Quantiser selection for interframe differential pulse code modulation of television pictures

A procedure based on subjective and objective assessments has been used to design an 8-level quantiser for an interframe d.p.c.m. digital television coding system handling monochrome 5.5 MHz 625-line pidura The quantiser reduces noise in a static picture over its 8-bit source and attempts to minimise the distortion of movement.     

Entropy-coded hybrid differential pulse-code modulation

A hybrid differential pulse-code-modulation (DPCM) system is presented to demonstrate the application of fuzzy set theory in data compression. The system involves entropy coding, Laplacian quantiser and fuzzy enhancement operations as applied on the DPCM signal. Saving of about 0.5 bit is found to be obtained when a DPCM signal is quantised to 32-level, and then Huffman-coded.     

Equivalent gain of an instantaneous quantiser with two independent random inputs

An extension of Booton's criterion for the definition of the equivalent gain of an instantaneous nonlinear device is found in the case of two statistically independent random inputs. The resulting formulas have been used for calculating interchannel crosstalk and idle channel noise in a noisy quantiser for p.c.m. telephone systems.     

Noninteger sampling to subcarrier frequency ratios in d.p.c.m. of PAL signals

A simple predictor having three coefficients is described for d.p.c.m. encoding of composite PAL colour signals. Noninteger ratios of sampling frequency fs to subcarrier frequency fsc can be selected. For a colour-bar signal, it is shown that the s.n.r. of the d.p.c.m. system using fs/fsc = 2.5 is approximately the same as when third-previous sample prediction is used, i.e. when fs/fsc = 3.0.     

Adaptive statistical encoding of d.p.c.m.-coded videotelephone signals

Adaptive statistical encoding of d.p.c.m.-coded video-telephone signals is considered. The need for an adaptive statistical encoder to operate on short-term batch statistics is explained and the effect on the bit rate of limiting the number of codes employed by the statistical encoder is reported.     

Design method of symmetric vector quantiser

A new design algorithm is presented for a symmetric universal vector quantiser based on the successive partitioning of normalised signal space. The universal vector quantiser of video signals is also shown as an example.     

P.c.m. nonlinear counting encoder

Companded encoders of high resolution, such as may be required for p.c.m. transmission of high-quality sound-programme signals, can be realised using the `counting? principle. In the reported implementation, a reference waveform of ramps of different slopes are generated by integrating the output from a d.a. convenor.     

Feasibility of using digital filters to interconnect p.c.m. and f.d.m. transmission systems

A time-division multiplex (t.d.m.) and a frequency-division multiple (f.d.m.) system may be interconnected by means of gates and lowpass filters. The use of digital filters (d.f.s) for this purpose appears attractive when the t.d.m. system uses pulse-code modulation (p.c.m.), because digital-analogue and analogue-digital conversion are unnecessary at the interface between the d.f. and the p.c.m. system. The problems involved in applying d.f.s in this application are discussed. It is concluded that the interconnection of p.c.m. systems with f.d.m. systems using quite low carrier frequencies requires the development of digital circuits operating at several hundred megahertz.     

Vector quantiser of video signals

An efficient design method is presented for a vector quantiser of 16-dimensional vectors based on a long training sequence of normalised video signals. The basic properties are demonstrated by examples.     

Lossless image compression by quantization feedback in acontent-driven enhanced Laplacian pyramid

In this paper, the effects of quantization noise feedback on the entropy of Laplacian pyramids are investigated. This technique makes it possible for the maximum absolute reconstruction error to be easily and strongly upper-bounded (near-lossless coding), and therefore, allows reversible compression. The entropy-minimizing optimum quantizer is obtained by modeling the first-order distributions of the differential signals as Laplacian densities, and by deriving a model for the equivalent memoryless entropy. A novel approach, based on an enhanced Laplacian pyramid, is proposed for the compression, either lossless or lossy, of gray-scale images. Major details are prioritized through a content-driven decision rule embedded in a uniform threshold quantizer with noise feedback. Lossless coding shows improvements over reversible Joint Photographers Expert Group (JPEG) and the reduced-difference pyramid schemes, while lossy coding outperforms JPEG, with a significant peak signal-to-noise ratio (PSNR) gain. Also, subjective quality is higher even at very low bit rates, due to the absence of the annoying impairments typical of JPEG. Moreover, image versions having resolution and SNR that are both progressively increasing are made available at the receiving end from the earliest retrieval stage on, as intermediate steps of the decoding procedure, without any additional cost.     

