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：

OpenCV移动端之android JNI_第1张图片

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：

OpenCV移动端之android JNI_第2张图片

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

OpenCV移动端之android JNI_第3张图片

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 /* Header for class xinyi61_opencvjni_OpencvJNI */#ifndef _Included_xinyi61_opencvjni_OpencvJNI#define _Included_xinyi61_opencvjni_OpencvJNI#ifdef __cplusplusextern "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 #include #include #include #include #include #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 __cplusplusextern "C" {#endifenum 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

OpenCV移动端之android JNI_第4张图片

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 $(CLEAR_VARS)OpenCV_INSTALL_MODULES := onOpenCV_CAMERA_MODULES := offOPENCV_LIB_TYPE :=STATICifeq ("$(wildcard $(OPENCV_MK_PATH))","")include $(LOCAL_PATH)/native/jni/OpenCV.mkelseinclude $(OPENCV_MK_PATH)endifLOCAL_MODULE := opencv_worldLOCAL_SRC_FILES := xinyi61_opencvjni_OpencvJNI.cppLOCAL_LDLIBS +=  -lm -lloginclude $(BUILD_SHARED_LIBRARY)

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

APP_STL := gnustl_staticAPP_CPPFLAGS := -frtti -fexceptionsAPP_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"?>

OpenCV移动端之android JNI_第5张图片
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"?>

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：

OpenCV移动端之android JNI_第6张图片

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

Android JNI和NDK学习(02)--静态方式实现JNI

Android JNI和NDK学习(03)--动态方式实现JNI

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