OpenCV移动端之android JNI

        OpenCV强大的图像处理被广泛应用与各行各业，如何将其部署到不同的平台是每个OpenCV开发人员必须面对解决的。对于OpenCV开发，很多选择C++实现基本的算法，而如何将算法应用到IOS、Android或嵌入式设备上却 是一个问题，这节将讲解OpenCV 在Android上的部署，这里选择在Android Studio上开发Android应用程序。

1.首先在Opencv官网下载Android SDK，这里选中最新的opencv-3.4.1-android-sdk.zip下载 ，解压得到OpenCV-android-sdk。

2.启动Android-stiudio（本人安装的是AS 3.1版本），新建一个Android项目，Application name填OpencvJNI,Company domaint填xinyi61，Package name者为xinyi61.opencvjni,并且选上Include C++ support，最终效果如下：

3.选中app/src/main右键 New->Folder->JNI Folder,这将在main下面创建一个jni的目录，将1解压文件夹下OpenCV-android-sdk/sdk下的native目录整个拷贝到jni目录下，此时jni目录展开如下：

4. 选中app/src/main/java/xinyi61.opencvjni 右键New->Java Class，新建一个OpencvJNI的java类，OpencvJNI如下所示

public class OpencvJNI {
    static {
        System.loadLibrary("imgproc");
    }

    public int api_method;
    public int img_width;
    public int img_height;
    public int retval;
    public int [] srcbuf;
    public int [] dstbuf;
    public int [] outmuf;
    public int [] inmask;
    public double clarityVal;
    public String version;

    public static native Object jniApiMethod(Object param);
}

5.编写带有native声明的方法的java类，使用 javac 命令编译所编写的java类。点击Build->Make Project,完成后会在app/build/intermediates/classes/debug/xinyi61/opencvjni下生成一个OpencvJNI.class,如下所示

6.使用 “ javah -jni java类名”  生成扩展名为h的头文件，使用C/C++实现本地方法。打开Android Studio的Terminal，cd 到app/src/main/jni目录下，输入

javah -jni -classpath ../../../build/intermediates/classes/debug xinyi61.opencvjni.OpencvJNI

自动生成头文件，查看jni下生成的头文件xinyi61_opencvjni_OpencvJNI.h，

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class xinyi61_opencvjni_OpencvJNI */

#ifndef _Included_xinyi61_opencvjni_OpencvJNI
#define _Included_xinyi61_opencvjni_OpencvJNI
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     xinyi61_opencvjni_OpencvJNI
 * Method:    jniMethod
 * Signature: (Ljava/lang/Object;)Ljava/lang/Object;
 */
JNIEXPORT jobject JNICALL Java_xinyi61_opencvjni_OpencvJNI_jniMethod
  (JNIEnv *, jclass, jobject);

#ifdef __cplusplus
}
#endif
#endif

选中jni右键New->C/C++ Source FIle 命名为xinyi61_opencvjni_OpencvJNI，作为对应的java类的JNI实现源文件，其中需要访问java中定义的类对象的实例，则由以下几步完成

1.通过GetObjectClass()函数获得该对象的类class，返回值是一个jclass；
2.调用GetFieldID函数得到需要访问的实例域（变量）在该c类中id
3.调用Get【Type】Field()得到访问的变量值。其中【Type】对应变量的类型。

最终实现为：

//
// Created by Administrator on 2018/7/3/003.
//
#include <jni.h>
#include <stdio.h>
#include <stdlib.h>
#include <string>
#include <iostream>
#include <android/log.h>
#include "opencv2/opencv.hpp"
#include "xinyi61_opencvjni_OpencvJNI.h"

#define   LOG_TAG    "MYJNI"
#define   LOGI(...)  __android_log_print(ANDROID_LOG_INFO, LOG_TAG, __VA_ARGS__)
#define   LOGE(...)  __android_log_print(ANDROID_LOG_ERROR, LOG_TAG, __VA_ARGS__)

#ifdef __cplusplus
extern "C" {
#endif

enum JNI_API__METHOD
{
    JNI_API_METHOD_GETVERSION=0,        /*get build version and time*/
    JNI_API_METHOD_IM2GRAY,             /* convert image to gray*/
    JNI_API_METHOD_INPAINT,             /* image restore */
    JNI_API_METHOD_AUTOCOMPLATE,        /* image auto restore */
    JNI_API_METHOD_AUTOWHITEBALANCE,    /* image auto white balance */
    JNI_API_METHOD_AUTOWHITEBACKGROUND, /* replace background with white */
    JNI_API_METHOD_ADJUSTIMAGECLARITY,  /* adjust image clarity*/
    JNI_API_METHOD_INTERACTIVEMATTING,   /* interactivate matting */
    JNI_API_METHOD_END = JNI_API_METHOD_INTERACTIVEMATTING
};

