PowerShell script to generate multi-size, multi-format thumbnails with exact dimensions. Supports cropping, aspect ratio control, format selection (JPG, PNG, WebP), and custom filename suffixes.

README-multi-thumbnail-generator.md

Multi-Thumbnail Generator (PowerShell + FFmpeg)

This PowerShell script generates WordPress-style image thumbnails at multiple sizes and formats with cropping and aspect ratio control. It uses FFmpeg for scaling, cropping, and encoding images into JPG, PNG, or WebP formats.

Features

• ✅ Generate thumbnails at any number of target widths
• ✅ Supports output in jpg, png, and webp formats
• ✅ Optional forced aspect ratio override (e.g., 16:9, 1:1)
• ✅ Precise cropping to produce exact WIDTH x HEIGHT dimensions
• ✅ Optional filename suffix (e.g., thumb-33 → image-thumb-33-300x169.jpg)
• ✅ Automatically cleans up previous thumbnails before generation
• ✅ Clean FFmpeg integration with format-specific quality settings

Usage

1. Requirements:

   • PowerShell (v5 or higher)
   • FFmpeg installed and added to your system PATH
   • FFprobe (comes with FFmpeg)

2. Place the script in the folder containing your image files.

3. Customize the configuration at the top of the script:

   $targetWidths     = @(820, 435, 300)
   $outputFormats    = @("jpg", "png", "webp")
   $forceAspectRatio = "16:9"     # Or $null for original aspect ratio
   $nameSuffix       = "thumb-33" # Optional: add between base name and size

multi-thumbnail-generator.ps1

# -------------------------------------------------------------------
# WordPress-Style Thumbnail Generator with Cropping (PowerShell + FFmpeg)
# -------------------------------------------------------------------

# === Configuration ===
$targetWidths     = @(820, 435, 300)
$outputFormats    = @("jpg") # @("jpg", "png", "webp") Supported formats
$forceAspectRatio = "1:1" # e.g., "16:9", "1:1", or $null
$nameSuffix       = "" # Optional suffix before WxH, e.g. "md-down"; set to "" to disable

# Format-specific quality settings
$jpgQuality     = 2     # JPEG: 2 = high quality (1 best, 31 worst)
$pngCompression = 3     # PNG: 0 = no compression, 9 = max compression
$webpQuality    = 95    # WebP: 0 (worst) – 100 (best)
# ======================

# === Cleanup: Delete all thumbnails like *-WIDTHxHEIGHT.anyExtension ===
$thumbPattern = "-\d+x\d+\.\w+$"

Get-ChildItem -File | Where-Object { $_.Name -match $thumbPattern } | ForEach-Object {
    try {
        Remove-Item -Path $_.FullName -Force -ErrorAction Stop
        Write-Output "🗑️ Deleted old thumbnail: $($_.Name)"
    } catch {
        Write-Output "⚠️ Could not delete: $($_.Name)"
    }
}

# === Thumbnail Generation ===
Get-ChildItem -File | Where-Object { $_.Extension -match "\.(jpg|png|webp)$" } | ForEach-Object {
    $originalPath = $_.FullName
    $filename     = $_.Name
    $cleanName    = $_.BaseName

    try {
        # Get original dimensions using ffprobe
        $width  = ffprobe -v error -select_streams v:0 -show_entries stream=width -of csv=p=0 "`"$originalPath`""
        $height = ffprobe -v error -select_streams v:0 -show_entries stream=height -of csv=p=0 "`"$originalPath`""
        $width  = [int]$width
        $height = [int]$height

        if ($width -eq 0 -or $height -eq 0) {
            Write-Output "⚠️ Skipping $filename (invalid dimensions)"
            return
        }
    } catch {
        Write-Output "❌ Failed to probe $filename. Skipping."
        return
    }

    $OAR = $width / $height  # Original Aspect Ratio

    foreach ($targetWidth in $targetWidths) {
        # === Determine target height ===
        if ($forceAspectRatio) {
            $parts = $forceAspectRatio -split ":"
            $faWidth = [int]$parts[0]
            $faHeight = [int]$parts[1]
            $targetHeight = [math]::Round($targetWidth * ($faHeight / $faWidth))
            $TAR = $faWidth / $faHeight
            Write-Output "📐 Using forced aspect ratio $forceAspectRatio → ${targetWidth}x${targetHeight}"
        } else {
            $targetHeight = [math]::Round($targetWidth / $OAR)
            $TAR = $targetWidth / $targetHeight
        }

        # === Cropping logic for consistent WxH thumbnails ===
        if ([math]::Round($OAR, 3) -eq [math]::Round($TAR, 3)) {
            $vfFilter = "scale=${targetWidth}:${targetHeight},setsar=1"
        }
        elseif ($OAR -gt $TAR) {
            $vfFilter = "scale=-2:${targetHeight},crop=${targetWidth}:${targetHeight}:(iw-${targetWidth})/2:0,setsar=1"
        }
        else {
            $vfFilter = "scale=${targetWidth}:-2,crop=${targetWidth}:${targetHeight}:0:(ih-${targetHeight})/2,setsar=1"
        }

        foreach ($fmt in $outputFormats) {
            # === Construct output filename with optional suffix ===
            if ($nameSuffix -ne "") {
                $outputName = "${cleanName}-${nameSuffix}-${targetWidth}x${targetHeight}.${fmt}"
            } else {
                $outputName = "${cleanName}-${targetWidth}x${targetHeight}.${fmt}"
            }

            switch ($fmt.ToLower()) {
                "jpg" {
                    $cmd = "ffmpeg -i `"$originalPath`" -vf `"$vfFilter`" -q:v $jpgQuality `"$outputName`" -y"
                }
                "png" {
                    $cmd = "ffmpeg -i `"$originalPath`" -vf `"$vfFilter`" -compression_level $pngCompression `"$outputName`" -y"
                }
                "webp" {
                    $cmd = "ffmpeg -i `"$originalPath`" -vf `"$vfFilter`" -q:v $webpQuality `"$outputName`" -y"
                }
                default {
                    Write-Output "❌ Unsupported format: $fmt — skipping."
                    continue
                }
            }

            try {
                Invoke-Expression $cmd
                Write-Output "✅ $filename → $outputName"
            } catch {
                Write-Output "❌ Error generating ${outputName}: $_"
            }
        }
    }
}

Write-Output "`n✅ Thumbnail generation complete."