GB2244888A

GB2244888A - Encoding auxiliary signals with colour television signals

Info

Publication number: GB2244888A
Application number: GB9108836A
Authority: GB
Inventors: Christopher Hugh Strolle; Werner Franz Wedam; Ko Jung-Wan; Chandrakant Bhailalbhai Patel
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 1990-05-31
Filing date: 1991-04-24
Publication date: 1991-12-11
Also published as: JPH0435189A; DE4036831A1; DE4036831C2; GB9108836D0; TW207596B; KR930006538B1; KR920005653A; JPH088701B2

Abstract

Apparatus and a method are disclosed for encoding, transmitting and decoding one or two auxiliary or control signals on a phase alternating carrier. The phase alternating carrier PAC is generated such that, in a given frame, it is in-phase on one scan line and out of phase on the next scan line relative to the conventional chroma carrier. The (I and Q) chroma information is modulated on the chroma carrier C in a conventional form to generate a chroma signal. The phase alternating carrier is modulated with one or two auxiliary signals from sources 32, 38 in a similar fashion. The encoded phase alternating carrier is then added to the modulated chroma carrier (chroma signal) and processed in the chroma channel for recording on a magnetic tape. A decoder or playback apparatus processes the chroma channel to decode the two modulated carriers. The modulated chroma carrier (chroma signal) is decoded in a conventional demodulator to recover the chroma (I and Q) information. The encoded phase alternating carrier is decoded to recover the original auxiliary signal. The auxiliary signals may be digital audio signals or motion signals indicative of motion in the scenes. <IMAGE>

Description

1 - VIDEO PROCESSING The present invention relates to processing video

signals comprising chroma and luma signals.

There is a need in the colour video cassette recording art to provide additional channels conveying auxiliary signals useful to the colour television signals, such as digital audio information andlor signals relating to the motion that occurs in the video scene.

In video recording systems, it is known to modulate the chroma signals conventionally appearing in the upper portions of the spectrum of a composite television signal to a position in the spectrum below the luma signals. Such a modulation or down-conversion system is known in the recording art as a colour-under recording system. In such a colour-under system, the in- phase (I) and quadrature (Q) components of the chroma information are processed in a conventional manner to develop the colour signals (C) for viewing a scene.

According to a first aspect of the invention, there is provided in a video signal processing system having a chroma carrier modulated with chroma information, means responsive to said chroma carrier for generating a phase alternating carrier, whereby said phase alternating carrier and said chroma carrier are one hundred and eighty degrees out-of-phase on alternate scan lines, means for modulating a first auxiliary signal on said phase alternating carrier and means for adding said phase alternating modulated carrier to said modulated chroma carrier at a given phase angle.

The present invention utilises, in its preferred form, the colour-under chroma channel to carry additional information, such as digital audio signals andlor signals manifesting motion that occurs in a viewed scene.

Preferably, a phase alternating carrier (PAC) is generated from a conventional 3.58 MHz (being equal to 455 fh/2) chroma carrier by line-to line multiplexing of this carrier and its one hundred and eighty degrees phase shifted version. Thus, the phase alternating carrier is one hundred and eighty degrees out of phase with respect to the phase of the chroma carrier on alternate lines; that is out of phase on odd lines and in-phase on even lines.

In a preferred embodiment, the PAC signal is modulated with a first auxiliary signal and a ninety degree phase shifted PAC is modulated with a second auxiliary signal. These two modulated PAC's are added to provide a signal, referred to herein as a phase alternating signal (PAS). The PAS is added to the conventionally modulated chroma carrier, referred to herein as the chroma signal (C). The sum of the two signals is referred to herein as an "augmented chroma signal". In a VHS system, an augmented chroma signal is down-modulated as colour-under signal at a frequency of 629 KHz, being equivalent to 40fh. The augmented chroma signal, along with processed luminance signal information, is passed to a recording medium, or other transmission medium, for utilisation on a real time basis, or stored on a tape or other storage medium for use at a subsequent time as desired.

1 The augmented chroma signal is decoded (played back) essentially by reversing the encoding process by a network of adders and line delays, whereby the chroma signal (C) and the phase alternating signal (PAS) are separated to provide the original chroma and the auxiliary signals at respectively separate outputs for utilisation by the playback apparatus as desired.

