Re: LCD TV as Monitor?

Sail@xxxxxxxxxxxxx wrote:

Dave, I have read your posts on the IDE Channels thread and agree with
your reasoning there. But here you are off base because of misuse of
terms that lead to misconceptions. Sorry. Please read to the end before
writing any reply.

I have read to the end and you're misinterpreting digital terms into analog terms.


You guys are confusing the lines of scanning (or for digital displays
the lines & columns of pixels) with the *resolution* a display is
capable of showing (or media capable of delivering).

Not so.


Yes so. 

No, not so.



The digital ratio of pixels for NTSC is 720 across and 480 down.

There is no 'digital ratio' for NTSC broadcast video (the topic for tuners). It's an analog system. 


Analog video as seen in television sets and analog monitors has NO
pixels.  They are only a factor in digital displays. Thus the term
"digital ratio" which is the number of columns vs rows.


Which is what I just said with "It's an analog system."

What you're describing is, as was said, the DVD encoding and that isn't the same thing. 


I am not describing "DVD encoding" at all. I am talking about displays,
analog and digital.


The number of pixels you mentioned was DVD resolution.


For analog it is 525 lines scanned horizontally, of which about 490 are visible. For analog PAL (European standard) it is 625 scanning lines, of which about 560 or so are visible.

The electron beam is going horizontally back and forth to make the horizontal scan lines but how many of them it stacks going from top to 

  > bottom is the vertical resolution (at best).

No it is not. You are confusing the number of horizontal scanning lines
with  "vertical resolution", which is a measurement.

Not in the computer display world. "Vertical resolution" is how many pixels are displayed top to bottom and that is one per visible scan line. E.g. the original VGA 640x480 monitor displays 480 horizontal scan lines and that is the '480' portion of the 640x480 resolution spec. And you can easily calculate the minimum video card frame memory needed to create it, 640 pixels per line times 480 scan lines times the bits color depth. For a 256 color display, 1 byte per pixel, that's 640 x 480 = 307,200 bytes and you'd need a 512k video card to do it (256k being too small).



(I have worked in
professional television production and post production for 25 years).
Vertical resolution is a measurement of the number of vertical lines
that can be resolved in a display. IOW, how many individual vertical
lines can be seen on a display. Thus "vertical resolution" depends on a
horizontal scan, passing  across each line.

The very confusion is that you've worked for years in television production and are trained on the 'lines' method of resolution but no one here is speaking of 'lines' in that context and that is the error you're making in presuming that when someone speaks of 'lines' that it has anything to do with the 'lines of resolution' you are used to working with.


And NTSC does 525 of them by the time it goes from top to bottom (twice: 252.5 each half interleaved with the other half).



RESOLUTION is a different latter altogether.

You've got it switched. 


No, I have it right, as described above. I've made my living in this biz
for a long, long time.

Which is why you have it switched: The computer world isn't that biz and the terminology is different.


Vertical resolution means
how many vertical lines can be discerned when scanned horizontally.

No. "Vertical resolution" is how many scan lines there are, assuming interleave is working perfectly.


Wrong. See above.

A computer monitor is not designed not spec'd for 'broadcast TV' and computer people do not use 'broadcast TV' terms when speaking of "resolution." It is a different world than the one you are used to.

In the computer monitor world, the number of visible scan lines is, indeed, the vertical resolution and not the 'discernible lines' you are used to.


Perhaps better, consider the meaning of the term "resolution". If we
accept your erroneous interpretation for sake of discussion, how many
horizontal lines can be discerned in a 500 horizontal scan line display?

Which is precisely the problem. 'Resolution' in the context of computer displays is not measured by 'discernible lines'.

(we will exclude any consideration of lines only carrying broadcast tech
data apart from visual information). 500? Nope. That would be a solid
display.  500 black lines would be a black screen. 500 white lines would
be a white screen.

Yes, it would be. Which is irrelevant as it still takes 500 (vertical) pixels, all the same illumination, to create that solid display and the computer must process and send all 500 to create that 'solid display'.


"Resolution" means how many individual lines can be
resolved.

Not in the computer display world. "Resolution" is how many pixels can be displayed and whether you make 'lines' with them, or not, is irrelevant.

Theoretically in this case the max answer would be 250 lines,
alternating black and white, so that the individual lines can be seen.

That is, indeed, how the broadcast TV industry determines 'lines of resolution' but it is not how the computer display world speaks of resolution.


In real world applications this level is not reached.     > How many
"vertical lines can be discerned" is the horizontal  > resolution. >  >>
(Think about it. you have a bunch of vertical lines. >  > No, you think
about it. 'We' didn't have a "bunch of vertical lines"  > till you
decided to claim that's what we meant when we didn't.

You may not mean it, but the professional world of video defines
vertical resolution as the ability to resolve individual vertical lines.
It's part of the SMPTE definitions and standards and has been for
decades. That's the world I come from and the standards we use.

I understand the 'TV' world you are in but that is not the one the computer display is in.

