J. L. P. De Lameillieure

Comment on "Algorithm for Construction of Variable Length Code with Limited Maximum Word Length"

In the above correspondence, two algorithms for the construction of a minimum redundancy code have been described. In this correspondence, it is pointed out that the strategy in the correspondence does not always lead to an optimal code. A correction of both algorithms is presented.

A heuristic algorithm for the construction of a code with limited word length (Corresp.)

A depth-first algorithm is presented for the construction of a binary minimum-redundancy variable length code with limited word length. In this algorithm, heuristic information on the mean word length is used for efficient searching. The extension to Q -ary codes is also discussed.

A transformation for the calculation of filter pairs for perfect reconstruction in subband coding with linequincunx subsampling

For a feasible calculation of filters for the subband coding of picture sequences with linequincunx subsampling, a coordinate transformation of the sampling raster is proposed. With the new coordinates, the linequincunx subsampling becomes a simple quincunx subsampling without interlace. This facilitates the mathematical derivation of three-dimensional perfect reconstruction filters. >

Correction to 'A heuristic algorithm for the construction of a code with limited word length'

In the above-named work (see ibid., vol.IT-33, p.438-43, May 1987), a method was presented for the construction of a variable length code with maximum word-length constraint. The algorithm is partially based on the algorithm of A.H. Murakami et al. (1984), and is extended with heuristic choices for the bifurcations. C.H. Lu (1988) explains why step (1) taken by Murakami, which is used in De Lameillieures contribution as condition (6), does not guarantee an optimum code when a word-length restriction is imposed. This step (1), or condition (6), does not take the bounded maximum word length into account. Therefore, in the present contribution the author rectifies this difficulty by proposing an adaptation of condition (6) into a composite condition for the case when there is a word-length constraint. Proofs of the components of this composite condition are presented together with numerical results. >

Comments on "A Predictor Switching Scheme for DPCM Coding of Video Signals"

In the above paper, conditions are derived for determining whether or not a scheme with transmission of predictor information for selected pels is better than a scheme with adaptive predictor switching only. These comments contain experimental evidence which proves that those conditions are not valid. Moreover, it is pointed out which part of the derivation of the above conditions is erroneous.

Comments on "A subjective evaluation of noise-shaping quantization for adaptive intra-/interframe DPCM coding of color television signals" (by B. Girod et al.)

In the above named work by B. Girod et al. (see ibid., vol.36, no.3, p.332-46, 1988), a stability condition for a DPCM (differential pulse code modulation) system with additional quantization error noise shaping has been proposed. In the present work, a correction of this stability condition is derived. >

Corrections to "Comment on ́Algorithm for Construction of Variable Length Code with Limited Maximum Word Length́"

In this correspondence we determine an upper bound on the error recovery time of a decision feedback equalizer (DFE) operating on a high signal to noise ratio channel of exponential impulse response to be used for binary transmission. This bound is related to the channel time constant and we show that exponential impulse response channels form a favourable class of channels with regard to DFE error recovery ‘properties. Paper approved by the Editor for Digital Communications of the IEEE Communications Society. Manuscript received November 25, 1986; revised March 6, 1987. This work was supported by the Australian Telecommunications and Electronics Research Board. The authors are with the Department of Systems Engineering, Research School of Physical Sciences, Australian National University, Canberra, A.C.T. 2601, Australia. IEEE Log Number 8715681. ~~