彩色转为灰度图片

package com.example.opencvapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
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 android.widget.Toast;

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

public class Expt_1 extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_expt1);

        initLoadOpenCV();
    //通过id查找按钮
        Button button_go_home1 = findViewById(R.id.go_home1);

        //添加按钮点击响应
        button_go_home1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //界面跳转
                startActivity(new Intent(Expt_1.this,MainActivity.class));
            }
        });
        Button btn_toGray =findViewById(R.id.btn_toGray);
        ImageView img_expt_1 =findViewById(R.id.img_expt_1);
        btn_toGray.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //读取图片
                Bitmap bitmap = BitmapFactory.decodeResource(getResources(),R.drawable.img_chapone);
                //彩色图片
                Mat src = new Mat();
                //灰度图片
                Mat dst = new Mat();
                //图片类型转换bitmap为mat
                Utils.bitmapToMat(bitmap,src);
                //彩色转灰度
                Imgproc.cvtColor(src,dst,Imgproc.COLOR_RGBA2GRAY);
                //图片类型转换mat为bitmap
                Utils.matToBitmap(dst,bitmap);
                //关联图片显示组件
                img_expt_1.setImageBitmap(bitmap);
                //清空变量内存
                src.release();
                dst.release();

            }
        });
    }

    private void initLoadOpenCV(){
        //初始化openCV
        boolean success = OpenCVLoader.initDebug();

        if(success){
            Log.i("CV_EXPT1_TAG","OpenCV Libraries load ...");
        }
        else {
            Toast.makeText(this.getApplicationContext(),"WARNNING:Could not load ...",Toast.LENGTH_LONG).show();
        }
    }
}