Re: LCD vs CRT resolution

Java Jive wrote:
On Wed, 27 Aug 2008 22:56:54 +0100, Andy Champ <no.way@xxxxxxxxxx>
wrote:
The most important point I'm trying to make is that the phosphor dots on a CRT are not a precise match to the pixels in the digital image you're trying to show.

Which by my measurements and the Samsung LE19R 86BDX specifications
supplied by none other than yourself is also true of the physical
pixels in LCD TVs.

With an LCD or plasma running in its native resolution their is a 1:1 match between the pixels coming out of the MPEG decoder and the little lights on the screen. With a CRT it is only an approximate match. I've enquired several times why I would want to buy a 900 line TV, and no-one has answered!


... If I run a CRT in a non-maximum resolution, the beam scanning will be at the resolution of the incoming picture. The phosphor dots of course won't move; but the spread of the beam (deliberate spread, if the CRT is smart enough to notice the lower input resolution) will result in an input pixel being shown as some blend of dots around the target.

Which by interpolation is potentially also true of LCDs.

See below.

With a plasma or LCD, as the resolution drops you have to do something drastic, probably involving lots of software running at high speed, to calculate the intermediate screen pixels. At the very least this will involve a store of several picture lines that can be accessed simultaneously by the logic handling the input picture and the logic drawing on the screen. And the two sets of logic will be running at different speeds.

Yes, but this is just reiterating what I've already posted, and still
doesn't tell us anything from real knowledge about how it's actually
done in practice. Also, you've contradicted yourself again ...


Keep looking down...

You don't need floating point, you only need fixed point. And IAC the price of a graphics chip capable of this kind of work is *plummeting*. It's one of the bits of the computer world that is exceeding Moore's Law; price:performance is halving more often than every 18 months.

I have no idea how broadcasters actually do it at the hardware level,
perhaps someone here can enlighten us, but I don't suppose their
equipment has FP coprocessors.
I do. My son's new graphics card will do about 2 teraflops. 2 million million floating point operations per second. Surely they can manage that?

So in one post it's "drastic", and the other it's "Surely they can
manage that?"!!!!!

Yes. Surely a broadcaster can manage something the equivalent of the hardware that is currently on the PC market for 300 quid. I'm pretty sure a TV manufacturer *cannot do it inside the box*. 300 quid is a small fraction of the costs of the BBC, but a large fraction of the cost of a TV.

When I play a composite signal through the LCD I have in front of me it looks pretty bad. The screen struggles to upscale the PAL picture to the screen resolution.

When I play a PAL image through my computer (DVD) it looks a lot better. This just might be something to do with the HW in my PC having a lot more horsepower than the screen.

I can't feed it an HD image, my PC isn't fast enough.


I think a CRT is better in one specific way; when it is running at a non-optimal resolution it will get much closer to its best picture than LCD/Plasma screens.

But the only hard *evidence* available, which comes from my own
photographic investigations, points to an opposite conclusion.

If you want to convince people, you have to find some actual evidence,
not just endlessly go round in circles repeating these same
unsubstantiated assertions, which is an especially dangerous habit for
you to indulge in, as you seem to have a knack of contradicting
yourself when doing it, which just results in you looking faintly
ridiculous.

Give us some facts, or give us a rest ...

Your photos don't point to a generic conclusion. The experiment we need involves two computer-quality screens of each technology, comparable size, and two different resolutions. I have no decent quality CRT available any more - only standard def. TVs. None of the LCDs I have available are anywhere near this low resolution.

I put it to you that a CRT will not lose as much quality as an LCD when fed a sub-optimal scan rate. I know this from many years of using displays of both technologies. However, as this has been almost entirely with computers I am happy for you to provide evidence proving the opposite.

My choice of technology, for picture quality, would be:

(1) LCD running at its native resolution, or an easy fraction of it.
(2) CRT running at any resolution
(3) LCD running at resolution unrelated to the source material.


Andy.
.

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