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Thread: Aspect Ratio - Centre Cut on 4:3 Screens

  1. #1
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    Aspect Ratio - Centre Cut on 4:3 Screens

    Would one of the members or SUB be able to explain the settings from the file CONFIG.XML, as I wish to correct the values for AspectRatioMode "Center Cut" on TVShape 4x3?
    In particular the values "-0.05,-0.17,1.04,1.17"

    <!-- Aspect Ratio settings -->
    <TvShape>4x3</TvShape>
    <AspectRatioModes shape="4x3">
    <AspectRatioMode name="Auto" ratio="0,0,0,0" />
    <AspectRatioMode name="Fill" ratio="0,0,1,1" />
    <AspectRatioMode name="LetterBox" ratio="0,0.125,1,0.875" />
    <AspectRatioMode name="Remove LetterBox" ratio="0,-0.125,1,1.125" />
    <AspectRatioMode name="Center Cut" ratio="-0.05,-0.17,1.04,1.17" />
    <AspectRatioMode name="PillarBox" ratio="0.08,0,0.92,1" />
    </AspectRatioModes>
    <AspectRatioModes shape="16x9">
    <AspectRatioMode name="Auto" ratio="0,0,0,0" />
    <AspectRatioMode name="Fill" ratio="0,0,1,1" />
    <AspectRatioMode name="Remove LetterBox" ratio="0,-0.125,1,1.125" />
    <AspectRatioMode name="PillarBox" ratio="0.08,0,0.92,1" />
    </AspectRatioModes>
    <AspectRatioModes shape="16x10">
    <AspectRatioMode name="Auto" ratio="0,0,0,0" />
    <AspectRatioMode name="Fill" ratio="0,0.05,1,0.95" />
    <AspectRatioMode name="PillarBox" ratio="0.08,0,0.92,1" />
    <AspectRatioMode name="Remove LetterBox" ratio="0,-0.125,1,1.125" />
    </AspectRatioModes>

    The setting should reflect the following values:

    Vertical Full Height (576, 720, 1080)
    Horizontal Pixels Cropped to reflect the correct aspect ratio

    Thanks in advance for your advice. Cheers. Ross.
    Last edited by Babylon; 2009-02-26 at 10:12 AM.

  2. #2
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    0,0,1,1 is (0,0) for the top left of the screen, and (1,1) for the bottom right of the screen. You'll have to do the math to determine what those numbers would be for the transformation you're wanting to do.

  3. #3
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    I use ratio="-0.15,0,1.15,1" for that purpose.

    To add to sub's explantion:

    The physical screen is 0,0,1,1 (0,0=x,y for the upper left of the screen, 1,1=x,y for the lower edge of the screen). The ratio numbers then describe how the video is to be drawn relative to the physical screen. So -0.15,0 means start the video 15% outside the left edge of the screen, but line it up with the top edge. Then 1.15,1 means stretch the video horizontally until it goes 15% off the right edge, but make it even with the bottom edge of the screen.

    At least that's how I understand it, and my ratios do what I expect them to do. I didn't do any exact math, I just started with a good guess, and tweaked a little until it looked right.

    I also use one I call 'Zoom' that gives me a center-cut for channels that use a 4:3 format, but broadcast with a 16:9 letterbox (and sometimes use a 4:3 frame inside that letterbox!). For that one my numbers are:

    ratio="-0.15,-0.15,1.15,1.15"

    Obviously that does 15% all around, just a linear zoom.

    Be aware that negative ratio numbers only work with the VMR9 renderers; EVR and Overlay will simply ignore any aspect ratio with a negative number in it. (much to my frustration since the only time I've ever gotten perfectly smooth video on 1080i hd channels was with EVR on Vista, but having to watch TV inside little boxes was too much to bear)

  4. #4
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    Thanks Sub & JohnsonX42 for the reply. I'll do the math as you suggested. X42 "I also use one I call 'Zoom' that gives me a center-cut for channels that use a 4:3 format, but broadcast with a 16:9 letterbox (and sometimes use a 4:3 frame inside that letterbox!). ", I can't believe that Broadcasters do 4:3 in 16:9 letterbox. There is no excuse, particularly when they can avail themselves to high quality Aspect Ratio Converters (ARC). I shake my head sometimes regarding this total disregard for poor resolution and standards, and I work as an engineer in the industry! Cheers.

  5. #5
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    Quote Originally Posted by Babylon View Post
    I can't believe that Broadcasters do 4:3 in 16:9 letterbox. There is no excuse, particularly when they can avail themselves to high quality Aspect Ratio Converters (ARC). I shake my head sometimes regarding this total disregard for poor resolution and standards, and I work as an engineer in the industry! Cheers.
    It only happens on one or maybe two channels, which are PBS sub-channels. My guess is they've set up to broadcast in 4:3 (the sub-channels are SD, and I think those more-or-less have to be 4:3), but they are re-broadcasting a 16:9 feed from somewhere else, so naturally they letterbox it. Then sometimes at the source, they've got a 4:3 program to show, so they pillarbox it into their 16:9 format.

    The really ridiculous bit comes in when as part of a 4:3 show that's been broadcast as above, they letterbox part of it for artistic effect or whatever reason... so you get a 16:9 letterbox in a 4:3 pillarbox in a 16:9 letterbox in the TV's 4:3 frame. It looks like a little band-aid in the middle of the screen, and my 61" inch big screen has shrunk down to 27" or so....

    I suppose you'd know if there's a good solution in those scenarios. Me, I'm just happy to have extra channels, and GB-PVR aspect ratio modes with negative numbers takes care of things nicely.

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