Abstract: During shuttle mode operation in a system for the reproduction and storage of frequency separated video signals, the read head intersects a plurality of tracks corresponding to different fields of the image rather than following complete tracks. Accordingly, the full information for any one field is not recovered. To provide an image during shuttle mode, the system reads the dc luminance information of the tracks it intersects at the part where this information is stored. As the information content of the dc luminance information is relatively high, a recognisable image can be formed from this information alone. The dc luminance information is stored in the centre of the tracks with the other components arranged in order of increasing frequency towards the edge of the tape. The data which is most important to generation of a high quality image is stored in a place where it is less likely to be degraded.

Abstract: Apparatus is described for multiplexing data recorded in a spatially and temporally demultiplexed manner on tape 12 and replayed by a plurality of replay heads A, B, C, D organized in groups, where each group includes a plurality of replay heads A/C, B/C, connected in common to a head channel 42, 44. First multiplexers 84, 92 multiplex the data in respective head channel, the output of the first multiplexers being stored in respective video buffers 86, 94. A second multiplexer 88 then selectively addresses the video buffers in response control signals to produce a multiplexed output which can reliably be reproduced even under extreme error conditions and in all playback modes.

Abstract: A data compression technique is described for use in systems employing frequency separation, such as wavelet separation, in which the sub bands (0 to 9) have different numbers of frequency component values therein. The sub bands are scanned to form a stream of data for feeding to an entropy encoder (30) in an order in which a number of samples from each sub band are taken in turn, that number being proportional to how many frequency values are in the particular sub band.

Abstract: A digital video tape recording/playback system having a plurality of recording heads (A, B, C, D) on a rotating head mechanism 94 for recording slanting tracks 108 which extend diagonally across a tape 82 provides processing of video signals in a plurality of data processing channels with selective connection of the data processing channels to the recording heads such that data from a plurality of data processing channels are stored in respective portions of a slanting track (A+/A-; B+/B-; C+/C-; D+/D-). The data in each data processing channel and recorded in each track portion is sampled with a substantially even distribution over a field of video signals to provide for effective concealment of recording/playback errors. Preferably, two data processing channels are recorded on each track, the respective portions being located in upper and lower portions of the tape, respectively.

Abstract: Apparatus for detecting synchronisation data in an input serial-bit digital signal formed of a series of word blocks each including a predetermined serial group of m bits forming said synchronisation data, comprises a deserialiser for deserialising the input signal to parallel-bit p-bit words where p<m, a delay for delaying at least p-1 bits of each p-bit word by one p-bit word period, and logic for receiving successive groups of 2p-1 bits each formed of a said p-bit word and the adjacent p-1 bits of the preceding or succeeding word. The logic is arranged to detect an initial portion of said synchronisation data by comparing bit sequences in a said group of 2p-1 bits with the bit sequence at the beginning of said predetermined group of m bits. On detection of said initial portion of the synchronisation data, bits of one or more succeeding groups of 2p-1 bits are compared with succeeding bits of said predetermined m bits in dependence upon the position of said initial portion in the corresponding 2p-1 bits.

Abstract: Apparatus for decoding an input digital signal by replacing successive n-bit groups of the input digital signal with respective ones from an ensemble of m-bit data words, each m-bit data word having an associated n-bit code word, where n is greater than m, comprises: means for determining the Hamming distance between an n-bit group of the input digital signal and each of the n-bit code words associated with the ensemble of m-bit data words; and means for replacing that n-bit group of the input digital signal with an m-bit data word from the ensemble of m-bit data words for which the Hamming distance between the n-bit code word associated with that m-bit data word and that n-bit group is the lowest.

Abstract: A video memory comprises a video store for storing video data comprising a plurality of input video data blocks, each input video data block comprising a plurality of pixel data words and one or more ancillary data words associated with that input video data block. The video memory allows the stored pixel data words to be read out, along with their associated ancillary data word(s), in a transposed order and comprises means for reading the ancillary data words associated with a predetermined sequence of input video data blocks into a recirculating output buffer, and serial reading means for reading successive output video data blocks from the video store, each output video data block comprising pixel data words from the predetermined sequence of the input video data blocks, the serial reading means and the recirculating output buffer being operable to output concurrently each pixel data word in each output video data block with its associated ancillary data word(s).

Abstract: Data compression apparatus is provided for compressing an input stream of n-bit data samples, possible input sample values being notionally divided into groups each containing a number of sample values equal to a respective power of two.

Abstract: A video replay store controller wherein appropriate ones of a plurality of field stores are selected for storing replayed video data in a digital video tape recorder (DVTR). The controller comprises a transition detector associated with each of a plurality of video replay heads, for detecting changes in field identifiers associated with consecutively replayed video data blocks received from that video replay head, thereby detecting a field transition in the data replayed by that video replay head.

Abstract: Spatial demultiplexing of data (e.g. video data) is employed in a digital recorder comprising four heads (A, B, C, D) organized as 2 groups (A/C; B/D) each of 2 heads, whereby a field of data comprising a plurality of lines is spatially demultiplexed into i.times.4 data processing channels such that each data processing channel receives a different set of pixels including alternating pixels on every fourth line. The technique finds particular application to the recording of video data in compressed form as the distribution of the pixels to the data processing channels enables efficient compression to be achieved. The video data can be decorrelated before compression. The spatial demultiplexing is then performed on the decorrelated data.

