er Line Frequency Frame Rate 1080 line 74.25 MHz 30.00 fps 720 line 74.25 MHz 60.00 fps 480 line (704 pixels) 13.5 MHz 59.94-Hz field rate afps stands for frames per second. 9 SMPTE stands for Society of Motion Picture and Television Engineers. 16.10 CONFERENCE TELEVISION In the coding process, advantage is taken of the differences in the ways humans perceive luminance and chrominance. The human visual system is less sensitive to the high fre- quencies in the chrominance components than to the high frequencies in the luminance component. To exploit these characteristics the chrominance components are low-pass fil- tered and subsampled by a factor of 2 along with the horizontal and vertical dimensions, thus producing chrominance components that are one-fourth the spatial resolution of the luminance components. 16.10 CONFERENCE TELEVISION 16.10.1 Introduction Video conferencing (conference television) systems have seen phenomenal growth since 1990. Many of the world's corporations have branches and subsidiaries that are widely dispersed. Rather than pay travel expenses to send executives to periodic meetings at one central location, video conferencing is used, saving money on the travel budget. The video and telecommunications technology has matured in the intervening period to make video conferencing cost effective. Among these developments we include: Video compression techniques Eroding cost of digital processing Arrival of the all-digital network Proprietary video conferencing systems normally use lower line rates than conventional broadcast TV. Whereas conventional broadcast TV systems have line rates at 525/480 lines (NTSC countries) or 625/580 for PAL/SECAM countries, proprietary video conferencing systems use either 256/240 or 352/288 lines. For the common applications of confer- ence television (e.g., meetings and demonstrations), the reduced resolution is basically unnoticeable. One of the compression schemes widely used for video conference systems is based on ITU-T Rec. H.261 (Ref. 20), entitled Video C