31st December 2008

Using Dual Monitor Wallpapers on Windows XP & Vista

Dual monitors have been around for a long time, yet still Microsoft hasn't included support for a single wallpaper to span all monitors. You can however use dual-monitor wallpapers in Windows with a little bit of fiddling.

Tiled Wallpapers Are Cool Again

Provided you have your left-most monitor as the primary monitor for your system, then all is well, find your dual-monitor wallpaper, set it in display properties, but make sure the image is set to tiled. You can edit the image so that it better matches your combined resolution.

If your left-most monitor isn't your primary monitor, don't despair, there is another even more fiddly solution. Read on.

Combined Resolution

You can calculate your combined resolution by adding up the resolutions of each monitor's axis where they join. For example, if you have two monitors at 1280x1024 side by side, your combined resolution will be 2560x1024, if you have them vertical, then your combined resolution would be 1280x2048.

The Alpha Monitor

The problem with dual-monitor wallpapers and Windows gets even more messy when the primary display isn't at the left. To put this simply, Windows (when tiled) will always draw the desktop wallpaper starting at the top left of the primary monitor. It will then flow onto the secondary monitors from left to right. Once it reaches the end of the monitor row, it will then go back to the start: any secondary monitors before your primary monitor.

This sounds complicated, and when things get complicated, diagrams help. Here is an example setup:

Secondary display on the left, with a resolution of 1280x1024, primary display on the right, with a resolution of 1680x1050
The physical setup, the right monitor is the primary display.

Using an image similar to that above as the wallpaper shows the problem. As said, Windows will draw the wallpaper from the top left of the primary display, and then wrap around onto the secondary display causing the image to break up:

Image showing the wallpaper being broken as Windows wraps it
The wallpaper will break in these circumanstances, due to Windows wrapping it badly.

In order to get the image to display properly, you need to edit it so that it wraps correctly. The rest of this article will explain how to do just that.

Bodge the Wallpaper

Until Microsoft decide to support dual-monitor wallpapers properly, you have a few choices. They are:

  • bodge the image, as described below
  • accept the fact that dual-monitor wallpapers are broken in Windows, and stick to single monitor wallpapers, that probably still display wrong because of the different resolutions of your monitors

For this tutorial, I'll be using the wallpaper shown below, you can find the original here. When finding an image to use, try to make sure it's dimensions are at least equivalent to your combined resolution, or as close as you can find. This is one of those areas that is really good at confusing people, including myself, so I'll try keep this simple.

Image showing the wallpaper being broken as Windows wraps it
The original wallpaper before editing.

To follow this tutorial, you will need an image editing application that supports layers, such as Adobe Photoshop, the GIMP or Adobe (Macromedia) Fireworks. It is still possible to do this without layers, but they make it a lot simpler.

  1. Scale the image so that it covers your entire desktop area, see the combined resolution section above for working this out.
  2. Create a duplicate layer of the wallpaper
  3. Set the X position of the top layer equal to the resolution of the primary monitor, in this case 1680
  4. Set the X position of the bottom layer to minus the resolution of your secondary monitor, in this case -1280
  5. Crop any areas going outside of the image area

You should end up with an image that looks like that shown below, the diagram shows how the image fits together when drawn by Windows.

Image showing how the wrapped modified image displays correctly
Shows the final image, and how it displays correctly when Windows draws it.

It's as simple as that :-)

I will when I have time, write a small application to make this automated. But not today.

6th Jan 2009 - Update: As promised, you can download the Dual-Monitor Wallpaper Tweaker from here.