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: A method for converting between relatively close field rates of perhaps 60 Hz and 59.94 Hz, monitors the phase difference between input and output field rates. Initially, output fields are created by synchronizing input fields. As the measured phase passes a threshold, the method switches to interpolation mode for a short, fixed interval and then returns to synchronization. The method offers much of the sharpness associated with simple synchronization but avoids the visible discontinuities of field drops or repeats.

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: A color television decoder or other signal processor has a gate controlling the passage of a notch filtered chrominance signal. A filter circuit produces a further chrominance signal which serves as the control signal for the gate.

Abstract: In video signal processing, diagonal lines or slopes are detected in the input material, and an adaptive spatial filter having positive, negative and linear filter apertures is employed. The positive filter aperture is employed upon detection of any positive slopes in excess of a defined positive threshold; the negative filter upon detection of negative slopes, and the linear filter otherwise.

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 video noise reducer, where pixel information is recursively filtered, with recursion being disabled at a disjuncture (caused by motion, planning, shot-change or otherwise), recursively filtered pixel information prior to disjuncture continues to be output until pixel information following the disjuncture has been recursively filtered to an appropriate degree of noise reduction.

Abstract: A video signal is enhanced using a non-linear combination of left and right difference signals (L and R), constrained to be zero if either L or R is zero, using a minimum absolute value function. Edge enhancement is provided when the polarities of L and R are the same and peak enhancement when the polarities are different. Difference signals are derived with delays (2 and 4) and a subtracter (3). The non-liner combinations are derived in a lookup table (30).

Abstract: In order to loop MPEG2 bitstreams without violating buffer occupancy constraints of downstream decoders, the replay bit rate is modified so the time taken to replay the looped sequence is made equal to the decode time. Looping of a sequence of compressed video bitstream is used for the purpose of testing MPEG2 decoders.

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: Cuts in a video signal are detected by first measuring a correlation parameter between successive images; this can be the sum of the maximum peak heights for each of 16 to 100 or more blocks in a block-based phase correlation procedure. An averaged value of this correlation parameter is maintained and the current measurement of the correlation parameter is compared with the averaged value. The presence of a cut is inferred where the current measurement drops beneath, say, 50% of the average value.

Abstract: A method of display unconversion wherein each output field line is interpolated from at least three input field lines from each of at least three input fields. By increasing the field rate by 1.5 (instead of simple field doubling) and by increasing the line rate by 1.5 (instead of simple line doubling) a substantial increase in picture quality can be achieved while maintaining data flow rates within manageable limits.

Abstract: Apparatus for creating video test patterns for outputting to a video test pattern generator enables individual lines to be built from standard components with appropriate parameters. Completed lines are held in a form which is television standard-independent and can be edited numerically or graphically. A test pattern is built from a set of lines and a part or fully completed pattern can be displayed to an operator in a picture representation which simulates the appearance of the test pattern when displayed on a television receiver.

Abstract: A signal processor for extracting chrominance information from a composite video signal has transversal filters developing first and second signals (A and B). A look-up table generates a control signal (C) which is a non-linear function of the ratio A/B and simultaneously develops the product B*C. A filter of this form can combine steep frequency response with minimal degradation of the response to pulses.

Abstract: A cinematographic camera is operated at three times normal frame rates and converted to digital video in a telecine operation. Motion estimation provides from the digital video motion vectors which are substantially free of temporal aliasing. These motion vectors are employed in film weave measurement and correction and in motion compensated noise reduction and scratch concealment to provide a high quality signal which can be displayed at the elevated frame rate or standards converted, using the high quality motion vectors, to any desired standard.

Abstract: A method for reducing the deleterious effects of motion in a video signal process. The video signal process is conducted at high bandwidth without motion compensation and a like video signal process is conducted at low bandwidth without motion compensation to produce a low bandwidth control signal. A similar video signal process with motion compensation is conducted at low bandwidth to produce a low bandwidth motion compensated signal. The low bandwidth control signal and low bandwidth motion compensated signal are compared to produce an error signal which is subtracted from the high bandwidth video signal process. Video signal procession apparatus includes parallel high and low bandwidth paths.

Abstract: A method for converting between relatively dose field rates of perhaps 60 Hz and 59.94 Hz, monitors the phase difference between input and output field rates. Initially, output fields are created by synchronising input fields. As the measured phase passes a threshold, the method switches to interpolation mode for a short, fixed interval and then returns to synchronization. The method offers much of the sharpness associated with simple synchronization but avoids the visible discontinuities of field drops or repeats.

Abstract: A group delay of a noise-reducing median filter for video or a video FIR filter is reduced by transferring filter contributions of fields in "time forward" to fields in "time past" with respect to an output sample point. No significant impairment is introduced by this time asymmetry.

Abstract: A rate converter for digitally converting the sample rate of a signal, has a first digital filter for deriving an intermediate signal at increased sample rate and a second digital filter for deriving an output signal at a decreased sample rate relative to that of the intermediate signal. The first filter is of relatively high order serving to double the frequency. Because the frequency change is a power of two, the aperture characteristic is straightforward and implementation is simple even at high order. The second filter is of relatively low order so that implementation is simple even with a time-varying aperture characteristic. The low order of the second filter does not however degrade the overall frequency characteristic.