Buying a Hi Def TV Set

October 24, 2010 at 10:03 am | Posted in Daily blogs and thoughts | Leave a comment

Everywhere you look today there is another company advertising high definition video and television.         

While most people will agree that watching a movie in your home with a high definition television is more of a “movie experience” than on a standard television, there are many confusions and misunderstandings about what high definition really is.

Lets go back in history about 70 years to the infancy of television to get a perspective about electronic pictures.

The earliest television sets, from the late 1930s and early 1940s, generated a picture that had a width to height ratio of 4 by 3.  That  means if your television picture tube was 4 inches wide, it would be 3 inches high.  If it was 8 inches wide, it would be 6 inches high.  The width to height ratio is today known as the picture “Aspect ratio.”

The 4 x 3 aspect ratio was the standard for television sets until the mid 1990’s, when television manufacturers were looking for new ways to re-create the “movie experience” and improve sports broadcasts to help sell more televisions.

Wide Screen Television

High definition TV was still an idea lurking over the horizon when “wide-screen” hit the markets.   The wide screen is considered a more natural image than 4 x 3 picture because it more naturally matches the viewing area of the human eye.  The aspect ratio of 16 x 9 was chosen because it was close to the size of a Panavision movie frame.  For example, compare these images as shown on a 16×9 television and a 4 x 3 television:

Panavision wide screen original Pan & Scan to 4 x 3

To fit the 4 x 3 television, broadcast stations must re-edit the movie through a process known as “Pan and Scan.”  Movie purists don’t care for pan and scan movies because you actually lose a large portion of the picture.  Notice how the 4 x 3 broadcast is missing the entire right side of the movie.

The new 16 x 9 televisions had a problem with normal television broadcasts, most of which were still 4 x 3.   Imagine spending thousands of dollars on a new TV, and having large black bars on the sides of your picture.   To compensate, television manufacturers set their widescreen televisions to stretch the 4 x 3 image to fill in the entire 16 x 9 picture:

4 x 3 in widescreen TV 4 x 3 stretched to fit widescreen

The results weren’t great.  But most early adopters who bought 16 x 9 televisions learned to live with it.  16 x 9 television, however, worked great with DVDs, which can have actual wide screen images on them.

As 16 x 9 televisions grew in popularity, manufacturers worked on improving the picture.  Unfortunately, the government never set standards for high definition the way it did for television 70 years ago.  Now, the lack of standards becomes confusing.  Consider a strip of movie film:

A movie consists of thousands of little pictures on a reel of film  The pictures are projected at the rate of 24 pictures per seconds.  The official term is 24 FRAMES per second.  Every frame is made up of one picture.

For a variety of technical reasons, when television was invented, it was based on 29.97 frames per second, which we will call 30 frames per second, just to keep it simple.   One video frame contains 625 electronic lines, and an electron gun in your television “paints” the line on the television screen.

However, to allow for more efficient broadcasting, each frame was broken up into two pictures.  The first picture was the even numbered lines and the second picture was the odd numbered lines.   Confused yet?  Take a look at this greatly simplified picture to get a better idea:

Odd TV lines Even TV lines

Your television first displays the even half of the picture, then the odd half of the picture.  The process is called interlacing.  Because it happens so fast, your eye is tricked into thinking it’s looking at the complete picture.  The effect is that your 30 frames per second television picture is actually made up of 60 interlaced pictures.

Still with us?  To sum up so far, a standard 4 x 3 television picture is made up of 60 interlaced half pictures being displayed per second.  The techie description for this standard television is 60i, for 60 pictures interlaced.

While broadcasting interlaced pictures worked great for a fledgling television broadcast industry, it was a compromise as far as picture quality is concerned.  This is most noticeable when watching fast moving objects, such as car racing and other sports.

A higher quality picture could be generated if they would just broadcast the 30 complete images.  This non-interlaced image is also called a Progressive image.  Once again, the techie description is 30p.

High Definition

So, do you need a high definition TV to enjoy your DVD’s?  Not at all.  Actually, the standard DVD you rent or buy today is ony Standard Definition.  They are not, have never been, and never will be high definition.  They can be wide screen, but there’s more to high definition than the shape of your television set. The scan lines we talked about earlier are used for analog transmission.  But most cable and satellite transmission today is digital.  The signal coming into your home over the wire is broken down in picture elements, or pixels.  Just like a computer screen.

Now we have one more techie term to talk about.  Let’s examine the 4 x 3 and 16 x 9 screen sizes in terms of those digital pixels.

The 4 x 3 picture is made up of 720 x 486 pixels.  That pixel ratio is expressed as the picture’s resolution.

Widescreen televisions come in a variety of sizes, but we’re going to limit our discussion to the two most common sizes, 720p and 1080i.

A 720p image is actually 1280 x 720 pixels in size.  The “p” means that it is a progressive image.  You will remember progressive means that 30 separate pictures are broadcast in a single second. A 1080i image is actually 1920 x 1080 pixels in size.  You would think that the picture would be much sharper because it has more picture elements in it, but that’s not the case.  1080i is an interlaced image, meaning it consists of 60 half pictures.

Wouldn’t it be great to mix the best of both technologies and create a 1080p television?  Well, there are 1080p displays out there.  The only problem is that nobody broadcasts in 1080p, and it’s not likely that any broadcasters will be upgrading their broadcast capabilities anytime soon.  1080p is available, however, in the Sony Playstation 3 and HD DVDs.

Oh, and right now, 1080p televisions carry a premium price.

So, which is better, 720p or 1080i?  Engineers have been arguing about this for years.  Both pictures will fit fine on your 16×9 television.  The “general thought” is that 720p is better for sports because high-speed action is clearer.  1080i is better for movies and drama, where speed is not a factor.  720p is used by ESPN, ABC and FOX.  1080i is used by CBS, NBC and HBO.

Most 16 x 9 televisions will show both 720p and 1080i with no problem.  Which is better for you as a consumer?  Believe it or not, the number of pixels isn’t the most important factor in the image quality.

Next time you’re in an electronics store, compare the LCD televisions to the Plasma televisions.  For the most part, plasma TV’s have better pictures.  The colors are richer, the blacks are blacker and the whites are whiter.  This is because the CONTRAST RATIO of a plasma screen is generally higher than in an LCD television.  Many consumer electronic sites that rate televisions will point out that it’s very difficult to tell the difference between 720p and 1080i, but a television with a 10,000:1 contrast ratio will look better than a television with a 3000:1 contrast ratio.

A Final TV Buying Tip

When shopping for a television, make sure the sets you are comparing are showing the type of show you normally watch.  Many electronics stores like to show computer animated programming in their showrooms.  There’s a reason.  Computer animated programming has fewer colors than actual movies and television shows, and therefore looks great on LCD and Plasma screens.  Make sure you watch a movie, or a sports broadcast for an accurate comparison.  Do not judge a televison picture while watching animation.  It’s not a true measure of the television’s capability or picture quality.

Also examine at the wires on the televisions you are comparing.  HDMI cables give the best possible picture.  The second best cabling system is component video, followed by S-video and composite video.  RF cables, also known as antenna wire, carries the worst picture.  When comparing television pictures, don’t be fooled by an electronics stores that uses modern high quality cabling on its expensive televisions and inexpensive antenna cables on the cheaper sets to discourage you from buying.

For more information, visit Wikipedia for a description of high definition television technology and cNet for a useful buying guide.


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