A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily enjoyed as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like members indicate the same or similar components, wherein:

Figure 1 is a block diagram of a colour-under system, embodying the present invention; Figure 2 is a block diagram showing the system for decoding or playing back the colour-under augmented chroma signal; Figure 3 is a schematic diagram showing the chroma vector resolved from the respective I and Q signals and relative positions of the auxiliary signals; Figure 4 is one embodiment of auxiliary signal demodulators for two auxiliary signals; and Figure 5 is another embodiment of an auxiliary signal demodulator for only one auxiliary signal.

The present description is made in the context of a television signal processing system in accordance with the NTSC standards adopted by the United States. Nevertheless, the principles of the invention may be applied to the PAL and SECAM systems used primarily in Europe. Moreover, the invention can have application to colour television transmission or recording systems while the chroma signal is not interleaved with the luminance signal in accordance with a standard NTSC colour television system.

Reference is made to Figure 1 for a block diagram illustrating the preferred embodiment of the invention. A source 10 of video signals and digital format is coupled to a luma/chroma (Y/C) separator 12 providing the luma signal (Y) to a luma processor 14 and the chroma signal (C) to a 3. 58 MHz chroma carrier oscillator 16. The Y/C separator is preferably of the type employing one-H combing of the chroma signal. The luma processor 14, of conventional form used in the video recording art, provides an FM modulated luma signal, which is coupled to an adder 18.

The chroma signal (C) is coupled to the oscillator 16 and to an adder 42. The chroma carrier oscillator 16 is responsive to a burst gate from synchronising separator 24 on path 25. The chroma carrier oscillator 16 generates a 3.58 MHz continuous wave cw carrier which is frequency and phase locked to an incoming burst signal, gated by the burst gate on path 25.

The oscillator 16 thereby provides a chroma burst-locked 3.58 MHz cw at zero degrees phase to a multiplexer (MUX) 20 and to a one hundred and eighty degree phase shifter 22.

1 The video source 10 is also coupled to the synchronising separator 24, which generates a horizontal synchronising signal (H) and the burst gate on path 25. The horizontal synchronisation signal (H) is applied to a divide- by two circuit 26, which provides the horizontal signal H/2 for controlling the MUX 20. The MUX 20, responding respectively to the chroma carrier at zero degrees and one hundred and eighty degrees, provides a phase alternating carrier (PAC) at output 28. A suitable phase (N degrees) of the PAC is selectable relative to the phase of the oscillator 16 output by a look-up table (LUT) 30.

In the preferred embodiment, the angle of the MUX output is fifty seven degrees advanced or thirty three degrees delayed, relative to the referenced 3.58 MHz chroma carrier, principally because this implementation of the system is relatively less costly. However, for certain applications it may be desirable to provide a different phase. Moreover, the function of providing the horizontal line selection for the phase of the PAC may be embodied in a programmable read-only memory (PROM). A PROM will provide the PAC that is precise and noise-free.

An auxiliary signal, AUXI, preferably low-pass one-H combed, from source 32, is modulated on one phase of the PAC, at the LUT 30 output by a modulator 34 which is coupled to one input of an adder 36. A second auxiliary signal, AUX2, preferably also low-pass one-H combed, if desired, may be modulated in quadrature with signal AUX1 by a ninety degree phaseshifted PAC from the phase-shifter 41 coupled to the output of the LUT 30. The signal AUXI can be suitably encoded digital audio signal, derived from the monaural or stereo TV audio system, not shown.

Moreover, the second auxiliary signal may be a control signal useful in operating the play-back system. Such a signal may be a motion signal indicative of motion occurring in the video scene. Suitable techniques known in the art may be used to derive either of the auxiliary signals. Other control signals may be used to be encoded on the phase alternating carrier (PAC) as will be apparent to those skilled in this art. Preferred forms of decoders for the auxiliary signals will be described, with reference to Figures 2, 4 and 5.

