title: How do you Draw Transparent Image using System.Drawing?
body: <p>I'm trying to return a transparent GIF from an .aspx page for display within a web page. I am trying to get the image to have transparency, but I just keep getting Black being where the image should be Transparent.</p>
  
  <p>Does anyone know what I'm doing wrong?</p>
  
  <pre><code>Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) _
    Handles Me.Load
      '' Change the response headers to output a GIF image.
      Response.Clear()
      Response.ContentType = "image/gif"
  
      Dim width = 110
      Dim height = width
  
      '' Create a new 32-bit bitmap image
      Dim b = New Bitmap(width, height)
  
      '' Create Grahpics object for drawing
      Dim g = Graphics.FromImage(b)
  
      Dim rect = New Rectangle(0, 0, width - 1, height - 1)
  
      '' Fill in with Transparent
      Dim tbrush = New System.Drawing.SolidBrush(Color.Transparent)
      g.FillRectangle(tbrush, rect)
  
      '' Draw Circle Border
      Dim bPen = Pens.Red
      g.DrawPie(bPen, rect, 0, 365)
  
      '' Fill in Circle
      Dim cbrush = New SolidBrush(Color.LightBlue)
      g.FillPie(cbrush, rect, 0, 365)
  
  
      '' Clean up
      g.Flush()
      g.Dispose()
  
      '' Make Transparent
      b.MakeTransparent()
  
      b.Save(Response.OutputStream, Imaging.ImageFormat.Gif)
      Response.Flush()
      Response.End()
  End Sub
  </code></pre>