evel of detail but, as in the previous sections, I shall focus on the key features and on the central role of data compression algorithms. MPEG-1 This is the early standard for digital video (DV), and is also videoCD/DVD compat- ible (see later). 41 It achieves audio and video multiplexing, synchronization, and data compression. The video quality is primarily defined according to the pixel resolution of the 2D image frame, namely 352 x 240 (NTSC system, used in North America) and 352 X 288 (PAL-SECAM system, used in Europe). The corresponding frame rates are 29.97 2 30 frame/s and 25 frame/s, respectively. There are four types of MPEG-1 frame: I, for intra-coded frames, which are individually compressed; P, for predictive frames, which code the frame image as a difference from that of the previous one in the sequence, B, for bidirectionally predictive frames, which codes the image as a dif- ference from both the previous and the next image, and D, which uses block coding on an average image from several successive frames. This type of low-quality resolution is only used for fast-forwarding visualization. A group of pictures (GOP)42 is then typi- cally formed by the 12-frame sequence IBBPBBPBBPBB, which always begins with an I-frame. The above sequencing makes it possible to encode movie pictures at rates 37 See, for instance: http://en.wikipedia.org/wiki/Multiple-image_Network_Graphics. 38 See, for instance: http://en.wikipedia.org/wiki/Tagged_Image_File_Format 39 See, for instance: http://en.wikipedia.org/wiki/Windows_bitmap. 40 See: www.mpeg.org; www.chiariglione.org/mpeg/. See, for instance: http://en.wikipedia.org/wiki/MPEG-1; www.chiariglione.org/mpeg/standards/mpeg- 1/mpeg-1.htm. 42 See, for instance: http://en.wikipedia.org/wiki/Group_of_pictures; http://rnvs.informatik.tu-chemnitz. de/~jan/MPEG/HTML/mpeg_tech.html. Appendix G between 1.2 Mbit/s and 1.5 Mbit/s. A main drawback of MPEG-1 is that it is based on the principle of progressive (or noninterlaced) image scanning. Images are scanned line by line, w