FR2550041A1 - METHOD AND DEVICE FOR TRANSMITTING AND RECEIVING MULTIPLEX VIDEO SIGNALS - Google Patents

Abstract

THE INVENTION RELATES TO A DEVICE FOR CODING A COLOR TELEVISION SIGNAL FOR ITS TRANSMISSION. ACCORDING TO THE INVENTION, A MULTIPLEX ANALOGUE SIGNAL CONSISTS OF A SEQUENCE OF COMPONENTS COMPRESSED IN THE Y, R-Y, B-Y TIME. IN ORDER TO JAM THE SIGNAL FOR ITS SAFETY, THE INDIVIDUAL COMPONENTS ARE SEPARATELY TURNED IN TIME. THE LOCKING LEVEL POSITION BETWEEN THE COMPONENTS IS UNCHANGED, TO REMOVE ANY INDICATION CONCERNING THE DEGREE OF ROTATION. THE INVENTION APPLIES IN PARTICULAR TO COLOR TELEVISION.

Description

The present invention relates to the transmission and reception of

  video signals This concerns the interference and suppression of the jamming of multiplexed analog video (MAC) signals. It is desirable to encode television signals to produce transmission in such areas as cable television, transmissions and video transmissions.

  satellite and television broadcasting for subscribers.

  The known coding arrangements may, in general, be considered as being of the altering type of the amplitude or of the alteration type of the sequence in time. The amplitude encoders comprise, by way of example, those which alter the amplitude of the vertical or horizontal sync pulse or which modulate the video signal by a coding waveform (such as a sine wave) and have the advantage that the decoder can be relatively simple and inexpensive Amplitude coding has the disadvantage that, in general terms, the codes are fairly easy to recognize and decipher, thereby creating a potential "black market" for unauthorized decoders. From a technical point of view , the amplitude distortion imparted to the video signal may not be fully removed by the decoder and critical adjustments of the decoder may be required to reduce the residual distortion of the signal. The other problems that are associated with the amplitude distortion type interference means include the degradation of the signal-to-noise ratio and the loss of the dynamic range of the alteration type encoders. of the sequence in time reorder the sequence of the video signal to create a non-standard sequence that can be -. randomly changed to provide a very high level of security Examples of such encoders include those that reverse the sequence of picture elements in a horizontal line, those that transpose or exchange lines in a frame, or that transpose or rearrange segments of each line. of the video signal as described in US Patent No. 4,070,693 of January 24, 1978 to the name HB Shutterly, incorporated herein.

for reference.

  The Shutterly system, which scrambles one line of video at a time- (in-line scrambling means), has the advantage of requiring fewer encoder and decoder memories than coders of the type modifying line sequences in blocks of data. Lines (intermixing scramble) In short, in the Shutterly system, each active line of the signal

  Composite video is "shot" around a predetermined point that is randomly changed from time to time.

  The information about the rotation point is transferred over a selected line of the vertical interval. The rotation code does not directly indicate the rotation point itself but rather is used to synchronize a statistical number generator in the decoder on a similar generator of statistical number 25 in the encoder so to offer a

  safety regarding the point of rotation.

  The present invention partially resides in the recognition that the method of rotational coding of the intralignment picture elements applied to conventional composite video signals results in a code which can be quite easily deciphered by applying to format video signals. video transmission

  of the type called "MAC" (multiplexed analog component).

  In MAC video transmission systems, a color video signal is transmitted by a channel (such as a satellite transponder, a cable or broadcast system, a video tape recorder, etc.) using analog components compressed in time and Serial transmission Serial transmission is preferred because only one channel is required. The use of time compressed components to present the color signal (i.e., Y, RY, BY or Y, U, V or Y, IQ or R, G, B, etc.) produces a desirable reduction in crosstalk between luminance and chrominance components. Generally, US Pat. No. 4,376,957 entitled "Transmission System" can be referred to. With the Sequential Time Compressed Baseband Color "of March 15, 1983 on behalf of Dischert et al. And US Patent Application No. 509,786 entitled" Worldwide Compatible Synchronizing Signal for Accurate Time Base Correction in An Analog Component Interface ". Standard "20 filed on June 30, 1983 by T M Gurley, each being

  incorporated herein by reference.

