WO1990009080A1

WO1990009080A1 - Enhanced television transmission and reception

Info

Publication number: WO1990009080A1
Application number: PCT/GB1990/000109
Authority: WO
Inventors: Robert White
Original assignee: Tvs Television Limited
Priority date: 1989-01-26
Filing date: 1990-01-26
Publication date: 1990-08-09
Also published as: AU4966190A; GB8901712D0

Abstract

Extra information is carried in a television signal (such as a PAL signal) comprising two chrominance signals (U, V) in phase quadrature via one or more enhancement signals (Ue, Ve) which are themselves in phase quadrature with the respective colour difference signals. In one embodiment of a receiver, a conventional PAL delay line decoder comprising a delay line (1), a subtractor (2) and an adder (3) is provided with an additional demodulator for the Ue signals (46) and an additional demodulator for the Ve signals (49). These demodulators are fed with carrier signals in phase quadrature with the respective carrier signals applied to the conventional U and V demodulators (5, 4) respectively. Accordingly, additional independent information carrying signals Ue and Ve can be derived. The signals Ue and Ve can for example be used to to carry luminance information and chrominance information relating to the edge portions of a wide-screen TV picture. The transmitted signal is compatible with an unmodified PAL receiver.

Description

Enhanced Television Transmission and Reception

The present invention relates to a method of transmitting extra information in a television signal, to a TV transmitter for generating such a signal, and to a TV receiver for receiving such a signal.

The present invention relates particularly but not exclusively to PAL transmission and reception.

Figure 1 of the accompanying drawings shows the basic principle of a PAL delay line decoder, along with vectors V , U_n, ^v _n+ι ^{and u} _n+ι representing the chrominance signals on lines n and n+1 respectively. The composite chroma signal is split into three branches, and fed into a delay line 1, an input of a subtractor 2 and an input of an adder 3. The delay line 1 delays the incoming signal by one line period (approximately 64 microseconds) such that, by the time the signal U+V of line n reaches one input of the subtractor 2 and adder 3, the signal appearing at their other input corresponds to line n+1 i.e. ϋ-V. Accordingly, the output of the subtractor 2 is the difference between U+V and U-V, i.e. 2V and the output of adder 3 is the sum of U+V and U-V, i.e. 2U. These output signals are modulated in phase quadrature and accordingly the subcarrier signals (not shown) fed to the demodulators 4 and 5 are also in phase quadrature. Furthermore, since the sign of the vector alternates at each successive line, it is necessary periodically to reverse the phase of the subcarrier signal fed to the V demodulator 4, as is well known by those skilled in the art.

In one aspect, the present invention provides a method of transmitting extra information in a television signal comprising two chrominance signals in phase quadrature, wherein a further signal carrying said extra information is added to said chrominance signals, said further signal being in phase quadrature with one of said chrominance signals and the phase relationship between said further signal and the other of said chrominance signals alternating at each successive line such that said further signal and said other chrominance signal are alternately in phase and in antiphase.

In a preferred embodiment, said television signal is a PAL composite video signal. Preferably two such further signals are added, one of said further signals being in phase quadrature with the U colour difference signal and the other of sa^'id further signals being in phase quadrature with the V colour difference signal, the phase of said other further signal alternating at each successive line.

This embodiment is illustrated in Figure 2 of the accompanying drawings, of which part (a) shows the composite chroma signal of line n. This signal comprises vectors V and u to which are added a first further signal (represented by vector V ) which is in phase quadrature with the U colour difference signal and a second further signal (U ) which is in phase quadrature with the V colour difference signal. As can be seen from part (b) of Figure 2, the phase of the second further signal alternates at line n+1, as represented by U ,_n+1x«

By adding the vectors V , V , U and U , and n en n en similarly by adding the vectors U. ₊₁> ,

^v(n+l) ^{and V}e(n+1)' ⁱ¹" ^{can be seen tnat "}the resulting enhanced composite chroma signal alternates between (U+V) + (U_e+v_e) and (U-V) + (V_e-U_e).

