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Widescreen aspect ratios - help sought

Discussion in 'Projectors, Screens & Video Processors' started by Bert Coules, Oct 13, 2004.

  1. Bert Coules

    Bert Coules
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    OK, I'm probably about to reveal my profound ignorance here, but what the hell...

    Why is it that when I play a widescreen DVD described on the sleeve as having an aspect ratio of 2.35:1, the projected image is different from that? With my Sanyo Z2 and my Yamaha DVD player set to "16:9", I get a display that measures almost exactly 2.17:1. Sky+ widescreen movies give exactly the same results.

    The discrepancy isn't extreme - it's about a 2.5" height difference on my 73" wide screen - but it is quite noticeable.

    As far as I can see, the images aren't distorted at all. But visually the viewing experience comes some way short of the "extreme widescreen" look that you see in a cinema.

    Am I simply misunderstanding something? Could I have set the equipment up wrongly? Or is this the way it's supposed to be? Any and all thoughts will be gratefully received.

    Bert
    http://www.bertcoules.co.uk
     
  2. Bristol Pete

    Bristol Pete
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    Isnt it because 2:35:1 is wider still than 16:9 and you would in effect need an electric screen similar to the 'real' cinema to see a true 2:35:1 image, which is impossible as our monitors i.e TVs, PJS, plasma/lcd are only really 16:9.....

    Correct me if I am wrong,

    Cap :)
     
  3. KraGorn

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    I see a difference on my Z200 between component and DVI .. I've always assumed it's caused by overscan on the analogue input, either caused by my Pio868 or the Z200, since the DVI image contains more width-wise content .. maybe this is the problem you're seeing Bert.
     
  4. Bert Coules

    Bert Coules
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    Captain Benefit,

    But surely the projector automatically displays the image as wide as it can, and adjusts the height according to the ratio of the recording?

    Robin,

    I am indeed using the component input. Perhaps that is a contributory factor.

    Bert
    http://www.bertcoules.co.uk
     
  5. MikeK

    MikeK
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    Many DVD transfers are actually 2.17:1 (despite what it might say on the package) - if everything looks OK, I really wouldn't worry about it!
     
  6. Bert Coules

    Bert Coules
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    If that's so, then I'm reassured to know that my gear's working properly. Thanks! I'd still like the correct ratio, though: in that one respect, everything doesn't actually look OK, at least not when compared what I see in the cinema.

    I suppose I could always mask off a strip along the top or bottom of the frame...

    Bert
    http://www.bertcoules.co.uk
     
  7. MikeK

    MikeK
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    :)

    Wouldn't be the same as the cinema though!
     
  8. LV426

    LV426
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    It's probably due to overscanning, which occurs on pretty well any display.

    Consider first the content of the video signal. The video signal coming off the disc is actually exactly 16x9 (assumes an anamorphic disc). For a really wide film (eg 2.35:1), it contains the film, plus some plain black padding above and below. The film itself occupies the full width of the signal, but only about 75% of it's height.

    Now, the display will in pretty well every case actually only show (in both directions, horizontal and vertical) a central portion of the image. It will (deliberately) crop all four sides to an extent. This is overscanning.

    Clearly, the cropping of the top and bottom, when this is plain black, is immaterial and has no effect on the height of the important (i.e. coloured and moving) part of the signal. However, the same cropping of the left and right will reduce the visible width.

    This is why the measured ratio is taller than it theoretically should be.
     
  9. Bert Coules

    Bert Coules
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    Nigel,

    Thanks for that explanation. My resolutely non-tecnical brain wonders why this overscanning is built-in, but basically I'm relieved to know that there's apparently nothing wrong with my set-up.

    Bert
    http://www.bertcoules.co.uk
     
  10. KraGorn

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    Nigel, any idea why my Pio868 or Sharp Z200E (whichever it is) overscans component but not DVI? It's by a good margin too, not just a this sliver.
     
  11. LV426

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    This is supposition only:

    Overscanning is there as a throwback to the old days of TV when

    a) All displays were 4x3 CRTs. And as we all know, the geometry on CRTs is rarely perfect. Overscanning conceals to an extent poor geometry by hiding curved or tilted edges to the picture

    b) Studio equipment wasn't up to the standard it is today and the precise positioning of the image wasn't as tightly controlled as it now can be with digital media and processing. Overscanning conceals any slight mis-positioning of the image.

    Also, old CRTs had curved screens with curved edges. Hence, all material destined for TV is composed such that anything critical is wholly contained in a central area of the signal (say about 90-95% width x height) and the remaining 5-10% is considered unimportant, except that it allows for a margin of error in either the display or studio output.

    These practices have (unnecessarily, it might be argued) been perpetuated into digital TV and digital displays. Although it's fair to say that the analog signal protocols used for regular video (eg RF, Video, SVideo, analog RGB) have been around for long enough to see why overscanning may well have been included.

    I would assume (rightly or wrongly) that DVI, as a brand new signal protocol, introduced into the retail market since the advent of digital sources (DVB, DVD etc), has been implemented without overscanning (because it's no longer really necessary).
     
  12. KraGorn

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    Thanks for that ideas, I'd not considered the deficiencies of CRTs prior to the 'flat screens' of modern times.

    If this is the casue then it seems probable it's the Pioneer generating an overscanned signal rather than the projector, I wonder if I can alter its' behaviour .. have to dig into the manual again.

    Cheers.
     
  13. stevelup

    stevelup
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    Hi

    There is quite a bit of default overscan on the Z1 and Z2 projectors. This can be corrected using a test pattern DVD and the service menus on the projector.