JNIEXPORT jobject JNICALL Java_bc_imgproc_jniapi_jniApiMethod
        (JNIEnv *env, jclass jcls, jobject jobj)
{
   jclass jclsinput = env->GetObjectClass(jobj);

    if (jclsinput == NULL)
    {
        return env->NewStringUTF("can not find class");
    }

    /* get jobj property id */
    jfieldID jfdmethod     = env->GetFieldID(jclsinput, "api_method", "I");
    jfieldID jfdimgwidth   = env->GetFieldID(jclsinput, "img_width", "I");
    jfieldID jfdimgheight  = env->GetFieldID(jclsinput, "img_height", "I");
    jfieldID jfdcallret    = env->GetFieldID(jclsinput, "retval", "I");
    jfieldID jfdsrc        = env->GetFieldID(jclsinput, "srcbuf", "[I");
    jfieldID jfddst        = env->GetFieldID(jclsinput, "dstbuf", "[I");
    jfieldID jfdinmask     = env->GetFieldID(jclsinput, "inmask", "[I");
    jfieldID jfdversion    = env->GetFieldID(jclsinput, "version", "Ljava/lang/String;");
    jfieldID jfdclarityVal = env->GetFieldID(jclsinput, "clarityVal", "D");
    /* create new object for return */
    jobject jobjret = env->AllocObject(jclsinput);
    /* get property value,get jni method */
    int japi_call_method = env->GetIntField(jobj, jfdmethod);
    LOGI("japi_call_method:%d", japi_call_method);
    if ((japi_call_method < JNIAPI_METHOD_VERSION) || (japi_call_method > JNIAPI_METHOD_END))
    {
        LOGE("RET_ERROR_JNI_METHOD_ISNOT_SURPPORT:%x", RET_ERROR_JNI_METHOD_ISNOT_SURPPORT);
        env->SetIntField(jobjret, jfdcallret, RET_ERROR_JNI_METHOD_ISNOT_SURPPORT);
        return jobjret;
    }

    if (japi_call_method == JNIAPI_METHOD_VERSION)
    {
        char buf[40];
        sprintf(buf, "V:%s Build Time:%s-%s", CV_VERSION, __DATE__, __TIME__);
        std::string version = buf;
        jstring     jstr    = env->NewStringUTF(version.c_str());
        if (jstr == NULL)
        {
            env->SetIntField(jobjret, jfdcallret, RET_FAILED);
            return jobjret;
        }

        env->SetObjectField(jobjret, jfdversion, jstr);
        env->SetIntField(jobjret, jfdcallret, RET_OK);
        return jobjret;
    }

    int ret = 0;
    /* get property value,img_width img_height */
    int w = env->GetIntField(jobj, jfdimgwidth);
    int h = env->GetIntField(jobj, jfdimgheight);
    if ((w < MINIMUM_IMAGE_WIDTH) || (h < MINIMUM_IMAGE_HEIGHT))
    {
        env->SetIntField(jobjret, jfdcallret, RET_ERROR_IAMGE_ISNOT_SURPPORT);
        return jobjret;
    }

    LOGI("00japi_call_method:%d", japi_call_method);
    jintArray jint_bufsrc = (jintArray)env->GetObjectField(jobj, jfdsrc);
    /* get srcbuf length */
    jsize len = env->GetArrayLength(jint_bufsrc);
    if (len <= 0)
    {
        env->SetIntField(jobjret, jfdcallret, RET_ERROR_IAMGE_LEN_ERROR);
        return jobjret;
    }

    /* get point to array object */
    jint    *bufsrc = env->GetIntArrayElements(jint_bufsrc, NULL);
    cv::Mat srcimg(h, w, CV_8UC4, (unsigned char *)bufsrc);
    cv::cvtColor(srcimg, srcimg, cv::COLOR_RGBA2BGR);
	cv::Size sz = srcimg.size();
    //cv::imwrite("/storage/emulated/0/imsrc.jpg", srcimg);
    LOGI("01srcimg size:%d len:%d w:%d h:%d", srcimg.size().area(), len, w, h);

    bc_jniapi_method method = (bc_jniapi_method)japi_call_method;
    bc_jniapi_in     inparam;
    inparam.srcimg = srcimg;
    bc_jniapi_out outparam;
    switch (japi_call_method)
    {
    case JNIAPI_METHOD_WHITEBALANCE:
        break;

    case JNIAPI_METHOD_INPAINT:
       {
           jintArray jint_bufinmask = (jintArray)env->GetObjectField(jobj, jfdinmask);
           jint      *bufinmask     = env->GetIntArrayElements(jint_bufinmask, NULL);
           inparam.maskimg = cv::Mat(h, w, CV_8UC1, (unsigned char *)bufinmask);
           break;
       }
    }

