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Getting true picture proportions from different sources?

Discussion in 'Movie Forum' started by kenfowler3966, Dec 30, 2001.

  1. kenfowler3966

    kenfowler3966
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    I have noticed that my Toshiba 210 switches happily between the various picture modes on the dvd using component input to my tv, but only with region 2 discs.
    With region 1 discs no such switching occurs, is this correct.
    Presumably I just set the tv to wide? Does this account for different numbers of horizontal lines between R1 and R2 discs, or do you end up with slightly squashed picture? The set automatically selects pal or ntsc? as required.

    Could someone explain how the tv copes with the differences in resolution between sources, ie about 230 lines for video 525 for R1 dvds, and 625? for pal?? As the picture can only display where the pixels are on the screen, I can only assume the electrons must miss as often as they hit when scanned across the tv?
    ie 600 lines of pixels on tv but 525 or 230 lines projected?

    Confused!!:confused:
     
  2. LV426

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    Re: auto switching:

    There are two ways to send a switching signal to a TV. The first is via one of the pins on a scart cable. This should work for all disc types.

    The second is via a little signal that is added to the picture in the blank bit you don't normally see. This works for all connection types.

    The location of this signal differs from PAL to NTSC. If the TV is only programmed to recognise this trigger in its PAL position, then it wont trigger on an NTSC source.

    Re: resolution

    Resolution is measured in two directions.

    Horizontal resolution (ie the number of vertical lines that can be clearly resolved) varies from source to source. For VHS the horizontal resolution is a bit over 200. For SVHS its around 400, and for DVD its over 500 typically. The effect of reduced horizontal resolution is blurring of the image in the horizontal direction.

    Vertical resolution is determined primarily by the TV standard, irrespective of the "quality" of the source (but there is an exception, see below). For all PAL sources it is always 576 horizontal lines, and for NTSC it is always 480 lines. A TV capable of reproducing both will simply fill the vertical dimension of the screen with the relevant number of lines, ie the top one is at the top, the bottom one is at the bottom, and the others are evenly spaced in between. This means that the horizontal lines of an NTSC picture are slightly further apart than a PAL pitcure.

    The exception is VCD. The vertical resolution of a VCD is exactly half the TV line standard ie for NTSC it is 240, for PAL it is 288. However, the signal going to the TV is still 480 or 576. The difference is made up by duplicating lines ie lines 1 & 2 are identical; lines 3 & 4 are, etc.....

    So, when you see different resolution figures quoted (eg VHS=230, SVHS=420, DVD=520 or whatever) this is the Horizontal value. The vertical value (for PAL) is always 576.
     
  3. Doubledoom

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    I agree.

    It sounds as if the tv is picking up line 23 WSS (PAL) with no problems but hasn't got theh ability to pick up line 21 WSS (NTSC)
     
  4. Kevo

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    None of my R1 WS DVDs auto switch. I always have to do it manually.

    This has occured on two diiferent makes of WS TVs I have owned, Sony CRT and Tosh RP TV.

    I've always assumed that a SCART cable carries the DVD ws signal for the TV to detect. As the US don't have SCART leads then I would have thought that this signal doesn't exist.

    If this is so, then how do US TVs auto detect WS DVDs?
     
  5. LV426

    LV426
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    At the risk of repeating myself (mods, please forgive the copy & paste):

    There are two ways to send a switching signal to a TV. The first is via one of the pins on a scart cable. This should work for all disc types.

    The second is via a little signal that is added to the picture in the blank bit you don't normally see. This works for all connection types.

    The location of this signal differs from PAL to NTSC. If the TV is only programmed to recognise this trigger in its PAL position, then it wont trigger on an NTSC source.
     
  6. Doubledoom

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    and read my response to which line it is.
     
  7. kenfowler3966

    kenfowler3966
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    Thanks for all the replies, however it hasn't really awnsered one of my questions:

    If the tv has been made with 576 horizontal lines of pixels, don't the lines the electron beam traces have to follow them. If the screen is then filled with 480 horizontal stripes from an ntsc source there must be many instances where the beam fails to exactly line up with the holes in the tv shadow mask? Is it just a matter of spraying the electons and the nearest pixels light up?

    Presumably then a w/screen video recording will be particularily poor quality when stretched to fill my set? does the set add information for the missing vertical lines or does it just space out what it has over the whole width of the screen? Presumably again the traversing electron beam from the gun is lighting 2 or 3 fixels width with the infornation normally used for one pixel?
     
  8. Doubledoom

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    I am not going into the technical bit behind it (as i don't know) but scan lines would be noticeable to keep the shame.

    It is one of the main reasons why i would never by a R1 non-anamorphic widescreen title.
     
  9. LV426

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    The array of phosphor dots on a CRT is much finer than the definition of the input signal ie there are many, many more than 576 pixels vertically. And, the bigger the screen, generally, the more phosphor dots. "Interference" patterns between the input signal (480 or 576 lines) are unheard of. The only time when these become visible is on PC monitors, when being driven at a resolution which gets closer to the native resolution of the tube - when you can get what are known as moire patterns. It doesn't happen on TVs.

    Also, FWIW, all Sony TV tubes have continuous vertical strips of coloured phosphors and therefore, their potential for vertical resolution is practically unlimited.
     

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