[PowerShell] Dynamic Light Mode Background (via Bing Wallpaper, no app required)

[mikejhill]

Native Version (Updated 2025/05/25)

The Bing Wallpaper app is no longer necessary. The recipe below downloads the current Bing Wallpaper image directly from Bing when switching to light theme or uses a static image when switching to dark theme. This also works much more seamlessly by avoiding sporadic race conditions with the Bing Wallpaper app, at the cost of not receiving automatic updates if Bing's API changes.

See comment revision prior to 2025/05/25 if you want a version which requires the Bing Wallpaper app instead of relying on the Bing Wallpaper API.

Purpose:

• Use Bing Wallpaper backgrounds in "light" mode (without needing the Bing Wallpaper app) while selecting an alternative wallpaper for "dark" mode.

Conditions:

• Internet connectivity.

Tested with:

• Windows 11
• Auto Dark Mode X 10.4.1.1
• PowerShell 5.1.26100.4061
• PowerShell 7.5.1
• Bing Wallpaper API (undocumented) (as of 2025/05/25)

scripts.yaml (update argument paths to match your environment and dark mode image):

Enabled: true
Component:
  Scripts:
  - Name: Wallpaper Management
    Command: powershell
    ArgsLight:
      - "-File"
      - "AutoDarkModeSetWallpaperBing.ps1"
    ArgsDark:
      - "-File"
      - "AutoDarkModeSetWallpaper.ps1"
      - "-ImagePath"
      - "C:\\Users\\MyUser\\Pictures\\Backgrounds\\starry_sky.png"
    AllowedSources: [Any]

AutoDarkModeSetWallpaperBing.ps1:

# Fetch Bing image metadata
$bingApi = "https://www.bing.com/HPImageArchive.aspx?format=js&idx=0&n=1&mkt=en-US"
$bingData = Invoke-RestMethod -Uri $bingApi
$baseUrl = "https://www.bing.com"

# Attempt resolution fallbacks
$urlBase = $bingData.images[0].urlbase
$resolutions = @("_UHD", "_1920x1200", "_1920x1080", "_1024x768", "_1280x720", "_1366x768")
$imgUrl = $null

foreach ($res in $resolutions) {
    $candidateUrl = "$baseUrl$urlBase$res.jpg"
    try {
        Invoke-WebRequest -Uri $candidateUrl -Method Head -TimeoutSec 5 -ErrorAction Stop | Out-Null
        $imgUrl = $candidateUrl
        break
    } catch {
        continue
    }
}

if (-not $imgUrl) {
    Write-Error "Failed to find an available wallpaper resolution."
    exit 1
}

# Extract image ID from URL query string
$uri = [System.Uri]::new($imgUrl)
$queryParams = [System.Web.HttpUtility]::ParseQueryString($uri.Query)
$imgId = $queryParams["id"]

# Format image file name with current date
$today = Get-Date -Format yyyyMMdd
$imgName = "${today}_$imgId"
$imgFile = "$env:TEMP\$imgName"

# Download image
Invoke-WebRequest -Uri $imgUrl -OutFile $imgFile
Write-Output "Downloaded wallpaper from $imgUrl to $imgFile."

# Set wallpaper
. "$PSScriptRoot\WallpaperFunctions.ps1"
Set-Wallpaper $imgFile

AutoDarkModeSetWallpaper.ps1:

param (
    [string]$ImagePath
)

if (-not $ImagePath) {
    Write-Error "An image path is required."
    exit 1
}

# Set wallpaper
. "$PSScriptRoot\WallpaperFunctions.ps1"
Set-Wallpaper $ImagePath

WallpaperFunctions.ps1:

function Set-Wallpaper {
    param (
        [Parameter(Mandatory=$true)]
        [string]$ImagePath,

        [ValidateSet("Fill", "Fit", "Stretch", "Tile", "Center", "Span")]
        [string]$Style = "Fill",

        [string]$MonitorID = $null  # Optional: target a specific monitor
    )

    # Validate path
    if (-not (Test-Path $ImagePath)) {
        throw "Image path '$ImagePath' does not exist."
    }

    # Map style to registry settings
    $styleSettings = @{
        "Fill"    = @{ WallpaperStyle = "10"; TileWallpaper = "0" }
        "Fit"     = @{ WallpaperStyle = "6";  TileWallpaper = "0" }
        "Stretch" = @{ WallpaperStyle = "2";  TileWallpaper = "0" }
        "Tile"    = @{ WallpaperStyle = "0";  TileWallpaper = "1" }
        "Center"  = @{ WallpaperStyle = "0";  TileWallpaper = "0" }
        "Span"    = @{ WallpaperStyle = "22"; TileWallpaper = "0" }
    }

    $settings = $styleSettings[$Style]

    # Standard wallpaper settings (global)
    if (-not $MonitorID) {
        Set-ItemProperty -Path "HKCU:\Control Panel\Desktop" -Name WallpaperStyle -Value $settings.WallpaperStyle
        Set-ItemProperty -Path "HKCU:\Control Panel\Desktop" -Name TileWallpaper    -Value $settings.TileWallpaper

        # Add type if needed
        if (-not ("Wallpaper" -as [type])) {
            Add-Type @"
            using System.Runtime.InteropServices;
            public class Wallpaper {
                [DllImport("user32.dll", SetLastError = true)]
                public static extern bool SystemParametersInfo(int uAction, int uParam, string lpvParam, int fuWinIni);
            }
"@
        }

        # Set the wallpaper globally
        $SPI_SETDESKWALLPAPER = 0x0014
        $SPIF_UPDATEINIFILE = 0x01
        $SPIF_SENDWININICHANGE = 0x02

        [Wallpaper]::SystemParametersInfo($SPI_SETDESKWALLPAPER, 0, $ImagePath, $SPIF_UPDATEINIFILE -bor $SPIF_SENDWININICHANGE) | Out-Null
    }
    else {
        # Per-monitor wallpaper configuration
        # This modifies the TranscodedImageCache / TranscodedImageCount / Registry blobs

        $regPath = "HKCU:\Control Panel\Desktop"
        $subkey = "HKCU:\Control Panel\Desktop\PerMonitorSettings\$MonitorID"

        if (-not (Test-Path $subkey)) {
            throw "MonitorID '$MonitorID' not found. Make sure the ID is correct (you can inspect the registry under 'PerMonitorSettings')."
        }

        # Per monitor wallpaper: Windows needs a wallpaper file per monitor
        # Best behavior is to copy the wallpaper to the expected location.
        $destPath = "$env:USERPROFILE\AppData\Roaming\Microsoft\Windows\Themes\CachedFiles\$((Get-Random).ToString('X')).jpg"
        Copy-Item $ImagePath $destPath -Force

        # Set per-monitor wallpaper registry
        Set-ItemProperty -Path $subkey -Name "WallpaperPath" -Value $destPath

        # Also update wallpaper style globally (affects scaling)
        Set-ItemProperty -Path $regPath -Name WallpaperStyle -Value $settings.WallpaperStyle
        Set-ItemProperty -Path $regPath -Name TileWallpaper    -Value $settings.TileWallpaper

        # Refresh desktop
        rundll32.exe user32.dll,UpdatePerUserSystemParameters
    }
}