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I installed Windows 7 on Boot Camp on my new iMac 27'' (ATI videocard) and everything was good until recently I noticed that the default Windows 7 background (then one on the background on login) looked jerky.

When I say jerky I mean the kind of jerky you get if you can't display enough colours, and instead of nice fading shades you just get stripes and jerky patterns. I am on native resolution but even if I go down to 1920x1080 I get the same.

This might have happened after a firmware update but as I don't use Windows very often I am not too sure it's what caused it.

Oh, and when I am playing games everything looks OK (as in not jerky!).

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    i don't think jerky is the word you're looking for. do you mean something like this upload.wikimedia.org/wikipedia/commons/b/be/…
    – Jay Wick
    May 17, 2010 at 22:21
  • yes - not as bad but that's the idea - which word would u suggest?
    – JohnIdol
    May 17, 2010 at 22:39
  • When gradients get compression artifacts, they're said to be "banded". When a bitmap gets enlarged beyond its native resolution, it's said to be "jaggy". Are you seeing jaggies, or banding, or both?
    – Spiff
    May 18, 2010 at 3:20
  • I think I am seeing banding. I get that at very high resolutions the wallpapers could become banded because of the stretch - but I do not get why it was not happening before then but just recently.
    – JohnIdol
    May 18, 2010 at 16:35
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    You mentioned a firmware upgrade. What was this firmware an upgrade for, the Monitor or something else?
    – Daisetsu
    Jun 1, 2010 at 21:18

2 Answers 2

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Does this happen in windowed applications (i.e., opening a photo)? This is often a sign that your monitor is running at a low depth of color. Banding generally isn't noticeable with 24- or 32-bit color depth, though with 16-bit depth is might be noticeable depending on content, and 8-bit or less will be extremely noticeable with todays applications/themes/pictures.

You can check/set the color depth for windows by going to the control panel -> Display -> Screen Resolution, click "Advanced Settings" -> Monitor Tab. At the bottom there should be a dropdown labelled "Colors:". What is this set to? If it is not set to "True color (32-bit)", try changing it to that.

Fullscreen games probably won't show the banding because they set the color depth when they take over the screen.

If you do not have 32-bit color available (perhaps only 16-bit or less) in the dropdown, I'd look for an update to your graphics drivers (either from ATI or Apple/Bootcamp). If 32-bit color is available and already selected, and other applications show images fine (it's just the login background), I would check that the file hasn't been modified (It's at C:\Windows\Web\Wallpaper\Windows\img0.jpg for me) - Right-click -> Properties -> Details -> Image -> Bit Depth (Should be "24").

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  • that dropdown already says true color (32bit) :(
    – JohnIdol
    Jun 4, 2010 at 19:57
  • @JohnIdol do other images show the banding when you open them in an image viewer? Jun 4, 2010 at 20:10
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This is gone after recent MacOS/Windows 7 updates - not sure exactly which!

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