Abstract: A method of compression is provided for transmission of digital video signals between an encoder buffer and a decoder buffer. A tunable delay is provided at the encoder, suitably in the form of a portion of encoder buffer memory, with data being read out to a communications channel at a rate determined by the input bit rate of signals received a predetermined number of frame periods later. Use of the tunable delay improves efficiency of decoder buffering by maintaining a relatively constant level of decoder buffer fullness irrespective of signal bit rates.

Abstract: A device for simultaneously transmitting a plurality of television signals comprises an adjusting circuit (5) for adjusting the bitrate for each television signal in dependence upon the complexity of this signal with respect to the joint complexity of the plurality of television signals. The device provides improvement of quality in Digital Video Broadcast systems. It has also been found to be possible to transmit extra signals through a given channel while maintaining the picture quality. Use of the device in optical recording provides the possibility of a longer playing time.

Abstract: Decoding method and device with which it is proposed, in order to reduce the switching time from one among n input digital video bitstreams corresponding to n programs to another one, to use under the supervision of control means (30) including a control unit (31) and a switch (32), while a selected digital video bitstream is presented for decoding and display, (n-1) buffers (22, 23) for the (n-1) extra bitstreams, these extra buffers being dimensioned so that they always comprise at least an intra frame, and preferably the most recent one, of each incoming extra bitstream. In a simpler embodiment where the next program switched to is one up or one down, only one or two extra buffers are necessary, subject to the knowledge of an information on how the incoming programs may be accessed, i.e. according to some defined order.

Abstract: A method and apparatus for improved motion vector selection in the motion estimator stage of a video encoder such as an MPEG coder are provided. From a received (re-ordered) image frame sequence, a first stage (14) of the estimator generates a set of candidate motion vectors, suitably from a list of half-pixel candidates from about each of N candidate integer pixels. Those candidate vectors, together with an indication of their respective accuracies, are passed to a vector selection stage (16). A vector bit counter (18) determines the number of bits required per vector and the selection stage (16) then selects those of the candidate vectors for a macroblock line (or "slice") which minimise a cumulative cost function for the line and provide the best trade-off between motion vector accuracy and required bit rate for each block of the line. The derivation of the cumulative cost function and its application to coding mode selection is described.

Abstract: A method of transcoding coded video signals and a corresponding device for implementing this method are described. The device comprises decoding and encoding sub-assemblies (201, 202) and, within the encoding sub-assembly, quantizer (23) and bitrate controller. This bitrate controller comprise, before the quantizer (23), circuit for computing a local target value for encoding each sub-picture of the images to which video signals correspond and circuit for controlling the step size during the quantizing step.

Abstract: System for transmitting n video programs simultaneously through a transmission channel having a predetermined bitrate, comprising in cascade a decoding assembly and an encoding assembly. The decoding assembly consists of n parallel decoding means provided in parallel for decoding the coded input signals corresponding to said programs, and the encoding assembly consists of n encoding means being in cascade with each of said decoding means and each comprising a quantizer having a variable step size and a variable length encoder. The system also comprises means for controlling the step sizes of said encoding means in dependence upon their respective output bitrates, and these control means are also provided for controlling the output bitrates of said encoding means in dependence upon complexity values associated to the coded input signals of each decoding means with respect to the joint complexity of the plurality of said coded signals.

Abstract: The picture quality of an MPEG-encoded video signal is improved considerably by reducing the coefficients after quantization in such a way that the "Lagrangian cost" D+.lambda.R (D is distortion, R is bitrate) is minimal for a given value of the "Lagrange multiplier" .lambda.. The distortion decreases because the step size is reduced while the bitrate remains equal.

Abstract: A device comprising an MPEG encoder (2) is provided with a preanalyser (8) which encodes each picture with a fixed step size (Q.sub.2). The preanalyser is coupled to a computing circuit (9) which computes, for each type of (I, P, B) picture, a target value (T) for the number of bits for encoding said picture, as well as a suitable distribution of the target value among the macroblocks of the picture. A proportionally integrating control circuit (7) controls the quantization step size (Q.sub.1). Since the PI control circuit does not introduce any residual errors, the desired number of bits per picture or per group of pictures is achieved within narrow limits. The output signal is eminently suitable for recording and subsequent editing.

Abstract: A device for transcoding coded digital signals which are representative of a sequence of images, which device comprises a variable length decoding channel (12) followed by a variable length encoding and decoding channel (13), is described. According to the invention, a prediction sub-assembly (140) is connected in cascade between these two channels, and this sub-assembly comprises, in series, between two subtracters (114, 45), a picture memory (41) and a circuit (42) for motion compensation in view of displacement vectors which are representative of the motion of each image. Other implementations are possible, and particularly a scalable one in which said prediction sub-assembly comprises at least two and more generally a plurality of similar encoding and decoding channels arranged in cascade and corresponding to the same number of image quality levels.

Abstract: The picture quality of an MPEG-coded video signal can be improved considerably by modifying selected coefficients after conventional quantization, for example by rendering them zero. The modification is such that the Lagrangian cost D+.lambda.R (D is distortion, R is bitrate) is minimal for a given value of a Lagrange multiplier .lambda.. A relatively simple process is disclosed in which the value of .lambda. is calculated by means of statistical analysis (6) of the picture to be coded. The statistical analysis comprises the estimation of the RD curve on the basis of the amplitude distribution of the coefficients. The searched .lambda. is the derivative of this curve at the desired bitrate.

