Summary

Compression is one of the technologies that enabled the multimedia revolution to occur. However, for the technology to be fully effective there has to be some degree of standardization so that equipment designed by different vendors can talk to each other. The process through which the first image compression standard, popularly known as Joint Photographic Experts Group (JPEG), was developed was highly successful and has become a model for the development of other compression standards. The JPEG standard is effectively two standards, one for lossy compression of still images, and another for lossless compression of still images. A third standard for compressing binary images, popularly known as Joint Bilevel Image Group (JBIG) for the committee that created it, completes the trio of current international standards for compressing images. There are also de facto standards such as Graphics Interchange Format (GIF) and Portable Network Graphics (PNG) that include compression of graphic images. However, these are not the subject of this chapter. While JPEG2000 and JBIG are current international standards, there are new international standards on the horizon at the writing of this chapter. These are the JPEG-LS standard, and a new standard from the JBIG committee popularly referred to as JBIG2. Unlike the JPEG and JBIG standards, JPEG2000, JPEG-LS, and JBIG2 try to include to some extent all three types of compression represented by the earlier standards. Thus, JPEG-LS has a binary mode for compression of bilevel images and a “near-lossless” mode that is essentially a lossy mode with pixel-level distortion constraints. The JPEG2000 standard has both a mode for bilevel images and a mode for lossless compression. The JBIG2 algorithm allows for lossy compression of bilevel images. However, each standard has a primary focus, with lossless compression being the focus of JPEG-LS, lossy compression the primary focus of JPEG2000, and lossless compression of bilevel images the primary focus of JBIG2. In the following sections we will describe the current standards in some detail and the proposed standards in as much detail as is available at the current time. We will describe the lossy portion of JPEG and the current status of the JPEG2000 standard in Section 5.2. The lossless part of JPEG and JPEG-LS are the subject of Section 5.3, and the JBIG and JBIG2 standards are described in Section 5.4.