World's Easiest Explanation of Anamorphic 16:9 WidescreenEnhancement in DVDs
Some DVDs are made in a special way that makes most letterboxedmovies 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 asit 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 thetop and bottom. The thickness of the bars depends on the width of the movie. Most moviestoday are 1.85 times as wide as tall, or 1.85:1. Many are wider, at 2.35:1. The widestpopular American movie was Ben-Hur (1959) at 2.76:1. Another popular width is1.66:1. Here's how they look on a standard television. The red squares are just forreference; 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 a2.35:1 movie is Star Wars. You might notice that the black bars are a littlenarrower on your television. That's due to overscan. If you see noblack 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'reshaped like this:
If you watch a letterboxed movie on it, you'll see grey bars on the sides as well asthe black bars on top and bottom, like this:
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%, 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 blackbars, it would be convenient if there was a way to take advantage of that storage area. Infact, there is a way to use some of it for the image. Anamorphic DVDs use 33% more of thestorage area for the image, by stretching the image vertically by 33%. As stored on theDVD, it looks like this:
Of course, you wouldn't want to view it stretched like that. When viewed on awidescreen television or on a computer screen, the image is again stretched 33% -- thistime 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 theincrease 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 increasein resolution is only 33%. The picture is 78% larger and looks 33% better than on astandard television.
But what if you want to view it on a standard television? You wouldn't want to see thevertically stretched image; everything would look tall and thin, like the red square inthe stretched picture.
DVD players are designed to squeeze the image back down to normal for standardtelevision sets. They use weighted averages to combine lines, scaling the image back downby 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 jobthan 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 scalingcompletely even on standard televisions; see The VerticalSqueeze Trick.
Standard televisions are already appearing that have a switch to squeeze the picturevertically by 25% without losing any resolution; the exact amount necessary to enjoyanamorphic DVDs at full resolution. The resulting picture is the same size as it wouldhave been after scaling; the only difference is the higher resolution. Like widescreentelevisions, standard televisions with this feature could be designed to automaticallydetect whether content is anamorphic and avoid squeezing non-anamorphic content. Since itcosts little to add this 25% "Vertical Squeeze" feature, within a few years itshould be common. In effect, it is like having a widescreen television of the samehorizontal width (but smaller diagonal measurement, of course).
How does your DVD player know whether to scale the image for a standard television, orto use the larger image for a widescreen television? Because your DVD player has a settingin 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 moviein 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 haveadditional 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 havemuch 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 tohow 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 usesup. 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 ina 4:3 image. Studios can't store additional pixels per frame on the disc because DVDplayers wouldn't understand. And for the same reason, they can't rearrange the pixels intoa wider image.
What about movies made at a narrower width than 1.78:1, the width of widescreentelevision 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 BeforeChristmas.
Can we gain some resolution from 1.66:1 movies? Unfortunately, there is a problem withthat first step of vertically stretching the image by 33%, then storing the stretchedimage on the DVD. If you stretch a 1.66:1 image vertically by 33%, it would be 6 1/4% tootall 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 bluebars in the picture above). That might make sense for some movies, but purists wouldn't bethrilled.
Can't it be stretched by only 25%, instead of 33%, so that it will exactly fit, likethis?
Sure, studios could do that, but you wouldn't want them to, because no DVD playerswould know how to stretch it horizontally by only 25%. Instead, players would stretch itby the usual 33%, resulting in an image like this, stretched too wide (the red square is alittle wider than tall in this picture):
Unfortunately, there just isn't any way to get the usual 33% improvement withoutcropping the image. However, there is a way to get an 18% improvementwhile retaining the entire image. The movie can be shrunk 6 1/4%, then"sideboxed" within vertical black bars on the left & right sides, thenstretched vertically 33%. Here's what it looks like as stored on the DVD:
That works great for widescreen televisions, standard televisions with a 25% verticalsqueeze 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 looklike 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'tknow how to discard the vertical black bars, and DVD players don't know how to discardthem either. You get an 11% smaller (100% / 1.0625 / 1.0625) image -- and 11% lowerresolution -- than a non-anamorphic letterboxed transfer. Here's what it would look likeon a standard television:
It would look the same on a standard television with a vertical squeeze feature, exceptwith the 18% higher resolution.
