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Thread: Screen lines at 75 hz

  1. #1
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    Ubuntu 12.10 Quantal Quetzal

    Smile Screen lines at 75 hz

    Hi everyone,

    I have made a clean install of Ubuntu 12.10 on a brand new HDD (my old one broke down a few days ago). I also dual-boot with Windows 7. This is the same configuration I had previously, with the same hardware, except of course for the HDD.

    First of all, it is worth noting that I don't use a computer screen but a Techwood television, model VL22TV1001.

    My screen experiences curious faint white lines, especially on the right side of the screen, and a little more toward the lower right side. However, it does this only when I put the screen refresh rate at 75 hz. If I put it to 60 hz, everything is fine. It looks like some white lines are moving too. However, this is hardly visible on a white background, but becomes very visible on a black one.

    I wouldn't mind staying at 60 hz (although I've read it's not as good for your eyes); however, the resolution I'd like to use (1280x768) can only be used with 75 hz, so I'm stuck with 1024x768 which happens to have a 60 hz option available. It does the same on Windows 7, but it doesn't seem to happen when the computer is powering up (before choosing an OS), although I could be mistaken. I suppose this is because the screen resolution on start-up is pretty low, and the refresh rate too.

    Don't take my word for it, but I seem to recall that I actually was using 1280x768 without those lines before (although I wouldn't know what refresh rate I was using). I may be wrong, though.

    Is there a way to get rid of those lines? Are they mainly on the right side of the screen because of a screen problem? Can I force the refresh rate somehow, making sure my screen wouldn't be damaged in the process? Why would it do this now when there didn't seem to be any problem before?

    I understand this doesn't seem to be linked to Ubuntu itself since the issue also takes place on Windows 7, but since I'm not so sure where the problem comes from...

    Thank you very much,

    Patrice


    Screen: Techwood VL22TV1001
    Motherboard: P35C-DS3R
    Processor: Q9300 Intel Core 2 Quad
    Memory: 8 gb
    Graphics card: ATi Radeon HD5850
    OS: Ubuntu 12.10 64 bit, Windows 7 64 bit

  2. #2
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    Smile Re: Screen lines at 75 hz

    A quick update to add two things:

    -it looks like it actually does have these faint white lines even while booting up the computer, but they are harder to see.

    -it also looks like those lines appear when I'm in 60 hz. I didn't see them before, because they are much, much less visible.

    Anybody have any idea? In any case, those lines appear mainly on the right, toward the bottom right hand corner of the screen.

    Thank you,

    Patrice

  3. #3
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    Smile Re: Screen lines at 75 hz

    I took a picture of Ubuntu 12.10 in 1024x768. The first picture is with a refresh rate of 60, the second, a refresh rate of 75. You can clearly see the difference, although it is slightly less visible than that in reality.

    Refresh rate of 60: http://i46.tinypic.com/10d5do0.jpg
    Refresh rate of 75: http://i48.tinypic.com/depe08.jpg

    Does anyone have any idea? I'm at a loss here!

  4. #4
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    Re: Screen lines at 75 hz

    It should be possible to make a custom modeline that just shifts the start/end of each scanline & so hide the edge.
    This is a form of overscan compensation.

    Is this TV connected by VGA?
    Are you using the std distro FOSS video driver "radeon"?

    Post your /var/log/Xorg.0.log file..

    xrandr --prop

    If the TV is a CRT then could also be possible to adjust the TV geometry via factory mode.
    The TV may have overscan settings but this could lose a lot of screen area.

  5. #5
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    Smile Re: Screen lines at 75 hz

    Thank you for your help, BicyclerBoy.

    When I go to "Details" on Ubuntu 12.10, and then in the Graphics tab, it just tells me:
    Driver Unknown
    Experience Standard

    I don't know if this is the answer you were waiting for, but if I go to Additional Drivers in Software Sources, the selected driver is "Using X.Org X server - AMD/ATI display driver wrapper from xserver-xorg-video-ati (open source, tested). I tried the other two ("Using Video driver for the AMD graphics accelerators from fglrx" and the same but with "fglrx-updates") and they didn't seem to work at all.

