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HD Europe spec and tv resolution confusion

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Anonymous
April 14, 2005 8:48:27 PM

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

Hi,

I am getting confused by Europe's new High Definition specs and
recommendations. In What Hi-Fi mag's glossary it says720 verticle lines must
be able to be displayed (this being one of the agreed HD output formats),
and an ideal example being the Toshiba TV which displays a 1366x768
resolution.

Now i'm sure there are not 48 lines of pixels left blank, so the picture
must either be stretched or the extra 48 lines invented by Interpolation
(like Photoshop?). Is this ideal, surely an exact 720 line display device
would be better?, but looking at the 32" LCD tvs reviewed in April 05 What
Hi-Fi, none of these have this. They all have 768 horizontal lines, which as
we know is a common PC monitor format (1024x768), there must be a connection
here!

Further, I remember Screenplay projectors being praised for having chips
which (although not HD), exactly matched the PAL 576 lines of resolution.

Am I missing something simple which would explain how having more pixel
lines is ideal when they won't map exactly?



Regards,
Andrew

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and www.sdttl.info for Southend League table-tennis site
Anonymous
April 14, 2005 10:03:09 PM

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

On Thu, 14 Apr 2005 16:48:27 +0100, "Andrew H" <andrew@sdttl.info>
wrote:

>Hi,
>
>I am getting confused by Europe's new High Definition specs and
>recommendations. In What Hi-Fi mag's glossary it says720 verticle lines must
>be able to be displayed (this being one of the agreed HD output formats),
>and an ideal example being the Toshiba TV which displays a 1366x768
>resolution.
>
>Now i'm sure there are not 48 lines of pixels left blank, so the picture
>must either be stretched or the extra 48 lines invented by Interpolation
>(like Photoshop?).

And 86 "columns".

>Is this ideal, surely an exact 720 line display device
>would be better?, but looking at the 32" LCD tvs reviewed in April 05 What
>Hi-Fi, none of these have this. They all have 768 horizontal lines, which as
>we know is a common PC monitor format (1024x768), there must be a connection
>here!

My LCD TV is in 15:9 format and has 1280x768 pixels.
When it displays in 16:9 it uses 1280x720 pixel.
24 *2 lines are left black.
In TV SD broadcast, there is a defined extra margin for tolerances and
variation. So the TV often zoom about 5 percent (often called
"overscan").

I conclude (after displaying the signal from digital satellite
broadcast on the PC, that it would not be a good thing to display all
the lines and pixels bacause the outmost lines often contains rubbish.
I don't know if the HD "spec" requires an overscan or if it is
guarantied that all pixels contain valid information.

The only LCD displays I have heard of with native 1280x720 are
projectors.

The question is, do the HDTV broadcasts fill all pixels with the
picture, so that we don┬Ęt need any "overscan" if we keep the signal in
the digital domain?

>Further, I remember Screenplay projectors being praised for having chips
>which (although not HD), exactly matched the PAL 576 lines of resolution.
>
>Am I missing something simple which would explain how having more pixel
>lines is ideal when they won't map exactly?

No.
And it is even more difficult to convert an interlace signal for a
progressive display (like 1920x1080i).
I know the effects it has on SD interlaced signal.

It is easier for Photoshop working with still pictures. The real
problem comes from the motion.

I admit that there is an advantage to upsample the signal to more
pixels in that the very sharp pixels which are created in a fixpixel
direct view display become less visible so we can use a larger/closer
picture. (Altough the image detail is not encreased.)
But the small increase from 720 to 768 can not be justified by this.

My opinion is that we would be better off if an HDTV standard could be
defined, and I mean a Standard and not several variants that are
impossible to display at optimum with the same hardware..

/Jan
!