Studios are understandably more interested in selling a product that works 11% betterfor 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 standardtelevisions with vertical squeeze have become more common than standard televisionswithout vertical squeeze.
On the bright side, most television sets have enough overscanthat the vertical black bars are hidden anyway, so most viewers on a standard televisionwouldn't know they were getting a smaller picture and less resolution. An advantage isthat it would partially compensate for overscan, allowing them to see more of the picture.In fact, "windowboxing" -- shrinking the image and surrounding it with blackbars on all 4 sides -- is often used for movies that make so much use of the outer edgesof the frame that overscan ruins the effect. This is often the case with films from theearliest years of cinema.
Of course, studios could crop tiny slivers -- 1% or so -- from the top and bottom, toget better resolution for both standard and widescreen televisions (because the imagewould 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 get18% more resolution on computer screens and widescreen television sets, perhaps morestudios 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 1.66:1anamorphic is possible, so each consumer who writes to studios about it should take careto explain how it is possible with sideboxing, and how resolution would still be increasedby 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 studiosprobably won't until widescreen television sets are much more common than they are at thetime of this writing in January 1999, unless enough people complain to studios that theywant them anamorphic now.
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 itbe the same width as the movie, losing no resolution at all to storing black bars? Due tothe higher resolution of most computer screens, you'd get all that resolution even if youmaximize the window (you'd still get black bars, but they'd be added by the software, notstored on the disc).
Well, why not just amend the DVD standard to allow for stretching the image by anypercentage (not just 33%)? Players would then be designed to add black bars of theappropriate 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 tothe 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 standardanamorphic, a lot of programming code was written to scale every 4 horizontal lines downinto 3. To get adjustable anamorphic, separate programming code would have to be writtenfor every possibility. Since the very widest movies are about 2.8:1, all possiblecombinations 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:
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 towrite all that programming code.
However, there is a good way to reclaim most of the wasted space on 2.35:1movies. 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% ofthe 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 squeezefeature, no scaling would need to be done, increasing resolution by 67%. For standardtelevisions that have a 25% vertical squeeze feature designed for 16:9 anamorphic, itwould scale every 5 lines into 4, the television would squeeze the result 25%, and youwould still get 33% better resolution.
To view it on a widescreen television, every 5 lines are scaled into 4, and then it'sstretched sideways 33%. Here's how it would look on a widescreen television:
Or, if the widescreen television is designed with a 20% vertical squeezefeature, 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 thantoday's anamorphic DVDs, and you could enjoy that extra resolution on both standard andwidescreen televisions.
Unfortunately, 20:9 anamorphic would be incompatible with existing DVD players, sincethe DVD standard doesn't recognize it -- 20:9 anamorphic discs would play, but would besqueezed. Studios would be reluctant to sell discs that won't play correctly in mostplayers. Although in many cases there would be enough room on the DVD to store bothstandard anamorphic and 20:9 anamorphic versions (as well as a pan & scan version) ondouble-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-resolutionDVD, called DVD-HD, is due around 2003, perhaps earlier. DVD-HD discs will be incompatiblewith today's DVD players, though DVD-HD players will play today's DVDs. Since DVD-HD willrequire new players anyway, that would be a great opportunity to add 20:9 anamorphic tothe standard. Who knows, maybe someday that might even lead to 20:9 television sets. Let'shope the industry players decide to make DVD-HD 20:9 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 apoint. But it's useful to refer to this kind of DVD as "anamorphic", becausethat is the widely recognized and accepted term, and is considered proper by almost allindustry 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 justone-dimensional points defined by their color and by their location in the grid of pixelsthat make up the image. They only become two-dimensional, gaining height and width, whenthey are displayed. A television simply displays the whole grid of pixels, soeach pixel's height is simply the television's height divided by the number of horizontalrows of pixels in the image, and each pixel's width is the television's width divided bythe number of vertical columns of pixels in the image. The software used to display a DVDon a computer screen knows that a 1.33:1 (or 1.78:1, if anamorphic) display area isexpected, 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 nor1.78:1. Instead, it would be exactly 1.5:1 -- 480 pixels by 720 pixels. So, a non-anamorphicimage, as stored on the DVD, can be considered to be actually stretched sideways a littlebit, if the pixels were square. But that's a moot point, because the pixels were neverintended to be displayed square.
