5 December 2001 Removal of boundary effects in image compression caused by transforms using nonsymmetric local trigonometric bases
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Abstract
In this paper, we introduce new approaches to remove the boundary artifacts of the reconstructed images caused by transforms using overlapping non-symmetrical cosine-IV bases in image compression. In the field of image compression, overlapping cosine-IV bases can reduce the block artifacts that occur in JPEG. These basis functions are longer than the block size and they decay to zero at their boundaries. These cosine-IV bases have, however, one important disadvantage. They are not symmetric. Therefore the symmetric periodic extension cannot be applied to sequences of finite length. Artifacts appear at low bit rates in image compression if only the periodic extension is used. With the aid of the folding operator, we derive the symmetric periodic extension for cosine-IV bases. Weighting functions are introduced. We point out that no artifacts appear at image boundaries if our weighting functions are used. In the second part of our paper, we present a new approach which avoids the extension of the image. There is no overlap at the image boundaries. The efficiency of our proposed methods in image compression is studied. We show, that there are no artifacts at image boundaries in the reconstructed image if our methods are used.
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Alexander Mali, Alexander Mali, Torsten Palfner, Torsten Palfner, Erika Mueller, Erika Mueller, } "Removal of boundary effects in image compression caused by transforms using nonsymmetric local trigonometric bases", Proc. SPIE 4475, Mathematics of Data/Image Coding, Compression, and Encryption IV, with Applications, (5 December 2001); doi: 10.1117/12.449598; https://doi.org/10.1117/12.449598
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