An on-screen display (abbreviated OSD) is an image superimposed on a screen picture, commonly used by modern television sets, VCRs, and DVD players to display information such as volume, channel, and time.
In the past, most adjustments on TV sets were performed with analog controls such as potentiometers and switches. This is still used in modern monochrome portable TVs. After remote controls were invented, digital adjustments became common. They needed an external display, which was LED, LCD, or VFD based. Including this display increased manufacturing costs.
When electronics became more advanced, it became clear that adding some extra devices for an OSD was cheaper than adding a second display device. TV screens had become much bigger and could display much more information than a small second display. OSDs display graphical information superimposed over the picture, which is done by synchronizing the reading from OSD video memory with the TV signal.
On-screen displays first began to appear in the 1980s on TVs. By the mid-1990s, VCRs with these displays became widely available. This made it possible to reduce the size (and cost) of the VFDs used in VCRs. Akai have been credited with the introduction of OSD in VCRs in the 1980s, including the introduction of on screen programming. All DVD players also use on-screen displays. Many PAL television sets use the internal Teletext decoder's graphics rendering system to further reduce costs.
More recently (as of about 2005), the decline in CRT-based TV sets and rise in LCD/plasma televisions has seen the use and availability of dedicated OSD devices decline, as it is more cost effective to integrate OSD functions inside the main graphics processor. Modern LCD television monitors usually incorporate only two or three integrated circuits. Examples of integrated circuits to perform dedicated OSD are MAX7456 and STV5730. Both operate with NTSC or PAL, mixing with an existing signal or self-generating. Both have slightly different capabilities. This can be done by PIC video superimposer too.
Some computer software also uses OSDs, especially support programs for so-called "enhanced keyboards", which often had additional media keys for actions like skipping through music tracks and volume adjustment. Their use outside this field is still uncommon. On-screen displays are also used in camcorders, and can display various information both on the viewfinder and on the TV set the camcorder is connected to.
Several problems exist with regard to on-screen displays. One of them is diagnostics if a television's display system is damaged. Without any external screens, it is almost impossible (without opening the TV) to determine the source of the error. TV accessories that depend heavily on OSDs, such as VCRs or DVD players, are also difficult to configure without the use of a TV. On older VCRs, it was possible to program recording timers without turning on the TV; a modern VCR requires the user to turn on the TV to do so. Usability is generally also decreased with OSDs, as it is necessary to control a multitude of parameters with a few buttons, where earlier, real analog controls with mechanical feedback were available.
The drawbacks of using OSDs do not outweigh their main advantage of being more cost-efficient, which has led to their widespread use.
Hobbyist use of OSD can provide significant benefit in terms of the amount of information that can be shown without resorting to specific displays (for example, dot matrix LCD or computer displays), as virtually every home has a TV.
|This article does not cite any references or sources. (August 2008)|