Convert BitmapImage to byte[] array in Windows Phone 8.1 Runtime

Question

There are a few samples to do this but they are for Windows Phone 8.0 or 8.1 Silverlight.

But how can you do this for Windows Phone 8.1 Runtime?

Answer 1

You cannot extract the pixels from a Windows.UI.Xaml.Media.Imaging.BitmapImage.

The most general solution is to use a WriteableBitmap instead of a BitmapImage. These classes are both BitmapSources and can be used almost interchangeably. The WriteableBitmap provides access to its pixel data via its PixelBuffer property:

byte[] pixelArray = myWriteableBitmap.PixelBuffer.ToArray(); // convert to Array
Stream pixelStream = wb.PixelBuffer.AsStream();  // convert to stream

Otherwise you will need to acquire the pixels from wherever the BitmapImage got them from. Depending on how the BitmapImage was initialized you may be able to find its origin from its UriSource property. The WinRT Xaml Toolkit has an extension method FromBitmapImage to create a WriteableBitmap from an BitmapImage based on its UriSource.

An ugly option would be to render the BitmapImage into an Image, create a RenderTargetBitmap based on the Image and then get its Pixels with RenderTargetBitmap.CopyPixelsAsync()