(MHz) (MHz) modulation carrier spacing (MHz) 625/50 Negative 625/50 Negative 625/50 Negative 625/50 Negative 625/50 Negative 625/50 Negative 625/50 Positive 525/60 Negative 625/50 Negative quency); and its intensity (saturation) which corresponds to its a matrixing network is designed such that Equation 57.1 is satis- colourfulness. fied. In colour television systems, chrominance information defines the hue and saturation of the pixels independently of the luminance, SO Y' = 0.3 R + 0.6 G' + 0.1 B' (57.1) that theoretically any distortion of the chrominance information does not affect the detail of the picture. A system designed to satisfy Since the four signals Y', R', G' and B' are related mathematically this condition is termed a constant luminance system, although in it is unnecessary to transmit all four. Since for compatibility a Y' practice some departure from this ideal is to be found in systems signal is needed, this is transmitted with two (chrominance) signals currently in use. obtained by taking the red and blue signals and subtracting from It was recognised that to achieve wide acceptability of colour in them Y', that is (R' Y') and (B' - Y'). (G' Y') can be derived within an era when black and white television had achieved popularity, a the receiver by matrixing. The transmitted signals are thus Y', as in colour system needed to be compatible, that is the colour trans- Equation 57.1 and (R - Y') and (B' - Y'). These three signals allow missions should be receivable as black and white pictures on a black Y', R', G' and B' to be recovered in the receiver. and white only receiver, and should also have reverse compatibility Tables 57.1 to 57.3 provide an overview of the international whereby black and white transmissions should be receivable as standards and the countries using them. Detailed information on the black and white pictures on a colour receiver. international standards for television broadcasting is given in CCIR The standard adopted to define whiteness is the colour tempera- Report 624 (ITU