Added Resize-Image

Author: alan-null

Photo.Shell/Public/Get-ImageCodecInfo.ps1

@@ -1,3 +1,5 @@
+# Table of file signatures (aka "magic numbers")
+# https://www.garykessler.net/library/file_sigs.html
 function Get-ImageCodecInfo {
     [CmdletBinding()]
     param (

Photo.Shell/Public/Resize-Image.ps1

@@ -0,0 +1,50 @@
+function Resize-Image {
+    [CmdletBinding()]
+    param (
+        [Parameter(Mandatory = $true)]
+        [byte[]]$Image,
+        [Parameter(Mandatory = $false, ParameterSetName = "Sizes")]
+        [switch]$ProportionalResize = $false,
+        [Parameter(Mandatory = $true, ParameterSetName = "Sizes")]
+        [int32]$Width,
+        [Parameter(Mandatory = $true, ParameterSetName = "Sizes")]
+        [int32]$Height,
+        [Parameter(Mandatory = $true, ParameterSetName = "Ratio")]
+        [decimal]$Ratio = 0.5
+    )
+
+    begin {
+        Write-Verbose "Cmdlet Resize-Image - Begin"
+    }
+
+    process {
+        Write-Verbose "Cmdlet Resize-Image - Process"
+
+        $stream = [System.IO.MemoryStream]::new($Image)
+        $img = [System.Drawing.Image]::FromStream($stream)
+
+        if ($PSCmdlet.ParameterSetName -eq 'Sizes') {
+            $ratioX = $Width / $img.Width;
+            $ratioY = $Height / $img.Height;
+            $ratio = [System.Math]::Min($ratioX, $ratioY);
+        }
+
+        $autoRatio = $PSCmdlet.ParameterSetName -eq 'Ratio'
+        [int32]$newWidth = if ($ProportionalResize -or $autoRatio) { $img.Width * $ratio } Else { $Width }
+        [int32]$newHeight = if ($ProportionalResize -or $autoRatio) { $img.Height * $ratio } Else { $Height }
+
+        $destImage = New-Object System.Drawing.Bitmap($newWidth, $newHeight)
+
+        $graphics = [System.Drawing.Graphics]::FromImage($destImage)
+        $graphics.DrawImage($img, 0, 0, $newWidth, $newHeight)
+        $graphics.Dispose()
+
+        $stream2 = [System.IO.MemoryStream]::new()
+        $destImage.Save($stream2, [System.Drawing.Imaging.ImageFormat]::Png)
+        $stream2
+    }
+
+    end {
+        Write-Verbose "Cmdlet Resize-Image - End"
+    }
+}

Tests/Photo.Shell.Tests.ps1

@@ -17,6 +17,16 @@ function Get-TestImage {
     $result.ToArray()
 }
 
+function Convert-BytesToImage {
+    param (
+        [byte[]]$testImage
+    )
+
+    $stream = [System.IO.MemoryStream]::new($testImage)
+    [System.Drawing.Image]::FromStream($stream)
+
+}
+
 Describe 'Photo.Shell.Tests' {
     Context "Get-ImageCodecInfo" {
         $testImage = Get-TestImage
@@ -41,4 +51,47 @@ Describe 'Photo.Shell.Tests' {
             Get-ImageCodecInfo $img | Select-Object -ExpandProperty MimeType  | Should -BeExactly $Expected
         }
     }
+
+    Context "Resize-Image" {
+        $testImage = Get-TestImage
+
+
+        It "should resize and keep ratio - smaller" {
+            # 1000 x 800
+            $img_before = Convert-BytesToImage $testImage
+
+            $img_after = Resize-Image -Image $testImage -Ratio 0.1 #10%
+            $img_after = [System.Drawing.Image]::FromStream($img_after)
+
+            $img_after.Width | Should -BeExactly ($img_before.Width * 0.1)
+            $img_after.Height | Should -BeExactly ($img_before.Height * 0.1)
+        }
+
+        It "should resize and keep ratio - bigger" {
+            # 1000 x 800
+            $img_before = Convert-BytesToImage $testImage
+
+            $img_after = Resize-Image -Image $testImage -Ratio 1.2 #120%
+            $img_after = [System.Drawing.Image]::FromStream($img_after)
+
+            $img_after.Width | Should -BeExactly ($img_before.Width * 1.2)
+            $img_after.Height | Should -BeExactly ($img_before.Height * 1.2)
+        }
+
+        It "should resize to a given size" {
+            $img_after = Resize-Image -Image $testImage -Width 200 -Height 200
+            $img_after = [System.Drawing.Image]::FromStream($img_after)
+
+            $img_after.Width | Should -BeExactly 200
+            $img_after.Height | Should -BeExactly 200
+        }
+
+        It "should resize to a given size with ratio" {
+            $img_after = Resize-Image -Image $testImage -Width 200 -Height 200 -ProportionalResize
+            $img_after = [System.Drawing.Image]::FromStream($img_after)
+
+            $img_after.Width | Should -BeExactly 200
+            $img_after.Height | Should -BeExactly 160
+        }
+    }
 }