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I installed Ubuntu 12.10 on my Mac Mini Server 2012 (6,2 I think). I have a Dell U2412M (1920x1200@60Hz) connected via a Thunderbolt-Displayport cable.

From the moment rEFIt hands over to GRUB, the graphics look quite poor. Gradients are rough or dithered (including the boot splash, greeter screen and desktop background), window title bars look awful, and there a number of other ugly artefacts. The resolution itself, however, is fine.

The kernel is 3.5.0-19-generic. lspci tells me I have:

00:02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09)

I can't see any errors in Xorg.0.log, but I don't want to paste the whole file here.

sudo lshw -C display gives:

       description: VGA compatible controller
       product: 3rd Gen Core processor Graphics Controller
       vendor: Intel Corporation
       physical id: 2
       bus info: pci@0000:00:02.0
       version: 09
       width: 64 bits
       clock: 33MHz
       capabilities: msi pm vga_controller bus_master cap_list rom
       configuration: driver=i915 latency=0
       resources: irq:49 memory:a0000000-a03fffff memory:90000000-9fffffff ioport:2000(size=64)

OpenGL info from glxinfo is:

OpenGL vendor string: Intel Open Source Technology Center
OpenGL renderer string: Mesa DRI Intel(R) Ivybridge Mobile 
OpenGL version string: 3.0 Mesa 9.0.1

lsmod shows that the i915 driver is loaded.

Taking a screenshot does not demonstrate the problem (it looks fine when it's opened on another OS). Windows 7 and OSX look just fine on the same monitor using the Displayport input, and Ubuntu looks fine using the HDMI output via a HDMI-DVI converter.

So how do I get the colors to look right?

share|improve this question
This is a tricky one. It's not a software problem if screenshots look Ok. It has to be a driver bug, so not something you can easily fix. – Alistair Buxton Nov 29 '12 at 2:45
@AlistairBuxton - "Driver problem" is my main theory, yeah. I've been playing around with the ubuntu-x-swat team PPA (which has a DKMS i915 driver), and the 3.6-rc7 kernel, but no luck so far. – detly Nov 29 '12 at 3:18
I think your best bet is to report it as a bug on under the intel driver. Taking a photo of the screen will probably help diagnose, and of course include everything you've posted here. This should "just work" so even if you find a workaround it still needs fixing. – Alistair Buxton Nov 30 '12 at 19:47
Something that just occured to me: have you checked the colour settings on your monitor? I have the U2410 and it has colour settings per input, ie the HDMI can be configured separately from the display port connector (no thunderbolt on this model though.) It also has a large number of settings including basic brightness/contrast, colour temp, and independent gain control for each channel. Apparent low colour depth could be caused by having the brightness too low and the contrast too high, or maybe the other settings are just messed up. – Alistair Buxton Nov 30 '12 at 19:49
@AlistairBuxton - I did check the colour settings, and alas they're not the culprit. The funny thing is, if I look closely at the HDMI/DVI output, it also shows some dithering/color banding. Anyway, filing a bug is probably the best approach. – detly Dec 1 '12 at 3:44

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