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

a method of color-television broadcasting quite different from the field-sequential method. In the fall of 1950 the NTSC set up a six-member Ad Hoc Committee to investigate the progress of these developments and to report back a recommendation as to whether or not NTSC should work actively toward the completion and experimental verification of a color-television signal based on all of these developments. In the spring of 1951 the Ad Hoc Committee turned in its report. The committee found that the developments had indeed reached the point where it seemed highly likely that further work would lead to a most advantageous form of color-television broadcast signal. The committee's report recommended that the NTSC proceed actively to study the signal, to arrange for such tests as were necessary to select the signal characteristics, and to pursue a program of field tests of such scope as to show clearly beyond any doubt whether or not the signal result ing from these choices was in fact possessed of the advantages claimed for it. The National Television System Committee approved the report of its Ad Hoc Committee and it proceeded in accordance with that report to establish additional panels organized specifically for the several tasks involved, as presented in Fig. 2. Panels 13 and 14 are responsible for establishing the signal specifications, Panels 15, 16 and 17, for the independent testing of the recommendations of the first-named two panels, and the remaining panels provide for important functions auxiliary to those already described. In the ensuing months the signal specification has been established, been subjected to extensive studies in both laboratory and field, and has been modified to make certain minor improvements. The committee's work is now at the point where the final field tests are expected to start in the immediate future. II. THE BASIC PRINCIPLES Out of the work in this field certain principles have emerged which appear to be basic to a system of color-television broadcasting if that system is to show full utilization of the portion of the frequency spectrum allocated to it. Among these principles are the following: 1. The electrical quantities in the signal shall represent the transmitted color in terms of its luminance, dominant wavelength and purity; alternatively, these may be thought of as brightness, hue and saturation. 2. The spectrum space occupied by the luminance information must be shared by the color information without adversely affecting the transmission of either. 3. The color-television signal must provide satisfactory black-and-white pictures on the present monochrome sets if color broadcasting is to grow rapidly into an important public service. These principles are worth examination in some detail. The Electrical Description of Color There are many ways of including in an electrical signal three quantities which when taken together can be used to represent a color. Only two of these need concern us here. In the first of these, separate elements of the signal are used to represent the respective intensities of three primary colors — for example, red, green and blue - which taken together will produce a resultant color which to the eye is a match for the original color. This method of electrically describing a color appears to be simple and straightforward, and it can be shown to have the further advantage that the three indications may be pre A. V. Loughren: Color Television 323