This paper deals with the efficient storage and transmission of stereo images. It introduces a compression algorithm based on the Discrete Wavelet Transform and an adapted SPIHT-coder. By using objective quality tests, it is shown that this coder is superior to all other coders published so far.
In this paper, new methods to eliminate boundary artifacts for overlapping trigonometric bases used in image compression are introduced. By applying overlapping cosine-sine-II bases to images instead of non-overlapping cosine-II bases used in the JPEG algorithm, block artifacts can be reduced. In contrast to non-overlapping transforms, an extension of the signal at the signal bounds is necessary. To prevent boundary artifacts in the reconstructed image, the symmetric periodic extension is preferred in image coding. The cosine-II and sine-II basis functions are symmetric, but nevertheless a conventional symmetric periodic extension is not possible, because different basis functions are used in adjacent intervals. In this paper, we derive weighting functions to make the symmetric periodic extension for these bases possible. We show, that compared to the periodic extension, no visible artifacts appear in the reconstructed image if our new approach is used. In addition, we show that the adaptation of the basis functions at the signal boundaries leads to a better quality of the reconstructed signal.
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.