at the first instance, wherein the remainder is retrieved from memory (10,17,19).

7. Method according to any one of the preceding claims, wherein the displayable part constitutes a part smaller than the totality of displayable contents of the page and the method includes retrieving selection criteria and selecting the displayable part for identifying the differing sections in accordance with the retrieved selection criteria.

8. Method according to claim 7, including receiving instructions representative of the selection criteria from a user input device (12) and storing the instructions in memory (10) for retrieval.

9. System for decoding a teletext service broadcast to a receiver (1) and structured in pages, including at least one module (7,17) arranged to acquire at least a part of a page's contents, and at least one module (14-17) for generating a signal for displaying a displayable part of a teletext page, wherein the system is configured to acquire at least a part of a page's contents as broadcast at a first instance and at least a part of the page's contents as broadcast at a subsequent instance, characterised in that the system further comprises at least one module (8,17) adapted to identify sections of a displayable part of the contents of the page differing between the first and the second instance, and in that the system is configured to generate a signal for displaying the displayable part of the page in such a manner that the identified sections are displayed in a distinctive manner.

10. System according to claim 9, adapted to execute a method according to any one of claims 1-8.

11. Broadcast receiver, for example a television set (1), provided with a system according to claim 9 or 10.

12. Computer program for controlling a teletext decoder, adapted, when ran on a programmable processing device, to enable the system including the programmable processing device and the teletext decoder to carry out a method according to any one of claims 1-8.