Abstract: A device for encoding a video signal comprises a picture transformer (22), a quantizer (23) and a variable-length encoder (24), as well as distribution device (6) for distributing a global target value (T) for the number of bits per picture or group of pictures in local target values (T.sub.n) for separate macroblocks of each picture. The device for encoding is provided with proportionally integrating control device for for controlling the quantization step size (Q.sub.1) in such a way that the buffer contents (b) of an output buffer (4) are in conformity with the target value. Since the PI control circuit does not introduce any residual errors, the desired number of bits per picture or group of pictures is achieved within narrow limits. The output signal is eminently suitable for recording and subsequent editing.

Abstract: Video signal encoding apparatus, suitably for multiple video channels (A,B) has respective encoder stages (10,12) which encode a received video signal according to a predetermined coding scheme, such as MPEG standard, and output a variable bit-rate data stream to encoder channel buffering (16) which is combined in a single buffer (16) having a fixed physical size with separate portions assigned to each channel. Buffer management (18) varies the size of the effective buffer areas assigned to the respective channels to maintain the total effective buffer area close to but within the physical limits of the buffer, as defined by the overall sum of encoder output bit rates. The outputs of the encoder buffer are combined into a single data stream, suitably by multiplexing (28), for subsequent separation and decoding by a receiver (30 to 36).

Abstract: Video images are encoded by transform coding, resulting in data blocks each including a DC-coefficient and a plurality of AC-coefficients. The coefficients of a number of said transform blocks are variable-length encoded and transmitted. In order to avoid a complete loss of datablocks in case of a transmission error, the most significant codewords of a group of blocks are transmitted first so as to achieve that at least the DC-level of the blocks is likely to be retained. The coefficients may also be recorded on a videorecorder. Fast playback of recorded images so encoded, leads to very poor quality because some data blocks are not being read in the search mode. To improve this quality the DC-coefficients and if desired predetermined AC-coefficients of selected ones of the transform blocks to be recorded on one track are packed together to form a DC-packet and such packet is recorded on a selected part of the track.

Abstract: Transmitter, encoding system and method for subband coding a digital signal. The encoding system includes a splitter unit for dividing the digital signal into subband signals SB.sub.1, . . . , SB.sub.p ; a quantizer unit for quantizing time-equivalent q sample signal blocks of the subband signals; a bit need determining unit and a bit allocation unit. The bit need determining unit determines a bit need b.sub.m which corresponds to the number of bits by which the q samples in a time-equivalent signal block in a subband signal SB.sub.m should be represented, where 1.ltoreq.m.ltoreq.P. The bit allocation unit allocates n.sub.m bits to each of the q samples of the time-equivalent signal block of subband signal SB.sub.m on the basis of the bit need b.sub.m and an available bit quantity B, n.sub.m being the number of bits by which the q samples in the time-equivalent signal block of subband signal SB.sub.m will be represented, where 1.ltoreq.m.ltoreq.P.

Abstract: Transmitter, encoding system and method for subband coding a digital signal. The encoding system includes a splitter for dividing the digital signal into subband signals SB.sub.1, . . . , SB.sub.M ; a quantizer unit for quantizing time-equivalent q sample signal blocks of the subband signals; a bit need determiner and a bit allocator. The bit need determiner determines a bit need b.sub.m which corresponds to the number of bits by which the q samples in a time-equivalent signal block in a subband signal SB.sub.m should be represented, where 1.ltoreq.m.ltoreq.M. The bit allocator allocates n.sub.m bits to each of the q samples of the time-equivalent signal block of subband signal SB.sub.m on the basis of the bit need b.sub.m and an available bit quantity B, n.sub.m being the number of bits by which the q samples in the time-equivalent signal block of subband signal SB.sub.m will actually be represented, where 1.ltoreq.m.ltoreq.M.

Abstract: A system for transmitting digitized analog information includes, for the purpose of transmitting an additional information signal apparatus for modifying the bit of low significance of every n-th data word representing the digitized information depending on the bits of an additional information signal. The apparatus for modifying is constructed in such a way that the modification depends both on the additional information signal and on other bits such as the most significant bit b7 of the data word which are not correlated with the bits of the additional information signal. This results in the intercorrelation between the errors in the data words introduced by the modification being reduced, so that a flatter power density error spectrum is obtained and the errors introduced in the data words by the modification are less conspicuous. A system for recovering the additional information signal from received modified data words includes similar apparatus for reversing the modification.

Abstract: For the transmission of a digital video signal via a transmission medium (11) consecutive pictures of N.times.M picture elements are subsivided into sub-pictures, a sub-picture being asembled from n.times.m picture elements. The maximum value and the minimum value (U.sub.max, U.sub.min) of a video signal component associated with the picture elements in a sub-picture are determined. In addition, the amplitudes of a video signal component associated with the picture elements in the sub-picture are quantized with a given number of p bits, by means of subdividing the dynamic range (DR) of the video signal component within this sub-picture, into 2.sup.p equal sub-ranges. At the receiver end dequantization is effected in the following manner. On dequantization, a value which is equal to the said maximum value (U.sub.max) is assigned, for at least one of the picture elements in the sub-picture for which the signal component has the highest quantized amplitude (U.sub.