I've used dual monitors for many years. I see absolutely no change when moving any image from one monitor to another in Photoshop 7.0.1 through 11 (CS4). Photoshop is smart enough to read the profile for each monitor on the fly.
HI> Although I'm new to the Mac platform, that has been my experience also.
Even when I place half of the image in one monitor and the other half in the other one, Photoshop uses the correct monitor for each respective half of the image.
HI> I agree, for CS3 and Lightroom that is how it works for me too.
My response to Ray's question ("Where does photoshop assign a primary monitor?") has absolutely nothing to do with monitor profiles, only with which monitor will be the primary monitor, i.e. the one that hosts the menu bar with the Apple menu.
That is what you can change in the Display Preferences > Arrangement (Mac System Preferences).
HI> Correct and I agree. But I believe Ray had that setup correctly to begin with, unless I did not understand him.
The one thing that did change in CS4 is that image files now will always open on the primary monitor. In previous versions of Photoshop, you could just move an image to the secondary monitor, close it, and it or the next image would open on your secondary monitor too. That is not possible in CS4, at least in the current version.
HI> My observation as well.
However, the monitor profile used on each monitor respectively remains the correct one as set in Display Preferences > Color.
Photoshop knows how to apply each monitor profile to each monitor, unless the user has messed that up in Display Preferences > Color.
HI> As stated, CS3 and Lightroom do apply colors correctly. CS4 does not.
In Edit > Color Settings, you should be set to the Adobe Color Engine (ACE), not to Color Sync.
HI> All my observations with CS4 have used ACE. I was getting frustrated and the ColorSync thing was an experiment to see if anything changed.
In my experience, the Apple CMM, Color Sync, has been unreliable for a long time. I just avoid it. (There are other legitimate uses for the ColorSync Utility, such as repairing profiles [Profile First Aid], visualizing and comparing their gamuts, etc.)
If both monitors are accurately calibrated and profiled, and if the appropriate monitor profiles are selected for each monitor separately in Display Preferences > Color, Photoshop will use them correctly on each monitor, in my experience.
HI> CS4 does not seem to work the same way. In fact, if you bring up the images in Bridge CS4 on my setup, the filmstrip version of the image will have the proper color profile (when I move it back and forth from one monitor to the other) and the selected preview image will not! I believe this is a bug in CS4! CS4 should apply the same color profile to each image in Bridge regardless of which monitor I move the window to.
Something is going wrong in Ray's setup, but there are not enough details to tell what. Screen shots of all the settings would be helpful.
HI> I'm not sure how your monitors are setup. Perhaps you have two monitors that are nearly the same and therefore your color profiles are close enough to not see the difference that Ray and I see. My monitors are setup correctly and I believe that Ray's are too.
Even the cheapest calibrator puck will produce a more accurate profile than can be achieved through Apple's built-in or any other eyeball calibrator like SuperCal.
HI> I use Graytag McBeth. However, even if I did not use any calibration, I should see the same results in the same window for Bridge CS4, regardless of how far the profiles were off! Comparing that with CS3 and Lightroom makes me believe that this is a software bug in CS4 not a setup issue.