Managing colours in Windows Vista

CMS in action
The discontinued ‘Color at Microsoft’ blog includes a JPEG file that has had its channels manipulated so that you can easily tell which, if any, CMS is employed in its display. The Ducati motorcycle appears blue if the embedded profile is ignored by the display application, green if the embedded ICC profile is honoured and red if the WCS profile iss honoured. The WCS profile is embedded in the ICC profile, enabling its use in non-WCS-aware applications.

If you download this file and preview it in Windows Photo Gallery, it should appear red. Adobe Photoshop Elements will display a green motorcycle using the embedded ICC profile.

And this brings us to Peter’s email. He’s been awaiting a fix for the so-called Vista gamma table bug. This affects those who are using monitor calibration and profiling devices such as Datacolor’s Spyder range to produce a custom profile for their display.

The calibration software saves the profile data along with gamma calibration curves. The profile data is then loaded on start-up and used to send the correct colour- and gamma-adjusted data via your graphics card to your profiled display.

The problem arises when Vista puts the display to sleep, you lock your PC by pressing the Windows key and L or an event occurs that requires authorisation using the User Account Control (UAC) manager.

These events dim the screen by adjusting the gamma look-up table used by your graphics card. When you wake up your display, unlock your PC or authorise the UAC message and the screen returns to normal, it should reload the original gamma LUT settings (provided by the profile) to your graphics card, but it doesn’t and hence your display is no longer accurate.

What can you do about it? You can disable UAC as well as avoid locking your PC or sending it to sleep, but that raises security issues and may still not prevent all the events that could trigger the problem. Rebooting will reload the profile and get everything back, but could become tedious.

A better fix comes in the form of a freeware utility called Displayprofile. This displays a list of all the installed profiles and allows you to switch between them. It even indicates with an asterisk the profiles that contain a gamma table. To switch display profiles, simply select a new one in the list. Switching from your default profile to an alternative and back again reloads the gamma look-up tables.

Microsoft has issued a fix for the Vista gamma table bug entitled ‘Custom gamma settings are lost on a Vista-based computer, on a Vista Service Pack One-based computer, or on a Windows Server 2008-based computer', but it seems to persist.

I couldn’t replicate the problem on 32-bit Vista Business or 64-bit Vista Ultimate. This, combined with people on forums reporting mixed results, suggests that the problem may be graphics hardware-specific.

The problem description specifies multiple display-based systems, which may explain why it has failed to resolve the issue for many Vista users with a single display. Either way, if you’re experiencing this problem the solution ­ installing the MS08-025 security update would seem a logical first step. Updating your display drivers to the most recent version also won’t do any harm.

Colour management resources
Discontinued ‘Color at Microsoft’ blog with WCS profile demo image

Colorwiki
Useful colour management articles including in-depth explanation of WCS

Neo Smart Files
Describes aspects of the gamma table bug

Microsoft Knowledgebase article and fix for the gamma table bug

Experimental implementation of the CIECAM02 colour appearance model in a Photoshop plug-in

Further information on Adobe’s Colour Management Module (CMM)

Home of the Spyder colour calibration tools

The International Color Consortium website