title: How to convert BitmapImage to WriteableBitmap in Universal application for windows 10?
body: <p>I am implementing a Universal Windows Application on Windows 10 using MVVM.
  I have a file picker allowing me to choose an image. This image is displayed in an Image Control. The source of the Image Control is bound to a property in my view model. This property is a byte array. I need a converter to convert the BitmapImage in a Byte Array.
  I have read lots of things but can't found something working.
  I have found interesting stuff on <a href="https://writeablebitmapex.codeplex.com/" rel="nofollow">https://writeablebitmapex.codeplex.com/</a> 
  but if i want to use this package i need a WriteableBitmap and not a BitmapImage.
  Thank you in advance for your help.</p>