Vertical blanking interval
Encyclopedia : V : VE : VER : Vertical blanking interval
The vertical blanking interval (VBI) or vertical interval for short is a video signal between the last line of one frame or field and the beginning of the next. It is present in analog television, VGA and DVI signals.
The VBI is needed because of the inductive inertia of the magnetic coils which deflect the electron beam vertically in a CRT; the magnetic field cannot change instantly. For horizontal deflection, there is also a gap between successive lines, to allow the beam to return from right to left, called the horizontal retrace or the horizontal blanking interval.
In analog television systems the vertical blanking interval can be used to carry data, since anything sent during the VBI would naturally not be displayed; various test signals, time code, closed captioning, teletext, CGMS-A copy-protection indicators, and various data encoded by the XDS protocol (e.g., the content ratings for V-chip use) and other digital data can be sent during this time period.
The pause between sending video data is used in real time computer graphics to perform various operations on the back buffer before copying it to the front buffer instead of just switching both pointers. Back Buffer may be briefly applied to a 3d mesh, allowing effects such as waves (vertex deformation) or broken glass (UVs deformation).
Most consumer VCRs use the known black level during the vertical blanking interval to set their recording levels. The Macrovision copy protection scheme uses pulses in the VBI on videotapes to disrupt recording.
External link
From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.