Questions on Resolution

Discussion in 'Plasma TVs Forum' started by RemotecUK, Jun 29, 2004.

  1. RemotecUK

    RemotecUK
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    Hi, a few questions on resolution .... Feel free to divert me to a FAQ on this if it exists :D

    My Panasonic Series 6 has a resolution of 640 x 480. Is this higher or lower than what you would expect on a high end CRT?

    If my screen has 480 lines containing pixels, is it fair to say that a video source also has a number of lines that are broadcast? If so how many lines are broadcast by Freeview and how many lines are on a DVD? Is it 625?

    If thats correct, its true that my display cant display the actual amount of lines that are contained on a DVD. I imagine that the inbuild scaler does the required work to display the 625 lines on my screen. Possibly by interlacing?

    If Im still on the right lines, technically speaking a higher resolution screen such as the Pioneer 434HDE should give a more crisp and clear picture but in this case the software inside the display would have to (excuse the terminology) fill in the blanks to display 625 lines on a 768 line display.

    Sorry its a bit of a brain dump - any answers greafully received :)
     
  2. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    The Panel is actually 852 x 480 I think, not 640x480

    The signal output by Set top boxes, video recorders, satellite recievers etc in UK is a 625interlaced signal. Of those 625 interlaced lines about 576 contain picture information. You are correct that your plasma doesn't have the required resolution to display all the picture information in a de-interlaced signal from one of these sources. The higher resolution panels do. SD panels downscale these signals and HD panels upscale them.

    It is not always the case though that higher resolution devices look sharper than lower resolution ones. It depends on how good the scaling is in each panel, how the panel itself displays the picture information (how the panel is driven) and also how far away you are from the display when viewing.

    Gordon
     
  3. Wazy

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    This FAQ has some info HERE - Read the part on ''1024X1024 VS. 853X480 Explained'' as well

    Yeah, the PW6 has a 852x480 resolution! :)
     
  4. LV426

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    Just to add to what Gordon says -

    the ultimate source for all PAL TV signals (whether Set Top Box, VCR, DVD, anything) has 576 lines of information (which defines the maximum theoretical vertical resolution of the signal).

    Any different value (higher or lower, whether done in the screen or in the source device) is the result of scaling.

    You can't ever actually get any more than 576 lines of vertical definition from any PAL TV source. However, scaling to a higher value, when done well CAN give the impression of greater definition. But it is just an impression.

    Any flat panel with a <anything> x 480 resolution is optimised for NTSC sources (which have 480 lines) and will by necessity degrade a PAL signal to this value for display.

    More subjectively, however, even downscaling done well can look quite reasonable.
     
  5. RemotecUK

    RemotecUK
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    Thanks for the information.

    The bottom line is that most plasma's in this country do some sort of scaling then?

    Does PAL define a horizontal line length in pixels?

    What about colours? I understand that a plasma pixel can display millions of colours which should be enough to display most images. However, my Panasonic (as mentioned in another thread) really seems to struggle with some inputs. Especially when there are gradients of colour involved e.g. scenes with fog. Is this a limitation of the video processing inside the display?
     
  6. LV426

    LV426
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    All digital display devices (Plasma, LCD, DLP etc) have to scale the input signal.

    The line length isn't defined exactly. Because the legacy is of a TV system based around reproduction on a CRT which is (nominally) not constrained by a fixed pixel array, but simply displays a sequence of scanlines -

    in the vertical direction, the number of scanlines IS defined - 576 for PAL, 480 for NTSC

    in the horizontal direction, the definition is really an expression of how many times, during its length, can the scanline change colour or brightness. And this is determined by the quality of the source. There is an absolute ceiling which is determined by the bandwidth of the TV carrier signal. And that ceiling is 720. However, many signal sources have a definition which is lower than this. A VHS machine, for example, is typically limited to about 240.

    The digital code on a DVD (which is in most cases converted to an analogue TV signal in the player - DVI protocols asdide) has the maximum - 720.
     
  7. RemotecUK

    RemotecUK
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    Thanks for the gen Nigel, just to clarify... when talking about the width (excuse terminology) the only constraint is technically what can be transmitted - and the TV simply scales the transmitted line to the screen size - or in the case of widescreen displays part of it (the middle) so you loose either side. Is that correct or am I thinking about this too simplistically?
     
  8. LV426

    LV426
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    Think of a TV signal as being a sequence of lines - because that's exactly what it is.

    There are 576 useful lines in a PAL TV signal; 480 in NTSC. This number is fixed. The vertical size of the image is determined by how far apart these lines are displayed, which in turn is normally determined by the physical height of the screen (give or take a bit of overscanning).

    There are two exceptions to this last point.

    1: A 4x3 device with a 16x9 mode will, in this mode, display the lines closer together, not occupying the full height of the screen.

    2: A 16x9 device with a "zoom" mode (used for letterboxed videos, laserdiscs and non-anamprphic DVDs) will display the lines further apart so as to occupy MORE than the height of the screen. The plain black content of the signal, above and below the usable screen is not displayed.

    The vertical resolution of the signal is determined by the number of lines - 576 or 480*

    The width of the picture is determined by the display device. The display device can display each line using all of the width of the screen, or part of it. If properly adjusted, a 4x3 display will use it's full width for each line (+/- overscanning).

    A 16x9 device can show lines at two widths; full, and 75% (approx). The full width option is used typically for

    - 16x9 (or anamorphic) video sources
    - 4x3 video sources where the content is letterboxed and the image is "zoomed" to more closely fill the screen (see exception 2 above)

    The 75% option is used for 4x3 material.

    The horizontal resolutionof the signal is determined by the number of times, during its length, that a line can change colour or brightness. This is in turn determined by the source. The best sources achieve 720 discrete changes of shade. VHS can only achieve about 240. VCD achieves 352.


    * for some carriers (VCD for example) the vertical definition is half this - and each alternate line is an exact duplicate of the one next to it.
     
  9. Plump

    Plump
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    It can be pain especially if you know it is downscaled
    And you know it now! :)
     

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