Nikola Sprljan

Modified SPIHT algorithm for wavelet packet image coding

This paper introduces a new implementation of wavelet packet decomposition which is combined with SPIHT (Set Partitioning in Hierarchical Trees) compression scheme. We provide the analysis of the problems arising from the application of zerotree quantisation based algorithms (such as SPIHT) to wavelet packet transform coefficients. We established the generalized parent-child relationships for wavelet packets, providing complete tree structures for SPIHT. The proposed algorithm can be used for both wavelet dyadic and Wavelet Packet decomposition (WP-SPIHT). An extensive evaluation of the algorithm was performed and it has been shown that WP-SPIHT significantly outperforms base-line SPIHT coder for texture images. For these images the suboptimal WP cost-function enables good enough energy compaction that is efficiently exploited by the WP-SPIHT.

Bit-stream allocation methods for scalable video coding supporting wireless communications

The demand for video access services through wireless networks, as important parts of larger heterogeneous networks, is constantly increasing. To cope with this demand, flexible compression technology to enable optimum coding performance, especially at low bit-rates, is required. In this context, scalable video coding emerges as the most promising technology. A critical problem in wavelet-based scalable video coding is bit-stream allocation at any bit-rate and in particular when low bit-rates are targeted. In this paper two methods for bit-stream allocation based on the concept of fractional bit-planes are reported. The first method assumes that minimum rate-distortion (R-D) slope of the same fractional bit-plane within the same bit-plane across different subbands is higher than or equal to the maximum R-D slope of the next fractional bit-plane. This method is characterised by a very low complexity since no distortion evaluation is required. Contrasting this approach, in the second method the distortion caused by quantisation of the wavelet coefficients is considered. Here, a simple yet effective statistical distortion model that is used for estimation of R-D slopes for each fractional bit-plane is derived. Three different strategies are derived from this method. In the first one it is assumed that the used wavelet is nearly orthogonal, i.e. the distortion in the transform domain is treated as being equivalent to the distortion in the signal domain. To reduce the error caused by direct distortion evaluation in the wavelet domain, the weighting factors are applied to the used statistical distortion model in the second strategy. In the last strategy, the derived statistical model is used during the bit-plane encoding to determine optimal position of the fractional bit-plane corresponding to refinement information in the compressed bit-stream. Results of selected experiments measuring peak signal to noise ratio (PSNR) of decoded video at various bit-rates are reported. Additionally, the PSNR of decoded video at various bit-rates is measured for two specific cases: when the methods for bit-stream allocation are used to assign quality layers in the compressed bit-stream, and when quality layers are not assigned.

Evaluation of Techniques for Modeling of Layered Motion Structure

Motion information scalability is important for scalable bit-stream adaptation on low bit-rates, when motion rate occupies a significant portion of the total bit-rate. This type of scalability can be achieved by layered representation of motion block partitioning and predictive coding of associated motion vectors across these layers. So far, several approaches for creating layered motion structure targeting quality scalability have been proposed and in this paper their accuracy is evaluated. For that purpose optimal motion models have been found. It has been shown that simple evaluation of reconstruction error at the encoder side improves suboptimal modeling techniques.

Motion driven adaptive transform based on wavelet transform for enhanced video coding

Spatial wavelet transform in video coding has traditionally been applied in a non-adaptive fashion. However, since motion compensation introduces specific structure into video frames, adaptive spatial transform can introduce additional coding gain. As the structure introduced by motion compensation depends on applied motion parameters, the same motion information can be used as an adaptation parameter in spatial decomposition. Specifically, in this paper motion driven adaptation on wavelet transform in its lifting implementation is proposed. The introduced computational complexity of the proposed method is low as only a few additional multiplications are introduced per lifting step. Since in this case the same motion information is available at both encoder and decoder, transmission of additional side information is not needed. Besides better energy compaction, the proposed scheme introduces considerable gain when applied in scalable video coding.

A resolution adaptive interpolation technique for enhanced decoding of scalable coded video

Subpixel accurate motion compensated temporal filtering introduces a significant coding gain in scalable 3D wavelet video codecs. The influence of the chosen subpixel interpolation technique has not yet been fully analysed in the context of resolution scalability. That problem is addressed in this paper. It is shown that support for increased accuracy and resolution adaptive spatial interpolation needs to be featured in a scalable video decoder, when low resolution sequences are targeted. Using the proposed resolution adaptive filters based on sinc kernels leads to improved decoding performance at low resolution in the sense of achieving higher quality while reducing the complexity of the system.

A fast error protection scheme for transmission of embedded coded images over unreliable channels and fixed packet size

Joint source-channel coding enables efficient transmission of embedded bitstreams over unreliable channels. We address channels with fixed packetisation and decoding without or with minimal delays. The computation of an optimal protection scheme for such bitstreams is generally an exponential complexity problem and hence not applicable in a straightforward implementation. Using the rate-distortion characteristics of the source bitstream and the dynamic programming approach we construct an efficient unequal error protection scheme for the predefined channels. Our algorithm is of linear complexity and thus applicable in real time scenarios.

Comparison of broadband network technologies

Consumer growing demand for data communications forced telecommunication operators to greatly extend capabilities and capacity of their networks and to offer acceptable prices for all available information and communications services with high speed Internet connection for the small business and individual users. The article analyses different broadband network technologies, and compares advantages and disadvantages of ISDN and ADSL network infrastructure and CATV cable modem systems for a home user. The costs for the consumer of these services in Croatia were also compared.

Bit-stream allocation methods for wavelet based scalable video coding

In wavelet based scalable video coding quality scalability is achieved using bit-plane coding techniques that result in embedded bit-stream. In order to minimise distortion when specific bit-rate is targeted, compressed data has to be optimally truncated in different layers that comprise the bit-stream. In this paper two methods for compressed bit-stream allocation are presented. First adopts assumption that same fractional bit-planes within same bit-planes of different wavelet subbands have nearly equal rate-distortion slopes, while the other takes into account the distortion caused by the quantisation of wavelet coefficients. First method is characterised by low complexity since distortion does not have to be assessed. For the second method, a simple yet effective statistical distortion model is derived. The experimental results show comparable performance of the two tested methods.

An Entropy Coding Scheme for Multi-Component Scalable Motion Information

Fully scalable video bit-stream requires layered structure of most of its components. For that reason few methods targeting scalability on motion information have been proposed over the last decade. However, layered representation requires new entropy coding strategies able to efficiently handling of redundancies between different layers. In this paper three methods for entropy coding of layered motion information are proposed. The influence of these schemes on the reconstructed video quality has been also studied

ImAn - educational tool for image analysis

In image compression system, statistical and subjective redundancies are removed to achieve bitrate reduction. Statistical and frequency characterization of image is an important step for understanding how image compression systems work. Students specializing in image and video system engineering need to know why these characteristics are important in their field of interest and to understand the influence of these characteristics on image quality. Therefore, we have developed educational software, called ImAn - Image Analyser, that helps students to analyze statistical and frequency characteristics of images that will be presented in this paper.