ates the datarates required to represent monochrome images for various different imaging devices. The addition of color information will increase these bitrate values between 1.5 and 3 times. Consider a digitized broadcast-quality DVD video used in the UK: 720 pixels/line with 576 lines/frame, 25 pictures/sec, 8 bits/sample, and 4:2:2 color format. This would Compression Overview Table 3.1 Raw Monochrome Bitrates for Imaging Devices System ABCD (Mbits/s) Low-quality videophone CIF videoconferencing Digital broadcast TV SHDTV require 166 million bits per second or 2600 telephone lines and fill a standard 4.7-GB DVD in less than 4 minutes. If this were HDTV this would be 664 million bits per second and would fill the DVD in less than 1 minute. Even with the smallest pictures, SQSIF (Ghan- bari, 1999), which is 120 pixels per line and 96 lines per frame at 10 frames per second using 4:2:0 color format, the required channel capacity is still three times that of normal telephony. Clearly, digital video on a DVD lasts longer than this, and SO the volume of data has in some way been reduced or compressed. The same is true when the informa- tion is transmitted using digital terrestrial broadcast, satellite, or networked-over-IP net- works, and SO on. Compression Overview Video and still images consume large amounts of memory when stored and require high bandwidth when transmitted over networks. Therefore, methods are required that reduce the bitrate requirement of the raw (PCM) data. Pulse Code Modulation Pulse code modulation (PCM) is a digital representation of an analogue signal. The analogue amplitude is sampled and then quantized into a number of discrete bands; for example, 8- bit resolution would constrain the signal level between 0 and 255. In video the PCM values form the starting point for subsequent analysis and compression. Lossless and Lossy Compression Two types of digital video compression schemes exist: lossless and lossy. A lossless codec has the ability to perfectly reconstruct the original image withou