Sunday, September 13, 2009

Getting the Most out of DVD on an HDTV Display

DVD has revolutionized the way we think about television. The digital disc with its remarkably clear picture has shown us that "home theater", once an exotic concept reserved for the privileged few, can now be embraced by all. For that ultimate movie-watching experience, a new generation of HDTVs, flat panels, plasma screens, and even home projectors can deliver bigger, sharper, brighter, and more enveloping video images than the small, boxy televisions of the past. However, simply buying a larger screen is not enough to truly achieve that movie theater-like ideal. For all of DVD's advances, it remains a Standard Definition video format that can use a little help translating to a High Definition screen. As it turns out, buying your HD display is only the first step in fulfilling your big-screen, home theater dream.
Knowing Your Video Formats
In the beginning, there was only one standard video resolution (known as Standard Definition, or SD) for displaying images on TV. In the NTSC television system used in North America, Standard Definition displays 30 still picture frames, of 480 horizontal lines of resolution each, per second. This video resolution is often called 480i, in which "i" stands for "Interlaced." Each of these picture frames is displayed line-by-line on the screen in two passes. Each pass consists of 240 alternating horizontal lines, which together are called a "field". Two passes or two interlacing fields make a full frame of 480 horizontal lines. The rapid succession of each 240-line field to the next gives viewers a sense of continuous motion through "persistence of vision", and to the naked eye the image looks solid and whole. This interlacing of the picture is due to historical limitations on the cost of electronics and the available bandwidth for conventional TV broadcasts. For many years, Standard Definition was good enough for viewing video programs on small screen TVs. However, as TV screen sizes increase, the drawbacks of 480i become more apparent in the form of visible scan lines, flickering images, and jagged lines.
Enhanced Definition (ED) was developed to address the weaknesses of Standard Definition. On an ED screen, each still picture frame of 480 horizontal lines is displayed in one whole pass rather than two interlaced fields. This process is called "Progressive Scan" and has been part of the computer monitor industry for many years before being adopted for use with television viewing as well. Since there is no interlacing, Progressive scan produces a more stable picture with better details. This video resolution is called 480p, in which "p" stands for "Progressive." Although the change from interlaced to progressive seems trivial, it greatly enhances the video quality. Lack of interlacing is the primary reason why small text is easily legible on a computer monitor, whereas it has traditionally been difficult to read on a Standard Definition TV due to flickering and poor detail.
High Definition (HD) is the next evolutionary step toward better video quality. HDTV supports many video formats with higher picture resolutions. The two most common formats are 720p, in which each picture frame consists of 720 horizontal lines displayed progressively, and 1080i, in which each picture frame consists of 1080 horizontal lines displayed in two interlaced passes of 540 lines each. Better video quality is achieved by having more lines in each picture frame so more details can be displayed.
In order for an HDTV to show the best possible picture quality, the video signal must be converted to the "native rate" of the display (the primary resolution that the screen supports). This can be performed either within the TV itself, or externally at the video source. Although it is true that every HDTV comes equipped with circuitry to perform this conversion, generally the set manufacturers use basic, unsophisticated scaling chips that do an inadequate job. The TV may enlarge the video to fill up the screen, but usually does not address many complicated issues in properly handling of the video signal to create the best possible picture quality. For optimal display result, it is best to feed the HDTV with a native HD video signal so that the TV does not have to do the zooming. How well the conversion from Standard Definition to High Definition is performed by the circuitry in the electronic devices will determine how good the video image looks on screen. In the case of DVD, which is still encoded at Standard Definition resolution, this is almost always best performed within the DVD player so that the display's own internal components won't have to struggle with these steps and can simply present exactly the signal provided to them.
The Right DVD Player for the Job
Once you've found the right HDTV display to center your home theater around, the next step is connecting the right DVD player to it. A common misconception is that DVD is a "plug and play" format, and that all you need to do is connect any DVD player to the TV by the most convenient video cable and everything will be instantly ready to go. After upgrading to a High Definition display, home theater fans quickly learn the folly of that mistake. The quality of video on the screen is only as good as the source delivering it, and chances are that the old DVD player you were using with your Standard Definition TV will be insufficient for the new display.
Not all DVD players are created equal. Connecting an average DVD player to a High Definition display can be a disconcerting experience. The process of converting a Standard Definition DVD signal to the native resolution of the display may cause a host of video artifacts if not performed properly. These flaws will be especially noticeable on large and high-resolution screens. Quality deinterlacing and scaling are the key components to stable, artifact-free movie watching, and frequently the components built into many DVD players to perform these tasks are not up to the challenge. Low-end DVD players may not even have them at all.
