Downsamples PDFs with ghostscript.

optimize-pdf.ps1

<#
    Downsample PDF and convert to gray if necessary.
    Requires Ghostscript (gswin64c).
#>

param (
    [string]$indir,
    [string]$outdir = $indir,
    [string]$gs = "gswin64c",
    [string]$dpi = "150"
)

# verbatim marker forces powershell to pass anything afterwards as-is, preserving quotes etc.
$verbatim = '--%'

$files = Get-ChildItem $indir -filter *.pdf

$i = 0
foreach ($file in $files) {

    $i++
    $inputFile = "`"$($file.FullName)`""
    $newFile = [System.IO.Path]::Combine($outdir, $file.Name)

    write-progress -activity "Optimizing PDFs..." -status "Processing $i of $($files.Count)" -percentcomplete (($i / $files.Count) * 100) 

    # call ghostscript
    & $gs `
        -o "$newFile" `
        -sDEVICE=pdfwrite `
        -dCompressPages=true `
        -dCompressFonts=true `
        -dDownsampleColorImages=true `
        -dDownsampleGrayImages=true	`
        -dDownsampleMonoImages=true	`
        -dColorImageResolution="$dpi" `
        -dGrayImageResolution="$dpi" `
        -dMonoImageResolution="$dpi" `
        -dColorImageDownsampleThreshold="1.0" `
        -dGrayImageDownsampleThreshold="1.0" `
        -dMonoImageDownsampleThreshold="1.0" `
        -dProcessColorModel=/DeviceGray `
        -dColorConversionStrategy=/Gray `
        -dCompatibilityLevel="1.7" `
        -dEmbedAllFonts=false `
        -c ".setpdfwrite <</AlwaysEmbed [ ] /NeverEmbed [/Courier /Courier-Bold /Courier-Oblique /Courier-BoldOblique /Helvetica /Helvetica-Bold /Helvetica-Oblique /Helvetica-BoldOblique /Times-Roman /Times-Bold /Times-Italic /Times-BoldItalic /Symbol /ZapfDingbats] /ColorImageFilter /DCTEncode /GrayImageFilter /DCTEncode /MonoImageFilter /CCITTFaxEncode /OutputICCProfile (None)>> setdistillerparams"	`
        -f `
        $verbatim $inputFile
}

write-host "Done optimizing PDFs." -ForegroundColor Green