What's the purpose of half resolution?

[Doc]

Archived from groups: rec.video.desktop (More info?)

What is the half resolution capture setting for? I find that when I
capture in that mode, playback looks elongated.

 

[martin]

Archived from groups: rec.video.desktop (More info?)

"Doc" <docsavage20@yahoo.com> wrote in message
news:f0c1bc20.0409220931.430adabd@posting.google.com...
> What is the half resolution capture setting for? I find that when I
> capture in that mode, playback looks elongated.

Think in terms of picture quality.

Half resolution = more bits per pixel = better quality.

martin.

 

[Doc]

Archived from groups: rec.video.desktop (More info?)

"Martin" <zedolf@o2.co.uk> wrote in message
news:2rdrflF18rfv3U1@uni-berlin.de...
>
> "Doc" <docsavage20@yahoo.com> wrote in message
> news:f0c1bc20.0409220931.430adabd@posting.google.com...
> > What is the half resolution capture setting for? I find that when I
> > capture in that mode, playback looks elongated.
>
> Think in terms of picture quality.
>
> Half resolution = more bits per pixel = better quality.

Okay, but what do you do with it? Obviously the elongated image isn't
usable. Is it meant for output to tv/video tape?

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

Doc wrote:

>>> What is the half resolution capture setting for? I find that
>>> when I capture in that mode, playback looks elongated.

>> Think in terms of picture quality.
>> Half resolution = more bits per pixel = better quality.

> Okay, but what do you do with it? Obviously the elongated image
> isn't usable. Is it meant for output to tv/video tape?

The image is not elongated. Rather, the area that each individual
pixel is considered to represent is just of some other shape than
square (rectangular, either way.)

Or more accurately, the sampling grid does not have the same density
in the X direction as it has in the Y direction.

Yet another way to look into it: the pixel aspect ratio (x/y or
y/x, whichever way you want to represent it) is something else
than 1/1.

If you see elongated images on your screen, that is because your
media player software lacks proper scaling (interpolating) and
aspect ratio support, and simply dumps the image data pixels 1:1
to the screen pixels.

* * *

Note that in the widely-used ITU-R BT.601 based full screen capture
resolutions (such as 720×576 or 704×576 for "PAL" and 720×480 or
704×480 for "NTSC") the pixels are not "square", either, but still
slightly elongated - so even images captured in these formats need
corrective scaling/interpolating in order to view them properly on
a computer using square pixels.

You might want to take a look at

<http://www.iki.fi/znark/video/conversion/> and
<http://www.lurkertech.com/lg/pixelaspect.html>

* * *

As for the purpose of half resolution, DVD players, for example,
can display 352×576 ("PAL") and 352×480 ("NTSC") images interpolated
over the full screen.

There are also other variations, such as the 2/3 BT.601 sampling
employed by the SVCD format (480 pixels across the screen, making
the image 480×576 for "PAL" and 480×480 for "NTSC" - yet the image
correctly fills up the screen when viewed on an SVCD [software or
hardware] player.)

--
znark

 

[martin]

Archived from groups: rec.video.desktop (More info?)

"Jukka Aho" <jukka.aho@iki.fi> wrote in message
news:GOm4d.360$nv.109@reader1.news.jippii.net...
> Doc wrote:
>
> >>> What is the half resolution capture setting for? I find that
> >>> when I capture in that mode, playback looks elongated.
>
> >> Think in terms of picture quality.
> >> Half resolution = more bits per pixel = better quality.
>
> > Okay, but what do you do with it? Obviously the elongated image
> > isn't usable. Is it meant for output to tv/video tape?
>
> The image is not elongated. Rather, the area that each individual
> pixel is considered to represent is just of some other shape than
> square (rectangular, either way.)
>
> Or more accurately, the sampling grid does not have the same density
> in the X direction as it has in the Y direction.
>
> Yet another way to look into it: the pixel aspect ratio (x/y or
> y/x, whichever way you want to represent it) is something else
> than 1/1.
>
> If you see elongated images on your screen, that is because your
> media player software lacks proper scaling (interpolating) and
> aspect ratio support, and simply dumps the image data pixels 1:1
> to the screen pixels.
>
> * * *
>
> Note that in the widely-used ITU-R BT.601 based full screen capture
> resolutions (such as 720×576 or 704×576 for "PAL" and 720×480 or
> 704×480 for "NTSC") the pixels are not "square", either, but still
> slightly elongated - so even images captured in these formats need
> corrective scaling/interpolating in order to view them properly on
> a computer using square pixels.
>
> You might want to take a look at
>
> <http://www.iki.fi/znark/video/conversion/> and
> <http://www.lurkertech.com/lg/pixelaspect.html>
>
> * * *
>
> As for the purpose of half resolution, DVD players, for example,
> can display 352×576 ("PAL") and 352×480 ("NTSC") images interpolated
> over the full screen.
>
> There are also other variations, such as the 2/3 BT.601 sampling
> employed by the SVCD format (480 pixels across the screen, making
> the image 480×576 for "PAL" and 480×480 for "NTSC" - yet the image
> correctly fills up the screen when viewed on an SVCD [software or
> hardware] player.)
>
> --
> znark
>