  It is an object of the present invention to obtain the benefits of inline pixel coding of picture elements in a multiplexed analog component type video transmission system without loss of coding security as will be explained subsequently. A method of encoding a television signal for transmission and embodying the present invention comprises providing a source of a television signal to be encoded, each line of said television signal comprising a luminance component and at least one component of chrominance First and second signal paths are provided for selectively applying the luminance component and the chrominance component, respectively, to an output terminal for

  selected intervals of time not overlapping.

  The luminance component in the first path is compressed in time by a given amount and the chrominance component in the second path

  is compressed in time by a larger amount.

  The sequence of the luminance components in the first path is rotated independently of the rotation of the sequence of the chrominance components in the second path to encode said luminance and chrominance components without altering the position, in

  the time, of said components in the coded line of the television signal that is obtained at the output terminal 15.

  The invention will be better understood, and other purposes, features, details and advantages thereof

  will become more apparent in the following explanatory description with reference to the accompanying schematic drawings given by way of example only

  illustrating an embodiment of the invention, and wherein: Figs. 1A and 1B show simplified waveforms illustrating intraligno rotation coding of MAC format video signals; FIGS. 2A and 2B are simplified waveforms illustrating the coding by intra-line rotation of MAC format video signals according to the invention; Figures 3A and 3B show detailed waveforms illustrating the principles of the invention applying to a video transmission system where three components are incorporated in each line; FIG. 4 gives a block diagram of an example of an encoder according to the invention; and Figure 5 gives a block diagram of an example

of a decoder according to the invention.

  Figure 1A is a simplified representation of a line of a "two-component" MAC waveform (receiver timing and timing signals are not shown) Region A is a signal blocking level In the two-component system, the color components U and V are transmitted on alternating lines, in opposition to a "three-component" system, or the luminance component and the two components of the two-component system. chrominance are transmitted during the duration of a horizontal line, which equates to approximately 63 / 1s. Region B corresponds to the interval of the blocking level between the chrominance component (U or V) and the luminance component Y. 1 B illustrates the effect of the "rotation" of the signal components of FIG. 1A around the 20-point K It is instructive to note that the regions A and B have slipped with respect to the beginning of the line (T 1, arbitrary point reference) and that this slip directly indicates the rotation of the image elements of the line. In more detail, the rotation point 25 K of FIG. 1A is delimited by the points N and O in the signal Y. a rotation (Figure l B), the new line starts at the point O of the Y signal and

  progresses through the points P, M and N, as can be seen, to form a new sequence of the "turned" signal for the transmitted line.

  The problem illustrated by FIGS. 1A and 1B is that the degree of rotation of the rotated line signal elements can be easily determined by simply measuring the time between the last horizontal sync pulse (not shown ) and one of the easily recognizable blocking level intervals A or B As a result, the scrambling code can easily be found, thus encouraging a "black market", so to speak, of "pirate" decoders This illustrates the problem ignored until now that the rotation of image elements inline that is very effective in video transmission systems

  composites of the type described by Shutterly, is not effective in video transmission in MAC format.

  Figures 2A and 2B are similar to Figures 1A and 1B, but illustrate the coding technique

  by intra-line rotation of the present invention.

  As is readily apparent, the gaps of the blocking level A and B in the uncoded line (FIG. 2A) and in the coded line (rotated) (FIG. 2B) transmit absolutely no information regarding the degree of rotation. In other words, the regions A and B of the blocking levels do not slip and are not in any way impaired by the spinning process. This desirable result, which offers a high level of security for the coded signal, is obtained according to FIG. by rotating each component individually relative to its own point of rotation (K and K ') By transposing this principle to a three-component system, each component is individually rotated relative to its own point of rotation (K, K 'and K ") for each respective component (i.e. Y, I and Q or Y, U and V,

or Y, R-Y and B-Y, etc.).

