My-PowerShell

[reflection.assembly]::LoadWithPartialName("System.Drawing")
$toresize = "..\images"
$SizeLimit=1024          # required size of picture's long side
$logfile="resizelog.txt" # log file for errors
 
Get-ChildItem -recurse $toresize -include *.jpg  | foreach {
$parent = $_.Directory.name
$backupdir = ".\backup\" + $parent + "\"
If (-not (Test-Path $backupdir)) { New-Item -ItemType Directory -Name $backupdir }
$backup = $backupdir + "\" + $_.Name
Copy-Item -Path $_.fullname -Destination $backup
 
  $OldBitmap = new-object System.Drawing.Bitmap $_.FullName # open found jpg
  if ($error.count -ne 0) {                                 # error handling
    $error | out-file $logfile -append -encoding default
    $error[($error.count-1)].TargetObject | out-file $logfile -append -encoding default
    echo $_>>$logfile
    $error.clear()
  }
  $LongSide=$OldBitmap.Width                                # locating long side of picture
  if ($OldBitmap.Width -lt $OldBitmap.Height) { $LongSide=$OldBitmap.Height }
  if ($LongSide -gt $SizeLimit) {                           # if long side is greater than our limit, process jpg
    if ($OldBitmap.Width -lt $OldBitmap.Height) {           # calculate dimensions of picture resize to
      $newH=$SizeLimit
      $newW=[int]($OldBitmap.Width*$SizeLimit/$OldBitmap.Height)
    } else {
      $newW=$SizeLimit
      $newH=[int]($OldBitmap.Height*$newW/$OldBitmap.Width)
    }
    $NewBitmap = new-object System.Drawing.Bitmap $newW,$newH # create new bitmap
    $g=[System.Drawing.Graphics]::FromImage($NewBitmap)
    $g.InterpolationMode = [System.Drawing.Drawing2D.InterpolationMode]::HighQualityBicubic # use high quality resize algorythm
    $g.DrawImage($OldBitmap, 0, 0, $newW, $newH)              # resize our picture
 
    $name=$_.DirectoryName+"\"+$_.name+".new"                 # generating name for new picture
    $NewBitmap.Save($name, ([system.drawing.imaging.imageformat]::jpeg)) # save newly created resized jpg
    $NewBitmap.Dispose()                                      # cleaning up our mess
    $OldBitmap.Dispose()
    $n=get-childitem $name
    if ($n.length -ge $_.length) {                            # if resized jpg has greater size than original
      Write-host -NoNewLine "+"                               # draw "+"
      $n.delete()                                             # and delete it
    } else {                                                  # if resized jpg is smaller than original
      if ($n.Exists -and $_.Exists) {
        $name=$_.FullName
        $_.Delete()                                           # delete original
        $n.MoveTo($name)                                      # rename new file to original name (replace old file with new)
        echo ($Name + " " + $LongSide)                        # write its name for visual control
      }
    }
 
  } else {                                                    # if long side is smaller than limit, draw dot for visual
    Write-host -NoNewLine "."
    $OldBitmap.Dispose()
  }
}