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The intent of this article is to explain High Definition Televiision (HDTV) resolution in terms that can be easily understood by the lay person.
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A television picture is made up of thousands of pixels, or "dots of colored lights", and the term resolution is used to describe the number of these dots that are used to create a picture. For the more curious, the display is logically divided into a grid and a pixel is actually a specific location activated by light, within that grid.
So what’s up with numbers and letters?
Resolution is normally expressed as a number followed by a letter such 1080p, 1080i, 720p or 720i.
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The number
represents number of horizontal lines of data in a HD signal, while the
letters, “p” for progressive and “i” for interlaced, signifies how the lines
are painted across the screen.
With progressive scan the lines of
information are painted top to bottom one after the other i.e. line 1 then
lines 2, 3, 4 etc. Interlaced by contrast paints every other line top to bottom
i.e. 1 then 3, 5, 7 … all the way to the last line then the process is repeated
a 2nd time, this time filling in the lines that were skipped. So on
the second pass, line 2, 4, 6 etc are painted.
Expressed in terms of pixels,
displays labeled as 720p generally have 1,366 pixels from left to right to make
up a line of picture and 720 lines from top to bottom (1366x720) or
1024x768. Those labeled as 1080p has
1,920 pixels left to right and 1,080 lines top to bottom.
As a general rule, progressive
scanned pictures are a lot better (and sharper) at presenting high speed
motion. An interlaced signal contains two fields of video captured
at different times, and as a result the edges of the images in motion may not
be as crisp.
How important is Resolution?
Not as much as you’d think. In
general a resolution of 1080p can display more and finer detail than a 720p
set, but the resolution alone is not the ultimate measure of picture quality.
Other important factors include black levels or contrast, brightness and color
accuracy.
The reality is, when it comes to
High Definition, the experience is more subjective than scientific, and even
though there is lots of buzz about resolution most people are satisfied with
the improved sharpness of the picture. Furthermore, the comparison between two
televisions is more readily seen in a store when they are side by side. The
differences aren’t that obvious when the two televisions are seen
independently; your television versus the one next door, for instance.
The higher 1080p resolution televisions carry a higher price premium, and their benefits are evident in
larger screen sizes or when viewed up close. However, as the screen size
decreases, 48 inches and below, or as the viewing distance increases, 6 feet
and up, the benefits of 1080p becomes less apparent and is probably not worth
the premium.
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Resolution
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Common Name
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Considered
High Def?
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Prevalence
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Typical TV types
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1,920x1,080
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1080p
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Yes
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Rare but
getting more common especially in larger TVs
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Flat-panel
LCD; DLP, LCD, and LCoS projection; very high-end plasma
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1,366x768
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768p
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Yes
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Very
common in all screen sizes
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Flat-panel
LCD; 50-inch plasma
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1,280x720
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720p
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Yes
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Common in
rear-projection but not flat-panels
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DLP, LCD,
and LCoS projection
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1,024x768
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HDTV plasma
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Yes
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The most
common plasma resolution
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37- and
42-inch plasma
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852x480
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EDTV plasma
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No
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Increasingly
rare
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37- and
42-inch plasma
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640x480
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VGA
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No
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Increasingly
rare
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Small LCD
TVs
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