The Digital Fact Book - Quantel

Y, Cr, CbThe digital luminance and color difference signals in ITU-R BT.601 coding. The Y luminancesignal is sampled at l3.5 MHz and the two color difference signals are sampled at 6.75 MHzco-sited with one of the luminance samples. Cris the digitized version of the analogcomponent (R-Y), likewise Cb is the digitized version of (B-Y). For the HD SMPTE 274Mstandard, sampling rates are 5.5 times greater – 74.25 MHz for Y and 37.125 MHz for Crand Cb.Y, R-Y, B-YThese are the analog luminance, Y, and color difference signals (R-Y) and (B-Y) of componentvideo. Y is pure luminance information whilst the two color difference signals togetherprovide the color information. The latter are the difference between a color and luminance:red – luminance and blue – luminance. The signals are derived from the original RGBsource (e.g. a camera or telecine).The Y, (R-Y), (B-Y) signals are fundamental to much of television. For example in ITU-RBT.601 it is these signals that are digitized to make 4:2:2 component digital video, in thePAL and NTSC TV systems they are used to generate the final composite coded signal andin DTV they are sampled to create the MPEG-2 video bitstream.See also: 4:2:2, Luminance, NTSC, Y,Cr,Cb, YUVYUVConvenient shorthand commonly – but incorrectly – used to describe the analogluminance and color difference signals in component video systems. Y is correct forluminance but U and V are, in fact, the two subcarrier modulation axes used in the PALcolor coding system. Scaled and filtered versions of the B-Y and R-Y color differencesignals are used to modulate the PAL subcarrier in the U and V axes respectively. Theconfusion arises because U and V are associated with the color difference signals butclearly they are not themselves color difference signals. Or could it just be because YUVtrips off the tongue much more easily than Y, R-Y, B-Y? Go figure.See also: PALYZZitsSpots that occasionally appeared on the faces of picture tubes showing digital pictureswhen the technology was in its youth. These were caused by technical limitations but nowthat designs have matured, today zits only now appear during fault conditions.182