Feature Article
1.66:1 Widescreen: Enhanced Versus Non-Enhanced
Introduction

1.66:1, one of the earliest "widescreen" formats, today remains one of the two most popular motion picture aspect ratios, the standard for European theatrical releases. The list of films formatted for 1.66:1 is extensive, and includes many classics of exceptional historical interest.

As is to be expected, the surging numbers of catalog titles released to the now-dominant DVD-Video format include many originally formatted using 1.66:1. With general practice in home video today being to format using Original Aspect Ratio (OAR) rather than the Modified Aspect Ratio (MAR) popular in the VHS era, more and more 1.66:1-formatted titles are reaching consumers letterboxed or pillarboxed to fit their video displays.

Coinciding with the growth of DVD-Video has been a sharp increase in the popularity of widescreen displays. These were originally marketed for use with the nascent HDTV systems, but the relative lack of HDTV programming up to now has meant that most are instead bought by those seeking enhanced DVD viewing. Because these sets can use more vertical resolution with letterboxed and pillarboxed transfers than their standard 4:3 counterparts, DVD-Video includes a provision for "enhancing" raw images to use vertical video information that would once have been wasted. This enhancement allows widescreen-ratio titles to display with sharply increased resolution on widescreen displays; however, with 1.66:1 titles (like all widescreen ratios less than 1.78:1), it can only be employed at the expense of both reduced resolution and wasted display area on traditional 4:3 sets. The wasted display area shows up in the form of "windowboxing," where black bars appear not only at the sides of the image, but at the top and bottom as well.

This problem can be averted by omitting enhancement, but only at the expense of display quality and ease-of-use on widescreen sets. When non-enhanced 1.66:1 is used with such sets, not only will the image be of lower resolution (about 16%, about half the drop with 1.78:1 and greater ratios), its proper formatting will, in most cases, present difficulties if the result is not to appear distorted or cropped.

This presents DVD labels with a quandary regarding their 1.66:1 product: enhanced or non-enhanced. The labels have split on the issue, with some releasing their 1.66:1 titles enhanced for widescreen displays, and others insisting on optimizing for 4:3.

Note: Although the solutions discussed in this article concern letterboxed and pillarboxed DVD, they also apply to 1.66:1 transfers on older formats like laserdisc and VHS.

Problems for Widescreen Displays

Why the fuss over the use of non-enhanced 1.66:1 material on widescreen displays? The fact that such transfers contain about 16% less resolution than their enhanced counterparts is one reason, but a more important one is that their proper exhibition on widescreen displays confounds some of the common solutions that work with other non-enhanced aspect ratios. If non-enhanced 1.66:1 is displayed using "4:3 letterboxed" mode, the image will be "windowboxed," with much of the display area wasted. "ZOOM" modes built into displays can scale the image to fill the screen, but often this functionality is poorly implemented, resulting in dreadfully inferior image quality. A "scaling" DVD player is available in the form of the Panasonic RP-91, but its "one-size-fits-all" scaling ratio is intended for use with aspect ratios of 1.78:1 or "wider," and it will crop the top and bottom of non-enhanced 1.66:1 (and, of course a scaling DVD player will not help at all with non-DVD formats like laserdisc). The only real option for many widescreen owners to thoroughly solve these problems is through the use of an external scaler, a solution that many non-technophiles find daunting.

To illustrate these points, below are four 1.78:1 renderings of the same 1.66:1 image taken from Anchor Bay Entertainment's non-enhanced DVD release of Return of the Blind Dead, each using a different technique: The first is the native 1.78:1, or FULL mode, which is non-proportional (due to horizontal stretching); the second is plain windowboxed 4:3, which is proportional, but wastes considerable display area; the third is a typical "ZOOM" rendering that scales the image so that it fills the screen (the slim black bars at the side are part of the original image), but crops it at the top and bottom; and the fourth uses scaling to pillarbox the image into the wider screen to fill as much of it as possible without cropping.

Return of the Blind Dead appears courtesy of Anchor Bay Entertainment

Native widescreen (FULL mode)
 
Windowboxed
 
Scaled, but cropped
 
Pillarboxed (scaled with no cropping)

One popular and inexpensive way to achieve the fourth and properly rendered formatting is through use of a home theater PC, or HTPC. Thanks to the new generation of inexpensive, powerful video adapters like the ATI Radeon, superb video processing capabilities once limited to costly boutique products are now available to the everyday public. In addition to serving as DVD players in their own right, HTPCs, when equipped with the appropriate hardware and software, can be used to process video signals from external devices, including DVD players, laserdisc players, and videocassette recorders. In both cases, scaling can be used to reshape the image so that it appears in its proper proportions on widescreen displays.

One Solution: Simulated Enhancement

One way to properly scale non-enhanced 1.66:1 for widescreen displays is through simulated enhancement. The process begins with an understanding of the differences between enhanced and non-enhanced images. The standard raw DVD image is composed of a 720x480 grid of pixels. Although the aspect ratio of this grid is 1.5:1, the individual DVD pixels are displayed as rectangles (with an aspect ratio of 72/79), and thus the image as a whole has an aspect ratio of about 1.37:1. When the image is sent to the display, the latter "stretches" it horizontally so that it assumes the aspect ratio of the screen, 1.78:1.

