In raster-scanned television technology, the period between (a) the end of one horizontal scanning line and the beginning of the next (the horizontal blanking interval,) or (b) the end of one field and the beginning of the next (the vertical blanking interval,) during which the display of picture information is suppressed. Note 1: Blanking intervals were a necessary part of the original NTSC and other, similar, television signal structures, which were based on the state of the art of electronics in the 1930s and even earlier. Both the camera and display (television receiver) were dependent upon specialized electron tubes that employed an electron beam that was swept (scanned) across the photosensitive or photoemissive area, respectively, of the tube in question. It was necessary that the beam be turned off during its return sweep (trace,) to avoid marring the image (trace. ) While television cameras based on charge-coupled devices (CCDs,) which have no such constraint, have supplanted cameras based on electron beams, most receivers still depend upon beam-based tubes. Note 2: To support a smooth transition (avoid obsolescence of older receivers) as the state of the art improved, the basic original signal structure was retained, with modifications (e.g., the superposition of signals necessary to support color. )