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<#
.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()
}
}
}
@XcelKhima
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XcelKhima commented Jan 20, 2020

how to preserve the image's transparent background ?

@jerry-ne
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jerry-ne commented Jul 23, 2020

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

@johandanforth
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johandanforth commented Mar 6, 2021

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

@johandanforth
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johandanforth commented Mar 6, 2021

how to preserve the image's transparent background ?

my .png files kept their transparency fine

@invokeImmediately
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invokeImmediately commented Apr 30, 2022

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.

@nate8282
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nate8282 commented Jun 14, 2022

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

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

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