DP/HDMI cable creating bad image

Discussion in 'Mac Pro' started by c:v, Apr 10, 2019.

  1. c:v macrumors regular

    Joined:
    Jan 20, 2010
    #1
    Hi guys,

    I have a 5.1 Mac Pro with RX580 connected to a Acer B276HUL display via DVI cable and all was fine. I had to move the Mac Pro further away and needed a longer cable to connect it back up but didn't have a long enough DVI cable.

    So I tried an HDMI and DP cable and both of them created a very bad image. Specifically the text and icons look over sharpened and perhaps didn't have any AA applied to them?

    What I have tried:

    • enabled/disabled font smoothing
    • tried to manually set font smoothing
    • checked display settings
    • reset display to factory settings
    Both HDMI and DP cable produce a normal image under Windows 10/BootCamp!

    I'm absolutely baffled by this. Anyone have any tips?

    Screenshot 2019-04-11 at 07.32.50.jpg Screenshot 2019-04-11 at 07.32.53.jpg Screenshot 2019-04-11 at 07.33.05.jpg
    Screenshot 2019-04-11 at 07.31.52.jpg Screenshot 2019-04-11 at 07.31.54.jpg
     
  2. c:v thread starter macrumors regular

    Joined:
    Jan 20, 2010
    #2
    Ok, so I found something else out:

    When manually enabling and selecting HiDPI mode under display settings, all icons ante text is now back to "normal" eg. high resolution, looks great. Obviously everything is at much larger scale, so it's not usable.

    But it does proof that the problem lies in Mac OS not "loading" proper assets for the display? I don't know why it does when using a DVI cable but not when using an HDMI or DP cable.

    Has no one else got any ideas at all?

    Screenshot 2019-04-12 at 16.44.24.jpg Screenshot 2019-04-12 at 16.44.30.jpg
     
  3. h9826790 macrumors G5

    h9826790

    Joined:
    Apr 3, 2014
    Location:
    Hong Kong
    #3
    Can't see anything wrong with your screen capture.

    If that's cabling issue, screen capture will not able to show the problem, because that's capturing the rendered image from the RAM.

    Anyway, if HiDPI work, you may use "super resolution" (e.g. 2560x1440 HiDPI) for your computer.

    I did that as well. Not because of having issue, but better font (AA), and better screen capture.

    My monitor's native resolution is 3840x1080
    Screenshot 2019-04-13 at 5.47.13 AM.png

    But I let the RX580 render at 7680x2160 (3840x1080 HiDPI) Screenshot 2019-04-13 at 5.47.15 AM.png

    You may see if ResXtreme allow you to do that.

    http://resxtreme.com/

    After you open the apps and select your monitor, click "scale", and all the x2 scale are the HiDPI options.
    CHG90 HiDPI options.png

    Anyway, here is comparison between HiDPI and non-HiDPI rendering. As you can see, HiDPI so so much better. The non-HiDPI font smoothing makes the text looks really bad.
    HiDPI Comparason.jpg
     
  4. c:v thread starter macrumors regular

    Joined:
    Jan 20, 2010
    #4
    Thanks for your help. I have downloaded the app and tried the HiDPI resolutions. It does look better but now everything is huge!

    Screenshot 2019-04-15 at 08.35.57.jpg Screenshot 2019-04-15 at 08.38.30.jpg
     
  5. h9826790 macrumors G5

    h9826790

    Joined:
    Apr 3, 2014
    Location:
    Hong Kong
    #5
    So, 2560x1440 HiDPI does not available, but only 1280x720 HiDPI?
     
  6. c:v thread starter macrumors regular

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    Jan 20, 2010
    #6
    Correct!
     
  7. h9826790 macrumors G5

    h9826790

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    Apr 3, 2014
    Location:
    Hong Kong
    #7
    Then you may really need SwitchResX
     
  8. c:v thread starter macrumors regular

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    Jan 20, 2010
  9. h9826790 macrumors G5

    h9826790

    Joined:
    Apr 3, 2014
    Location:
    Hong Kong
    #9
    Custom resolution in SwitchResX?
     