In order to avoid over-modulation of the transmitted signal, it will normally be desirable to reduce the amplitudes of the colour difference signals to a predetermined portion of the amplitude required for the standard modulation depth of the vision carrier. The remaining proportion of the amplitude required for the standard modulation depth is then available for the further information-carrying signals U and

V . For example, the U and V signals may have an amplitude of between 65 % and 85% of the amplitude required for the standard modulation of the vision carrier, and the further signals U and V may have an amplitude of between 35% and 15% of the standard amplitude of the U and V signals. In a preferred embodiment described below, the ratio of the peak amplitude of the V signals to the peak amplitude of the V signals and the ratio of the peak amplitude of the U signals to the peak amplitude of the U signals are both 75:25, or 3:1.

In a preferred embodiment, the further signals U and V carry additional picture information representative of one or more picture regions of the transmitted picture which are outside the region of the transmitted picture represented by the U and V signals. For example, the additional picture information can be used to transmit 'wide screen' TV pictures with an aspect ratio of 16:9 as against the 4:9 aspect ratio of a standard TV picture.

In a preferred embodiment, there are two such additional picture regions adjacent to the left and right hand borders respectively of the region of the transmitted picture represented by the U and V signals, one said further signal being a luminance signal which carries the luminance information of the left hand additional picture region, the other said further signal being a luminance signal which carries the luminance information of the right hand additional picture region, and the chrominance information of the additional picture regions being carried during field blanking intervals and/or picture lines between successive frames.

In another preferred embodiment the further signals

Ve_ and e are delta modulated such that their instantaneous amplitudes represent the rate of change of luminance or chrominance (as the case may be) across each line.

In another aspect, the present invention provides a TV transmitter comprising:

a) means for generating a luminance signal;

b) means for generating two chrominance signals in phase quadrature; c) means for generating a further information-carrying signal which is distinct from said chrominance signals;

d) means including switching means which is sychronised with the line frequency so as alternately to add and subtract said further signal from one of said chrominance signals at each successive line, and;

e) means for combining said luminance signal and the output of said adding means (d) to generate a composite video signal incorporating said information-carrying signal.

In a preferred embodiment, in use, the amplitude of at least one of said further signals is increased in a predetermined manner in the regions of each TV line which are at the boundary of the standard width of a TV picture, thereby to minimise changes in the resolution of the transmitted TV picture at said regions. In the TV receiver, the gain applied to these further signals (which are typically luminance and chrominance signals) may be decreased in a complimentary manner at these regions. By such a compounding process, the resolution at the junction of the edge information and the normal picture may be maximised and any discontinuity in the resolution of the TV picture may be minimised.

Alternatively, in order to conceal the "joins" between the central portion of the TV picture corresponding to the standard width and the portions added by the U and V signals corresponding to the extra width, the signals U and V may be arranged to carry slightly more information than is absolutely necessary for the boundary of the central and edge portions of the TV picture, and a dissolve may be applied to the overlaps of the central and edge pictures.

Additionally, it may be desirable to compensate for a reduction in the vertical resolution owing to the use of the further signals U and V . This may be achieved by vertical aperture correction or simple interpolation.

In another aspect, the invention provides a TV receiver comprising means for demodulating and processing a luminance signal, means for demodulating and processing two chrominance signals in phase quadrature, and means for demodulating and processing a further information-carrying signal which is distinct from said chrominance signals and which is in phase quadrature with one of said chrominance signals.

In a preferred embodiment, the TV receiver is a wide-screen TV receiver having a display whose aspect ratio is greater than 4:3, the receiver incorporating means arranged to receive two further information-carrying signals and to derive therefrom supplementary chrominance signals relating to the colour of peripheral portions of the TV picture adjacent to the left- and right-hand edges of a standard-width TV picture, and incorporating means for deriving a supplementary luminance signal relating to said peripheral portions from portions of a video signal received during field blanking intervals and/or between successive frames, and means for generating and displaying a wide-screen TV picture from U and V colour difference signals, the supplementary chrominance signals, and the above first-mentioned luminance signal and the supplementary luminance signal.

