<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 tools:context=".MainActivity" >
 <ImageView
  android:id="@+id/img"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:background="@drawable/dilireba"
  android:layout_centerInParent="true"/>
 <Button
  android:id="@+id/btn_gray_process"
  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>

package com.example.op;
import androidx.appcompat.app.AppCompatActivity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import org.opencv.android.BaseLoaderCallback;
import org.opencv.android.OpenCVLoader;
import org.opencv.android.Utils;
import org.opencv.core.Mat;
import org.opencv.imgproc.Imgproc;
public class MainActivity extends AppCompatActivity {
 Button btnProcess;
 Bitmap srcBitmap;
 Bitmap grayBitmap;
 ImageView img;
 private static boolean flag = true;
 private static boolean isFirst = true;
 private static final String TAG = "MainActivity";
 private BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {
  @Override
  public void onManagerConnected(int status) {
   // TODO Auto-generated method stub
   switch (status){
    case BaseLoaderCallback.SUCCESS:
     Log.i(TAG, "baseloader success");
     break;
    default:
     super.onManagerConnected(status);
     Log.i(TAG, String.valueOf(status));
     break;
   }
  }
 };
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  btnProcess = (Button)findViewById(R.id.btn_gray_process);
  img = (ImageView)findViewById(R.id.img);
  Log.i(TAG, "initUI sucess...");
  btnProcess.setOnClickListener(new ProcessClickListener());
 }
 public void procSrc2Gray(){
  Mat rgbMat = new Mat();
  Mat grayMat = new Mat();
  srcBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.dilireba);
  grayBitmap = Bitmap.createBitmap(srcBitmap.getWidth(), srcBitmap.getHeight(), Bitmap.Config.ARGB_8888);
  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
  Log.i(TAG, "procSrc2Gray sucess...");
 }
 private class ProcessClickListener implements View.OnClickListener {
  @Override
  public void onClick(View v) {
   // TODO Auto-generated method stub
   if(isFirst)
   {
    procSrc2Gray();
    isFirst = false;
   }
   if(flag){
    img.setImageBitmap(grayBitmap);
    btnProcess.setText("gray image");
    flag = false;
   }
   else{
    img.setImageBitmap(srcBitmap);
    btnProcess.setText("rgb image");
    flag = true;
   }
  }
 }
 @Override
 protected void onResume() {
  // TODO Auto-generated method stub
  super.onResume();
  //load OpenCV engine and init OpenCV library
  OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION, getApplicationContext(), mLoaderCallback);
  Log.i(TAG, "onResume sucess load OpenCV...");
 }
}

implementation project(path: ':openCVLibrary341')

adb install OpenCV_3.4.1_Manager_3.41_x86.apk