This continues every other odd numbered line until the bottom of the screen is reached and 262 lines have been scanned. The beam then returns to the top and begins to scan the even numbered 262 lines. On the receiving end, an electron beam is traced upon the phosphorous surface of a cathode ray tube. The phosphors glow in relation to the strength of the electron beam, whose strength is determined by the brightness of the original scene. This glow disappears before the electron beam hits it again.
Persistence of vision makes the screen appear to be filled with picture.
The standards were revised in 1953 to allow for color transmission. The apparent sharpness was lowered as a result of the compromises inherent in the chosen system. In spite of on-going work with High Definition Television, the present standard isn't going to disappear in the near future. Working within the limits of the technology, it is possible to work around the defects.