I like to use my photos as desktop images and I expect that the way I see them full screen in Aperture is the way I see them on my desktop. This is however not the case. The picture are on the desktop much darker. I have a custom profile for my screen created using Supercal. I switched the proofing profile to these Supercal settings and switched proofing profile off alltogether, but Aperture and the Desktop remain wide apart.
I beleive that the picture placed on your desktop is the jpeg preview generated by Aperture and not the master file. Is it possible that you haven't update the image preview after you made your adjustments?
try updating the image preview in Aperture, then switch your desktop image to any other image and than come back to your image (just to have it refreshed). this should do it.
Refreshing the previews did not work unfortunately, but I feel there is some logic in both of your suggestions, for which I want to thank you by the way. Probably the desktop image is not the original RAW picture and that is one way or the other the reason that the desktop looks different. Nevertheless I find it strange and I'm not happy with it.
Oh yes, I did not quite follow the 'hardware callibration'. Is there a difference?
This is very odd, but the reason for this problem seems to be a Kensington 7 in 1 card reader. Don't ask me how this is possible, but removing it from the slot solved the issue.