Vertical blanking interval
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In a raster scan display, the vertical blanking interval (VBI), also known as the vertical interval or VBLANK, is the time between the end of the final visible line of a frame or field[1] and the beginning of the first visible line of the next frame or field. It is present in analog television, VGA, DVI and other signals.
In raster
The VBI was originally needed because of the inductive inertia of the magnetic coils which deflect the electron beam vertically in a
In analog television systems the vertical blanking interval can be used for datacasting (to carry digital data), since nothing sent during the VBI is displayed on the screen; various test signals, VITC timecode, 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.
In U.S. analog broadcast television, line 19 was reserved for a Ghost-canceling reference and line 21 was reserved for NABTS captioning data. The obsolete Teletext service contemplated the use of line 22 for data transmission.
The pause between sending video data is sometimes used in real time computer graphics to modify the
On many consoles there is an extended blanking period, as the console opts to paint graphics on fewer lines than the television would natively allow, permitting its output to be surrounded by a border. On some very early machines such as the Atari 2600, the programmer is in full control of video output and therefore may select their own blanking period, allowing arbitrarily few painted lines. On others such as the Nintendo Entertainment System, a predefined blanking period could be extended.
Most consumer
Vertical blanking interval in digital video
While digital video interconnects (such as DVI and HDMI) generally do have a "vertical blanking" part of the datastream, they are unable to carry closed caption text or most of the other items that, in analog TV interconnects, are transmitted during the "vertical blanking interval". This can lead to closed captioning § Digital television interoperability issues.
See also
- Vertical blank interrupt
- Datacasting
- Horizontal blanking interval
- Nominal analogue blanking
- Raster scan
References
- ISBN 9781136069819.