Abstract: By utilizing parameters derivable from a compressed bit-stream, measures are obtained of the subjective quality of a decoded picture, without the necessity for reference to source material. A blockiness measure is derived both locally and globally and used to control a de-blocking filter. An estimate of signal-to-noise ratio is derived from quantization values.

Abstract: A method of detecting I-frames in a video signal which has previously been MPEG coded, involves taking a DCT and analyzing the frequency of zero value coefficients. An I-frame, which does not utilize prediction coding is expected to have a higher number of zero coefficients than a predicted P- or B-frame.

Abstract: In MPEG2 encoding, the quantiser is controlled to manage the occupancy of a video buffer. A dynamically varying working range is determined by forecasting from recent coding history the number of bits required in coding of future pictures, and deriving upper and lower ends of the working range which correspond respectively with attainment within the forecast period of predetermined maximum and minimum buffer occupancies. The quantiser scale is then controlled through the position of the actual buffer occupancy within that working range.

Abstract: In segmenting multidimensional image data, the data is represented as a set of points in a vector space which is the product of the vector space of pixel values and the vector space of pixel locations. Segments are determined by the result of clustering of the points, typically by simulating gravitational clustering of the points considered as point masses. From time to time the points are merged according to a proximity criterion, typically defined by mutual occupancy of a pre-defined hypercube in the vector space. The mapping of original pixels to points is tracked during the simulation process, so that pixels may be mapped to segments.

Abstract: In compression coding of picture sequences, a measure of picture difference is generated and compared with a picture difference threshold. The comparison is used in selecting between the use of predicted (P-pictures) and non-predicted has an initial value adapted to promote the use of an I-picture at or close to a scene change in the picture sequence, and changes in time in such a manner as to increase the probability of selection of a I-picture with an increase in the time since selection of the last I-picture.

Abstract: In a process for reducing the data rate of motion vector information, the components of the motion vectors are quantised, the quantised values are compressed and transmitted and the quantisation errors are additionally transmitted, whenever sufficient channel capacity is available. When not transmitted, the quantisation errors may be recreated at the encoder receiving the transmission. Where appropriate vectors may be translated to equivalent velocity values and passed through a linear transform, further reducing the required bit capacity.

Abstract: After decoding of an MPEG bitstream to the form of a video signal, an information stream signal in the form of all or part of the MPEG bitstream, is transmitted alongside the video signal, embedded in the least significant bit. Recording may simply involve extraction of the embedded MPEG bitstream or, if only part of the bitstream has been embedded, an essentially “dumb” coding operation guided by the information stream signal.

Abstract: In compression encoding of a digital signal, such as MPEG2, transform coefficients are quantised with the lower bound of each interval being controlled by a parameter &lgr;. In the MPEG2 reference coder, for example, &lgr;=0.75. Because the quantised coefficients are variable length coded, improved quality or reduced bit rates can be achieved by controlling &lgr; so as to vary dynamically the bound of each interval with respect to the associated representation level. The parameter &lgr; can vary with coefficient amplitude, with frequency, or with quantisation step size. In a transcoding operation, &lgr; can also vary with parameters in the initial coding operation.

Abstract: An MPEG-2 or other compressed video stream (CP) can be manipulated as separate information bus (IB) and coefficient (CP*) streams. The information bus stream (IB) contains motion vector information but also information derived from a previous decoding operation (14, 18) for use in a subsequent coding operation (22). Processing in the coefficient domain enables bit rate conversion without decoding to the pixel level and also simplifies the combination of MPEG layers.

Abstract: After decoding of an MPLFG bitstream to the form of a video signal, an information stream signal in the form of all or part of the MPEG bitstream, is transmitted alongside the video signal, embedded in the least significant bit. Recording may simply involve extraction of the embedded MPEG bitstream or, if only part of the bitstream has been embedded, an essentially “dumb” coding operation guided by the information stream signal.

Abstract: An apparatus for testing a compression decoder, includes a compression encoder having a picture input for receiving picture material and a coding decision input for receiving coding decisions from a set of legal coding decisions, where the compression encoder is adapted to encode picture material utilising the received coding decisions, a generator for generating random coding decisions from the legal set, and a playback device for communicating encoded picture material from the encoder to a decoder under test.

Abstract: Apparatus for the playback and monitoring of bit-rate reduced bitstreams, comprising buffer means for communication with bitstream storage; an interface; and a bi-directional processing array connected between the buffer means and the interface, the processing array being configurable to modify and process data flowing in a first direction in a plurality of playback modes and to analyse and process data flowing in a second direction in a plurality of monitoring modes.

Abstract: An integrated circuit for MPEG2 has a variable length decoder; a variable length coder; a decoder; and a coder. An information bus switch passes an information bus signal to the variable length coder, and as a control to the decoder and to the coder; and a picture bus signal switch is capable of routing signals through the coder and the decoder and to the variable length coder.

Abstract: An MPEG-2 or other compressed video stream (CP) can be manipulated as separate information bus (IB) and coefficient (CP*) streams. The information bus stream (IB) contains motion vector information but also information derived from a previous decoding operation (14, 18) for use in a subsequent coding operation (22). Processing in the coefficient domain enables bit rate conversion without decoding to the pixel level and also simplifies the combination of MPEG layers.

Abstract: An MPEG-2 or other compressed video stream (CP) can be manipulated as separate information bus (IB) and coefficient (CP*) streams. The information bus stream (IB) contains motion vector information but also information derived from a previous decoding operation (14, 18) for use in a subsequent coding operation (22). Processing in the coefficient domain enables bit rate conversion without decoding to the pixel level and also simplifies the combination of MPEG layers.

Abstract: In a signal transmission chain containing, for example MPEG2 coders (12, 20, 28) and decoders (24, 30), an information channel extends throughout the signal chain. Signal processing elements in the chain take advantage of information (VP) on the information channel and also add to it information (VP) concerning the process performed by that signal processing element. The information channel, towards the end of the signal transmission chain, therefore carries information (VP) relating to all or most of the various processes performed by in the chain.

Abstract: In the combination of a video signal coder and a video signal decoder, synchronization is achieved by the addition of absolute time reference signals at the coder. These time reference signals are independent of the time base of the coder and are inserted after the coder buffer. At the decoder, the time reference signals are stripped out and used to set the decoder time base.

Abstract: High definition television coder/decoder a high definition coder or decoder includes a number of parallel sub-decoders or coders. The image to be coded or decoded is divided into a number of stripes, a given stripe being coded or decoded by a single sub-coder or sub-decoder. Every N.sup.th stripe is coded or decoded by the same sub-coder/sub-decoder, where N is the number of sub-coders or sub-decoders. The number of sub-coders is independent of the number of sub-decoders whereby a reduction in the number of sub-coders with increasing bit-rate capacity does not necessitate a change in decoder.