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Barco Question : Clamp Mode?

Discussion in 'Projectors, Screens & Video Processors' started by Leon Rees, Jun 4, 2001.

  1. Leon Rees

    Leon Rees
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    Can anybody shed any light on what Clamp Mode on a Barco 808s is for?

    Two choices Restoration or Normal? Which do I choose and why?

    Thanks,

    Leon
     
  2. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Clamp locks incoming black level signal I think. Not sure which setting does what on your projector.

    Play something like the end credits of a film with a black background and scrolling text and switch between the two. I seem to remember I had a problem on scene like that with a unit (prob not Barco though) and adjusting Clamp fixed it.

    If you get a reply from Barco or anyone else canyou post it here so we can all learn thanks.

    Gordon
     
  3. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    This is really one for Jim at Ellie. It's been answered here before.

    Here's my understanding. The Ellie doesn't have the range in it's size and blanking adjustments to re-size a 4:3 image to fit within a 16:9 screen. There are ways round this though.

    1: Distort the image as little as possible and create a slightly stretched and cropped top image.(not sure if it can do this but would guess it can)

    2: Watch all 4:3 material in anmorphic mode so everyone is short and dumpy (not recommended)

    3: Use an external scaler or doubler with aspect ratio control to do the re-sizing for you and just use the anamoprhic setting for both and letterbox for letterbox dvd's and video's. Suitable video processor would be the Iscan.......

    Number 2 will work the others need to be verified by Jim or current Ellie owners.

    Gordon
     
  4. Leon Rees

    Leon Rees
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    So, I take it my thread has been hijacked. Thanks Metric! :mad: Hint : it is possible to delete/edit ones own posts

    Does anybody else have anything to contribute to the Clamp mode discussion?

    I read somewhere that restoration clamping should be used for inputs that have separate syncs. Anybody care to confirm?

    Thanks,

    Leon

    [ 05-06-2001: Message edited by: Leon Rees ]
     
  5. Metric

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    chill...i did apologise, just found you can delete threads, cheers Gordon though..back to nipple clamps
     
  6. Oasis

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    I'm not 100% sure exactly what Barco mean on their implementation of this control, but, generally it would be used to compensate for poorly controlled source signals.

    The idea of black level clamp is to identify an area of a picture that is always black and use this level as the reference for the picture black. The reference used is usually during blanking (the period in the signal while the scan is returning to the start of the line)This will give a good stable black for most sources.

    However in poorly designed sources the absolute signal level of black will drift significantly during each line or frame. with this kind of signal an additional section of electronics (usually just a different combination of capacitors) in the input circuit is used to filter this line or frame tilt (on an oscilloscope the waveform tilts up).What you would see on screen would be wide bars horizontally or vertically on the screen where the brightness of the picture changes , or where the black level generally changes significantly as the picture content changes.

    With this kind of control you should leave it on normal, unless the other position makes a visible improvement. Using the restoration setting when not needed can cause problems in getting a really good setup. Restoration is really only there for the bad industrial installations, any home cinema installation should never need it.

    I hope this helps.

    Oasis
     
  7. Roland @ B4

    Roland @ B4
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    I agree with Oasis

    I had to use the restoration setting once, which was on a very complicated silicon graphics source, running sync on green at the top of the projectors resolution.

    It shortens the projectors sampling of the video black measurementa dn will make the black level start to rise.

    Quite simply leave the clamping mode on normal. Nothing in HC is likely to need it.

    B4
     

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