    The TV is connected by HDMI. The funny thing is, I used another screen (a computer screen this time) for just a few minutes before plugging in my TV, and there was a strange behavior: it would keep on reacting as if I was pressing random buttons on the screen (Menu, Brightness, Contrast, etc.). That didn't happen the last time I used it. But I suppose there's no link between this problem and the one with my TV?


    The result of xrandr --prop:

    xrandr --prop
    Screen 0: minimum 320 x 200, current 1024 x 768, maximum 8192 x 8192
    DisplayPort-0 disconnected (normal left inverted right x axis y axis)
    underscan vborder: 0 (0x00000000) range: (0,128)
    underscan hborder: 0 (0x00000000) range: (0,128)
    underscan: off
    supported: off on auto
    coherent: 1 (0x00000001) range: (0,1)
    HDMI-0 connected 1024x768+0+0 (normal left inverted right x axis y axis) 16mm x 9mm
    EDID:
    00ffffffffffff003cad003700000000
    0a120103801009780a6837a454489a25
    0f4a4c3fef8001010101010101010101
    010101010101011d8018711c1620582c
    250010090000009e011d007251d01e20
    6e28550010090000001e000000fc0032
    32575f4c43445f54560a2020000000fd
    00314b0f2e08000a20202020202000fc
    underscan vborder: 0 (0x00000000) range: (0,128)
    underscan hborder: 0 (0x00000000) range: (0,128)
    underscan: off
    supported: off on auto
    coherent: 1 (0x00000001) range: (0,1)
    1920x1080i 30.0 +
    1280x720 60.0
    1024x768 75.1 70.1 60.0*
    1024x576 60.0
    832x624 74.6
    800x600 72.2 75.0 60.3 56.2
    848x480 60.0
    640x480 72.8 75.0 66.7 60.0
    DVI-0 disconnected (normal left inverted right x axis y axis)
    load detection: 1 (0x00000001) range: (0,1)
    underscan vborder: 0 (0x00000000) range: (0,128)
    underscan hborder: 0 (0x00000000) range: (0,128)
    underscan: off
    supported: off on auto
    coherent: 1 (0x00000001) range: (0,1)
    My /var/log/Xorg.0.log is quite long. Should I just copy-paste it here like xrandr --prop above?

    Finally, I think my TV is an LCD? If a CRT TV is necessarily those old TV sets, then no, it's not. I already tried going in the menu but I can't find anything to adjust anything except Contrast, Brightness and Colors (and it's not even accessible in Game Mode).

    What feels really curious to me is that the more I'm using this computer since the clean install, the more I feel like this problem wasn't here before: the lines are far too visible on a dark background at 75hz, I would have noticed them before.

    Thank you for your help!

  6. #6
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    Re: Screen lines at 75 hz

    Internally most LCD (DFPs) refresh at 60Hz.
    LCD TVs in US/Japan/SAm at 60Hz & most of the rest of world at 50Hz.
    The next gen TVs push this to 100/120.

    Most TVs & monitors have an input pre-scaler circuit block. That's how it can accepts lots of video modes etc..

    With DFP the refresh rate only effects motion blur/judder; there is no eye strain with static images.

    Pushing video at the display at non-native refresh scan rates is asking for terrible jitter motion juddering.

    The best image PQ/sharpness is at the native resolution.

    Why do you want a non-native resolution?
    You can over-ride the screen dimensions to scale the desktop icons etc..
    xrandr --fbmm XmmxYmm

    You could try:
    xrandr --output HDMI-0 --scale 0.99x0.99

    Can you try just:
    xrandr

  7. #7
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    Smile Re: Screen lines at 75 hz

    Alright, so I understand I better stick to one of the native resolutions. The reason I didn't want to was that all the native resolutions either do not fit the screen, or everything is way too small (this TV isn't too big).

