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Q: DVD's on HDTV ( Answered 5 out of 5 stars,   3 Comments )
Subject: DVD's on HDTV
Category: Miscellaneous
Asked by: esarkissian-ga
List Price: $5.55
Posted: 27 Jan 2004 23:24 PST
Expires: 26 Feb 2004 23:24 PST
Question ID: 301032
If memory serves me correctly, standard NTSC is 525 scan lines, and
HDTV is 720p & 1080i.  I've heard (but can't confirm) that DVD's are
recorded at 480p (regular DTV).  If this is in fact true, then:

1)  will DVD's look better on the HDTV ONLY because it's
digital-to-digital (no analog conversion), and NOT have anything to do
with better resolution/more scan lines?

2) how are the 480 lines "stretched" vertically to fit the 720 or 1080
(or even 525 for that matter)?

How does all this work?  So confused...


Clarification of Question by esarkissian-ga on 28 Jan 2004 10:50 PST
abhisingh-ga and markj-ga,

Thank you for your comments.  Abhisingh-ga, you start off by saying
that DVD's look better on HDTV primarily because of better resolution,
but you don't give a reason why.  How can you get better resolution
out of something that only has so much to begin with?  Wouldn't it
have to be recorded at a better resolution to begin with (better than
480p)?  I already know about interlaced vs. progressive scanning,
bandwidth, etc.

If HDTV (720 or 1080) has twice the vertical resolution as a standard
TV (525), why does it matter since a DVD is 480?  If you have
something recorded at 480 lines, how does it 'expand' to 720 or 1080
Subject: Re: DVD's on HDTV
Answered By: alexander-ga on 30 Jan 2004 01:31 PST
Rated:5 out of 5 stars
A lot of misinformation floating around here. Let's clear it up.

The 525 and 480 designations are exactly the same thing. In both
cases, the video signal is comprised of 525 scanlines, but only 480
contain actual picture information. The other 45, which do not contain
any picture information, are provided for timing reasons.

The native format of DVD is 480i, the operational mode of traditional
televisions. 480i is also the native format of traditional video
cameras. Most DVDs, however, are sourced from film, not video. Film is
natively 24 frames per second, and not interlaced. When a film is made
into a DVD, It is converted to 480i through a technique called "3:2

On a "normal" TV, this is how the DVD would be displayed -- as a 480i
conversion of a 24fps source. To our eyes, this looks perfectly

It is not, however, an accurate representation of the film.
Fortunately, it is not difficult to reconstruct the original film
frames via a process known, not surprisingly, as "reverse 3:2
pulldown". This is why "progressive scan" is a buzzword around DVDs --
applying reverse 3:2 pulldown to a film-sourced DVD yields a
progressive image. (Ideally, it would be displayed at 24 frames per
second, or a multiple such as 48 or 72 frames per second.)

Most HDTVs are capable of performing reverse 3:2 pulldown, and perform
it automatically when film-sourced material is detected. This is one
reason why DVDs usually look better on HDTVs.

Another reason is due to the fact that HDTVs are generally far more
capable display devices than tradtional televsions. HDTVs come in many
different varieties (CRT direct-view, CRT rear projection, DLP, LCD,
LCOS, plasma, etc.), and the details vary considerably between them,
but the general idea is that they have a much higher "fill rate" than
typical televisions--more of the image is illuminated at once, at a
higher refresh rate. This provides a richer, more vivid image with
fewer temporal artifacts, such as flicker. In the CRT world, simply
providing more scan lines provides a more pleasing image, even if
there is no additional detail. This is particularly true for larger
screen sizes.

In addition, most widescreen DVDs will actually show higher resolution
on an HDTV, because of anamorphic encoding. Anamorphic encoding
involves stretching the widescreen content vertically to cover the
entire video frame during the encoding process. This allows the full
resolution of the DVD format to be used. All DVD players are capable
of the inverse transformation -- squashing the picture vertically to
the correct aspect ratio for display on a normal 4:3 aspect ratio
televsion (and losing some detail in the process). A properly
configured HDTV setup will perform this transformation such that the
full resolution encoded on the DVD can be used.

