Specifications

Video Display Technologies

875

Figure 15.4 Conventional VGA cards, CRTs, and analog-compatible LCDs use the standard VGA connec-

tor. Early digital LCDs and their matching video cards often used the DFP connector. Most recent digital

LCD panels use the DVI-D connector, whereas video cards used with both analog and digital displays use the

DVI-I connector.

Before you rush to the store to purchase an LCD desktop monitor, you should consider several poten-

tial drawbacks:

■ If you routinely switch display resolutions (as Web developers do to preview their work), LCD monitors

must take one of two approaches to change resolutions. Some older units might reduce the onscreen

image to occupy only the pixels of the new resolution, thus using only a portion of a typical

1024×768 LCD panel to display a 640×480 image, whereas newer units might scale the image to

occupy the entire screen. Scaling is becoming common because the Digital Display Work Group

standard for LCD desktop displays specifies that the scaling must take place in the display panel,

the graphics controller, or both places. Look at the quality of a scaled image if using different

resolutions is important to you.

■ If you choose an analog LCD panel, you’ll usually save money and be able to use your existing video

card or onboard video port. However, image quality for both text and graphics can suffer because

of the conversion of the computer’s digital signal to analog (at the video card) and back to digi-

tal again (inside the LCD panel). The conversion can lead to pixel jitter or pixel swim, in which

adjacent LCD cells are turned on and off by the display’s incapability to determine which cells

should stay on and stay off. Most panels come with adjustment software to reduce this display-

quality problem, but you might not be able to eliminate it entirely.

■ Digital LCD panels avoid conversion problems when attached to a digital-compatible display card.

However, most low-cost, off-the-shelf display cards don’t support digital signals yet, and the

onboard video circuits built into some motherboards don’t support DVI yet.

Note

Video card and chipset makers, such as NVIDIA, Matrox, and ATI, have added support for digital and analog display

panels to most of their recent 3D chipsets and video cards. Check the specifications for a particular video card to verify

support.

Chapter 15

VGA

connector

DFP

connector

DVI-D

connector

Pin 1

DVI-I

connector

Pin 1

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