Some DVDs are made in a special way that makes most letterboxed 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.

First, here's the shape of a 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 a letterboxed 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 is 1.66:1. Here's how they look on a standard television. The red squares are just for reference; they'll come in handy later on:

1.66:1	1.85:1	2.35:1	2.76:1

For this example, I'll use the widest common movie width -- 2.35:1. An example of a 2.35:1 movie is Star Wars. You might notice that the black bars are a little narrower on your television. That's due to overscan. If you see no black bars at all on Star Wars, you're probably viewing a Pan & Scan version.

Widescreen television sets are already available and will soon replace 4:3 sets. Widescreen televisions are about 1.78 times as wide as they are tall, or 16:9. They're shaped like this:

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, like this:

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

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%. As stored on the DVD, it looks like this:

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%. On a standard television, it would once again look like this:

Of course, the scaled picture isn't quite perfect, and some DVD players do a better job than others. But in most cases it's very good, and the technology continues to improve. The DVD player that is generally considered to do the best scaling (often called "down-conversion") is the Sony DVP-S7700. But you can often avoid the scaling completely even on standard televisions; see The Vertical Squeeze Trick.

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 16:9 window. 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 televsion.

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.

1.66:1 Movies

What about movies made at a narrower width than 1.78:1, the width of widescreen television sets? For example, many movies are made at 1.66:1, like this:

A popular example of a 1.66:1 movie is Tim Burton's animated The Nightmare Before Christmas.

Can we gain some resolution from 1.66:1 movies? Unfortunately, there is a problem with that first step of vertically stretching the image by 33%, then storing the stretched image on the DVD. If you stretch a 1.66:1 image vertically by 33%, it would be 6 1/4% too tall to be stored on the disc:

3 1/8% would have to be cut off of the top, and 3 1/8% from the bottom (the light blue bars in the picture above). That might make sense for some movies, but purists wouldn't be thrilled.

Can't it be stretched by only 25%, instead of 33%, so that it will exactly fit, like this?

Sure, studios could do that, but you wouldn't want them to, because no DVD players would know how to stretch it horizontally by only 25%. Instead, players would stretch it by the usual 33%, resulting in an image like this, stretched too wide (the red square is a little wider than tall in this picture):

Unfortunately, there just isn't any way to get the usual 33% improvement without cropping the image. However, there is a way to get an 18% improvement while retaining the entire image. The movie can be shrunk 6 1/4%, then "sideboxed" within vertical black bars on the left & right sides, then stretched vertically 33%. Here's what it looks like as stored on the DVD:

That works great for widescreen televisions, standard televisions with a 25% vertical squeeze feature, and computer screens. Shrinking the image reduces resolution by 6 1/4% horizontally and 6 1/4% vertically, and stretching the image anamorphicaly adds back 33% vertical resolution. You get an 18% increase in overall resolution (1.3333 / 1.0625 / 1.0625). On a widescreen television, it fills the screen vertically.

On a widescreen television or computer screen, the image is 57% larger (1.3333 x 1.3333 / 1.0625 / 1.0625) than non-anamorphic, and looks 18% better. Here's what it would look like on a widescreen television or computer screen:

An example of a 1.66:1 anamorphic DVD is Damage, directed by Louis Malle.

But what about standard television sets without a vertical squeeze feature? They don't know how to discard the vertical black bars, and DVD players don't know how to discard them either. You get an 11% smaller (100% / 1.0625 / 1.0625) image -- and 11% lower resolution -- than a non-anamorphic letterboxed transfer. Here's what it would look like on a standard television:

It would look the same on a standard television with a vertical squeeze feature, except with the 18% higher resolution.

Studios are understandably more interested in selling a product that works 11% better for the majority of the market than 18% better for those with widescreen televisions. Perhaps we'll see more 1.66:1 anamorphic movies after widescreen televisions and standard televisions with vertical squeeze have become more common than standard televisions without vertical squeeze.

On the bright side, most television sets have enough overscan that the vertical black bars are hidden anyway, so most viewers on a standard television wouldn't know they were getting a smaller picture and less resolution. An advantage is that it would partially compensate for overscan, allowing them to see more of the picture. In fact, "windowboxing" -- shrinking the image and surrounding it with black bars on all 4 sides -- is often used for movies that make so much use of the outer edges of the frame that overscan ruins the effect. This is often the case with films from the earliest years of cinema.

Of course, studios could crop tiny slivers -- 1% or so -- from the top and bottom, to get better resolution for both standard and widescreen televisions (because the image would not have to be shrunk as much to allow the vertically stretched image to fit).

