Android获取本地文件字节

我正在尝试获取保存在手机本地的图像的字节数组。我正在使用代码：

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.upload);

    // Look in the Device
    startActivityForResult(new Intent(Intent.ACTION_PICK, android.provider.MediaStore.Images.Media.INTERNAL_CONTENT_URI), 1);
    // Look in the SD Card
    // startActivityForResult(new Intent(Intent.ACTION_PICK, android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI), 1);
}

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
  super.onActivityResult(requestCode, resultCode, data);
  if (requestCode == 1)
    if (resultCode == Activity.RESULT_OK) {
      Uri selectedImage = data.getData();
      Cursor Cur = Upload.this.managedQuery(selectedImage, null, null, null,null);
      if (Cur.moveToFirst()) {
          File Img = new File(selectedImage.getPath());
          long Length = Cur.getLong(Cur.getColumnIndex(ImageColumns.SIZE));
          byte[] B = new byte[(int)Length-1];
          FileInputStream ImgIs;
          try {
            ImgIs = new FileInputStream(Img);
            ImgIs.read(B);
          } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
          } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        int i = B.length;
      }
    } 
}

但它抛出一个FileNotFound exception上

ImgIs = new FileInputStream(Img) 我如何获得字节？