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: A serial data decoder is described for decoding interleaved variable length and fixed length codes. The decoder includes a state machine which moves between a branching hierarchy of states in dependence upon the bits of received serial data. When the state machine reaches a state corresponding to a complete variable length code having been received, it then enters a delay state lasting for the length of time necessary to receive the following fixed length code prior to return to a reset state. The state machine can be implemented using a static ram 10 storing data including pointers for controlling the movements between states.

Abstract: In order to reduce the effects of discontinuities at the edge of a picture and reduce erosion of the usable picture area caused by a filtering or interpolation operation, the edges of the picture are extrapolated prior to such an operation. This may be achieved by a circuit which receives an input line of active pixel data; forms from the input line a delayed line of the active pixel data; produces at least one additional start pixel data derived from a pixel data at or adjacent the start of the input line; produces at least one additional end pixel data derived from a pixel data at or adjacent the end of the input line; and forms an output sequence of pixel data by selecting for the output sequence the additional start pixel data, then at least part of the delayed line, and then the additional end pixel data. This circuit therefore performs zero-order (repeat) extrapolation at the beginning and end of each line.

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: Digital filters are described for filtering blocks of data values. In order to reduce edge effects, symmetric data extension at the edges of the blocks is used. Multiplexers 34, 40, 46, 52 are used to pass data values between non-adjacent delay elements 36, 38, 42, 44, 48, 50 at leading and trailing edges of a data block to effect symmetric extension. The delay elements can be multisample delay elements and data being filtered can be multiplexed data.

Abstract: A video image filtering system is described which utilises multi-tap filters (70). In order to reduce the effects of edge distortion due to the finite size of the input image, extension data is added both the beginning and end of each raster line of data fed to the multi-tap filter (70). The function of the extension data is to pre-load the multi-tap filter (70). With a system constrained to operate at a constant sample rate, there is insufficient inter-raster line separation to accommodate the extension data needed for a long multi-tap filter (70). The system transforms the input video signal format (24) to a reformatted video signal format (28, 30) in which either the horizontal blanking or vertical blanking period has been maximised at the expense of the corresponding other blanking period.

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 data compression system in which decorrelated data is fed to an entropy encoder (20) in batches having an internal monotonic decrease in average information content from start to end. This results in longer zero runs and more rapid attainment of end of block codes. A data sequencing circuit (18) comprising nested inter-sub band (60) and intra-sub band (72) counters for use with sub band filtered video data is also described.

Abstract: Apparatus for storing a plurality of fields of digital video signal where each field consists of a plurality of n-bit words and n may vary downwards from a maximum value, comprises circuits for arranging the n-bit words of each incoming field in n bit-planes, each bit-plane containing a respective bit from each n-bit word, a video signal store comprising a plurality of memories each capable of storing the bits of a bit-plane, a common data bus for supplying the bit-planes to the memories, and circuits for controlling writing of the bit-planes in the memories such that a first field is written in a first n of the memories, the next field is written in a second n of the memories, and so on until all memories have been written in.