Android：在服务中使用 OpenCV VideoCapture

Posted 2023-04-17

【中文标题】Android：在服务中使用 OpenCV VideoCapture

【英文标题】：Android: using OpenCV VideoCapture in service

【发布时间】：2013-10-27 00:57:38

【问题描述】：

我正在使用在 android 设备启动时启动的服务。这是因为我不需要可见的活动。到目前为止工作正常。但现在我正在尝试打开相机（在 MyService.onStart 中）并进行一些基本的图像处理。我知道默认的 Android 相机类需要一个用于视频预览的表面。这就是我想使用 OpenCV 的 VideoCapture 的原因。

但我收到此错误：

没有找到原生的实现 lorg/opencv/highgui/VideoCapture;.n_VideoCapture:(I)J

我想知道这是否是因为我没有使用主 Activity 的 OpenCV 示例中使用的以下行。问题是，如何将它集成到我的服务中，以及何时初始化 VideoCapture 成员。

OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_2_4_5, this, mLoaderCallback);

到目前为止，这是我的代码。大部分OpenCV代码取自OpenCV的NativeCameraView和CameraBridgeViewBase

package com.example.boot;

import org.opencv.android.Utils;
import org.opencv.core.Mat;
import org.opencv.core.Size;
import org.opencv.highgui.Highgui;
import org.opencv.highgui.VideoCapture;

import android.app.Service;
import android.content.Intent;
import android.graphics.Bitmap;
import android.os.IBinder;
import android.util.Log;
import android.widget.Toast;

public final class MyService extends Service

    private static final String TAG = "MyService";
    private boolean mStopThread;
    private Thread mThread;
    private VideoCapture mCamera;
    private int mFrameWidth;
    private int mFrameHeight;
    private int mCameraIndex = -1;
    private Bitmap mCacheBitmap;

    @Override
    public IBinder onBind(Intent intent) 
        return null;
    

    public void onDestroy() 

        this.disconnectCamera();

        Toast.makeText(this, "service stopped", Toast.LENGTH_LONG).show();
        Log.d(TAG, "onDestroy");
    

    @Override
    public void onStart(Intent intent, int startid)
               
        Log.d(TAG, "service.onStart: begin");

        try
        
            if (!connectCamera(640, 480))
                Log.e(TAG, "Could not connect camera");
            else
                Log.d(TAG, "Camera successfully connected");
        
        catch(Exception e)
        
            Log.e(TAG, "MyServer.connectCamera throws an exception: " + e.getMessage());
        

        Toast.makeText(this, "service started", Toast.LENGTH_LONG).show();
        Log.d(TAG, "service.onStart: end");
    

    private boolean connectCamera(int width, int height) 
        /* First step - initialize camera connection */
        if (!initializeCamera(width, height))
            return false;

        /* now we can start update thread */
        mThread = new Thread(new CameraWorker());
        mThread.start();

        return true;
    

    private boolean initializeCamera(int width, int height) 
        synchronized (this) 

            if (mCameraIndex == -1)
                mCamera = new VideoCapture(Highgui.CV_CAP_ANDROID);
            else
                mCamera = new VideoCapture(Highgui.CV_CAP_ANDROID + mCameraIndex);

            if (mCamera == null)
                return false;

            if (mCamera.isOpened() == false)
                return false;

            //java.util.List<Size> sizes = mCamera.getSupportedPreviewSizes();

            /* Select the size that fits surface considering maximum size allowed */
            Size frameSize = new Size(width, height);

            mFrameWidth = (int)frameSize.width;
            mFrameHeight = (int)frameSize.height;

            AllocateCache();

            mCamera.set(Highgui.CV_CAP_PROP_FRAME_WIDTH, frameSize.width);
            mCamera.set(Highgui.CV_CAP_PROP_FRAME_HEIGHT, frameSize.height);
        

        Log.i(TAG, "Selected camera frame size = (" + mFrameWidth + ", " + mFrameHeight + ")");

        return true;
    

    protected void AllocateCache()
    
        mCacheBitmap = Bitmap.createBitmap(mFrameWidth, mFrameHeight, Bitmap.Config.ARGB_8888);
    

    private void releaseCamera() 
        synchronized (this) 
            if (mCamera != null) 
                mCamera.release();
            
        
    

    private void disconnectCamera() 
        /* 1. We need to stop thread which updating the frames
         * 2. Stop camera and release it
         */
        try 
            mStopThread = true;
            mThread.join();
         catch (InterruptedException e) 
            e.printStackTrace();
         finally 
            mThread =  null;
            mStopThread = false;
        

        /* Now release camera */
        releaseCamera();
    

    protected void deliverAndDrawFrame(NativeCameraFrame frame) 
    
        Mat modified = frame.rgba();

        boolean bmpValid = true;
        if (modified != null) 
            try 
                Utils.matToBitmap(modified, mCacheBitmap);
             catch(Exception e) 
                Log.e(TAG, "Mat type: " + modified);
                Log.e(TAG, "Bitmap type: " + mCacheBitmap.getWidth() + "*" + mCacheBitmap.getHeight());
                Log.e(TAG, "Utils.matToBitmap() throws an exception: " + e.getMessage());
                bmpValid = false;
            
        
        

    private class NativeCameraFrame 
    
        public Mat rgba() 
            mCapture.retrieve(mRgba, Highgui.CV_CAP_ANDROID_COLOR_FRAME_RGBA);
            return mRgba;
        

        public Mat gray() 
            mCapture.retrieve(mGray, Highgui.CV_CAP_ANDROID_GREY_FRAME);
            return mGray;
        

        public NativeCameraFrame(VideoCapture capture) 
            mCapture = capture;
            mGray = new Mat();
            mRgba = new Mat();
        

        private VideoCapture mCapture;
        private Mat mRgba;
        private Mat mGray;
    ;

    private class CameraWorker implements Runnable 
    
        public void run() 
        
            do 
            
                if (!mCamera.grab()) 
                    Log.e(TAG, "Camera frame grab failed");
                    break;
                

                deliverAndDrawFrame(new NativeCameraFrame(mCamera));

             while (!mStopThread);
        
    

【参考方案1】：

你提到的那行 (initAsync) 实际上是用来加载 OpenCV 管理器的。这应该是你做的第一件事，因此它可能应该放在onStart() 的开头。

【讨论】：

是的，我会试试的。我发现this article 也这么说。

也没有用。加载 OpenCV 以这种方式工作，但在内部 OpenCV 会引发无法连接到相机服务的异常。通过创建一个虚拟 EGL SurfaceTexture 并将该纹理设置为相机的预览，我最终在服务中使用了默认的 Android 相机实现。有关详细信息，请参阅this article。