如何从SD卡解码qr代码

Question

我想从我的SD卡上的图像解码qr代码，我不想使用外部扫描仪。我用Zxing库。我有一些代码

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main); 

    TextView txt = (TextView)findViewById(R.id.textView1);
    ImageView img=(ImageView)findViewById(R.id.imageView1);
    img.setImageResource(R.drawable.qr);

    Bitmap bt = BitmapFactory.decodeFile(Environment.getExternalStorageDirectory().getAbsolutePath()+"/cameraApplicationSe/qr.png");

    img.setImageBitmap(bt);
    int [] pix = new int[bt.getWidth() * bt.getHeight()];
    LuminanceSource qr=new RGBLuminanceSource(bt.getWidth(),bt.getHeight(),pix);
    BinaryBitmap bitmap = new BinaryBitmap(new HybridBinarizer(qr));

    Reader reader = new MultiFormatReader();        
    Result result;          
    try {
        result = reader.decode(bitmap);
        txt.setText(result.getText());
    } catch (NotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        txt.setText("NotFoundException");
    } catch (ChecksumException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (FormatException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }       
}

在Manifest文件中添加读写外部存储的用户权限。我在TextView中收到的所有尝试 - NotFoundException。在图像中我有QR码，独立创建。在网站上。 哪里有错误？求你帮帮我。