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1、An overview of the JPEG 2000 still image compression standardMajid Rabbani*, Rajan JoshiEastman Kodak Company, Rochester, NY 14650, USAAbstract In 1996, the JPEG committee began to investigate possibilities for a new still image compression standard to serve current and future applications. This ini
2、tiative, which was named JPEG 2000, has resulted in a comprehensive standard (ISO 15444|ITU-T Recommendation T.800) that is being issued in six parts. Part1, in the same vein as the JPEG baseline system, is aimed at minimal complexity and maximal interchange and was issued as an International Standa
3、rd at the end of 2000. Parts 2-6 define extensions to both the compression technology and the file format and are currently in various stages of development. In this paper, a technical description of Part 1 of the JPEG 2000 standard is provided, and the rationale behind the selected technologies is
4、explained. Although the JPEG 2000 standard only specifies the decoder and the codesteam syntax, the discussion will span both encoder and decoder issues to provide a better understanding of the standard in various applications. 2002 Elsevier Science B.V. All rights reserved. Keywords: JPEG 2000; Ima
5、ge compression; Image coding; Wavelet compression 1. Introduction and backgroundThe Joint Photographic Experts Group (JPEG) committee was formed in 1986 under the joint auspices of ISO and ITU-T1 and was chartered with the “digital compression and coding continuous-tone still images”. The committees
6、 first published standard 55,32,commonly known as the JPEG standard, provides a toolkit of compression techniques from which applications can select various elements to satisfy particular requirements. This toolkit includes the following components: (i) the JPEG baseline system, which is a simple an
7、d efficient discrete cosine transform (DCT)-based lossy compression algorithm that uses Huffman Coding. operates only in sequential mode, and is restricted to 8 bits/pixel input;(ii) an extended system, which introduces enhancements to the baseline algorithm to satisfy a broader set of applications;
8、 and (iii) a lossless mode, which is based on a predictive coding approach using either Huffman or arithmetic coding and is independent of the DCT. The JPEG baseline algorithm has since enjoyed widespread use in many digital imaging applications. This is due to its technical merits and status as a r
9、oyalty-free international standard, but perhaps more so, it is due to the free and efficient software that is available from the Independent JPEG Group (IJG) 57. Despite the phenomenal success of the JPEG baseline system, it has several shortcomings that become increasingly apparent as the need for
10、image compression is extended to such emerging applications as medical imaging, digital libraries, multimedia, internet and mobile. While the extended JPEG system addresses some of these shortcomings, it does so only to a limited extent and in some cases, the solutions are hindered by intellectual p
11、roperty rights (IPR) issues. The desire to provide a broad range of features for numerous applications in a single compressed bit-stream prompted the JPEG committee in 1996 to investigate possibilities for a new compression standard that was subsequently named JPEG 2000.In March 1997 a call for prop
12、osals was issued 58,59,seeking to produce a standard to “address areas where current standards failed to produce the best quality or performance”, “provide capabilities to markets that recently do not use compression”, and “provide an open system approach to imaging applications”. In November 1997,
13、more than 20 algorithms were evaluated, and a wavelet decomposition approach was adopted as the backbone of the new standard. A comprehensive requirements document was developed that defined all the various application areas of the standard, along with a set of mandatory and optional requirements fo
14、r each application. In the course of the ensuing three years, and after performing hundreds of technical studies known as “core experiments”, the standard evolved into a state-of-the-art compression system with a diverse set of features, all of which are supported in a single compressed bit-stream.
