Abstract: To increase the horizontal bandwith of the Weston PAL chrominance signal spectrum folding techniques are used. Spectral components with high horizontal frequency and low vertical and/or temporal frequency are carried as components with low horizontal frequency and high vertical and/or temporal frequency. A matrix (120) forms U+V(P) and U-V(M) chrominance signals which are then prefiltered using either rhombic spatial filters or rhombic vertical-temporal filters (122, 124). The two signals are then sampled by sampler (126, 128) which together with switch (136) form U+V samples on alternate lines to the U-V samples. The sampling patterns for the P and M signals are identical but shifted.

Abstract: An assembler and splitter of a Weston PAL (W-PAL) video signal has filter functions F.sub.1, F.sub.2 at the assembler for the luminance and chrominance components and corresponding functions F.sub.3, F.sub.4 at the splitter. The transfer functions are defined as F.sub.1 =(L.sub.2 +L.sub.1)/2+(L.sub.2 -L.sub.1)z-.sup.1 /2, F.sub.2 =-(H.sub.1 -H.sub.2)/2+(H.sub.1 +H.sub.2)z.sup.-1 /2, F.sub.3 =(L2-L.sub.1)/2+(L.sub.2 +L.sub.1)z.sup.-1 /2, F.sub.4 =(H.sub.1 +H2)/2-(H.sub.1 -H.sub.2)z.sup.-1 /2 and wherein H.sub.1 (f)=L.sub.2 (2fsc-f) and H.sub.2 (f)=L.sub.1 (2fsc-f). Thus the filters are non-sharp cut and are compatible with normal PAL.

Abstract: A video display device has a scanning standard which is instantaneously adaptively dependent on the presence of movement in the picture. With a 625/50/2:1 input signal, in the absence of motion the standard used is 625/100/2:1. In the presence of motion the standard can remain 625/50/2:1. The video input is applied to aline store (108) and through an attenuator (102) to field stores (104). An appropriate one of the store outputs is selected by a switch (12) in dependence on a movement signal (116). In a preferred alternative, in the presence of motion the standard is altered to 625/50/1:1.

Abstract: Conventionally, transmission of television images is performed by Raster scanning. To avoid the problems associated with flyback, and the limiting of Raster scanning to image scanning standards it is proposed to transmit images by scanning along a locus defined by a fractal curve. A Peano curve is particularly suitable. Image resolution may be varied by varying the order of curve used to scan the image. Smoothing of a curve of a given order results in a graceful degradation to a curve of lower order so that the image created by a given order is still recognizable when displayed by a lower or higher order.

Abstract: To provide improved resolution of a television, e.g. CRT, display with reduced large-area flicker, twittering of horizontal edges, and line structure of the picture, the field rate is doubled and the number of lines per field is doubled from that of a received input television signal. Preferably a 21/2 field store arranged in half-field units is used, together with a four-line store arranged in one line units to provide line interpolation, which can be adaptively dependent upon the presence or absence of motion.

Abstract: Digital sampling of the luminance component of an N.T.S.C. color television signal is achieved by sampling with a mean frequency of twice the color subcarrier frequency to produce a sub-Nyquist sampled luminance signal. The sampling phase is changed between each pair of lines by an amount equal to half the interval between samples. The digital sampling can be applied to separate luminance and chrominance signals, to encoded N.T.S.C., and to the conversion of N.T.S.C. signals into signals of other form including PAL. Further, phase-perturbed sampling techniques permit the construction of an advantageous N.T.S.C. coder and de-coder system. The coder operates to cause spectrum folding of a luminance input signal by multiplying by a phase perturbed signal of twice the color subcarrier, and adding, the resultant being comb filtered to select frequencies which are multiples of the line frequency. The chrominance signals I, Q are combined into I.+-.

