ication of Internet websites, the compression of images is playing an increasingly important role. Not only does it save memory space, but its also make it possible to speed up the downloading of web pages or email picture attachments, up to the point of instant gratification. The most commonly used standard, JPEG, is the creation of the Joint Photographic Expert Group, which was launched in the mid 1980s under the ISO standardization body. 29 The JPEG standard, which is defined through various filename extensions .jpg, .jpeg, .jpe, jfif, and .jif, is a lossy compression codec. This feature is illustrated in Fig. G3. The original file size corresponding to the top-left image (as converted for simplicity into a grayscale one) is 683 kbyte. Compressing the same image through a photo editor by command factors of 50%, 75%, and 100% reduced the file size to 102 kbyte, 65 kbyte, and 15 kbyte, respectively. A look at the close-ups reveals that the effect of lossy compression is not noticeable at a 50% factor (nicely, the file size has, however, been reduced to 15% of the original). At a 75% factor and above, the loss of pixel information becomes apparent, to the point of yielding an image of poor quality, with observed "blocky and blurry" artifacts. Clearly, the amount of compression is a matter of subjectively determining the trade-off between file size and image quality, which depends on the final application, for instance either a screen wallpaper, a web banner, or a file icon. See, for instance: http://en.wikipedia.org/wiki/JPEG; www.imaging.org/resources/jpegtutorial/index.cfm. Overview of data compression standards 4:4:4 4:2:2 4:2:0 Figure G4 Compressing the two 8 X 8 chroma blocks of 4:4:4, resulting in 1/3 size (4:2:2) and 1/2 size (4:2:0) reductions. It is beyond the scope of this appendix to run into the complex details of image analysis and the JPEG encoding algorithm. Here, I shall just provide a brief summary of the main concepts and features of JPEG. Digital images are made of two-dimensional (2D) pixel ar