How to implement OpenCV-4.5.1 to Android projects

Mehmet Emin Gülşen

3 min readJan 17, 2021

I will try to explain how to import OpenCV-4.5.1 to your Android project step-by-step.

Step-1

Download OpenCV-4.5.1 for Android. You can also choose other versions of OpenCV.

OpenCV Releases

OpenCV-4.5.1 for Android

Step-2

Create an Android project. If you already have a project, you can pass this step and continue with Step-3.

Create New Project like given in the below.

Choose “Empty Activity”

Name your project. In my case it was “OpenCV-Android-Example” with package name “com.example.opencv_android_example”.

Step-3

Import OpenCV module to your project by following the path :

File > New > Import Module

You should choose the folder in the following path

OpenCV-android-sdk > sdk

After selecting the OpenCV folder, ADT Import Preferences will be showed and in this step you can select all and finish.

Step-4

Open build.gradle file of your project that should be look like given below and type “implementation project(path: ‘:opencv451’)”, “:opencv-451” can be changing based on your module name. (When importing module it automatically name it to “sdk”, so I have changed it to “opencv451” by right clicking on sdk module and refactoring module name)
After typing “implementation project(path:’opencv451’)”, you should Sync Project and it should be ready to go.

You should also check that minimum sdk version of both opencv and your app should be same. In my case, it was 21.

Step-5

So, we are ready to go now. Let’s check if everything works correctly. In this regard, we should write a simple application which has only a Button and ImageView, my activity_main.xml file like below.

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">
    
    <ImageView
        android:id="@+id/image_view"
        android:layout_width="300dp"
        android:layout_height="300dp"
        android:scaleType="centerInside"
        android:layout_centerInParent="true"/>
    
    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:backgroundTint="@color/white"
        android:text="Click"
        android:textColor="@color/black"
        android:layout_marginTop="20dp"
        android:layout_centerHorizontal="true"
        android:layout_below="@+id/image_view"/>
</RelativeLayout>

And, the MainActivity.java look like this.

package com.example.opencv_android_example;

import androidx.appcompat.app.AppCompatActivity;

import android.graphics.Bitmap;
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.LoaderCallbackInterface;
import org.opencv.android.OpenCVLoader;
import org.opencv.android.Utils;
import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.core.Point;
import org.opencv.core.Scalar;
import org.opencv.imgproc.Imgproc;

public class MainActivity extends AppCompatActivity {


    Button button;
    ImageView imageView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        OpenCVLoader.initDebug();
        button = findViewById(R.id.button);
        imageView = findViewById(R.id.image_view);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                hello();
            }
        });
    }


    private void hello(){
        Mat emptyMat = new Mat(500,500, CvType.CV_8UC3);
        Imgproc.circle(emptyMat,new Point(250,250),25,new Scalar(255,255,255));
        Bitmap bitmap = Bitmap.createBitmap(500,500, Bitmap.Config.RGB_565);
        Utils.matToBitmap(emptyMat,bitmap);
        imageView.setImageBitmap(bitmap);
    }

}