Abstract: To portray movement in a television display, a field of the signal is stored in an image store (110), and subsequent input fields are compared in a motion detector (104) with the stored field to detect differences between them due to movement. A flag is retained in an auxiliary store (114) to indicate the positions in the field of the detected differences. For those positions for which a new difference is detected, i.e. for which no difference has been detected previously, the corresponding portions of the then current input scan are stored in the image store (110), by a switch (106) being connected to the input (102). For portions which are flagged, the output of the auxiliary store (114) causes the switch (106) to take the output of the image store (110), thus insetting past positions of movement into the current field. The background of the field in the image store is nevertheless updated by the background of the input field.

Abstract: A single field of a PAL color television signal is stored in a store (50) and provides a signal at an input (52). The signal is delayed by one-line delays (56,58) in series to provide one and two-line delayed signals. Separate switching units (60,62) select desired ones or combinations of the input and delayed signals to constitute respectively the low-frequency and chrominance part of the signal at the output (82). The switch positions are changed between fields, and for at least some fields of the PAL sequence each component of the output signal is formed by combining signals from more than one line, i.e. a halving adder (64;66) averages successive lines for the low frequency part of the signal and a halving subtractor (68) forms the difference between lines two lines apart for the chrominance part. The selector unit outputs are combined in an adder (78) which receives the output of the first selector (60), and also the difference between the output of the two selectors after band pass filtering (76).

Abstract: Reduction of noise in a television signal is achieved by comparing signals from successive scans to produce a difference signal. Low amplitude differences are assumed to represent noise and are attenuated. Differences above a predetermined level are assumed to represent movement and are not so attenuated. The attenuation is achieved by a multiplier which receives as multiplier the output of a non-linear transfer characteristic element. The non-linear element receives the differences after rectification and after passing through a variable-gain element. The non-linear element is such that above a predetermined value a constant predetermined minimum attenuation factor applies. A noise measurement circuit measures the noise present in the difference signal and controls the gain of the variable-gain element accordingly. Several noise-measurement circuits may be provided, a selected one of which is used in dependence upon the magnitude of the input signal to the apparatus.

Abstract: In a method of and apparatus for processing 625-line PAL colour television signals, in which in conjunction with each line of the signal there is provided an additional signal for use therewith, the additional signal is formed essentially of the luminance component of a signal equivalent to the signal 625 lines previous to the current line, and the chrominance component of a signal substantially equivalent to the signal 624 lines previous to the current line. Alternatively, the difference of the chrominance components 624 and 626 lines previous may be used. For 525-line N.T.S.C. the luminance component is derived from the signal 525 lines previous, and the chrominance component is the chrominance component of the signal 524 or 526 lines previous to the current line, or an average of these. The form of the chrominance component may be selected automatically in dependence upon vertical chrominance detail.

Abstract: In a method and apparatus for transcoding digital PAL color television signals between (i) a 2fsc format consisting of an encoded signal of PAL type sampled at 2fsc and (ii) a 3fsc format consisting of a luminance signal Y at 2fsc and a chrominance signal C sampled at fsc and comprising U+V and U-V on alternate lines (or either the luminance signal or composite chrominance signal by itself), avoid the need to convert the signal to analogue PAL form as an intermediate step. Converting from the 2fsc to the 3fsc format, over the chrominance bandwidth undelayed and 1- and 2-line delayed samples are combined in the proportions 1/4:1/2:1/4, and below the chrominance band the 1-line delayed samples are low-pass filtered, these together providing the luminance signal Y. To provide the chrominance signal C the undelayed and 2-line delayed signals are combined in the proportions -1/4:1/4. The low- and band-pass filters are digital transversal filters operating on adjacent samples in the signal.

Abstract: Reduction of noise in a television signal is achieved by comparing signals from successive scans and noting the differences. Low amplitude differences are assumed to represent noise and are attenuated. Differences above a predetermined level are assumed to represent movement and are not so attenuated. The attenuation is achieved by a multiplier which receives as multiplier the output of a non-linear transfer characteristic element. The non-linear element receives the differences after rectification and after passing through a variable-gain element. The non-linear element is such that above a predetermined value a constant predetermined minimum attenuation factor applies.