nternational standard in September 2001. CCIR-601 CIR-601 is the ISO/IEC standard that defines the image format, acquisition semantic, and parts of the coding for digital "standard" television signals. Because many chips that support this standard are available, CCIR-601 is commonly used in digital video applications for computer systems and digital television. It is central to the MPEG, H.261, and H.263 compression specifications. CCIR-601 is applicable to both NTSC and PAL/SECAM systems. In the U.S., CCIR- 601 is 720x243 fields (not frames) of luminance information, sent at a rate of 60 per second. The fields are interlaced when displayed. The chrominance channels are 360x243 by 60 fields a second, again interlaced. CCIR-601 represents the chroma signals (Cb, Cr) with half the horizontal frequency as the luminance signal, but with full vertical resolution. This particular ratio of sub- sampled components is known as 4:2:2. The sampling frequency of the luminance signal (Y) is 13.5 MHz. Cb and Cr are sampled at 6.75 MHz. CCIR-601 describes the way in which analog signals are filtered to obtain the samples. Often RGB signals are converted to YCbCr. The formulas given for the CCIR-601 color conversion are for gamma corrected RGB signals. The gamma for the different television systems are specified in CCIR Report 624-4. The encoding of the digital signal is described in detail in CCIR Rec. 656. The correspondence between the video signal levels and the quantization levels is also specified. The scale is between 0 and 255, the luminance signal provides for 220 quantization levels; for the color-difference signals, it provides for 225 quantization levels. The signals are only coded with 8-bits per signal. WORLD TELEVISION AND COLOR SYSTEMS Country Television System PTT Digital Service Network Interface Abu Dhabi No digital services Afghanistan PAL B, SECAM B No digital services Albania PAL B/G No digital services Algeria PAL B/G No digital services Andorra No digital services Angola PAL I No digital services Antarcti