Question

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.

Does anyone know what I’m doing wrong?

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 

Answer 1

Unfortunately, there is no easy way to create a transparent Gif using a Bitmap object. (See this KB article)

You can alternatively use the PNG format that supports transparency with the code you are using.