the word was used before..............
[this section to be continued]
If you view Anamorphic DVDs on a standard 4x3 television set, in most cases you canstill get the extra resolution with a technique known as "The Vertical SqueezeTrick". For easy instructions on how to do it, see my VerticalSqueeze Trick page.
Additional discussions of and information about anamorphic DVDs are at:
Feedback from the following people resulted inimprovements to this page:
This page has been translated intoFrench.
Copyright �1999 by Greg Lovern.All rights reserved. No part of this document may be reproduced or used in any form or byany means -- graphic, electronic or mechanical, without written permission from theauthor.
Although 20 divided by 9 is a little over 2.22, the specification is actually 2.21. Ifsomeone can explain to me how the MPEG2 specification for 20:9 is really 2.21 rather than2.22, it would be much appreciated.
Most movies made since the mid-1950's are wider than a standard television set. While astandard television set is 1.33 times as wide as it is tall, or 1.33:1, most movies madetoday 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 canblock off the top and bottom strips of film to get the wider format. This technique iscalled "Hard Matte". More frequently, they frame their shots for widescreen butinclude the extra film negative at the top and bottom, simply making sure to exclude suchdistractions as microphones, edges of sets, stagehands lying on the floor holding upprops, etc. This is called "Soft Matte". When shown in theaters, theprojectionist mattes the film, blocking off the extra portions at the top and bottom. Whenshown on television, the extra strips of film at top and bottom can be shown. This iscalled "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 are2.35:1, and these most often use a special lens that squeezes the wide image horizontallyto fit on the more squarish film frame. Then, the projector has a special lens that doesjust the opposite -- widens the squarish image to it's original width. The advantage ofthis technique is that more film is used to store the image, and as a result the image hasmore resolution -- so it's more clear and detailed.
When making a home video edition of movies that were not made using the "SoftMatte" technique, studios must choose between chopping off the sides, moving back andforth to keep the main action in view (called "pan & scan"), or leavingblank horizontal bars at the top and bottom of the image (called"letterboxing"). Most movies made today are 39% wider than a television set, andmany are 74% wider. The best directors tend to make full use of the wide screen, and thebest cinematographers compose the image with great care and aesthetic sensibility. As aresult of cutting off visual information from the sides, some scenes in the Pan & Scanversion of some movies are boring or don't even make sense. More often, they are just lessinteresting and/or less beautiful.
When making a home video edition of movies that were made using the "SoftMatte" technique, studios simply have to choose whether to include the extra (OpenMatte), or not (matted). Open Matte sacrifices compositional integrity, but is certainlypreferable to Pan & Scan.
In some cases, it's a mixture of Pan & Scan and Open Matte -- some extraneousmaterial 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 carefullyin widescreen, then cropped for the Pan & Scan version, while the other shots addextraneous material to the top and bottom.
To avoid confusion, both Pan & Scan and Open Matte versions, as well as films neverintended to be widescreen, are often called "Full Frame" or "StandardFormat".
I have tried to keep the discussion of letterboxing on this page to a minimum. If youwould like more information, an excellent place to start is Henrik Herranen's How Film is Transferred toVideo.
Most television sets magnify the image a little too much, cutting off a little from allfour sides. Some cut off as much as 20% of the total image. Trained television technicianscan usually fix overscan.
