Binaryworld - ResizeImage - Resize an image, and optionally keep the original ratio ... [ VB.net -> Graphics ]

' Resize the specified image file - The new dimensions are expressed in
' percentage of the original size.
' The resized image overwrites the original file.
' Note: requires the GetImageFormat function
'
' Example:
'  ResizeImage("D:\sample.gif", 50.0, 50.0) ' make the image half the
' original size
'  ResizeImage("D:\sample.gif", 200.0, 300.0) ' double the width and triple
' the height

Sub ResizeImage(ByVal imgPath As String, ByVal widthPerc As Double, _
  ByVal heightPerc As Double)
  ' throw an exception if not both arguments are positive values
  If widthPerc <= 0 OrElse heightPerc <= 0 Then
    Throw New ArgumentException("widthPerc AND heightPerc arguments must be " _
      & "positive values")
  End If

  Dim currWidth, currHeight As Integer
  Dim newWidth, newHeight As Integer
  ' get the image's current width/height
  Dim img As System.Drawing.Image = System.Drawing.Image.FromFile(imgPath)
  currWidth = img.Width
  currHeight = img.Height
  img.Dispose()
  ' calculate the new size in pixel
  newWidth = currWidth * widthPerc / 100
  newHeight = currHeight * heightPerc / 100
  ' call the overloaded method that takes explicit width/height in pixels
  ResizeImage(imgPath, newWidth, newHeight)
End Sub

' This overloaded version takes the new width/height in pixel,
' instead of the percentage of the original size.
' Either the width/height (but not both) can be 0,
' and the size will be calculate to maintain the ratio of the original image
' Example:
'  ResizeImage("D:\sample.gif", 100, 50) ' resize to 100x50
'  ResizeImage("D:\sample.gif", 100, 0) ' the height will be calculated
' according to the new width

Sub ResizeImage(ByVal imgPath As String, ByVal width As Integer, _
  ByVal height As Integer)
  ' throw an exception if both arguments are not positive integers
  If width <= 0 AndAlso height <= 0 Then
    Throw New ArgumentException("Width and/or Height arguments must be " _
      & "positive integers")
  End If

  ' select the format of the image to write according to the current extension
  Dim imgFormat As System.Drawing.imaging.ImageFormat = GetImageFormat _
    (imgPath)
  ' open the image file
  Dim img As System.Drawing.Image = System.Drawing.Image.FromFile(imgPath)

  ' if either the specified height or width are 0, calculate it to maintain
  ' the same ratio of the original image
  If width <= 0 OrElse height <= 0 Then
    If width <= 0 Then
      width = img.Width / (img.Height / height)
    ElseIf height <= 0 Then
      height = img.Height / (img.Width / width)
    End If
  End If

  ' create a new empty bitmpat with the specified size
  Dim bmp As New System.Drawing.Bitmap(width, height)
  ' retrieve a canvas object that allows to draw on the empty bitmap
  Dim g As System.Drawing.Graphics = System.Drawing.Graphics.FromImage( _
    DirectCast(bmp, System.Drawing.Image))
  ' copy the original image on the canvas, and thus on the new bitmap,
  ' with the new size
  g.DrawImage(img, 0, 0, width, height)
  ' close the original image
  img.Dispose()
  ' save the new image with the proper format
  bmp.Save(imgPath, imgFormat)
  bmp.Dispose()
End Sub