HD	vs.	SD

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 large you want your TV. Now there are different HDTV broadcast standards, different type of video/audio inputs, different TV technologies …. LCD, DLP, plasma, CRT, LaserVue, SED, FED, OLED … 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 a list of upside and downside attributes for each one.

What to Look for in a HDTV

• Resolution and Frame Rate – resolution is measured in horizontal pixels by vertical pixels. Think of each pixel as a dot of resolution holding one specific color. Each pixel is too small to see with the naked eye (depending on how close you are) and makes up an image when combined with other pixels.

 Frame rate is the rate that an image is refreshed on the TV. 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 an 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:

• 480i = 640 (or 720) x 480 pixels @ 30 fps (frames per second)
• 480p = 640 x 480 pixels @ 60 fps
• 540p = 960 x 540 pixels @ 60 fps
• 720p = 1280 x 720 pixels @ 60 fps
• 1080i = 1920 x 1080 pixels @ 30 fps
• 1080p = 1920 x 1080 pixels @ 60 fps

Standard Definition (SD) video is 480i while Enhanced Definition (ED) is 540p. High Definition (HD) video is 720p, 1080i, 1080p and higher. The “i” stands for interlaced, and the “p” stands for progressive.

Future standards are in the works such as Extreme Definition (XD), which has a resolution/frame-rate of 1440p. Extreme Definition will mostly be used by computers with newer computer monitors capable of displaying 1440p (2560 x 1440 pixels @ 60fps).

• 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 two 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 cause 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. Therefore, 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.

16:9 HD Aspect Ratio

4:3 SD Aspect Ratio

	What to Look For in a HDTV Continued
HDTV Introduction What to Look For in a HDTV LCD Plasma DLP LaserVue OLED SED FED HDTV Tips Front Projectors HD vs. SD Examples Connection Diagram yourHTN BuyHDTVsnow.com HDTV Forum (NEW)