OpenCV4 调用摄像头黑屏问题
OpenCV 调用 Android 摄像头这一块，我之前研究了好几天，都是一片黑，毫无头绪。后来发现 OpenCV4 要想调用摄像头，必须继承自 OpenCV 的 CameraActivity ！！！
CameraActivity.java 的源码如下，可以看出大部分代码都是为了 Android M（6.0）以上请求权限而生的，只有两个地方非常关键
-
protected List<? extends CameraBridgeViewBase> getCameraViewList() { …… }
子 Activity 在继承 CameraActivity 后，需要复写该函数，把 JavaCamera2View 或 JavaCameraView 送入 List 作为返回值。
-
cameraBridgeViewBase.setCameraPermissionGranted()
相机视图初始情况下是黑屏的，即不工作状态。只有当权限授予完毕，调用了 setCameraPermissionGranted 之后，OpenCV 才开始调用相机并把数据输出到 SurfaceView 上。
public class CameraActivity extends Activity {
private static final int CAMERA_PERMISSION_REQUEST_CODE = 200;
protected List<? extends CameraBridgeViewBase> getCameraViewList() {
return new ArrayList<CameraBridgeViewBase>();
}
protected void onCameraPermissionGranted() {
List<? extends CameraBridgeViewBase> cameraViews = getCameraViewList();
if (cameraViews == null) {
return;
}
for (CameraBridgeViewBase cameraBridgeViewBase: cameraViews) {
if (cameraBridgeViewBase != null) {
cameraBridgeViewBase.setCameraPermissionGranted();
}
}
}
@Override
protected void onStart() {
super.onStart();
boolean havePermission = true;
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (checkSelfPermission(CAMERA) != PackageManager.PERMISSION_GRANTED) {
requestPermissions(new String[]{CAMERA}, CAMERA_PERMISSION_REQUEST_CODE);
havePermission = false;
}
}
if (havePermission) {
onCameraPermissionGranted();
}
}
@Override
@TargetApi(Build.VERSION_CODES.M)
public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
if (requestCode == CAMERA_PERMISSION_REQUEST_CODE && grantResults.length > 0
&& grantResults[0] == PackageManager.PERMISSION_GRANTED) {
onCameraPermissionGranted();
}
super.onRequestPermissionsResult(requestCode, permissions, grantResults);
}
}
实现要领
- 首先，要继承 CameraActivity，之前已经说过了。这个基类会去申请权限，然后通知 javaCameraView 已获取到权限，可以正常使用。
- 复写父类的 getCameraViewList 方法，将 javaCameraView 回送回去，这样当权限已被赋予时，就可以通知到预览界面开始正常工作了。
- OpenCV 已经为我们实现了 Camera 和 Camera2 的函数，如果应用最低版本 minSdkVersion > 5.0，建议使用 JavaCamera2View 的相关函数，否则使用 JavaCameraView。
- 在 onResume 时判断 opencv 库是否加载完毕，然后启用预览视图。在 onPause 时由于界面被遮挡，此时应该暂停摄像头的预览以节省手机性能和电量损耗。
- 切换前后摄像头时，要先禁用，设置完后启用才会生效。
- Camera2 和 Camera 的绝大部分差异 OpenCV 均已经为我们屏蔽在类的内部了，唯一的差别就是两者实现的 CvCameraViewListener 监听器里的预览函数 onCameraFrame 的参数略有不同。从下面的源码可以看出 CvCameraViewListener2 的 inputFrame 由 Mat 类型改为了 CvCameraViewFrame 类型，它额外提供了一个转化为灰度图的接口。
CvCameraViewListener
public interface CvCameraViewListener {
/**
* This method is invoked when camera preview has started. After this method is invoked
* the frames will start to be delivered to client via the onCameraFrame() callback.
* @param width - the width of the frames that will be delivered
* @param height - the height of the frames that will be delivered
*/
public void onCameraViewStarted(int width, int height);
/**
* This method is invoked when camera preview has been stopped for some reason.
* No frames will be delivered via onCameraFrame() callback after this method is called.
*/
public void onCameraViewStopped();
/**
* This method is invoked when delivery of the frame needs to be done.
* The returned values - is a modified frame which needs to be displayed on the screen.
* TODO: pass the parameters specifying the format of the frame (BPP, YUV or RGB and etc)
*/
public Mat onCameraFrame(Mat inputFrame);
}
CvCameraViewListener2
public interface CvCameraViewListener2 {
/**
* This method is invoked when camera preview has started. After this method is invoked
* the frames will start to be delivered to client via the onCameraFrame() callback.
