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1

Improved vector quantization scheme for grayscale image compression

Hu Y. C., Chen W. L., Lo C. C., Chuang J. C.

Opto-Electronics Review

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2012

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Vol. 20, No. 2

187-193

EN

This paper proposes an improved image coding scheme based on vector quantization. It is well known that the image quality of a VQ-compressed image is poor when a small-sized codebook is used. In order to solve this problem, the mean value of the image block is taken as an alternative block encoding rule to improve the image quality in the proposed scheme. To cut down the storage cost of compressed codes, a two-stage lossless coding approach including the linear prediction technique and the Huffman coding technique is employed in the proposed scheme. The results show that the proposed scheme achieves better image qualities than vector quantization while keeping low bit rates.

2

Variable-rate colour image quantization based on quadtree segmentation

Hu Y. C., Li C. Y., Chuang J. C., Lo C. C.

Opto-Electronics Review

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2011

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Vol. 19, No. 3

282-289

EN

A novel variable-sized block encoding with threshold control for colour image quantization (CIQ) is presented in this paper. In CIQ, the colour palette used has a great influence on the reconstructed image quality. Typically, a higher image quality and a larger storage cost are obtained when a larger-sized palette is used in CIQ. To cut down the storage cost while preserving quality of the reconstructed images, the threshold control policy for quadtree segmentation is used in this paper. Experimental results show that the proposed method adaptively provides desired bit rates while having better image qualities comparing to CIQ with the usage of multiple palettes of different sizes.

3

Efficient greyscale image compression technique based on vector quantization

Hu Y. C., Chuang J. C., Lo C. C., Li C. Y.

Opto-Electronics Review

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2011

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Vol. 19, No. 1

104-113

EN

In this paper, a novel greyscale image coding technique based on vector quantization (VQ) is proposed. In VQ, the reconstructed image quality is restricted by the codebook used in the image encoding/decoding procedures. To provide a better image quality using a fixed-sized codebook, the codebook expansion technique is introduced in the proposed technique. In addition, the block prediction technique and the relatively address technique are employed to cut down the required storage cost of the compressed codes. From the results, it is shown that the proposed technique adaptively provides better image quality at low bit rates than VQ.