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()
        }
    }
}

@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

I appreciate the helpful function! It saved me a lot of time looking for needles in haystacks of hi-res photos sitting behind a slow network connection.

I did find a minor bug that only affects processing more than one image. Say that I set the $MaintainRatio flag and provide the $Width as the absolute basis for resizing an array of images with length > 1. I would expect the height of each image to be calculated based on this provided width and each image's original aspect ratio. But because lines 89 through 94 are inside the For-Each, this is not technically what happens. The first iteration through the For-Each, the expected behavior does occur. Alas, every additional iteration through the For-Each after the first ends up recalculating the $Width based on the $Height that was determined during the first iteration. In effect, the original $Width parameter gets ignored after the first image is processed. Because of this, there is a chance that most images processed will end up with an unexpected width.

Worked great. I added the following line so I could batch convert all images within a folder. Thanks!

$ImagePath = (Get-ChildItem -Path $ImagePath).FullName

nice, maybe you could add some test-paths to see if the image output path already exists and offer to overwrite or skip?

This does not work anymore for me on macos. I get "System.Drawing.Common is not supported on this platform.".
Think this is due to the following breaking change: https://learn.microsoft.com/en-us/dotnet/core/compatibility/core-libraries/6.0/system-drawing-common-windows-only