Determination of Lifting Direction of Integer DCT for Low Sensitivity

Yoshihide TONOMURA  Masahiro OHNISHI  Masahiro IWAHASHI  

A - Abstracts of IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences (Japanese Edition)   Vol.J91-A   No.3   pp.339-348
Publication Date: 2008/03/01
Online ISSN: 1881-0195
Print ISSN: 0913-5707
Type of Manuscript: PAPER
image coding,  integer DCT,  lossless compression,  sensitive coefficient,  lifting structure,  

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The international standard for video or image coding such as MPEG or JPEG utilizes the discrete cosine transform (DCT) to increase coding efficiency. As a result, the colored spectrum of an input image is whitened. In case of the "normal DCT" is used, a coding system becomes "lossy" since quantization is necessary to convert real number into integer so that the signal can be entropy coded. On the other hand, in case of the "integer DCT" is used, a coding system can be "lossless". The integer DCT outputs integer signal and therefore quantization, which makes "loss", is not necessary. Recently, effect of finite word length expression (sensitivity) of multipliers of an integer rotation transform (IRT) in the integer DCT was investigated. However, direction of the lifting in the IRT is limited to only one ignoring another possible direction. In this paper, we analyze effect of using another direction in an IRT on the multiplier's sensitivity and find significant difference of changing the direction for colored signal. Utilizing this property, we determine the best direction for each of the IRTs in the integer DCT. As a result, we propose the least sensitive combination of the IRTs of the integer DCT. Significance of the proposed method is confirmed as 1.5 [dB] in PSNR improvement for image signal.