WHAT IS HIGH-DEFINITION VIDEO?
We are all familiar with standard-definition (SD) analog television. It is the television (TV) we have known and watched for decades. NTSC TV (used in North America and a few other parts of the world) displays pictures consisting of 525 lines of resolution at 30 frames per second. PAL TV (used in the rest of the world) displays 625 lines of resolution at 24 frames per second. Still pictures are first drawn on all the odd numbered resolution lines; after that, the same picture information is drawn from the even numbered lines. Given there are two frames painted on the monitor, this is referred to as 50/60 fields per second. This odd/even drawing pattern is called interlacing, which was developed to conserve transmission bandwidth (the data rate capacity of a given network connection). This resolution is referred to as 480i, and it provides 240 unique lines of picture information. The bandwidth required for SD at home is 45-90 Mbps.
For small video monitors (less than 27 inches), standard-definition television looks reasonably sharp and smooth. However, as screens increase beyond 27 inches, it is easy to see degradation in picture quality with the 480i format. Jagged lines, blurry outlines, washed-out colors, visual noise, and choppy movements may be noticed.
The progressive scan format is an alternative to interlacing that improves picture quality on larger screens. Progressive scanning combines 480 unique lines of picture information into one picture frame and corrects picture quality automatically. Progressive scanning reduces jagged pictures and smoothes movement on larger monitors. For standard-definition television, this resolution is known as 480p.
True high-definition video displays picture resolutions of 1080i or 720p. Resolutions other than these are not truly high-definition.

Of the many formats available, the following six are considered true high-definition formats.

The high-definition formats provide more visual information than any standard-definition format. If the screen resolutions are converted to pixels, it is easy to see that the high-definition formats can provide at a minimum up to four times more visual information than the 480i format. The following table gives the screen resolution in pixels for the common formats and aspect ratios.

To understand this visually, think of the television screen as a computer monitor. Imagine what would happen to the quality of a 640 X 240 (480i equivalent) low-resolution digital picture if stretched across a 42-inch screen. The image would be distorted due to not enough picture information being available to provide a high quality view of the low-resolution picture. The increased pixel count inherent in the high-definition formats provides better picture quality and makes viewing images on larger screens clearer and easier to watch. In video conferencing, this enhances the overall viewing experience and eliminates meeting fatigue. Colors are also more vibrant and realistic, and movements are sharp and smooth.

One Response to “The Evolution Of Video Conferencing”

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