Yasuhiko Yasuda

Performance evaluation of subband coding and optimization of its filter coefficients

Abstract In this paper, two analytical methods for evaluating the coding efficiency of subband coding are proposed, and optimization of filter coefficients of the perfect reconstruction FIR filter banks is considered, based on a new performance measure called unified coding gain. First, matrix representation of the subband coding in the time domain is considered, and conventional subband filter banks are classified into orthogonal ones such as the QMF and nonorthogonal ones such as the SSKF. For the orthogonal filter banks, the coding gain shown by Jayant and Noll is introduced, and their theoretical performance evaluation is carried out. However, this first method cannot be applied to nonorthogonal filter banks any longer because the coding gain is defined on the assumption of filter orthogonality. Therefore, an optimum bit allocation problem for subband coding is considered, and the unified coding gain, which can be applied to arbitrary subband filter banks, is derived as a new performance measure to take the place of the coding gain. This second method enables us to estimate the coding efficiency of arbitrary transform techniques as well as the subband approaches, and its result suggests that the SSKF(5 × 3) outperforms the QMF as long as the number of subbands is not too large, even though its filter length is much shorter. This result encourages us to find filter coefficients that maximize the unified coding gain according to filter length. In addition, new perfect reconstruction FIR filter banks which have not only low computational complexity but also good energy compaction properties are presented.

The evaluation of delay jitter for haptics collaboration over the Internet

What we are concerned with in this paper is a shared virtual environment (SVE) on a non-dedicated network like the Internet. Especially, we address haptics on an SVE for the new generation of network applications. The goal of our research Is to build an SVE system in which multiple participants can collaborate using haptics feedback, even though the participants are located around the world. One of the problems for this system is network impairment, and we have examined the effect of constant network delay and packet loss on the haptics collaboration system. In this paper we examine and evaluate the effect of delay jitter on the system when using media synchronization and dead reckoning.

Data compression for check processing machines

A technique of compressing image data derived from personal checks which possess several gray levels is described. Check images consist of both essential information such as printed and handwritten characters and nonessential background pattern or picture. Only the character plane is to be coded. Our proposed technique is divided into two phases: character plane extraction and character plane coding. In the first phase, a character plane which is composed of character pels on a uniform background is extracted from an original digital check image by using a combination of fundamental techniques of image segmentation. In the second phase, the extracted character plane is separated into a bit plane and a gray-level plane. The bit plane which preserves the position information of character pels on the character plane is conditional entropy coded. An adaptive two- or one-dimensional predictive coding scheme is applied to the gray-level plane which consists of only the character pels on the character plane. The check data are stored for further use as a combination of the codes derived from the bit plane encoder and the gray-level encoder in a check processing machine. A comparative study shows that the proposed coding scheme performs much better than conventional predictive coding schemes. For 8 gray-level image data, a compression factor of about 8:1 has been achieved.

Overview of digital facsimile coding techniques in Japan

This paper surveys recent progress in digital facsimile coding techniques in Japan. First, the digital facsimile coding techniques are classified into two major categories: information-preserving coding and non-information-preserving coding. Second, various two-dimensional coding algorithms which fall into the category of information-preserving coding are selected and discussed. Two-dimensional coding is divided into two categories: simultaneous coding of n lines and line-by-line sequential coding. Third, the READ coding scheme, which was proposed by Japan to CCITT SG XIV as the standard of two-dimensional coding, is explained in detail. Fourth, recent developments concerning non-information-preserving coding are explained. Finally, related coding techniques and applications of digital facsimile coding are briefly described.

Packet video transmission through ATM networks

The basic aspects of packet video transmission technology are described, and some new results are presented. The advantages of packet video transmission through ATM (asynchronous transfer mode) networks and items to be solved are discussed from both the network and the user sides. Modeling methods, including burstiness measures are described. Examples of modeling based on the Markov modified Poisson process are shown. Packet loss protection and recovery methods are discussed, and the effects of a layered coding scheme are described. Subjective picture quality based on variable rate video transmission is demonstrated.<<ETX>>

