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Moving to HD TV

by David Wimsett

People have been talking about improved television picture and sound for decades. The move has involved political and technical posturing between countries, companies, and special interest groups. There are many standards around the world that are all deeply entrenched. Some carry a sense of national pride. All are costly to change.

HD TV possesses many technical challenges as well, not the least of which is the nature of the analog signal. Transmitting a high definition picture with an analog signal would require 4 times the bandwidth of a standard TV. This would either restrict the number of stations that could be broadcast or take bandwidth away from other devices such as radios, radar, cell phones, satellites, and even keyless entry clickers that unlock car doors.

A breakthrough came with advances in digital technology and data compression. Instead of using a wave to represent the luminosity values for every dot (now called a pixel in the digital world), the brightness and colour information was converted to a code of zeros and ones. Once digitized, the data stream could be compressed to fit into a smaller bandwidth. If an area of sky is the same shade of blue for the top 40 scan lines, an analog signal would have to transmit a stream that included the luminance and colour information for every dot. A compressed data stream can send a small code that says, “Make all these pixels blue.” As well, compression can analyze the previous frame, determine which pixels have changed, and send only the data for the changes. All this can dramatically reduce the information sent and, hence, the required bandwidth. With data compression, high definition signals can be realistically broadcast, or placed on a recorded medium, such as Blu-Ray® disks.

Because of this, HD TV is now a reality and the difference is breathtaking. The picture is clear and sharp with excellent colour rendition. Instead of 525 lines, HD TV delivers up to 1080 lines of resolution. The aspect ratio of the screen has changed to 16:9 (16 units wide and 9 units high). This closely approximates the 1.78:1 aspect ratio of most modern movies, which eliminates the need for letterboxing except for extremely wide pictures. Sound has been greatly improved to include technologies such a Dolby Digital® and DTS® that provide true theatre quality surround sound.

You literally have to see it to believe it. Many video stores play standard and HD material side by side. The standard TV will look good until you compare it to the HD set. Then, the older model will seem muddy and blurry. I remember seeing a baseball game on HD for the first time and being astonished when I could make out individual blades of grass on the field.

Next: Part III – Moving to HD TV

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