HDTV formats and resolutions

30 April 2007 One Comment

HDTV Formats

HDTV comes in three distinct formats: 720p, 1080i and 1080p. The number of each of these formats represents the number of vertical pixels the HDTV can display (i.e. 720 or 1080 vertical lines of pixels), while the p and i stand for progressive and interlaced. Progressive simply means that each line of pixels is displayed one after the other, starting at the top and progressing vertically downwards. Thus, each frame of HDTV content is displayed in one pass.

Interlaced, however, means that each frame is displayed in two passes, with alternate lines being displayed in one pass, with the remaining lines displayed in the second pass. For example, lines 1, 3, 5, 7, etc. will be displayed on the first pass, and lines 2, 4, 6, 8, etc. displayed in the second pass.

HDTV Pixel Density

The more pixels you have in your HDTV, the smoother your image will look, as the HDTV has greater pixel density (more pixels per square inch). 720p HDTVs typically have 1280 horizontal pixels per line, while 1080 HDTVs (both p and i) have 1920 pixels. Thus, a 1080 screen should look smoother than a 720 screen.

You also get the bonus that different colour shades seem to blend together more smoothly when positioned next to each other, as the finer grained pixels are too small to be distinguished by the eye as individual pixels. This is increasingly important as the size of the HDTV increases, as the pixels on a large HDTV will naturally be larger than those on a smaller HDTV if they both share the same number of pixels.

Progressive vs Interlaced

Deciding between progressive and interlaced is more tricky, however. At first glance, a 1080i HDTV should produce better results than a 720p HDTV, as it has more pixels. However, the interlaced nature of a 1080i HDTV makes matters more complicated. Because each frame in an interlaced image is displayed in two passes rather than one, the resultant image can appear less smooth and sharp than its progressive equivalent, particularly where motion is concerned.

As such, a relatively static image, such as a news broadcast, should appear better on a 1080i HDTV than on a 780p one, but a fast-moving image, such as sport, may appear better on a 780p HDTV.

Note the terms should and may though – some 1080i HDTVs do a superb job of splicing the two alternate lines together, so you don’t actually notice the difference. It all depends on the HDTV, though, so read reviews thoroughly of the model you’re thinking of buying, and if possible, see it in action yourself.

1080p HDTV

Of course, the holy grail is 1080p HDTV – non-interlaced and maximum resolution. The only downsides to 1080p is include cost, and the current lack of 1080p content, but these should change soon as more 1080p HDTVs are released and competition forces prices down, and broadcasters start broadcasting full 1080p content as more 180p HDTVs are bought.

A note of caution should be made, though, before you decide to shell out for a full 1080p HDTV. Any HDTV format presents content to a very high standard – much better than your traditional analogue TV.

However, the difference between HDTV formats is not so great, and in many cases, is completely undetectable, particularly when you watch the HDTV further away than 1.5 times its diagonal length. If you buy a HDTV that’s less than 50 inches, you’ll find it nearly impossible to tell the difference between 1080p, 1080i, or even 780p.

As CNet say, “unless you have a very large television and excellent source material, you’ll have a hard time telling the difference between any of the HDTV resolutions. It’s especially difficult to tell the difference between 1080i and 1080p sources.”

What does make more of a difference is contrast ratio, colour saturation and colour accuracy, in that order. Only then do you need to worry about resolution.

  1. 1). HDTV Formats and Resolutions
  2. 2). HDTV Connections – from HDMI to Composite Video
  3. 3). HDTV Sources – Hi-Def DVD players, Games Consoles, Cable and Internet
  4. 4). HDTV Aspect Ratios
  5. 5). HDTV Plasma TVs vs HDTV LCD TV – which is best?
  6. 6). HDTV Info Summary

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