If enough consumers tell studios they want 1.66:1 movies in sideboxed anamorphic to get 18% more resolution on computer screens and widescreen television sets, perhaps more studios can be persuaded. Eventually, everyone will have a widescreen television anyway, or standard televisions with a vertical squeeze switch.

Unfortunately, some studio decision-makers don't seem to understand that 1.66:1 anamorphic is possible, so each consumer who writes to studios about it should take care to explain how it is possible with sideboxing, and how resolution would still be increased by 18% even after sideboxing, and refer to Damage as an example.

So, although it's possible to make an anamorphic DVD of a 1.66:1 movie, most studios probably won't until widescreen television sets are much more common than they are at the time of this writing in January 1999, unless enough people complain to studios that they want them anamorphic now.

Adjustable Anamorphic?

Even on anamorphic discs, some space is still wasted on black bars. No television set -- either standard or widescreen -- would be able to take advantage of that space anyway, but your computer can. Since a window on a computer screen can be any width, why can't it be the same width as the movie, losing no resolution at all to storing black bars? Due to the higher resolution of most computer screens, you'd get all that resolution even if you maximize the window (you'd still get black bars, but they'd be added by the software, not stored on the disc).

Well, why not just amend the DVD standard to allow for stretching the image by any percentage (not just 33%)? Players would then be designed to add black bars of the appropriate thickness, and scale down the image if necessary by the appropriate percentage (not just by 33%), and computer software would be designed to adjust the window's width to the movie. For lack of a better term, I'll call this hypothetical DVD standard amendment "adjustable anamorphic".

Unfortunately, adjustable anamorphic would be very difficult to implement. For standard anamorphic, a lot of programming code was written to scale every 4 horizontal lines down into 3. To get adjustable anamorphic, separate programming code would have to be written for every possibility. Since the very widest movies are about 2.8:1, all possible combinations in which the resulting number of horizontal lines was more than about 35.7% of the number of source horizontal lines would have to be programmed. That would be:

• 2 lines scaled down into 1
• 3 lines scaled down into 2
• 4 lines scaled down into 3 (already done for standard anamorphic)
• 5 lines scaled down into 4, 3, and 2
• 6 lines scaled down into 5
• 7 lines scaled down into 6, 5, 4, and 3

And so on, all the way up to 480 lines scaled down into.....well, you get the idea. Since the payoff would be limited to computer screens, it wouldn't be cost-effective to write all that programming code.

20:9 Anamorphic

However, there is a good way to reclaim most of the wasted space on 2.35:1 movies. A standard already exists, and the code already written, to scale 5 lines into 4, and 5 lines into 3. By vertically stretching a 2.35:1 movie 67% instead of 33%, only 5% of the storage area is used to store black bars. This is called 20:9 anamorphic (20:9 Anamorphic is part of the "MPEG2" specification used by DVD). As stored on the DVD, it looks like this:

To view it on a standard television, every 5 lines are scaled into 3, like this:

Or, if the standard television is designed with a 40% vertical squeeze feature, no scaling would need to be done, increasing resolution by 67%. For standard televisions that have a 25% vertical squeeze feature designed for 16:9 anamorphic, it would scale every 5 lines into 4, the television would squeeze the result 25%, and you would still get 33% better resolution.

To view it on a widescreen television, every 5 lines are scaled into 4, and then it's stretched sideways 33%. Here's how it would look on a widescreen television:

Or, if the widescreen television is designed with a 20% vertical squeeze feature, no scaling would need to be done, increasing resolution by 25%.

To display it on a computer screen, it's simply stretched sideways 67%, like this:

What this means is that DVDs of 2.35:1 movies could be 25% higher resolution than today's anamorphic DVDs, and you could enjoy that extra resolution on both standard and widescreen televisions.

Unfortunately, 20:9 anamorphic would be incompatible with existing DVD players, since the DVD standard doesn't recognize it -- 20:9 anamorphic discs would play, but would be squeezed. Studios would be reluctant to sell discs that won't play correctly in most players. Although in many cases there would be enough room on the DVD to store both standard anamorphic and 20:9 anamorphic versions (as well as a pan & scan version) on double-sided, double-layered DVDs when they become available, it's expensive -- typically $50,000 - $100,000 -- to create the additional transfer.

So, 20:9 anamorphic probably won't happen for DVD. However, a new, higher-resolution DVD, called DVD-HD, is due around 2003, perhaps earlier. DVD-HD discs will be incompatible with today's DVD players, though DVD-HD players will play today's DVDs. Since DVD-HD will require new players anyway, that would be a great opportunity to add 20:9 anamorphic to the standard. Who knows, maybe someday that might even lead to 20:9 television sets. Let's hope the industry players decide to make DVD-HD 20:9 anamorphic!

No Such Thing As Anamorphic?