And let's not forget VCD resolution - it's valid for DVD too.
352x288 PAL or 352x240 NTSC.

Martin.

 

[Doc]

Archived from groups: rec.video.desktop (More info?)

"Jukka Aho" <jukka.aho@iki.fi> wrote in message
news:GOm4d.360$nv.109@reader1.news.jippii.net...

> The image is not elongated. Rather, the area that each individual
> pixel is considered to represent is just of some other shape than
> square (rectangular, either way.)

Hmm. Not sure if I get it. I'll elaborate where the settings are.

The settings occur in a box labeled "Frame Adjust"

Under "Horizontal" are selections for Full Res. and Half Res.

Under "Vertical" are selections for One or Both Fields.

Then there's the cropping selections.- None or TV.

When "half resolution" is picked,the AV_IO interface becomes narrow, and on
playback on the computer, the image does the same whether played back within
AV_IO, Windows Media Player or WinDVD. However, I do notice that if I
playback the image to a TV, it looks normal.

 

[Guest]

Archived from groups: rec.video.desktop (More info?)

Doc wrote:

> When "half resolution" is picked,the AV_IO interface becomes
> narrow, and on playback on the computer, the image does the
> same whether played back within AV_IO, Windows Media Player
> or WinDVD. However, I do notice that if I playback the image
> to a TV, it looks normal.

This is quite normal. AV_IO is primarily a capture utility; it
probably does not care about aspect ratios at all. (Instead of
trying to make the image look "right" on a computer screen, it
simply displays the raw, captured pixel data, mapped 1:1 to the
screen pixels.)

As for why you get the same behavior from the Windows Media
Player or WinDVD, I can only guess, but maybe the capture
utility (or rather, the codec that you use while capturing)
does not record the meta information about the correct frame
aspect ratio into the AVI files.

You might want to try viewing them in a bit more versatile
program, such as Media Player Classic [1], and experimenting
with the different scaling options:

[1] <http://www.afterdawn.com/software/video_software/
video_players/media_player_classic.cfm>

* * *

Anyhow, even though there was some sort of problem in getting the
standard Windows Media player to display the files correctly, you
can still use them as a source material for e.g. creating a
half-res DVD. It all really boils down to your application. What
is your source material? What is your target format? Where do you
want to use the video files?

These days, people usually want to make DVD's out of their captured
video. Is this what you are trying to do? Or is it something else?
Using half-res captures may help you in saving space if you need to
squeeze lots of material on a single DVD disc. If encoded to MPEG-2
properly, the images will stil display correctly on a tv as far as
proportions go; they are just going to have a bit more mushy look
since there is less of horizontal resolution.

Knowing what you actually intend to _do_ with the captured video
would help in making a better judgement about whether using the
halved capture resolution would be of any real use (or benefit)
to you.

--
znark

 

[Doc]

Archived from groups: rec.video.desktop (More info?)

"Jukka Aho" <jukka.aho@iki.fi> wrote in message
news:z8z4d.505$Gk6.248@reader1.news.jippii.net...

Your explanation helped make things clearer, thanks.

> Knowing what you actually intend to _do_ with the captured video
> would help in making a better judgement about whether using the
> halved capture resolution would be of any real use (or benefit)
> to you.

Primarily DVD perhaps some VCD too.