Abstract: The invention provides a system of encoding broadcast-quality television signals to enable their transmission as a embedded code.A preferred embodiment provides a hybrid interpolative/predictive coding algorithm acting on all sampled sites of a television signal. One sub-set of samples are adaptively interpolatively coded; a 3-state interpolator switching signal is produced at each site, redundancy is removed and the signal transmitted. The interpolator switching signal also acts as a descriptor at sites surrounded each sample to be predicted. Adaptive prediction is used for the other sub-set of samples the particular predictor used at a sample site being determined by the surrounding descriptors.

Abstract: A method of processing digital information prior to recording comprises converting input digital words into code words, each of the same period as the input digital word but containing a greater number of time slots than the number of bit locations in the digital word, providing a plurality of groups of code words and selecting the group from which a code word will be taken in any instance on the basis of the immediately preceding code word. The code words are defined such that there is a minimum spacing of three time slots between transitions and no transition is permitted in the last time slot. Two main groups of code words are provided which each have a transformed version. Apparatus for carrying out the method as described as is apparatus for decoding the encode words in replay.

Abstract: A conditional access system for over-air transmission and reception of scrambled television signals improves the reliability of the reception by transmitting a key signal for use in descrambling the television signal in a block of information which is itself encyphered by the key signal. On reception, the receiver after decyphering of the block of information compares the key signal recovered from the block with the key signal provided at the receiver for decyphering the block. Descrambling will only be allowed if comparison shows the two key signals to be the same. The system also provides for information relating to the credit status of each user to be transmitted over-air. In order to ensure rapid operation, the credit status signal is sent repeatedly and a further signal is appended which is used at the receiver to prevent repeated accumulation of credit.

Abstract: A method of encrypting a television signal having in each ruster scan line a digital section of information and chrominance and luminance sections of information comprising cutting either or both of the chrominance and luminance sections and rotating the cut sections within a normal line period. If one of the sections is uncut, it may be translated in time with respect to the line period by having one of the rotated cut sections placed before the uncut section and one placed after the uncut section. The cutting point or points are determined by a pseudo random number generator. Receiving apparatus for receiving such an encrypted signal is also disclosed in which a complementary pseudo random number generator is used responsive to receipt of an encryption key to control addressing of a descrambling store in order to reconstitute the original signal.

Abstract: In a method of transmitting and receiving Multiplexed Analog Component (MAC) television signals by producing first chrominance component and luminance component signals representing lines of a television signal capable of reconstruction in a conventional MAC television receiver to produce a first television picture having a first aspect ratio and a first number of lines and wherein the component signals for each line are time-compressed and placed sequentially at times appropriate to allow reconstruction of the television picture but occupying less than the whole line time, the improvement whereby further luminance component and chrominance component signals are generated and added to portions of the television signal not containing the first signals such that the further component signals are capable of being reproduced together with the first signals to produce an extended definition picture with the further component signals not interfering with the picture reproduction from the first chrominance and lumin

Abstract: A conditional access system for transmitting and receiving scrambled television signals over-air includes means for addressing each of the receiving apparatus with an over-air signal whereby to permit reception and descrambling of the signal. The transmitter is provided with means for assembling a cipher block of information including a first key for use in descrambling the television signal and information relating to a plurality of users, and means for encyphering the cipher block with a second key which is common to the plurality of users. On reception a receiver applies the second, common keys to the received cipher block, recovers the first key for use in descrambling the signal and the information relating to the respective user and descrambles the television signal. Further, it is proposed to transmit a further key in encrypted form and to use the first key to decrypt the further key which is then used to descramble the television signal.

Abstract: A movement detector for detecting movement in a television picture comprises a local movement detector which produces an output signal as a result of comparing similar input signals from different fields and the detector output signal is processed in a field store processor which spreads the output signal in space and in time. The processor comprises a recursive loop, a field delay element and a look-up table, with the latter receiving as inputs the output from the recursive loop and the instantaneous input to the processor to produce a control signal output. A line interlace to non-interlace transformation circuit including such a movement detector is also disclosed.

Abstract: Receiving apparatus for receiving multiplexed analogue component signals each of which represents a line of a television picture and includes a burst of digital signals, at least one of the multiplexed analogue component signals including at a predetermined location within its digital burst an indication of further information, the apparatus comprising a demodulating device for demodulating received multiplexed analogue component signals, means responsive to the output of the demodulating device for synchronizing the receiving apparatus to the received multiplexed analogue component signals, and a data extraction circuit responsive to the synchronizing means for extracting from the demodulated signals the indication of further information and for controlling the operation of the demodulating device in accordance with the further information.

Abstract: A broadcast signal transmitter utilizes a klystron and a transmitter amplifier (10) operating in a pulsed mode. Two feedback loops are provided for controlling the output of the amplifier (10). A first feedback loop includes a control circuit (14) for providing automatic gain control of the black level of a vision signal to be transmitted while the second feedback loop includes a further control circuit (18) for improving the linearity of the transmitter. The first feedback loop output control signal at line rate while the second feedback loop output signals at first rate, both being operative during the period when an insertion test signal (I.T.S.) is supplied to the transmitter.

Abstract: A movement detector is included in television signal processing apparatus in order to improve the performance of the apparatus. The detector evaluates an absolute frame difference signal on a sample by sample basis and, after comparison with a threshold level signal in order to remove the effects of noise is fed to an isolated point removal circuit where samples deemed to indicate movement are compared with surrounding samples and if identified as isolated are ignored. Adaptive control is provided if the threshold, the isolated point removal circuit and a quantizer circuit for non-linearly altering the frame difference signal.

