Blanking is a blanking of a screen signal. In raster displays such as interlacedtelevision, the screen signal contains the brightness information and controls the electron beam to be brighter or darker as it is deflected from left to right. When the beam reaches the right edge of the screen, the beam resets to the left edge of the screen, to the position from which the next line is to be displayed.
This line reset must be suppressed, since it would disturb the normal display. Similarly, the image reset must be suppressed, which starts when the beam has written the last line of an image during the interlacing process and must be returned from the lower edge of the screen to the upper edge of the screen. Dark blanking of the horizontal and vertical beam return occurs in the horizontal and vertical blanking intervals, Horizonntal Blanking Interval (HBI) and Vertical Blanking Interval (VBI), during line and frame return. Once the electron beam reaches the right edge of the screen, it is darkened or blanked. This takes a few microseconds. When blanking the image return, it can take a few milliseconds.