Clarity
In addition to the wider image, HDTV’s digital signals are much clearer than regular television’s analog signals. It’s like the difference between your old phonograph (did you even have one of those?) and a CD player. Think of two delivery trucks bringing the signals to your home. The analog signal is like something carried on an uncovered flatbed. Parts of the signal get lost in the wind, while unwanted dirt and grime might get mixed in with the surviving signal as it travels down the signal path to your TV. By contrast, the digital truck is enclosed, air-conditioned and airtight. So long as the truck reaches your house, whatever gets put into it is what’s delivered to your display. There’s no added grain, ghosts, distortion or loss in quality. Even if there isn’t a difference in resolution, signals recorded and transmitted digitally will be clearer and cleaner than their analog counterparts.
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| DETAIL AND COLOR THEORY: High-
definition TV uses a greater quantity of much smaller pixels, or picture
elements (simulated close-up at left), to create the image. The system also uses a wider color palette and has improved dynamic range. The result is a picture that’s substantially sharper with richer colors and a more three-dimensional appearance as compared to
regular analog signals (simulated, at top). |
Detail
The country’s new digital television system allows broadcasters to alternate between a single HDTV signal and multiple standard resolution signals (visit the San Francisco PBS station’s website at www.kqed.org/
tv/digitaltv for a great example). Standard definition doesn’t necessarily offer any additional resolution over analog signals and therefore isn’t considered HDTV, but rather merely DTV. While this might still look better than analog signals, high definition, as the name implies, offers much higher resolution and looks substantially better. Most broadcasters use an interlaced HDTV format with a horizontal to vertical resolution of 1920 by 1080 picture elements, or pixels. This is commonly referred to as 1080i. Compare this with regular television, which has a vertical resolution of 480i and a horizontal resolution of 330 pixels or less per picture height, and you can see the difference without even seeing an image.
Even DVD’s resolution, 720 by 480p, is no match for HDTV. The 1080i format has more than twice the vertical resolution and more than three times the horizontal resolution of regular television. Where before you could barely read the name on the back of a football player’s jersey, now you can practically count the individual blades of Astroturf.
There’s also a second, progressively scanned HDTV format called 720p (used by ABC, Fox and ESPN), which offers a 1280 by 720 resolution. Progressive images, without delving too deeply, have roughly twice the vertical resolution per sixtieth of a second of a comparable interlaced image. This gives the 720p format roughly three times the vertical resolution and over twice as much horizontal resolution as a normal TV signal. This resolution also matches with many digital display technologies, like plasma, DLP and LCoS. In fact, few displays as of yet can take advantage of 1080i’s full horizontal resolution.
Color and Dynamic Range
HDTV signals also have improved color and dynamic range. The color palette with high definition is much wider than with regular TV. Reds and greens can be much deeper and more saturated, which gives the image a much richer and more vibrant appearance. Dynamic range, or the difference between peak white and pitch black, is also slightly improved. This means that gradations from light to dark are smoother. These elements combine with the increased resolution to make HDTV look great.
