5 research outputs found
BurrowsâWheeler compression: Principles and reflections
AbstractAfter a general description of the BurrowsâWheeler transform and a brief survey of recent work on processing its output, the paper examines the coding of the zero-runs from the MTF recoding stage, an aspect with little prior treatment. It is concluded that the original scheme proposed by Wheeler is extremely efficient and unlikely to be much improved.The paper then proposes some new interpretations and uses of the BurrowsâWheeler transform, with new insights and approaches to lossless compression, perhaps including techniques from error correction
Empirical analysis of BWT-based lossless image compression
The Burrows-Wheeler Transformation (BWT) is a text transformation algorithm originally designed to improve the coherence in text data. This coherence can be exploited by compression algorithms such as run-length encoding or arithmetic coding. However, there is still a debate on its performance on images. Motivated by a theoretical analysis of the performance of BWT and MTF, we perform a detailed empirical study on the role of MTF in compressing images with the BWT. This research studies the compression performance of BWT on digital images using different predictors and context partitions. The major interest of the research is in finding efficient ways to make BWT suitable for lossless image compression.;This research studied three different approaches to improve the compression of image data by BWT. First, the idea of preprocessing the image data before sending it to the BWT compression scheme is studied by using different mapping and prediction schemes. Second, different variations of MTF were investigated to see which one works best for Image compression with BWT. Third, the concept of context partitioning for BWT output before it is forwarded to the next stage in the compression scheme.;For lossless image compression, this thesis proposes the removal of the MTF stage from the BWT compression pipeline and the usage of context partitioning method. The compression performance is further improved by using MED predictor on the image data along with the 8-bit mapping of the prediction residuals before it is processed by BWT.;This thesis proposes two schemes for BWT-based image coding, namely BLIC and BLICx, the later being based on the context-ordering property of the BWT. Our methods outperformed other text compression algorithms such as PPM, GZIP, direct BWT, and WinZip in compressing images. Final results showed that our methods performed better than the state of the art lossless image compression algorithms, such as JPEG-LS, JPEG2000, CALIC, EDP and PPAM on the natural images
BurrowsâWheeler postâtransformation with effective clustering and interpolative coding
Lossless compression methods based on the BurrowsâWheeler transform
(BWT) are regarded as an excellent compromise between speed and
compression efficiency: they provide compression rates close to the PPM
algorithms, with the speed of dictionaryâbased methods. Instead of the
laborious statisticsâgathering process used in PPM, the BWT reversibly
sorts the input symbols, using as the sort key as many following
characters as necessary to make the sort unique. Characters occurring in
similar contexts are sorted close together, resulting in a clustered
symbol sequence. Runâlength encoding and MoveâtoâFront (MTF) recoding,
combined with a statistical Huffman or arithmetic coder, is then
typically used to exploit the clustering. A drawback of the MTF recoding
is that knowledge of the character that produced the MTF number is
lost. In this paper, we present a new, competitive BurrowsâWheeler
posttransform stage that takes advantage of interpolative codingâa fast
binary encoding method for integer sequences, being able to exploit
clusters without requiring explicit statistics. We introduce a fast and
simple way to retain knowledge of the run characters during the MTF
recoding and use this to improve the clustering of MTF numbers and
runâlengths by applying reversible, stable sorting, with the run
characters as sort keys, achieving significant improvement in the
compression rate, as shown here by experiments on common text corpora.</p