Ghim Hwee Ong

A simple partitioning approach to fractal image compression

This paper presents a binary partitioning method for fractal image compression. The method makes use of self-similarities existing in an image and applies a simple block splitting strategy to generate more rectangular and square image blocks at different resolutions under a set of affine transformations in order to achieve better compression. Experimental results show that binary partitioning consistently gives better compression than the conventional quadtree partitioning method without degrading the image fidelity.

A data compression scheme for Chinese text files using Huffman coding and a two-level dictionary

Abstract This paper presents a data compression scheme for Chinese text files. Due to the skewness of the distribution of Chinese ideograms, the Huffman coding method is adopted. By storing the frequencies of the encoding symbols rather than their Huffman codes in a dictionary, applying differential coding where it saves space, and structuring the dictionary in the Huffman coding scheme into a two-level dictionary structure, the algorithm produces significant improvement on the compression results. The proposed method is evaluated by comparing its performance with three well-known compression algorithms. This algorithm should also be applicable to other ideogram-based or oriental-language texts. Also, it has the potential to reduce the dictionary size in a bigram- or trigram-based semi-adaptive compression scheme for English texts.

A binary partitioning approach to image compression using weighted finite automata for large images

Fractal-based image compression techniques give efficient decoding time with primitive hardware requirements, and favor real-time communication purposes. One such technique, the weighted finite automata (WFA), is studied on grayscale images. An improved image partitioning technique-the binary or bintree partitioning-is tested on the WFA encoding method. Experimental results show that binary partitioning consistently gives higher compression ratios than the conventional quadtree partitioning method for large images. Moreover, the ability to decode images progressively rendering finer and finer details can be used to display the image over a congested and loss-prone network such as the image transport protocol (ITP) for the Internet, as well as to pave way for multilayered error protection over an often unreliable networking environment. Also, the proposed partitioning approach can be parallelized to reduce its high encoding complexity.

Performance evaluation of an Ethernet network

Abstract A detailed performance measurement study has been carried out to determine the network-server capability of a 3Com Ethernet network. The server is subjected to simultaneous access from a number of workstations performing read/write operations with a large block of data. Three different servers are examined. A special timing program is written to provide accurate timing measurements and automatic recordings. The throughput and response characteristics of the network are then determined from the measured data. The results yield performance ratings from an independent source, which are much sought after by network consumers.

Compression of Chinese text files using a multiple four-bit coding scheme

This paper reports on the results of the study of a two-pass reversible data compression scheme. The restricted variable length coding method using multiples of 4-bit code values is simple in concept and easy to implement. The compression results and the compression/decompression times regarding four large Chinese text files are superior to those using character-based two-pass Huffman coding and adaptive Huffman coding methods. The compression results are comparable with what the LZW method achieves, and the compression/decompression process it slightly faster.<<ETX>>

A Two-Pass Improved Encoding Scheme for Fractal Image Compression

An improvement scheme, so named the two-pass improved encoding scheme (TIES), for the application to image compression through the extension of the existing concept of fractal image compression (FIC), which capitalizes on the self-similarity within a given image to be compressed, is proposed in this paper. We first briefly explore the existing image compression technology based on FIC, before proceeding to establish the concept behind the TIES algorithm. We then devise an effective encoding and decoding algorithm for the implementation of TIES through the consideration of the domain pool of an image, domain block transformation, scaling and intensity variation, range block approximation using linear combinations, and finally the use of an arithmetic compression algorithm to store the final data as close to source entropy as possible. We then conclude by explicitly comparing the performance of this implementation of the TIES algorithm against that of FIC under the same conditions, in which the TIES algorithm exhibits significantly better compression performance for large images (1024times1024px) compared to the FIC algorithm

Dynamic Markov Compression Using a Crossbar-Like Tree Initial Structure for Chinese Texts

This paper proposes the use of a crossbar-like tree structure to use with dynamic Markov compression (DMC) for the compression of Chinese text files. DMC had previously been found to be more effective than common compression techniques like compress and pack and gives a compression gain of between 13.1% and 32.0%. This initial structure is able to improve on DMCs compression results, and outperforms the various initial structures commonly adopted, such as the single-state, linear, tree or braid structures by a gain ranging from 1.5% to 9.6%

An efficient data compression scheme based on semi-adaptive Huffman coding for moderately large Chinese text files

This paper presents a data compression scheme for Chinese text files. Due to the skewness of the distribution of Chinese ideograms, the Huffman coding method is adopted. By storing the Huffman tree in the coding table and representing the Huffman tree using the Zaks sequence, the algorithm produces significant improvement on the compression results. The proposed method is evaluated by comparing its performance with three well-known compression algorithms and an algorithm specially designed to compress the coding table. This algorithm should also be applicable to other ideogram-based or oriental language texts. Also, it has the potential to reduce the dictionary size in a bigram or trigram-based semi-adaptive compression scheme for English texts.

Compressing Chinese text files using an adaptive Huffman coding scheme and a static dictionary of character pairs

The compression method for Chinese text files proposed in this paper is based on a single pass data compression technique, adaptive Huffman coding. All Chinese text files to be compressed are modeled to contain not only ASCII characters, Chinese ideographic characters and punctuation marks, but also commonly used Chinese character pairs. The approach of using a static dictionary is employed to maintain about 3000 most frequently occurring character pairs found in general Chinese texts. This is to define the extension to the standard source alphabet in ideogram-based adaptive Huffman coding. The performance in compression ratio and CPU execution time of the proposed method is evaluated against those of the adaptive byte-oriented Huffman coding scheme, the adaptive ideogram-based Huffman coding scheme, and the adaptive LZW method. The experimental results have shown that the proposed method based on adaptive Huffman coding with an extended source alphabet yields better compression on Chinese text files.

A semi-adaptive arithmetic coding scheme for Chinese textual data

This paper presents a compression scheme for Chinese text files. Due to the skewness of the distribution of Chinese ideograms the arithmetic coding method is adopted. To reduce the overhead incurred by the frequency table in the compressed output due to the large number of Chinese ideograms, differential coding and arithmetic coding are used to produce a two-level storage structure for the frequency table. Evaluations of the proposed algorithm against several popular compression schemes show that the compression efficiency is significantly improved. This algorithm should also be applicable to other ideogram-based or oriental language texts.