Horizontal blanking interval refers to a part of the process of displaying images on a computer monitor or

television Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertising, ...

screen via raster scanning. CRT screens display images by moving beams of electrons very quickly across the screen. Once the beam of the monitor has reached the edge of the screen, the beam is switched off, and the deflection circuit voltages (or currents) are returned to the values they had for the other edge of the screen; this would have the effect of retracing the screen in the opposite direction, so the beam is turned off during this time. This part of the line display process is the Horizontal Blank. In detail, the Horizontal blanking interval consists of: * front porch – blank while still moving right, past the end of the scanline, * sync pulse – blank while rapidly moving left; in terms of amplitude, "blacker than black". * back porch – blank while moving right again, before the start of the next scanline.

Colorburst Colorburst is an analog video, composite video signal generated by a video-signal generator used to keep the chrominance subcarrier synchronized in a color television signal. By synchronizing an oscillator with the colorburst at the back p ...

occurs during the back porch, and unblanking happens at the end of the back porch. In the

NTSC The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...

television standard, horizontal blanking occupies out of every scan line (17.2%). In PAL, it occupies out of every scan line (18.8%). Some modern monitors and video cards support ''reduced blanking'', standardized with Coordinated Video Timings."What does 'Rb' mean?"
In the PAL television standard, the blanking level corresponds to the black level, whilst other standards, most notably NTSC, set the black level slightly above the blanking level on a ''pedestal''.

HBlank effects

Some graphics systems can count horizontal blanks and change how the display is generated during this blank time in the signal; this is called a raster effect, of which an example are

raster bar The raster bar (also referred to as rasterbar or copperbar) is an effect used in demos and older video games that displays animated bars of colour, usually horizontal, which additionally might extend into the border, a.k.a. the otherwise unalte ...

s. In video games, the horizontal blanking interval was used to create some notable effects. Some methods of parallax scrolling use a raster effect to simulate depth in consoles that do not natively support multiple background layers or do not support enough background layers to achieve the desired effect. One example of this is in the game Castlevania: Rondo of Blood, which was written for the PC Engine CD-ROM which does not support multiple background layers. The

Super Nintendo Entertainment System The Super Nintendo Entertainment System (SNES), commonly shortened to Super NES or Super Nintendo, is a 16-bit home video game console developed by Nintendo that was released in 1990 in Japan and South Korea, 1991 in North America, 1992 in Eu ...

Mode 7 Mode 7 is a graphics mode on the Super Nintendo Entertainment System video game console that allows a background layer to be rotated and scaled on a scanline-by-scanline basis to create many different effects. The most famous of these effects ...

uses the horizontal blanking interval to vary the scaling and rotation, per scan line, of one background layer to make the background appear to be a 3D plane.

References

{{DEFAULTSORT:Horizontal blanking interval Video signal Television technology Television terminology

HBlank effects

See also

References