Basics

• Every HDTV has a native resolution, which is the only resolution the television can display. All broadcasts or digital formats it receives displays in the native resolution. An HDTV converts each signal that differs from its native resolution to the native resolution. Lower resolutions are upgraded, and higher resolutions are downgraded.
  
  

Types of HD Formats

• Part of the confusion about HD is the difference between "p" and "i" formats. For example, one television's resolution may be 720p, while another television's resolution is 1080i. The letters p and i are short for the picture-scanning methods progressive and interlaced, respectively. Interlaced means that a tube television draws the picture in two passes; one pass is for odd-numbered lines and the other for even-numbered lines. Progressive means that a tube television draws each frame in a single pass, resulting in a smoother picture. All non-tube televisions, including plasmas, LCDs and DLP, LCD and LCoS rear-projection HDTVs, convert everything to progressive scan, making it even harder to see differences between the two broadcast formats.
  
  

Actual Difference

• Televisions designated 1080 have 360 more lines of resolution than 720 models, which increases picture details. That equals about a 33.3 percent improvement in quality over 720 televisions of the same size.