    But I understand, from what you say, that I can perfectly choose a native resolution that doesn't fit the screen, and then scale it down a little. That might work indeed.

    However, when I try xrandr --output HDMI-0 --scale 0.99x0.99, it doesn't make any noticeable change. I tried 0.80x0.80, but it only seemed to resize the bottom and the right of the screen; I still couldn't see the top and left parts.

    I am not sure how to use xrandr --fbmm XmmxYmm so I didn't try putting random numbers in case my screen explodes. How am I supposed to use it, say, with 1280x720 and with 1920x1980 (all 16:9 don't fit the screen entirely, while all 4:3 seem to do the trick)?

    Finally, here is the output for xrandr:

    Screen 0: minimum 320 x 200, current 1268 x 713, maximum 8192 x 8192
    DisplayPort-0 disconnected (normal left inverted right x axis y axis)
    HDMI-0 connected 1280x720+0+0 (normal left inverted right x axis y axis) 16mm x 9mm
    1920x1080i 30.0 +
    1280x720 60.0*
    1024x768 75.1 70.1 60.0
    1024x576 60.0
    832x624 74.6
    800x600 72.2 75.0 60.3 56.2
    848x480 60.0
    640x480 72.8 75.0 66.7 60.0
    DVI-0 disconnected (normal left inverted right x axis y axis)
    If I understand, this means 1920x1080 works only with a refresh rate of 30? Since I use this computer for gaming too, should I try 1280x720 instead?

    My apologies for all the questions.
    Thank you!

  8. #8
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    Smile Re: Screen lines at 75 hz

    Alright, I just managed to scale down the screen on Windows 7 by simply putting a 1280x720 resolution and then using the Catalyst Control Center (for ATi Radeon graphics cards) to put an underscan of 6%. Since it is in 59 hz, there are no white lines anymore.

    I suppose that, if I have the correct Terminal command to do the same in Ubuntu 12.10, it would achieve the same result.

  9. #9
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    Re: Screen lines at 75 hz

    The 1080i 30Hz mode is an interlaced mode; 30 frames/sec, 60fields/sec.
    The field rate is 60Hz.
    Good de-interlacering doubles the frame rate 30 -->60/sec.

    If you TV is cheap then it's de-interlacer will be horrible better to output 720p (p denotes progressive frames=fields)

    This line from xrandr:
    HDMI-0 connected 1280x720+0+0 (normal left inverted right x axis y axis) 16mm x 9mm
    - it thinks your screen is 16mm by 9mm..I think your TVs EDID has been created by someone with no understanding..

    "$xrandr --fbmm XmmxYmm" where X & Y are in "mm" (m/1000)
    Measure your screen with a ruler & use the right numbers..
    i.e.
    "$xrandr --output HDMI-0 --mode 1024x768"
    "$xrandr --output HDMI-0 --scale 1x1"
    "$xrandr --fbmm 400x200"
    Can use --dpi to change the desktop text/gadget size.

    You can use the linux AMD Catalyst fglx driver.

    Aspect ratio:
    get the screen size right first..
    This issue is complicated because:
    - pixel aspect ratio of SD & HD material is different
    - your display has 4:3 screen pixel aspect ratio for 16:9 physical size

    Is your display a true 16:9 or 16:10 or 4:3?
    Last edited by BicyclerBoy; January 19th, 2013 at 11:00 PM.

  10. #10
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    Smile Re: Screen lines at 75 hz

    The TV indeed seems to be a pretty cheap one given the deal my parents got on it.

    I measured the TV and it is approximately 47,5 cm by 26,7 cm. Does that answer whether it's a 16:10, 16:9 or 4:3? I have no idea how to obtain this information.

    When I input $xrandr --fbmm 47mmx26mm, it says --fbmm: command not found. The same goes for the two $xrandr --output HDMI-0 commands you advised: --output: command not found.

    As for the linux AMD Catalyst fglx driver, I tried to install it via Software Sources (more information on my first post), but it didn't seem to be recognized. Tough luck!

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