PowerShell: Resize-Image

<#
.SYNOPSIS
   Resize an image
.DESCRIPTION
   Resize an image based on a new given height or width or a single dimension and a maintain ratio flag. 
   The execution of this CmdLet creates a new file named "OriginalName_resized" and maintains the original
   file extension
.PARAMETER Width
   The new width of the image. Can be given alone with the MaintainRatio flag
.PARAMETER Height
   The new height of the image. Can be given alone with the MaintainRatio flag
.PARAMETER ImagePath
   The path to the image being resized
.PARAMETER MaintainRatio
   Maintain the ratio of the image by setting either width or height. Setting both width and height and also this parameter
   results in an error
.PARAMETER Percentage
   Resize the image *to* the size given in this parameter. It's imperative to know that this does not resize by the percentage but to the percentage of
   the image.
.PARAMETER SmoothingMode
   Sets the smoothing mode. Default is HighQuality.
.PARAMETER InterpolationMode
   Sets the interpolation mode. Default is HighQualityBicubic.
.PARAMETER PixelOffsetMode
   Sets the pixel offset mode. Default is HighQuality.
.EXAMPLE
   Resize-Image -Height 45 -Width 45 -ImagePath "Path/to/image.jpg"
.EXAMPLE
   Resize-Image -Height 45 -MaintainRatio -ImagePath "Path/to/image.jpg"
.EXAMPLE
   #Resize to 50% of the given image
   Resize-Image -Percentage 50 -ImagePath "Path/to/image.jpg"
.NOTES
   Written By: 
   Christopher Walker
#>
Function Resize-Image() {
    [CmdLetBinding(
        SupportsShouldProcess=$true, 
        PositionalBinding=$false,
        ConfirmImpact="Medium",
        DefaultParameterSetName="Absolute"
    )]
    Param (
        [Parameter(Mandatory=$True)]
        [ValidateScript({
            $_ | ForEach-Object {
                Test-Path $_
            }
        })][String[]]$ImagePath,
        [Parameter(Mandatory=$False)][Switch]$MaintainRatio,
        [Parameter(Mandatory=$False, ParameterSetName="Absolute")][Int]$Height,
        [Parameter(Mandatory=$False, ParameterSetName="Absolute")][Int]$Width,
        [Parameter(Mandatory=$False, ParameterSetName="Percent")][Double]$Percentage,
        [Parameter(Mandatory=$False)][System.Drawing.Drawing2D.SmoothingMode]$SmoothingMode = "HighQuality",
        [Parameter(Mandatory=$False)][System.Drawing.Drawing2D.InterpolationMode]$InterpolationMode = "HighQualityBicubic",
        [Parameter(Mandatory=$False)][System.Drawing.Drawing2D.PixelOffsetMode]$PixelOffsetMode = "HighQuality",
        [Parameter(Mandatory=$False)][String]$NameModifier = "resized"
    )
    Begin {
        If ($Width -and $Height -and $MaintainRatio) {
            Throw "Absolute Width and Height cannot be given with the MaintainRatio parameter."
        }
 
        If (($Width -xor $Height) -and (-not $MaintainRatio)) {
            Throw "MaintainRatio must be set with incomplete size parameters (Missing height or width without MaintainRatio)"
        }
 
        If ($Percentage -and $MaintainRatio) {
            Write-Warning "The MaintainRatio flag while using the Percentage parameter does nothing"
        }
    }
    Process {
        ForEach ($Image in $ImagePath) {
            $Path = (Resolve-Path $Image).Path
            $Dot = $Path.LastIndexOf(".")

            #Add name modifier (OriginalName_{$NameModifier}.jpg)
            $OutputPath = $Path.Substring(0,$Dot) + "_" + $NameModifier + $Path.Substring($Dot,$Path.Length - $Dot)
            
            $OldImage = New-Object -TypeName System.Drawing.Bitmap -ArgumentList $Path
            # Grab these for use in calculations below. 
            $OldHeight = $OldImage.Height
            $OldWidth = $OldImage.Width
 
            If ($MaintainRatio) {
                $OldHeight = $OldImage.Height
                $OldWidth = $OldImage.Width
                If ($Height) {
                    $Width = $OldWidth / $OldHeight * $Height
                }
                If ($Width) {
                    $Height = $OldHeight / $OldWidth * $Width
                }
            }
 
            If ($Percentage) {
                $Product = ($Percentage / 100)
                $Height = $OldHeight * $Product
                $Width = $OldWidth * $Product
            }

            $Bitmap = New-Object -TypeName System.Drawing.Bitmap -ArgumentList $Width, $Height
            $NewImage = [System.Drawing.Graphics]::FromImage($Bitmap)
             
            #Retrieving the best quality possible
            $NewImage.SmoothingMode = $SmoothingMode
            $NewImage.InterpolationMode = $InterpolationMode
            $NewImage.PixelOffsetMode = $PixelOffsetMode
            $NewImage.DrawImage($OldImage, $(New-Object -TypeName System.Drawing.Rectangle -ArgumentList 0, 0, $Width, $Height))

            If ($PSCmdlet.ShouldProcess("Resized image based on $Path", "save to $OutputPath")) {
                $Bitmap.Save($OutputPath)
            }
            
            $Bitmap.Dispose()
            $NewImage.Dispose()
            $OldImage.Dispose()
        }
    }
}

Fixed an issue with the percentage variable.

Thanks for this function! I'm including it in an upcoming TechSnips.io video I'm doing. You may want to include Add-Type -AssemblyName 'System.Drawing' though. It won't work without it loaded.

Good work on this. Feel free to join us if you'd like. ;) https://www.techsnips.io/join-us

I tried this on a bunch of JPEGs at 50%, but whilst the pixel sizes were halved, the file sizes all went up! Think there is a quality setting you need to expose somewhere.

@piers7, You must save the file as a jpeg, the default value is png.

ie use

    $Bitmap.Save($OutputPath, [System.Drawing.Imaging.ImageFormat]::Jpeg)

Probably worth to add $OldImage.Dispose() next to

            $Bitmap.Dispose()
            $NewImage.Dispose()

to release original files.

@Kirill Yea that's a great idea! Thanks. Updated the gist.

I used your function as a starting place for a project I was working on (I really like it, thanks!)

One addition I added was the ability of grabbing the "Date Taken" attribute from a photograph.

The code for grabbing that property was something like this:

        $Image = "\\Full\Path\To\Image.jpg"
        [reflection.assembly]::LoadWithPartialName("System.Drawing") | Out-Null
        $pic = New-Object System.Drawing.Bitmap($Image)
        $bitearr = $pic.GetPropertyItem(36867).Value 
        $string = [System.Text.Encoding]::ASCII.GetString($bitearr) 
        $DateTime = [datetime]::ParseExact($string,"yyyy:MM:dd HH:mm:ss`0",$Null)
        $FormattedDate = Get-Date $DateTime -Format "yyyyMMdd"
        $FormattedDate
        $pic.Dispose() 

how to preserve the image's transparent background ?

Great function, thx! As @adbertram wrote, adding Add-Type -AssemblyName 'System.Drawing' is necessary for proper working!

Nice stuff! Helped me save a lot of time, and worked nice. Perhaps a -Replace and -Verbose option would be nice

how to preserve the image's transparent background ?

my .png files kept their transparency fine