Overscan Questions

Discussion in 'Displays' started by Dave H, Oct 17, 2005.

  1. Dave H

    Dave H Producer

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    How does one read overscan correctly? For example, when I put in Avia's overscan grid, I see 4% around three of four sides. Usually one side is closer to 5% but I think this is because Sony "shifts" the picture ever so slightly, presumably to held prevent burn-in.

    So, is my overscan around 4%? Just making sure I'm "reading" it correctly.
     
  2. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

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    Greetings

    Yup ... it's just as it reads. 4% overscan. Sounds like a plasma unit.

    Panasonic uses about 3% overscan as does Samsung for their plasma units.

    Regards
     
  3. Dave H

    Dave H Producer

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    Mike,

    My TV is a Sony CRT RPTV (KP-57WS520).

    I had an ISF tech last year set it to this percentage. Does this sound about right for this set? He said reducing any more than this started to cause too much line bending. Your thoughts and experience with this kind of set? Thanks.
     
  4. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

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    Each set is different. Even within the same model line. Some can go to 2% ... others can go to 4%. However ... setting it to less than 4% usually adds one additional problem. It disables the flash focus feature.

    Aside from that ... any kind of size change to the image will introduce geometry changes to the image. IT is normal ... and generally fixable. The only trade off is that a few of the top corner lines might curve a bit more, but this is out in the top 1 to 2 inches of each corner. Considered minor and no one can see that anyway from normal viewing distances.

    On some Sony sets, you don't have to physically squeeze in the image. RAther, there are parameters where you can rescale the image to fit the visible screen surface. When this is used, the overscan can usually be safely set to 2% without any problems or geometry issues. YOu just don't ever want to go to 0% overscan or 1% as that is a bad idea.

    Regards
     
  5. Dave H

    Dave H Producer

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    Michael,

    The Sony parameters you refer to which allow one to safely set to 2% without any problems or geometry issues...are these the 'mid' parameters? Do you know off the top of your head?

    I wouldn't mind exploring these a bit.

    Thanks!
     
  6. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

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    Yes ... the MID 1 or Mid 3 parameters ...

    Test them out.

    Regards
     
  7. Dave H

    Dave H Producer

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    Will do, thanks.

    Oh, also...does changing these require convergence changes.
     
  8. John S

    John S Producer

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    You are brave.. 4% is spec no?


    Let us know how it goes for you.
     
  9. Dave H

    Dave H Producer

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    I think spec is much higher....can't remember for sure.
     
  10. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

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    Greetings

    Spec is usually 5% on Sony sets.

    You won't need to redo convergence if you are rescaling the image.

    Regards
     
  11. John S

    John S Producer

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    Ok he is brave.. 4% is already under spec. [​IMG]
     
  12. Dave H

    Dave H Producer

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    Hey Mike,

    The mid only seems to affect the positioning of the image..not overscan.

    Hsiz and vsiz affect overscan on my set.

    When I set overscan to about 3% (or very slightly less), the line bending wasn't too bad at all. I would just need to re-tune convergence.

    I might try straightening out one of the lines with skew.
     
  13. Dave H

    Dave H Producer

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    Well, second thought, maybe I'll wait. [​IMG]

    Requires some major convergence work and I would need a grid.

    Maybe I'll just keep it as is for now.
     
  14. Michael TLV

    Michael TLV THX Video Instructor/Calibrator

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    Greetings

    There are MID items that affect position and others that affect sizing. You just have to look for them.

    Hiding in plain sight.

    Regards
     
  15. Dave H

    Dave H Producer

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    Hmmm...I cycled though each mid (1-3) and experimented. Here they are:

    mid1 dycd
    mid1 dysd
    mid1 mdvp

    mid2 msys

    mid3 mhph
    mid3 shph




    I was able to center image a bit better to have 4% equal on each side (no convergence needed here).
     
  16. Allan Jayne

    Allan Jayne Cinematographer

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    Plasma (and LCD) sets should be able to be calibrated to have less than one percent overscan. Depending on your DVD player, videocassettes, cable/dish system provider, and local TV stations you may need more overscan because the video material might not be spread wide enough.

    On some CRT sets the entire picture may grow or shrink slightly depending on the overall scene brightness. This is somewhat hidden with more overscan.

    Video hints:
    http://members.aol.com/ajaynejr/video.htm
     

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