Tutorials

Historical Note

This page was written back in 2004. A lot of things have changed since then; CRTs have pretty much gone away, DVD authoring suites have gotten smarter, Artisan Entertainment has long since gone out of business, and DVDs themselves have pretty much fallen by the wayside anyway thanks to digital distribution and various high-definition formats (most of which ONLY support 16:9 to begin with). Some of the issues are still valid, but not really worth worrying about anymore. So, keep that in mind.

Also, looking back there was one major inaccuracy even at the time, regarding how progressive scan works. While DVDs support 480p24, almost all DVDs are encoded at 480i60, so really, all DVDs would be subject to the "interlace" blur, including 16:9 ones.

My new summary would really be: encode your video at the resolution and aspect best-matching the original source material.

Anamorphic DVDs and You

When encoding a DVD with wide-screen content, always encode at 16:9 aspect.

When purchasing a DVD with wide-screen content, make sure that it was encoded at 16:9 aspect (usually there will be something on the back saying "enhanced for wide-screen TVs" or the horribly imprecise "presented in anamorphic format").

Introduction

As both an avid consumer of movies and someone who occasionally dabbles in the odd video project, I have an interest in maximizing the image quality of various video formats. One subject which seems to cause much trouble to various purveyors of DVDs is how to encode widescreen (i.e. 16:9 or wider) content.

Far too many DVDs I've purchased (notably ones produced by Artisan) are encoded at 4:3 aspect, which is the aspect ratio of a traditional television set. (The aspect ratio, if you don't know, is the ratio of the width of an image to its height. So, a 4:3 ratio means that if a television set is 400cm wide, it will be 300cm tall. A 4:3 ratio is also written as 1.33:1, and 16:9 is also commonly written as 1.77:1.)

Most movies are wider than 1.77:1; the most common formats seen in movie theatres today are "flat" (1.85:1) or "scope" (2.35:1). Obviously, when a movie is brought to the home, it must be made to fit on a television screen, and the preferred method for this is letterboxing, where black bars are put at the top and bottom to make the displayed aspect the same on the television as on the original projected film. (This is for widescreen editions; fullscreen editions are simply cropped to 4:3, which is an entirely different matter which has already been explored at great length by many other websites.)

DVD Aspects

When the DVD format was established, it was based around the MPEG-2 video format. As DVDs were designed specifically for output to a television set, the designers decided to limit the number of ways the video could be represented.

The first limit is that the resolution of the image is fixed at 720x480.

The second limit is that there are only two image aspects supported - 4:3 and 16:9.

One thing you might notice is that a 720x480 resolution is neither a 4:3 nor 16:9 ratio. The pixels as stored on a DVD are not square, like on a computer monitor (technically they're not square on most computer monitors either, but they're close enough for most people). Instead, they're slightly narrower than they are tall — which makes perfect sense on a television, because although the vertical resolution is fixed, the horizontal resolution can be pushed a bit further by cramming pixels closer together. Televisions don't actually have a fixed horizontal resolution. (Obviously this only applies to CRTs, and not LCD or plasma displays, but I'll get into that later.)

So, we need to make a few adjustments to account for this in order to show visually the effects of different aspects.

Effective Resolutions

Because the pixels on a monitor are square and we want to display the effects of resampling in a fair manner, we only want to scale the final images up in size. So first we need to decide what we'll be displaying.

To bring 720x480 to a 4:3 resolution, we would resample it to 720x540 (3*720/4).

However, to bring a 720x480 image to a 16:9 resolution, we would resample it to 853x480 (16*480/9).

Because we're focusing on formats wider than 16:9, we'll go with the effective screen resolution of 16:9 - 853 pixels wide.

So, now that we've decided on our width, how about the height?

Because we have to letterbox no matter what, let's go with the most extreme example in common usage - 2.35:1. Many films of a very visual nature use this aspect ratio, because it provides the viewers with a grand, sweeping vista. So, movies which are the most likely to be affected by poor choices in encoded formats will probably be in 2.35:1 aspect.

If a 16:9 aspect image has 480 lines of resolution, then in that same format, a 2.35:1 image will have 363 lines of resolution (480*1.77/2.35).

So, we'll use 853x363 as the "common ground" to display our images at.

Stock image

Assuming that we could put the most pristine quality of image onto the screen at our effective resolution, we would get something which looks like this:

This image was taken by scanning a color slide at 1200dpi, cropping it to 1500x638, then scaling it to 853x363. It represents the platonic gold standard for the image quality we could get at that size.

16:9 Encoding

When we encode the image to 16:9 format, we essentially reduce it in size to 720x363, and then when the DVD player displays it on the screen it scales it back up to our screen resolution. If we're on a wide-screen TV, then we still have the full 480 lines of DVD resolution (meaning the full 363 lines of effective resolution), and the image is stretched horizontally, so it looks something like this, created by taking our 1500x638 image, scaling it down to 720x363, then scaling up to 853x363:

Although there is a very slight drop in horizontal resolution (about 15%), it's not enough to be important to the human eye. (Of course, compared to the original film stock it can be quite a bit of difference, but we're comparing apples to apples here.)

4:3 Encoding

But what if we encode the DVD at 4:3? When it's put into the DVD frame, it must be reduced to a mere 271 (480*1.33/2.35) lines of resolution - we have just lost 25% of our vertical resolution! This image was created by scaling the original 1500x638 image down to 720x271, then up to 853x363:

We can start to see a little bit of loss of quality at this level. But it gets worse.

