Scanning - (in terms of TV) - Scanning is the technique of building up a TV image as a series of horizontal lines. The beams from the electron guns (if electronic guns are used) at the rear of the picture tube scan the image from right to left and top to bottom. The number of lines is a measure of the resolution. A standard (analog) TV picture uses interlaced scanning, where each complete picture is displayed as 2 frames; the first frame having the odd-numbered lines and the second frame having the even-numbered lines. Each screen phosphor emits light for a short time after being struck by the moving electron beam. This, together with persistence of human vision, gives the appearance of a flicker-free complete continuous image.