  Figs. 3A and 3B provide a detailed example of the principles of the invention applying to a three-component MAC-format video transmission system of the type described, for example, in the above-mentioned US patent application of US Pat. TM Gurley It should be noted that, as in the examples of FIGS. 2A and 2B, the "flags" (blocking levels) maintain the same positions in the scrambled signal (FIG. 3B) as in the unscrambled signal (FIG. A) and that there is no identifiable fixed pattern for suppressing the interference of the signal. In this system, the "non-scrambled" waveform (3 A) begins with a horizontal sync pulse at -40 IRE units followed by a burst of the delay signal (T). The burst T has peak-to-peak values of -20 and +20 IRE units and it is used in the receiver / decoder to synchronize a locked-in-phase loop (PLL) which produces the decoder timing signals and is not the conventional color burst signal used in

  composite television transmissions.

  The luminance component Y, the color difference component R-Y and the color difference component B-Y follow the time component, T, in the order indicated. However, the order of the components

  does not matter in the context of the present invention.

  It is important that each individual component is rotated around its own separate point of rotation, which are: K 1 for Y, K 2 for RY and K 3 for BY 25 and all levels of blocking in the coded signal (3 B ) are aligned with the corresponding levels

of the uncoded signal (3 A).

  In more detail, the uncoded Y component starts at point A with the rotation point K 1 at location B, B 'and ends at point C. When the Y component is rotated, the rotated component starts at point B' This is followed by the segment B 'to C, the point K' and then the segment K to B. The component Y thus begins, in this example, with the region B'-C, followed by the point A (the starting point no coded) and the point B This rotation, in other words, places the last signal elements of the Y component at the beginning of the Y component in the coded signal but the order of the picture elements in each turned segment remains unchanged Each of the Y components,

  R-Y and B-Y has its own respective point of rotation.

  It can be noted that all blocking levels (ie O IRE and + 50 IRE) between the components maintain

  their exact positions in the coded component as in the uncoded component.

  The principles of the present invention have general utility in video transmission systems

in MAC format.

  FIG. 4 illustrates the one-component rotational coding scheme of the present invention applied to a MAC transmission encoder disclosed in the aforementioned U. Gurley patent application. The Gurley system is a

  a single channel where the Y, R-Y and B-Y components are transmitted during each interval of a line.

  The encoder comprises a source 400 of the component video signal which applies a luminance component Y to an analog to digital converter (A / D) 402, a first color difference component RY to an analog / digital converter 404 and a second difference component By way of example, the source 400 may comprise a matrix circuit for converting the outputs R, G and B of a color camera 30 or any other appropriate source of the Y, RY and BY components. The converters 402, 404 and 406 may comprise conventional eight-bit flash converters.

  operation at video frequencies are well known and commercialized.

  The digital form outputs of the converters 402, 404 and 406 are applied by three respective paths (path one, path two and path three respectively) to a multiplexer 410 which selectively links the paths to an output terminal 408. The switching unit The multiplexer 410 receives the three signals Y, RY, BY from the paths at its inputs to apply some of these selected signals to the terminal 408 by a digital-to-analog converter 412 coupled in series with a signal insertion unit.

timing and code 414.

  A timing signal source 416 applies clock signals to the analog-to-digital converters (and also to rotators and time compressors in the paths, as will be described). The source 416 also applies selection signals via a bus. 418 to the multiplexer switch 410 and applies horizontal and vertical synchronization signals (HS, VS), a burst signal at the reference frequency 20 and blocking level enable signals to the insertion means 414 via the bus 420 Each of the three signal paths comprises a serial connection of a rotator and a compressor in time (422, 424 respectively in path one, 426, 428, 2 d respectively in path two, and 430, 432, respectively in the path 3) The digital-analog time compressors and the signal sequence rotators are quite well known Examples are given in the patents The insertion means 414 is also coupled to receive the rotation code signals K 1, K 2 and K 3 from a source code 450 of the rotator apparatus, which signals are also respectively applied to rotator devices 422, 426 and 430 In short, compressors 424, 428 and 432 compress over time the video components Y, RY and BY by factors of 2: 1, 4: 1 and 4: 1, respectively source 416 operates the multiplexer 410 to

  sequentially selecting the outputs of the two and three paths for application to the converter 412.

