Hello minermbel,
Thank you for your question.
I have found no better explanation of the difference between "true"
progressive scan and progressive scan that the excellent Archives of
Home Theater Magazine article, excerpted below:
http://www.hometheatermag.com/showarchives.cgi?69
"Progressive-Scan or Progressive Scam?
By Mike Wood, May 2001
The truth behind progressive-scan DVD players.
...Rumors abound that progressive-scan DVD players aren't truly
progressive. This is absolutely true. These same rumors argue that
existing "progressive" DVD players use internal line doublers to
create the progressive image. This, too, is true (and has been stated
by nearly every manufacturer)..
...NTSC, the four letters we banter about when we don't feel like
saying "the TV system that the vast majority of people watch every
day," is an interlaced system. This means that the system's 480
horizontal lines are drawn from the top to the bottom of your screen
every thirtieth of a second. However, since the frame is interlaced,
it's split into two fields (smaller, faster frames), each containing
half, or 240 lines, of the frame, displayed every sixtieth of a
second...
...In order for DVD to be compatible with this type of system, the
player's output is interlaced. The problem is that, on displays larger
than 32 inches, interlaced scan lines become obvious, especially when
your eye follows vertical motion in the image...
...On the other hand, a progressively scanned image draws all 480
lines of the image completely, in one pass, every sixtieth of a
second. This creates a smoother, more-solid image with more apparent
resolution. Due to the advent of larger and larger television screens,
as well as HDTV, manufacturers have found the need to make TV monitors
that can accept and display a progressively scanned image. While these
TVs have mediocre line doublers built into them, DVD is a potential
source for native progressive images...
...According to our sources, since most DVDs originate from film, they
can be (and usually are) recorded as a progressive image. The image on
the disc contains 24 frames per second, which corresponds to a film's
original 24 frames. As with NTSC images, though, a process called 3:2
pulldown is used in order for the 24 frames to keep time with video's
60 fields...
...3:2 pulldown splits every film frame into two interlaced fields and
then adds an additional field for every other film frame. The result
is two fields that correspond to one film frame, followed by three
fields of the next frame, then back to two fields, and so on. With TV
broadcasts and videotapes, this process is added at the studio when
the film is transferred to video. With DVD, it's added by the player
so that the output is compatible with the vast majority of TV sets...
...A true progressive-scan DVD player would bypass the interlace step
and output the original progressive signal, but it would still have to
add the 3:2 sequence. Unfortunately, for incredibly technical reasons,
almost none of the existing players that we know of actually
accomplish this seemingly simple task. On the other hand, some
computer manufacturers claim that their progressive DVD cards can do
this, as can one consumer manufacturer's standalone player. For
reasons I'll explain later, it's impossible to tell the difference and
possibly not even a good idea...
So, how do the consumer manufacturers get away with saying their
players are progressive? Simple: They output a signal that's identical
to what you would get if the player were truly progressive. How? The
vast majority of manufacturers take the interlaced but still digital
output of the player's MPEG decoder and feed it directly into a video
processor (aka line doubler). This, in and of itself, creates a better
picture than you would get from feeding the DVD player's analog output
into an external line doubler-be it a separate component or one built
into a television. The external doubler must convert its analog input
back into a digital signal for processing, then back to analog at the
output (see diagrams A and B). By avoiding the unnecessary
digital-analog-digital step, the picture stays cleaner and more
detailed, regardless of the quality of line doubler used. ...
...While this process may benefit many systems, it doesn't yet compare
with a true progressive signal...
...Most "progressive" DVD players use a video processor that in some
way recognizes 3:2 pulldown. As this is all done digitally, the
resulting output is then identical to what you would have gotten had
the player been truly progressive and bypassed the interlace step.
This is also why we can't tell you whether or not a particular player
is truly progressive. There's no way to tell. So, we are willing to
call them progressive-scan players...
...While any given sales rep will say that the other manufacturers are
using line doublers and not a true progressive output, it really
doesn't matter. Recognizing properly coded software and outputting a
progressive image are relatively easy. The difference between the
so-called true progressive player and the one that properly
deinterlaces the image is academic, at best. The real test of a
progressive DVD player is the quality of its onboard line doubler
that's used for titles that aren't progressive or that can't be read
as such...
Do read the entire article!
Search Strategy:
"true progressive scan" +dvd
I trust my research has answered the question. If a link above should
fail to work or anything require further explanation, please do post a
Request for Clarification and I will be pleased to assist further.
Regards,
-=clouseau=- |
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