It will be noted that although the present invention in its preferred embodiment is applicable to wide-screen television, the or each further signal U and/or V_& may be used to carry information other than picture information, for example Teletext or other numerical or textual information. It is also possible to use the further signals U and V to generate a complete, but reduced-size image for 'picture-in-picture' use, or to carry enhancement detail for addition to the main picture to increase the resolution thereof.

Although in its preferred embodiments the present invention is applicable to PAL television -systems, in principle the invention may be applied to any television system utilising a luminance signal and two chrominance signals in phase quadrature such as, for example, the NTSC system.

In order that the invention may be more readily understood, reference will now be made, by way of example only, to Figures 1 to 8 of the accompanying drawings, in which:

Figure 1 is a schematic representation of a conventional PAL delay line decoder; Figure 2 illustrates the addition of two further signals U and V_e to the U and V colour difference signals of the PAL system;

Figure 3 is a block diagram of part of a television transmitter arranged in accordance with the invention;

Figure 4 is a block diagram of the remainder of the television transmitter shown in Figure 3;

Figure 5 is a block diagram of part of a television receiver arranged in accordance with the invention;

Figure 6 is a block diagram of the remainder of the television receiver shown in Figure 5;

Figure 6a is a representation of the signals U and V received by the demultiplexer and first A/D converter of Figure 6;

Figure 7 is a modification of the part of the transmitter shown in Figure 4, and;

Figure 8 is a block diagram of a corresponding modification to the part of the TV receiver shown in Figure 5.

Figures 1 and 2 have already been referred to in. the preamble.

Figures 3 and 4 show a PAL transmitter in accordance with the invention. Referring to Figure 3, green, red and blue signals G' , R'and B' from a TV camera (not shown) are fed to a luminance matrix amplifier 6 which derives a luminance signal Y'(Y'= 0.59 G' + 0.3 R'+ 0.1IB ') in a conventional manner. Matrix circuits 7 and 8 derive colour difference signals U' and "V in a conventional manner. The three signals Y' , U' and V' are converted to digital form by an analogue to digital converter 9 and are then fed to a digital frame store 10. The Y' , U' and V signals represent a wide-screen TV picture having an aspect ratio of 16:9. The frame store 10 stores a complete frame of such a TV picture and includes a series of memory locations 10c which store those Y', U' and V digital samples which correspond to the central portion of a picture of standard aspect ratio 4:3. These digitised samples are fed via a digital to analogue converter 11 and demultiplexer 12 to a colour matrix amplifier 13 which generates red, green and blue colour signals R, G and B which correspond to luminance and two colour difference signals Y, U and V respectively derived from the central portion 10c of digital frame store 10.

One array of memory locations 10a of the digital frame store contains luminance and chrominance digitised samples corresponding to the extreme left-hand portion of the transmitted picture and another array of memory locations 10b similarly contains digitised luminance and chrominance samples corresponding to the extreme right-hand portion of the transmitted picture. The luminance and colour difference samples corresponding to left- and right-hand edges of the picture are referred to as the Y", U" and V" samples. The U" and V" samples are fed in parallel to a multiplexer 16 which outputs the U" and V" samples from the left hand and right hand areas 10a and 10b of digital frame store in the order V" (left), V" (right), U" (left), U" (right). These digital samples are converted to analogue form by digital to analog converter 17 and are output as a first 'further information-carrying signal' U .

This corresponds to supplementary chrominance signal U whose wave form is shown in the upper portion of

Figure 6a and which is processed in the receiver of Figures 5 and 6 as will substantially be described.

