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Posted by M.I.5 on 01/18/07 08:03
"Joshua Zyber" <joshzyber@comcast.net> wrote in message
news:y8adnazRPO53vzPYnZ2dnUVZ_uSgnZ2d@comcast.com...
> "M.I.5" <no.one@no.where.NO_SPAM.co.uk> wrote in message
> news:45add5bc$1_1@glkas0286.greenlnk.net...
>> Your choice of wording is suggesting to me that it is you who doesn't
>> really quite appreciate what is going on here.
>
> Funny, that's exactly what I've been saying about you all along.
>
>> I think you (and many
>> others here) have assumed that when you play a 720 x 576 DVD source
>> into a 720 x 576 LCD or Plasma display device, that the pixels are
>> mapped on a 1:1 basis. This just doesn't happen. The DVD is
>> converted to the analogue domain and sent to the display as a CVBS,
>> S-Video, RGB or YCBCR analogue signal (the last two giving by far the
>> best display).
>
> Modern HDTVs have digital HDMI connections that avoid the conversion to
> analog.
>
But only the very latest and high end DVD players do.
>> The display then maps the analogue signal back to a
>> digital granularity in the X and Y axis (though retains the analogue
>> in the Z axis). There is nothing in the analogue signal that allows
>> the display to map the original pixels 1:1. It might be close, except
>> that displays usually lose the outer parts of the picture (overscan).
>> The use of displays with larger numbers of pixels that are available
>> in the consumer market still are not an integral multiple of the
>> original source, but the finer granularity allows a better
>> interpolation of what is contained in the analogue video.
>
> So then you admit that any added pixels are interpolated, not real detail
> found in the original source?
>
No detail can be added that isn't there. But if the display is about the
same resolution and the pixels aren't quite mapped 1:1 then detail can be
lost or unwanted artifacts can appear (depending on the exact mapping - and
a reletively small mapping error can do this). The higher the resolution of
the display, the less this effect occurs with a limit of 2:1 mapping after
which no benefit occurs. The 2:1 limit occurs with a display 1440x1152
given 720x576 source material. Even my HD LCD display (can't rememer its
exact pixel size, but it is certainly larger than a DVDs) gives noticeable
image degradation on certain scenes. Of course if the DVD pixel map was
mapped perfectly in 1:1 correspondence with a 720x576 display, then none of
the above would occur, but it doesn't. Even with the video streamed over a
digital connection (be it DVI or HDMI or whatever), the outside border of
the actual picture is outside of the display - this is by design.
>> And the pixels on most displays aren't square either. And that phrase
>> 'directly mapped' tells me that haven't got it. See above.
>
> I'll remind you that you're the one who came up with the ridiculous
> 1440x1152 claim, not me. I've never claimed that the displays contained an
> even multiplier of the source pixels. I'm trying to debunk your claim that
> such is necessary.
>
You can debunk all you like. All the professional AV engineers that we
contract to seem to understand all this - and as I said, Wikipedia has a
very good discussion of the subject (somewhere).
>> Some newer DVD players now feature HDMI (digital) interfaces, but as
>> these are used with HD ready displays, a 1:1 correspondence still does
>> not occur.
>
> Of course not. DVD pixels aren't square, but the display's pixels are.
> Further, HD displays have much higher pixel counts than a DVD source.
> There will never be a direct 1:1 correspondence. Interpolation will always
> be necessary for those reasons. But that doesn't mean that only a
> 1440x1152 display can capture DVD resolution. Watching a Standard
> Definition DVD on a higher resolution screen requires scaling.
> Interpolated pixels are not found in the source, obviously.
>
No, but as I said, Aliasing and artifacts from the interpolation will occur.
>>> Where did you even come up with this ridiculous 1:2 ratio between DVD
>>> resolution and display pixels? Do you not realize that DVD pixels
>>> aren't square? A 720x576 DVD image directly 1:2 mapped to a 1440x1152
>>> would give you a picture in the wrong shape!
>>
>> And the pixels on most displays aren't square either.
>
> The only digital displays that use non-square pixels are plasmas. LCD,
> DLP, and LCOS/D-ILA all use square pixels.
>
Not necessarily. Some may well do, but not necessarily all. But in any
event this is entirely incidental to the point.
>>> And puzzle this over, smarty pants: If a meager DVD really requires a
>>> 1440x1152 display to resolve it, wouldn't that also mean that a true
>>> High Definition image would require 3840x2160 pixels? So does that
>>> mean that all of the HDTVs out there aren't really capable of
>>> displaying HD content at all? And by the same logic, an HD signal on
>>> a current "HDTV" screen would show no improvement over a DVD, which
>>> is already barely taking advantage of the screen?
>>
>> The current crop of HD displays are caoable of displaying an HD image.
>> They are just not capable of displaying it as well as they could,
>> especially given that the pixel resolution of displays in the consumer
>> market does not exactly match any of the recognised HD formats.
>
> 720p, 1080i, and 1080p are not recognized HD formats anymore? When did
> that happen?
>
Which displays have a vertical pixel count of 720 or 1080 pixels? OK, there
are quite a few in the professional market but the vast majority in the
consumer market don't. And even if there were, the mapping would still not
be mapped 1:1 because of the undsiplayed border that this type of video
signal is usually displayed with. (I'm trying to look out the
specification)
> Do you own an HDTV? Have you even seen one in person? It certainly sounds
> as if you've never tried watching both DVD and HD content on one, or you
> would understand the difference.
>
Yes, yes, yes and yes.
>>> Ludicrous. Simply ludicrous.
>>
>> I suggest you research the issue, and once you see the flaws in your
>> arguments, it may all start to make sense.
>
> I suggest you do the same. Your claims about DVDs requiring a 1440x1152
> display are absurd to say the least.
I don't need to - I already have. You clearly haven't and are merely
reiterating what seems obvious to you.
I can lead the horse to water, but if he won't drink there is nothing
further that I can do.
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