www.iec.ch) that is in charge of developing standards for coded represen- tation of digital audio and video. It has created the MPEG compression algorithm, which reduces redundant information in images. One distinguishing characteristic of MPEG compression is that it is asymmetric: A lot of work occurs on the compression side, and very little occurs on the decompression side. It is offline versus real-time compression. Offline allows 80:1 or 400:1 compression ratios, SO it takes 80 or 400 times longer to compress than to decompress. Currently, MPEG-2 generally involves a compression ratio of 55:1, which means it can take almost an hour to compress 1 minute of video. The advantage of this asymmetrical approach is that digital movies compressed using MPEG run faster and take up less space. There are several MPEG standards, in various stages of development and com- pletion, and with different targeted uses. The following are some of the most com- mon MPEG standards: MPEG-1-MPEG-1 is a standard for storage and retrieval of moving pictures and audio on storage media. MPEG-1 is the standard on which such products as Video CD and MP3 are based. MPEG-1 addresses VHS-quality images with a 1.5Mbps data rate. MPEG-1 can play back from a single-speed CD-ROM player (150Kbps or 1.2Mbps) at 352 x 240 (i.e., quarter-screen) resolution at 30fps. MPEG-2-MPEG-2 is the standard on which such products as DTV set-top boxes and DVD are based, and at this point, it is the compression scheme of choice. It addresses DTV- or computer-quality images. MPEG-2 carries compressed broadcast NTSC at a 2Mbps to 3Mbps data rate, broadcast PAL at 4Mbps to 6Mbps, broadcast HDTV at 10Mbps to 12Mbps, and profes- sional HDTV at 32Mbps to 40Mbps. MPEG-2 supports both interlaced and progressive-scan video streams. (Interlaced and progressive-scan tech- niques are discussed later in this chapter.) MPEG-2 on DVD and Digital Video Broadcasting (DVB) offers resolutions of 720 X 480 and 1,280 X 720 at up to 30fps, with full CD-quality audio. On MPEG-2 over Adv