Wednesday, January 3, 2007

Basic comparison: AnalogTV, SDTV. EDTV and HDTV

There was a time when we had only one choices while buying a TV i.e conventional Analog TV or CRT TV. But today we have so many choices. First of all we have our conventional CRT(cathode ray tube) TV. Along with this we have new choices like HDTV, EDTV and SDTV. But what is right for you? What are the main differences in them? Let’s try to understand the very basic about each of them.

Conventional Analog TV:
First of all let’s talk about our conventional CRT TV. Video screen of CRT TV contains 525 lines of resolution, although only 480 lines are displayed. These lines getting painted with “interlacing” technique. In this technique first it paints all the odd numbered lines from 1 to 479. Immediately after that it paints all even numbered lines from 2 to 480. This standard analog TV format represents as 525 interlaced or 525i, this also represent with term “480i”. The aspect ratio of the screen is 4:3. This TV has inbuilt NTSC tuner, so by default they can’t tune Digital TV broadcast.

Analog TV:
with NTSC broadcasting was dominating since last 50 years. But it is time when DTV (Digital TV) gradually replacing the Analog one. Digital television is a new type of broadcasting technology that offers television with movie-quality pictures and Dolby digital surround sound, along with a variety of other enhancements. This Digital TV works with ATSC broadcasting instead of NTSC. Currently there are three types of digital broadcast signal: SDTV, EDTV and HDTV. Aspect ratio for DTV is 16:9.

Like Analog TV, SDTV also 480i. Here the advantage compare to Analog one is SDTV can receive digital broadcast signal.

So far 480i resolution TVs worked fine. That is because TVs sizes are limited to 19 inch or 20 inch. But limitation of 480i resolution surfaced when same technology applies in large screen. Interlacing techniques does not work for larger screen. The visible scan lines and jaggies are annoying. The best solution is to avoid interlacing. Initially Interlacing was invented to save transmission bandwidth. But in current technology transmission in much higher rate is possible. So, there is no need of interlacing. It is possible to paint the lines sequentially from 1,2,3….up to 480, this is called “"progressive scanning". With this technology using same 480 resolution lines we can get better video quality, jaggies can be totally eliminated. This 480 lines progressive scan technique is commonly known as 480p. This concept in the consumer market known as Enhanced Definition Television, or EDTV.

Both SDTV and EDTV also receive the 16-by-9 broadcasts along with the 4-by-3 aspect ratio.


Even though we have digital broadcasting system SDTV and EDTV, maximum attention attracted towards HDTV. Main advantage here is increased number of scan lines on the screen. HDTV comes with three flavors 720p, 1080i and most recent one 1080p. As the name says first resolution displays 720 lines progressively and in the second one displays 1,080 lines interlaced. If we compare this two, we can say both of them are good. In general 720p is more appropriate for fast action as it uses progressive frames; alternatively 1080i is very good for slow moving picture (probably this is the reason in most of the HDTV show room you can see slow moving movies) . 1080p on the other hand providing an image resolution of 1920 by 1080 pixels. This one provides best display compare to other ones. This is because 1080p contains maximum number of pixels compare to other varieties, plus 1080 lines progressively scanned line which considers better then interlaced one.

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