Abstract: A phase lock loop demodulator has its loop transfer function (F(s)) optimized to: F(s)=A+B/s+CF.sub.1 (s)+DF.sub.2 (s) where CF.sub.1 (s) is a chrominance sub-carrier term DF.sub.2 (s) is a sound sub-carrier term and A, B, C and D are constants whereby to minimize the phase error signal appearing at the output of the phase comparator (10) of the loop. An equalizer circuit (14) may be added at the output of the loop in which case the transfer function (F.sub.T (s)) of the equalizer circuit is as follows: F.sub.T (s)=KoKd+s/F(s) where F(s) is the transfer function of the loop amplifier circuit (12) and A, Ko and Kd are constants.

Abstract: A filter for filtering analog or digital samples using two sections, each including a multiplier stage having a plurality of multiplier sections, each with a respective output but a common input for applying a plurality of coefficients to a sample input to the multiplier stage, and a delay and summing network comprising a plurality of delay sections and alternate summing networks connected in series, the output of one of the multiplier sections being connected to the first delay sections in the series with each output of the other multiplier sections being connected to a respective summing network, the delay and summing network of one section being interleaved in series with the delay and summing network of the other section, and further comprising means for omitting alternate samples.

Abstract: Chrominance component signals of two different types are produced such that the chrominance signals alternate within a field and between adjacent fields in order to provide an improved amount of information from which to enhance the vertical chrominance resolution of a television receiver. The appropriate chrominance structure is either provided by a special source or else a conventional source is filtered in order to produce the appropriate structure. The filter comprises two portions, one for filtering chrominance signals of a first type from a first field and one for filtering chrominance signals of a second type from the first field in order to provide interpolated signals. A specific filter structure is disclosed which may be used for either pre- or post-filtering.

Abstract: Method and apparatus for deriving line and frame frequency synchronization signals from a received television signal which has a repeated sequence of a plurality of different digital words, each word being in a respective one of a plurality of lines, as synchronization signals. One of the digital words is recognized and a first signal indicative of the recognition of one of the digital words is generated. Another digital word is recognized and at least one further signal indicative of recognition of the respective further word is generated. The first and second signals are used to determine the sequence and timing of the first and further signals to, in turn, generate a signal indicative of synchronization signal detection. The initiation of receiver sync signals at the line and frame frequency is obtained in response to the signal produced as a result of the signal indicative of synchronization signal detection.

Abstract: A method and apparatus for error-correcting a digital signal by reception of an error-protected digital signal including error correction information and further information representing a parameter of the signal in each of a plurality of blocks of digital information present in the signal, deriving the further information from the signal, decoding error protection information from the signal, deriving protected signal information and separating it into blocks, correcting errors in each block of protected digital information in response to information derived from the further information and the error protection information including pre-correcting the protected digital information using the further information and error-correcting the thus pre-corrected signal using the error protection information.

Abstract: In a system in which an information signal is transmitted along with digital data from a transmitter to a receiver, transmitter circuitry is provided which produces digital data indicative of parameters relating to noise reduction for the information signal, and receiver circuitry is provided responsive to the digital data so as to optimize reception of the information signal. In one embodiment of the invention, one of a plurality of different pre-emphasis levels is applied to a signal and digital data is produced according to a value of pre-emphasis added. The digital data and the pre-emphasized signal are then transmitted. The receiver decodes the digital data and adds a corresponding amount of de-emphasis to the received information signal. In another embodiment the digital data indicates an optimum value for a parameter to be applied to a threshold extension demodulator in the receiver.

Abstract: A demodulator for television signals includes a feedback loop which incorporates a delay for feeding back a first portion of a modulating signal to be compared with a following portion of the signal. This allows correlation of the modulating signals between the first portion of the signal and the following portion. Such correlation can be applied in feedback type demodulation such as phase-locked loops, to increase the threshold performance of the loop. The circuitry can be applied in normal demodulation circuits to effect a frequency tracking circuit allowing the use of a band pass filter with a narrower band than would be normally allowable.

Abstract: Vertical synchronization information in a multiplexed analogue component (MAC) television signal is included in a line scan period, the amplitudes of the waveform being chosen so as to represent a position in the color space outside that occupied by the picture signal; preferably, the amplitudes are chosen to be at the limits of the picture signal amplitude. By these means, the normal horizontal synchronization information can still be included in the form of transitions 1 and 2, and the chance of the synchronization and picture signals interfering with each other is minimized.

Abstract: In a television receiver for a transmission system in which the video signal is scrambled to allow only for its authorized reception, a video signal processor (8) is provided in which the scrambled video signal is de-scrambled. A low rate encrypted signal present at an output (11) of a sound/data signal processor (10) is decrypted and employed to periodically set (say once every one or two seconds) a master pseudo ramdom pulse generator (12B) producing an output of pseudo random configuration at the frame rate which is used to periodically set a video slave pseudo random pulse generator (15) to produce an output of pseudo random configuration at line frequency. This is applied to an input S of the processor (8) and forms the scrambling key for the line-by-line de-scrambling of the video signal.

Abstract: The present invention relates to digital television tape recording and more particularly to such recording using helical scan apparatus of the segmented type i.e. where one field of video is recorded by a plurality of rotations of the headwheel.The invention also provides apparatus for recording or playing back a digital television signal comprising a helical scanning device including a drum which may be a rotatable headwheel provided with a plurality of recording/playback heads, guide means for wrapping a magnetic recording tape around a portion of the circumference of the drum, means for rotating the headwheel, and means for moving the tape around the surface of the drum whereby one field of a television video picture is recorded or played back by a plurality of rotations of the headwheel, characterized in that the recording/playback heads are disposed on the headwheel.