  The insertion means 414 adds HS, VS, the signal to the reference frequency and produces the blocking under

control of the source 416.

  According to the present invention, the code source 450 of the rotator apparatus applies the rotation codes K 1, K 2 and K 3 to the rotator devices of signal elements 422, 426 and 430 which, independently of one another, rotate the elements of the component Y in the path one, the component RY in the path number two and the component B-Y in the path number three As a result, there is no change in the relative positions of the components or blocking levels of the component signals during a rotation as previously described with reference to FIG. 3, and thus there is no indication in the position of the component signal contained in the coded signals appearing in FIG. terminal 408. The source 450 also applies the rotation codes K 1, K 2 and K 3 to the insertion means 414 for transmission during the vertical interval of the video output signal to the terminal 408. The security of the rotation codes can be improved by the previously described Shutterly technique or the rotation codes can be transferred by other means (such as a separate transmission channel, a permanently programmed read-only memory or any other secure transmission system). It is important in the context of the present invention, as previously indicated, that each transmitted component is rotated or otherwise encoded in a non-positional manner, in the

time, transmitted components.

2550041,

  The security coding system of the video signal in the MAC format of FIG. 4 can be applied to the decoder by a satellite communication link, by a direct cable transmission system or by any other suitable communication channel. FIG. example of a decoder suitable for the encoder

of Figure 4.

  In FIG. 5, the coded signal is applied to the input terminal 502 which is connected to a regenerator 504.

  timing signals, a digital analog converter 506 and a rotation code detector 508.

  The regenerator 504 includes a phase locked loop (PLL) and counters, and responds to the reference frequency component of the input coded signal to produce clock signals for the expansion means, the rotator devices and the digital converters in the decoder The regenerator 504 also triggers the code detector of the rotary apparatus 508 while

  the appropriate line of the vertical interval for decoding the rotation codes K 1, K 2 and K 3.

  The output of the converter 506 is applied to a demultiplexer or switching unit 510 controlled by the regenerator 504 to selectively couple the output of the converter 506 to the signal outputs one, two and three respectively in synchronism with the transmission of the component signals Y, RY and BY, The path 1 comprises a first digital-to-analog converter 514 whose output is coupled to an output terminal 508 of the Y component and whose input is coupled by a series connection of a rotator 516 of elements of the signal and a time expansion means 518 of 1: 2 at the output of the Y component of the switching unit 510 In the two and three paths, the digital-to-analog converters 520 and 526, the rotary devices 522 and 528 and the expansion means

2550041.

  In time 524 and 530 are similarly connected. The time expansion means for the color difference signals RY, BY, however, produce an expansion of 1: 4 compared to the expansion factor of 1: 2 for the means of expansion

  of the component of Y in the path one.

  The operation of the decoder of FIG. 5 is essentially as described in Gurley's patent application with the exception of the presence of the rotator apparatus code detector 508 and the individual rotators 516, 522 and 528. The three rotational codes transferred during the vertical interval of the input signal applied to the terminal 502 are detected by the detector 508 and applied to the three component rotators 516, 522 and 528 in the one, two and three paths, respectively, which rotate the respective elements of the Y, RY and BY signals in a direction opposite to the original rotation, thereby decoding the individual components

Y, R-Y and B-Y.

  It may be noted that the application of the principles of

  the invention to Gurley's three-component system Y, R-Y, B-Y is only one example of the invention.

  The individual rotation of the chrominance and luminance components in multiplexed analog video signal (MAV) transmission systems offers the simplicity of an in-line scrambling characteristic of the component E transmission systems but avoids the previously mentioned problem of time-shift components in proportion to the in-line rotation to thereby give an indication of the offset in time or rotation required for decoding. The present invention, in other words, provides, to the sequential systems of transmission of the components, the typical security level of conventional line-rotation composite video transmission systems The principles of the invention are of general utility and can be applied to two- or three-component systems (as previously mentioned) and can be applied to components including Y, I and Q or Y, U and V as well as the given example of Y, R-Y

and B-Y.