Rate-distortion analysis of nonlinear quantisers for MPEG videocoders: sigmoidal and unimodal quantiser control functions

Quantisation is employed in MPEG video coders as a video rate control scheme to regulate the data rate of the compressed video bit stream entering the transmission buffer. For constant bit rate applications, the quantiser has a crucial effect on the video data rate and video quality. It has been a challenging task to optimise the quantiser step size for both bit rate and quality since they are mutually exclusive parameters, as defined by rate-distortion theory. The quantiser step size is generally determined by a linear relationship with respect to the buffer occupancy. Two nonlinear quantiser control functions are investigated, sigmoidal and unimodal, which achieve superior video rate control performance while maintaining similar video quality to the linear one. These two functions are analysed in the framework of rate-distortion theory. Their performance for video rate fluctuation has also been analysed. Encoding results for the two functions are compared to the MPEG2 TM5 evaluation model     

New scheme for vector quantisation of speech signals

The design theory of a vector quantiser is valid only on some assumptions which are unfortunately not satisfied in most real-world cases. A decomposition procedure of speech signals is described which leads to a proposed method for designing the vector quantisers in a reasonable way.<>     

Low-complexity GMM-based block quantisation of images using the discrete cosine transform

While block transform image coding has not been very popular lately in the presence of current state-of-the-art wavelet-based coders, the Gaussian mixture model (GMM)-based block quantiser, without the use of entropy coding, is still very competitive in the class of fixed rate transform coders. In this paper, a GMM-based block quantiser of low computational complexity is presented which is based on the discrete cosine transform (DCT). It is observed that the assumption of Gaussian mixture components in a GMM having Gauss–Markov properties is a reasonable one with the DCT approaching the optimality of the Karhunen–Loève transform (KLT) as a decorrelator. Performance gains of 6–7 dB are reported over the traditional single Gaussian block quantiser at 1 bit per pixel. The DCT possesses two advantages over the KLT: being fixed and source independent, which means it only needs to be applied once; and the availability of fast and efficient implementations. These advantages, together with bitrate scalability, result in a block quantiser that is considerably faster and less complex while the novelty of using a GMM to model the source probability density function is still preserved.     

Detection and partial correction of isolated errors from the received data in a 1st-order d.p.c.m. codec

A detection and partial-correction (d.p.c.) system located at the receiver in a 1st-order d.p.c.m. system enables isolated transmission errors that would cause gross distortion in the recovered signal of a conventional d.p.c.m. decoder to be corrected from the received data, providing that the input signal does not exhibit a rapid change in its slope during a sampling period. The d.p.c. system is disabled when this occurs.     

Hybrid p.c.m.?an experimental video system

Hybrid pulse-code modulation (h.p.c.m.) is a variant o. multilevel p.c.m., in which the least significant digit(s) is made to describe the quantising noise exactly. A theoretical and practical feasibility study has been made of the application of h.p.c.m. to the transmission of 625-line Pal colour signals over low-quality narrowband circuits.     

Spectra of biternary digital f.m.

Spectra of digital f.m. have been published recently for general n-level transmission. However, biternary signals, as used in p.c.m. systems, are not covered by the published formulas and require a special treatment. Spectrum density and spectrum distribution are derived for biternary transmission, numerical curves are presented for certain values of f.m. deviation, and the results are compared with ordinary binary transmission.     

1-bit quantiser with rail to rail input range for sub-1 V /spl Delta//spl Sigma/ modulators

A new, fully differential comparator with rail to rail input range is presented. This comparator can be used as a 1-bit quantiser in sub-1 V /spl Delta//spl Sigma/ modulators. The quantiser is laid out in 0.18 /spl mu/m CMOS technology. The post-layout simulation results show that the quantiser is capable of working at 10 MHz with 10 /spl mu/V resolution. This quantiser is successfully used in 0.8 V first-order and second-order fully differential /spl Delta//spl Sigma/ modulators.     

Long-term step response of a chain of a.c.-coupled amplifiers

In the long-distance transmission of television signals, the long-term step response of a chain of a.c.-coupled amplifiers is of interest. A solution is obtained for the asymptotic response, where the transfer functions are first-order, and some speculations are included about generalising the result to higher orders.     

Pitch synchronous 1st-order linear d.p.c.m. system

A system called p.s.f.o.l.d. is described which exploits the correlation between successive pitch periods of a speech signal. This system is a differential one and can employ various types of encoders. We describe a p.s.f.o.l.d. system using a 1st-order d.p.c.m. encoder and show that for a speech utterance this system has a peak signal/noise ratio which is 6 dB larger, and has an increase in dynamic range of 13 dB, compared with a 1st-order d.p.c.m. codec.     

Optimised frequency-domain bit allocation for video coding

An optimal frequency domain bit allocation technique is presented. A Lagrange multiplier based approach is used for the rate-distortion optimisation of a quantisation matrix in video coding. Since the optimal quantisation matrix is heavily dependent on the choice of quantiser, the quantiser is also jointly optimised in order to alleviate the interaction between the two. The complexity of the algorithm is analysed, and it is shown to be directly proportional to the number of possible quantisation matrices and quantisation scales. Experimental results comparing the new technique with a conventional video encoder are also presented.