HD - High Definition Television

The most misused term in consumer tech, HD is simply a higher-resolution, more data-rich standard for television production and distribution. Think of the difference between cassettes and CDs.

As happens with new standards and platforms, there are standards wars being fought in HD. The principal one is between 1080i and 720p. What this means:

1. The numbers refer to the number of scan lines that make up one frame (either 1080 or 720). The higher the number, the more data devoted to the image.

2. The letters stand for interlace and progressive, respectively. Interlace refers to the standard television process of combining two images or fields to create each frame of a TV signal. These fields alternate line by line, weaving together or interlacing to form one image to the eye. Standard TV CRT technology is based on the use of interlace, which began as a technique to avoid flicker. Progressive scan draws each image from top to bottom rather than using interlace. All computer monitors are progressive.

In theory, progressive scan is better for fast-motion footage, while greater number of scan lines is better for richer, high-resolution images (barring fast action). In keeping with this, ESPN and all Fox outlets use 720p, as does ABC. NBC, CBS, HBO and others use 1080i. Proponents of 720p often argue that the extra scan lines are not discernable to the human eye, while a progressive signal is a noticeable benefit over interlace. In reality they both look good, with the advantage arguably going to 720p, as current TV tends to be a high motion business. The major downside of the duopoly the impact to operators, who often jump through agonizing hoops to convert one to the other for air. Not a process for the faint-hearted.