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| Calibrating Dual Or Multiple Monitors |
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Last Updated
28th of November, 2011
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Before reading this article, you might want to refresh your knowledge on How Monitor Profiles Work.
Also please note that because this is very hardware specific and differs with each and every set up, we can offer no further support in this area beyond this article - you will need to do your own research and testing (see notes below) to determine if you can achieve successful multi monitor calibration on your system.
General Notes on Multi Monitor Calibration - Mac
In general, on a Mac, this just works, as Mac video cards must support separate LUTs for each video output to be allowed to work with the Mac system. Just drag your profiling app to each screen in turn, perform the calibration, and you should be done.
General Notes on Multi Monitor Calibration - PC
On PCs, the key issue is to be aware of how many LUTs (Look Up Tables) your video card has, and to check that you can address each LUT individually. Unfortunately this information can be hard to find - we suggest contacting the maker of your video card directly to ask this question as typically computer stores/review etc, usually won't have a clue about this.
The normal situation is - with fairly current video cards, and Windows 7 - dual monitor calibration usually works out of the box. It's pretty unusual to come across hardware without dual LUTs these days.
The easiest way to achieve multiple monitor calibration with older hardware/OSes is to attach each monitor to a separate video card. Each card will have a separate LUT (almost all video cards do) and thus it will be easy to associate a separate profile with each monitor.
If you have a dual headed video card, this situation is a LOT more complicated. First, the card must offer separately addressable LUTs for each output and oddly many newer video cards do not offer this, while many older dual headed cards do. Some claim not to but actually do (but you often have to use separate tools to actually use the LUTs), while others claim to have multiple LUTs but they are not seen as such by the operating system and can't be accessed. Some recent driver updates for popular cards have indeed *disabled* the second LUTs and so older drivers are required to get this working (which can have other negative side effects).
It's worth asking yourself if the effort is really worth it - very often it is easy to use the second screen as just a browsing and palettes monitor, so colour management is not really required on the second screen (you can of course still manually adjust it as best you can to match your primary screen, although we recommend you keep the brightness on your secondary screen significantly lower than your primary screen in this scenario to make sure you eye will white balance using the white point of the primary display).
The situation under various Windows versions is at present quite confused.
Under Windows XP you can use this handy applet from Microsoft to load separate profiles into video cards that offer separate LUTs. You must install it in your start-up folder and use the /L switch to use it as a LUT loader.
In Vista and Windows 7 you must use the inbuilt Colour Control Panel to manage profiles under Vista, and generally this will let you associate separate profiles for separate devices but on Vista won't actually load the LUTs properly when the machine is booted. You can use the tools below to help with this and manually 'poke' profiles into LUTs. Windows 7 has a built in LUT loader that works with dual monitors.
PC Tools For Explicitly Checking Your Monitor LUTs
X-Rite offer a handy and free tools that can be useful to determine what is actually going on with your multi monitor set up, and in pricnciple would be able to tell you whether you can individually load LUT tables for each of your displays separately.
Basic LUT Tester (test if your video card has a LUT at all)
LUT Tester and Poker Tool (test and manually change the LUTs for video cards, supports multiple displays)
In theory the above tools should help you to test and/or achieve a working multiple calibrated monitor scenario, however sometimes these tolls will seem to imply you do have access to two LUTs yet in practice the process will still fail!
Ok I have two separate LUTs - now what?In principle this means the process should work, but in practice it may still fail as even if you have two separate calibrations stored in two separate LUTs, AND you can associate two separate colour profiles for your screens in the Colour control panel applet, the reality is it usually still doesn't work. Under Windows XP, it often does work, but under Vista there are usually still problems with the operating system failing to return the correct profile for the second screen when you, say, drag an image from one screen to the other.
Under Vista, the only reliable solution is to use two separate video cards. Under XP it can sometimes me made to work but in our experience it isn't reliable and often times it will work until you go and re-calibrate and then it will get all confused again, requiring manual intervention. In the end, we recommend two video cards as the only really viable long term solution to the problem under Windows.
Under Windows 7, dual monitor calibration generally works well using either the built in LUT loader (it's automatic if the profile associated with a device has LUT information in it), or you can use the LUT loaders that come with the various calibration packages - this is usually the better option as they tend to have checking systems to make sure nothing else tries to manipulate the LUT.
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