MAJOR iMac 27" display issue under Windows 7

Discussion in 'Windows, Linux & Others on the Mac' started by Verxion, Jan 4, 2010.

  1. Verxion macrumors member

    Dec 21, 2009
    Under Windows 7, if I go to the following URL, I see a MAJOR problem:

    There is something like 256 distinct shades in each horizontal bar. NOTHING MORE.

    If I simply drag my web browser over to my second monitor, a 28" 1920x1200 monitor hooked to the mini displayport, it displays PERFECT gradients. WHAT GIVES?!?!?

  2. Verxion thread starter macrumors member

    Dec 21, 2009
    Interesting. I just booted into OSX and that gradient is far better on the iMac screen in OSX than in Windows, but it STILL isn't nearly as smooth as on my 28" monitor...

    Something seems amiss here folks!

    Anyone else seeing similar issues?

  3. Verxion thread starter macrumors member

    Dec 21, 2009
    Another test - if I set my display under Windows 7 to "16 bit color" then BOTH monitors exhibit the same banding. So it appears that in windows 7, even if you set the display to 32 bit, it is ACTUALLY just running in 16 bit color.

  4. Verxion thread starter macrumors member

    Dec 21, 2009
    This is with ATI drivers dated 11-24-2009, driver version 8.681.0.0 - the latest you can download from ATI's site...

  5. ildondeigiocchi macrumors 6502a


    Dec 30, 2007
    Actually they're reached at 9.12. Check it out:ATI DRIVERS FOR 4850
  6. Verxion thread starter macrumors member

    Dec 21, 2009
    I installed the 9.12 drivers. They are the ones that gave me this driver version number.

  7. Verxion thread starter macrumors member

    Dec 21, 2009
    Some more information. If I set the display to 16bit color, both displays exhibit the same banding. If I set it to 32bit color, then ONLY the 27" iMac display has the issue - the other monitor is perfect.

  8. Verxion thread starter macrumors member

    Dec 21, 2009
    In case anyone cares, I found a 9.12 hotfix driver release that fixed the problem.

    The driver shows up as version 8.641.1.0 with a date of 8-24-2009.

  9. Superhero360 macrumors newbie

    Jul 4, 2008
    Could you give us a direkt link?

  10. bamtan macrumors newbie

    May 16, 2009
    Having the same issue since updating to Bootcamp 3.1 It was fine before installing that - even with the regular Bootcamp 3.0 drivers. Strange.

    Do you have a link to the hotfix that cured the problem?

    Edit: I fixed the banding issue by downloading the Radeon HD 4800 Series installer, and using the 'Uninstall ATI Components' option. Windows then used its own driver, seemingly dating back to 23/9/09, version 8.661.0.0.

    This does have an issue with the iMac display in that the bottom half of the screen will sometimes switch with the top half, after altering the resolution (i.e. going into a game) - but to fix that I just tinker with the resolution till it's back to normal.
  11. Zathu macrumors regular


    Nov 16, 2006
    I've been battling with this problem for over a month. The 3.0 boot camp drivers don't have this issue, however can cause the split screen problem. Last month I updated the ATI drivers with Mobility Modder.NET and experienced this gradient problem, something very noticeable in skymaps in games. 3.1 seems to use a similar driver with the same problem..

    A faster workaround is to lock and unlock the screen (Windows-L)
  12. Zathu macrumors regular


    Nov 16, 2006
    I rolled back to ATI driver version 8.661.0.0 from 9/23/2009 and the problem instant went away.

    I *think* this was the driver included in the version of Boot Camp prior to 3.1.
  13. iDarbert macrumors regular

    Feb 12, 2008
    I think I finally managed to solve the issue for good.
    Driver version 8.661 kept crashing for me so the rollback was not an option, and 8.681 exhibited the gradient banding which is extremely annoying, so I took a while to try some drivers and I finally found a version that doesn't seem to have either issues.

    This webpage collects official ATI Mobility drivers from several manufacturers since ATI does not support mobility drivers by themselves, I found out that this driver package

    Works wonders on an iMac i5 with ATI Radeon HD 4850.
    The only problem is that these drivers lack of an installer, so they must be installed manually using Windows' "Update driver" feature, under Windows 7 the steps are

    1. Right click on the Desktop, select display resolution
    2. Click on the Advanced Settings lik near the display resolution dropdown menu
    3. Click on Properties button
    4. Select the driver tab
    5. Click on the Update Driver button
    6. Select the second option
    7. Select the option to manually select the driver
    8. Click on the Have Disk button
    9. Select the folder with the drivers you just downloaded and select one of the files you see
    10. Windows will automatically filter out the uncompatible drivers, leaving you with one option: ATI Mobility Radeon HD 4850 to select.

    After this is done the screen will go black for a while and come back, hopefully with no gradient banding issues.