Abstract: Image processing apparatus is described for filtering a digital representation of a raster scanned image into a plurality of sub-bands in the two-dimensional spatial frequency domain, the resolution of the raster scanned image in a first direction (usually the horizontal direction) being greater than the resolution of the raster scanned image in a second direction (usually the vertical direction). The image processing apparatus has a decimation filter means comprising a number of multi-tap digital decimation filters for spatial filtering in the first and second directions. The mean of the filter lengths of the filters used for filtering in the first direction is greater than that of the filters used for filtering in the second direction. Complementary interpolation apparatus for reconstructing the image from the plurality of sub-bands is also described.

Abstract: Apparatus for coding a television signal in common image format in which the video frame rate may have any one of a plurality of predetermined different values and the number of pixels or the spatial resolution per video frame of which is the same for all frame rates, comprises a video encoder for coding the video information of each video frame into a format suitable for recording in oblique tracks on a magnetic tape, and an audio encoder for coding the audio information associated with each video frame into blocks for recording with the video information, each audio block comprising digital audio data and a pointer indicating that portion of the block containing the audio data, and preferably also the sample rate of the audio data.

Abstract: Error concealment apparatus for concealing corrupted data elements in frequency separated digital image data (such as sub-band coded image data) is described. Depending on the spatial frequency represented by a corrupted data element, one of a number of error concealment means is selected to conceal the error. In this way the error concealment used can be tailored to suit the different properties of the various spatial frequency components in the frequency separated image.

Abstract: During shuttle mode operation in a system for the reproduction and storage of frequency separated video signals, the read head intersects a plurality of tracks corresponding to different fields of the image rather than following complete tracks. Accordingly, the full information for any one field is not recovered. To provide an image during shuttle mode, the system reads the dc luminance information of the tracks it intersects at the part where this information is stored. As the information content of the dc luminance information is relatively high, a recognisable image can be formed from this information alone. The dc luminance information is stored in the center of the tracks with the other components arranged in order of increasing frequency towards the edge of the tape. The data which is most important to generation of a high quality image is stored in a place where it is less likely to be degraded.

Abstract: Image data multiplexing apparatus for multiplexing digital luminance and chrominance data of a representation of an image into multiplexed data blocks of a predetermined length, along with a corresponding demultiplexing apparatus, is described. Each of the multiplexed data blocks comprises a luminance data section comprising luminance data from a portion of the representation, a chrominance data section comprising chrominance data from the portion of the representation, a portion address indicative of the position in the representation of the portion, and a block offset pointer indicative of the position in the multiplexed data block of the boundary between the luminance data section and the chrominance data section.

Abstract: A television standards converter for converting an input digital video signal from one television standard to another, comprises a high-pass filter (36) for filtering the input video signal horizontally and vertically, a plurality of parallel processing channels comprising respective circuits (43 to 58) for determining pixel by pixel of the high-pass filtered video signal the correlation magnitudes for a range of horizontal and vertical pixel offsets, respective low-pass filters (59) for filtering the resulting correlation magnitudes, subtracters (55 to 58) for subtracting from each correlation magnitude in the range the correlation magnitude corresponding to zero pixel offset, a selector (62) for determining for each pixel of said video signal the motion vector corresponding to the maximum correlation magnitude, and a temporal interpolator (FIG. 14) for deriving interpolated fields or frames by combining sample values offset by the motion vectors.

Abstract: A sub-band filter system in which the frequency separated data is multiplexed together at the output of each filter stage. The stream of multiplexed data produced can have a block-by-block format or a sample-by-sample format. In the latter case, the filtering can be effected by a finite impulse response filter with switchable tap coefficients for effecting both decimation and high and low pass filtering.

Abstract: A television standards converter for converting an input digital video signal from one television standard to another, comprises a first low-pass filter (35) for filtering the input video signal, a high-pass filter (36) for filtering the low-pass filtered input video signal horizontally and vertically, a plurality of parallel processing channels comprising respective circuits (43 to 58) for determining pixel by pixel of the high-pass filtered video signal the correlation magnitudes for a range of horizontal and vertical pixel offsets, respective second low-pass filters (59) for filtering the resulting correlation magnitudes, a selector (62) for determining for each pixel of said video signal the motion vector corresponding to the maximum correlation magnitude, and a temporal interpolator (FIG. 14) for deriving interpolated fields or frames by combining sample values offset by the motion vectors.

Abstract: Apparatus for storing a video signal includes a signal compression arrangement constituted by a spatial two-dimensional sub-band filtering arrangement that filters a digital video signal to form data sets constituting respective sub-bands of the two-dimensional spatial frequency domain, a quantizer that quantizes the data sets in accordance with respective values which are such that the amount of quantization of one of the data sets constituting a sub-band to which dc luminance information of the signal is at least predominantly confined is less than the average of the amounts of quantization of the remaining data sets, and an entropy encoder that selectively encodes at least some of the quantized data sets so that the quantized data sets, as selectively entropy encoded, form a compressed video signal. The signal compression arrangement is followed by a storage arrangement for storing the compressed video signal.

Abstract: To enable a digital composite color video signal (NTSC or PAL) to be compressed directly, that is without dividing it into its components and compressing the components separately, the digital composite color video signal is decorrelated, for example by spatial sub-band filtering, to form data sets, for example sub-bands, representing dc luminance information, ac luminance information and dc chrominance information. The data sets are then quantized in accordance with respective quantization values from a quantization matrix, those quantization values being such that the amount of quantization of each of some of the data sets to which the dc luminance information and the dc chrominance information is at least predominantly confined is less than the average of the amounts of quantization of the remaining data sets. At least some of the quantized data sets are then entropy encoded.