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Shih-Fu Chang, David G. Messerschmitt. Comparison of Transform Coding Techniques for Arbitrarily-Shaped Image Segments. Springer Verlag Journal of Multimedia Systems, 1994, 1(6):231-239, 1994.

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Envisioned advanced multimedia video services include arbitrarily-shaped (AS) image segments as well as regular rectangular images. Images segments of the TV weather reporter produced by the chromo-key technique [1] and image segments produced by video analysis and image segmentation[2,3,4] are typical examples of AS image segments. This paper explores efficient intraframe transform coding techniques for general two-dimensional (2D) AS image segments, treating the traditional rectangular images as a special case. In particular, we focus on transform coding of the partially-defined image blocks along the boundary of the AS image segments. We recognize two different approaches - the brute-force transform coding approach and the shape-adaptive transform coding approach. The former fills up the uncovered area with the optimal redundant data such that the resulting transform spectrum is compact. A simple but efficient mirror-image extension technique is proposed. Once augmented into full image blocks, these boundary blocks can be processed by traditional block-based transform techniques like the popular Discrete Cosine Transform (DCT). In the second approach, we change either the transform basis or the coefficient calculation process adaptively based on the shape of the AS image segment. We propose an efficient shape-projected problem formulation to reduce the dimension of the problem. Existing coding algorithms, such as the orthogonal transform by Gilge [5] and the iterative coding by Kaup and Aach [6], can be intuitively interpreted. We also propose a new adaptive transform basis by applying the same principle as that used in deriving the DCT from the optimal Karhunen-Loeve Transform (KLT). We analyze the tradeoff relationship between compression performance, computational complexity, and codec complexity for different coding schemes. Simulation results show that complicated algorithms (e.g. iterative, adaptive) can improve the quality by about 5-10 dB at some computational or hardware cost. On the other hand, the simple mirror-image extension technique improves the quality by about 3-4 dB without any overheads. The contributions of this paper lie in efficient problem formulations, new transform coding techniques, and numerical tradeoff analyses


Shih-Fu Chang

BibTex Reference

   Author = {Chang, Shih-Fu and G. Messerschmitt, David},
   Title = {Comparison of Transform Coding Techniques for Arbitrarily-Shaped Image Segments},
   Journal = {Springer Verlag Journal of Multimedia Systems, 1994},
   Volume = {1},
   Number = {6},
   Pages = {231--239},
   Year = {1994}

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