The respective modulated phase alternating carriers (PACs) carrying auxiliary signals AUX1 and AUX2 are added at adder 36, the output of which is coupled to an input of adder 42. The second input of adder 42 is coupled to the chroma signal (C) derived from the separator 12. The output of adder 42 is the augmented chroma signal, comprised of the chroma signal encoded with chroma information and the combined phase alternating carriers encoded with one (or two) auxiliary signals. The invention can have application to colour television transmission systems where the chroma signal is not interleaved with the luminance signal, in accordance with a standard NTSC colour television system.

However, the preferred form of the invention is used in video recording systems in which the transmission path is a magnetic tape. The magnetic tapes used in the industry presently are bandwith limited and accordingly dictate that the chroma carrier be placed in the so-called colour under format, whereby the signal, equivalent to the output adder 42, is remodulated in modulator 44 to the spectrum below the luma channel. Typically, the colour under carrier is at 629 KHz (equivalent to 4NJ in the VHS system.

The means to generate the signals in the colour- under format will now be described. The output from adder 42, consisting of the chroma signal (C) and the PAS signal from adder 36, are coupled on path 43 to a first input of modulator 44. The second input to the modulator 44 is a 4.21 MHz carrier signal, which is the output of the band-pass-filter, BPF 47 coupled to the 1 output of the modulator 46. The BPF filter 47 passes only the 4.21 MHz sideband to the modulator 44. The modulator 46 has two inputs; a zero degrees phase cw chroma carrier from oscillator 16 and a 629 KHz (equivalent to 4NJ carrier coupled to the output of the ninety degree phase shifter/El-line 49a. The 629 KHz carrier is frequency and phase locked to the input video signal, since the phase shifter is coupled to the 629 KHz oscillator 48, which is under the control of the horizontal synchroniser H, derived from the video and a 30 Hz switching signal, derived in the recorder, to identify the two recorded tracks on the magnetic tape. The modulation product of modulator 44 has the chroma signal and the auxiliary signals modulated on the 3.58 MHz plus or minus 4.21 MHz carriers. The low-pass filter 51 passes only the 629 KHz sidebands. The 629 KHz carriers are known as the colourunder carriers. The modulated 629 KHz signal is the colour-under signal used in this invention. The colour-under signal and the fm luminance signal are passed through the adder 19 for recording onto the magnetic tape. The input to the recorder thus consists of the fin luminance signal and the two colour under carriers, modulated respectively with the chroma and the auxiliary signal.

It will be appreciated by those skilled in this art that the processing of the phase alternating carrier to be modulated with one or two other auxiliary signals is analogous to the modulation of a chroma carrier in zero degrees and ninety degrees with I and Q chroma components respectively, to generate the chroma signals. Thus the modulator auxiliary signals of the present invention are quadrature, analogous to the I and Q signals of the conventional chroma signal.

The operation of the system of Figure 1 will be further explained in conjunction with the vector diagram of Figure 3. A study of the vector diagram of the two carriers, chroma and PAC, shown in Figure 3 and Tables I and II presented below, show the phase increments of each of the carriers through two frames and several lines of operation. In conventional operation, according to the specifications of the NTSC, the 3.58 MHz carrier is phase alternating by one hundred and eighty degrees on each successive line being scanned. At the start of the first and second fields on lines I and 263 respectively of video frame one, the phase of the chroma carrier is at zero degrees. At the start of the first and second field of two frames, however, the phase of the chroma carrier is at minus one hundred and eighty degrees. The phase of the PAC, moreover, it should be understood, is at zero degrees at the start of each field of frames one and two. These phase values are shown in Table I.

The relative positions of the I and Q vectors and the vectors of the auxiliary signals one and two are shown in Figure 3. In this embodiment, the value of N for the angle of the phase of the signals AUX1 and AUX2, shown as S1 and S2 respectively in Figure 3, are the same as the phase angle of the I and Q signals. As mentioned above, N can be any desired value. The diagram would be more complex if drawn to illustrate the other possible values N and this is not considered necessary for an understanding of the operation of the system, as will be apparent to those skilled in this art.

It is seen that the position of the I and Q vectors remain constant relative to the chroma burst vector which, nevertheless, it should be understood, is alternating line to line. However, because the PACs carrying the auxiliary signals AUX1 and AUX2 are varying relative to the chroma carrier, the auxiliary signals are in phase with the I and Q signal on odd lines and out of phase on even lines, as shown in Figure 3.