  10. c:v thread starter macrumors regular

    Joined:
    Jan 20, 2010
    #10
    I don't understand how to save them? Screenshot 2019-04-15 at 10.51.00.jpg
    --- Post Merged, Apr 15, 2019 ---
    Managed to save the custom resolution but now get a black screen after login and I can’t see anything. I’ve booted into recovery mode and manually removed the app and pref pane but the resolution seems to stick around. Any ideas?

    This is going from bad to worse lol!
     
  11. c:v thread starter macrumors regular

    Joined:
    Jan 20, 2010
    #11
    Managed to restore a local snapshot from earlier this morning.
     
  12. h9826790 macrumors G5

    h9826790

    Joined:
    Apr 3, 2014
    Location:
    Hong Kong
    #12
    Remove the DP cable, and plugin the HDMI cable should go back to native resolution automatically
     
  13. c:v thread starter macrumors regular

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    Jan 20, 2010
    #13
    Thanks - I tried that and many other things before I restored local time machine snapshot.
     
  14. krakman macrumors regular

    Joined:
    Dec 3, 2009
    #14
    hi i think you need to force RGB mode.

    The clue is in the monitor resolutions window..... you are showing 1080p and 1080i these are TV resolutions because your mac thinks the monitor is a TV and is probably outputting YCbCr instead of RGB.

    the solution is here: https://www.mathewinkson.com/2013/0...ix-the-picture-quality-of-an-external-monitor

    I had the same issue after running the rgb override the GUI loks good and 1080p & 1080i resolutions disappear from the bottom of the list.

    Screenshot 2019-04-15 14.09.07.jpg
     
  15. h9826790 macrumors G5

    h9826790

    Joined:
    Apr 3, 2014
    Location:
    Hong Kong
    #15
    That may help in some case, but I don't think it's "TV" related.

    My setup also has 1080P and 1080i option. And from post #3 screen captures, you can see that my setup shows "Television: Yes", but still using RGB 30bit output.
     
  16. c:v thread starter macrumors regular

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    Jan 20, 2010
    #16
    OMG you are a god damn legend! That did the trick. Thank you so much for everyone's help!
     
  17. krakman macrumors regular

    Joined:
    Dec 3, 2009
    #17
    Yes its a bit of a conundrum!

    When I used a pair of 27 inch 1920x1080 monitors I didn't experience any issues. but as soon as I upgraded to higher res monitors on my system I began to notice the over sharpened text as mentioned by the OP.

    There are a lot of people complaining about various monitor issues on the blog post that i linked to. It seems to have started a few years ago with Mavericks.

    The screen shot below shows my current set up, the 32 inch screens needed the RGB override but the 34 inch ultra wide shows the 1080p/i resolutions but the display is crisp and clear, perhaps because I have it in HDPI mode?

    In the office we have another 3 mac pros with various monitors ( generally 32 inch AOC) and I have applied the RGB fix to all of them - I think.

    IF
    i get time i will investigate to see if i can find a pattern to this behaviour.


    Screenshot 2019-04-15 16.21.23.jpg
     
  18. c:v thread starter macrumors regular

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    Jan 20, 2010
    #18
    I did think it was strange that the display works fine with a DVI cable but goes bad when using HDMI and DP cable. Together with the fact that under Windows, it all looks fine regardless of which cable/port I use clearly indicates that this is a software bug with OS X.
     
  19. krakman macrumors regular

    Joined:
    Dec 3, 2009
    #19
    Yes it think you are right!!!!

    I used mDP to DVI cables with my 1920x1080 monitors and all was good. Upgrading to 32 and 34 inch monitors required use of DP/HDMI cables and thats when the issue appeared.

    My upgrading of monitors coincided with Mavericks so the bug/issue may have been present in older versions of OSX ???

    The first time I experienced it was with a 2 monitor setup. One monitor was HD, the second was a 21:9 2560x1080 connected by DP

    My hypothesis:

    Monitor with >HD resolution + DP/HDMI cable = MAC OS outputs YCbCr instead of RGB

    But there is evidence that this issue does not occur with all monitors, only some brands/models of monitor.

    Also my wife had the issue on her monitor but she did not notice it until I pointed it, so I wonder if many people are simply not noticing the issue??
     
  20. c:v thread starter macrumors regular

    Joined:
    Jan 20, 2010
    #20
    Let's hope search engines will pick this up and get people to resolve their issue if they have the same one.
     

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