With modern DVD players and televisions, if you have a 16:9 DVD displayed at 16:9 aspect (either on a widescreen TV, or on one of the 4:3 TVs which supports 16:9 sources), it usually uses progressive scan, which gives you the full vertical resolution. However, on many of these televisions, if the source is 4:3 format, then it only supports interlaced format, which essentially halves the vertical resolution, so you end up with something like this:

At this point, much of the detail is visibly lost. In a highly-visual film, this can make the difference between enjoying the filmed splendor and constantly squinting (you're probably really tempted to squint just looking at that picture right now), trying to make out detail which isn't there.

Degradation

This is the "ideal," the 16:9 resolution, the 4:3 progressive scan resolution, and the effective 4:3 interlaced resolution, side-by-side for your direct comparison:

So what?

Unless you're a connoisseur of film, you might not think that this is that big a deal. After all, don't movies, well, move? Why bother spending a lot of time focusing on the little details?

Well, this is exactly part of the problem of it being so coarse. Moving video doesn't get even close to the same amount of resolution as these still images — there will be one frame of this level of quality, and then a number of frames which are displayed by modifying the previous frame. So if there's less source material to work with in one frame, then the quality of all of the other frames will become much worse. Even if you're using a conventional 4:3 television, this can make a huge difference in the resulting visual quality — and the lower quality will cause a feeling of it being out-of-focus, causing you to squint, causing you to not appreciate the movie as much at a conscious level because it's "harder to watch."

Also, if you're watching a movie on your computer, most (good) DVD player programs will scale the image of a 16:9 DVD up to monitor resolution (i.e. 853x480) rather than scaling it down, giving you the full effective resolution of 853x363. However, if the DVD is encoded at 4:3, then it will be scaled to 720x540, with the effective resolution of 720x271 scaled up to 720x304.

Essentially, a 2.35:1 film has an encoded resolution of 720x363 at 16:9, but only 720x271 at 4:3 - a 25% difference in quality. (It is always a 25% difference regardless of the source material's aspect, in fact, but on a 2.35:1 film this becomes all the more important. This still applies to 16:9 or 1.85:1 as well though.)

But what about films shot in 4:3?

A number of directors actually shoot their films in 4:3 but compose them to work in both 4:3 and 1.85:1 for theatre projection, meaning that for the home DVD release it's just cropped to 4:3 or 16:9 with no letterboxing and that's the end of it. As a result, some directors (notably James Cameron) actually prefer the 4:3 version of the film because it presents more of the "artistic vision." On the other hand, Stanley Kubrick also shot in 4:3, but he only composed for 1.85:1 — essentially he didn't mask the frame out until later, but didn't intend for any of his films to be presented in 4:3. Regrettably, some of his films such as 2001 were shot in 4:3, cropped to 1.85:1, then re-cropped again for the 4:3 pan-and-scan presentation!

In any case, for movies shot in 4:3, you'd expect a 4:3 fullscreen DVD to be better quality since it encompasses more of the original image, right?

Well, that depends. If you're watching the 4:3 DVD on a 4:3 screen which is incapable of using the full 480 lines of a 16:9 encode, then you probably do want the fullscreen edition.

But if you ever move to a higher-definition display which accepts 16:9 input (or a computer or whatever), then the exact same quality loss occurs for the 4:3 display, for the exact same reasons.

Basically, if you display a fullscreen 4:3 image as 16:9 by just cropping the top and bottom of the image off, then you're getting a resolution of 720x360 - because the top and bottom 60 lines are being cropped. However, if the image is already cropped to a 16:9 aspect, you still get the full resolution of 720x480, which is 33% sharper.

Since the movie is already formatted so that nothing important is lost when it's cropped, you're not losing any important visual information by getting it pre-cropped for widescreen, but you're getting a much sharper image. Even on a 4:3 display it'll still be sharper because of the intra-frame motion issues described above.

So, basically, any content which can be encoded at 16:9 should be encoded at 16:9, in order to preserve as much of the original clarity as possible.

Side-topic: Format fandango

Currently, most televisions only accept some form of NTSC or PAL signal (whether it's composite, s-video, or component). NTSC is fixed at a 4:3 aspect — the way that most 16:9-capable televisions get a 16:9 image out of it is to simply squish the image down (which is why when you see wide-screen TVs at pretty much any television store, everyone looks like they've put on a lot of weight). Currently it's up to the TV operator to set up the DVD player and television set for the correct aspect ratios on a per-DVD basis.

Fortunately, higher-end equipment is starting to use DVI connections, which both gives a cleaner signal and allows the DVD player and/or TV to upsample everything to a native high-resolution format. So if a DVD player gets a 16:9 DVD, it can go, "Hey, TV! This image is 1920x1080 interlaced" and the TV happily switches to whichever mode is most suitable for that size - going to letterbox if it's 4:3, or fullscreen if it's 16:9. (Also, the TV can tell the DVD player what its supported resolutions are, so no more autoconfiguration.) Alternatively, for a 4:3 DVD on a 16:9 screen, the TV will put on sidebars.

Unfortunately, this also means that if you have an inappropriately 4:3 DVD (such as, say, the Artisan release of Oliver Stone's The Doors which is an extremely visual 2.35:1 film and is the reason I decided to create this page to begin with), the DVD player, not knowing any better, goes, "Hey, TV! This is a 1280x960 progressive-scan image!" and the TV goes "Okay" and puts on sidebars, shrinking the image down to unusable sizes. Meaning that the TV operator needs to override it and tell the TV (or DVD player) to crop it to 16:9 instead of keeping the full 4:3 frame. On a per-DVD basis. Making all of this progress moot, while still destroying the image quality.

So, please, use forward thinking and encode your wide-format DVD streams at 16:9. Thank you.