bmp.save image format jpeg problem

Hello everyone, I have a question. I would like to save all the uploaded image to .jpeg format. Here is my code:
Dim result As New Bitmap(CInt(Math.Truncate(nWidth)), CInt(Math.Truncate(nHeight))) ..... result.Save(HttpContext.Current.Server.MapPath(path) + fileName, ImageFormat.Jpeg) However, when I uploaded a .png image, the uploaded file is still a png file. Is there a way I can save all uploaded images to jpeg format? I used this link http://msdn.microsoft.com/en-us/library/ms142147.aspx but it seems not working for me.
Thanks. 



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