The JPEG 2000 Still Image Compression Standard
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The JPEG 2000 Still Image Compression Standard Athanassios Skodras, Charilaos Christopoulos, and Touradj Ebrahimi he development of standards (emerging and es- new call for contributions was launched for the tablished) by the International Organization for development of a new standard for the compression of Standardization (ISO), the International Tele- still images, the JPEG 2000 standard [28], [29]. This T communications Union (ITU), and the Inter project, JTC 1.29.14 (ISO/IEC 15444-1 or ITU-T Rec. - national Electrotechnical Commission (IEC) for audio, T.800), was intended to create a new image coding sys- image, and video, for both transmission and storage, has tem for different types of still images (bilevel, gray level, led to worldwide activity in developing hardware and soft- color, multicomponent), with different characteristics ware systems and products applicable to a number of di- (natural images, scientific, medical, remote sensing, text, verse disciplines [7], [22], [23], [55], [56], [73]. Although rendered graphics, etc.) allowing different imaging mod- the standards implicitly address the basic encoding opera- els (client/server, real-time transmission, image library tions, there is freedom and flexibility in the actual design archival, limited buffer and bandwidth resources, etc.) and development of devices. This is because only the syntax preferably within a unified system. This coding system and semantics of the bit stream for decoding are specified should provide low bit-rate operation with rate distor- by standards, their main objective being the compatibility tion and subjective image quality performance superior and interoperability among the systems (hardware/soft- to existing standards, without sacrificing performance at ware) manufactured by different companies. There is, thus, other points in the rate-distortion spectrum, and at the much room for innovation and ingenuity. same time incorporating many interesting features. One Since the mid 1980s, members from of the aims of the standardization com- both the ITU and the ISO have been mittee has been the development of working together to establish a joint in- Part I, which could be used on a roy- ternational standard for the compression alty- and fee-free basis. This is impor- of grayscale and color still images. This tant for the standard to become widely effort has been known as JPEG, the Joint accepted, in the same manner as the Photographic Experts Group. (The original JPEG with Huffman coding is “joint” in JPEG refers to the collabora- now. The standardization process, tion between ITU and ISO; see Fig. 1). which is coordinated by the Officially, JPEG corresponds to the JTC1/SC29/WG1 of ISO/IEC (Fig. ISO/IEC international standard 1) has already (since December 2000) 10928-1, digital compression and cod- produced the International Standard ing of continuous-tone (multilevel) still (IS) for Part I [41]. images or to the ITU-T Recommenda- In this article the structure of Part I tion T.81. The text in both these ISO of the JPEG 2000 standard is presented and ITU-T documents is identical. The and performance comparisons with es- process was such that, after evaluating a tablished standards are reported. This number of coding schemes, the JPEG article is intended to serve as a tutorial members selected a discrete cosine trans- © 2001 IMAGESTATE for the JPEG 2000 standard. In the next form(DCT)-based method in 1988. section the main application areas and From 1988 to 1990, the JPEG group continued its work by their requirements are given. The architecture of the stan- simulating, testing and documenting the algorithm. JPEG dard follows afterwards, with the description of the tiling, became Draft International Standard (DIS) in 1991 and multicomponent transformations, wavelet transforms, International Standard (IS) in 1992 [55], [73]. quantization and entropy coding. Some of the most sig- With the continual expansion of multimedia and nificant features of the standard are presented next, such as Internet applications, the needs and requirements of the region-of-interest coding, scalability, visual weighting, er- technologies used grew and evolved. In March 1997, a ror resilience and file format aspects. Finally, some com- 36 IEEE SIGNAL PROCESSING MAGAZINE SEPTEMBER 2001 1053-5888/01/$10.00©2001IEEE parative results are reported and the future parts of the sion technology where the image coding system is opti- standard are discussed. mized not only for efficiency, but also for scalability and interoperability in network and mobile environments. Digital imaging has become an integral part of the Why Another Internet, and JPEG 2000 is a powerful new tool that pro- Still Image Compression