Contrast in Kinescopes

One of the problems in the art of reproducing a scene by television is to obtain an image with adequate contrast. Although a relatively low contrast range may suffice for the transmission of intelligence, a much greater contrast range is essential for the reproduction of clear, lifelike images. The factors harmful to contrast in the kinescope are well known and may be studied in a variety of ways. In the belief that the reaction of the observer is the ultimate criterion for judging the perfection of the image, the author began the present investigation with a series of viewing tests designed to determine the relative psychological effects of the various factors harmful to contrast. On the basis of these tests, it was definitely concluded that halation is far more detrimental to image quality than screen curvature or bulb-wall reflections. Experimental evaluation of the relative importance of the individual factors harmful to contrast leads to the same conclusion, and it is evident that a considerable improvement in contrast could be effected by reducing halation. A detailed analytical study of halation shows how it depends upon various parameters. Particularly significant is the conclusion that halation may be reduced several fold by introducing a small amount of light-absorbing material in the kinescope face. According to this analysis, a 10 to 20 per cent absorption should give a three-to sixfold reduction in halation. Developmental kinescopes made in accordance with these principles give greatly improved contrast.