An analysis of the phase progression of the colour-under chroma carrier at 629 KHz, depends on an understanding of VHS standards, wherein the phase angle of the 629 KHz carrier is retarded by ninety degrees per H- line for field 1 and, reversing the process, said phase angle is advanced by ninety degrees per H-line for field 2. Reference may be made to Table II for a tabulation and details of these phase changes.

As indicated in Table IL the PAC colour-under carrier is in phase with the chroma colour-under carrier on odd lines and one hundred and eighty degrees out of phase on the even lines, for frame 1. This is due to the constrained alternation of the PAC carrier phase, as described above. Table II indicates that on any two given adjacent lines in a frame, the two 629 KHz carriers are always out of phase on one line and in-phase on the other line. The relative position of the I and Q vectors and the auxiliary signals vectors S1 and S2 remains the same for the colour-under mode, as shown in Figure 3. It should be understood that Table II refers to the carriers without modulation.

Thus, reference is made to Figure 2 for a preferred form of playback decoder. Figure 2 shows a block diagram of the decoder or playback system, utilising the present invention. The fm luminance and the 629 KHz carriers modulated with the chroma and the auxiliary signals are applied on path 100, which is coupled to a low pass filter 102 and a high pass filter 104 respectively. The high pass filter 104 passes the fm luma signal into a known luma processing circuit 106.

The low pass filter 102 passes the LPF output to a ninety degree phase shifter 103. The shifter 103, similar to phase shifter 49a of the encoder of Figure 1, provides a ninety degree phase shift on a line by line basis. A 30 Hz switching signal controls this ninety degree phase, said phase being advanced or delayed, depending upon whether it is an odd field or an even field. The phase shifter 103 passes the 629 KHz signal on paths 108 and 110 to one input of an adder 114 and to the input of adder 112 respectively. The output of 103 is also passed through a 1H delay 111, the output of which is coupled with a second input, respectively, of the adders 112 and 114.

Accordingly, the chroma signal with auxiliary signal information removed by adder 112, is passed on line 116 to a suitable colour processing demodulator 118, which provides the base-band 1 and Q colour components to a colour utilisation device 120. A suitable colour demodulator 118 is described in a co-pending Patent Application Number (Agents Ref D966) entitled "Apparatus for Restoring the Correct Phase Relation of the Chroma and Luminance Signals Passed Through Separate Paths".

The 629 KHz carriers modulated only by auxiliary signals, AUX1 and AUX2, are recovered as the output of adder 114 and are coupled to an auxiliary signal processor 124. The processor 124 demodulates the PAC, encoded with the auxiliary signals and provides them at separate outputs 126 and 128 for use as desired.

A preferred processor 124 is shown in Figure 4. The augmented chroma signal is coupled to the 1 -H delay line 111 and to the other input of the adder 114. the PH delayed signal is applied to the other input of the adder 114. The output of the adder 114 is the PAS conducted on path 122 to the respective input of modulators 130 and 132. The colour oscillator 16 output on path 133 is applied to an N degree phase shifter 134 and then to multiplexer 136. MUX 136, in a similar manner as MUX 20 of the encoder of Figure 1, provides a line separator directly to modulator 130 or, by a ninety degree phase shifter 138, to modulator 132. Modulators 130 and 132 demodulate the encoded carriers to extract the respective audio signals, AUX l and AUX2, after being passed through the low pass filter 140 and 142. The auxiliary signal demodulator or processor shown in Figure 4 is useful for demodulating two auxiliary signals and can be used even if only one auxiliary signal is to be demodulated. However, for systems in which only one auxiliary signal is to be demodulated, a simplified and more efficient circuit may be used, as shown in Figure 5.

Figure 5, responding to the augmented chroma signal with PAS with only one auxiliary signal, is passed through the IR delay 111, and the adder 114. The output is coupled to an envelope detector 150, comprised of an absolute value detector 152, such as a PROM, and then to a low pass filter 154. The output is the auxiliary signal provided at either source 32 or 38 of Figure 1.

While the invention has been described using a 3.58 MHz chroma carrier and subsequently modulated to the colour under carrier of 629 KHz, the invention can be embodied with the base band chroma directly modulating a 629 KHz carrier.

