HDTV resolution 101

In most reviews, resolution is one of the main reasons given that makes HDTV look a lot better than analog TV or standard definition TV (SDTV).  It refers to the values 720p, 1080i or 1080p that you usually see in TV display specs.  So what do these numbers and the letters “i” and “p” mean?  Is 1080i better than 720p?  It is the purpose of this article to answer those simple questions and provide basic information on HDTV resolution.

What is resolution?

Resolution refers to the number of pixels a TV monitor can display.  The higher the resolution, the better the quality of the picture. The usual numbers you will see for HDTV are 720 and 1080.  To understand the significance of the letters “i” and “p” associated with these numbers, let’s return to the basics of how images are produced in analog TV and film.  In a traditional cathode ray tube TV (CRT), a picture image is made up of interlaced scanned frames similar to how it is done in 1080i displays.  In film, the moving images on the other hand are made up of progressively displayed complete frames similar to what is happening in 720p or 1080p displays.  So which provides better picture quality, 1080i or 720p?  Theoretically, 720p should be better because each picture image is a complete frame. In 1080i, two half-resolution frames are interlaced to form a complete picture image.  This issue though is a continuing debate in the HDTV industry.

Signal Source Resolution

HD signal can come from a variety of sources like digital terrestrial TV, satellite and IPTV broadcasts.  It is also available in optical media like HD DVD and Blu-ray.  Game consoles like Xbox 360 and PlayStation 3 have also adopted 1080p.  Most broadcasters transmit at 720p while some at 1080i.  Some maybe doing it at 1080p but at the expense of big channel bandwidth.

The above resolution figures can also be preceded by these numbers: 25i, 25p and 50p for 50 Hz countries and 30i, 60i, 30p and 60p for 60Hz countries. As the figures denote, 60i means 60 interlaced frames per second while 30p means 30 progressive frames per second.  There is another variant, 24p or 24 progressive frames per second, which is used to display film-like images.  Independent film enthusiasts use this format to produce film-like content.

Display Resolution

After learning about the resolution of HD signal sources, let’s examine corresponding resolution for display devices.  There are several types of HDTV displays available in the market - plasma, LCD and DLP.  Each have their own strengths and weaknesses which are discussed in other reviews.  There are resolution formats more common to certain types of display device as follows:

Upconverting and Downconverting

The best picture quality can be obtained if the display’s native resolution matches that of the source.  If the resolution of the source is higher than that of the display, the signal should be downconverted to fit available number of pixels in the display.  Conversely, if resolution of source is lower than that of the display, the signal should in turn undergo upconversion.  This is standard feature of almost all HDTV displays available in the market.

The picture quality advantage of HDTV displays over analog TV and SDTV displays are very noticeable.  The visual difference, however, between HDTV displays with different resolutions is hard to tell.  When you do side-by-side comparison using 720p, 768p or 1080p displays, it’s difficult to see the difference.  I’m not saying 1080p is not better than the others because it definitely will deliver more detail.  What I’m trying to say is if you’re conscious with your budget, you can still settle for 720p or 768p because going for 1080p will cost you extra bucks.