Journal of the Society of Motion Picture and Television Engineers (1950-1954)

color standards have been accepted and established by the Federal Communications Commission, is thus seen to be extremely great. With compatibility, color television can be given a flying start by its parent, monochrome television ; without compatibility, color television must start from a complete standstill; it must face the terrible economic difficulty represented by the situation "too few viewers, therefore very little sponsor money, therefore poor programs, therefore too few viewers." Important though compatibility is to the rapid introduction of color tele vision, it is perhaps not important enough to justify of itself the adoption of a colortelevision system markedly inferior to a system which could be developed disregarding compatibility. We should note however that we are not faced with this question; instead, we have the sitution in which the basic technical considerations important in the design of a color-television signal coincide with those controlling the design of a monochrome signal, and in satisfying these considerations we find compatibility as an automatic by-product. III. GENERATION OF THE SIGNAL A block diagram of the essential elements of the transmitting apparatus is shown in Fig. 6. A camera at the left generates three signals which collectively represent the luminance, hue and saturation of the scene, element by element; in the example shown the actual camera outputs correspond to the red, green and blue components. Gamma correction — to improve the signal-tonoise ratio and incidentally to match approximately the receiver picture-tube curvature — may be introduced at this point. The resulting signals are electrically added, in the proportions of their respective luminances, to form the monochrome or luminance signal. Normal adjustment for the system is such as to make the three signals from the camera equal if the color represented is that corresponding to standard Illuminant C; under this condition the luminance signal EY' is also equal to the gamma corrected voltages EG', ER' and EB'.* The negative of the luminance signal is developed by the phase inverter; in the two adders shown below it, this signal is added to the red and the blue color * See the Appendix for definitions of symbols and formulas not explained in the text and illustrations. signals, respectively, thus forming in the adder the two color-difference signals corresponding to these two primaries. Examining the red color-difference signal in some detail, it is noted that this signal was generated by addition and subtraction of the signals originally produced by the camera. These signals, of course, have their components at even harmonics of one-half the line frequency like the components shown solid in Fig. 4; of course, addition and subtraction of such components does not change their frequency into the positions of the lowvisibility, odd-harmonic components, and yet we want these components to be translated into odd-harmonic components so that they may be interleaved between the components of the luminance signal for transmission. If we generate a subcarrier frequency at such a frequency value as, for example, the 455th harmonic of one-half the line frequency, it will be a low-visibility signal, like the dotted line in Fig. 4. If we then use our red color-difference signal to modulate this subcarrier, the sidebands which appear with the subcarrier as a consequence of the modulation process, will be separated from the subcarrier frequency by the same interval that separates the original sidebands from zero frequency; in other words, all of 328 April 1953 Journal of the SMPTE Vol. 60