How to Load an Image using OpenCV in Android?

package com.example.open_cv;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

import android.Manifest;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.graphics.Bitmap;
import android.os.Bundle;
import android.provider.MediaStore;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

import org.opencv.android.OpenCVLoader;
import org.opencv.android.Utils;
import org.opencv.core.Mat;
import org.opencv.imgproc.Imgproc;

import java.io.IOException;

public class MainActivity extends AppCompatActivity {

    // initializing variables
    Button select,camera;
    ImageView imageView;
    Bitmap bitmap;
    int select_code=100,camera_code=102;
    Mat mat;

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

          // to check if openCV is loaded
        getPermission();
        if(OpenCVLoader.initDebug())
            Log.d("Loaded","success");
        else
            Log.d("Loaded","error");

        camera=findViewById(R.id.Camera);
        select=findViewById(R.id.select);
        imageView=findViewById(R.id.imageView);

        // for select button
        select.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent=new Intent(Intent.ACTION_GET_CONTENT);
                intent.setType("image/*");
                startActivityForResult(intent,select_code);
            }
        });

        // for the camera button
        camera.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent=new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
                startActivityForResult(intent,camera_code);
            }
        });
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if(requestCode==select_code && data!=null)
        {
            try {
                bitmap= MediaStore.Images.Media.getBitmap(this.getContentResolver(),data.getData());
                imageView.setImageBitmap(bitmap);

                  // using mat class
                mat=new Mat();
                Utils.bitmapToMat(bitmap,mat);

                  // converting RGB to gray
                Imgproc.cvtColor(mat,mat,Imgproc.COLOR_RGB2GRAY);

                Utils.matToBitmap(mat,bitmap);
                imageView.setImageBitmap(bitmap);

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

        if(requestCode==camera_code && data!=null)
        {
            bitmap=(Bitmap) data.getExtras().get("data");
            imageView.setImageBitmap(bitmap);

              // using mat class
            mat=new Mat();
            Utils.bitmapToMat(bitmap,mat);
            Imgproc.cvtColor(mat,mat,Imgproc.COLOR_RGB2GRAY);

            Utils.matToBitmap(mat,bitmap);
            imageView.setImageBitmap(bitmap);
        }
    }

      // get camera permission
    void getPermission()
    {
        if(checkSelfPermission(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(requestCode==101 && grantResults.length>0)
        {
            if(grantResults[0]!=PackageManager.PERMISSION_GRANTED)
            {
                getPermission();
            }
        }
    }
}