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HTPC resolution and picture size

Discussion in 'Desktop & Laptop Computers Forum' started by mjwhitehouse, Aug 1, 2001.

  1. mjwhitehouse

    mjwhitehouse
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    OK this may be a stupid question but why is it when I change the resolution on my monitor from 640 x 480 to 800 x 600, the picture size stays the same but the icons get smaller but when I do this with my projector, the icons still get smaller but so does the size of the projected image?
     
  2. Stuart Wright

    Stuart Wright
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    What projector have you got?
     
  3. mjwhitehouse

    mjwhitehouse
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    Sorry guys, I am using an Ellie and VGA out from the HTPC. This overcomes the 'bounce' effect I occasionally get from SVGA or composite.
     
  4. Blade

    Blade
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    and what output type are you using? VGA Out? TV-Out?
     
  5. mjwhitehouse

    mjwhitehouse
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    Sorry to do this but I am really curious about this so I am getting the question back into focus.
     
  6. Jeff

    Jeff
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    OK lets think through this one. The reason that setting on a higher res on a monitor makes the icons get smaller is because the size in pixels of the icons doesn't change.

    It might make sense if the image on the projector was smaller at the lower res, this is how LCD screens work. With LCD the number of pixels and the size of the screen can't change so if you choose a lower res is desktop uses less pixels so appears smaller on the screen.

    If your projector is doing the opposite to this its got me stumped. Can you confirm? In any case if the Icons aren't smaller in comparison to the rest of the desktop when running at 800x600 it means that the higher res isn't working. In fact this maybe the answer, it sounds like you are setting the resolution on the projector but not the PC.

    Jeff
     
  7. mjwhitehouse

    mjwhitehouse
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    It definitely changes on the PC as well as the projector because once you set 800 x 600 on the PC, you have to re-synch the projector to the frequency coming in. I have tried Powerstrip and by changing the frequency the picture gets a little bit bigger but before it gets back to where it was the picture becomes unusable and the projector won't re-synch. It just seems odd.
     
  8. Guest

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    Mark,<br /> What is the optimum resolution the Ellie can do?<br />At what scanning rate? 75hz?<br />I heard the Ellie would not lock onto anything other than 640 x 480? This is why i would not consider it.<br />How have you got round this?<br />Doug.
     
  9. Chris Frost

    Chris Frost
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    The problem isn't going to be easily solved by tweaking the PC; it's more of a projector issue.

    The factors involved are Image Resolution, Refresh Rate and Time. A full explanation would take lots of time to read so I'm going to keep it short and cut a few corners. Apologies to the purists out there.

    Whenever your Ellie (or any other CRT projector) displays an image, the picture is written line by line scanning from left to right and from top to bottom of the screen - these are the scan lines.

    At 640x480 res (equivalent to line doubled NTSC), your projector is writing a horizontal line containing 640 dots, and doing this 480 times down the screen in (typically) 1/60th of a second (60Hz).

    A line doubled PAL signal has slightly higher resolution than NTSC, but uses a slower refresh rate (50Hz) so the net effect is the two signals are similar; i.e. the picture sizes are fairly close to each other. A CRT projector is usually converged for NTSC and PAL to iron out any minor differences between the signals.

    Increasing the resolution to 800x600 at 60Hz means writing more information in the same amount of time (1/60th of a second). Typically, a CRT projector will respond by drawing a smaller image. This is exactly what you have seen happen.

    The next stage is to reconverge the projector to accept the new signal. Part of this process involves stretching the width and height so the picture fills your screen again. These new settings are then stored as a new convergence memory.

    Increasing the refresh rate to 75Hz has a similar effect, and you'll need another convergence memory to cope.

    As you increase the scan rate and/or resolution, the resulting image will get smaller and smaller until the convergence controls run out of the necessary adjustment range to expand the image.

    Those projectors that can handle a wide range of resolution/refresh rate combinations tend to be very expensive. They are classed as Data Grade CRT projectors and command new prices of £15K+. Product with a more limited range is classed as Multimedia product. These feature full electronic convergence and multiple memory banks. Products include Barco 808/Cine6/Cine7 , Seleco 400/420/450/500, Sony D50. Prices range from £5K to £12K. Video Only product such as the Seleco 320/350/390, Barco 508/Cine5, Sony VPH1000/1020 will only handle a simple video signal in either native NTSC or PAL format, but won't accept a line doubled signal. They normally use some form of combined electronic/manual convergence. Prices range from £3K to £5K.

    The Ellie falls in between Video Only and Multimedia. It can accept a selected number of higher resolution signals but only under very specific circumstances.

    Although the Ellie has Multiple Memory Banks, it does not have Full Electronic Convergence. This is not surprising given the price of only £4K for a line doubled CRT projector.

    According to the manual on a machine I saw recently, the convergence set-up requires a physical adjustment to the magnetic yokes on each tube. True Multimedia projectors do not use this convergence method as it requires a major hands-inside-the-product reconvergence job every time you change from 640x480 to any other resolution. This is part of the reason why the Ellie is only £4K.

    In theory, it may be possible to set the Ellie one resolution/refresh rate setting and keep the PC at that frequency. But in pratice this won't work as PAL and NTSC discs use different refresh rates and external signals such as Satellite/TV/VCR would still come in via the Ellie line doubler at 50Hz.

    The answer is to stick with 640x480 at 50 or 60Hz from the PC. This is a close match to the signal from Ellies own line doubler and avoids reconvergence problems.

    For a more detailed explanation I'm sure Jim from Ellie distributor Screens UK would be able to help.

    Regards
     
  10. mjwhitehouse

    mjwhitehouse
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    Doug, just so you know, if you select 800 x 600 on the PC and leave it at adapter default, the screen will be unreadable. If yu then press the 9 key and hold it it forces the projector to re-synch to the signal coming in and hey presto! a perfect 800 x 600 image. This is good for Internet or games but not good for DVD which I always set on 640 x 480. Chris thanks for the info, I think I understand.
     
  11. Guest

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    Mark,<br /> would it not be better to set to 720 x 576?..or as close to-say 720 x 480?<br />When you say hold the 9 key,do you mean hold the 9 key down?(..for a few seconds..)...what refresh rate do you use.<br />I`m intrigued,because I`m quite interested in the Ellie.<br /> Thanks,<br /> Doug <img src="wink.gif" border="0">
     
  12. mjwhitehouse

    mjwhitehouse
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    I have just downloaded an application that may let me set some custom resolutions and to be honest I haven't tried any other than 640x480 and 800x600. Yes you hold the 9 key down for a few seconds, not too sure how long but this both switches the projector to bank 9 and then after the "few" seconds makes the projector re-synch to the incoming signal. This is detailed at the back of the manual. It works for some frequencies but not for others. I know 60Hz works well. I have been very happy with 640 x 480 , especially when I watched Dungeons and Dragons. I intend trying other resolutions and will let you know the result.
     

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