HDTV resolution

cafink

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Carl Fink
I've been considering purchasing an HDTV soon, but there's one issue about which I'm somewhat befuddled.

All HD sources have a vertical resolution of either 720 or 1080 lines, don't they? Why, then, does the resolution of so many HDTVs match neither of these figures? In particular, a lot of models are said to be "720p," but have 768 vertical lines of resolution. What is the reason for this, and how does it affect the viewing experience? Will a 720p signal actually be scaled to 768 lines? Wouldn't that be detrimental to the picture quality?

It just seems to me that an HDTV ought to have a native resolution of either 720 or 1080 lines, and I can't figure out why this wouldn't be the case. Any information on the subject is appreciated.
 

Michael TLV

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Greetings

768 comes from the computer world. 1024 x 768 ... sound familiar? Easier to create panels where one dimension still matches the needs of the computer world.

I'm sure if you gave the companies a large enough purchase order on just 720 panels ... that they'd stop this practice.


Everything gets scaled anyway ... regardless of the panel size. That's why there is "overscan" on TV sets.

Regards
 

cafink

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Thanks for the response, Michael.

In looking at HDTVs, I've been keeping in mind the philosophy espoused by RAF in this post: "make sure that your display can accept the native resolution that it displays." That idea makes a lot of sense to me. I was under the impression that many HDTVs were available with native resolutions of 720 or 1080 lines, and that these models could display a 720p or 1080i (or even 1080p) HD image with no scaling or processing at all, allowing that to be handled by a more capable external device.

1024×768 pixel displays, in particular, seem like a very bad idea to me. They are described as "720p" displays, but I wouldn't imagine that 720 lines would scale very neatly to 768--at least not in real-time, as would have to be done.

If, indeed, "everything gets scaled anyway," then RAFs "native resolution" ideal is unattainable, isn't it? What am I missing?

Thanks again.
 

Allan Jayne

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The biggest shortcomings seen in some CRT HDTVs are beam spot size (a little too fat for 1080 scan lines although all 1080 are drawn) and electronics bandwidth (may make it impossible to change from white to black within 1/1920'th or even 1/1280'th of th screen width to achieve 1920 or even 1280 pixels across with)

It is actually equally difficult to achieve 1280 pixels across with 720p as it is to achieve all 1920 pixels across with 1080i, using analog circuits including component video cables plugged into the TV inputs in back.

Usually there is no problem displaying 720p shows on 768 scan line TV's.

Currently there is a major shortcoming showing 1080i material on most 1080 line, 768 line and 720 line non-CRT TV's. The needed processing (de-interlacing) is on average not all that great and in some cases only 540 lines of resolution vertically are achieved. Some sets preserve all 1080 scan lines of detail but leave behind an uncanny motion blur where subject motion on the even scan lines does not match subject motion on the odd scan lines.
 

Michael TLV

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Greetings

You normally can only achieve pure native resolution with zero overscan in computer applications.

The TV programming has built in overscan on the TV end since it is there to "hide" stuff that has nothing to do with the TV itself but problems with the incoming signal. Some channels are not actually centered and with zero overscan, you will see which channels these are ... fast.

As an average consumer ... if they have zero overscan, and thus see a 1 inch black bar on the right side of the screen on their local ABC channel ... who are they most likely to call about the "problem?" The TV maker of course ... and they send a tech out ... and finds nothing wrong with the TV ... and go back and bill "Sony" for instance for 1 hour of their time. The problem has nothing to do with the TV and yet it just cost the TV maker money.

There is a lot more to image quality than just resolution.

In the grand scheme of things ... image resolution ranks as #4 in importance ... not #1.

#1 ... Dynamic Range
#2 ... Color Saturation
#3 ... Color Accuracy
#4 ... Resolution

Regards
 

Mike Romo

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I had the same questions..but I ended up asking them AFTER I bought a set (so dumb, I know). I was so freaked out about it that I almost cancelled my order, but when I realized that there was no way to get what I wanted (a 42" plasma that could show a 1080 image), I kind just let it go.

I found this article really, really helpful and you might too:
http://www.cnet.com/4520-7874_1-5137...html?tag=today

in the end? I am totally fine with "just" 720p and am very much enjoying HDTV!
-mike
 

Ken Chan

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There are a few sets with 1-for-1 pixel mapping as a feature. Toshiba has a few. Maybe Sony. As Michael said, overscan is an issue with TV (shouldn't be for DVD). I would prefer that they simply mask off the edge pixels at the native resolution (if displaying 720 on a 1080, it probably doesn't matter as much) -- but I can totally understand why they don't, because people will think their TV is broken.

There's also the issue of whether you get all of the horizontal resolution. Last week, someone linked to a test, and the only set that displayed all 1920 out of the box was the $10,000 Pioneer plasma. But again I agree that this might not be the most important factor when choosing a display.
 

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