Powershell: Bilder verkleinern oder an bestimmte Größe anpassen

function Resize-Image{
    param(
        [parameter(mandatory=$true,ValueFromPipeline=$true,ValueFromPipelineByPropertyName=$true,ParameterSetName='A')][parameter(mandatory=$true,ValueFromPipeline=$true,ValueFromPipelineByPropertyName=$true,ParameterSetName='B')][alias("FullName")][string[]]$images,      
        [parameter(mandatory=$true,ValueFromPipeline=$true,ValueFromPipelineByPropertyName=$true,ParameterSetName='A')][parameter(mandatory=$true,ValueFromPipeline=$true,ValueFromPipelineByPropertyName=$true,ParameterSetName='B')][alias("DirectoryName")][string]$OutPath,      
        [parameter(mandatory=$true,ParameterSetName='A')][parameter(mandatory=$true,ParameterSetName='B')][int32]$NewWidth,      
        [parameter(mandatory=$true,ParameterSetName='A')][parameter(mandatory=$true,ParameterSetName='B')][int32]$NewHeight,      
        [parameter(mandatory=$false,ParameterSetName='A')][switch]$AppendSizeToFilename,      
        [parameter(mandatory=$true,ParameterSetName='B')][switch]$ReplaceOriginal,      
        [parameter(mandatory=$false)][switch]$DownSizeOnly,
        [parameter(mandatory=$false)][ValidateSet('Original','Scale')][string]$AspectRatio = 'Original',    
        [parameter(mandatory=$false)][switch]$RotateByExifOrientation,
        [parameter(mandatory=$false)][switch]$KeepOriginalDates
    )
    begin{
        Add-Type -AssemblyName System.Drawing
        if($rotatebyexiforientation.IsPresent){
            $shell = New-Object -com Shell.Application
        }
    }
    process{
        foreach($imagepath in $images){
            $finfo = Get-Item -LiteralPath $imagepath
            $newImagePath = ""    
            if ($finfo.Extension -match "\.(bmp|jpe?g|gif|tiff?|png)$"){      
                Try{
                    $img = [System.Drawing.Bitmap]::FromFile($imagepath)
                    $percentWidth = $newWidth / $img.Width
                    $percentHeight = $newHeight / $img.Height
                    if ($percentWidth -lt $percentHeight){$ratio = $percentWidth}else{$ratio = $percentHeight}
                    switch ($aspectratio){
                        'Original' {      
                            [int32]$nWidth = $img.Width * $ratio
                            [int32]$nHeight = $img.Height * $ratio
                        }
                        'Scale' {      
                            [int32]$nWidth = $newWidth
                            [int32]$nHeight = $newHeight
                        }
                    }
                    if ($replaceoriginal.IsPresent -and $ratio -ge 1){
                        continue
                    }
                    if($DownSizeOnly.IsPresent -and $ratio -ge 1){
                        if (!(Test-Path -LiteralPath (join-path $outPath $finfo.Name))){  
                            copy-item -LiteralPath $imagepath -Destination $outPath
                        }else{
                            Write-Warning "Image '$($finfo.Name)' already exists in destination directory, skipping image."    
                        }
                        continue
                    }
                    
                    $newImg = new-Object System.Drawing.Bitmap($nWidth,$nHeight)
                    ([System.Drawing.Graphics]::FromImage($newImg)).DrawImage($img,0,0,$newImg.Width,$newImg.Height)
                    
                    # respect exif orientation information if desired
                    if($rotatebyexiforientation.IsPresent){
                        # get rotation information (https:{{comment_single_line_double_slash:0}}
                        [int]$rotation = $shell.NameSpace($finfo.DirectoryName).ParseName($finfo.Name).ExtendedProperty("{14B81DA1-0135-4D31-96D9-6CBFC9671A99} 274")    
                        # rotate image when needed
                        switch -Regex ($rotation){
                            6 {$newImg.RotateFlip([System.Drawing.RotateFlipType]::Rotate90FlipNone);$oldw = $nWidth; $nWidth = $nHeight; $nHeight = $oldw}
                            8 {$newImg.RotateFlip([System.Drawing.RotateFlipType]::Rotate270FlipNone);$oldw = $nWidth; $nWidth = $nHeight; $nHeight = $oldw}
                            3 {$newImg.RotateFlip([System.Drawing.RotateFlipType]::Rotate180FlipNone)}
                        }
                    }

                    if ($replaceoriginal.IsPresent){
                        $newImagePath = Join-Path $outPath ([IO.Path]::GetRandomFileName())
                        while(Test-Path $newImagePath){
                            $newImagePath = Join-Path $outPath ([IO.Path]::GetRandomFileName())
                        }
                    }elseif($AppendSizeToFilename.IsPresent){
                        $newImagePath = join-path $outPath "$($finfo.Basename)_${nWidth}x${nHeight}$($finfo.Extension)"      
                    }else{
                        $newImagePath = join-path $outPath $finfo.Name
                    }
                   if(!(Test-Path $outPath)){new-item -ItemType Dir -Path $outPath -Force | out-null}

                    $newImg.Save($newImagePath,$img.RawFormat)
                    
                    if($KeepOriginalDates.IsPresent){
                        Get-Item -LiteralPath $newImagePath | %{
                            $_.CreationTime = $finfo.CreationTime
                            $_.LastWriteTime = $finfo.LastWriteTime
                        }
                    }
                    if ($replaceoriginal.IsPresent){
                        $img.Dispose()
                        Remove-Item -LiteralPath $imagepath -Force
                        Rename-Item -LiteralPath $newImagePath -NewName $finfo.Name
                    }
                }catch{
                    Write-Error -Message $_.Exception.Message
                }finally{
                    if ($img){$img.Dispose()}
                    if ($newImg){$newImg.Dispose()}
                }
            }else{
                Write-Error -Message "The image '$imagepath' uses an unsupported format. Only the following image types are supported: bmp|jpg|gif|tif|png"    
            }
        }
    }
    end{
        if ($img){$img.Dispose()}
        if ($newImg){$newImg.Dispose()}
        [System.GC]::Collect()
    }
}

Get-ChildItem -Path "D:\Bilder\*.jpg" -File | Resize-Image -OutPath "D:\Bilder\klein" -NewWidth 800 -NewHeight 600 -DownSizeOnly

Get-ChildItem -Path "D:\Bilder" -File -Filter *.jpg -recurse | Resize-Image -OutPath "D:\Bilder\klein" -NewWidth 800 -NewHeight 600 -DownSizeOnly -AppendSizeToFileName

Get-ChildItem -Path "D:\Bilder" -include "*.jpg","*.png" -recurse -file | Resize-Image -OutPath "D:\Bilder\klein" -NewWidth 800 -NewHeight 600 -AppendSizeToFileName

Resize-Image -images "D:\Bilder\testbild.jpg" -OutPath "D:\Bilder\klein" -NewWidth 320 -NewHeight 240

Get-ChildItem -Path "D:\Bilder" -include "*.jpg","*.png" -recurse -file | Resize-Image -NewWidth 320 -NewHeight 240 -ReplaceOriginal