* @param width - the width of the frames that will be delivered
* @param height - the height of the frames that will be delivered
*/
public void onCameraViewStarted(int width, int height);
/**
* This method is invoked when camera preview has been stopped for some reason.
* No frames will be delivered via onCameraFrame() callback after this method is called.
*/
public void onCameraViewStopped();
/**
* This method is invoked when delivery of the frame needs to be done.
* The returned values - is a modified frame which needs to be displayed on the screen.
* TODO: pass the parameters specifying the format of the frame (BPP, YUV or RGB and etc)
*/
public Mat onCameraFrame(CvCameraViewFrame inputFrame);
};
/**
* This class interface is abstract representation of single frame from camera for onCameraFrame callback
* Attention: Do not use objects, that represents this interface out of onCameraFrame callback!
*/
public interface CvCameraViewFrame {
/**
* This method returns RGBA Mat with frame
*/
public Mat rgba();
/**
* This method returns single channel gray scale Mat with frame
*/
public Mat gray();
};
示例程序
下面使用 Camera2 来实现拍照功能（ 注意：Camera2 只能用于 Android 5.0 以上的手机 ）
Java代码
public class OpencvCameraActivity extends CameraActivity {
private static final String TAG = "OpencvCam";
private JavaCamera2View javaCameraView;
private Button switchCameraBtn;
private int cameraId = JavaCamera2View.CAMERA_ID_ANY;
private CameraBridgeViewBase.CvCameraViewListener2 cvCameraViewListener2 = new CameraBridgeViewBase.CvCameraViewListener2() {
@Override
public void onCameraViewStarted(int width, int height) {
Log.i(TAG, "onCameraViewStarted width=" + width + ", height=" + height);
}
@Override
public void onCameraViewStopped() {
Log.i(TAG, "onCameraViewStopped");
}
@Override
public Mat onCameraFrame(CameraBridgeViewBase.CvCameraViewFrame inputFrame) {
return inputFrame.rgba();
}
}
private BaseLoaderCallback baseLoaderCallback = new BaseLoaderCallback(this) {
@Override
public void onManagerConnected(int status) {
Log.i(TAG, "onManagerConnected status=" + status + ", javaCameraView=" + javaCameraView);
switch (status) {
case LoaderCallbackInterface.SUCCESS: {
if (javaCameraView != null) {
javaCameraView.setCvCameraViewListener(cvCameraViewListener2);
// 禁用帧率显示
javaCameraView.disableFpsMeter();
javaCameraView.enableView();
}
}
break;
default:
super.onManagerConnected(status);
break;
}
}
};
//复写父类的 getCameraViewList 方法，把 javaCameraView 送到父 Activity，一旦权限被授予之后，javaCameraView 的 setCameraPermissionGranted 就会自动被调用。
@Override
protected List<? extends CameraBridgeViewBase> getCameraViewList() {
Log.i(TAG, "getCameraViewList");
List<CameraBridgeViewBase> list = new ArrayList<>();
list.add(javaCameraView);
return list;
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_camera);
findView();
setListener();
}
private void findView() {
javaCameraView = findViewById(R.id.javaCameraView);
switchCameraBtn = findViewById(R.id.switchCameraBtn);
}
private void setListener() {
switchCameraBtn.setOnClickListener(view -> {
switch (cameraId) {
case JavaCamera2View.CAMERA_ID_ANY:
case JavaCamera2View.CAMERA_ID_BACK:
cameraId = JavaCamera2View.CAMERA_ID_FRONT;
break;
case JavaCamera2View.CAMERA_ID_FRONT:
cameraId = JavaCamera2View.CAMERA_ID_BACK;
break;
}
Log.i(TAG, "cameraId : " + cameraId);
//切换前后摄像头，要先禁用，设置完再启用才会生效
javaCameraView.disableView();
javaCameraView.setCameraIndex(cameraId);
javaCameraView.enableView();
});
}
@Override
public void onPause() {
Log.i(TAG, "onPause");
super.onPause();
if (javaCameraView != null) {
javaCameraView.disableView();
}
}
@Override
public void onResume() {
Log.i(TAG, "onResume");
super.onResume();
if (OpenCVLoader.initDebug()) {
Log.i(TAG, "initDebug true");
baseLoaderCallback.onManagerConnected(LoaderCallbackInterface.SUCCESS);
} else {
Log.i(TAG, "initDebug false");
OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION, this, baseLoaderCallback);
}
}
}
布局文件
布局文件很简单，核心就是这个 JavaCamera2View 视图
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
<org.opencv.android.JavaCamera2View
android:id="@+id/javaCameraView"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:show_fps="true"
app:camera_id="any" />
<Button
android:id="@+id/switchCameraBtn"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="切换摄像头"
app:layout_constraintBottom_toBottomOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
全屏预览
虽然使用了上述方法，但相机的预览视图还是只占了屏幕的一小丢丢，而且还是头朝左的。
此时需要修改 OpenCV 的源码里 CameraBridgeViewBase.java 中的 deliverAndDrawFrame 方法，对图像进行旋转缩放。
/**
* 获取屏幕旋转角度
*/
private int rotationToDegree() {
WindowManager windowManager = (WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE);
int rotation = windowManager.getDefaultDisplay().getRotation();
int degrees = 0;
switch(rotation) {
case Surface.ROTATION_0:
if(mCameraIndex == CAMERA_ID_FRONT) {
degrees = -90;
} else {
degrees = 90;
}
break;
case Surface.ROTATION_90:
break;
case Surface.ROTATION_180:
break;
case Surface.ROTATION_270:
if(mCameraIndex == CAMERA_ID_ANY || mCameraIndex == CAMERA_ID_BACK) {
degrees = 180;
}
break;
}
return degrees;
}
/**
* 计算得到屏幕宽高比
*/
private float calcScale(int widthSource, int heightSource, int widthTarget, int heightTarget) {
if(widthTarget <= heightTarget) {
return (float) heightTarget / (float) heightSource;
} else {
return (float) widthTarget / (float) widthSource;
}
}
/**
* This method shall be called by the subclasses when they have valid
* object and want it to be delivered to external client (via callback) and
* then displayed on the screen.
* @param frame - the current frame to be delivered
*/
protected void deliverAndDrawFrame(CvCameraViewFrame frame) {
Mat modified;
if (mListener != null) {
modified = mListener.onCameraFrame(frame);
} else {
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;
}
}
if (bmpValid && mCacheBitmap != null) {
Canvas canvas = getHolder().lockCanvas();
if (canvas != null) {
canvas.drawColor(0, android.graphics.PorterDuff.Mode.CLEAR);
if (BuildConfig.DEBUG) Log.d(TAG, "mStretch value: " + mScale);
//TODO 额外添加，让预览框达到全屏效果
int degrees = rotationToDegree();
Matrix matrix = new Matrix();
matrix.postRotate(degrees);
Bitmap outputBitmap = Bitmap.createBitmap(mCacheBitmap, 0, 0, mCacheBitmap.getWidth(), mCacheBitmap.getHeight(), matrix, true);
if (outputBitmap.getWidth() <= canvas.getWidth()) {
mScale = calcScale(outputBitmap.getWidth(), outputBitmap.getHeight(), canvas.getWidth(), canvas.getHeight());
} else {
mScale = calcScale(canvas.getWidth(), canvas.getHeight(), outputBitmap.getWidth(), outputBitmap.getHeight());
}
if (mScale != 0) {
canvas.scale(mScale, mScale, 0, 0);
}
Log.d(TAG, "mStretch value: " + mScale);
canvas.drawBitmap(outputBitmap, 0, 0, null);
/*
if (mScale != 0) {
canvas.drawBitmap(mCacheBitmap, new Rect(0,0,mCacheBitmap.getWidth(), mCacheBitmap.getHeight()),
new Rect((int)((canvas.getWidth() - mScale*mCacheBitmap.getWidth()) / 2),
(int)((canvas.getHeight() - mScale*mCacheBitmap.getHeight()) / 2),
(int)((canvas.getWidth() - mScale*mCacheBitmap.getWidth()) / 2 + mScale*mCacheBitmap.getWidth()),
(int)((canvas.getHeight() - mScale*mCacheBitmap.getHeight()) / 2 + mScale*mCacheBitmap.getHeight())), null);
} else {
canvas.drawBitmap(mCacheBitmap, new Rect(0,0,mCacheBitmap.getWidth(), mCacheBitmap.getHeight()),
new Rect((canvas.getWidth() - mCacheBitmap.getWidth()) / 2,
(canvas.getHeight() - mCacheBitmap.getHeight()) / 2,
(canvas.getWidth() - mCacheBitmap.getWidth()) / 2 + mCacheBitmap.getWidth(),
(canvas.getHeight() - mCacheBitmap.getHeight()) / 2 + mCacheBitmap.getHeight()), null);
}
*/
if (mFpsMeter != null) {
mFpsMeter.measure();
mFpsMeter.draw(canvas, 20, 30);
}
getHolder().unlockCanvasAndPost(canvas);
}
}
}
