So clearly ALL television sets are defective (overscan)

Discussion in 'Displays' started by Curtis Anderson, Feb 10, 2004.

  1. Curtis Anderson

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    Overscan serves no purpose, does it? In my mind this is one of those things like interlaced video that just never should have come into existence. So let's talk about it and we can cathartically work through this.

    I wonder, do CRT sets usually have more overscan than LCD / Plasma / DLP type sets?

    I can solve the overscan problem on my CRT computer monitor by making the entire image area smaller. This is how I noticed on my LEON dvd that they slightly made the image smaller so that it wouldn't be affected by the overscan. Or something. Any input will be appreciated. Thanks.
     
  2. Allan Jayne

    Allan Jayne Cinematographer

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    Only CRT's have optical overscan which is adjusting the scan line length and spacing. Any kind of TV, LCD, Plasma, etc. may have electronic overscan which is stretching the video signal timing relative to the waveform that sweeps the electron beam or feeds the pixels.

    The original reason for overscan was varying line voltage back in the early days of TV, the picture would grow and shrink. (This is still true for a few cheap TV sets today.) Because people complained that the TV was defective, manufacturers adjusted the picture so that after the maximum expected shrinkage the picture still filled the screen.

    On some TV sets (CRT only) the picture also grows and shrinks slightly depending on the average scene brightness.

    Occasionally the "duty cycle" or portion of the scan line used for picture material may vary from one DVD player or VCR to another, or as you explained, from one DVD or tape to another. If it is less, the finished picture might not fill the screen.

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

    Michael TLV THX Video Instructor/Calibrator

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    Greetings

    Now look for a computer monitor the same size as an RPTV or what have you with that same ability. What does that TV cost you?

    What is the cost of a 27" datagrade tube?

    If humans are not perfect, why would we expect that TV's should be?

    You might understand overscan, but what about the millions out there that won't and will complain that there is a black line on the top of their TV ... ? How does a manufacturer deal with that and at what cost?

    Regards
     
  4. Garrett Lundy

    Garrett Lundy Producer

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    I thought LCD and plasma monitors had no overscan when professionally calibrated?[​IMG]
     
  5. ChrisWiggles

    ChrisWiggles Producer

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    There is a lot of erroneous data and noise sometimes at the edge of the picture. This is yet another reason for some very slight overscan. You don't want a bunch of fuzz and strange stuff at the edges of the screen, that's very distracting.
     
  6. Steve Schaffer

    Steve Schaffer Producer

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    In my experience with calibrating upwards of 7 different dvd players on various televisions with AVIA, almost all are off-center a bit when displaying the 16/9 pattern, sometimes by as much as 2 inches or so on a bigscreen set.

    Thanks to overscan this has not noticeably affected regular movie presentation on any of these sets from any of the players.
     
  7. JohnnyG

    JohnnyG Screenwriter

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  8. Richard Paul

    Richard Paul Stunt Coordinator

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    The only reason overscan exists is because of bad analog signals and CRT limitations. A slight overscan of 2-4% can help hide both bad analog signal's and CRT blanking intervals. The reason for 8-12% overscan, which is common on most CRT televisions, is purely because of cheap CRT's.

    With digital signals from Firewire or HDMI/DVI (or very well done analog signals) there is no reason for overscan on non-CRT televisions. Most fixed pixel displays (DLP, LCD, LCOS, Plasma) can do a pixel perfect image.
     

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