public class MainActivity  extends Activity {

    static{System.loadLibrary("opencv_java3"); }


    private Button btn;
    private ImageView img;
    private Bitmap srcBitmap;
    private Bitmap grayBitmap;
    private static boolean flag = true;
    private static boolean isFirst = true;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        img = (ImageView)findViewById(R.id.img);
        btn = (Button)findViewById(R.id.btn);
        btn.setOnClickListener(new ProcessClickListener());
    }

    public void procSrc2Gray(){
        Mat rgbMat = new Mat();
        Mat grayMat = new Mat();
        srcBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.genie);
        grayBitmap = Bitmap.createBitmap(srcBitmap.getWidth(), srcBitmap.getHeight(), Bitmap.Config.RGB_565);
        Utils.bitmapToMat(srcBitmap, rgbMat);//convert original bitmap to Mat, R G B.
        Imgproc.cvtColor(rgbMat, grayMat, Imgproc.COLOR_RGB2GRAY);//rgbMat to gray grayMat
        Utils.matToBitmap(grayMat, grayBitmap); //convert mat to bitmap
    }


    public class ProcessClickListener implements View.OnClickListener{
        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            if(isFirst){

                 Runnable runnable=new Runnable () {
                            @Override
                            public void run() {
                                procSrc2Gray();
                            }
                        };
                new Thread (runnable) .start ();
                isFirst = false;
            }
            if(flag){
                img.setImageBitmap(grayBitmap);
                btn.setText("查看原图");
                flag = false;
            }else{
                img.setImageBitmap(srcBitmap);
                btn.setText("灰度化");
                flag = true;
            }
        }
    }
}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:layout_width="match_parent"
                android:layout_height="match_parent">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:text="OpenCV"/>

    <ImageView
        android:id="@+id/img"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:background="@drawable/genie"/>

    <Button
        android:id="@+id/btn"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/img"
        android:layout_centerHorizontal="true"
        android:text="灰度化"/>"

</RelativeLayout>