MainActivity.java

package com.programminghut.edge_detector;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.content.ContextCompat;

import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.util.Log;
import android.widget.Toast;

import org.opencv.android.CameraActivity;
import org.opencv.android.CameraBridgeViewBase;
import org.opencv.android.JavaCamera2View;
import org.opencv.android.JavaCameraView;
import org.opencv.android.OpenCVLoader;
import org.opencv.android.Utils;
import org.opencv.core.Core;
import org.opencv.core.Mat;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.imgproc.Imgproc;

import java.util.Collections;
import java.util.List;

public class MainActivity extends CameraActivity {

    JavaCameraView cameraBridgeViewBase;

    Mat gray;

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

        get_permissions();

        cameraBridgeViewBase = findViewById(R.id.cameraView);
        cameraBridgeViewBase.setCvCameraViewListener(new CameraBridgeViewBase.CvCameraViewListener2() {
            @Override
            public void onCameraViewStarted(int width, int height) {

            }

            @Override
            public void onCameraViewStopped() {

            }

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

                Imgproc.Canny(gray, gray, 80, 100);
                Core.bitwise_not(gray, gray);

                return gray;
            }
        });

        if(OpenCVLoader.initDebug()) {
            Toast.makeText(this, "opencv loaded success....", Toast.LENGTH_SHORT).show();
            cameraBridgeViewBase.enableView();
        }
    }

    @Override
    protected List<? extends CameraBridgeViewBase> getCameraViewList() {
        return Collections.singletonList(cameraBridgeViewBase);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        cameraBridgeViewBase.disableView();
    }

    void get_permissions(){
        if(ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED)
        {
            requestPermissions(new String[]{Manifest.permission.CAMERA}, 101);
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if(grantResults[0]!=PackageManager.PERMISSION_GRANTED){
            get_permissions();
        }
    }
}