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June 28, 2000. The HDTV spec mandates a 16:9 frame. This is approximately the same shape as the 1.85:1 films common for many modern films. But it's significantly wider (more rectangular) than the older academy ratio films which are basically the same squarish shape of NTSC television.
This makes HDTV great for many modern movies, which fit the screen naturally. But things get more complicated when trying to fit old fashioned 4:3 images or modern 2.35:1 films, which are even wider than the 16:9 shape of HDTV. The common solution, if preserving the original aspect ratio of the material is the goal, is to fit the image into the screen without distortion or cropping and then mask the leftover area with black. This is no different that the concept of "letterboxing" widescreen movies to fit them into the standard 4:3 shaped television frame of NTSC.
To fit a 1.33:1 (conventional 4:3 shaped image, like the Wizard of Oz) into a 16:9 frame, vertical letterboxing or windowboxing bars are "hard coded" into the 16:9 image. Wider-than-16:9 2.35:1 films are horizontally letterboxed in the 16:9 frame the same way widescreen movies are often letterboxed in a 4:3 frame.
So what's wrong with this? After all, don't we want to preserve the original aspect ratio of all films, especially those transferred to High Definition mediums? Of course we do. But the dark side of letterboxing is that every pixel that gets used to record the letterboxing bar is one less pixel that can be used to record real picture information. In some cases, up to 1/3 (or more) of the available pixels may be wasted on recording the static black masking bars!
This wasted resolution may be an even more important loss for High Definition transfers: Nobody ever thought that a Standard Definition digital master, which is created and intended for NTSC displays, could be considered an "archival" digital master capable of preserving the film beyond the life-span of the original film elements. On the other hand, High Definition transfers are very often considered exactly that way. Most of our films are eventually going to be archived as digital High Definition transfers. In many cases, the film elements are either so deteriorated or expensive to maintain that the HD master made from them may be the only (and last) chance to preserve the film. These digital transfers should therefore utilize the maximum resolution possible within the High Definition specification. That means, among other things (such as 1080P encoding), not wasting pixels on black bars if you don't have to.
DVD allowed for a nice advantage in that it could be encoded for two aspect ratios: 4:3 and 16:9. 1:33 films can be encoded with the 4:3 aspect ratio, and widescreen films (although 2.35:1 films still require moderate letterboxing) can be encoded with the 16:9 aspect ratio. This means that both 4:3 full-frame and widescreen films could achieve the best resolution of the 480-by-720 frame a DVD can store. That's a win-win. Had DVD incorporated MPEG2s option for 20:9 aspect ratio encoding (which I'll talk more about in a moment), even 2.35: films would have received the red carpet!
HDTV is taking a step backwards. If we don't want our widescreen films to lose potential resolution by being recorded as horizontally letterboxed images in a 4:3 frame on DVD, why would we want 1.33:1 transfers to loose resolution by being recorded as vertically letterboxed images in a 16:9 frame in High Definition?
While we're making sure that 4:3 aspect ratio material gets the most it can from HD's pixel potential, how about films wider than 1.85:1? I'd like to see the HDTV format used for archiving films allow for multiple aspect ratios...to maximize resolution for images narrower and wider than 16:9 (1.78:1) in shape. 20:9 encoding, which is already part of the MPEG2 spec, would increase the resolution of 2.35:1 films over letterboxing them in a 16:9 frame the same degree that 16:9 encoding 1.85:1 films increases resolution over letterboxing in a 4:3 frame. For those of you who can appreciate the improvement that 16:9 (anamorphic) encoding of DVD offers over 4:3 letterboxing, just imagine that same gain doubled for 2.35:1 films! Already "High Definition" digital projections in theaters are using this concept to digitally encode and project 2.35:1 films using the full vertical resolution of the 1080 vertical lines, so it's obviously enough resolution to make a difference.
How It Relates To The Studios...
It is my hope that studios preparing High Definition masters of 4:3 source material would master anamorphically (wide), utilizing full horizontal resolution for the image. If these archival masters then have to then be downconverted to hard-coded "windowboxed" images for broadcasting in the meantime, that would be tolerable. But for all the energy, expense, and technical wizardry that goes into film restoration and High Definition archival preparation, it would be a serious shame if the digital High Definition master that ultimately may serve as the best surviving incarnation of The Wizard of Oz discards 1/3 of its potential resolution right from the beginning.
For those of you who think the studios are smart enough and care enough about films to figure this out on their own—think again. When Fox spent LOTS of money restoring The Sound Of Music a few years back for laserdisc, they didn't have the foresight to do a 16:9 master along side the 4:3 letterboxed master used for laserdisc, despite the fact that other studios were beginning to do just that. Criterion went through incredible care to (only) prepare 4:3 letterboxed masters for many of the films they were releasing even AFTER DVD—with its 16:9 capability—was a reality!
How It Relates To Home Theater and You, The Consumer...
HDTVs could easily be designed to display 4:3 HD images in native form, the same way that they offer a mode for viewing 4:3 NTSC and SD images.
Many current High Definition projectors could easily be configured to make use of a 4:3 encoded High Definition images for 1.33:1 OAR films as well as 20:9 encoded High Definition images for 2.35:1 films. The resolution gain of 20:9 encoding would be especially helpful for large-screen front projection systems, many of which "zoom in" 2.35:1 films (while widening the screen) so that all images, regardless of aspect ratio, maintain a constant height as they do in a real theater.
For display systems that aren't 4:3 HD or 20:9 HD compatible, HD-DVD players could downconvert these images to 16:9 the same way that today's DVD players downconvert 16:9 material to 4:3. Why compromise the source, especially if it's the only HD for playback and display on obsolete technology that will be replaced with better and cheaper technology month by month?
The only danger I see by providing a 4:3 HDTV option is the possibility that some studios would encode widescreen films as 4:3 Pan-and-Scan full frame High Definition images. Or (worse?) encode them as 4:3 letterboxed High Definition 4:3 images that then need to be "zoomed" to fill the screen! Sounds crazy, but I can see a few (can you guess the names?) studios doing it.