When you see a 17 inch monitor spec'd with 1280x1024 maximum resolution they are not speaking of your TV world 'lines'. They are speaking of pixels and if they're all the same illumination then, yes, you'd have a 'blank' screen of that illumination.

And to get the 1024 pixels of vertical resolution it takes 1024 scan lines, one per pixel, (plus off screen and sync). And that is precisely how it is sent to the monitor.


It  is the
horizontal scan which will discern between them.) The number of
"vertical lines of resolution" therefor has nothing to do with the
number of pixels arranged vertically.

Only because you're jumbling the words midstream. No one meant "vertical lines" as in lines going up and down on the screen. They meant the vertical resolution is how many scan lines there are.


Exactly. Read your words closely. 

Take a breath because I am seeking understanding, not a fight.

Your last line reads, "They meant the vertical resolution is how many
scan lines there are."

Those are Two Different Things, which has been my whole point. "How many
scan lines there are" is, well, "how many scan lines there are".

"Vertical Resolution" is the ability to discern vertical details.

Not in the computer display world it isn't or, rather, it's inherent in the monitor's pixel resolution specification since those pixels can, of course, be 'discerned'.


Those are two completely different issues. My posting was about the
correct definitions of those two issues.

The rest of your post quotes my comments on the loss of resolution when
passing through copied generations from the master down to copies,
thence through transmitters, into receivers, and eventual home display.
We have no apparent disagreement there. 

And you note that:

"And there is the problem because the signal is encoded NTSC to get on
that  radio frequency and NTSC bandwidth, hence the available resolution
when  decoded, stinks."

Yes, and you are on the same page with me if you will consider your use
of terms here. 

My point in talking about that procession is that the number of scanning
lines, or rows of pixels on a digital display, do not change. But the
quality of the picture degrades substantially - it loses resolution.

It shouldn't or, rather, doesn't have to. Vertical resolution is entirely preserved as each scan line is converted one to one. I.E first visible scan line is converted to a digital scan line, second to the second,... up to the maximum 'visible' of 480. There is no loss to interleave jitter, phosphor blooming, or anything else.

Horizontal is affected by the sample rate (and clock stability) vs nyquist frequency of the original content and the typical computer tuner card is sampling lower than optimum but, in theory, there's no reason why it couldn't be sampled at, say, 2048 per horizontal line even though the video content is lower than that. It isn't typically done in your 'normal' tv tuner card because that would require some serious digital processing and simply sampling at the corresponding horizontal pixel rate matching the vertical scan lines, e.g. 640(720)x480, is a lot simpler as it translates directly to the computer screen it's eventually going to. It doesn't need 'conversion' past the digitizing and de-interlace (which is why some cards get really nasty and just pull 240).


Because, once again, scanning lines and resolution being separate
matters. Resolution is a quality issue.

It isn't in computer displays or, rather, it's inherent in the pixel resolution specification (barring how 'sharply' the pixels are displayed)

Put another way, both a 'low quality' and a 'high quality' 1280x1024 monitor will display 1280x1024 pixels but the 'high quality' one may be 'sharper' than the other. The 'high quality' monitor's tube might, in theory, be capable of displaying more of your 'lines' but it can't because of the scan rates. e.g. the video amplifier bandwidth is sufficient to do 1280 horizontal pixels and there are 1024 visible scan lines making up the 1024 vertical resolution, in both the 'high quality' and 'low quality' monitors.

You simply never have the 'computer world' equivalent of your 'TV world' case where "this crappy 1280x1024 monitor only does '400 lines'." Computer displays are specified by pixel resolution and if it only does '400 lines' then it isn't a 1280x1024 monitor.


Scanning lines, or digital pixel
ratios, are technical specifications. You can have a very high number of
scan lines. such as 1080 for HD, but still have a very low _Resolution_
image displayed (perhaps as low as "180 vertical lines of resolution".

You're speaking in TV terms again. A computer display spec'd at 1080 will do 1080. What you send to it, e.g. a low resolution TV signal, is another matter entirely.

Again, you simply don't have a computer world equivalent to the 'TV world' case where vertical resolution is lost to zitter, overlapping scan lines, or any of the other 'TV monitor' maladies. It wouldn't be a 1080 monitor.


So an NTSC system will not have "525 lines of vertical resolution". Nor
will PAL have "625 lines of vertical resolution". They do have those
numbers of "scanning lines". (Not all of which are for visual image
capture but that's a whole different discussion).

The point here is that when you hear people in the computer world speak of 'lines of vertical resolution', in that context, they do, indeed, mean the scan lines since that is precisely how computer displays operate, how they're spec'd, and is the meaning of 'resolution' in their context.


Hope this clarifies. When talking tech it is important to be careful and
precise in the use of terms. The short cut memory is that scanning
lines, or rows & columns of pixels, are a technical specification.
Resolution is a quality issue.


Hopefully you see what I am talking about too.

FWIW the confusion between the two is not new. Been going on among the
lay for about 60 years.

Except there weren't any PC monitors to cause the particular kind of confusion we have here.


.

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