    It is adjustable on a mode by mode basis so you can - for example - leave the overscan in place for interlaced material (Sky etc) and remove every last trace of it for progressive material (DVD).

    I'll warn you though, lots of DVD's have black stripes down the left and right hand sides too! These are sometimes many tens of pixels wide. If you get rid of your overscan, you then can't fill the screen horizontally...

    Steve
     
  14. Bert Coules

    Bert Coules
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    Nigel,

    That's a very clear explanation. Thanks.

    Stevelup,

    I don't know if I'm bold enough to start fiddling with the service menus in my Z2 (and in any case I don't know how to get to them). How straightforward a job is it? Is it simply a matter of finding a particular menu-entry and altering a numerical setting? Or is there a certain amount of experimentation required? Presumably it would be easy enough to undo any changes if I didn't like the result?

    Bert
    http://www.bertcoules.co.uk
     
  15. stevelup

    stevelup
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    Bert,

    As long as you make a note of the settings before you change them, you should be fine.

    Basically you press and hold the menu button (on the projector) for five seconds.

    Here is a list of all the settings (it is for the Z1 but most of them are the same). http://www.xs4all.nl/~etmriwi/ht/register.pdf

    You will see that for each input mode (480i, 480p, 575i and 575p) you can adjust horizontal and vertical scale along with horizontal and vertical position.



    Steve
     
  16. Bert Coules

    Bert Coules
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    Steve,

    Thanks for that. Presumably I would have to be careful to adjust not only the horizontal (where the problem lies) but also the vertical (in order to keep the projected aspect ratio correct). You mentioned a test pattern DVD: am I right in thinking that circles would be the easiest visual guide to getting the ratio correct? Or is there a more sophisticated way?

    Bert
    http://www.bertcoules.co.uk
     
  17. stevelup

    stevelup
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    Hi

    Circles are indeed ideal. I wouldn't do it visually though - use a tape measure!

    Steve
     
  18. Bert Coules

    Bert Coules
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    Steve,

    Actually, my eye is pretty good when it comes to stuff like that. But I'll have a tape measure standing by...

    Bert
    http://www.bertcoules.co.uk
     
  19. Bert Coules

    Bert Coules
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    Steve,

    I just tried to make the adjustments on my Sanyo Z2. Unfortunately, pressing and holding the projector's Menu button does not call up the service menu. I tried for five seconds, ten, fifteen, and finally upwards of thirty.

    I'll have a hunt around to see if I can dig up any more information, but in the meantime do you have any thoughts?

    Bert
    http://www.bertcoules.co.ukl
     
  20. stevelup

    stevelup
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    Sorry, I was daydreaming. MENU+INPUT

    ps. I have the Z2 service manual if you are interested?

    Steve
     
  21. Bert Coules

    Bert Coules
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    Steve,

    Well, that was fun. Your new instructions worked a treat and I got into the service menu with no problems.

    After a bit of experimentation I discovered that for an input of 575p, menu setting 316 adjusts the height of the image and 317 the width. The factory setup was:

    316 = 10
    317 = 34

    Using a 16:9 geometry chart I adjusted the width to get as much of the image as I could. I ended up with a new setting of zero, though the extreme edges of the chart were clearly still not being projected.

    Then, using the circles on the chart, I adjusted the height to suit. Again, a setting of zero seemed spot-on.

    After a couple of false tries, I discovered that the way to clear the service menu was to press the Power switch.

    Then I bunged in a 2.35:1 DVD...

    Well, the result was certainly an improvement, but it still isn't quite there. Measuring the image revealed an aspect ratio of 2.25:1 - better than the 2.17:1 I was getting before, but not by as much as I would have liked.

    Mind you, the disc (like many I looked at) gave the ratio as "2.35: 1 *Approx*". So perhaps I'm striving for something that isn't actually attainable.

    In any case, I'm pleased to have given things even a small nudge in the right direction. Many thanks for your help.

    Bert
    http://www.bertcoules.co.uk
     
  22. stevelup

    stevelup
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    Hi

    It is possible that some of the overscan is also being caused by your DVD player.

    Glad it helped a little bit.

    Regards,

    Steve
     
  23. Bert Coules

    Bert Coules
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  24. Bert Coules

    Bert Coules
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    A brief follow-up: adjusting the "expand/contract ratio" settings in the Z2 service menu has a knock-on effect: reducing the horizontal ratio figure does indeed put more of the recorded image onto the screen but it also introduces an overall sideways shift to the right; and this shift isn't correctable with the "position" settings.

    At the moment, I find that I like the more accurate widescreen aspect ratio and can live with the fact that - for example - credits that are supposed to be centred are actually offset to the right. But it does seem a pity...

    Bert
    http://www.bertcoules.co.uk
     
  25. stevelup

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    Hi

    Could you not use the optical zoom / lens shift to recentre the image?

    Steve
     
  26. stevelup

    stevelup
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    Just had another thought.

    Try menu options 1,2 and 3.

    They shift the red, green and blue images independently of each other. Just make sure you adjust all three by the same amount to ensure that you don't mess the horizontal convergence up.

    If you reduce all three by the same amount, that could possibly shift the whole image to the left. I've not tried this by the way!

    Steve
     
  27. Bert Coules

    Bert Coules
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    No, because that would move the whole projected frame; the off-centre image would still be off-centre within it.

    If I'm feeling brave I might try that red/blue/green shift idea. Thanks for the thought.

    Bert
    http://www.bertcoules.co.uk
     

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