Monday, January 31, 2011

Computer monitor 6

Color misregistration
With exceptions of correctly aligned video projectors and stacked LEDs, most display technologies, especially LCD, have an inherent misregistration of the color channels, that is, the centers of the red, green, and blue dots do not line up perfectly. Sub-pixel rendering depends on this misalignment; technologies making use of this include the Apple II from 1976[3], and more recently Microsoft (ClearType, 1998) and XFree86 (X Rendering Extension).

Incomplete spectrum
RGB displays produce most of the visible color spectrum, but not all. This can be a problem where good color matching to non-RGB images is needed. This issue is common to all monitor technologies that use the RGB model. Recently, Sharp introduced a four-color TV (red, green, blue, and yellow) to improve on this.

Display interfaces
Computer terminals
Early CRT-based VDUs (Visual Display Units) such as the DEC VT05 without graphics capabilities gained the label glass teletypes, because of the functional similarity to their electromechanical predecessors.

Some historic computers had no screen display, using a teletype, modified electric typewriter, or printer instead.

Composite signal
Early home computers such as the Apple II and the Commodore 64 used a composite signal output to drive a TV or color composite monitor (a TV with no tuner). This resulted in degraded resolution due to compromises in the broadcast TV standards used. This method is still used with video game consoles. The Commodore monitor had S-Video input to improve resolution, but this was not common on televisions until the advent of HDTV.

Digital displays
Early digital monitors are sometimes known as TTLs because the voltages on the red, green, and blue inputs are compatible with TTL logic chips. Later digital monitors support LVDS, or TMDS protocols.

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