If the 480 scanlines of data are "expanded" to 720 or 1080, it is
performed in exactly the same manner as resizing an image on your
computer -- no additional information is added. The increase in image
quality is not a direct result of the image being resized, but rather
because display devices typically produce a more pleasing picture with
more scanlines.

If you have a particular interest in a specific display device, I'd be
happy to go into greater depth about how it is affected by these

Request for Answer Clarification by esarkissian-ga on 17 Feb 2004 11:22 PST

Can you please clarify my questions in the "answer rating" portion?  I
suppose I went about this all wrong, but I gave the tip as payment in
advance for answering my additional questions in the rating portion. 
I'd appreciate your help.


Clarification of Answer by alexander-ga on 17 Feb 2004 19:14 PST
My apologies--we don't get automatically notified when rated, only
when a clarification request is posted.

1) Yes, both 480p and 480i (NTSC) have the same number of lines: 480.
However, 480p has twice as much "information", because the complete
frame is updated every 1/60th of a second. In 480i, only half of the
frame (alternating sets of alternating lines) is updated each 1/60th
second. When creating 480p from a 480i source, as most displays
capable of displaying 480p do, there is obviously no more detail
available, but the "upconversion" still looks better, much as a
smoothly scaled image on a computer looks better then a poorly scaled

2) Progressive scan from a progressive scan DVD player playing a film
source, yes. "Real" 480p/60 frames from video cameras is possible
("FOX Widescreen" DTV may do this, I'm not sure), but you're not going
to get that from a DVD player.

3) There are no "30fps" TVs. (see next answer) On a 480p (60fps) set,
it would be displayed with each frame being accurate to a film frame,
but the timing would be slightly inaccurate--2 copies of one frame,
then 3 copies of the next frame, etc.

4) On a 480i TV, yes, the progressive scan feature is not used.

5) I'm assuming we're talking about a widescreen anamorphic DVD here,
which most film-based DVDs are. Let's use one that has an aspect ratio
of 16:9.

The resolution stored on the DVD is actually 720x480. However, to get
the correct 16:9 aspect ratio, we'll have to stretch it a little, to

A 720p 16:9 display has a resolution of 1280x720, clearly more than
the 853x480 the DVD is providing, so yes, it's simply scaled up. The
"full resolution" of the display isn't being used.

A 480i 4:3 display has a resolution (assuming square pixels) of
640x480. However, to display widescreen material, only a portion of
this can be used. For 16:9 material, the usable "window" is only 360
lines high, far less than the 853x480 resolution from the DVD. So it
must be downscaled, and you are actually losing resolution from the
DVD. The resolution is lost *because* of the difference in aspect

This may seem counterintuitive, because both the TV and the DVD are
natively 480i, but it occurs because of the anamorphic encoding,
described in my original answer, used to push the DVD format to its
limits, and provide extra resolution to displays capable of using it.

The difference is even more pronounced when viewing a "wider" film
with an aspect ratio greater than 16:9. "Scope" films are also very
common, and have an aspect ratio of 2.35:1. On a 480i set, the usable
window would be only 272 lines high, resulting in use of only 57% of
the resolution available from the DVD.
esarkissian-ga rated this answer:5 out of 5 stars and gave an additional tip of: $5.00
Thank you alexander-ga!  A lot of what you say makes sense.  I'm still
having trouble with a few things, so if you could please
confirm/correct the following I would be grateful:

1) A DTV (480p) and a standard NTSC TV have the same number of visible
lines?  Given an analog signal, a DTV looks better only because
progressive looks better to the eye than interlaced?

2) Progressive scan is just basically reverse 3-2 pulldown, in essence
"un-interlacing" the images and reverted them back to 24fps?

3) If the above is correct, how is this displayed on a 30fps TV?

4) Is a progressive scan DVD player pointless on a NTSC Television?