Standard? vides power capabilities for designers and users of net- The JPEG standard has been in use for almost a decade worked image applications [41]. now. It has proved a valuable tool during all these years, The JPEG 2000 standard provides a set of features that but it cannot fulfill the advanced requirements of today. are of importance to many high-end and emerging appli- Today’s digital imagery is extremely demanding, not only cations by taking advantage of new technologies. It ad- from the quality point of view, but also from the image dresses areas where current standards fail to produce the size aspect. Current image size covers orders of magni- best quality or performance and provides capabilities to tude, ranging from web logos of size of less than 100 markets that currently do not use compression. The mar- Kbits to high quality scanned images of approximate size kets and applications better served by the JPEG 2000 of 40 Gbits [20], [33], [43], [48]. The JPEG 2000 inter- standard are Internet, color facsimile, printing, scanning national standard represents advances in image compres- (consumer and prepress), digital photography, remote IEC ISO JTC 1 SC 29 AG WG AGM RA WG 1 WG 11 WG 12 SG SG SG JBIG Requirements MHEG-5 Maintenance JPEG Systems Video MHEG-6 Audio L 1. Structure of the standardization bodies and related terminology. ISO: International Organization for Standardization, ITU: Interna- tional Telecommunications Union, IEC: International Electrotechnical Commission, JTC: Joint Technical Committee on Information Technology, SC: Subcommittee, SG: study group, WG: working group, AHG: ad hoc group, JPEG: Joint Photographic Experts Group, JBIG: Joint Bi-Level Image Group, MPEG: Moving Picture Experts Group, MHEG: Multimedia Hypermedia Experts Group, AG: advisory group, AGM: Advisory Group on Management, and RA: registration authority. SEPTEMBER 2001 IEEE SIGNAL PROCESSING MAGAZINE 37 feature include medical images, where loss is not always tolerated; image archival applications, where the highest JPEG 2000 represents advances quality is vital for preservation but not necessary for dis- in image compression technology play; network applications that supply devices with dif- ferent capabilities and resources; and prepress imagery. It where the image coding system is also desired that the standard should have the property is optimized for efficiency, of creating embedded bit stream and allow progressive lossy to lossless buildup. scalability, and interoperability in L Progressive transmission by pixel accuracy and resolution: network and mobile Progressive transmission that allows images to be recon- structed with increasing pixel accuracy or spatial resolu- environments. tion is essential for many applications such as web browsing, image archival and printing. sensing, mobile, medical imagery, digital libraries/ar- L Region-of-interest (ROI) coding: Often there are parts of chives, and E-commerce. Each application area imposes an image that are of greater importance than others. This some requirements that the standard, up to a certain de- feature allows users to define certain ROIs in the image to gree, should fulfill. Some of the most important features be coded and transmitted in a better quality and less dis- that this standard should possess are the following [33]: tortion than the rest of the image. L Superior low bit-rate performance: This standard should L Open architecture: It is desirable to allow open architec- offer performance superior to the current standards at ture to optimize the system for different image types and low bit rates (e.g., below 0.25 b/p for highly detailed applications. With this feature, a decoder is only required gray-scale images). This significantly improved low to implement the core tool set and the parser that under- bit-rate performance should be achieved without sacrific- stands the code stream. ing performance on the rest of the rate-distortion spec- L Robustness to bit errors: It is desirable to consider robust- trum. Network image transmission and remote sensing ness to bit errors while designing the code stream. One are some of the applications that need this feature. application, where this is important, is transmission over L Continuous-tone and bilevel compression: It is desired to wireless communication channels. Portions of the code have a coding standard that is capable of compressing stream may be more important than others in determin- both continuous-tone and bilevel images. If feasible, this ing decoded image quality. Proper design of the code standard should strive to achieve this with similar system stream can aid subsequent error correction systems in al- resources. The system should compress and decompress leviating catastrophic decoding failures. images with various dynamic ranges (e.g., 1 to