The digitised luminance samples Y" represent a luminance signal of frequency approximately 3.75MHz and this signal must be transmitted within a chroma channel bandwidth of approximiately 1.25MHz. However, because the wide screen TV picture has an aspect ratio of 16:9 (ie 5 1/3:3), whereas the standard picture corresponding to central portion 10c of digital frame store 10 has an aspect ratio of 4:3, the extra luminance information is concentrated in 1/3 of a line (i.e. one quarter of (5 1/3 - 4)). Accordingly, a processor 14 is used to spread out the Y" samples in time such that the period between outgoing samples is three times the period between incoming samples. Accordingly by feeding the outgoing samples to a digital/analogue convertor 15 the resulting second 'further information carrying signal' V has a correspondingly reduced frequency, namely 1.25MHz.

Referring to Figure 4, the R, G and B signals from colour matrix amplifier 13 (Figure 3) are fed to a luminance matrix 18, and the signals U_e and V generated by the circuitry of Figure 3 are fed to PAL switches 26 and 32 respectively. Luminance matrix 18 generates a luminance signal Y which is equal to 0.59G + 0.3R + 0.11B. U matrix 22 compares signals Y and B and generates a signal U = 0.493(B-Y). Similarly, V matrix 30 compares signals Y and R and generates a signal V = 0.877(R-Y). These U and V colour difference signals are fed to modulators 23 and 31 respectively which receive signals + or - U_e and V from PAL switches 26 and 32 respectively.

These PAL switches are controlled by switching pulses of half the line frequency and accordingly the output of these switches is alternately in phase with and in antiphase with the associated colour difference signal U or V at each successive line. The modulators 23 and 31 attenuate the colour difference signals U and V to 75% of the standard amplitude and the peak amplitude of the signals U and V is 25% of this standard amplitude such that the peak amplitude of the composite signals is equal to the peak amplitude of the colour difference signals in a conventional PAL transmitter. These composite signals are fed to U and V modulators 24 and 33 respectively, where they are modulated onto a carrier signal generated by an oscillator 27. As is conventional in a PAL transmitter, the modulated signals generated by modulators 24 and 33 are in phase quadrature, and this is achieved in a conventional manner by means of a 90 degrees phase shifter 28 in conjunction with a PAL switch 29 which alternates the phase of the carrier signal fed to V modulator 33 in synchronism with PAL switch 26. The resulting signals are added in an adder 25 and are then fed to an adder 19 where they are combined with the luminance signal Y and also with conventional sync pulses. The resulting signal is amplified in an amplifier 20 and fed to a modulator 21 where it is modulated onto a video carrier generated by oscillator 34. The resulting composite video signal is then combined with a modulated audio signal derived from a sound carrier oscillator 35 and a modulator 36 in conventional fashion and then fed to the transmitting aerial (not shown) .

Figures 5 and 6 show a PAL receiver which is suitable for receiving the signal transmitted by the transmitter of Figures 3 and 4. Referring to Figure 5, the signal from the receiving aerial (not shown) is fed via a tuner 37 to a video detector 38 from which signals to a audio detector (not shown) and to a sync separator 39 are generated. The composite video signal from video detector 38 is fed to a sub- carrier luminance filter 41 from which a luminance signal Y is output to a 0.5 microseconds delay line 40, and is also fed to a chrominance band pass filter 42 which feeds a composite chroma signal to an amplifer 44 and a burst gate 43. Burst gate 43 is of a conventional type and is controlled by gating pulses derived from the line flyback in a conventional manner. The output signals from burst gate 43 are fed through an amplifer 45 to a phase locked sub-carrier generator 100 which generates a sub-carrier which is synchronised with the colour burst signals detected by burst gate 43. This sub-carrier is fed via a 90 degrees phase shifter 47 to a U demodulator 5 and via a sub-carrier switch 48 operating at half line frequency to a V demodulator 4 in conventional manner.

The composite chroma signal from amplifier 44 is fed to a PAL delay line decoder which, it will be noted, resembles the decoder shown in Figure 1 but which is additionally provided with demodulators 46 and 49 for demodulating the U and V signals respectively.

