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Plasma panel pixel dimensions - why 768?

Discussion in 'Plasma TVs' started by Colgate7110, Jul 14, 2005.

  1. Colgate7110

    Colgate7110
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    It's just occurred to me that plenty of HD plasma panels are 1024 or 1280 pixels wide by 768 pixels tall depending on the pixel shape in use but HD content runs at either 720p or 1080i/p. Standard definition PAL DVD content uses 576 lines and NTSC DVD content uses 480 lines. Finally, PAL as a standard employes 625 lines while NTSC uses 525. Now, for those still awake after that barrage of numbers, why are plasma panels often 768 pixels tall? :confused:

    I can understand why plasmas used to commonly use 480 lines for progressive scan playback - it matched the content perfectly. I'm guessing that 1080i content is scaled down to work on the current batch of HD screens branded HD ready (such as the Pioneers and Pannys) but don't actually feature 1080 vertical pixels. But surely by building a panel with 768 vertical lines then every piece of content played on the screen must be scaled regardless of it's native resolution. 768px plasmas don't feature horizontal bars at the top and bottom filling in the other 48 pixels do they?

    I'm obviously familiar with 768 pixel heights from computer video cards - is this where the 768 was derived from? I would have thought it would make sense to build a plasma panel with a native height of 720 pixels.

    Any clues to this most trivial of issues most appreciated :)

    Cheers,

    Colin
     
  2. MAW

    MAW
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    It's just history, PC history. The 1st plasmas were computer monitors, hence the 768 lines. The updating of the plants is happening, we will have video resolution plasmas, but it's a big expensive job to change. PCs are of course becoming more video friendly too, so now there's no resistance from the corporate side it'll help speed things up.
     
  3. SimonMallion

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    Sharp are developing an LCD with 540 lines: http://www.homecinemachoice.com/cgi-bin/shownews.php?id=8211 to match PAL broadcast signals. It explains why 540 lines further down the page:

     
  4. Colgate7110

    Colgate7110
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    I'm not convinced by the purported benefits of this 540 line panel. I can't believe that the PAL spec says "let's transmit a 625 line frame split across 2 fields of 288 active lines for a total picture size of 576 lines then we'll let people chop of another 36 lines/7% to account for overscan"...

    It seems like they really just chose 540 because it's a nice multiple of 270 and then claim it's HD compatible. The idea of taking a 1080 signal and halving it 540 lines doesn't strike me as a great use of resource and since you can't just remove every second line without ripping out half the detail they're going to have to average every alternate field to produce a completely falsified image. I can't say I'm keen on the 720 down to 540 conversion either - it's processing on a round pixel ratio but it's still downscaling...

    Besides, surely overscan only exists because of poor quality control combined with cheap components? It's a manufacturer-created problem and they've decided that to fix it they're going to lop 7% off the screen size!

    I just think Sharp are developing a product for what will surely be a dwindling market for PAL users to replace their analogue CRTs with LCD TVs which is neither particularly future proof (lacking true HD playback) or presumably cheap.

    Sorry Simon - bit of a rant there but I'm just not sure that Sharp have fully thought this one through. :) Surely what market needs now is just for manufacturers to re-tool (as MAW says, they're getting underway with this process) to produce 720 line panels, benefiting the volume/cost ratio, boosting the market for HD screens, lowering prices etc etc rather than continuing to develop products for a limited marketplace supporting an age old television format.

    Cheers,

    Colin
     
  5. Welwynnick

    Welwynnick
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    Wondered when somebody would ask that.
    1024 is 2 to the power 10 (1k in computers)
    768 is 3/4 of 1024.
    576 is 3/4 of 768 or 9/16 of 1024!
    I think 480 comes from VGA.
    That's it.
    Nick
     
  6. MAW

    MAW
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    Colin's quite right about this, the 540 line format is what we call 1/4 HD, it's an easy scale for 1080i. It's been seen before in the sanyo z1 projector. The PAL bit is just marketing bull, I reckon. Just trying to put a positive spin on a problem.
     
  7. leeboy22001

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    also some dvd players output 540P, so no need for scaling.
     
  8. MAW

    MAW
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    Do they? Never heard of it, but who knows. The scaling would occur inside the DVD player if it's true, as this format would never be the one on the disc.
     
  9. Colgate7110

    Colgate7110
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    Turns out the American's have gone gung ho on 50" RPTVs which support 1080i or 540p content. Hitachi, Toshiba and Zenith (after a quick Google) all seem to support sets based on the res. As you say though MAW, there's no content in this ratio so if it's not the set scaling it then it's the DVD scaling it so again, why??? :rolleyes:

    Surely most HD content produced for TV is shot for 720 or 1080 - this idea of distilling the resolutions into some baby progressive scan setup just seems like a bad idea to me. What I loved about DVD was that the industry got together, bashed their heads and came up with one specification and it exploded onto the marketplace as a massive success. Now we have the ongoing BD/HD-DVD farce and what looks like two approaches to HD screen content too...

    You only have to spend 5 minutes in a shop selling PC games after Christmas to see the armies of parents complaining that such and such a game didn't work on their PC or it was too slow or it said this driver version was outdated, etc etc to realise that most people don't care for the technicalities of how their computer works let alone worry about their TV. For years, it's been simple - it used to be did you want colour or black and white. Now though it's do you want CRT, plasma or LCD and would you like that in progressive scan or interlace scan and will you be wanting to watch standard definition or high definition content on your new TV sir? Oh high definition, you say? Well would like our 540p model or our 720p/1080i model sir?

