HDTV : Viewing : 4:3 VS 16:9 : What's The Dif ?

[Kramer]

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4:3 or 16:9 ?




First things first...what does "aspect ratio" mean?

The term aspect ratio refers to the ratio of a picture's width to its height. If the aspect ratio of a picture were 1 to 1 (or 1:1), the width and height would be the same, and you'd have a square.


Standard NTSC video has an aspect ratio of 4:3. That means for every four units of width, the picture will be three units high. HDTV standards call for an aspect ratio of 16:9, which describes a rectangle that is wider relative to its height than NTSC's 4:3.

Let's start with some basics. LCD (Liquid Crystal Display) projectors make an image by shining light through glass LCD panels made up of thousands of little dots called pixels. Each pixel controls the amount of colored light it will project. Depending on the resolution of the projector, the projected image is produced by 1 to 4 million pixels.



1. DLP projectors make an image by bouncing light off a DMD chip (Digital Micromirror Device) that is populated with thousands of tiny mirrors which are the equivalent of LCD pixels. Each mirror is electronically adjusted to control the amount of colored light it reflects.


The physical array of pixels on an LCD panel or a DMD chip is fixed. At the moment, most DMDs and LCDs have a 4:3 aspect ratio with pixel arrays of 800 x 600 (SVGA) or 1,024 x 768 (XGA). Aspect ratios of 5:4 are also available to support 1280 x 1024 (SXGA) projectors
movies look 33% better when viewed on a widescreen television set or on a computer screen.


Here's a very easy (but also very thorough) explanation of how it works.

standard television set. It's about 1.33 times as wide as it is tall -- usually called 4:3 because its width is 4/3 of its height.

When you watch movie on it, you see black bars at the top and bottom. The thickness of the bars depends on the width of the movie. Most movies today are 1.85 times as wide as tall, or 1.85:1.

Many are wider, at 2.35:1.

The widest popular American movie was Ben-Hur (1959) at 2.76:1.


Another popular width is1.66:1.
For this example, I'll use the widest common movie width -- 2.35:1.


An example of a2.35:1 movie is Star Wars.

Widescreen televisions are about 1.78 times as wide as they are tall, or 16:9.


If you watch a letterboxed movie on it, you'll see grey bars on the sides as well as the black bars on top and bottom

Since this will obviously be a very common problem, widescreen television sets have acontrol that allows you to stretch the picture 33% horizontally and 33% vertically, enlarging the total picture are by 78%

However, that doesn't make the picture look significantly better; it's just bigger.
Since some of the disc storage area is already being wasted on the horizontal black bars, it would be convenient if there was a way to take advantage of that storage area.


In fact, there is a way to use some of it for the image. Anamorphic DVDs use 33% more of the storage area for the image, by stretching the image vertically by 33%

Of course, you wouldn't want to view it stretched like that. When viewed on a widescreen television or on a computer screen, the image is again stretched 33% -- this time horizontally instead of vertically -- to fit the screen:

The image is 78% larger than before (1.3333 x 1.3333 = 1.78). Since only 33% of the increase has come through using additional storage area on the DVD, and the next 33%increase has come through simply stretching the image to fit the wide screen, the increase in resolution is only 33%.



The picture is 78% larger and looks 33% better than on a standard television.
But what if you want to view it on a standard television? You wouldn't want to see the vertically stretched image; everything would look tall and thin, like the red square in the stretched picture.



DVD players are designed to squeeze the image back down to normal for standard television sets. They use weighted averages to combine lines, scaling the image back down by 33%

Standard televisions are already appearing that have a switch to squeeze the picture vertically by 25% without losing any resolution; the exact amount necessary to enjoy anamorphic DVDs at full resolution. The resulting picture is the same size as it would have been after scaling; the only difference is the higher resolution.



Like widescreen televisions, standard televisions with this feature could be designed to automatically detect whether content is anamorphic and avoid squeezing non-anamorphic content. Since it costs little to add this 25% "Vertical Squeeze" feature, within a few years it should be common. In effect, it is like having a widescreen television of the same horizontal width (but smaller diagonal measurement, of course).


How does your DVD player know whether to scale the image for a standard television, or to use the larger image for a widescreen television? Because your DVD player has a setting in which you tell it which kind of television you have.


What if you're watching an anamorphic DVD on your computer? You normally view the movie in a window, and the software has a setting that switches between a 4:3 window and a 16:9window.



If you choose 16:9 and then maximize the window, you will of course have additional horizontal black bars at the top and bottom, since the computer screen is 4:3.HOWEVER, you STILL get the additional 33% resolution, since most computer screens have much higher resolution than a standard television. The image will look like the one above, but will look 33% better than on a standard television.




By the way, the waste of disc storage area on the black bars does not refer to how many bytes the movie uses up on the disc. The black bars are stored very efficiently, and pixel for pixel, they use up far fewer bytes on the disc than the picture area uses up. Instead, what is wasted is some of the pixels available for each frame of the movie.

The DVD standard only allows for storing a certain number of pixels per frame, and only in a 4:3 image. Studios can't store additional pixels per frame on the disc because DVD players wouldn't understand. And for the same reason, they can't rearrange the pixels into a wider image.


Regular old tv shows tv is 4:3 setting
HDTV is 16:9 setting ...

don't forget to change the settings between types of channels ...