Advances in FAX

One of the most important techniques introduced into the recent facsimile is redundancy-reduction coding. The CCITT already standardized the coding schemes to be employed in Group 3 and Group 4. There are, however, left for further study the optional non-information-preserving coding scheme for black-and-white pictures and the coding scheme for multilevel and color pictures. Much work has been carried out with respect to these kinds of coding, including pattern-matching coding for black-and-white pictures and various information-preserving and non-information-preserving coding for multilevel and color pictures. The Group 4 apparatus is a new generation facsimile apparatus, which is mainly operated on public switched data networks. This kind of facsimile apparatus features higher resolution and error-free reception, and has the teletex-facsimile mixed mode capability as an option. The most important technical problem in the standardization of the Group 4 facsimile is the communication protocol which has been developed based on the existing teletex protocol. Facsimile communication is carried out not only on general public switched telephone or data networks, but also on specialized networks dedicated to it. Some sorts of communication processing such as speed conversion, automatic appending function, repeated delivery attempt, etc., are incorporated into these networks. The development of facsimile equipment has also shown progress in these few years. For example, a very compact apparatus has been developed using a new contact type imager and a codec built by special-purpose LSIs. The press fax apparatus employing flat-bed scanner and multicolor facsimile apparatus have also been put into market. This paper describes the outline of recent advances in facsimile, including the above-mentioned items.

Improved Coherent Detection of GMSK

It is pointed out that the degradation effect due to premodulation filtering in GMSK (Gaussian-filtered minimum shift keying) is largest at the edges of time slots, which instant has been adopted as the sample timing in the conventional coherent detector of GMSK. Then a new coherent detector employing signals sampled at a different timing in a deviated-frequency-locking scheme is presented to achieve a better bit-error-rate performance versus carrier-to-noise ratio.

Hierarchical representation of the motion of a walker and motion reconstruction for model-based image coding

We apply a model-based image coding scheme to the scene of a human walker. In our scheme, the motion of a whole human body is represented in 3-D stick motion. We concentrate on the following subjects: modeling of a walker by a stick model, the motion analysis algorithm based on the stick model, and the scheme to reconstruct continuous stick motion by the analyzed results. We determine both the form of a 3-D human stick model and how the model walks, and define the parameters of the model to represent the real motion in the scene. Then, we propose a three-layer motion representation scheme by using three stick models with different degrees of coarseness. Also, we present an algorithm for estimating the parameters of these stick models from monocular moving pictures. With this algorithm, the parameters of each model are estimated efficiently in the order of coarseness of model. We have applied his scheme to two experimental scenes where the identical walker is walking straight to the different direction. While the estimated 3-D motion has included some errors, the availability of this motion representation scheme to the model-based image coding system has been confirmed.

An improved power saving mechanism for MAC protocol in ad hoc networks

Ad hoc networks have recently become a hot topic. In ad hoc networks, battery power is an important resource, since most terminals are battery powered. Terminals consume extra energy when their network interfaces are in the idle state or when they overhear packets not destined for them. They should, therefore, switch off their radio when they do not have to send or receive packets. IEEE802.11 features a power saving mechanism (PSM) in the distributed coordination function (DCF). In PSM for DCF, nodes must stay awake for a fixed time, called the ATIM window (ad-hoc traffic indication map window). If nodes do not have data to send or receive, they enter the doze state except for during the ATIM window. However, ad hoc networks with PSM have larger end-to-end delays to deliver packets and suffer lower throughput than the standard IEEE802.11. To solve this problem, this paper proposes a protocol that reduces delay and achieves high throughput and energy efficiency. Simulation results show that our proposal outperforms other PSMs in terms of throughput, end-to-end delay and energy efficiency.

Short-tap and linear-phase PR filter banks for subband coding of images

This paper presents a filter design algorithm in order to realize high efficient image codec system based on subband decomposition, and also describes unified frameworks to interpret various image coding techniques. First, various image coding techniques based on the linear transform are dealt with in an unified manner, where both the matrix representation in time domain and the multirate filter bank concept are introduced. Reconsideration about the DPCM is stressed here because the subband coding and the transform coding have been already formulated in some common frameworks. Neither the filters frequency response nor its orthogonality are taken into consideration because they dont necessarily play an important role in our formulation, particularly in case of the DPCM and the SSKF. Secondly, statistical optimization of short tap and linear phase PR (perfect reconstruction) filter banks is considered. The UCG (unified coding gain) that we proposed at the VSIP 91 as a performance measure of energy compaction properties of the multirate filter bank is expanded to multiple layer cases, and several new examples are presented. The short tap structure leads to low computational complexity, and the linear phase property contributes not only to remove phase distortion but also to solve the so-called border problem. Simulation results are also shown, and the validity of our approach is confirmed.