horizontal scanning

the scanning of a television image with an electron beam on the target of a transmitting television camera or the screen of a receiving tube in a horizontal direction to form distinct television scanning lines. The set of lines forms the television raster.

The total, or nominal, number of lines z in one frame is determined by the parameters of the given television system. The movement, usually linear, of the electron beam across the target or screen from left to right relative to the object whose image is being transmitted or to the viewer is called the forward trace; movement in the opposite direction is called the retrace. The electron beam is extinguished during the retrace, which occupies approximately 18 percent of the line time. Because some of the lines in each frame coincide with the vertical retrace, the actual number of lines is 0.92z.

The frequency of scanning (line frequency) f_s is related to the frame frequency n by the formula f_s = nz. For example, where n = 25 hertz and z = 625 (the standard figure for USSR television broadcasting), f_s = 15,625 hertz. Horizontal scanning generators are used to effect the scanning.