Make Thumbnail - Transparent Gif problem - Black Background

Hi,

I have the following code to create thumbnail images on the fly. It works fine with .jpg, however when a .gif is passed in as the image the background of the image
turns black.

I understand there is a problem with keeping the transparency of gif images within .net
I would be happy if the background colour was just white.

Any Ideas?


-----------------
     Public fileName As String
    Public imageWidth As Integer
    Public imageHeight As Integer


    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'Put user code to initialize the page here

        'get filename, width and height
        fileName = Request.QueryString("file")
        imageWidth = Request.QueryString("w")
        imageHeight = Request.QueryString("h")


        'imageWidth = 250
        'imageHeight = 400

        If imageWidth = Nothing Then
            imageWidth = 250
        Else
            imageWidth = imageWidth
        End If

        If imageHeight = Nothing Then
            imageHeight = 400
        Else
            imageHeight = imageHeight
        End If

        imageResize()

    End Sub

    Function ThumbnailCallback() As Boolean
        Return False
    End Function


    Function imageResize()

        Dim fullSizeImg, thumbNailImg As System.Drawing.Image


        'Read in the image filename to create a thumbnail of
        Dim imageUrl As String = fileName

        'Read in the width and height
        'Dim imageHeight As Integer = "200" 'Request.QueryString("h")
        'Dim imageWidth As Integer = "200" 'Request.QueryString("w")


        'Make sure that the image URL doesn't contain any /'s or \'s
        If imageUrl.IndexOf("/") >= 0 Or imageUrl.IndexOf("\") >= 0 Then
            'We found a / or \
            Response.End()
        End If

        'Add on the appropriate directory
        imageUrl = "media/" & imageUrl
        fullSizeImg = System.Drawing.Image.FromFile(Server.MapPath(imageUrl))


        Dim maxWidth, MaxHeight As Integer
        ' Get width using QueryString.
        If imageWidth = Nothing Then
            maxWidth = fullSizeImg.Width
        ElseIf imageWidth = 0 Then
            maxWidth = 100
        Else
            maxWidth = imageWidth
        End If

        ' Get height using QueryString.
        If imageHeight = Nothing Then
            MaxHeight = fullSizeImg.Height
        ElseIf imageHeight = 0 Then
            MaxHeight = 100
        Else
            MaxHeight = imageHeight
        End If


        Dim imgHeight, imgWidth As Integer
        Try
            fullSizeImg = fullSizeImg.FromFile(Server.MapPath(imageUrl))
            imgHeight = fullSizeImg.Height
            imgWidth = fullSizeImg.Width

            If imgWidth > maxWidth Or imgHeight > MaxHeight Then
                'Determine what dimension is off by more
                Dim deltaWidth As Integer = imgWidth - maxWidth
                Dim deltaHeight As Integer = imgHeight - MaxHeight
                Dim scaleFactor As Double

                If deltaHeight > deltaWidth Then
                    'Scale by the height
                    scaleFactor = MaxHeight / imgHeight
                Else
                    'Scale by the Width
                    scaleFactor = maxWidth / imgWidth
                End If

                imgWidth *= scaleFactor
                imgHeight *= scaleFactor
            End If

        Catch
            fullSizeImg = fullSizeImg.FromFile(Server.MapPath("\ssm\images\ac_image\error.gif"))
        End Try


        'Do we need to create a thumbnail?
        Response.ContentType = "image/Jpeg"

        If imageHeight > 0 And imageWidth > 0 Then

            Dim dummyCallBack As System.Drawing.Image.GetThumbnailImageAbort
            dummyCallBack = New System.Drawing.Image.GetThumbnailImageAbort(AddressOf ThumbnailCallback)


            thumbNailImg = fullSizeImg.GetThumbnailImage(imgWidth, imgHeight, dummyCallBack, IntPtr.Zero)

            ' send the resized image to the viewer  
            thumbNailImg.Save(Response.OutputStream, Imaging.ImageFormat.Jpeg) ' output to the user
        Else
            fullSizeImg.Save(Response.OutputStream, Imaging.ImageFormat.Jpeg)
        End If

        'Disposing the objects.
        thumbNailImg.Dispose()
        fullSizeImg.Dispose()

    End Function
------------------