It will be noted that the output of subtractor 2 is 1.5V + 2U_ and the output of adder 3 is 1.5U + 2V . This can be shown by analogy with the result previously shown for the PAL delay decoder of Figure 1. As can be seen from Figure 2, since .the signal U is in phase quadrature with the colour difference signal V and the signal V_e is in phase quadrature with the signal U the signals U and V can be extracted by applying to the demodulators 46 and 49 the same sub-carrier signals that are applied to the U and V demodulators 5 and 4 respectively.

Accordingly, the two further information-carrying signals U and V are derived by the circuitry shown in Figure 5, as well as the conventional luminance signal Y and the PAL colour difference signals u and V.

It will be recalled from the discussion of the transmitter circuitry of Figure 3 that the signal U comprises supplementary colour difference signals U" and V" which are in multipexed form as shown in the upper part of Figure 6a and which relate to the edge portions of the transmitted TV picture. Furthermore it will be recalled that the signal V represents a time-expanded version of a supplementary luminance signal Y" which relates to the edge portions of the transmitted TV picture and whose waveform is shown in the lower part of Figure 6a. More precisely, the signal V is a time-expanded version of portions of the supplementary luminance signal relating to left and right edges of the transmitted TV picture in multiplexed form. These left and right-hand portions of the supplementary luminance signal are denoted by L and R in the lower part of Figure 6a and relate to the digitised Y" values stored in parts 10a and 10b respectively of the digital frame store 10 shown in Figure 3.

As shown in Figure 6, a frame store 54 in conjunction with a digital processor 53 is used to reassemble each frame of the picture displayed by the TV receiver. Accordingly, the conventional Y , U and V signals from the receiver circuitry shown in Figure 5 are multiplexed in a multiplexer 59, converted to digital form by an analogue to digital convertor, and fed to the central portion of frame store 54 which corresponds to the central, standard-width portion of the displayed wide-screen picture. The multiplexed supplementary colour difference signals which -are incorporated within the signal U are demultiplexed in a demultiplexer 50, converted to digital form by analogue to digital converters 51 and 52 and fed via a processor 53 to portions 54a and 54b of frame store 54 which correspond to the edge portions of the displayed picture. Similarly the supplementary luminance signal Y" which is incorporated within the signal V and which contains the luminance information of the edge portions of the picture is derived from V by converting the latter to digital form in an analogue to digital converter 56, compressing the resulting signals in time in a ratio of 3 to 1 in a processor 58 so as to compensate for the expansion performed in processor 14 (Figure 3) and then feeding through processor 53 to the portions 54a and 54b of frame store 54. Accordingly, frame store 54 stores digitised samples of luminance and chrominance corresponding to the entire area of the TV picture to be displayed. These digitised samples are converted to composite video signals by means of digital to analogue convertor 55 and fed via a matrix amplifier 56 in the form of red, green and blue signals R, G and B to a wide-screen TV display such as a cathode ray tube (not shown) . It will be appreciated that the frame store 54 is replenished frame by frame, so that a continuous TV picture can be generated.

It should be noted that in an alternative embodiment, the supplementary luminance signal Y" could be incorporated in the U signal and the supplementary colour difference signals U" and V" could be incorporated within the V signal.

Because the U and V signals can be considered merely as additional information carriers, they can be used in a variety of different ways. For example, the luminance signal of the left-hand edge portion of the wide-screen picture could be expanded by a factor of 6 to fill a whole line period and used as the U (or alternatively the V ) signal. Similarly, the luminance signal for the right hand edge portion of the wide screen TV picture could be expanded by a factor of 6 to fill a whole line period and used as the V_e (or alternatively the ϋ ) signal. The chrominance signal required for these left and right hand edge portions could then be carried in the field blanking intervals in place of some Teletext signals or on some lines on the top and bottom of the active picture. The system described, as with the PAL system in general, relies on the vectors on adjacent lines in time being of equal amplitude for complete cancellation and separation at the output of the delay line of the PAL circuit (Figure 5). In practice this will not be the case except for full colour fields where there are no transitions in the vertical direction. Consequently in general there will be a certain degree of cross-talk from one chrominance vector into the other and from the vectors V and U into the main picture.

