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Old 03-12-2005, 15:36
stvn758
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Just wondering what the screen resoulution of a standard TV is. I have a Phillips 28inch model, if you connected a SKY HD box to it what would happen, the full 625 lines used up = added quality. What were those gimmicks for increasing the resolution on standard TV's they made all the fuss about a while ago before Plasma and LCD took over? I downloaded some 1080 HD demos and watched them on my PC and was quite impressed, I record clips off TV, music/entertainment etc, and post them on forums, I'd love to do some HD ones. They won't encrypt everything just for the hell of it will they?
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Old 03-12-2005, 16:35
Dino
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LCD and Plasma screens have a native resolution, i.e. the number of pixels across and down. That is the maximum resolution that the display will support without scaling the image.

CRT's work on a different principle. There is a horizontal and vertical frequency; the higher the frequency the more pixels you can fit on a line. Same for the vertical frequency. There is also the quality of the tube; how quickly the phosphors can react to the guns, the quality of the mask, etc.

PAL has a h frequency of 15.625Khz and a v frequency of 50Hz. With those timings, I think the maximum resolution you can fit on a 4:3 screen is in the order 800 x 600; assuming you cannot see the overscan area.

I have seen some professional tellys that'll do more with VGA input, but that's probably the best you'll get out of a standard telly.

I don't know much about the Sky HD boxes, I guess they'd output a standard PAL signal on all regular analogue outputs, i.e. RF, Scart, S-Video or Composite.
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Old 03-12-2005, 17:08
stvn758
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Thanks. Don't think I'll be able to afford a plasma for about a year when hopefully a good brand should be under a thousand, then there's blu-ray... so many new toys.
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Old 03-12-2005, 17:20
meltcity
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What is the screen resolution of a standard CRT TV? It depends.

In simple terms the maximum resolution that can be displayed on a standard TV set is 720 x 576 for PAL compatible signals, and 720 x 480 for NTSC signals. For various reasons the actual displayed resolution will be less than this.

The quality of the TV itself is a major determining factor for CRT resolution, as is the quality of the incoming signal. Non-flat FST screens typically have very poor resolution when compared with pure flat models. In a digital TV broadcast overcompression of the channel by the broadcaster also limits the visible resolution. On most TVs RGB SCART delivers a visibly sharper picture than composite SCART/RF.

I think the 'gimmick' you are referring to for improving the resolution of a CRT is 100Hz processing. They generally produces sharper pictures than a 50Hz model, but they have their problems: pixelation, juddering during fast motion, etc.
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Old 04-12-2005, 14:37
pHo
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Originally Posted by stvn758
I have a Phillips 28inch model, if you connected a SKY HD box to it what would happen, the full 625 lines used up = added quality.
You'd only be able to connet up via an RGB/svideo/composite connection (providing the box has them for VCR use etc, i have no idea what the current spec of box is) and that connection will only output SDTV, so you won't see any difference from the box itself. However, due to the fact the images wil be recorded in HDV/HDCAM etc rather thn SD Digibeta/DVCAM you'll benefit from the fact that hidefinition video tends to downscale to standard def nicely, often looking better than an equivalent camera thats SD.
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Old 04-12-2005, 19:16
sanderton
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PAL CRT TVs have 576 horizontal scan lines, some of which are off the screen top and bottom, so maybe 540 lines are displayed.

The horizontal resolution is analogue so can't readily be given as a number of pixels.
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Old 05-12-2005, 09:19
Dino
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Originally Posted by sanderton
The horizontal resolution is analogue so can't readily be given as a number of pixels.
It can; the horizontal frequency of the screen (15.625Khz for Pal) can be used to determine the max horizontal resolution, just like on an analogue PC monitor, therefore the lower the resolution. The frequency needs to allow for a horizontal overscan and not all of the range is used for pixel data.

It works the same way as the vertical frequency (the number of lines is also "analogue"), but much faster, and you can give a pixel count for the vertical, so you can therefore give a pixel count for the horizontal, no real difference between the two.
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Old 05-12-2005, 10:03
Jay C
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An interesting question is whether it is theoretically possible to modify a high quality 100Hz TV to give a 720p display.
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Old 05-12-2005, 10:06
sanderton
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Loads of difference between the two. Each scan line is a clear and discrete thing and so can be easily be "converted" to a pixel count. 576 scan lines; 576 pixels.

