title: Download and save png picture to local storage Windows Phone background agent
body: <p>I'm downloading a picture from internet and saving it to the local storage in a backgroundAgent. With ".jpg" it works fine using <a href="http://msdn.microsoft.com/en-US/library/windowsphone/develop/system.windows.media.imaging.extensions.savejpeg%28v=vs.105%29.aspx" rel="nofollow">SaveJPeg</a>.
  But, if I ddownload a ".png" or ".wdp" file I don't know how to save it in the correct format. The namespace "System.Windows.Media.Imaging" does not provide any method to save in another format. 
  EDIT: I need the image to set it as lockscreen background.</p>