15、The JPEG 2000 standard is scheduled to be issued in six parts. Part 1, in the same vein as the JPEG baseline system, defines a core coding system that is aimed at minimal complexity while satisfying 80% of the applications 60.In addition, it defines an optional file format that includes essential in
16、formation for the proper rendering of the image. It is intended to be available on a royalty and fee-free basis and was issued as an International Standard (IS) in December 2000.Parts 2-6 defines extensions to both the compression technology and the file format and is in various stages of developmen
17、t. The history and the timeline of the various parts of the standard are shown in Table 1. Part 2 is aimed at enhancing the performance of Part 1 with more advanced technology, possibly at the expense of higher complexity 61.It is intended to serve those applications where maximal interchange is les
18、s important than meeting specific requirements. The code stream generated by part 2 encoders is usually not decodable by Part 1 decoders, and some of the technology in Part 2 might be protected by IPR. Part 3 defines motion JPEG 2000(MJP2) and is primarily based on the technology in Part 1 with the
19、addition of a file format62.It results in an encoder that is significantly less complex than the popular MPEG family of standards (due to lack of motion estimation)and provides full random access to the individually coded frames(albeit at the expense of compression efficiency).It is intended for app
20、lications such as digital still cameras with burst capture mode, video editing in post-production environments, and digital cinema archive and distribution. Part 4 defines conformance testing 63, similar to the role of JPEG Part 2, to ensure a high-quality implementation of the standard. As mentione
21、d earlier, a key factor in the JPEG baseline systems success as a widely used standard was the availability of efficient and free software. Part 5 defines a reference software implementation for Part 1 of the JPEG 2000 standard 64. PartTitleCFPWDCDFCDFDISIS1JPEG2000 image coding system: core coding
22、system97/0399/0399/1200/03.00/1000/122JPEG2000 image coding system: extensions97/0300/0300/0800/1201/0701/103Motion JPEG200099/1200/0700/1201/0301/0701/104Conformance testing99/1200/0700/1201/0701/1102/035Reference software99/1200/0300/0700/1201/0801/116Compound image le format97/0300/1200/0301/1102
23、/0302/05CFP=Call for Proposals, WD=Working Draft, CD=Committee Draft, FCD=Final Committee Draft, FDIS=Final Draft International Standard, IS=International StandardCurrently, two implementations are available. One is a Java implementation by the JJ2000 group 65 consisting of Canon Research France, Er
24、icsson and EPFL. The other is a C implementation by Image Power and University of British Columbia 2. Finally, Part 6 defines a compound image file format for document scanning and fax applications 66. It is noteworthy that the real incentive behind the development of the JPEG 2000 system was not ju
25、st to provide higher compression efficiency compared to the baseline JPEG system. Rather, it was to provide a new image representation with a rich set of features, all supported within the same compressed bit-stream that can address a variety of existing and emerging compression applications. In par
26、ticular, the Part 1 of the standard addresses some of the shortcomings of baseline JPEG by supporting the following set of features: * Improved compression efficiency.* Lossy to lossless compression.* Multiple resolution representation.* Embedded bit-stream (progressive decoding and SNR scalability)
27、.* Tiling. * Region-of-interest (ROI) coding. * Error resilience.* Random code stream access and processing. * Improved performance to multiple compression/decompression cycles.* A more flexible file format.The JPEG 2000 standard makes use of several recent advances in compression technology in orde
28、r to achieve these features. For example, the low-complexity and memory efficient block DCT of JPEG has been replaced by the full-frame discrete wavelet transform (DWT).The DWT inherently provides a multi-resolution image representation while also improving compression efficiency due to good energy
29、compaction and the ability to decorrelate the image across a larger scale. Furthermore, integer DWT filters can be used to provide both lossless and lossy compression within a single compressed bit-stream. Embedded coding is achieved by using a uniform quantizer with a central deadzone (with twice t
30、he step-size). When the output index of this quantizer is represented as a series of binary symbols, a partial decoding of the index is equivalent to using a quantizer with a scaled version of the original step-size, where the scaling factor is a power of two. To encode the binary bitplanes of the q
