Convert Bitmap Image to byte array (Windows phone 8) - arrays

Question

I am new to windows phone dev. My small app need a bytesarray from image (photo gallery). I tried many ways to convert, but it did not work fine.
here is my code:
public static byte[] ConvertBitmapImageToByteArray(BitmapImage bitmapImage)
{
using (var ms = new MemoryStream())
{
var btmMap = new WriteableBitmap(bitmapImage.PixelWidth, bitmapImage.PixelHeight);
// write an image into the stream
btmMap.SaveJpeg(ms, bitmapImage.PixelWidth, bitmapImage.PixelHeight, 0, 100);
return ms.ToArray();
}
}
But then I saved this byte array to image in photogallery, I was be a black image!
public static void SavePicture2Library(byte[] bytes)
{
var library = new MediaLibrary();
var name = "image_special";
library.SavePicture(name, bytes);
}
Could anyone help me?
Please test your code :( Thanks so much!
Update resolved!
var wBitmap = new WriteableBitmap(bitmapImage);
wBitmap.SaveJpeg(stream, wBitmap.PixelWidth, wBitmap.PixelHeight, 0, 100);
stream.Seek(0, SeekOrigin.Begin);
data = stream.GetBuffer();

Answer 1

To anyone who finds this, this works;
Image to bytes;
public static byte[] ImageToBytes(BitmapImage img)
{
using (MemoryStream ms = new MemoryStream())
{
WriteableBitmap btmMap = new WriteableBitmap(img);
System.Windows.Media.Imaging.Extensions.SaveJpeg(btmMap, ms, img.PixelWidth, img.PixelHeight, 0, 100);
img = null;
return ms.ToArray();
}
}
Bytes to Image
public static BitmapImage BytesToImage(byte[] bytes)
{
BitmapImage bitmapImage = new BitmapImage();
try
{
using (MemoryStream ms = new MemoryStream(bytes))
{
bitmapImage.SetSource(ms);
return bitmapImage;
}
}
finally { bitmapImage = null; }
}

Answer 2

for windows phone 8
using System.IO;
public static class FileToByteArray
{
public static byte[] Convert(string pngBmpFileName)
{
System.IO.FileStream fileStream = File.OpenRead(pngBmpFileName);
using (MemoryStream memoryStream = new MemoryStream())
{
fileStream.CopyTo(memoryStream);
return memoryStream.ToArray();
}
}
}
byte[] PasPhoto = FileToByteArray.Convert("Images/NicePhoto.png")