Abstract: A switch arrangement is provided for MPEG or other bit-rate signals. An output switch (66) is arranged to switch between bitstream A; an interim bitstream developed about the switch point; and bitstream B. The interim bitstream is provided by a re-coder (64) the input to which is switched at (58) between a decoder (52) for bitstream A and a decoder (56) for bitstream B.

Abstract: A method of generating motion vectors from a video signal, for use in motion compensation, is applicable to interlaced video signals. In the method alternate video fields are shifted vertically so as to align the picture lines of interlaced fields, by moving the lines of one field up by half a picture line and the lines of the next field down by half a picture line. The fields of each resultant pair are compared to produce a set of motion vectors which can be used to motion compensate the video signal. The accuracy may be improved using temporal filters operative on correlation surfaces derived over tow or more field intervals.

Abstract: A video signal 21 is input to a motion-compensated median filter to produce a preliminary blemish-concealed signal 23. The preliminary signal and the original input signal are passed via appropriate delays to respective inputs of a selector switch 31 and to a side chain circuit. The selector switch is controlled by the side chain circuit output and the selector switch output 22 forms a final blemish-concealed video signal. In the side chain circuit a difference signal C is generated to indicate differences between the input signal and the preliminary signal. The difference signal C is processed in two parallel circuit branches to remove differences having gently-sloping edges and differences corresponding to similar-sized differences in similar areas of adjacent frames, which are likely to be motion artifacts.

Abstract: In a method of processing 16:9 pictures for display on a screen with a 4:3 aspect ratio, each line of the television signal is compressed and/or expanded so that the ratio of the length of a segment of unprocessed signal to the length of the resultant signal derived from it, varies along the line. Preferably, each line is subject to "cylindrical" processing such that it is compressed as though the line were extended along an arc of a circle and projected along a direction onto a flat plane joining the ends of the arc. The picture may also be subject to slight vertical stretching to give a final image which is subject to distortion at an acceptable level while retaining a good level of vertical detail.

Abstract: Non-linear picture transformations in a video image motion compensation system are caused by camera zooms or rotations. Sets of trial vectors are derived for each block of the image representing peak correlation values between adjacent images in the sequence. A constant representing the non-linear transformation is estimated using the sets of trial vectors and this enables a vector representing the non-linear transformation to be added to the trial vector list for each block.

Abstract: Motion compensated image processing is performed by producing vectors assigned to elementary areas of video fields. These are produced from at least two video fields in a sequence. A first technique is used to produce the vectors. If an error signal is produced by the first technique then a second technique is used for the production of vectors.

Abstract: In the combination of a video signal coder and a video signal decoder, synchronization is achieved by the addition of absolute time reference signals at the coder. These time reference signals are independent of the time base of the coder and are inserted after the coder buffer. At the decoder, the time reference signals are stripped out and used to set the decoder time base.

Abstract: A receiver for orthogonal frequency division multiplexed signals includes means (14) for calculating the (discrete) Fourier Transform of the received signal, and means (20) for calculating the phase error due to local oscillator errors.

Abstract: A broadcast receiver is disclosed which separates 16-bit binary program labels from a transmitted television signal and applies the television signal to a recorder. The viewer enters, via a keyboard, short program labels which up to three decimal digits in length. These entered short labels are then converted into 16-bit binary program codes by a mapping function processor. Each of the 16-bit codes differs in at least two binary positions from any other 16-bit codes. These codes are stored and compared with received codes and when they agree the video recorder is controlled so as to record the TV signal. Thus, the viewer does not have to enter long codes but can use short labels to identify the programs. The short labels can be obtained by the viewer from a printed TV listing.

Abstract: A digital broadcast transmission system comprises a plurality of spaced transmitters (6). Each transmitter (6) receives signals for transmission from a master transmitter (2), e.g. on a satellite, along with a reference frequency (F.sub.REF). The reference frequency is used to generate the transmission frequency at each spaced transmitter. At a receiver (12), conversion means can be used, to enable signals from the master transmitter (2) and from the other transmitter(s) to be received. A preferred application is digital audio broadcasting (DAB). Specifically, the present invention is useful in connection with Coded Orthogonal Frequency Division Multiplex (COFDM) modulation.

Abstract: High definition television coder/decoder a high definition coder or decoder includes a number of parallel sub-decoders or coders. The image to be coded or decoded is divided into a number of stripes, a given stripe being coded or decoded by a single sub-coder or sub-decoder. Every N.sup.th stripe is coded or decoded by the same sub-coder/sub-decoder, where N is the number of sub-coders or sub-decoders. The number of sub-coders is independent of the number of sub-decoders whereby a reduction in the number of sub-coders with increasing bit-rate capacity does not necessitate a change in decoder.

