How clever is the scaling on plasmas/LCDs?

Discussion in 'LCD & LED LCD TVs Forum' started by GadgetObsessed, Jan 14, 2003.

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  1. GadgetObsessed

    GadgetObsessed
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    For example if a plasma has a vertical resolution of 480 (Panasonic) but is being used to display 625 lines of analogue TV does it just throw away the extra 145 lines? The only other option that I can see is to break each frame down into polygons and translate to the 480 screen size based on how big each polygon is in relation to the size of the screen.

    Similarly with 1024 lines (Hitachi) does the display simple repeat some of the broadcast lines, interpolate some new ones or something else?

    From my experience with LCD monitors it seems that fixed pixel displays simply repeat or throw away the lines of the input source as required. (Alternatively display a lower res input on only part of the screen.) Effectively this means that the display makes text unreadable unless it is being driven by the same res input as its native pixel count.
     
  2. StooMonster

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    PAL has 576 visible lines of the 625 total lines, like NTSC is 480 visible lines of 525. In a down-scaling example such as this you effectively lose 96 lines.

    With upscaling, e.g. to 768 lines (50" Panny), the picture is "stretched" to cover physical pixels.

    There are a varity of algorithms to do this, e.g. multi-tap, but best thing is to get a demo and see what you think.

    StooMonster
     
  3. MAW

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    This is THE dilemma, whatever you are viewing with. It's why many watch their movies on a HCPC, to remove the resposibility for scaling from the plasma (or projector) and take control of the process. There's a large variation in how well screens do their scaling, check the titles on a dvd when at the dealers, they are often a giveaway.
     
  4. GadgetObsessed

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    Does anybody think that a plasma will ever be released here that is optimised for PAL rather than NTSC i.e. has 576 lines rather than 480? Surely that would be the best option for present day PAL viewers. (granted that such a display would be no more flexible in displaying HD pictures but that seems a long way off here in the UK.)

    Do any screens give you an option for how to scale? For example when showing PAL on a 480 line display you could either throw away the extra 96 lines from the top or bottom and have no scaling i.e. zoom, or remove roughly one line in 5, or do a combination of both.
     
  5. StooMonster

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    No I do not think there will be a PAL plasma, as both US and Japan use NTSC.

    However, if you've demoed a 480 line 42" plasma and don't like the picture; try one that has a higher vertical resolution. Panasonic and NEC both do 42" screens with 1024x768 resolution; Pioneer do 43" screens with 1024x768 resolution; Fujitsu and Hitachi and Sony do 42" screens with 1024x1024 resolution.

    Or go for 50" plasmas that are all either 1366x768 or 1280x768. ;)

    Up-scaling is not a problem at all, down-scaling is where you lose picture information.

    StooMonster
     
  6. JamesTapp

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    So how does your plasma invent information that isn't there, that's clever....:D

    Trust your eyes go with the picture you like the best, I have a Panny 4, 480 lines. No one has ever said to me, you've got 96 lines missing...
     
  7. GadgetObsessed

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    I didn't start this thread as a discussion of whether hi-res or low-res displays are better or whether up scaling is better than down scaling. (I've nearly decided on a Hitachi display anyway - irrespective of the resolution.)

    I was just wondering how up/down scaling was generally achieved. For example do any displays give you a choice of scaling method and do any scale by cropping top/bottom?
     
  8. JamesTapp

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    Gary,

    Scaling is a complex issue, and I've not seen much of the mechanics discussed, although I believe interpolation is probably used, although not all plasmas are equal as far as I can tell. I certainly haven't seen an "option" to use different algorithms.

    Can it be improved, definitely, using the external scalers available can take load off the plasma and give you a better picture by adopting the native rate of the plasma screen.

    As you have selected the plasma, ask to see some material from Sky demonstrated, particularly sport. If it is a good AV dealer they may be able to show you the kit with an external scaler/deinterlacer as well for comparison.

    At the end of the day, if you like what you see, it doesn't really matter how it gets there.;)
     
  9. StooMonster

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    In my first reply, I said "There are a varity of algorithms to do this, e.g. multi-tap" which is generally used in upscaling.

