British Broadcasting Corporation

The Marconi Company Limited

Standard Telephones & Cables Limited

British Broadcasting Corporation of Broadcasting House

John O Drewery

Richard Storey

Martin Weston

Nicholas Dominic Wells

Michael G Croll

Arthur Howard Jones

Victor G Devereux

Arthur V Lord

Kenneth Hacking

A plasma display device ( ) is provided with circuitry ( ) which modifies at least the R and B color component signals so as to compensate for the displacement of the display elements or sub-pixels for each color component relative to each other in the array. Surprisingly, this increases the ratio of wanted signal to alias spectrum. The modification is effected by an interpolator comprising transversal filters ( R, B). The circuitry can be combined with down-converters ( ) when a high definition source is used. In this case a transversal filter ( G) is also included for the G color component signal.

Color displays

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.

Method of showing 16:9 pictures on 4:3 displays

Television systems

Non-sharp cut filters for assembling and splitting in Weston Clean PAL

Method and apparatus for adaptively displaying video signals

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.

Scanning techniques using hierarchical set of curves

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.+-.Q and are modulated onto phase-perturbed subcarrier, the resultant being comb filtered to select frequencies which are of integral multiples of half the line frequencies. The two signals are then added. The comb filters mentioned can be based on one line delays or on odd multiples of one line, particularly 263 or 525 lines. A converse decoder filters then spectrum folds the luminance component, and filters and multiplies by subcarrier to derive the chrominance. Once an N.T.S.C. signal has been encoded by use of the encoder, subsequent decoding and recoding produces no theoretical impairment into the signal.

Processing of N.T.S.C. color television signals

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.

Television display system

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. To allow for the 4-field NTSC or 8-field cycle, transducers, or predictors, (170,160) are placed at the input and output of the image store (110) such that the image store retains information in one state only of the cycle. The motion detector (104) comprises a subtractor, a rectifier and a low-pass filter.

Method of and apparatus for movement portrayal with a raster e.g.

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 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). The store (50) can be replaced by a random access store capable of outputting three successive lines simultaneously. The apparatus has special utility in equipment for movement portrayal.

Method of and apparatus for deriving a PAL color television signal

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.

Video noise reduction system

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.

Circuitry providing a delayed color television signal having luminance

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 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. Transcoding in the other direction is similar.

Processing pal color television signals

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.

Noise reduction in electrical signals

Reduction of noise in a television signal is achieved by comparing signals from successive frame or field 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 by a factor K. Where there are inherent differences between the signals compared, for example they are different fields of an interlaced scan or are color signals with different subcarrier phases, the signal from the earlier scan is modified to compensate for these differences and provide a signal for comparison which is a better estimate of the expected signal on the later scan.

Growing community of inventors

Coulsdon, United Kingdom

John O Drewery