Opencv In Android

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this article is ready for a people who has some knowledge on android develop and a newer about how use opencv SDK in android .

一: what is opencv

简单的来说, opencv 是跨平台的计算机视觉开源库, 它包含了很多图像识别算法
In simple terms , opencv is a open source library about Cross-platform computer vision

here is opencv
here is opencv source code

二: Setting up OpenCv Library inside Android

1, first our develop environment

Android Studio
Opencv SDK 3.2

2, you need download and import Opencv library SDK into android studio peoject

SDK

然后你需要使用sdk的java 部分的代码作为你项目的moudle

From File -> New -> Import Module, choose folder OpenCV-android-sdk -> sdk -> java

then add module dependency to your project

in android studio, Application -> Module Settings , select the Dependencies tab , click + icon at bottom ,choose Module Dependency and select the have imported Opencv moudle
it will looks like that :
Opencv moudle
copy libs folder under sdk/native to Android Studio under app/src/main , and rename libs to jniLibs ,

Opencv libs

3, use opencv library

to use opencv, first you need to modify your Activity xml file . example activity_main.xml

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<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:opencv="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
    <org.opencv.android.JavaCameraView
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:visibility="gone"
        android:id="@+id/tutorial1_activity_java_surface_view"
        opencv:show_fps="true"
        opencv:camera_id="any" />
</FrameLayout>

then modify your activity , load the libopencv_java3.so , in here , Note: for OpenCV version 3 at this step you should instead load the library opencv_java3. OpenCV version 2, you should load the opencv_java

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package com.example.huanjulu.opencvinandroidexample;
import org.opencv.android.BaseLoaderCallback;
import org.opencv.android.CameraBridgeViewBase.CvCameraViewFrame;
import org.opencv.android.LoaderCallbackInterface;
import org.opencv.android.OpenCVLoader;
import org.opencv.core.Mat;
import org.opencv.android.CameraBridgeViewBase;
import org.opencv.android.CameraBridgeViewBase.CvCameraViewListener2;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.MenuItem;
import android.view.SurfaceView;
import android.view.WindowManager;
public class MainActivity extends Activity implements CvCameraViewListener2 {
    private static final String TAG = "OCVSample::Activity";
    private CameraBridgeViewBase mOpenCvCameraView;
    private boolean mIsJavaCamera = true;
    private MenuItem mItemSwitchCamera = null;
    private BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {
        @Override
        public void onManagerConnected(int status) {
            switch (status) {
                case LoaderCallbackInterface.SUCCESS: {
                    Log.i(TAG, "OpenCV loaded successfully");
                    mOpenCvCameraView.enableView();
                }
                break;
                default: {
                    super.onManagerConnected(status);
                }
                break;
            }
        }
    };
    static {
        System.loadLibrary("opencv_java3");
    }
    /**
     * Called when the activity is first created.
     */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        Log.i(TAG, "called onCreate");
        super.onCreate(savedInstanceState);
        getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
        setContentView(R.layout.activity_main);
        mOpenCvCameraView = (CameraBridgeViewBase) findViewById(R.id.tutorial1_activity_java_surface_view);
        mOpenCvCameraView.setVisibility(SurfaceView.VISIBLE);
        mOpenCvCameraView.setCvCameraViewListener(this);
    }
    @Override
    public void onPause() {
        super.onPause();
        if (mOpenCvCameraView != null)
            mOpenCvCameraView.disableView();
    }
    @Override
    public void onResume() {
        super.onResume();
        if (!OpenCVLoader.initDebug()) {
            Log.d(TAG, "Internal OpenCV library not found. Using OpenCV Manager for initialization");
            OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_3_0_0, this, mLoaderCallback);
        } else {
            Log.d(TAG, "OpenCV library found inside package. Using it!");
            mLoaderCallback.onManagerConnected(LoaderCallbackInterface.SUCCESS);
        }
    }
    public void onDestroy() {
        super.onDestroy();
        if (mOpenCvCameraView != null)
            mOpenCvCameraView.disableView();
    }
    public void onCameraViewStarted(int width, int height) {
    }
    public void onCameraViewStopped() {
    }
    public Mat onCameraFrame(CvCameraViewFrame inputFrame) {
        return inputFrame.rgba();
    }
}

You can create the Main Activity copying the above code.

First you would like notice is that MainActivity implements CvCameraViewListener2 interface , this interface woulf enfore us to implement few methods which are related to the camera

then 

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public Mat onCameraFrame(CvCameraViewFrame inputFrame) {
        return inputFrame.rgba();
    }

这个是你使用opencv Java code 很重要的一个方法, 它接受相机的每帧原始数据, 并且你可以在这个方法内做所有的图片片处理工作, 它返回 Mat 作为相机要接受的帧数据.

it is the best importment method for you use opencv , this will receiver the vedio as frames and you can do all the image processing inside this method and return a Mat thie this image :)

dont forget the permission of camera in your AndroidMainfest.xml 

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<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.huanjulu.opencvinandroidexample">
    <supports-screens android:resizeable="true"
        android:smallScreens="true"
        android:normalScreens="true"
        android:largeScreens="true"
        android:anyDensity="true" />
    <uses-sdk android:minSdkVersion="8" />
    <uses-permission android:name="android.permission.CAMERA"/>
    <uses-feature android:name="android.hardware.camera" android:required="false"/>
    <uses-feature android:name="android.hardware.camera.autofocus" android:required="false"/>
    <uses-feature android:name="android.hardware.camera.front" android:required="false"/>
    <uses-feature android:name="android.hardware.camera.front.autofocus" android:required="false"/>
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

when open this application , if you get the follow prompt :

It seems that you device does not support camera (or it is locked ). Application will be closed.

at this moment , you need manually turn on the camera Permission in device settting

okay ,then yon can enjoy it