Digital Image Formats - A Practical Guide to Video and Audio Compression - page 116

6.3 Computer Video Display Standards

In recent times, a variety of popular image sizes have become de-facto standards. These
are related to the 640 480 image size that is based on the 525-line TV service. Other deriv-

atives are based on a computer display known as VGA (video graphics adapter). These are
also derived originally from TV standard sizes. In addition, a set of image sizes is defined
for video conferencing by the ITU (the International Telecommunications Union). These
screen sizes are also used in other contexts.
Computer video displays on personal computers were originally implemented by
plugging in domestic TV monitors. The resolution and scan rates were related to the same
picture sizes. Some modifications began with improvements to the computers, and the
displays became a product that was more specialized and designed for use with a com-
puter. The changes involved improvements to power-supply regulation so that the display
would not breathe in and out as the content changed in brightness, and progressive scan-
ning became popular. All of this was embodied in standard chipsets that started to be used
on computer motherboards.
The earliest commonly used standard was called VGA (video graphics adapter). As
successive generations of computers were manufactured, the standard evolved accord-
ingly. Today's monitors are able to accommodate a variety of display standards, and the
graphics adapters also allow you to define your picture size and scan rate in a very flexi-
ble way.
Table 6.1 gives the basic modes showing the names and dimensions of the screen
display. Other modes are available but mnemonic names are not defined for them. The
scanning rates are not standardized so rigorously.

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Table 6-1 Standardized Computer Display Resolutions

Name Width Height

QVGA 320 240

VGA 640 480

SVGA 800 600

XGA 1024 768

SXGA 1280 1024

WXGA 1366 768

UXGA 1600 1200

UXGA-W 1920 1200

QXGA 2048 1365

Apple 30 inch 2560 1600

QUXGA-W 3840 2400

Digital Display Working Group: http://www.ddwg.org/