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HDTV
HDTV Introduction
It used to be so simple to shop for a TV. You would walk into a store, and the only thing that
mattered was how big did you want your TV. Now there are different TV technologies, different HDTV broadcast
standards, different type of video / audio inputs ….
LCD
,
DLP
,
plasma
,
CRT
,
LCoS
,
D-ILA
,
SXRD
, … how confusing?
Be informed. Below is a list of “things to look for” in a High Definition TV (
HDTV
), and then a description of
each TV technology with an upside and downside attributes list of each one.
What To Look For In a HDTV
- Resolution and Frame Rate
– resolution is measured in horizontal pixels by vertical pixels. Look at each pixel as a dot of resolution holding one specific color. Each pixel is to small to see with the naked eye (…depending on how close you are) and makes up an image when combined with other pixels.
Now that you have an image, you need multiple images to make a video. This is where the frame rate comes into play. There are two types of frame rates,
progressive
and
interlaced
. In high definition, progressive is when the
full
image is refreshed every 1/60th of a second. Interlaced is when every other line of pixels (or a field) is refreshed every 1/60th of a second. Therefore the full image is combined by the two fields and refreshed every 1/30th of a second. The illustration below describes a standard definition interlaced signal where two 1/60th of a second fields are combined to make a 1/30th of a second frame.
The standard frame rates and resolutions are:
- Screen Size
– measured diagonally off of viewing surface only. See illustration below for an example.
- Screen Aspect Ratio
– The ratio is in width over height of the television screen. For example, a 4:3 ratio means the picture is 4 units wide for every 3 units of height. The 2 most popular ratios are 4:3 ( or 1.33) and 16:9 (or 1.78). Almost every HDTV has the widescreen format of 16:9, while most standard definition TVs have a 4:3 ratio. The different ratios causes the “black bars” that everyone grumbles about. Playing a 4:3 image onto a 16:9 screen will cause vertical black bars on the right and left, while playing a 16:9 image on a 4:3 screen will cause horizontal black bars on the top and bottom. To make things more difficult, DVDs don’t have a standard widescreen aspect ratio. So you can get a DVD with an aspect ratio of 1.78, 1.85, 2.00, 2.35, 2.4, 2.5, or more . Anamorphic Widescreen aspect ratio of 2.35:1 is what most film is filmed in, and is a popular ratio for DVDs. Thankfully, most high definition TVs allow you to zoom in or stretch an image to get rid of the black bars.
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