Abstract: In a digital video display system, a composite time-compensated video picture, generated from a plurality of input fields, includes discontinuities, e.g. aliases resulting from relative movement of a foreground object and a background. These discontinuities are the results of time-projections from the sequential input fields or frames, which include movement of objects between the respective instants of the frames. These discontinuities are detected and are smoothed by a softening filter, in order to improve the quality of the resulting output image. In a preferred embodiment, the filtering is applied directionally, based on the nature of the discontinuity detected.

Abstract: A frequency-division multiplexer for carrying an OFDM signal on a large number of closely-spaced carriers receives the digital data at an input (12), applies coding such as convolutional coding (14), time interleaves (16) the signals, and assembles them frame-by-frame in a matrix (18). The data are converted to parallel form by a shift register (18), frequency interleaved (24), differentially encoded (26), and quadrature-phase-modulated (28) on several hundred or more closely-spaced carriers. A first inverse Fast Fourier Transform (FFT) circuit (30) transforms this information from the frequency domain into the time domain. Instead of being transmitted directly, the resultant signals are then amplitude-limited (42) and applied to an FFT (44) to reconvert them into the frequency domain. The phases of the wanted signals are then re-set, and the amplitudes of the signals near the edges of the band are reduced, in correction circuits (46).

Abstract: A composite video signal is formed in which high luminance frequencies are modulated so that they occupy frequencies above the chrominance band. A sub-band coder is used to split the luminance frequency band into high and low frequencies at the coder, and an inverse sub-band coder combines the high-frequency luminance and the chrominance components. The two resultant signals are applied to a phase-segregated Weston Clean PAL coder to provide a composite video signal, which is compatible with a conventional PAL signal.

Abstract: Video signals are sampled at 4Fsc locked onto sub-carrier phase and frequency. The active picture lines of each field are divided into 6 blocks of 47 lines and the active line periods of those lines scrambled on a block by block basis by line order shuffling. The shuffling algorithm is generated by a line shuffling permutator driven by a PRBS generator (controls 36, 38). Active line period samples for one block are written in unscrambled form into a first memory block (32) and samples from the previous block are read out in scrambled form from a second memory block (34) for transmission. The complementary process takes place in the decoder.

Abstract: In signal processing circuitry using active devices, non-linearity of the device causes distortion of pure tones and the generation of intermodulation products for more complex signals. The transfer characteristics of such active devices may be considered as the accumulated characteristics of input and output filter stages separated by a non-linear region. To compensate for non-linearities and reduce intermodulation products, a drive circuit comprises pre- and post-correction filters separated by a compensating amplifier. The frequency response of the pre-correction filter corresponds to that of the input filter stage but is reversed in the frequency spectrum; with conventional I.F. the transfer characteristic of the amplifier and frequency response characteristic of the post-correction filter are the respective complements, of those of the non-linear region and pre-correction filter.

Abstract: Studio camera position and motion may be derived from the camera image by separating out the background and deriving from a background having a number of areas of hue and/or brightness different from adjacent areas estimates of movement from one image to the next. The initial image is used as a reference and amended with predicted motion value. The amended image is compared with incoming images and the result used to derive translation and scale change information. Once the proportion of the reference image contained in an incoming image falls below a threshold a fresh reference image is adopted.

Abstract: A synchronizing signal separator receives synchronizing signals from a remote source. A window generator opens a window for a period and a counter regenerates synchronizing signals detected when the window is open. Detection of an incoming synchronizing signal when the window is open causes a window counter to be stopped to reduce the window duration to approach a set minimum width. The window generator and the counter are controlled by a voltage controlled oscillator whose oscillation frequency varies according to a feedback signal derived from the sense of the phase error between an external counter of the window generator and the regeneration counter.

Abstract: In signal processing circuitry using active devices, non-linearity of the device causes distortion of pure tones and the generation of intermodulation products for more complex signals. The transfer characteristics of such active devices may be considered as the accumulated characteristics of input and output filter stages separated by a non-linear region. To compensate for non-linearities and reduce intermodulation products, a drive circuit comprises pre- and post-correction filters separated by a compensating amplifier. The frequency response of the pre-correction filter corresponds to that of the input filter stage but is reversed in the frequency spectrum; with conventional I.F. the transfer characteristic of the amplifier and frequency response characteristic of the post-correction filter are the respective complements, of those of the non-linear region and pre-correction filter.