Because the PAL system uses interlaced scanning adjacent line in time i.e. field 1, line 1,2,3 etc. are actually scanning lines 1,3,5 etc. in spatial sequence. Accordingly, it should be possible to reduce the cross-talk from the edge portions of the picture (carried by the additional signal U and V ) into the central portion of the picture by transmitting the enhancement signals in spatial sequences i.e. field 1 line 1, field 2 line 1, field 1 line 2, field 2 line 2, etc. This could be achieved by reading out in appropriate sequence from the appropriate addresses of digital frame store 10 in Figure 3. Similarly, the signals would be read out of the receiver frame store 54 (Figure 6) in an interlaced sequence to restore the signals to their original positions.

Figure 7 shows a variant of part of the transmitter shown in Figure 4 which is arranged to increase the amplitude of the U and V signals in response to a drop in the amplitude of the U and/or V colour difference signals. The U matrix 22' and V matrix 30' are essentially identical to the corresponding circuits shown in Figure 4 and the U and V modulators 23' and 31' are also essentially identical to the modulators 23 and 31 shown in Figure 4. However, in accordance with the variant shown in Figure 7, the signal + or - U_e is fed to modulator 23' via a variable gain amplifier 64 rather than directly, and similarly the signal V is fed to modulator 31' via a variable gain amplifier 66. A comparator 62 detects whichever is the greater of the peak amplitudes of the U and V signals via peak detectors 61 and 63 and transmits this peak amplitude to an inverting amplifier 65. Accordingly, the greater the amplitude fed to inverting amplifier 65, the smaller the gain of amplifiers 64 and 66, and vice versa. Thus, the available modulation depth provided by the vision carrier signal is utilised to the full and the signal-to-noise ratio of the signals U and V is maximised.

Figure 8 shows a variant corresponding to Figure 7 applied to the receiver circuitry of Figure 5. Demodulators 4', 5', 46' and 49' are essentially as shown in Figure 5 but variable gain amplifiers 71 and 72 are inserted in the output signal paths of demodulators 46' and 49' respectively. These amplifiers restore the amplitudes of the signals U and V to the appropriate value in response to output signals from an inverting amplifier 70 which is in turn responsive to the higher of the peak amplitudes of colour difference signals U and V as determined by comparator 68 and peak detectors 67 and 69. It will be appreciated that the invention is not limited to the embodiments herein described, but includes all modifications and variations falling within its scope.

Claims

_ _1<μ

1. A method of transmitting extra information in a television signal comprising two chrominance signals in phase quadrature, wherein a further signal carrying said extra information is added to said chrominance signals, said further signal being in phase quadrature with one of said chrominance signals and the phase relationship between said further signal and the other of said chrominance signals alternating at each successive line such that said further signal and said other chrominance signal are alternately in phase and in antiphase.

2. A method as claimed in claim 1 wherein said television signal is a PAL composite video signal having a luminance component, and said chrominance signals are U and V colour difference signals, the phase of the V colour difference signal alternating at each successive line.

3. A method as claimed in claim 2 wherein two such further signals are added, one of said further signals being in phase quadrature with the U colour difference signal and the other of said further signals being in phase quadrature with the V colour difference signal, the phase of said other further signal alternating at each successive line^*.

4. A method as claimed in claim 3 wherein said further signals carry additional picture information representative of one or more additional picture regions of the transmitted picture which are outside the region of the transmitted picture represented by said U and V signals. 5. A method as claimed in claim 4 wherein a first said further signal which is added to one of the U and V colour difference signals comprises two chrominance signals in phase quadrature which carry the chrominance information of said one or more additional picture regions and wherein a second said further signal which is added to the other of the U and V colour difference signals is a luminance signal which carries the luminance information in said one or more additional picture regions.

6. A method as claimed in claim 4 wherein there are two such additional picture regions adjacent the left and right hand borders respectively of the region of the transmitted picture represented by said U and V signals, wherein one said further signal is a luminance signal which carries the luminance information of the left hand additional picture region, wherein the other said further signal is a luminance signal which carries the luminance information of the right hand additional picture region, and wherein the chrominance information of said additional picture regions is carried during field blanking intervals and/or within picture lines between successive frames.

