equirement inhibits the use of all digital techniques, although it is recognized that a 12GHz chan- Target areas for the development of HDTV and Advanced nel could support digital transmission of HDTV pictures at bit rates TV(ATV) systems include: of the order of 140Mbit/s, which has been shown to be a practical bit rate for the distribution of HDTV pictures/sound. 1. Image quality directly comparable with that of film. A complete HD-MAC system, shown in Figure 57.14 uses three 2. Elimination of large area and interline flicker present with basic techniques to reduce the bandwidth of the channels while 50Hz and, to a lesser extent, 60Hz interfaced TV systems. retaining as much of the original image quality as possible. Elimination of the cross colour defects inherent in composite 1. Diagonal filtering which can reduce the bandwidth by a factor coded colour systems. of two with very little reduction in subjective picture quality. Television transmission 57/11 f==72 (20 MHz) Vertical Horizontal filtering f = 33 3/4 camera processing fs=167/8 1250/2:1 compression 20 MHz/16:9 conversion Subsampling (2 x 5 1250/2:1/50 625/2:1/50 channel (8.4 MHz) f==44 fs=27 (20 MHz) conversion fs=333/4 Horizontal display f = 16 7/8 signal 1250/2:1/50 expansion Vertical recon- 20 MHz/16:9 filtering struction Standard TV Standard 625/2:1/50 0.5 MHz/4:3 decoder Figure 57.14 Complete HD-MAC system 2. The exchange of spatial and temporal resolution. posed MUSE systems that would permit the transmission of NTSC 3. Motion compensated temporal resolution. compatible ADTV wide screen pictures on terrestrial AM channels: MUSE-9 in 9MHz channels: MUSE-6 in 6MHz channels. Technique (2) is used in conjunction with (3). A digital signal of about 1Mbit/s is added to the digital sound/data channel to provide the digitally assisted television (DATV) information needed to 57.2.4.3 All digital systems assist the receiver decoder. A bandwidth reduction of another factor of about two can be achieved by the exchange of spatial and In 1990, the USA began t