    LOGI("02bc_algorithm_api call:%d", japi_call_method);
    ret = bc_algorithm_api(method, &inparam, &outparam);
    LOGI("111bc_algorithm_api call end ret:%d result mat:%zu %d", ret, outparam.dstimg.size(), outparam.dstimg[0].channels());
    /* new an jintArray object */
    jintArray retdst = env->NewIntArray(outparam.dstimg.size() * w * h);
    if (retdst == NULL)
    {
        env->SetIntField(jobjret, jfdcallret, RET_MALLOC_MEMORY_ERROR);
        return jobjret;
    }

    LOGI("03bc_algorithm_api call:%d", japi_call_method);
    jint *dbuf = env->GetIntArrayElements(retdst, NULL);
    for (int i = 0; i < outparam.dstimg.size(); ++i)
    {
        cv::cvtColor(outparam.dstimg[i], outparam.dstimg[i], cv::COLOR_BGR2RGBA);
		cv::resize(outparam.dstimg[i],outparam.dstimg[i], sz, cv::INTER_AREA);
        //char buf[60];
        //sprintf(buf, "/storage/emulated/0/imresut_%d.jpg", i);
        //LOGI("return result mat rows:%d cols:%d channels:%d",
        //     outparam.dstimg[i].rows, outparam.dstimg[i].cols, outparam.dstimg[i].channels());
        //cv::imwrite(buf, outparam.dstimg[i]);
		env->SetIntArrayRegion(retdst, i * w * h,  w * h, (int *)outparam.dstimg[i].data);
    }
	
    env->SetObjectField(jobjret, jfddst, retdst);
    env->SetIntField(jobjret, jfdcallret, ret);
    env->ReleaseIntArrayElements(jint_bufsrc, bufsrc, 0);
    env->ReleaseIntArrayElements(retdst, dbuf, 0);

    LOGI("0000000api_call_method call end with ret:%d", ret);
    return jobjret;
}


#ifdef __cplusplus
}
#endif

其中java数据类型和c数据类型关系如下表所示

7. 将C/C++编写的文件生成动态连接库。选中jni右键New->File 建立jni的Android.mk，

LOCAL_PATH:=$(call my-dir)

include $(CLEAR_VARS)
OpenCV_INSTALL_MODULES := on
OpenCV_CAMERA_MODULES := off
OPENCV_LIB_TYPE :=STATIC

ifeq ("$(wildcard $(OPENCV_MK_PATH))","")
include $(LOCAL_PATH)/native/jni/OpenCV.mk
else
include $(OPENCV_MK_PATH)
endif
LOCAL_MODULE := opencv_world
LOCAL_SRC_FILES := xinyi61_opencvjni_OpencvJNI.cpp
LOCAL_LDLIBS +=  -lm -llog
include $(BUILD_SHARED_LIBRARY)

选中jni右键New->File 建立jni的Application.mk，

APP_STL := gnustl_static
APP_CPPFLAGS := -frtti -fexceptions
APP_PLATFORM := android-14

直接到Terminal下的jni目录运行ndk-build，此时就会在app/src/main/libs下生成各个平台的libopencv_world.so 。
libopencv_world.so 就可以拿来使用了。
这里简单写个demo程序进行验证，最后结果图如下所示：

 

8.修改app/src/main/res/layout/activity_main.xml,修改后为下

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">

        <TextView
        android:id="@+id/processTime"
        android:layout_width="fill_parent"
        android:layout_height="20dp"
        android:text="" />

    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal">

        <Button
            android:id="@+id/chooseImg"
            android:layout_width="187dp"
            android:layout_height="wrap_content"
            android:text="选图" />

        <Button
            android:id="@+id/processImg"
            android:layout_width="187dp"
            android:layout_height="wrap_content"
            android:text="处理" />
    </LinearLayout>

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_weight="1" />
    <TextView
        android:id="@+id/bccvVersion"
        android:layout_width="fill_parent"
        android:layout_height="20dp"
        android:text="" />
</LinearLayout>

9，选图按钮实现从手机中选中一副图片，这就需要给手机开权限，到app/src/main/res下修改AndroidManifest.xml,修改后的文件
如下，加粗体部分为添加的部分。

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="xinyi61.opencvjni">
       <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.VIBRATE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />
    <uses-permission android:name="android.permission.WRITE_CONTACTS" />
    <uses-permission android:name="android.permission.WRITE_SETTINGS" />
    <uses-permission android:name="android.permission.CHANGE_CONFIGURATION" />
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
    <uses-permission android:name="android.permission.MOUNT_FORMAT_FILESYSTEMS"/
    <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>
    <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>

