How to fix 'only black frames receiving' in Android with OpenCV

asked 2019-05-18 13:01:26 -0500

thadaBoy gravatar image

I was developing a Augmented Reality feature similar to inkHunter for a mobile application using python and openCV. The code worked well as I expected even-though it had some over-kills. I needed to make an android app and I knew that I need to convert that python code to C++ and run it in android with ndk since it had a real-time process. I was able to load openCV libraries to my android project and pass data between native class and the MainActivity as well. Then I converted my python code to C++(which is I'm not much familiar with) and then ran the project. But it gives me only black frames. The program shows no errors, but I don't get the expected output.

I'm trying with Android Studio 3.3.2 and OpenCV4Android 4.1.0

I used templateMatching method to detect the input template from the captured frame and then paste a png on the detected area using alpha blending and finally add that area to the frame using homography.

This is my code,

MainActivity.java

public class MainActivity extends AppCompatActivity implements CameraBridgeViewBase.CvCameraViewListener2 {



    private static String TAG = "MainActivity";
    private JavaCameraView javaCameraView;

    // Used to load the 'native-lib' library on application startup.
    static {
        System.loadLibrary("native-lib");
        System.loadLibrary("opencv_java4");
    }

    private Mat mRgba;



    BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {
        @Override
        public void onManagerConnected(int status) {
            switch(status){
                case BaseLoaderCallback.SUCCESS:{
                    javaCameraView.enableView();
                    break;
                }
                default:{
                    super.onManagerConnected(status);
                    break;
                }
            }
        }
    };

    private Mat temp, tattoo;

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

        javaCameraView = (JavaCameraView)findViewById(R.id.java_camera_view);
        javaCameraView.setVisibility(SurfaceView.VISIBLE);
        javaCameraView.setCvCameraViewListener(this);

        AssetManager assetManager = getAssets();

        try {
            InputStream is = assetManager.open("temp.jpg");
            Bitmap bitmap = BitmapFactory.decodeStream(is);
            Bitmap bmp32 = bitmap.copy(Bitmap.Config.ARGB_8888, true);
            temp = new Mat(bitmap.getHeight(), bitmap.getWidth(), CvType.CV_8UC4);
            Utils.bitmapToMat(bmp32, temp);

        } catch (IOException e) {
            e.printStackTrace();
        }

        try {
            InputStream isTattoo = assetManager.open("tattoo2.png");
            Bitmap bitmapTattoo = BitmapFactory.decodeStream(isTattoo);
            Bitmap bmp32Tattoo = bitmapTattoo.copy(Bitmap.Config.ARGB_8888, true);
            tattoo = new Mat(bitmapTattoo.getHeight(), bitmapTattoo.getWidth(), CvType.CV_8UC4);
            Utils.bitmapToMat(bmp32Tattoo, tattoo);

        } catch (IOException e) {
            e.printStackTrace();
        }




    }

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

    @Override
    protected void onDestroy(){
        super.onDestroy();
        if(javaCameraView != null){
            javaCameraView.disableView();
        }
    }

    @Override
    protected void onResume(){
        super.onResume();
        if(OpenCVLoader.initDebug()){
            Log.i(TAG, "OpenCV Loaded successfully ! ");
            mLoaderCallback.onManagerConnected(LoaderCallbackInterface.SUCCESS);
        }else{
            Log.i(TAG, "OpenCV not loaded ! ");
            OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION, this, mLoaderCallback);
        }
    }

    @Override
    public void onCameraViewStarted(int width, int height) {
        mRgba = new Mat(height, width, CvType.CV_8UC4);

    }

    @Override
    public void onCameraViewStopped() {
        mRgba.release();

    }

    @Override
    public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
        mRgba = inputFrame.rgba();

        augmentation(mRgba.getNativeObjAddr(), temp.getNativeObjAddr(), tattoo.getNativeObjAddr());

        return mRgba;
    }


    public native void augmentation(long matAddrRgba, long tempC, long tattooDesign);
}

native-lib.cpp

#include <jni.h>
#include <string>
#include <opencv2/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <iostream>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/opencv.hpp>

using namespace cv;
using namespace std;

extern "C" {



// Alpha Blending using direct pointer access
Mat& alphaBlendDirectAccess(Mat& alpha, Mat& foreground ...
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