31、uantizer index, JPEG 2000 has replaced the Huffman coder of baseline JPEG with a context-based adaptive binary arithmetic coder with renormalization-driven probability estimation, known as the MQ coder. The embedded bit-stream that results from bitplane coding provides SNR scalability in addition to
32、 the capability of compressing to a target file size Furthermore, the bitplanes in each subband are coded in independent rectangular blocks and in three fractional bitplane passes to provide an optimal embedded bit-stream, improved error resilience, partial spatial random access, ease of certain geo
33、metric manipulations, and an extremely flexible codestream syntax. Finally, the introduction of a canvas coordinate system facilitates certain operations in the compressed domain such as cropping, rotations by multiples of 901, flipping, etc. Several excellent review papers about JPEG 2000 Part 1 ha
34、ve recently appeared in the literature 3,13,16,18,27,37, and a comprehensive book describing all of the technical aspects of the standard has been published 45. In this paper, a technical description of the fundamental building blocks of JPEG 2000 Part 1 is provided, and the rationale behind the sel
35、ected technologies is explained. Although the JPEG2000 standard only specifies the decoder and the codestream syntax, many specific decoder implementation issues have been omitted in our presentation in the interest of brevity. Instead, the emphasis has been placed on general encoder and decoder tec
36、hnology issues to provide a better understanding of the standard in various applications. Therefore, readers who plan range on implementing the standard should ultimately refer to the actual standard 60. This paper is organized as follows. In Section 2, the fundamental building blocks of the JPEG 20
37、00 Part 1 standard, such as preprocessing, DWT, quantization, and entropy coding are described. In Section 3, the syntax and organization of the compressed bit-stream is explained. In Section 4, various rate control strategies that can be used by the JPEG 2000 encoder for achieving an optimal SNR or
38、 visual quality for a given bit-rate are discussed. In Section 5, the tradeoffs between the various choices of encoder parameters are illustrated through an extensive set of examples. Finally, Section 6 contains a brief description of some additional JPEG 2000 features such as ROI, error resilience
39、and file format, as well as a summary of the technologies used in Part 2.2. JPEG 2000 fundamental building blocks The fundamental building blocks of a typical JPEG 2000 encoder are shown in Fig. 1.These components include preprocessing, DWT, quantization, arithmetic coding (tier-1 coding), and bit-s
40、tream organization (tier-2 coding). In the following, each of these components is discussed in more detail. The input image to JPEG 2000 may contain one or more components. Although a typical color image would have three components (e. g .,RGB or YCbCr ),up to 16 384(214) components can be specified
41、 for an input image or accommodate multi-spectral or other types of imagery. The sample values for each component can be either signed or unsigned integers with a bit-depth in the range of 1-38 bits. Given a sample with a bit-depth of B bits, the unsigned representation would correspond to the range
42、 (0, 2B-1), while the signed representation would correspond to the range(-2B-1, 2B-1-1).The bit-depth, resolution, and signed versus unsigned specification can vary for each component. If the components have different bit-depths, the most significant bits of the components should be aligned to faci
43、litate distortion estimation at the encoder. 2.1. Preprocessing The first step in pre-processing is to partition the input image into rectangular and non-overlapping tiles of equal size (except possibly for those tiles at the image borders). The tile size is arbitrary and can be as large as the orig
44、inal image itself (i.e.,only one tile) or as small as a single pixel. Each tile is compressed independently using its own set of specified compression parameters. Tiling is peculiarly useful for applications where the amount of available memory is limited compared to the image size. Next, unsigned s
45、ample values in each component are level shifted (DC offset) by subtracting a fixed value of 2B-1 from each sample to make its value symmetric around zero. Signed sample values are not level shifted. Similar to the level shifting performed in the JPEG standard, operation simplifies certain implement
46、ation issues (e.g.,numerical overflow, arithmetic coding context specification, etc.), but has no effect on the coding efficiency. Part 2 of the JPEG 2000 standard allows for a generalized DC offset, where a user-defined offset value can be signaled in a marker segment. Finally, the level-shifted values can be subjected to a forward point-wise intercomponent transformation to decorrelate the color data. One restriction on applying the intercomponent transformation is that the components must have identical bit-depths and dimensions.