7. A method as claimed in claim 5 or claim 6 wherein the or each said further signal which is a luminance signal is added to a U or V colour difference signal, is transmitted during substantially all .of the line period, and is reduced in frequency by a factor which is inversely related to the proportion of each line period which carries said additional picture information.

8. A method as claimed in any of claims 4 to 7 wherein said further signals are delta modulated such that their instantaneous amplitudes represent the rate of change of luminance or chrominance (as the case may be) across each line. - II-

9. A method as claimed in any of claims 1 to 7 wherein the instantaneous amplitude of at least one said further signal is scaled in dependence upon the instantaneous amplitude of the chrominance signal to which it is added such that its amplitude increases with decreasing amplitude of the chrominance signal to which it is added.

10. A method as claimed in claim 3 wherein said further signals carry additional information representative of a picture-in-picture image.

11. A method as claimed in claim 3 wherein said further signals carry additional information suitable for enhancing the transmitted picture represented by the U and V signals.

12. A TV transmitter comprising:

(a) means for generating a luminance signal;

(b) means for generating two chrominance signals in phase quadrature;

(c) means for generating a further information carrying signal which is distinct from said chrominance signals;

(d) means including switching means which is synchronised with the line frequency so as alternately to add and subtract said further signal from one of said chrominance signals at each successive line, and;

(e) means for combining said luminance signal and the output of said adding means (d) to generate a composite video signal incorporating said information carrying signal. _ η_fl_ lj. A TV.transmitter as claimed in claim 12 which is a PAL transmitter in which said chrominance signals are U and V colour difference signals, wherein said generating means (c) is arranged to generate two such further information-carrying signals which are each distinct from said U and V signals, and wherein said adding means (d) is so to arranged that in use, one of said further signals is in phase quadrature with, the U colour difference signal and the other of said further signals is in phase quadrature wit the V colour difference signal, the phase of said other further signal alternating at each successive line.

14. A TV transmitter as claimed in claim 13, comprising means for generating signals representative . of a wide screen picture, memory means arranged to store a series of samples of the generated signals and means arranged to extract those samples corresponding to the end regions of TV lines from the memory means and to generate said further signals from the extracted samples.

15. A TV transmitter as claimed in claim 14 wherein said extracting means comprises a first signal-processing chain arranged to receive sampled U and V colour difference signals and a second signal-processing chain arranged to receive sampled luminance signals, said first signal-processing chain being arranged to generate a first said further information-carrying signal comprising said sampled U and V colour difference signals in time multiplexed form and said second signal-processing -chain being arranged to reduce the frequency of the sampled luminance signal by a time expansion process to a frequency compatible with the bandwidth available for the U and V colour difference signals and to output the resulting reduced frequency signal as a second further information-carrying signal. _ _r> _

16. A TV transmitter as claimed in claim 14 or claim 15 wherein in use the amplitude of at least one of said further signals is increased in a predetermined manner in the regions of each TV line which are at the boundary of the standard width of a TV picture, thereby to minimise changes in the resolution of the transmitted TV picture at said regions.

17. A TV transmitter as claimed in any of claims 12 to 16 comprising means for limiting ^* the peak amplitude of said chrominace signals generated by said generating means (b) to a predetermined proportion of the amplitude required for the standard modulation depth of the vision carrier, the remaining proportion of the amplitude required for said standard modulation depth being substantially the peak amplitude of said further information carrying signals.

18. A TV transmitter as claimed in claim 17 wherein said predetermined proportion is from 0.65 to 0.85.

19. A TV transmitter as claimed in any of claims 12 to 16 comprising means for adjusting the instantaneous amplitude of said further information carrying signals in dependence upon the instantaneous amplitude of said chrominance signals generated by said generating means (b) such that the first mentioned instantaneous amplitude is increased in response to a drop in the second mentioned instantaneous amplitude.