Claims (5)

R E V E N D I C A T I 0 N S CLAIMS =: =: =: =: =: =: =: =: =: =: =: =: =   A method of encoding a color television signal for a transmission characterized by the steps of: (a) providing a source (400) of color television signals to be encoded, each line of the television signal comprising a luminance component and minus one chrominance component; (b) providing a first signal path and at least one other signal path for selectively coupling said luminance component (Y) and the or each chrominance component (RY or BY), respectively, to an output ( 408) during selected intervals of time not overlapping; (c) compressing, in time (424), said luminance component in the first path by a predetermined amount and compressing, in time (428 or 432), the or each chrominance component in the or each other path of a predetermined larger quantity; and (d) independently rotating (422, 426, 430, 450) said sequence of luminance components in said first path and rotating the one or each chrominance component in the or each other path in time to encode said luminance and chrominance components without altering the position in time of said components in the coded line of said signal   television at said output (408).   A method of decoding a color television signal having a luminance component and at least one chrominance component transmitted as a component in time sequence wherein each component is separately encoded by rotation of the signal elements in the component, characterized by the steps of: (a) providing a first path for coupling the luminance component (Y) of the television signal to an output (508) during a first period of time; (b) providing at least one other path for coupling the or each chrominance component (RY, BY) of said television signal to an output (510, 512) for a second period of time, said second period of time being spaced from said first period of time by a predetermined period of time during which the television signal is blocked at a blocking level; and (c) rotating (516, 522, 504, 508) the signal elements of said luminance component (Y) during said first period of time in order to restore said luminance signal to its original sequence over time and separately rotating the signal elements of the or each chrominance component (RY) during the second period of time in one direction to restore   the or each chrominance component to its original sequence in time.   3 Apparatus for coding a color television signal for transmission, characterized by: (a) a source (400) of color signals to be encoded, each line of said television signal comprising a luminance component (Y) and at least one chrominance component; (b) a first signal path and at least one other signal path for selectively coupling said luminance component and the or each chrominance component (RY, BY), respectively, to an output (408) during selected intervals not overlapping with time; (c) means for compressing, in time, said luminance component (Y) in said first path of a , AT ' -, 2550 <1   predetermined amount and compressing, in time, the or each chrominance component (RY, BY) "in the or each other traj and a predefined amount more important; and (d) a means for making Independently, turning the sequence of component components in the first path into time, and rotating the or each component of the chrominance signal (RY, BY) in the respective one or each other. signal path for encoding said luminance (Y) and chroma (RY, BY) components without altering the position, in time, of said components in the coded television signal line produced at the output (408).   Apparatus for decoding a color television signal having a luminance component and at least one chrominance component transmitted in a time-sequenced form wherein each component is 'separately encoded' by rotation of elements of the signal 20 in the component characterized by: (a) a first path for coupling the luminance component (Y) of said television signal to one output during a first period of time; (b) at least one other path for coupling the or each chroma component (RY, BY) of the one-output television signal (5-10, 51 2) for a second period of time, said second period of time being spaced from said first period of time by a predetermined period during which the television signal is blocked at a given blocking level; and (c) means (516, 522, 504, 508) for rotating the signal elements of the luminance component (Y) during the first period of teps'afin to restore the luminance signal to its original sequence in time and separately rotate the elements in the signal of the or each chrominance component (RY, BY)   during the second period of time in a sense to restore the or each chroma component to its original sequence over time.   A television system characterized by a coding device according to claim 3 and a   decoding device according to claim 4.   A color television transmission system characterized by: (a) a source (400) of a television signal   in color in the form of components;   (b) means (432, 428, 424) for compressing the components of said quantity television signal.   to allow serial transmission of each line during each interval of a line; (c) means (450, 430, 426, 422) for separately rotating, in time, the signal sequence of each component of each line; (d) a transmission medium (410, 412, -414, 416) for serially transferring the compressed components over time and individually timed to a receiving means, said receiver means comprising (e) a means (510) to separate the components transferred in series and individually rotated the weather;.   (f) means for rotating (516, 522, 528, 508, 504) over time (530, 524, 518) each of said separated components in a complementary manner to the first rotation in time and to the first compression in time mentioned