    And what happens when you sit down on Bank Holiday Monday to watch The Great Escape and the warning box flashes up on your TV to say that this particular high definition broadcast isn't compatible with your screen? Okay, so that's exaggerated - these 540p sets will downscale 720/1080 content so it's still compatible but you'd feel pretty short changed if you were sold one as a high def only to find out you were getting more lines per image from your old CRT TV and I'm worried the high street retailers will offload these cheaper sub-high def sets as full blown "HD ready" not through any malice, just technical ineptitude. (That's absolutely not a dig at specialist retailers)

    It seems my simple question about why plasma panels are the pixel height they are has me worrying about the direction the entire market is moving in now... Another thing that's just started to dawn on me is the speed at which formats are evolving. In about six-eight years, we've gone from VHS to DVD and now we're on the cusp of high definition DVDs in one or two formats which are ushering in a new generation of displays. Does that mean that in another 8 years we'll have Super HD DVDs running at 2160p and even newer, sharper, thinner, denser screens again? If I had the money (and you can always find money for AV ;)), I'd be over the moon with the latest and greatest but is the massmarket knowledgable and savvy enough for digital home entertainment? It's questionable whether we need to go above 1080i/1080p - that's a massive vertical resolution for a TV image - but when DVD came out at 480/576 lines, did anyone think then, next to VHS, "gee, that's all very nice but I think we need to double the resolution" because they did it anyway...

    Look at the end of the day, all I'm really worried about his many more bloody versions of the original Star Wars Trilogy I am going to have buy in my lifetime and with each new configuration and format, that number isn't getting any smaller ;)
     
  10. hornydragon

    hornydragon
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    The thing about all fixed pixel devices is SCALING is going to happen what do you do with legacy SD res on720 or 1080 vertical res displays???? Far more important than native RES is having a good scaling engine as scaling is going to happen have top notch scaling and get the BEST out of your pixels or BUY monster RES devices like JVC's 4000X3000 RES LCOS projector and run everthing at native res and hence massively varying picure sizes.........................................imagine chaning channel from 720x576 PAL SD to 1920x1080 HD and the picture getting 3 times larger!!!! then you have to had huge Zoom optics making the pixels larger to maintain image size ;) FUN
     
  11. Colgate7110

    Colgate7110
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    Don't get me wrong hornydragon - I appreciate that scaling is a necessity and has been since the advent of TFT laptop monitors years and years ago for non-native resolutions. Today, the Dell flat panels we're using at work use Genesis processors (doubt anybody is casually browsing this topic now but, if they are, Genesis ultimately own Faroudja who's scaling processors are in countless AV products such as projectors, DVD players and surround amps) so I can definitely see the benefits of a quality scaler on a fixed pixel device as the picture is brilliant - I wouldn't want to work with it all day but I could watch a movie on it without too many complaints.

    My only criticism of the 540p panels emerging is why, now, in 2005, build a panel with a resolution lower than any current format's vertical height requiring downscaling across every signal? Would it not make sense to at least build the baseline height to conform to one of the standards and up/downscale from there so at least one of the format options is true 1:1? If HD is the future, why introduce a playback standard and panel size to encourage continued growth in a sub-HD technology?
     
  12. hornydragon

    hornydragon
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    540 panels thats just down to cost..............................
     
  13. LV426

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    It all makes sense to me. Well, to a degree. Overscan is part of the TV system specification - always has been - the correct nominal value is 5% all round. And it's not wholly about the quality of displays; it's also (historically) about the quality of what's broadcast. Overscan was designed to hide inaccuracies in the positioning of the image in (old analog) studio equipment, and things like geometry errors on CRTs.

    Theoretically, nothing important should be contained in the extreme 2.5% of each edge.

    So, it's a legacy, but one which still exists in the standard definition TV world. I can't comment on whether or not HD has the same standard.
     
  14. Molly

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    Avland are showing the res for the new Pioneer PDP436xde as 1280 x768.

    Is this the new typical HD res for a plasma?

    Why still produce a panel which is 15:9 not 16:9?

    Would this work better with a HTPC with 1:1 pixel matching and no aspect ratio problems?
     
  15. MAW

    MAW
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    AVland are wrong, it will be XGA just like it is now, or I'll eat my shorts (famous last words, better get the ketchup ready)
     
  16. Colgate7110

    Colgate7110
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    Well, that I did not know :) I suppose I didn't think the standards committee had the foresight to assume that the kit of the day wasn't up to the task of rendering a geometrically perfect image and then to write a permissable error mechanism in the form of 5% overscan. I'm not surprised that overscan occurred in the "early days of PAL" given the quality and selection of the components available at the time - I'm surprised that the standards committee specifically excused it by compromising the spec if you know what I mean. It's slightly dismaying though that in setting this tolerance - which you see countless sets still failing to meet - the PAL spec set a precedent and get-out-of-jail free card for manufacturers of both studio kit and home televisions to not conform. :( Nonetheless, cheers for the info!
     
  17. LV426

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    Actually, it goes back well before PAL, to 405 lines (whatever that was called). There is (and, again, always has been) a similar standard on NTSC.

    On the odd occasion when you see a "making of...." programme about a TV show (recent Dr Who follow-ups on BBC3 are an example) and you see the monitors used by the film crew, they are marked out with the "safe area", a touch smaller than the full image. Nothing important in the show should fall outside this area.
     

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