A New Technique for Improving the Sharpness of Television Pictures

Abstract

In conjunction with the CBS color-television system a method has been developed for improving the apparent picture definition, called "crispening." It uses nonlinear circuitry to decrease the apparent rise time of an isolated step input which is applied to a bandwidth limited system. This gives the color-television pictures (with the exception of repetitive patterns representing frequencies beyond system cutoff) the appearance of having been transmitted through a system of greater bandwidth. The basic idea is to add to a waveform with a slow transition a second waveform, representing the difference between the desired waveform and the original waveform. A simple circuit is described which utilizes nonlinear means for reforming the roughly triangular differential of the step signal into a narrower "spike," roughly triangular in shape, which is superimposed on the original waveform to obtain a response corresponding to about half the original rise time. Various crispening circuits have been designed for specific applications and will be discussed in more detail. These crispening circuits can be applied to standard monochrome pictures. The resultant increase in sharpness, however, would be less apparent because of the law of diminishing returns. The doubling of the bandwidth, that is, halving of the rise time (which is the effect of crispening) will be less apparent in the already high-resolution monochrome pictures than in the lower resolution color pictures. Various subject matter and test patterns as photographed from the screen of color receivers are shown for 4.