TELEVISION RECEIVERS

Abstract: Colour television receiver 1 has a control unit 4 which acti­ vates a counter 5 at the start of the chrominance portion of a line of time-multiplexed video information. Counter 5 produces a first timing pulse which ensures switch 6 directs the chromi­ nance portion of the line to a store 7 and a second timing pulse at the end of the chrominance portion so that the luminance portion is fed directly to video processing unit 8 for display.

Description: TELEVISION RECEIVER The present invention relates to a television receiver for use in a television transmission system in which the video information is in time-multiplexed form. One example of a time-multiplexed television system is that recently proposed by the Independent Broadcasting Authority and named the Multiplexed Analogue Component (MAC) system, whereby the chrominance component of information within each line is separated in time from the luminance component. Thus, taking a line of 64 P secs of video information in the correct sequence of transmission, there is an initial line sync word followed by a signal containing the audio information, these being of lijisec in total duration, then a chrominance signal of 17.5 it secs duration containing half the necessary colour information for that line (the chrominance information of the previous line constituting the remaining half); there follows a luminance signal of 35 1 secs containing the necessary brightness (or contrast) information for that line and terminated by another line sync word. Each television receiver has an information store into which the lines of information are put as they are received and a processor to take out the information necessary each display line, when required, from the store. The present invention provides a television receiver ciaracterised by means to process at least the luminance .portions of a time-multiplexed video signal in order to provide an image for display, the receiver having no means to store the luminance portions. In one form of the present invention, a colour television receiver has means to store the chrominance portion of lines of time-multiplexed video information, means to process the chrominance information for each line, after storage, with the luminance portion of the line of time-multiplexed video information, the receiver having no means to store the luminance portion. Thus the receiver need only have a storage means of sufficient capacity to store and combine the chrominance signals. Also, here--are no luminance signals to be taken from store by the processing means, which can hence have less sophisticated operations than otherwise. Both of these factors contribute towards a simplification of the operation of the receiver and can result in a reduction of the manufacturing cost. Preferably, the receiver has a line scan across the screen of the same duration as that of the luminance signal in each line of video information. Thus there need be no time length change in each luminance signal before display. As an example of this feature, a receiver which is compatible with the MAC system may have a line scan of 35 P secs (as compared with the 64 P sec line scan of existing receivers). In another form of the present invention, a monochrome television receiver has means to synchronise the start of each line scan across the screen with the beginning of the luminance portion of a line of time-multiplexed video information, and means to display, without storage, the luminance portion. If the television system in operation is such that, within a line of video information, the luminance portion follows immediately after the line sync pulse, then preferably the synchronization means initiates the line scan upon detection of the line sync pulse. If however there is a time interval between the line sync pulse and the luminance portion, then preferably the synchronization means includes means to delay initiation of the line scan by an appropriate length of time. As an example of this latter feature, a receiver for use with the MAC system may have a delay means which operates for 28.5 P secs. As in the previous form, the receiver may have a line scan of the same duration as that of the luminance portion of each line. In this form of the present invention the chrominance portion of each line is not used in the display. Technical details on ways of achieving the above-described features of the present invention would be evident to a person skilled in the art. In order that the invention may more readily be understood, a description is now given by way of example only, reference being made to the accompanying drawings, in which: Figure 1 is a block diagram of a colour television receiver embodying the present invention; and Figure 2 is a block diagram of a monochrome television receiver embodying the present invention A colour television receiver 1, shown diagrammatically in Figure 1, has an aerial 2 to receive time-multiplexed video signals of a form corresponding to that of the MAC television transmission system. Audio processor 3 monitors the received signal and, when it identifies a line sync word, it separates out the audio component and sends the remaining signal on to control unit 4. This control unit detects the line sync word, delays for 11 P secs and then sends a control pulse to reset to zero a counter 5 formed by one or more monostable circuits. Counter 5 produces a first timing pulse at the end of the period originally containing the audio component to activate a switch 6 which then directs the incoming video signal (which comprises the chrominance portion) to two separate sections of a colour information store 7. The first of these sections simultaneously receives, from a third section of store 7, the chrominance portions of the previous line of video information received, the resultant combination of the two chrominance portion providing all the colour information necessary for one display line. The second of the two sections to receive the incoming chrominance portion retains it for combination with the successive chrominance portion of the next display line. Counter 5 produces a second timing pulse 17.5 P secs after the first (thereby corresponding with the end of the chrominance portion of the line of video information); this pulse is passed to switch 6 in order to halt flow of the incoming signal to store 7 and instead to pass the signal (which is now the luminance portion of the line) to a video processing unit 8. The second timing pulse is also used to instruct the third section of store 7-to clock out all the chrominance information necessary for the display line, at half the input rate, to the unit 8 for combination with the incoming luminance; the resultant signal is then displayed on a screen 9 with a suitably synchronised audio accompaniment. Thus, the store 7 need only be large enough to accommodate and combine the chrominance portion of two lines of video information, rather than two entire lines, thereby minimising the cost for this component. Figure 2 shows diagrammatically the major components in a monochrome television receiver 20 embodying the present, invention. Receiver 20 includes an aerial 21 to receive video signals in the MAC format and an audio processor 22 which monitors the received signal. When processor 22 identifies a line sync signal, it separates out the audio component and sends on the remaining signal. When control unit 23 detects the line sync signal, it sends out a control pulse to a counter 24 which is thereby reset to zero and produces a first timing pulse. This timing pulse is passed to a switch 25 so as to set it (if it were not already so) in a mode whereby it prevents the passage of any incoming signals. Counter 24 produces a second timing pulse 28.5it secs later (thereby corresponding with the end of the chrominance portion of the line of video information); this pulse is passed to switch 25 which is thereby activated in order to allow the incoming video signal (which is now solely the luminance portion of the line) to pass onto the video processing unit 26 for display on screen 27 with a suitably synchronised audio accompaniment.

Claims: CLAIMS 1. A television receiver characterised by means to process at least the luminance portions of a time-multiplexed video signal in order to provide an image for display, the receiver having no means to store the luminance portions. 2. A colour television receiver characterised by means to store the chrominance portion of lines of time-multiplexed video information, means to process the chrominance information for each line, after storage, with the luminance portion of the line of time-multiplexed video information, the receiver having no means to store thefluminance portion. 3. A monochrome television receiver characterised by means to synchronise the start of each line scan across the screen with the beginning of the luminance portion of a line of time-multiplexed video information, and means to display, without storage, the luminance portion. 4. A receiver according to Claim 3 characterised by synchronisation means to initiate the line scan upon detection of the line sync pulse. 5. A receiver according to Claim 3, characterised by the synchronization means including means to delay initiation of the line scan by an appropriate time period. 6. A receiver according to any one of the preceding claims, characterised by the receiver having a line scan across the screen of the same duration as that of the luminance signal in each line of video information.

Inventors: HASTINGS, JOSEPH FRANCIS CONWAY, WESTWOOD, DAVID JOHN SIDNEY
Applicants: THORN EMI FERGUSON LIMITED
Application year: 1983
Main classification: H04N5
IPC codes: H04N9