Application of K-Rating to USA NTSC Systems

Waveform testing methods are commonly used to determine the performance of video channels.1,2These testing methods use the distortion introduced by a channel on a specified test signal as a measure of channel performance. Results are presented of a study on using a 2 T pulse, a waveform that has received increased attention in the U.S. for the evaluation of linear distortion, and an oscilloscope graticule to interpret the pulse response in terms of K-rating for NTSC systems. The K-rating method specifies the performance of a channel in terms of a K-rating factor, which is given in per cent and represents a degree of subjective picture impairment equivalent to that occurring in a channel having a single well-displaced echo of K%. The recent study found that the use of a scaled 2 T pulse graticule on NTSC systems may result in K-ratings that are high by a factor of 1.8. A modified 2 T pulse K-rating graticule based on subjective test data using NTSC signals is presented that maintains the one-to-one correspondence between K-rating and picture impairment caused by a single echo.