Moreover, for systems such as PAL, Beta tape formats and similar systems where the chroma carrier is encoded with different phase relationships than the VHS format, the present invention would be embodied in such systems with the encoded alternating carrier in phase alternation relative to the chroma carrier.

The embodiment of the invention described herein first alternates the carrier which is subsequently encoded with one or two auxiliary signals. It will be apparent to those skilled in this art that the process can be reversed. Thus, the carrier may be first encoded with the desired auxiliary signals and subsequently the carrier can be phased alternated. Otherwise, the process described above will be followed.

Furthermore, while the invention has been described for applications in the particular embodiments illustrated, other applications will be readily apparent to those skilled in this art limited only by the appended claims.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

.- Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly z - 13 stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAINIS carrier and 1. In a video signal processing system having a chroma

carrier modulated with chroma information, characterised by: means responsive to said chroma carrier for generating a phase alternating carrier, whereby said phase alternating carrier and said chroma carrier are one hundred and eighty degrees out of phase on alternate scan lines, means for modulating a first auxiliary signal on said phase alternating means for adding said phase alternating modulated carrier to said modulated chroma carrier at a given phase angle.

is
2. A system according to Claim 1, characterised by: modulating means for generating, in response to said chroma carrier and said phase alternating carrier, a colourunder'chroma carrier with line to line and frame to frame phase inversion of one hundred and eighty degrees relative to said chroma carrier, wherein said colour-under phase alternating carrier is one hundred and eighty degrees out of phase relative to said colour20 under chroma carrier.
3. A system according to Claim 1, including means for adding a second auxiliary signal to said phase alternating carrier, whereby said modulated phase alternating carrier includes said first and second auxiliary 25 signals.
4. A system according to Claim 1, wherein said phase alternating carrier generating means comprises a PROM.

z
5. A system according to Claim 1, wherein said first auxiliary signal is a digital audio signal.
6. A system according to Claim 5, wherein said audio signal comprises a frequency multiplexed signal of one or more audio signals.
7. A system according to Claim 1, wherein said first auxiliary signal is a signal indicative of motion in said video signal.
8. A system according to Claim 3, wherein said first auxiliary signal is a digital audio signal and said second auxiliary signal is a motion indicating signal.
9. A system according to Claim 2, wherein said phase alternating carrier is at zero degrees phase angle relative to the phase of said colourunder carrier.
10. A method of operating a video signal processing system, having a chroma carrier modulated with chroma information, characterised by the steps of.

generating, in response to said chroma carrier, a phase alternating carrier, with line to line phasing inversion of one hundred and eighty degrees relative to said chroma carrier, wherein said phase alternating carrier is one hundred and eighty degrees out of phase relative to said colour-under carrier; modulating said phase alternating carrier by a first auxiliary signal; and adding said modulated phase alternating carrier to said chroma carrier at a given phase angle.
11. A method according to Claim 10, characterised by:

generating, in response to said modulated chroma carrier and said modulated phase alternating carrier, a colour-under chroma carrier with line to line phase inversion of one hundred and eighty degrees relative to said chroma carrier, wherein said colour-under modulated phase alternating carrier is one hundred and eighty degrees out of phase relative to said colour- under chroma carrier.
12. A method according to Claim 10 or Claim 11, further including the step of adding a second signal which is the phase alternating carrier in quadrature modulated by a second auxiliary signal to said first signal, wherein said encoded signal includes said first and second auxiliary signals.
13. A method according to Claim 10, wherein said first signal modulating step includes modulating said first alternating carrier with a digital audio signal.
14. A method according to Claim 13, wherein said audio signal comprises a time division multiplexed carrier with one or more audio signals.
15. A method according to Claim 10, wherein the step of modulating said alternating carrier signal with said first signal comprises a signal indicative of motion in a video scene.
16. A video signal processor having a chroma carrier modulated with chroma information, comprising:

means responsive to said chroma carrier for generating a phase alternating carrier, 1 Z means for modulating a first auxiliary signal on said phase alternating carrier with line to line and frame to frame phase inversion of one hundred and eighty degrees relative to said chroma carrier, wherein said modulated phase alternating carrier is one hundred and eighty degrees out of phase relative to said colour-under chroma carrier; means for adding said modulated phase alternating carrier to said chroma carrier at a given phase angle, thereby to provide said chroma carrier combined with said modulated phase alternating carrier modulated with said first auxiliary signal; and means responsive to said modulated phase alternative carrier and said colour-under carrier to separate said chroma carrier and said first auxiliary signal into respective separate output channels.
17. A system according to Claim 16, including: modulating means for generating, in response to said chroma carrier and said modulated phase alternating carrier, modulated colour-under carriers responding respectively to said modulated chroma carrier and modulated phase alternating carrier.
18. A processor according to Claim 16, wherein said separating means includes a PH delayed line coupled to the combined modulated carriers and to a pair of summers arranged to provide the sum of the two modulated carriers at the output of one of said summer, and the difference of said modulated carriers at the output of the other summer, the respective summers being coupled to the delayed carriers at the output of said PH delay line.
19. A processor according to Claim 17, including means for modulating said phase alternating colour-under carrier by a second auxiliary signal, wherein said auxiliary signal includes said first and second auxiliary signals, and said separating means separates both of said modulated phase alternating carrier and said modulated chroma carrier into respective separate channels.
20. A processor according to Claim 19, wherein said separating means includes a PH delayed line coupled to the combined modulated carriers and to a pair of summers, arranged to provide the sum of the two modulated carriers at the output of one of said summer, and the difference of said modulated carriers at the output of the other summer, the respective summers being coupled to the delay carriers at the output of said PH delay line.
21. A processor according to Claim 18, further including means for demodulating said first auxiliary signal from a phase alternating colourunder carrier signal, to demodulate first auxiliary signal from said colour-under carrier.
22. Apparatus for conveying modulation of two carriers to a remote position, in a system having signals derived along parallel scan lines, said apparatus including means for encoding a modulated first carriers and a modulated second carrier, comprising:

a source of a modulated first carrier, said first carrier being such that, in its unmodulated state, it is one hundred and eighty degrees out of phase at corresponding points along consecutive scan lines, a source of a modulated second carrier, said second carrier being such that, in its unmodulated state, it is in phase at corresponding points along consecutive scan lines, and adding means coupled to said source.
23. Apparatus according to Claim 22, including means coupled to said adding means for conveying representation of said modulated first and second carriers to a remote point.
24. Apparatus according to Claim 23, including PH delay means having a delay of one scan line, said delay means having an input coupled to said remote point and an output, said means having inputs respectively coupled to said remote point and the output of said delay means so as to provide signals corresponding to the modulation of said phase alternating second carrier, and subtracting means having inputs respectively coupled to an inverted output of said remote point and the output of said delay means so as to 15 provide signals corresponding to the modulation of said first carrier.
25. Apparatus according to Claim 22, wherein said modulated phase alternating carrier has quadrature components thereof respectively modulated with first and second auxiliary signals.
26. Apparatus according to Claim 22, wherein said first and second carriers have the same frequency.
27. Apparatus according to Claim 22, wherein said first carrier is a colour subcarrier of an NTSC system and said second phase alternating carrier has the same frequency as said colour subcarrier.

is
28. Apparatus according to Claim 27, wherein said means of conveying representations of said modulated first and second carriers to said remote points includes: means for modulating signals supplied by said adding means with signals having a frequency different from the frequency of either of said first and phase alternating carriers so as to produce the representation of said modulated first and phase alternating carriers so as to produce the representation of said modulated first and phase alternating carriers at a different frequency, recording means coupled to record the signals provided by said modulating means; and means coupled to said recording process for producing carrier waves having the same phase relationship with respect to the same lines as the modulated first and phase alternating carriers.
29. A video signal processing system substantially as herein described with reference to the accompanying drawings.
30. A method of processing video signals substantially as herein 20 described with reference to the accompanying drawings.

Published 1991 at 7be Patent Office. Concept House. Cardiff Road, Newport. Gwent NP9 I RH. Further copies nuty be obtained frorn Sales Branch. Unit 6. Nine Mile Point, Cwrnfelinfhch, Cross Keys, Newport. NP1 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.