Mailing List Archive

On Mon, Jan 18, 2010 at 1:52 PM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
> Does that mean that you have to adjust your TV every time the format changes!?
>
> Usually when I am in the US and watch TV in my hotel room the picture is
> always distorted. I really hope that is not normal behavior for NTSC and
> widescreen TVs.

In the United States, NTSC is expected to be in 4x3, and if the
content is widescreen then the content provider uses black bars above
and below to preserve the aspect ratio.

Televisions have various features to allow the user to decide whether
to stretch the 4x3 video or to preserve the 4x3 aspect ratio on the
widescreen display (by adding black bars to the left and right).
There are also zoom features built into televisions to attempt to crop
out where the black bars would be. But none of this is automatic.

It's really unfortunate that WSS functionality was never adopted in
the US, since it's really annoying to get a widescreen program coming
over an NTSC signal in 4x3 format with black bars and not have it show
up in it's natural aspect ratio even on a widescreen television.

The United States has basically concluded that the only way to get
true widescreen is to watch digital HD TV.

Devin

--
Devin J. Heitmueller - Kernel Labs
http://www.kernellabs.com

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----- "Hans Verkuil" <hverkuil@xs4all.nl> wrote:
> On Monday 18 January 2010 19:42:45 Devin Heitmueller wrote:
> > On Mon, Jan 18, 2010 at 1:35 PM, Hans Verkuil <hverkuil@xs4all.nl> wrote:
> > > - NTSC and WSS. I still do not know how NTSC determines whether the source is
> > > 4x3 or 16x9. PAL uses the WideScreen Signal (WSS). A similar feature exists
> > > for NTSC, but it is unclear whether it is actually used by broadcasters.
> > > Nobody seems to know.
> >
> > The reality is that for NTSC there is no standard. There is an NTSC
> > variant of WSS discussed in the WSS specification, as well as a way of
> > representing the info in EIA-608. As far as I have been able to
> > gather though, neither have actually ever been used in production. If
> > someone wants to offer some evidence to the contrary, I would be happy
> > to add the support to tvtime and test it with some of my tuner boards
> > (and fix any bugs that in the driver I find).
>
> Does that mean that you have to adjust your TV every time the format
> changes!?
>
> Usually when I am in the US and watch TV in my hotel room the picture is
> always distorted. I really hope that is not normal behavior for NTSC and
> widescreen TVs.

The *actual* reality is that an NTSC signal has an inherent *signal* aspect
of 4:3. If you're looking at it off a composite cable, or a cable/OTA tuner
you can force 4:3. The *image* aspect may be different: wider aspects
are generally accomplished by letterboxing, though some consumer camcorders
will record a 16:9 image as a 4:3 signal by doing an anamorphic squeeze of the
video image.

If it came in from a digital source, like a DTV tuner, things are murkier.

I *assume* there's an aspect flag, and I assume tuners will set it, but
both of these issues should be orthogonal to IVTV, I think, cause we're
only concerned with composite NTSC and OTA RF NTSC-M, and you can safely
force 4:3 on both.

This is my technical understanding based on 20 years of making and editing
the stuff; if anyone has a counterexample concerning broadcast or composite
transmission that I haven't already noted, bring citations. :-)

Cheers,
-- jra

--
Jay R. Ashworth Baylink jra@baylink.com
Designer The Things I Think RFC 2100
Ashworth & Associates http://baylink.pitas.com '87 e24
St Petersburg FL USA http://photo.imageinc.us +1 727 647 1274

Start a man a fire, and he'll be warm all night.
Set a man on fire, and he'll be warm for the rest of his life.

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