Getting Connected
The first criteria to look for in a suitable DVD player for an HDTV display is a direct-digital video connection of either the DVI or HDMI type (the two cable types are compatible; a DVI output on the DVD player may be connected to an HDMI input on the TV via a simple adaptor cable). With this type of connection, the data stays entirely in the digital domain, avoiding the digital-to-analog conversion required with analog output cables such as S-video or Component video. A player connected by analog cabling must convert the digital data present on the DVD into an analog TV signal, after which point the HDTV receiving the video will re-digitize the signal for its own internal processing. Performing dual conversions like this is not only unnecessarily complicated, it introduces the risk of analog signal noise or transcoding errors affecting the data. The conversions also usually involve filtering so that the signals work across the widest range of source content, some of which may be poor-quality. A direct-digital connection from DVD player to display bypasses extraneous conversion steps, delivering exactly the bits encoded on the disc without conversion noise or filtering. A pure digital video interface results in a far more compelling image that is razor sharp and wonderfully vibrant.
The Complexities of Deinterlacing
Since DVD video is stored on disc in an interlaced format, in order to view this material on a progressive scan screen the separate fields must first be combined into whole frames through a process called deinterlacing. In order to achieve this result, two interlaced picture fields are merged into a single progressive frame. This may sound simple, but in actuality turns out to be surprisingly difficult to do well. Poor quality deinterlacing results in "jaggies" and combing artifacts when interlaced fields are not matched together correctly. U nfortunately, deinterlacing can be easily complicated by the nature of film-based, video-based, or mixed-source content.
Take the example of a DVD movie that was originally produced and released on 35mm film for theatrical release. Film-based motion pictures are photographed at a rate of 24 picture frames per second (fps). When the film is scanned into video to be released on DVD, the publisher has to convert 24 film frames into 60 interlaced video fields because the DVD must produce a rate of 30 frames per second in order to be displayed on a television. In order to achieve this, the conversion needs to produce 5 video fields from each 2 original film frames. The first film frame produces 3 video fields: a field of the odd numbered scan lines (1, 3, 5, 7, etc.), a field of the even numbered scan lines (2, 4, 6, 8, etc.), and a repeated field of the odd numbered scan lines. The second film frame produces 2 video fields: a field of the even numbered scan lines, and a field of the odd numbered scan lines. This complicated conversion process is known in the industry as 3:2 pull-down.
When the DVD is played on a regular Standard Definition TV, due to the interlaced nature the picture quality is as good as SDTV can get. However, when a progressive scan or upconverting DVD player deinterlaces the video, it becomes tricky to accurately reproduce the original film frames. An unsophisticated DVD player simply combines each two video fields into a progressive frame. This resulting first frame may be the same as the original film frame, but the second frame will be a mix-up of the odd numbered scan lines from the first original film frame and the even numbered scan lines of the second film frame. Although the two film frames are only slightly different, this error is enough to produce visible artifacts such as blurry pictures and jagged lines. A good progressive scan DVD player must detect that the DVD is mastered from a film source and use intelligent deinterlacing algorithms to accurately reconstruct the original film frames.
Another deinterlacing challenge is the playback of TV shows or other content originally shot on video. When a video program is recorded, the video camera records 60 interlaced fields per second. Between each field there is a 1/60 second time delay. When the scene in the video changes quickly, the time delay is enough to make two fields belonging to the same frame look very different. If simply combined together, the resulting video frame will look blurry. As if that weren't difficult enough, many programs available on DVD contain a mixture of film and video cadences. Some TV shows are shot on film but include video-based overlays such as credits or visual effects that greatly confuse unsophisticated deinterlacing algorithms. Good progressive scan DVD players such as the OPPO OPDV971H have a feature called "Directional Correlation Deinterlacing", or DCDi. With this feature, the DVD player can detect, adapt to, and compensate for the motion in both film and video scenes, and will produce smooth and stable pictures no matter the content.
The Benefits of Upconversion
After deinterlacing, the Standard Definition DVD video must then be scaled (or "upconverted") to the higher resolution of the HD display. The standard DVD resolution is 720x480 pixels, or 345,600 pixels in each frame. The 720p HD resolution is 1280x720, and the 1080i HD resolution is 1920x1080. In order to produce an HD video signal suitable to be displayed on an HDTV with the higher resolution and best picture quality, an upconverting DVD player must scale up the video frames.
