Feature Article - "The 16:9 Enhanced DVD: Demystified" - November, 1999
If you've digested our feature article on Video Resolution, you are ready for the next topic: 16:9 enhancement in DVDs. The fact that you are here at Secrets, reading this essay, substantially increases the odds that you not only like movies, but you appreciate what a wide, letterbox presentation can mean. This article is an update from the one we published last year.
Widescreen images on conventional TVs
Look at your TV and get a feel for its shape. The image area is almost, but not quite a square. The ratio of width to height is 4:3 (termed the "aspect ratio"), and so we call regular TVs 4:3. If you divide out the ratio, it comes to 1.33:1, another way of expressing it. However, when modern movies are made, theyre not even close to a square, but rather the shape of a wide rectangle (some wider than others). In order for us to see all of the movies image (its "frame"), it needs to be located inside of the square frame of our TV. This produces an image with blank bars at the top and bottom, and the image we then see is called "widescreen" or "letterbox". Although the widescreen image is physically smaller in terms of actual square inches, there is one very important advantage that outweighs the bad: We dont miss out on any of the frame compared to the much more common practice (called Pan-and-Scan or P&S) where the left and right sides of the frame are cut off so as to fill the TV screen with movie image. Have you ever taken note of the statement at the beginning of such a film: This film has been modified from its original version. It has been formatted to fit your TV? Most people prefer the P&S versions because they fill the TV screen. However, from an artistic point of view, the "widescreen" version is what the movie director intends for us to see, and it is what we see at the commercial movie theater.
The problem: One of resolution
There has always been one problem. Maybe not a problem but rather just a shame: resolution. Since the black bars above and below the widescreen movie image are part of the TV signal, we lose those lines of resolution because those bars make up a significant part of the 525 scanning lines (remember from the resolution essay, vertical resolution is fixed in the NTSC television system). Those black bars dont contribute to the detail in the picture. If, just for sake of discussion, we assume that a DVDs picture has a resolution of 720 x 480, and that we present a film in the letterbox format, not all of those pixels are contributing to picture detail. (The number 720 refers to the horizontal resolution, and means the number of vertical columns the image can display, side by side. The number 480 is the vertical resolution, and means the number of scanning lines that are in the image, each line arranged horizontally across the screen. It is 480 with NTSC TV because 45 lines are lost due to information for the TV studio being shown out of the range of view, and the finite time it takes for the scanning process to start over after the last field was shown.) Many of the pixels are used to display the black bars. Between 130 and 190 lines of vertical resolution (number of horizontal scanning lines) get used in presenting the black bars, so the actual picture area has a resolution of roughly 720 x 330 or even less. It is a shame, but there is nothing that can be done about that within the confines of a square TV, if we want to see the whole film frame as the director intended.
A partial solution
One solution which was sometimes (rarely) used on laserdiscs in an effort to take advantage of all of the picture area available, was a technique called anamorphic. Simply stated, the full, wide movie frame was recorded using all available pixels. In order for this to look right, it must be played back on a TV whose shape is the same as the original image. There are such NTSC TVs available. Their aspect ratio is 16:9, closer to the wide rectangle of the movies. Great! Right? Not quite. The moment you lend such laserdiscs to your friend without a wide TV, the image they see on their screen looks wrong, as if squished from the left and right. The shape of the TV does not match the shape of the image. Precious few laserdiscs were made this way due to the rarity of 16:9 TVs at that time.
DVDs bridging the gap
DVDs hold digital picture data, as compared to VHS tapes and laserdiscs, which hold analog video data. Digital data can be manipulated fairly easily, without a lot of expense. As such, at the movie producer's option, DVDs can store 16:9 picture data that support both traditional 4:3 TVs and newer (and gradually more common) wide 16:9 TVs. Such DVDs have come to be known as 16:9 enhanced, Anamorphic Widescreen, and Enhanced for 16:9 TVs (just to name a few of the terms used).
Again, let's say that DVD stores its image at a resolution of 720 x 480. Rather than waste some of that resolution for a classic letterbox presentation, a studio can use all 720 x 480 pixels to encode the entire picture area of the movie. If, in your DVD player's menu setup you have it configured for a 16:9 TV, it passes the signal along untouched, to be played back on the wide TV. Movies with an original aspect ratio of 1.85:1 occupy just about the entire 720 x 480 pixel array with enhanced DVDs. In the case of a scope 2.35:1 movie, it is still necessary to encode small back bars, but far fewer pixels are used to do so as compared to the non-enhanced DVD. So now the resolution of the actual film frame is just about 720 x 480 for a "Flat (1.85:1) film and 720 x 380 for a "scope" (2.35:1) film. Contrast those resolutions with the corresponding ones for a letterbox presentation (720 x 330 for flat and 720 x 270 for scope) and you can appreciate the benefits of these DVDs coupled with 16:9 televisions.
So, how is it these discs don't get "squished" in on the sides, when watching them on regular 4:3 TVs, like those rare laserdiscs? Thats where it gets interesting! True, if left untouched, the image would have that distorted look. But, when you set your DVD player for a 4:3 screen, and it plays a 16:9 enhanced signal, it actually shrinks the image down, on the fly, and then adds black bars, top and bottom, all by itself. The actual resolution of the image we end up with is no better or worse than if it were a classic letterbox presentation. The wonderful thing is that we can have the one disc accommodate both old 4:3 TVs and new 16:9 TVs. So, even if you have a 4:3 TV today, you should still want to see more 16:9 enhanced material, because later, when you get a 16:9 TV (and someday you will), you can pull out all your 16:9 enhanced movies and see them with even more detail and resolution than before! (Progressive Scanning is another capability of DVDs and their players, but we will talk about that in a later article.)
- Brian Florian -
(Last Updated - 4/10/2001)
The ability of a DVD player to squeeze down a 16:9 enhanced image for a 4:3 TV is something that is coming under more and more scrutiny. It has been demonstrated that there is a noticeable difference between very high tech players and mass market units in their ability to maintain original quality when doing this.
Although a DVD contains 720 x 480 pixels in a digital sense, numerous technical factors substantially limit the number of actual pixels that show up on your TV.
In the case of non-16:9 enhanced presentations, 16:9 TVs can zoom the image so that it is as large as can be, overscanning some or all of the black bars. They do not gain back any resolution in doing so, but it does maximize the physical size of the image shown.
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