1.40 What's a progressive DVD player?
Description
This article is from the DVD Formats FAQ, by jtfrog@usa.net (Jim Taylor) with numerous contributions by others.
1.40 What's a progressive DVD player?
A progressive-scan DVD player converts the interlaced (480i) video from DVD
into progressive (480p) format for connection to a progressive display
(31.5 kHz or higher). (See 3.8 for an explanation of interlaced and
progressive scanning.) Progressive players work with all standard DVD
titles, but look best with film source. The result is a significant
increase in vertical resolution, for a more detailed and film-like picture.
Toshiba developed the first progressive-scan player (SD5109, $800) in mid
1998, but didn't release it until fall of 1999 because of copy protection
concerns. Panasonic also released a progressive-scan player (DVD-H1000,
$3000) at about the same time. At the January 2000 CES show, most DVD
player manufacturers talked about upcoming progressive players. It's also
possible to buy an external line multiplier, such as the DVDO, to convert
the output of a standard DVD player to progressive scanning. All DVD
computers are progressive players, since the video is displayed on a
progressive monitor, but quality varies a lot. (See 4.1 and 2.12.)
Converting interlaced DVD video to progressive video involves much more
than putting film frames back together. There are essentially two ways to
convert from interlaced to progressive:
1- Re-interleaving (also called weave). If the original video is from a
progressive source, such as film, the two fields can be recombined into a
single frame.
2- Line doubling (also called bob). If the original video is from an
interlaced source, simply combining two fields will cause motion artifacts
(the effect is reminiscent of a zipper), so each line of a single field is
repeated twice to form a frame. Better line doublers use interpolation to
produce new lines that are a combination of the lines above and below. The
term line doubler is vague, since cheap line doublers only bob, while
expensive line doublers (those that contain digital signal processors) can
also weave.
(3- There's actually a third way, called field-adaptive de-interlacing,
which examines individual pixels across three or more fields and
selectively weaves or bobs regions of the picture as appropriate. Most
systems that do this well cost $10,000 and up, so it will be a while before
we see it in consumer DVD players.)
(4- And there's also a fourth way, called motion-adaptive de-interlacing,
which examines MPEG-2 motion vectors or does massive image processing to
identify moving objects in order to selectively weave or bob regions of the
picture as appropriate. Most systems that do this well cost $50,000 and up
(aside from the cool but defunct Chromatic Mpact2 chip).
There are three common kinds of de-interlacing systems:
1- Integrated. This is usually best, where the de-interlacer is integrated
with the MPEG-2 decoder so that it can read MPEG-2 flags and analyze the
encoded video to determine when to bob and when to weave. Most DVD
computers use this method.
2- Internal. The digital video from the MPEG-2 decoder is passed to a
separate deinterlacing chip. The disadvantage is that MPEG-2 flags and
motion vectors are no longer available to help the de-interlacer determine
the original format and cadence.
3- External. Analog video from the DVD player is passed to a separate line
doubler or to a display with a built-in line doubler. In this case, the
video quality is slightly degraded from being converted to analog, back to
digital, and often back again to analog. However, for high-end projection
systems, a separate line multiplier (which bobs, weaves, and interpolates
to a variety of scanning rates) may achieve the best results.
(Note: from what I've been able to gather, the Panasonic DVD-H1000 and the
Toshiba models (SD5109, SD9100, SD6200, SD9200) all use an internal Genesis
gmVLX1A de-interlacing chip. The Princeton PVD-5000 uses a Sigma Designs
decoder with integrated de-interlacing. Toshiba's "Super Digital
Progressive" players and the Panasonic HD-1000 use 4:4:4 chroma
oversampling, which provides a slight quality boost from DVD's native 4:2:0
format.)
A progressive DVD player has to determine whether the video should be
line-doubled or re-interleaved. When re-interleaving film-source video, the
player also has to deal with the difference between film frame rate (24 Hz)
and TV frame rate (30 Hz). Since the 2-3 pulldown trick can't be used to
spread film frames across video fields, there are worse motion artifacts
than with interleaved video. However, the increase in resolution more than
makes up for it. Advanced progressive players such as the Princeton
PVD-5000 and DVD computers can get around the problem by displaying at
multiples of 24 Hz such as 72 Hz, 96 Hz, and so on.
A progressive player also has to deal with problems such as video that
doesn't have clean cadence (as when it's edited after being converted to
interlaced video, when bad fields are removed during encoding, or when the
video is speed-shifted to match the audio track). Another problem is that
many DVDs are encoded with incorrect MPEG-2 flags, so the re-interleaver
has to recognize and deal with pathological cases. In some instances it's
practically impossible to determine if a sequence is 30-frame interlaced
video or 30-frame progressive video. For example, the documentary on Apollo
13 is interlaced video encoded as if it were progressive. Other cases of
improper encoding are Fargo and More Tales of the City.
A growing problem is that many TVs with progressive input don't allow the
aspect ratio to be changed. When a non-anamorphic signal is sent to these
TVs, they stretch it out! Before you buy an HDTV, make sure that it allows
aspect ratio adjustment on progressive input.
Just as early DVD players did a poor job of progressive-scan display of
DVDs, the first generation of progressive consumer players may be a bit
disappointing. But as techniques improve, and as DVD producers become more
aware of the steps they must take to ensure good progressive display, and
as more progressive displays appear in homes, the experience will
undoubtedly improve, bringing home theaters closer to real theaters.
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