srcsetgenerator.ps1

Param ( [Parameter(Mandatory=$True)] [ValidateNotNull()] $imageSource, [Parameter(Mandatory=$true)][ValidateNotNull()] $quality )

if (!(Test-Path $imageSource)){throw( "Cannot find the source image")}
if ($quality -lt 0 -or $quality -gt 100){throw( "quality must be between 0 and 100.")}

[void][System.Reflection.Assembly]::LoadWithPartialName("System.Drawing")
$resolvedPath = Join-Path $PWD -ChildPath $imageSource
$bmp = [System.Drawing.Image]::FromFile($resolvedPath)

#hardcoded canvas size...
$canvasWidths = @(200, 400, 600, 800)

foreach($canvasWidth in $canvasWidths){
    #Encoder parameter for image quality
    $myEncoder = [System.Drawing.Imaging.Encoder]::Quality
    $encoderParams = New-Object System.Drawing.Imaging.EncoderParameters(1)
    $encoderParams.Param[0] = New-Object System.Drawing.Imaging.EncoderParameter($myEncoder, $quality)
    # get codec
    $myImageCodecInfo = [System.Drawing.Imaging.ImageCodecInfo]::GetImageEncoders()|where {$_.MimeType -eq 'image/jpeg'}

    #compute the final ratio to use
    $ratioX = $canvasWidth / $bmp.Width;
    $ratioY = $canvasWidth / $bmp.Height;
    $ratio = $ratioY
    if($ratioX -le $ratioY){
        $ratio = $ratioX
    }

    #create resized bitmap
    $newWidth = [int] ($bmp.Width*$ratio)
    $newHeight = [int] ($bmp.Height*$ratio)
    $bmpResized = New-Object System.Drawing.Bitmap($newWidth, $newHeight)
    $graph = [System.Drawing.Graphics]::FromImage($bmpResized)

    $graph.Clear([System.Drawing.Color]::White)
    $graph.DrawImage($bmp,0,0 , $newWidth, $newHeight)

    $targetFileName = [System.IO.Path]::GetFileNameWithoutExtension($imageSource) + "-" + $canvasWidth + ".jpg"
    $dir = [System.IO.Path]::GetDirectoryName($resolvedPath)
    $targetFilePath = Join-Path $dir -ChildPath $targetFileName
    Write-Host "Saving file" $targetFilePath
    #save to file
    $bmpResized.Save($targetFilePath,$myImageCodecInfo, $($encoderParams))
    $graph.Dispose()
    $bmpResized.Dispose()
}
$bmp.Dispose()