Mailing List Archive: Re: [ivtv-devel] NTSC & WSS (was: ivtv TODO list)

Re: [ivtv-devel] NTSC & WSS (was: ivtv TODO list)

Jan 18, 2010, 11:30 AM

Post #1 of 4 (2240 views)

On Mon, Jan 18, 2010 at 2:24 PM, Jay R. Ashworth <jra@baylink.com> wrote:
> I don't believe it actually has to be HD. I think that OTA DTV can actually
> utilize widescreen SD resolutions akin to 800x480.

It is true - you can do SD resolutions with digital TV. However, what
I was alluding to was that, in the United States, people associate "HD
TV" with "widescreen", and with DTV you typically only find digital SD
resolutions when displaying legacy NTSC content (hence it's in 4x3).

We're just not used to the fact that everywhere else in the world,
people have had widescreen television long before there was HD or
digital TV.

Like I said, I would be thrilled to see more content providers
properly denoting widescreen NTSC content. It's pretty frustrating
watching a "widescreen DVD" on an "widescreen television" and still
getting black bars on the top/bottom (and currently the only way to
work around it nowadays is if the television is smart enough to
heuristically detect the black bars).

If they had actually followed the recommendations in EIA-608 (setting
the aspect ratio in the line 21 VBI data), none of this would be a
problem.

Devin

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

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Re: [ivtv-devel] NTSC & WSS (was: ivtv TODO list) [ In reply to ]

jra at baylink

Jan 18, 2010, 11:24 AM

Post #2 of 4 (2149 views)

Permalink

----- "Devin Heitmueller" <dheitmueller@kernellabs.com> wrote:
> 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.

What he said. :-)

> 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.

Actually, newer sets will in fact try to auto-zoom when they detect
lettterbox, pillarbox, or both at the same time. They often get it wrong, though.

My sister has a Philips that actually does a pretty decent job.

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

I don't believe it actually has to be HD. I think that OTA DTV can actually
utilize widescreen SD resolutions akin to 800x480.

[ checks Wikipedia ]

704x480 for NTSC, in fact:

http://en.wikipedia.org/wiki/Digital_television

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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Re: [ivtv-devel] NTSC & WSS (was: ivtv TODO list) [ In reply to ]

hverkuil at xs4all

Jan 18, 2010, 11:42 AM

Post #3 of 4 (2154 views)

Permalink

On Monday 18 January 2010 20:20:53 Jay R. Ashworth wrote:
> ----- "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.

I only know the situation from a PAL/SECAM perspective: here the use of WSS is
standard. If missing, then the source is 4x3, if it is present then it will tell
you exactly what aspect ratio it is. Usually 4x3 or 16x9 (i.e. letterboxed,
possibly with extra PALplus encoding although that isn't used much anymore),
but I have also seen anamorphic encoding (pretty rare, though).

In practice it works perfectly for PAL and SECAM. I'm frankly amazed that
there is no such equivalent for NTSC in use. I always assumed it was encoded
in the XDS or with some proprietary encoding that I didn't know about.

Regards,

Hans

> 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
>
>

--
Hans Verkuil - video4linux developer - sponsored by TANDBERG

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Re: [ivtv-devel] NTSC & WSS (was: ivtv TODO list) [ In reply to ]

jra at baylink

Jan 18, 2010, 11:45 AM

Post #4 of 4 (2154 views)

Permalink

----- "Devin Heitmueller" <dheitmueller@kernellabs.com> wrote:
> Like I said, I would be thrilled to see more content providers
> properly denoting widescreen NTSC content. It's pretty frustrating
> watching a "widescreen DVD" on an "widescreen television" and still
> getting black bars on the top/bottom (and currently the only way to
> work around it nowadays is if the television is smart enough to
> heuristically detect the black bars).
>
> If they had actually followed the recommendations in EIA-608 (setting
> the aspect ratio in the line 21 VBI data), none of this would be a
> problem.

No, but they'd take the rap for the fact that the image would look Even Worse,
and if they make you set it, then they don't have to. :-)

And, to be pedantic about it again, there is *no such thing* as "widescreen
NTSC content". If it's NTSC, it's 4:3. Period. End of report. If you want
to put letterboxed or anamorphic content in that image well, that's your own
lookout. But we're sure as hell not going to encourage you: NTSC looks bad
enough.

Well, unless you have Faroudja SuperNTSC encoders and a clean analog chain at
the station. :-)

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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