5) I'm still most confused on this concept, so please bear with my
thought process...

A DVD is 480i, the same as a standard TV.  However, the entire image
on the DVD isn't displayed on a standard TV because of a different
aspect ratio- nothing to do with resolution, correct?

But if you pop this 480i DVD into a 720p widescreen HDTV, the entire
picture on the DVD will be shown because the aspect ratio is similar-
not really anything to do with the extra scan lines, correct?  The
HDTV will then automatically do reverse 3-2 pulldown and show the DVD
progressively- but it still then only becomes 480p, while the HDTV is
720p- there are 240 lines left over.  The original image on the DVD is
480 lines, so there's no more of the original image to display.

I see it as taking an existing picture and just placing it on a bigger
canvas.  There's just going to be more 'whitespace' around the
picture, unless you enlarge the picture to fill more of the screen. 
But by enlarging it, isn't that like enlarging an image on your
computer, thereby reducing resolution by pixelation?

Thank you again, alexander.  I'm just trying to put all of this together.


Subject: Re: DVD's on HDTV
From: abhisingh-ga on 28 Jan 2004 06:07 PST
Hi esarkissian,
you r right as far as scanning of lines are concerned.
First of all I will just say that  DVD's do not look better on the
HDTV ONLY because it's
digital-to-digital (no analog conversion), but it is majorly concerned with  do
with better resolution/more scan lines?
First of all let me tell you some thing about HDTV
High-definition television, or HDTV, provides better quality video for
television, using approximately twice the vertical and twice the
horizontal resolution of today's analog television. HDTV uses more
bandwidth since it uses a digital signal with about five times as much
picture information (pixels). In the future, broadcasters may choose
to transmit different levels of resolution during the broadcast day,
perhaps transmitting daytime programs using lower resolution digital
signals in order to reserve bandwidth for multiple-channel
broadcasting or interactive programming, then switching to HDTV at
night for movies or specials.
And clarity of picture in a TV comes from:
A television picture created by separating the lines which make up an
image into two sets of lines (each containing half the scan
lines--every other one) and then displaying the frame by "interlacing"
these two sets of lines on the screen to create a solid picture. This
is the technology used in today's standard definition televisions.

480i, 480p, 720p and 1080i: 
For eg:a 480i picture contains 480 lines displayed per screen in an
interlace format.
To understand Progressive Scanning for DVD material, you must first
understand how the image is laid on the DVD disk.  DVD standard states
that the video image is encoded in 720 lines horizontally and 480
lines vertically.  This image is defined as a "frame", a full snap of
a picture from the original film with the full 720x480 lines of image.

Progressive scan imaging was designed to show both of the fields in
one pass, doubling the scan frequency and eliminating the artifact of
interlacing.  To do so required re-engineering the display device and
the type of input connector used.
Subject: Re: DVD's on HDTV
From: markj-ga on 28 Jan 2004 06:35 PST
Depending on how much technical detail you want (or don't want), the
link below might answer your question sufficiently.
The somewhat oversimplified bottom line is:

--the native format of DVDs is 480p;
--480p signals are displayed as 480i on analog receivers
--480p is not an HDTV format, but it is cleaner and sharper than a
standard analog picture
--full 480p resolution can be achieved on any digital receiver (not
just HDTV-ready sets) with a signal from a DVD player, as long as the
DVD player has a progressive scan or a component video output and the
digital receiver has the corresponding input.

Subject: Re: DVD's on HDTV
From: markj-ga on 28 Jan 2004 11:59 PST
I will leave it those with an engineering background to fill in detail
or to declare me wrong (my "expertise" comes from working with DTV for
years from the legal/policy stabdpoint), but my answer to your
question is that an HDTV set does not "expand" a 480p signal to 720
(or 1080) lines.

The DTV technical standard provides that an HDTV receiver must be able
to process and display signals from lower-definition sources (like a
DVD's 480p)in their native (e.g,480 lines-progressive)format.


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