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A photo of the computer screen -- what causes vertical lines

  1. Jan 28, 2017 #1
    https://www.dropbox.com/s/be52pax3jezv3cb/IMG_20170128_170143.jpg?dl=0 https://www.dropbox.com/s/be52pax3jezv3cb/IMG_20170128_170143.jpg?dl=0 I have question what causes vertical lines on the photo of the screen of my laptop?
    But I would like to find out it alone. Could someone lead me?
    I know the screen works with some frequency and it "blinks". Something around 75Hz I guess. But why it makes such vertical lines...I don't have any idea. Maybe problem is I don't know how works camera in my phone. Please advise.
    Thank you for your posts.
    Picture is here: https://www.dropbox.com/s/be52pax3jezv3cb/IMG_20170128_170143.jpg?dl=0
     
  2. jcsd
  3. Jan 28, 2017 #2

    lewando

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    Gold Member

    Interesting question. Lines are horizontal when my phone is horizontal--vertical lines when phone is vertical. Investigate how your laptop updates its screen image AND investigate how your camera digitally processes an image.
     
  4. Jan 28, 2017 #3
    Does it happen only with laptop ? did you try that on TV or other screen ?
     
  5. Jan 30, 2017 #4
  6. Jan 30, 2017 #5
    It is very interesting. Asus and LCD TV don't have any lines. And old tube television in portrait mode produces oblique lines :-D Landscape photo of old TV produces horizontal lines...don't understand anything :-)
    Any idea, why sometimes there are lines and sometime not? What can be different in these screens?
     
  7. Jan 31, 2017 #6
    Try changing the refresh rate of the monitor.
    Then click the pictures.
     
  8. Jan 31, 2017 #7
  9. Jan 31, 2017 #8
  10. Jan 31, 2017 #9
    No doesn't matter. Do you have any idea what is happaning with my camera?
     
  11. Feb 1, 2017 #10

    rcgldr

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    Homework Helper

    The effect is related to the camera. I tested a Note 4 camera with a CRT monitor. The camera is sensitive to refresh rate and brightness. At 60 hz or 120 hz, at normal brightness I don't see lines, but if I dim the brightness somewhat, I see thick moving darker lines, but if I continue to dim below some threshold, I don't see lines. At 70hz or 85hz, there are always lines present. I see moving darker lines that change speed and generally get thicker as the image on the CRT monitor gets dimmer. At normal brightness levels, the lines are thin similar to the images posted earlier. On a very dim setting the darker lines are so thick that the effect is like thin brighter lines. At 70hz / 85 hz, normal brightness: if the camera is horizontal (landscape) I see horizontal lines; if the camera is vertical (portrait), I see angled lines; if the camera is held about 30 degrees counter-clockwise from vertical, I see vertical lines on the camera.

    The Note 4 uses a IMX240 EmorRS CMOS sensor.

    http://en.wikipedia.org/wiki/Exmor#List_of_Exmor_RS_sensors

    The CMOS sensors have an effective scan rate, which causes the artifacts you see with moving objects, or objects like a CRT monitor where the phosphors fade until refreshed by the sweeping beam. This web site includes a video animation of the effective scanning across then down rows, comparing CMOS versus CCD sensors.

    http://www.popphoto.com/clever-animated-videos-explain-how-cmos-and-ccd-camera-sensors-work

    More info:

    http://electronics.howstuffworks.com/cameras-photography/digital/question362.htm

    http://www.teledynedalsa.com/imaging/knowledge-center/appnotes/ccd-vs-cmos
     
    Last edited: Feb 1, 2017
  12. Feb 1, 2017 #11
    Great. Thank you, I will study your links :)
     
  13. Feb 1, 2017 #12
    I think you are getting this kind of effect from the refresh rate of the screen.

    propeller.jpg

    My guess is that the screen changes in brightness during each refresh for a moment, and the scan-rate of the camera is catching that.
     
  14. Feb 2, 2017 #13
    Could you be more specific please? What is name of this effect. Honestly, I'm not sure what is exactly happening at your picture. Could you send some link with description of this effect or something like that?
     
  15. Feb 2, 2017 #14

    f95toli

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    Science Advisor
    Gold Member

    The effect is seen in many different systems. A good example would be an old fashioned (mechanical) strobe tuner for a guitar.
    See


    The "lines" you see is because the two systems (your laptop and your camera) are "out of tune" (not synchronized).
     
  16. Feb 2, 2017 #15
  17. Feb 9, 2017 #16
    Thank you all!! I hope I understand ;-)
     
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