High definition television is part of a larger standard known as DTV, or Digital Television. DTV is actually comprised of 18 different standards, six of which are High Definition. Of these, five are progressive standards, while one is interlaced (1080i). Of the remaining formats, eight are SDTV (four wide-screen formats with 16:9 aspect ratios, and four conventional formats with 4:3 aspect ratios), and the remaining four are video graphics array (VGA) formats. Broadcasters are free to choose which formats to broadcast.

The most common DTV formats are:

  • 480p - 480 vertical pixels progressive

  • 720p - 720 vertical pixels progressive

  • 1080i - 1080 vertical pixels interlaced

  • 1080p - 1080 vertical pixels progressive

"Interlaced" or "progressive" refers to the display type. In an interlaced format, the screen shows every odd line during one scan (or field), and then follows that up with the even lines in a second scan, displaying each half frame in 1/60th of a second. These two fields then combine into a single frame of video lasting 1/30th of a second. As a result, your NTSC TV acts very much like a high frequency strobe light, with two lights flashing alternately. This, obviously, is not the best way to show a moving picture; image noise and distortion are common. As screens get larger, these distortions show up as flicker, ghosting, and other types of “noise”. For smaller screens, this is less noticeable. 

Progressive scanning shows the whole picture, every line at the same instant, every sixtieth of a second. This provides for a much smoother picture, but uses more bandwidth – the picture information is twice as large. The resulting image is superior because progressive scanning (or “full frame”) reduces undesirable features like ghosting and image artifacting, as well as producing a more natural transition between frames; you eyes and brain don’t have to work as hard to blend the still images into one fluid sequence. 

HD vs. HD Ready 

Plasmas are available in two DTV formats, HD and ED. HD units, like the Pioneer PDP-4350HD, PDP-5050HD, PDP-6100HD, all have screen resolutions of 1024x768 (XGA) or higher, and are capable of displaying HD without significant down-sampling of the image (see below). Enhanced definition, or HD “Compatible” units, like the Pioneer PDP-42A3HD are capable of receiving HD input, but resize the image to fit onto their lower resolution displays (852x480). It’s worth noting that there is absolutely no problem displaying HD on an ED display, and at average viewing distances, the difference between HD and ED is very difficult to see. 

The current generation of 50 inch and larger plasmas are always HD units, with resolutions of 1280x768 or greater. 

Understanding Resolution 

The first number in your plasma’s pixel ratio refers to the horizontal pixel rows, the pixels running up and down arranged horizontally, like the slats in a picket fence. The second number, the lower number, refers to the pixel rows running vertically, from side to side, like layers in a cake. Your plasma display has a fixed number of pixels, and compensates for the various DTV formats by resampling the DTV signal into something which conforms to the actual, physical pixels present in the display panel. Most US broadcasters are choosing to broadcast HD in the 1080i format. This doesn’t mean your HD or HD ready monitor won’t display these images. It simply means that even the most modern, up to date plasma down-samples these resolutions while still retaining exceptional image clarity.

DVDs are currently encoded at 480i, or 480p for Progressive Scan enabled units. Due to limitations of compression technology, true HD encoded DVDs aren’t yet available (August 2005). There are exceptions: “Superbit” discs push the limit of modern encoding, often obtaining resolutions in excess of 500 lines. Microsoft has a true HD compressor / decompressor, similar to the one used for WMV files. As of this writing, there aren’t any DVD player manufacturers who support the WMV format. Currently there are DVD players on the market that up-convert DVDs to HD resolution, but this is really a stop-gap measure, as picture quality is limited by the source material which is still encoded at 480 lines.