LOCO-I (LOw COmplexity LOssless COmpression for Images) is the algorithm at the core of the new ISO/ITU standard for lossless and near-lossless compression of continuous-tone images, JPEG-LS. It is conceived as a "low complexity projection" of the universal context modeling paradigm, matching its modeling unit to a simple coding unit. By combining simplicity with the compression potential of context models, the algorithm "enjoys the best of both worlds." It is based on a simple fixed context model, which approaches the capability of the more complex universal techniques for capturing high-order dependencies. The model is tuned for efficient performance in conjunction with an extended family of Golomb-type codes, which are adaptively chosen, and an embedded alphabet extension for coding of low-entropy image regions. LOCO-I attains compression ratios similar or superior to those obtained with state-of-the-art schemes based on arithmetic coding. Moreover, it is within a few percentage points of the best available compression ratios, at a much lower complexity level. We discuss the principles underlying the design of LOCO-I, and its standardization into JPEG-LS.

Abstract: Full-text database systems require an in-dex to allow fast access to documents based on their content. We propose an inverted file indexing scheme based on compression. This scheme allows users to retrieve documents using words occurring in the doc-uments, sequences of adjacent words, and statistical ranking techniques. The compression methods cho-sen ensure that the storage requirements are small and that dynamic update is straightforward. The only as-sumption that we make is that sufficient main memory is available to support an in-memory vocabulary; given this assumption, the method we describe requires at most one disc access per query term to identify an-swers to queries.

We present a new low-complexity method for modeling and coding the bitplanes of a wavelet-transformed image in a fully embedded fashion. The scheme uses a simple ordering model for embedding, based on the principle that coefficient bits that are likely to reduce the distortion the most should be described first in the encoded bitstream. The ordering model is tied to a conditioning model in a way that deinterleaves the conditioned subsequences of coefficient bits, making them amenable to coding with a very simple, adaptive elementary Golomb code. The proposed scheme, without relying on zerotrees or arithmetic coding, attains PSNR vs. bit rate performance superior to that of SPIHT, and competitive with its arithmetic coding variant, SPIHT-AC. Keywords: Progressive image compression; Laplacian density; Run-length coding; Rate-distortion. 1 1 Introduction Progressive image compression refers to the encoding of an image into a bitstream that can be parsed efficiently to obtain ...

: Full-text retrieval systems typically use either a bitmap or an inverted file to identify which documents contain which words, so that the documents containing any combination of words can be quickly located. Bitmaps of word occurrences are large, but are usually sparse, and thus are amenable to a variety of compression techniques. Here we consider techniques in which the encoding of each bitvector within the bitmap is parameterised, so that a different code can be used for each bitvector. Our experimental results show that the new methods yield better compression than previous techniques. Categories and Subject Descriptors: E.4 [Coding and Information Theory]: Data compaction and compression; H.3.2 [Information Storage]: File organisation . Keywords: Full-text retrieval, data compression, document database, Huffman coding, geometric distribution, inverted file. 1 Introduction Full-text retrieval systems are used for storing and accessing document collections such as newspaper a...

We describe a class of parameterizedreversible variable length codes that have length distributions identical to Golomb-Rice-codes and exp-Golomb codes. The pdfs to which these codes correspond are well matched to statistics of image and video data, thus enabling an increase in robustness to channel errors with no penalty in coding efficiency. These codes are applicable to MPEG-4 and other algorithms that aim to use variable length codes in error-prone environments.

: Bitmaps are data structures occurring often in information retrieval. They are useful; they are also large and expensive to store. For this reason, considerable effort has been devoted to finding techniques for compressing them. These techniques are most effective for sparse bitmaps. We propose a preprocessing stage, in which bitmaps are first clustered and the clusters used to transform their member bitmaps into sparser ones, that can be more effectively compressed. The clustering method efficiently generates a graph structure on the bitmaps. In some situations, it is desired to impose restrictions on the graph; finding the optimal graph satisfying these restrictions is shown to be NPcomplete. The results of applying our algorithm to the Bible is presented: for some sets of bitmaps, our method almost doubled the compression savings. 1. Introduction Textual Information Retrieval Systems (IRS) are voracious consumers of computer storage resources. Most conspicuous, of course, is the...

Test data compression and test resource partitioning (TRP) are necessary to reduce the volume of test data for system-on-a-chip designs. We present a new class of variable-to-variable-length compression codes that are designed using distributions of the runs of 0s in typical test sequences. We refer to these as frequency-directed run-length (FDR) codes. We present experimental results for ISCAS 89 benchmark circuits and two IBM production circuits to show that FDR codes are extremely effective for test data compression and TRP. We derive upper and lower bounds on the compression expected for some generic parameters of the test sequences. These bounds are especially tight when the number of runs is small, thereby showing that FDR codes are robust, i.e., they are insensitive to variations in the input data stream. In order to highlight the inherent superiority of FDR codes, we present a probabilistic analysis of data compression for a memoryless data source. Finally, we derive entropy bounds for the benchmark test sets and show that the compression obtained using FDR codes is close to the entropy bounds.

The International Telecommunications Union (ITU) recently adopted reversible variable length codes (RVLCs) for use in the emerging H.263+ video compression standard. As the name suggests, these codes can be decoded in two directions and can therefore be used by a decoder to enhance robustness in the presence of transmission bit errors. In addition, these RVLCs involve little or no efficiency loss relative to the corresponding non-reversible variable length codes. We present here the ideas behind two general classes of RVLCs and discuss the results of applying these codes in the framework of the H.263+ and MPEG-4 video coding standards.

There are several advantages to be gained by storing the lexicon of a full text database in main memory. In this paper we describe how to use a compressed inverted file index to search such a lexicon for entries that match a pattern or partially specified term. Our experiments show that this method provides an effective compromise between speed and space, running orders of magnitude faster than brute force search, but requiring less memory than other pattern-matching data structures; indeed, in some cases requiring less memory than would be consumed by a single pointer to each string. The pattern search method is based on text indexing techniques and is a successful adaptation of inverted files to main memory databases.

: We describe the use of various forms of bitmaps as a basic tool for improving the search algorithms in medium sized information retrieval systems. The bitmaps considered include and extend known techniques using occurrence maps and signatures. Such an approach to text retrieval is flexible, efficient and, relative to the customary concordance approach, inexpensive in storage costs. 1. Introduction Our ability to control textual information is being strongly influenced by a variety of technological advances. These include new means of storing and sharing information that makes possible and realistic an information system model in which large bodies of full text are compactly stored, widely distributed, and shared by a large number of interested persons. Such changes require a careful search for techniques that promise convenient and effective access to such textual databases. The research that is required in this environment differs from that traditional in Information Retrieval (IR)...