Thumbnail Image Creation and Image format Conversion Utility

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Generally we were required, in our classic ASP applications, to generate thumbnail images by using a 3rd party COM component. To do the same in the .NET Framework, you need not depend any more on those tools. It has built in functionality which will convert an original image to a thumbnail without ever writing a physical file to the hard disk. Of course, you have the option to save the result if you want. It will allow users to specify the width and height of the thumbnail image using a QueryString. It handles exceptions by throwing an image not found, in case you give a bad filename or invalid parameters. This code can be written within an aspx page, there is no need to use code behind.

<script language="VB" runat="server">

  Sub Page_Load(Sender As Object, E As EventArgs)
	
        Dim originalimg, thumb As System.Drawing.Image
        Dim FileName As String
        Dim inp As New IntPtr()
        Dim width, height As Integer
        Dim rootpath As String

        rootpath = Server.MapPath("/") ' Get Root Application Folder


        FileName = rootpath & Request.QueryString("FileName") ' Root Folder + FileName

        Try
            originalimg = originalimg.FromFile(FileName) ' Fetch User Filename

        Catch
            originalimg = originalimg.FromFile(rootpath & "error.gif") ' Fetch error.gif

        End Try

        ' Get width using QueryString.

        If Request.QueryString("width") = Nothing Then
            width = originalimg.Width  ' Use original Width. 

        ElseIf Request.QueryString("width") = 0 Then  ' Assign default width of 100.

            width = 100
        Else
            width = Request.QueryString("width") ' Use User Specified width.

        End If

        ' Get height using QueryString.

        If Request.QueryString("height") = Nothing Then
            height = originalimg.Height ' Use original Height.

        ElseIf Request.QueryString("height") = 0 Then ' Assign default height of 100.

            height = 100
        Else
            height = Request.QueryString("height") ' Use User Specified height.

        End If

        thumb = originalimg.GetThumbnailImage(width, height, Nothing, inp)

        ' Sending Response JPEG type to the browser. 

        Response.ContentType = "image/jpeg"
        thumb.Save(Response.OutputStream, Imaging.ImageFormat.Jpeg)

        ' Disposing the objects.

        originalimg.Dispose()
        thumb.Dispose()

  End Sub
</script>

Usage

http://<servername>/thumbnailimage.aspx?filename=<filename>&width=75&height=75

Where filename should be path relative to the root of the application folder. width & height are optional. If not specified, then the original width and height will be used.

If width or height are specified as 0, then the default width / height of 100 pixels is used.

Examples

http://localhost/thumbnailimage.aspx?filename=win2000.gif

http://localhost/thumbnailimage.aspx?filename=win2000.gif&width=0&height=0

http://localhost/thumbnailimage.aspx?filename=win2000.gif&width=50&height=50

http://localhost/test/thumbnailimage.aspx?filename=test/win2000.gif

Notes

By default the thumbnail image generated is of type JPEG. One can change the Response.Type by changing the following code.

Response.ContentType = "image/jpeg"
thumb.Save(Response.OutputStream, Imaging.ImageFormat.Jpeg) 'Change jpeg word 

with the required supported format(Gif, Png, Bmp etc).