[mdlug] Building a Linux PVR

[Dan Pritts]

Hi, a late reply here, catching up on some old mail

On Thu, Nov 23, 2006 at 08:59:11PM -0800, Ron Blanchett wrote:
>    Yes and No. High Definition Video only refers to the resolution of the
>    video.
>    There are several different resolutions that qualify as being HD.
>    They are 720i, 720p, 1080i, 1080p.
>    Don't be fooled by these numbers though because 1080i is really no
>    better than 720p.
>    Why you ask?
>    Because when your TV receives a 1080i signal it has to down convert it
>    to 720p.

This just isn't true.

I fear that my response may not clear things up totally, and I don't
have time to rewrite it.  The wikipedia article is informative.
  http://en.wikipedia.org/wiki/High-definition_television

Ron has part of this right.  The number in an hdtv resolution indicates 
the number of horizontal *lines* of video.  The i or p indicates
progressive or interlaced scan. 

progressive scan means that for each frame update (for normal HDTV, about
30 frames/sec), each and every line is updated.

interlaced means that for each frame update, only every other line is
updated.  

The bottom line of all this is that the important thing here is the
native resolution of your TV; 720 lines, 768 lines, 1080 lines are
common for flat panels and rear-projection sets.  Tube-based HDTVs 
can typically alter their scan rate and truly show 720p or 1080i.

Any HDTV set, of any of these varieties, should be able to *display*
either 720p or 1080i content.  

While it is true that an LCD or plasma display does not have a
scanning gun like a CRT, and thus interlacing doesn't happen on the
display, it *does* come through in the signal.  If the TV's native
resolution is 1080 lines, then it will show you all 1080 lines, and
just update them when it goes a new frame.  So really these are
1080p displays showing 1080i content.  

Now, it *is* true that the ability to *display* 1080i content doesn't
mean that the TV is necessarily any better; it could be set with a native
720-line display, in which case the signal is scaled down as Scott
describes.  Note that the scaling is very simple - 1080:720 :: 3:2

typically with LCDs and plasmas, the native resolution is 768 lines,
so that either a 720-line or 1080-line signal is scaled to that
native resolution.  Note that some cheap plasmas are only 1024
pixels wide and must be scaled in that direction, even if they are
really 720 or 768 pixels tall.

However, true 1080-line displays do exist.   

Conventional wisdom is that for slow-moving content (eg, movies),
the additional pixels provided by 1080i makes things look better.
For fast-moving content like sports, the higher frame rate is better.

There really is no such thing as 720i.  If it existed, it would be a
720-line, interlaced display.  

720x480 or 640x480 content is 480p or 480i.  


>    Why you ask?
>    Because most TV's are incapable of displaying an Interlaced signal and
>    that is what the I stands for in 720i and 1080i.
>    So when your TV receives that 1080i signal it has to down convert it
>    to a 720p signal to display it as a Progressive Scan signal.
>    So if you own one of those great new HD TV's and you bought it because
>    the guy/gal in the store up sold you on the idea that 1080i is way
>    better than 720p, you where taken for a ride. Just about every none
>    tube based TV is Progressive Scan and said TV has to Down Convert
>    1080i (if that is the highest resolution it can display) to 720p to be
>    able to display it on the screen. And 720p has a resolution of 1280 x
>    720, hence the 720p.
>    So to answer your question, if your DVI LCD monitor can display
>    1280x720 without a problem you don't need a new one for HD content as
>    long as that content is output at the equivalent of 720p (which in
>    case you missed it is 1280x720). And since your display is an LCD
>    monitor it should be Progressive Scan.
>    Oh one more thing, 720i is the equivalent of 480p which is the
>    progressive scan equivalent of Standard-definition TV.
>    Any more questions?????
>    Is any of this a little confusing?
>    I hate to say it but the TV industry wants you to be confused about
>    all of this. It helps them sell TV's.
>    Also those new "HD" monitors are just something else the industry is
>    doing to try to get you to upgrade your equipment and guess what M$ is
>    in the boat with them as far as the forced upgrade cycle goes, Vista
>    will not display all of its new eye candy if you are not using an HDMI
>    HD Monitor as your display. Forget buying into needing an HD Monitor
>    to display HD video, as long as your monitor can display a minimum of
>    1280x720 you are already capable of displaying HD video on it.

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danno
--
dan pritts
danno at umich.edu
734-929-9770