What the heck is 1:1 pixel mapping?

Discussion in 'Archived Threads 2001-2004' started by Gordon Moore, Aug 12, 2002.

  1. Gordon Moore

    Gordon Moore Second Unit

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    Been reading on this and other boards got me wondering why 1:1 pixel mapping is a good thing with projectors. What's the alternative if you don't achieve this? That is, what does the projector do if you can't set a rez that gives 1:1 pixel mapping...maybe I don't quite understand what this is.
    Helllllllllp [​IMG]
     
  2. Bill Slack

    Bill Slack Supporting Actor

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    If you input anything else the projector itself will have to scale the image. Usually, an outboard scaler or HTPC will do a superior job in terms of image quality, because of this.
     
  3. Gordon Moore

    Gordon Moore Second Unit

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    Okay (I'm still new to this)...so if you set your rez on the pc incorrectly, the scaler in the projector takes over rather than the PC. is that correct?... I always thought that the advantage to an HTPC is that you could scale to much higher rez's and refresh rates...or am I screwing up my terminology?

    856*480 =16:9 right?

    712*400 =16:9 right?

    by picking a resolution and multiplying by 1.78 is that roughly how the correct rez for a projector is chosen and scaled? (with the appropriate refresh)

    and scaling is not the same as line doubling right in effect that's refresh?
     
  4. Bill Slack

    Bill Slack Supporting Actor

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    A fixed pixel display (LCD, DLP, D-ILA...) has a specific resolution of the panels.

    1368x768 is found in some DLP projectors. You want your PC to output at exactally 1368x768. When you do this, the projector had to do no scaling, which is what you're after. Now CRT projectors are another beast. They can take all sorts of resolutions, and usually some fine tuning in between, as they can usually accept a range of frequencies. But there is still an optimal range, and that's what you want a HTPC for.

    The refresh rate is optimally set (and outputted) at a multiple of 24 (e.g. 72) for film based or of 30 (e.g. 60) for video based, but that's not necessarily possible in all projectors (but should be on most CRTs.) Some devices may only accept (or display) @ 60hz.

    In terms of line doubling, it's usually refering to de-interlacing, since the base video signal is interlaced. This often involves 3:2 pull-down as well, to reconstruct the original film element correctly (24fps v. 30fps) Scaling is just changing the resolution of the output, and will generally include de-interlacing. A good scaler will also stretch a non-anamoprhic image into an anamorphic image, so no optical zoom or additional blank space is required.
     
  5. Gordon Moore

    Gordon Moore Second Unit

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    Thanks Bill you've been very helpful just trying to get some lightbulbs to fire up.

    Ah...so that's what they mean when they talk about the native resolution of a projector. One that has caught my eye is the panasonic AE100. So you want to achieve the projectors native mode to avoid the projector from scaling versus the superior GPU in the graphics card (sorry for reiterating ...just trying to get it clear for me). So you can't fire the projector all sorts of wacky resoultions that it can't handle cause it will either scale them back or not display the image I guess.

    Is that why 800X600 projectors aren't that great for 16:9 because they have to rescale the image into a 800X600 square and throw up the black bars.

    Also the max refresh is as good as the weakest link which in this case would be the display and not the graphics card 'cuz they can hit all sorts of crazy refresh rates these days at unholy resolutions.

    So, if your desktop is set to 16:9 to match a native 16:9 projector and you go and play a 4:3 sdtv program from the tuner in your pc, the projector's scaler kicks in (I imagine) to display the 4:3 picture properly? or do you need to reset your desktop and that's where powerstrip comes in handy?
     
  6. Gabriel_Lam

    Gabriel_Lam Screenwriter

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  7. Bill Slack

    Bill Slack Supporting Actor

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    Yes, my memory failed me. That's common on LCD (and some Plasma) but I can't find a single DLP that's 1368x768.
    Whoops! [​IMG]
     

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