Scaling involves creating new pixels by selectively copying pieces of the surrounding pixels using various mathematical techniques to interpolate what the video signal would look like at a different resolution. A good upconverting DVD player scales the DVD video using fast processing electronics and intelligent algorithms. It can detect and compensate for motion, scene transitions, foreground and background objects, and noise from video in real time and handle each situation intelligently. The scaled-up video is rich in detail, with little or no visible artifacts introduced by the upconversion process.
There are some upconverting DVD players on the market that cannot do the job well. Perhaps they employ low-quality detail enhancement circuitry to simply enlarge video pixels from the original DVD to fill up the HD screen, or perhaps the electronics and algorithms used to handle the tasks are not adequate. Viewers will notice artifacts such as v isible pixelation, color shifting, jagged lines, and "ringing" borders introduced by the poor upconversion. These artifacts are often mistaken for digital compression flaws in the DVD itself, when in fact the DVD player and/or display may be causing them. The high-quality upconversion performed by a player such as the OPPO OPDV971H makes certain that what you see on screen accurately represents what is really on the disc.
Other Criteria
Once you've limited your choice of DVD player to those with direct-digital video connections, sophisticated motion-adaptive deinterlacing for both film and video content such as the renowned Faroudja DCDi solution, and high-quality intelligent upconversion algorithms, the next step is to look at the feature set and convenience factors that will make a specific DVD player the right fit for your needs.
Versatility is key. Home theater fans require flexibility in the amount and types of content they play. Will the machine play both NTSC and PAL discs with accurate conversion of either video format to the viewer's display type? Does it offer the stunning sound quality of the high-resolution DVD-Audio format for an audiophile audience? In addition to standard DVD-video, is it compatible with DiVx or XviD files with subtitles in multi-formats? Can it support playback of DVD-R, DVD+R, DVD-RW, DVD+RW, CD, VCD, SVCD, HDCD, CD-R, CD+R, CD-DA, Kodak Picture CD, WMA and other audio formats, MPEG1, MPEG2, and JPEG content? Home theater is about more than just DVD. Sometimes the content we desire to watch comes in unusual formats. A quality DVD player must also be a versatile hub ready for all of your multi-media needs.
Full aspect ratio control is an additional advantage of a good DVD player. Many HDTVs automatically lock into a widescreen stretch mode on all progressive scan or HD resolutions. This is fine when watching an HDTV feed or anamorphically enhanced DVD, but becomes problematic if viewing TV shows or older movies in a 4:3 shape, or DVDs encoded in a non-anamorphic letterbox format. To avoid unwanted stretching and distortion, a DVD player should be able to reformat the video image into the proper aspect ratio centered in the middle of a widescreen display with pillar boxes on the sides, or to zoom a non-anamorphic letterbox image to fill the screen with correct picture geometry. Such a feature sounds like it ought to come standard in every DVD player, but unfortunately is not required by the official DVD spec and is left out of the majority of DVD players on the market.
To further enhance the DVD-viewing experience, a select few DVD players like the OPPO OPDV971H also offer a digital frame buffer that provides an extremely fast layer change transition to avoid distractions from unwanted pauses in the middle of a movie.
Finally, we have by far the most important criteria for any home theater connoisseur: Value. Yes, there are DVD players on the market that may deliver all of the above features while charging a premium price. If you're lucky, they might provide the picture quality performance you want, but may cost as much or more than the HDTV you'll be connecting them to. On the other hand, t he OPPO OPDV971H represents high-end performance for a reasonable price, featuring video processing quality to match even the most expensive DVD players on the market. OPPO Digital is dedicated to the home theater consumer, and offers stellar customer service support that has been the talk of the entire home theater community. As new features are developed for the player, easy-to-install user-upgradeable firmware updates available on the web site ensure that your DVD player will never be outdated.
As your video display moves into the High Definition era, don't leave your DVD collection behind. Even while looking forward to a future with more High Definition content availability, we must not forget the great wealth of material already available on the DVD format. A DVD collection can represent a sizable investment, both financially and emotionally, in our favorite content. That content deserves to look its very best on any type of screen. Considering the performance quality and abundance of useful features it offers, a good upconverting DVD player such as the OPPO OPDV971H is a small but essential investment toward making your home theater dreams a reality.

Wednesday, September 2, 2009

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