OTHER TECH

A digital TV's vertical resolution is given as the number of horizontal scan lines, or rows of pixels, from top to bottom of the screen. Its horizontal resolution is the maximum number of discernible vertical lines, or columns of pixels, from left to right across a screen width equal to the height of the picture. (This keeps widescreen sets from having higher resolution than sets with the squarer 4:3 aspect ratio simply because of their shape.)

One of the two commonly used high-def signal formats is 720p (progressive-scan), which has 720 lines of vertical resolution. There are 1,280 dots, or pixels, in each widescreen line, giving it a horizontal resolution of 720 pixels when the width is limited to the height. The other is 1080i (interlaced), which has 1,080 lines with 1,920 pixels per widescreen line, or 1,080 pixels horizontally when similarly limited. By contrast, traditional 480i TV signals have 480 lines of vertical resolution and up to 720 pixels per line, for a maximum horizontal resolution of 540 lines.

It would be nice if all HDTVs had resolutions of 1080i or 720p, but unfortunately the specs can vary a lot - especially among two kinds of fixed-pixel displays, plasma and LCD. Some screens might match up perfectly with one of the high-def formats, but many have native resolutions like 1,024 x 1,024 pixels, so the TVs convert incoming video to match. These models are still considered HDTVs, which have come to be defined as any sets that can display at least 720 lines of vertical resolution.

In the video world, every color and shade is produced by different combinations of red, green, and blue light at different levels of intensity. Full black is a complete absence of light, and peak white is produced by an equal mix of colors at maximum intensity. The grayscale is the range of steps between full black and peak white. Ideally, the only thing that changes from one shade of gray to the next is the intensity of the light, not the color mix.

For various reasons, however, most video displays find it hard to reproduce full black - CRTs do this best. Peak white also varies from the ideal, the variations being measured in terms of color temperature, which for a TV can range from 4,000 to 5,000 K (or kelvins), orangeish whites as from a 60-watt bulb, to well over 10,000 K, a bluish white produced by some high-intensity lamps. In 1953, the National Television System Committee decided that the correct shade of white for U.S. TVs is about 6,500 K, or the color of sunlight at noon on a clear day (at least under an unpolluted North American sky). The new digital TV system carries over the same color-temperature reference point.

Why does this matter? Since the largest part of a video signal consists of black-and-white information, any deviation from the white-level reference of 6,500 K - whether toward the red end of the spectrum or the blue end - will bias all images in the same way. More specifically, since the studio monitors used for color-correcting TV shows and DVD masters are calibrated to 6,500 K, your TV must be set to the same color temperature if you want it to accurately recreate the images.