The horizontal resolution is different; its a continuously variable analogue signal. How you devide that up into horzontal units for pixels is entirely arbitary.

Presumably there is a a minimum resolvable size horiziontally which when divided by the width of the screen would give you a maximum resolution; however it's I don't think that the the 720 pixels used in DVDs and most TV broadacasts is that limit; it's just a neat multiple of the 576.
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Old 05-12-2005, 11:15
Dino
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Originally Posted by sanderton
Presumably there is a a minimum resolvable size horiziontally which when divided by the width of the screen would give you a maximum resolution; however it's I don't think that the the 720 pixels used in DVDs and most TV broadacasts is that limit; it's just a neat multiple of the 576
It rather depends upon the quality of the TV how many individual effective pixels can be seen, i.e. how sharp an image can be seen. If you remember the old test card on BBC1/2, it used to have a series of lines getting progressively thinner. On some TV's, the thinner closer together lines would blur into a grey block. If you had a good, well adjusted TV, you could probably make out those lines.

You may find on some sets that you can actually only see 300-400 pixels; my point was that given the PAL frequencies, you could probably get around 800x600 maximum.

If anyone wants to double-check the maths I'd be grateful!
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Old 05-12-2005, 11:29
sanderton
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I think it would depend on the size and aspect ratio of the TV. I'm sure it's possible to calculate from the various frequencies used what the theoretical maximum is. But if its 720 for a 4:3 screen, its unlikley to be 720 for a 16:9 screen.
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Old 05-12-2005, 11:38
Dino
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Originally Posted by sanderton
I think it would depend on the size and aspect ratio of the TV. I'm sure it's possible to calculate from the various frequencies used what the theoretical maximum is. But if its 720 for a 4:3 screen, its unlikley to be 720 for a 16:9 screen.
16:9 screens may have wider effective pixels.
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Old 05-12-2005, 12:08
sanderton
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Well in digital broadcast terms they do (720 is spread across the screen for both) but in terms of resolution per centimeter fed an analogue I don't see why a 16:9 screen would be lower?

I feed mine 1024 x 576 from MCE.
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Old 05-12-2005, 12:19
Dino
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Originally Posted by sanderton
Well in digital broadcast terms they do (720 is spread across the screen for both) but in terms of resolution per centimeter fed an analogue I don't see why a 16:9 screen would be lower?

I feed mine 1024 x 576 from MCE.
Interesting. I wonder whether if you did a graphic that had pixel thin alternating black and white vertical stripes, each one exactly 1-pixel wide, I wonder whether you could see all of them, or whether you'd get scaling before output, or grey blurring as the CRT merges pixels??

If you get a mo, might be worth a try.
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Old 05-12-2005, 15:34
sanderton
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I have been meaning to try exactly that! I'll let you know.
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Old 05-12-2005, 16:11
Dino
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Originally Posted by sanderton
I have been meaning to try exactly that! I'll let you know.
Brill. I'll keep watching this thread! Also, what video card have you got?
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Old 05-12-2005, 17:50
Geordie_Cy
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Originally Posted by sanderton
PAL CRT TVs have 576 horizontal scan lines, some of which are off the screen top and bottom, so maybe 540 lines are displayed.

The horizontal resolution is analogue so can't readily be given as a number of pixels.

No, they don't. PAL has 625 lines, of which 576 are active (within the viewable part of the display).
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Old 05-12-2005, 17:51
Geordie_Cy
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Originally Posted by sanderton
I think it would depend on the size and aspect ratio of the TV. I'm sure it's possible to calculate from the various frequencies used what the theoretical maximum is. But if its 720 for a 4:3 screen, its unlikley to be 720 for a 16:9 screen.

it's 720 for both, the picture elements (pixels) are a different shape.
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Old 05-12-2005, 18:06
Geordie_Cy
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Originally Posted by Dino
It rather depends upon the quality of the TV how many individual effective pixels can be seen, i.e. how sharp an image can be seen. If you remember the old test card on BBC1/2, it used to have a series of lines getting progressively thinner. On some TV's, the thinner closer together lines would blur into a grey block. If you had a good, well adjusted TV, you could probably make out those lines.

You may find on some sets that you can actually only see 300-400 pixels; my point was that given the PAL frequencies, you could probably get around 800x600 maximum.