    Others include "Clear Matrix Pro", "Oplus" does upscaling/downscaling, and manufactures' own upscaling algorithms are typically: nearest-neighbour, bilinear, and bicubic algorithms.

    Check out this article http://www.rgbintegration.com/tech_art/scalers.htm

    Read this recently too
    "Maintaining good video quality is more difficult when downscaling, for example, if you're playing a DVD movie in a less-than-full-screen window or in a window whose native aspect ratio doesn't match the aspect ratio of the display or for picture-in-picture applications. By inadvertently discarding important image details, such as the contours of a human face, you don't want to end up with a presentation that viewers find disagreeable. You also don't want to distort the image by disproportionally shrinking an object's dimensions.

    Envision a picket fence consisting of equal-width boards, a crosshatch grid, or any other sequence of parallel lines. Displaying a downscaled image in which some lines disappear and others end up fatter or thinner than others or in which downscaling alters the spacing of a group of previously equidistant lines won't work. The inverse relationship between time, or in this case location, and frequency requires that the downscaling filter length increase in proportion to the downscaling factor."

    AFAIK, no plasmas crop top/bottom for down-scaling. None offer choice of how scaling is done; only internal vs external.

    StooMonster
     
  10. prusling

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    I have the Hitachi 32PD3000 which is 852*1024 and plan to buy a PC Xcard or graphics card with Powerstrip, either of which allow you to set the required resolution.

    Its probably a stupid question but what resolution would I set these to in order to get the best from the panel - 1820*1024, 910*512, or 1024*576 for PAL pro! I assume that you need a 16:9 ratio or do you have to consider anamorphic expansion? I guess it all depends which scalar has the best performance. My brain hurts...

    Cheers, Peter
     
  11. StooMonster

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    You should set your PC's output to match the native resolution of the plasma to get best results, which in your case is 852x1024.

    Picture can then be further enhanced by "snapping in" the picture, to do this you need two native resolution images (852x1024 in your case) of alternate black and white lines: one horizontal and one vertical. Display them in turn and adjust the h/v position and h/v size until the "rainbows" go away. It will be immediately apparent. This is so there is a one-to-one pixel match from graphics card to physical pixels in plasma, and therefore no scaling or mis-positioning; if you just plug PC in and set h/v size/positions to default this won't be the case.

    StooMonster
     
  12. philipb

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    Stoo

    some questions -

    How did you generate the images?

    When adjusting the horiz/vertical position/size, are you doing this with the plasma adjustments, or using the adjustments on the PC in the settings menu?

    The kit is a GeForce Ti 4200 with Powerstrip, and the plasma is a Pio 433. connection is via DVI.
    Are there any special points about the Pio 433 that you know of?


    Thanks.
     
  13. StooMonster

    StooMonster
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    You don't have to do this with DVI -- it's a digital connection!

    This methodology is when using analogue RGBHV in VGA.

    StooMonster
     
  14. prusling

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    Thanks, Stoo

    I'd like to know how these images can be easily generated.

    Cheers, Peter
     
  15. philipb

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    Thanks Stoo.
     
  16. StooMonster

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    I use Adobe Photoshop, but only because I love it so, any "paint" package will do.

    Create one file for native resolution, fill with red, draw one horizontal white line, underneath that draw a black line, select two lines, copy and paste them underneath, select four lines, copy and paste them underneath, select eight lines, etc.

    Follow the same process for vertical line image.

    Voila, two image files; one alternate black and white hotizontal lines, the other alternate black and white vertical lines.

    Next step, plug in PC via VGA and set to desired resolution and refresh rate. Display horizontal image at full screen, adjust vertical size and positoning on plasma. Next, display vertical image at full screen, adjust horizontal size and positoning on plasma. It will be immediately apparent when settings are correct as "rainbows" will go away. Also note down setting, so you don't have to do this again if you swap kit round or inputs in VGA.

    Finally, adjust "sharpness" setting; some people report even better results with this set to 0.

    All this effort will result in the best possible PC picture on a plasma.

    StooMonster
     

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