20. A TV receiver comprising means for demodulating and processing a luminance signal, means for demodulating and processing two chrominance signals in phase quadrature, and means for demodulating and processing a further information-carrying signal which is distinct from said chrominance signals and in phase quadrature with one of said chrominance signals. _^_

21. A TV receiver as claimed in claim 20 which is a PAL TV receiver arranged to demodulate and process U and V colour difference signals, the U and V colour difference signals being in phase quadrature and the phase of the V colour difference signal alternating at each successive line.

22. A TV receiver as claimed in claim 21, comprising means for demodulating and processing two such further information carrying signals, one of said further signals being in phase quadrature with the U colour difference signal and the other of said further signals being in phase quadrature with the V colour difference signal, the phase of said other further signals alternating at each successive line.

23. A TV receiver as claimed in claim 21 or claim 22 which is a PAL-D receiver incorporating delay means arranged to delay a composite chroma signal for a line period and to feed the delayed signal to an adder and a subtractor which are each arranged to receive the non-delayed composite chroma signal at their other inputs and to output modulated U and V colour difference signals respectively which are fed to demodulating means, wherein further demodulating means are arranged to receive said output modulated U and V colour difference signals and to demodulate said further information carrying signals which are in phase quadrature with the U and V colour difference signals respectively.

24. A TV receiver as claimed in claim 22 or claim 23 which is a wide-screen receiver having a display whose aspect ratio is greater than 4:3, the receiver incorporating means arranged to receive one of said further information carrying signals and to derive therefrom supplementary chrominance signals relating to the colour of a peripheral portion of the TV picture, means arranged to receive the other of said further information-carrying signals and to derive therefrom a supplementary luminance signal relating to the luminance of said peripheral portion, and means for generating and displaying a wide-screen TV picture from the U and V colour difference signals, the supplementary chrominance signals and the first- mentioned and supplementary luminance signals.

25. A TV receiver as claimed in claim 22 or claim 23 which is a wide-screen TV receiver having a display whose aspect ratio is greater than 4:3, the receiver incorporating means arranged to receive both said further information-carrying signals and to derive therefrom supplementary chrominance signals relating to the colour of peripheral portions of the TV picture adjacent the left and right hand edges of a standard width TV picture, and incorporating means for deriving a supplementary luminance signal relating to said peripheral portions from portions of a video signal received during field blanking intervals and/or between successive frames, and means for generating and displaying a wide-screen TV picture for the U and V colour difference signals, the supplementary chrominance signals, and the first mentioned and supplementary luminance signals.

26. A TV receiver according to claim 24 or claim 25 which is arranged in use to reduce the amplitude of at least one of the supplementary luminance and supplementary chrominance signals in a predetermined manner in the regions of each TV line which are at the boundary of the standard width of a TV picture, thereby to accommodate a complementary increase in the amplitude of the corresponding transmitted signal at these regions and to minimise change in the resolution of the display TV picture at these regions. - '2b-

27. A TV receiver as claimed in any of claims 22 to 26, further comprising analogue to digital conversion means which is arranged to convert the luminance and chrominance signals to digital form and processing means including a memory which is arranged to store successive arrays of the digitised luminance and chrominance signals corresponding to successive frames of the TV picture, and incorporating digital to analogue conversation means for generating a TV picture from said arrays.

28. A TV receiver as claimed in any of claims 20 to 27 wherein said means for demodulating and processing said further information carrying signal is responsive to the instantaneous amplitude of at least one of said chrominance signals such that its gain is increased in response to a drop in said instantaneous amplitude.

29. A method of transmitting extra information in a television signal, substantially as described hereinabove with reference to any of Figures 2, 3 and 4, optionally as modified in accordance with Figure 7 of the accompanying drawings.

30. A TV transmitter substantially as described hereinabove with reference to Figures 3 and 4, optionally as modified in accordance with Figure 7 of the accompanying drawings.

31. A TV receiver substantially as described hereinabove with reference to Figures 5 and 6, optionally as modified in accordance with Figure 8 of the accompanying drawings.