Android OpenCV 相机示例只是显示黑屏

Question

Android OpenCV 相机示例只是显示黑屏

Mar*_*ayo 6 java android opencv javacameraview

我花了几天（好吧，晚上）试图解决这个问题。网上有很多例子是针对不同版本的 Android Studio、不同版本的 Android、不同版本的 OpenCV，我无法让它们中的任何一个进入最终的“工作”阶段。

这个例子（基于youtube 教程，我到了需要权限的地步。没关系，我添加了它并检查它们，它会弹出询问用户相机权限。但屏幕保持空白。我已经进行了 logcat 调试，似乎所有正确的方法都被调用了。希望得到任何帮助。

代码：

Manifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.mytestopencvapp" >

    <uses-permission android:name="android.permission.CAMERA"/>


    <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>

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主活动.java

package com.example.mytestopencvapp;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;

import android.Manifest;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.util.Log;
import android.view.SurfaceView;

import org.opencv.android.BaseLoaderCallback;
import org.opencv.android.CameraBridgeViewBase;
import org.opencv.android.JavaCamera2View;
import org.opencv.android.JavaCameraView;
import org.opencv.android.OpenCVLoader;
import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.imgproc.Imgproc;

public class MainActivity extends AppCompatActivity implements CameraBridgeViewBase.CvCameraViewListener2 {

    private static String TAG = "MainActivity";

    JavaCameraView javaCameraView;
    Mat mRGBA, mRGBAT;

    private final int PERMISSIONS_READ_CAMERA=1;

    BaseLoaderCallback baseLoaderCallback = new BaseLoaderCallback(MainActivity.this) {
        @Override
        public void onManagerConnected(int status) {
            Log.d(TAG, "callbacksuccess");
            switch (status)
            {
                case BaseLoaderCallback.SUCCESS:
                {
                    Log.d(TAG, "case success");
                    javaCameraView.enableView();
                    break;
                }
                default:
                {
                    Log.d(TAG, "case default");
                    super.onManagerConnected(status);
                    break;
                }

            }

        }
    };

    static
    {
        if (OpenCVLoader.initDebug())
        {
            Log.d(TAG, "OpenCV is intialised");
        }
        else
        {
            Log.d(TAG, "OpenCV is not initialised");
        }
    }


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d(TAG, "onCreate");
        setContentView(R.layout.activity_main);
        javaCameraView = (JavaCameraView)findViewById(R.id.my_camera_view);
        javaCameraView.setVisibility(SurfaceView.VISIBLE);
        javaCameraView.setCvCameraViewListener(MainActivity.this);

// Here, thisActivity is the current activity
        if (ContextCompat.checkSelfPermission(this,
                Manifest.permission.CAMERA)
                != PackageManager.PERMISSION_GRANTED) {

            // Permission is not granted
            // Should we show an explanation?
            if (ActivityCompat.shouldShowRequestPermissionRationale(this,
                    Manifest.permission.CAMERA)) {
                // Show an explanation to the user *asynchronously* -- don't block
                // this thread waiting for the user's response! After the user
                // sees the explanation, try again to request the permission.
            } else {
                // No explanation needed, we can request the permission.
                ActivityCompat.requestPermissions(this,
                        new String[]{Manifest.permission.CAMERA},
                PERMISSIONS_READ_CAMERA);

                // MY_PERMISSIONS_REQUEST_READ_CONTACTS is an
                // app-defined int constant. The callback method gets the
                // result of the request.
            }
        } else {
            Log.d(TAG, "PERMISSIOns granted");
            // Permission has already been granted
        }


    }

    @Override
    public void onCameraViewStarted(int width, int height) {
        Log.d(TAG, "onCameraViewStarted");
        mRGBA = new Mat(height, width, CvType.CV_8UC4);
    }

    @Override
    public void onCameraViewStopped() {
        Log.d(TAG, "onCameraViewStopped");
        mRGBA.release();
    }

    @Override
    public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame)
    {
        Log.d(TAG, "onCameraFrame");
/*        mRGBA = inputFrame.rgba();
        mRGBAT = mRGBA.t();
        Core.flip(mRGBA.t(), mRGBAT, 1);
        Imgproc.resize(mRGBAT, mRGBAT, mRGBA.size());
        return mRGBAT;*/

        mRGBA = inputFrame.rgba();
        Core.transpose(mRGBA, mRGBAT);
        Imgproc.resize(mRGBAT, mRGBAT, mRGBAT.size(),0,0,0);
        Core.flip(mRGBA.t(), mRGBA, 1);
        return mRGBA;
    }


    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "onDestroy");
        if (javaCameraView != null)
        {
            javaCameraView.disableView();
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        Log.d(TAG, "onPause");
        if (javaCameraView != null)
        {
            javaCameraView.disableView();
        }

    }

    @Override
    protected void onResume() {
        super.onResume();
        Log.d(TAG, "onResume");
        if (OpenCVLoader.initDebug())
        {
            Log.d(TAG, "OpenCV is intialised again");
            baseLoaderCallback.onManagerConnected((BaseLoaderCallback.SUCCESS));
        }
        else
        {
            Log.d(TAG, "OpenCV is not working");
            OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION, this, baseLoaderCallback);
        }
    }
}

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而我的 res 布局 activity_main.xml 文件：

<?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">

    <org.opencv.android.JavaCameraView
        android:id="@+id/my_camera_view"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        />


</RelativeLayout>

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据我所知，我已经正确链接了它们，我可以确认 OpenCV 初始化，检查并授予权限，但是……JavaCameraView 只是黑色的。

Answer 1

Jan*_*nik 10

您需要告诉CameraView相机权限已被授予。您可以通过调用该setCameraPermissionGranted()函数来完成此操作。此函数调用应进入onCreate方法中的“已授予权限”块，如下所示：

if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA)
        != PackageManager.PERMISSION_GRANTED) {
    // More code here ...
} else {
    Log.d(TAG, "Permissions granted");
    javaCameraView.setCameraPermissionGranted();
}

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此外，您可能希望在onRequestPermissionsResult()尚未授予权限的情况下调用此函数。该onRequestPermissionsResult()函数位于您的Activity班级中。当用户授予或拒绝应用程序发出的权限请求时调用它。这可能如下所示：

@Override
public void onRequestPermissionsResult(
        int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {

    // Ensure that this result is for the camera permission request
    if (requestCode == PERMISSIONS_READ_CAMERA) {
        // Check if the request was granted or denied
        if (grantResults.length > 0
                && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
            // The request was granted -> tell the camera view
            javaCameraView.setCameraPermissionGranted();
        } else {
            // The request was denied -> tell the user and exit the application
            Toast.makeText(this, "Camera permission required.",
                    Toast.LENGTH_LONG).show();
            this.finish();
        }
    } else {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    }
}

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有关 Android 上的权限系统的更多信息，请查看以下资源：

请求应用程序权限该站点描述了请求权限的过程以及所有必要的步骤。
权限概述uses-feature该站点在清单文件中提供了相关信息。您可能需要将以下行添加到清单文件中：<uses-feature android:name="android.hardware.camera" android:required="true" />以防止在没有摄像头的设备上安装。

现在您将看到，onCameraFrame回调函数实际上被调用了。这会导致一个NullPointerException因为mRGBAT没有初始化。要仅查看相机图像，您可以inputFrame.rgba()直接在此函数中返回。这至少会显示相机图像。所有进一步的步骤都是正常的图像处理以旋转/镜像图像。

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