screen4screen

Per-monitor wallpapers on Windows, chosen from each monitor's native resolution, re-applied automatically when you dock, undock or plug in an external display.

Built for the usual laptop setup: a 1920x1200 panel, a 5120x2160 ultrawide at the desk, the 1920x1080 projector in a meeting room. Each one gets an image that was actually made for its aspect ratio instead of a cropped or stretched compromise.

No dependencies. PowerShell and Windows 8 or later, nothing else to install.

The window speaks French, English, German and Italian, and follows Windows for both its language and its light or dark appearance.

How it works

1. Attached monitors are enumerated with EnumDisplayDevices and their native mode is read with EnumDisplaySettings(ENUM_CURRENT_SETTINGS). This yields real pixels, unaffected by DPI scaling (a 5120x2160 display at 150 % reports 5120x2160, not 3413x1440).
2. Each monitor is matched to its IDesktopWallpaper entry by device interface path.
3. An image is picked by naming convention (below) and applied per monitor through IDesktopWallpaper::SetWallpaper.
4. A hidden window listens for WM_DISPLAYCHANGE, so docking or undocking is picked up at once; a slow poll (-PollSeconds, default 15) is only a fallback for when that window cannot be created. Either way the change is followed by a short settle delay and then two passes, because Windows likes to restore its own cached wallpaper right after a topology change.

Image naming

Put your images in one folder (by default the wallpapers folder next to the script, which ships with three samples). For a given monitor the script tries, in order. Note that for each name a folder is tried before a file:

Priority	Name	Meaning
1	1920x1200\	folder: random image from it
2	1920x1200.jpg	exact resolution
3	ratio-8x5\	folder: random image from it
4	ratio-8x5.jpg	reduced aspect ratio
5	default\	folder: random image from it
6	default.jpg	fallback

Extensions: .jpg, .jpeg, .png, .bmp, .webp.

Pinning one image to one monitor

The table above keys off resolution, which cannot tell two identical panels apart. A monitor can instead be pinned to an explicit image, which wins over every row above. Those choices live in wallpapers.json at the root of your image folder, keyed on the monitor's device interface path:

Import-Module .\Screen4Screen\Screen4Screen.psd1
$d = @(Get-AttachedDisplay)[0]
Set-WallpaperAssignment -Root 'D:\Wallpapers' -DevicePath $d.DevicePath -Image 'D:\Wallpapers\left.webp' -Friendly $d.Friendly
Remove-WallpaperAssignment -Root 'D:\Wallpapers' -DevicePath $d.DevicePath   # back to automatic

Assignments for monitors that are currently unplugged are kept, not discarded, and reconnect silently when the monitor comes back.

Reduced ratios for common panels:

Resolution	Ratio name
1920x1200	ratio-8x5
1920x1080	ratio-16x9
2560x1440	ratio-16x9
3840x2160	ratio-16x9
3440x1440	ratio-43x18
5120x2160	ratio-64x27

The graphical manager

Double-click screen4screen.exe. It ships with the repository, so a clone works straight away.

It carries the program icon in Explorer and opens the window with no console at all. To rebuild it after changing build/Launcher.cs or the icon:

.\build\Build-Launcher.ps1

The compiler it uses ships with Windows, so nothing needs installing. screen4screen.cmd does the same job without the .exe, but shows a console window.

You can also run:

.\screen4screen.ps1 -Gui

One window: pick the image folder and the fit mode, see every attached monitor with the image it will get, pin a different image to any one of them, and turn the automatic behaviour on or off with a single switch. It refreshes itself when you dock or undock.

It opens on wallpapers the first time, and takes its language and its light or dark appearance from Windows. It speaks French, English, German and Italian; the button showing the current code in the top right switches between them, and remembers your choice. The sun/crescent button in the top right switches between the two and remembers your choice; the ? next to it explains exactly what the tool changes on your machine.

Turning the switch on registers the logon task through conhost --headless, so no console window flashes when it starts. Windows builds older than 22621 fall back to the plain host, where a brief flash remains.

The timing knobs (-PollSeconds, -SettleDelay) are deliberately not in the window; they stay on the command line.

Usage

Test first. This prints what is detected and applies once:

.\screen4screen.ps1 -Once -Verbose

Install as a background task that starts at logon:

.\screen4screen.ps1 -Install -WallpaperRoot 'D:\Wallpapers' -Position Fill
Start-ScheduledTask -TaskName screen4screen

Remove it:

.\screen4screen.ps1 -Uninstall

Parameters:

Parameter	Default	Notes
-WallpaperRoot	wallpapers next to the script	image folder
-Position	Fill	Center, Tile, Stretch, Fit, Fill, Span
-PollSeconds	15	fallback poll, used only when WM_DISPLAYCHANGE is unavailable
-SettleDelay	2	seconds to wait after a change before applying
-Gui		open the graphical manager
-Once		apply once and exit
-Install		register the logon task
-Uninstall		remove the logon task

Log file: %LOCALAPPDATA%\screen4screen\log.txt.

The module's state-changing functions support -WhatIf, so you can see what would be applied without touching anything:

Import-Module .\Screen4Screen\Screen4Screen.psd1
Set-WallpapersNow -Root .\wallpapers -PositionName Fill -WhatIf

Before you start

Disable Windows Spotlight and the wallpaper slideshow in Settings > Personalization > Background. Both will fight the script.

If powershell.exe refuses to run the script, the scheduled task already passes -ExecutionPolicy Bypass; for a manual run use:

powershell -ExecutionPolicy Bypass -File .\screen4screen.ps1 -Once

Known limitations

• Reaction is event-driven: a hidden window catches WM_DISPLAYCHANGE and the watcher wakes immediately, then waits SettleDelay for Windows to finish rearranging. PollSeconds (default 15) is only a fallback for the case where that window cannot be created.
• The -Position mode is global; Windows does not expose per-monitor fit.
• The logon task runs through conhost --headless, so nothing flashes at logon. Windows builds older than 22621 do not have it and fall back to the plain host, where a brief console flash remains.
• -ExecutionPolicy Bypass is a Process-scope setting, so it loses to an execution policy set by Group Policy. On a managed machine where that is in force the window will not start; it now says so rather than failing silently.

Roadmap

See CLAUDE.md for the working notes and the list of planned improvements.

License

MIT, see LICENSE.