HDTV Rocks

HDTV

High definition television (HDTV) varies from CDTV in 4 ways:

Spatial Resolution

HDTV is the highest quality of television signal available. The difference between HDTV and SDTV or EDTV is the number of scan lines that can be drawn on the television. HDTV has 720 or 1,080 scan lines.

Normal televisions have 480 scan lines of resolution. Even DVDs only provide this quality with 480 scan lines. DVDs provide about EDTV quality. HDTV provides 50% more scan lines at 720 or 225% the vertical quality at 1,080 scan lines. Couple more scan lines with two to three times the horizontal resolution, then you have HDTV. See the theoretical difference on this page.

Here's a quick comparison.

Most people are used to watching television at the quality of the picture shown below. Normal television is composed of 480 scan lines with about 440 horizontal pixels in each scan line. The resulting pixels aren't square since the 440 pixels need to be stretched to the 4:3 aspect ratio of normal televisions. A square pixel would result if the input signal was 640 x 480. Although cable or satellite signals could provide this quality with their digital signals, they usually compress it to less than 440 horizontal pixels. These signals work pretty good for televisions up to 35".

Standard Television

480 scan lines with about 440 horizontal pixels in a 4:3 aspect ratio.

HDTV = 1280 x 720 scan lines or 1,920 x 1,080 scan lines with a 16:9 aspect ratio.
(This image is only 400 pixels tall because a 1080x1920 image is huge - Here's an example of one).

Less than a million people are enjoying HDTV in it's full glory. Most people watch DVDs (~EDTV) on their HDTVs and think it's great. HDTV can offer so much more. The best comparison to the actual resolution is the number of pixels that a signal delivers every second. Most TVs display about 6 Megapixels per second. DVDs provide 10. If the HDTV is not compressed like crazy, it delivers between 55 and 62 Megapixels per second. So HDTV is about 10 times the resolution of normal television and 6 times the resolution of DVDs. Most people compare HDTV to looking out the window.

Format	Vertical Pixels	Horizontal Pixels	Spatial Resolution (pixels)	Frame Rate (frames/sec)	Pixel Rate (Megapixels/sec)
Most broadcasts	480	440	211,200	60i = 30	6.3
DVD	480	720	345,600	60i = 30p = 30	10.4
720p HDTV	720	1,280	921,600	60p = 60	55.3
1080i HDTV	1,080	1,920	2,073,600	60i or 30p = 30	62.2

HDTV has two basic flavors - 720p and 1080i. 720p offers twice the temporal resolution of 1080i, but 1080i has a much higher spatial resolution at over 2 million pixels per frame. You usually won't see much difference between 30 fps and 60 fps, so the advantages of 1080i's spatial resolution is high. The 60 fps does come in handy when you show sports in slow motion. Slow motion 60p can yield temporal clarity that doesn't exist in 1080i. Any DTV tuner can decode 1080p as well, but the frame rate is only 30 fps so you still get the 62.2 Megapixels per second. Many people prefer the 1080p over 1080i.

To find out about viewing distance and what television to buy, go here.

Surround Sound

One of the major improvements with HDTV is that the audio signal is often in Dolby Digital Surround Sound instead of stereo. Instead of a left and right speaker, you'll get 5 speakers that surround you with a shaking subwoofer as well. This means there is 6 speakers in all - even though the misleading 5.1 might make you think that there are 5 speakers. Surround Sound does make a big difference and helps suck you into the movie. Just don't look behind you for the monster.

TV
DTV
CDTV
SDTV
EDTV
HDTV - Spatial Resolution - Temporal Resolution - Aspect Ratio
Video Quality
Television is a very complex topic. If you would like to add some comments, corrections or additional topics, please e-mail info@broadent.com.