If anyone wants to double-check the maths I'd be grateful!
Test card F:
ftp://ftp.bbc.co.uk/pub/video/stills/tcf.gif

(NB You need Test Card W to line up a widescreen set)

The active viewing area of a MPEG encoded PAL signal is 704 by 576. In its analogue form there is no such thing as a pixel.

The frequency bars are on the right, one of them also tests the separation between the chrominance and luminance signals.

There are also tests for:
Centre - the X on the noughts and crosses
Colour Bars
Overscan
Pluge
Superblack
crhominance/luminance delay
and others
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Old 05-12-2005, 18:28
stvn758
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There were a lot of CRT computer monitors, and very expensive I recall. Are they just better made or different in design to a standard TV.
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Old 05-12-2005, 18:51
Dino
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Originally Posted by stvn758
There were a lot of CRT computer monitors, and very expensive I recall. Are they just better made or different in design to a standard TV.
CRT stands for Cathode Ray Tube and up until a couple of years ago was the standard monitor for PC's. CRT monitors have been replaced by LCD monitors. I prefer LCD monitors as they have a smaller footprint, esp. when you start talking about monitors from 17" upwards.

The CRT is not especially different from a TV's CRT, indeed I used to have a Dell monitor, I think, which had a Sony Trinitron tube. The tubes may be of a higher quality (smaller dot pitch for smaller sharper pixels). The video circuitry is obviously different.

CRT's not an especially new technology, must be at least 100 years old, and is used in varied technologies that are not necessarily TV's, like oscilloscopes. Early computers used to use CRT's like RAM, probably 1940's, 50's. Data was written to the screen phosphors, could be read and was refreshed to prevent natural phosphor decay from losing the data. Probably where the term RAM refresh rate comes from.
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Old 05-12-2005, 18:55
Dino
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Originally Posted by Geordie_Cy
Test card F:
ftp://ftp.bbc.co.uk/pub/video/stills/tcf.gif

(NB You need Test Card W to line up a widescreen set)

The active viewing area of a MPEG encoded PAL signal is 704 by 576. In its analogue form there is no such thing as a pixel.

The frequency bars are on the right, one of them also tests the separation between the chrominance and luminance signals.
Thanks! I actually use this at work to test monitors still, but a good thing to post in this thread!! A very good thing to have handy, esp. if you work with screens a lot. I can't remember where I got it from, might have been from a contact from the Beeb. Didn't know it was publicly available.

I actually reckon on a 702 wide viewing area, with 9 pixels overscan either side for PAL MPEG, seems to be the industry standard. We get PAL encoded MPEG stuff in all the time at work, full 720 width, has to be cropped by my software before we send it out for playback on our video network.
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Old 06-12-2005, 09:48
sanderton
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Originally Posted by Geordie_Cy
No, they don't. PAL has 625 lines, of which 576 are active (within the viewable part of the display).
No, that's not right. There are 625 scan lines in PAL, but only 576 of which contain picture data, and several of those are off-screen in the overscan of a CRT telly, leaving ~540 visible depending on how you have your TV adjusted.

On an LCD/plasma all 576 are visble, but this thread is about CRT.
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Old 06-12-2005, 10:06
Geordie_Cy
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Originally Posted by sanderton
No, that's not right. There are 625 scan lines in PAL, but only 576 of which contain picture data, and several of those are off-screen in the overscan of a CRT telly, leaving ~540 visible depending on how you have your TV adjusted.

On an LCD/plasma all 576 are visble, but this thread is about CRT.

Depends on how well you've got the Overscan set up.
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Old 06-12-2005, 11:28
2Bdecided
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Originally Posted by sanderton
No, that's not right. There are 625 scan lines in PAL, but only 576 of which contain picture data, and several of those are off-screen in the overscan of a CRT telly, leaving ~540 visible depending on how you have your TV adjusted.
Overscan is usually quoted 10%, making it nearer 520.

On an LCD/plasma all 576 are visble
That's often said, but it's simply not true. Many flat panels overscan by amounts comparable with CRTs. Some by less, and very few have no overscan at all. On some, it depends on the signal format (e.g. composite is overscanned more than component, for example).

Anyway, there aren't 576 lines in an analogue video signal. It's 574 plus two half lines.

With a composite connection on a basic TV, the 720 horizontal pixels are not resolvable, since the chroma information interferes with anything over ~450 pixels per line. With RGB or component signals, decent CRTs can resolve 720 pixels - there are higher resolution CRT devices for HDTV and PC use, and have been for at least a decade!

Cheers,
David.
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