A few folks are fond of insisting that anamorphic DVDs are not really "anamorphic". It depends on how you define the word, and in a way they have a point. But it's useful to refer to this kind of DVD as "anamorphic", because that is the widely recognized and accepted term, and is considered proper by almost all industry insiders.

In this paper I've refered to the image stored on a DVD as having a width of 1.33:1, but that is actually an oversimplification that makes the concept easier to understand. Technically, pixels stored on a DVD do not have any defined width or height; they are just one-dimensional points defined by their color and by their location in the grid of pixels that make up the image. They only become two-dimensional, gaining height and width, when they are displayed. A television simply displays the whole grid of pixels, so each pixel's height is simply the television's height divided by the number of horizontal rows of pixels in the image, and each pixel's width is the television's width divided by the number of vertical columns of pixels in the image. The software used to display a DVD on a computer screen knows that a 1.33:1 (or 1.78:1, if anamorphic) display area is expected, so it displays the image in a window of that width.

If the pixels were displayed as exactly square, the image would be neither 1.33:1 nor 1.78:1. Instead, it would be exactly 1.5:1 -- 480 pixels by 720 pixels. So, a non-anamorphic image, as stored on the DVD, can be considered to be actually stretched sideways a little bit, if the pixels were square. But that's a moot point, because the pixels were never intended to be displayed square.

The Vertical Squeeze Trick

If you view Anamorphic DVDs on a standard 4x3 television set, in most cases you can still get the extra resolution with a technique known as "The Vertical Squeeze Trick". For easy instructions on how to do it, see my Vertical Squeeze Trick page.

Glossary

20:9 Anamorphic

Although 20 divided by 9 is a little over 2.22, the specification is actually 2.21. If someone can explain to me how the MPEG2 specification for 20:9 is really 2.21 rather than 2.22, it would be much appreciated.

Letterboxing, Pan & Scan, & Soft Matte

Most movies made since the mid-1950's are wider than a standard television set. While a standard television set is 1.33 times as wide as it is tall, or 1.33:1, most movies made today are 1.85:1. Many are 2.35:1. Very few are narrower than 1.66:1.

Most movies are shot on 35mm film, which is approximately 1.37:1. The filmmakers can block off the top and bottom strips of film to get the wider format. This technique is called "Hard Matte". More frequently, they frame their shots for widescreen but include the extra film negative at the top and bottom, simply making sure to exclude such distractions as microphones, edges of sets, stagehands lying on the floor holding up props, etc. This is called "Soft Matte". When shown in theaters, the projectionist mattes the film, blocking off the extra portions at the top and bottom. When shown on television, the extra strips of film at top and bottom can be shown. This is called "Open Matte". Of course, it can be matted for television, too. Often, both Open Matte and matted versions are made for television.

Soft Matte is not often used for films much wider than about 1.85:1. Many films are 2.35:1, and these most often use a special lens that squeezes the wide image horizontally to fit on the more squarish film frame. Then, the projector has a special lens that does just the opposite -- widens the squarish image to it's original width. The advantage of this technique is that more film is used to store the image, and as a result the image has more resolution -- so it's more clear and detailed.

When making a home video edition of movies that were not made using the "Soft Matte" technique, studios must choose between chopping off the sides, moving back and forth to keep the main action in view (called "pan & scan"), or leaving blank horizontal bars at the top and bottom of the image (called "letterboxing"). Most movies made today are 39% wider than a television set, and many are 74% wider. The best directors tend to make full use of the wide screen, and the best cinematographers compose the image with great care and aesthetic sensibility. As a result of cutting off visual information from the sides, some scenes in the Pan & Scan version of some movies are boring or don't even make sense. More often, they are just less interesting and/or less beautiful.

When making a home video edition of movies that were made using the "Soft Matte" technique, studios simply have to choose whether to include the extra (Open Matte), or not (matted). Open Matte sacrifices compositional integrity, but is certainly preferable to Pan & Scan.

In some cases, it's a mixture of Pan & Scan and Open Matte -- some extraneous material is added to the top and bottom, and some of the picture is cut off of the sides. Sometimes it varies within a given movie -- the special effects shots are framed carefully in widescreen, then cropped for the Pan & Scan version, while the other shots add extraneous material to the top and bottom.

To avoid confusion, both Pan & Scan and Open Matte versions, as well as films never intended to be widescreen, are often called "Full Frame" or "Standard Format".

I have tried to keep the discussion of letterboxing on this page to a minimum. If you would like more information, an excellent place to start is Henrik Herranen's How Film is Transferred to Video.

Overscan

Most television sets magnify the image a little too much, cutting off a little from all four sides. Some cut off as much as 20% of the total image. Trained television technicians can usually fix overscan.