    I hope this helps you guys out, it sure solved my problem for now
  14. scastlet macrumors newbie

    Mar 3, 2010

    When i download it it says that is is invalid. :(
  15. iDarbert macrumors regular

    Feb 12, 2008
    Yes, I get that a lot. It appears the zip file is actually a 7zip file so you'll either need 7zip or the latest version of WinRAR. the server is also known to halt the transfer prematurely giving you a corrupt file so I mirrored it on my DropBox ATI Drivers for (original file 26MBs) ATI Drivers for iMac (uncompressed and recompressed with OSX's archive utility, 70MBs)
  16. gutch macrumors newbie

    Mar 27, 2010
    I had the same banding problem, but because I don't trust drivers posted on unofficial websites I used the official AMD drivers instead of the ones on (not that there is necessarily anything wrong with, I just prefer to be careful).

    I found that version 8.661 of the AMD driver (Catalyst 9.10) returns the display to full colour, with no banding. All you have to change is one line that identifies your hardware. Here's what to do:

    NOTE: These instructions are for a 27" iMac with ATI Radeon HD 4850
    -- the line to paste in will be different if you have the ATI Radeon HD 4670 (which the 21.5" has and some 27" models have)

    1. Download the Catalyst 9.10 Display Driver from
    2. Run the installer (9-10_vista64_win7_64_dd.exe)
    3. On the first screen, click Install
    4. When that installer closes, and a new one opens saying 'Welcome', click Cancel, then Yes to exit
    5. Using Windows Explorer, browse to where the installer files are: C:\ATI\Support\9-10_vista64_win7_64_dd\Packages\Drivers\Display\W76A_INF
    6. Right-click on C7_83743.inf and choose Open
    7. Under the heading [ATI.Mfg.NTamd64.6.1] paste in the following line:
    "ATI Radeon HD 4850 " = ati2mtag_R7X, PCI\VEN_1002&DEV_944A&SUBSYS_00B5106B
    • Save your changes to the C7_83743.inf file
    • Now manually install that driver, similar to the instructions above.

    If you're unsure what I mean by manually installing, do this:
    • Right-click on the desktop, choose Display Resolution or Screen Resolution
    • Click Advanced Settings
    • Click Properties
    • Click Update Driver
    • Click Browse my computer for driver software
    • Click Let me pick from a list...
    • Click Have Disk...
    • Select your folder (C:\ATI\Support\9-10_vista64_win7_64_dd\Packages\Drivers\Display\W76A_INF)
    • There should be one item shown: ATI Radeon HD 4850
    • Select that and click Next
    • The screen should briefly go black and when it comes back you'll be in full colour! Click Finish or whatever Windows says here.
  17. Superhero360 macrumors newbie

    Jul 4, 2008
    Ok updated to Catalyst Radeon mobility 10.3 official drivers now. Still color banding. A fix for this anywhere?
  18. iDarbert macrumors regular

    Feb 12, 2008
    Version 8.661 it's the one bundled with Boot Camp 3.0 and cause crashes under some circumstances
  19. Creash macrumors newbie

    Apr 19, 2010
    Sorry to bring this topic up... but:

    The gradient issue on my imac 27 is very annoying (Just Cause 2's sky looks ugly :) ) so I followed the instructions above here. Except it didn't work (windows 7 says that my drivers are already updated). I decided to choose another option, the one where you can choose your drivers from a list. By mistake, I selected microsoft drivers and now I have a black screen. I guess it's the regular black screen/windows 7 problem.
    Do you think I should dç the black screen method used when you install the OS (macfuse + manual delete of the driver) to solve my problem?

    French here, I hope my english is not that bad.

    Enjoying a lot my new iMac i7!
  20. iDarbert macrumors regular

    Feb 12, 2008
    Yes, that's the best way to deal with it
  21. Creash macrumors newbie

    Apr 19, 2010
    My two problems are solved!

    The mistake I made was repaired by the Black screen/Windows 7 method (deleting a file a in windows' drivers folder).

    And the gradient issue on my iMac with 7 is over thanks to Windows Update.
  22. iDarbert macrumors regular

    Feb 12, 2008
    I would check the driver version, if what I think happened actually happened you will have sub-par 3D performance.
  23. 39 Cent Stamp macrumors newbie

    Jun 13, 2010

    Rolling back the drivers solved the gradient banding issues for me.

    This version works

    ATI Radeon HD 4850
  24. ChrisRS macrumors newbie

    Jul 2, 2010
    this is awsome !!!!!!! I had the gradient too and your solution worked perfectly !!!!! thanx a million
  25. aki macrumors 6502a

    Mar 2, 2004
    FYI I have a 27" iMac with the 4850 and the other day I downloaded and installed the latest Catalyst mobility package from the official website (10.6) under Windows 7 64 bit.

    Using the Catalyst configuration app I was able to change various settings including the colors to 32bit. Every thing seems peachy. Was gaming last night and all looked beautiful. Don't seem to be any banding effects or other problems.

    So I think the problems are solved touch wood? Seems to be for me anyway best I can tell.

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