10.编辑app/src/main/java/xinyi61.opencvjni/MainActivity下实现整个处理，

package xinyi61.opencvjni;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;
import android.content.Context;
import android.content.Intent;
import android.database.Cursor;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Bitmap.Config;
import android.net.Uri;
import android.provider.MediaStore;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.TextView;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
public class MainActivity extends AppCompatActivity {

    // Used to load the 'native-lib' library on application startup.
    static {
        System.loadLibrary("native-lib");
        System.loadLibrary("opencv_world");
    }

    private static final int IMAGE = 1;
    private TextView processTime;
    private TextView bccvVersion;
    private ImageView imageView;
    private Button btnChooseImg;
    private Bitmap yourSelectedImage = null;

    private Process myjni = new Process();
    private Process res = new Process();
    private static final String TAG = "bccv";
    Bitmap bm;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        processTime = (TextView) findViewById(R.id.processTime);
        bccvVersion = (TextView) findViewById(R.id.bccvVersion);
        imageView = (ImageView) findViewById(R.id.imageView);

        btnChooseImg = (Button) findViewById(R.id.chooseImg);
        btnChooseImg.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                switch (v.getId()) {
                    case R.id.chooseImg: {
                        Intent intent = new Intent(Intent.ACTION_PICK, null);
                        intent.setDataAndType(MediaStore.Images.Media.EXTERNAL_CONTENT_URI,"image/*");
                        startActivityForResult(intent, 0x1);
                        break;
                    }
                }
            }
        });

        Button processImg = (Button) findViewById(R.id.processImg);
        processImg.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                switch (v.getId()) {
                    case R.id.processImg: {
                        imageView.setDrawingCacheEnabled(true);
                        //Bitmap bitmap = imageView.getDrawingCache();
                        int w = bm.getWidth();
                        int h = bm.getHeight();
                        int[] pix = new int[w * h];
                        bm.getPixels(pix, 0, w, 0, 0, w, h);
                        long start_time = System.currentTimeMillis();
                        /* call jni api */
                        myjni.api_method =7;
                        myjni.srcbuf = new int[w * h];
                        bm.getPixels(myjni.srcbuf, 0, w, 0, 0, w, h);
                        myjni.img_width = w;
                        myjni.img_height = h;
                        Log.e(TAG, "111111111111111111a:" + myjni.api_method + " w:" + w + " h:" + h);
                        //res = (Process)myjni.jniApiMethod(myjni);
                        res =(Process)com.example.imageproc.Process.jniApiMethod(myjni);
                        if (myjni.api_method == 0)
                        {
                            bccvVersion.setText(res.version);
                            break;
                        }
                        else
                        {
                            Bitmap bm = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888);
                            bm.setPixels(res.dstbuf, 0, w, 0, 0, w, h);
                            long end_time = System.currentTimeMillis();
                            long procss_time = end_time - start_time;

                            imageView.setImageBitmap(bm);
                            imageView.setDrawingCacheEnabled(false);
                            Log.e(TAG, "process time:" + procss_time);
                            processTime.setText("w:" + w + " h:" + h + " ProcessTime:" + procss_time + "ms");
                            bccvVersion.setText(res.version);
                            break;
                        }
                    }
                }
            }
        });
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        /* get image path */
        if (requestCode == IMAGE && resultCode == RESULT_OK && data != null) {
            Uri selectedImage = data.getData();
            String[] filePathColumns = {MediaStore.Images.Media.DATA};
            Cursor c = getContentResolver().query(selectedImage, filePathColumns, null, null, null);
            c.moveToFirst();
            int columnIndex = c.getColumnIndex(filePathColumns[0]);
            String imagePath = c.getString(columnIndex);
            showImage(imagePath);
            c.close();
        }
    }

    /* load image */
    private void showImage(String imaePath){
        bm = BitmapFactory.decodeFile(imaePath);
        ((ImageView)findViewById(R.id.imageView)).setImageBitmap(bm);
    }
}

最终运行效果图如下：

备注：第一次接触Android平台，都是各种baidu完成的，很多Java上的术语不知道怎么说，只能以记流水的形式记录下整个实现过程，以备后期参考，各位看官勿喷。

感谢以下小伙伴的精华帖，

点击打开链接Android JNI 传递对象

JNI层与Java层结构体传递

Java中JNI的使用详解第五篇:C/C++中操作Java中的数组

Java与c++通过JNI的完美结合

Jni函数调用

[JNI]开发之旅