Do Stretch and Zoom on a 4:3 HDTV lower the resolution unn..

Archived from groups: alt.tv.tech.hdtv (More info?)

Lawrence G. Mayka (lgmayka000@ameritech.net) wrote in alt.tv.tech.hdtv:
> I have seen a post in this newsgroup claiming that a 4:3 HDTV such as mine
> essentially comprises two virtual screens, one 1920x1080
> widescreen/letterboxed and one 640x480 fullscreen. The implication, I
> think, is that whenever I stretch or zoom an originally letterboxed picture
> to make it fullscreen, I am forcing a downconversion to 640x480, with a
> significant loss of picture resolution. Is this true?

This completely depends on the set. I'm not familiar with exactly how Zenith
does this, but it could be true.

The right way to design a 4:3 HDTV would be to have it be able to draw 1440
scan lines from top to bottom of the full screen (1920x1440 pixels, if it was
a fixed-pixel display). Then, 1080i would be letterboxed in the middle
using 1080 scan lines, 480i could be line-tripled, and the "zoom the 4:3
picture inside a 1080i transmission mode" could actually be an *up*-convert
(from 1440x1080 to 1920x1440).

I doubt any 4:3 HDTVs are actually designed this way, but it would result in
the best possible picture in every mode.

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Archived from groups: alt.tv.tech.hdtv (More info?)

"Lawrence G. Mayka" <lgmayka000@ameritech.net> wrote in message news:<Wjahc.10119$nj6.7209@newssvr31.news.prodigy.com>...
> I have a Zenith C32V37 HDTV, 32" and 4:3. It supports display at 480i,
> 480p, and 1080i. (720p input is accepted but converted on output.) Most
> programs, particularly outside of the prime hours, appear banded on all four
> sides; they are presumably being displayed at 1440x1080i (through
> interpolation if necessary). Needless to say, a consumer's first impulse is
> to zoom these programs in order to fill up the 4:3 screen. A rare exception
> is our local ABC affiliate, WLS, which broadcasts a vertically scrunched
> 720p picture which *must* be stretched simply in order to avoid the
> carnival-mirror look.
>
> I have seen a post in this newsgroup claiming that a 4:3 HDTV such as mine
> essentially comprises two virtual screens, one 1920x1080
> widescreen/letterboxed and one 640x480 fullscreen.

Even 16:9 HDTVs have at least two modes (one for 1080i (or 720p) on
the other being for SDTV 480i).

> The implication, I
> think, is that whenever I stretch or zoom an originally letterboxed picture
> to make it fullscreen, I am forcing a downconversion to 640x480, with a
> significant loss of picture resolution. Is this true?
>

In general, anytime a zoom mode is applied (on 4:3 or a 16:9 set) the
resolution of the image you see on screen is downgradeded a bit, just
as if you opened a paint program on a computer and stretched an image
to fill a windows background (sorry couldn't think of a better
analogy).


> Now some people would claim that the 4-banded programs, and perhaps even the
> vertically scrunched programs, actually originate from lower-definition
> sources anyway, and hence 640x480 is sufficient not to lose any of the
> original quality. But I would point out that even artificial, interpolated
> pixels (inserted by the HDTV in order to expand the picture to 1440x1080)
> are of *some* advantage to human perception.
>

Some of this you probably know, bear with me. The four banded programs
you see (ie: top, bottom, left, right black bars around a framed
image) are upconverted to 1080i. Since 1080i is a 16:9 resolution,
these stations broadcast 4:3 upconverted content with left and right
bars... When you switch to any HD channel your TV automaticly kicks
into HD resolution mode. So you're stuck with the black bars at the
top and the bottom for all programming in this mode because your HDTV
is 4:3 and the HD standard calls for 16:9. So when you watch 4:3
upconverted programming the left and right black bars are part of the
signal (because the singal must be in a 16:9 format to be sent out in
1080i).

When you apply a zoom mode you're still taking a small image and
enlarging it though the magnification inside the TV. So you will see
noticible a degrade in image quality on the 4:3 set with zoom applied
over a similarly sized 16:9 set with the same verticle length (one
that is displaying the upconverted content natively)

Don't take my word for it, do the same test I did. Go to a local
retailer in a slow period and play around with the zoom mode on 4:3
set and compare it to 16:9 native displaying an upconverted 4:3 image,
you'll see a difference. I had the ability to compare two sets of the
same brand in the same series (both Hitachi models) this where I draw
my conclusion from.



On the few sets I've tried this on (not Zenith sorry),

> So the bottom-line question is, Do Stretch and Zoom on a 4:3 HDTV lower the
> resolution in these cases?