A video is just a sequence of images (plus sound). If we could find a good algorithm for encoding a single image, this algorithm could be applied to each image in succession to achieve video compression. Good still image compression algorithms exist, so let us start our study of video compression there. The JPEG (Joint Photographic Experts Group) standard for compressing continuous-tone still pictures (e.g., photographs) was developed by photographic experts working under the joint auspices of ITU, ISO, and IEC, another standards body. It is important
for multimedia because, to a first approximation, the multimedia standard for moving pictures, MPEG, is just the JPEG encoding of each frame separately, plus some extra features for interframe compression and motion detection. JPEG is defined in International Standard 10918.
JPEG has four modes and many options. It is more like a shopping list than a single algorithm. For our purposes, though, only the lossy sequential mode is relevant, and that one is illustrated in Fig. 7-15. Furthermore, we will concentrate on the way JPEG is normally used to encode 24-bit RGB video images and will leave out some of the minor details for the sake of simplicity.
