Как изменить область сканирования Zbar?

Я хочу изменить область сканирования камеры. Теперь я беру изображение для сканирования размером с экран устройства. Я пытаюсь обрезать изображение для анализа. Таким образом, только центр предварительного просмотра будет источником сканирования. Есть ли возможность установить захваченный предварительный просмотр меньшим или создать Bitmap из данных byte [] и обрезать, это единственный способ получить меньшую площадь? Я пытался что-то прокомментировать, но документация для Zbar Android очень плохая (сравнение с iOs).

Изображение здесь: http://postimg.org/image/4wk4u0mln/

MainActivity

public class MainActivity extends Activity
{
    private Camera mCamera;
    private Context context;
    private CameraPreview mPreview;
    private Handler autoFocusHandler;

    TextView scanText;
    Button scanButton;

    ImageScanner scanner;
    private PowerManager.WakeLock wl;

    private boolean barcodeScanned = false;
    private boolean previewing = true;

    static {
        System.loadLibrary("iconv");
    } 

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);



        setContentView(R.layout.activity_main);

        setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);

        autoFocusHandler = new Handler();
        mCamera = getCameraInstance();


        context = getApplicationContext();

        /* Instance barcode scanner */
        scanner = new ImageScanner();

        scanner.setConfig(0, Config.X_DENSITY, 3);
        scanner.setConfig(0, Config.Y_DENSITY, 3);

        mPreview = new CameraPreview(this, mCamera, previewCb, autoFocusCB);
        FrameLayout preview = (FrameLayout)findViewById(R.id.cameraPreview);
        preview.addView(mPreview);

        scanText = (TextView)findViewById(R.id.scanText);


    }

    @Override
    public void onPause() {
        super.onPause();
        releaseCamera();
    }

    @Override
    protected void onResume() {
        // TODO Auto-generated method stub

        onStart();
    }

    @Override
    protected void onStop() {
        // TODO Auto-generated method stub
        super.onStop();

        finish();
    }

    /** A safe way to get an instance of the Camera object. */
    public static Camera getCameraInstance(){
        Camera c = null;
        try {
            c = Camera.open();
        } catch (Exception e){
        }
        return c;
    }

    private void releaseCamera() {
        if (mCamera != null) {
            previewing = false;
            mCamera.setPreviewCallback(null);
            mCamera.release();
            mCamera = null;
        }
    }

    private Runnable doAutoFocus = new Runnable() {
            @Override
            public void run() {
                if (previewing)
                    mCamera.autoFocus(autoFocusCB);
            }
        };

    PreviewCallback previewCb = new PreviewCallback() {
            @Override
            public void onPreviewFrame(byte[] data, Camera camera) {
                Camera.Parameters parameters = camera.getParameters();
                Size size = parameters.getPreviewSize();
                //HERE we read taken picture from prieview
                Image barcode = new Image(size.width, size.height, "Y800");

                barcode.setData(data);


                int result = scanner.scanImage(barcode);

                if (result != 0) {
                    previewing = false;
                    mCamera.setPreviewCallback(null);


                    mCamera.stopPreview();



                    SymbolSet syms = scanner.getResults();
                    for (Symbol sym : syms) {

                    if (sym.getType() == Symbol.CODE128) {
                        sym.getData());
                        MediaPlayer mp = MediaPlayer.create(context, R.raw.beep_ok); 
                        mp.start();


                    } else {

                        MediaPlayer mp = MediaPlayer.create(context, R.raw.beep_wrong); 
                        mp.start();
                    }


                        mCamera.setPreviewCallback(previewCb);
                        mCamera.startPreview();
                        previewing = true;
                        mCamera.autoFocus(autoFocusCB);



                    }
                }
            }
        };

    // Mimic continuous auto-focusing
    AutoFocusCallback autoFocusCB = new AutoFocusCallback() {
            @Override
            public void onAutoFocus(boolean success, Camera camera) {
                autoFocusHandler.postDelayed(doAutoFocus, 1000);
            }
        };


        //Method to crop Bitmap in case of use
        public Bitmap scaleCenterCrop(Bitmap source, int newHeight, int newWidth) {
            int sourceWidth = source.getWidth();
            int sourceHeight = source.getHeight();

            float xScale = (float) newWidth / sourceWidth;
            float yScale = (float) newHeight / sourceHeight;
            float scale = Math.max(xScale, yScale);

            float scaledWidth = scale * sourceWidth;
            float scaledHeight = scale * sourceHeight;

            float left = (newWidth - scaledWidth) / 2;
            float top = (newHeight - scaledHeight) / 2;

            RectF targetRect = new RectF(left, top, left + scaledWidth, top + scaledHeight);


            Bitmap dest = Bitmap.createBitmap(newWidth, newHeight, source.getConfig());
            Canvas canvas = new Canvas(dest);
            canvas.drawBitmap(source, null, targetRect, null);

            return dest;
        }

}

CameraPrieview.java

public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
    private SurfaceHolder mHolder;
    private Camera mCamera;
    private PreviewCallback previewCallback;
    private AutoFocusCallback autoFocusCallback;

    public CameraPreview(Context context, Camera camera,
                         PreviewCallback previewCb,
                         AutoFocusCallback autoFocusCb) {
        super(context);
        mCamera = camera;
        previewCallback = previewCb;
        autoFocusCallback = autoFocusCb;

        /* 
         * Set camera to continuous focus if supported, otherwise use
         * software auto-focus. Only works for API level >=9.
         */
        /*
        Camera.Parameters parameters = camera.getParameters();
        for (String f : parameters.getSupportedFocusModes()) {
            if (f == Parameters.FOCUS_MODE_CONTINUOUS_PICTURE) {
                mCamera.setFocusMode(Parameters.FOCUS_MODE_CONTINUOUS_PICTURE);
                autoFocusCallback = null;
                break;
            }
        }
        */

        // Install a SurfaceHolder.Callback so we get notified when the
        // underlying surface is created and destroyed.
        mHolder = getHolder();
        mHolder.addCallback(this);

        // deprecated setting, but required on Android versions prior to 3.0
        mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
    }

    @Override
    public void surfaceCreated(SurfaceHolder holder) {
        // The Surface has been created, now tell the camera where to draw the preview.
        try {
            mCamera.setPreviewDisplay(holder);
        } catch (IOException e) {
            Log.d("DBG", "Error setting camera preview: " + e.getMessage());
        }
    }

    @Override
    public void surfaceDestroyed(SurfaceHolder holder) {
        // Camera preview released in activity
    }

    @Override
    public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
        /*
         * If your preview can change or rotate, take care of those events here.
         * Make sure to stop the preview before resizing or reformatting it.
         */
        if (mHolder.getSurface() == null){
          // preview surface does not exist
          return;
        }

        // stop preview before making changes
        try {
            mCamera.stopPreview();
        } catch (Exception e){
          // ignore: tried to stop a non-existent preview
        }

        try {
            // Hard code camera surface rotation 90 degs to match Activity view in portrait
            mCamera.setDisplayOrientation(90);

            mCamera.setPreviewDisplay(mHolder);
            mCamera.setPreviewCallback(previewCallback);
            mCamera.startPreview();
            mCamera.autoFocus(autoFocusCallback);
        } catch (Exception e){
            Log.d("DBG", "Error starting camera preview: " + e.getMessage());
        }
    }
}