OpenCv video frame accessing

package com.darekk.opencv_test;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.SurfaceView;
import android.view.WindowManager;
import org.opencv.android.*;
import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.core.Scalar;
import org.opencv.videoio.VideoCapture;


public class MyActivity extends Activity implements CameraBridgeViewBase.CvCameraViewListener2 {
    private static String LOG_TAG="opencv";

    private CameraBridgeViewBase cameraView;


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
        setContentView(R.layout.main);
        cameraView=(JavaCameraView)findViewById(R.id.HelloOpenCvView);
        cameraView.setVisibility(SurfaceView.VISIBLE);
        cameraView.setCvCameraViewListener(this);
       // Mat m = imread("/media/path_to_image");
    }


    @Override
    public void onCameraViewStarted(int width, int height) {

    }

    @Override
    public void onCameraViewStopped() {

    }

    @Override
    public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
        //Do your processing here, for example:
        Mat image = inputFrame.rgba();
        Mat ret_mat=new Mat();
        Core.add(image, new Scalar(40, 40,40,0), ret_mat); //change brightness of video frame

        return ret_mat;
    }

    private BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {
        @Override
        public void onManagerConnected(int status) {
            switch (status) {
                case LoaderCallbackInterface.SUCCESS:
                {
                    Log.i(LOG_TAG, "OpenCV loaded successfully");
                    cameraView.enableView();
                } break;
                default:
                {
                    super.onManagerConnected(status);
                } break;
            }
        }
    };




    @Override
    public void onResume()
    {
        super.onResume();
        OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_3_0_0, this, mLoaderCallback); //OPENCV_VERSION_2_4_6
    }

    @Override
    public void onPause()
    {
        super.onPause();
        if (cameraView != null)
            cameraView.disableView();
    }

    public void onDestroy() {
        super.onDestroy();
        if (cameraView != null)
            cameraView.disableView();
    }

}