Enhanced images are formatted to occupy the full height they will assume on a 1.78:1 screen, but are compressed inwards to fit into the narrower width of the standard DVD image and thus require horizontal stretching to assume their proper proportions. Non-enhanced images are formatted in their proper proportions in both the horizontal and vertical axes (once the pixel aspect ratio has been applied) Because the standard widescreen stretch only occurs in the horizontal axes, a non-enhanced image is not suitable as a direct input.

Contrasting examples of both enhanced and non-enhanced images are shown below. Both are 1.66:1 ; the top image is enhanced and pillarboxed, while the bottom one is non-enhanced and letterboxed.

Return of the Blind Dead appears courtesy of Anchor Bay Entertainment

Raw enhanced
 
Raw non-enhanced

However, what is not readily apparent is the fact that not all of the horizontal information in the non-enhanced image can be used in simulated enhancement. This is because images with aspect ratios narrower than 1.78:1 (the aspect ratio of the display) must be horizontally compressed in preparation for the final stretching the display will perform. Non-enhanced 1.66:1 images, however, extend all the way across across the image width, and thus to simulate an enhanced input, require two modifications: Like all non-enhanced letterboxed images, the must be stretched vertically, and they must also be compressed horizontally.

Simulating 16x9-enhancement: Stretch to fill vertical image area...
 
...and then compress image inward

Standard simulated enhancement of non-enhanced letterboxed images will scale in the vertical axis that central portion of the image equivalent to 1.78:1 so that it occupies the full height it will assume in the display area. Anything above and below this area is cropped off. When the image is received by the display, it will be stretched horizontally by about 33%.

The proper shaping of images having aspect ratios under 1.78:1 and greater than 1.33:1 (where the need for stretching ends) for simulated enhancement is different in two regards: Less vertical stretching is needed, and the image must be compressed inwards (in preparation for the 33% horizontal stretch it will be given by the display). The simulated enhancement "ZOOM" mode of the popular Panasonic RP-91 will simply stretch vertically using the standard ratio, with the result being that the image is in its correct proportions, but extended above and below outside the display area, lopping off portions of the top and bottom. To properly format the non-enhanced 1.66:1 (or any other sub-1.78:1 letterboxed) image as simulated enhanced, special scaling must be used.

A flexible video processing solution like an HTPC can correctly perform the modifications outlined previously, although the correction can only be done at the expense of throwing away a considerable amount of resolution.

Relative portion of original image used in simulated enhancement
A Better Solution: Full Digital Scaling

Simulating enhancement works in that it results in a properly proportioned image that fills the display area to the maximum extent possible without cropping. However, it has one problem (common to all 4:3 images displayed in FULL mode) in that analog displays will likely perform the final 33% stretch in the analog domain, with sub-optimal results. Also, in the case of letterboxed images with aspect ratios under 1.78:1, some resolution is thrown away, as illustrated earlier. Both these problems can be avoided by working with FULL mode instead of against it, by formatting the image area within a 1.78:1 rectangle instead of the standard 1.33:1 (which requires an additional 33% stretch). This little-known technique has been used for years by HTPC enthusiasts (and is employed in a few high-end DVD players), but has never been widespread public knowledge.

This technique can be implemented on a home theater PC through a combination of setting the video card mode to a 1.78:1 resolution (possibly through use of the Powerstrip software), and afterwards configuring the player or deinterlacing software resolution (in some cases, this is done manually, as with the TheaterTek software DVD player, while in others, like the dScaler deinterlacing software, it is a preconfigured option).

As an example, use of TheaterTek with a display resolution of 856x480, combined with a custom player aspect ratio of 800x600, will result in a properly scaled non-enhanced 1.66:1 image within a 1.78:1 window that will not be altered when received by the display. Not only is it properly formatted without loss of resolution, this solution employs the sophisticated scaling capabilities of the video card throughout the formatting process, with no intervention in the analog domain, bringing improvements such as the smoothing of "staircased" edges and the lowered visibility of scan lines (these latter benefits will be realized with all images, be they enhanced or non-enhanced).

Raw 1.5:1 image in 1.78:1 image window
 
Stretch image vertically by 25%...
 
...and horizontally by 9%
Conclusions

Today, more and more titles released to DVD-Video are formatted for 1.66:1. This aspect ratio is problematic, because it requires that transfers be optimized for one of the two popular display types at the expense of the other. Transfers optimized for widescreen (via 16x9-enhancement) will enjoy a 16% boost in resolution, at the expense of wasted display area on traditional 4:3 sets. Transfers optimized for 4:3 will be difficult to properly display on widescreens, and standard solutions here will result in one or more of the following: cropping, wasted display area, and poor image quality. If an HTPC solution is used, these problems can be avoided, although the results will generate somewhat less detail than had the source material been enhanced, all other factors being equal (the drop in resolution will be less than that experienced with "wider" aspect ratios.

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