People who are interested in home entertainment today find themselves constantly bombarded with the term “HDTV.” Studies confirm that most of us are very confused about what the term actually means, much less how to experience the full benefits of high definition television in our own homes.
So what exactly is HDTV? Where does it come from? More importantly, how do I get it? Even if you think you know the answers to these common questions, this tutorial may come in handy.
A Word of Caution
What commonly passes for “HD” on the market is not always what it appears to be.
Example: You just bought an amazing LCD TV with 1024×768 screen resolution. Have you arrived in high definition heaven? Technically, the answer is no. In fact, your expensive new TV is about 135,168 pixels shy of the minimum 1280×720 pixels (that’s 1280 pixels across and 720 from top to bottom) that are required to meet the official HD standard.
In this series of articles defining HDTV we’ll look at the three primary criteria for attaining the definition high experience: Resolution, audio and programming. In this article we’ll discuss resolution, perhaps the most important element of defining HD.
Visual displays work by drawing a picture, line by line and dot by dot. The way these images are created on the screen depends on the type of technology in use – CRT, LCD, plasma, etc – however, the number of dots used to make the picture is what really matters when it comes to HDTV.
The term resolution is used to describe how much information the screen can display. In the case of a TV screen, this is usually stated in terms of how many lines it can show.
Most TVs in the United States are designed to display 480 vertical lines (the actual number of lines is slightly higher, but only about 480 lines show up on the screen). This is the way TV stations have broadcast their signal over the airwaves for more than 50 years. It is, in fact, a standard defined by the National Television Systems Committee, and therefore known as NTSC. It’s also commonly called Standard Definition, or SD.
High definition TV is answerable to a higher standard, namely, more lines: at least 720 lines, to be exact. HDTV can offer even higher resolution, as well. The highest of high definition — at least for the moment — is 1,080 lines.
So you’ve got standard definition and high definition, but what about the middle ground? The standards committees have that covered, as well. Enhanced definition (ED) lies between standard and high definition, requiring only 480 lines of resolution. ED is extremely popular among plasma TV buyers – in fact, EDTV currently represents the majority of plasma TV sold in the United States. The reason is simple: ED screens cost less to make, and therefore, less to buy.
“So,” you might ask, “if SD consists of 480 lines, and ED does, too, why is ED better than SD?” The answer lies in the manner in which the lines are drawn, or scanned, onto the screen. There are two methods: interlaced or progressive. Standard definition is made up of 480 interlaced lines (also known as 480i), while enhanced definition uses 480 progressive lines (480p).
Progressive scanning draws each line of the image in succession, creating a smooth, complete and flicker-free picture. Interlaced scanning is a method that draws every other line, then goes back and draws the ones in-between. It’s great for sending image information efficiently and economically over the airwaves, but interlaced scanning provides a picture that’s inferior to progressive scanning TV technology.