我们如何在Android平台上使用OpenCV(Opencv4Android)对从摄像头传来的实时视频帧执行某些基本的图像处理技术?
提供这么少的信息,我们无法提供太多帮助。不过,我会发布一些代码,用于对相机流执行简单的图像处理技术:将帧转换为灰度。
您需要声明以下内容:
private CameraBridgeViewBase mOpenCvCameraView;
public CvCameraViewListener2 camListener;
接下来,您需要初始化OpenCV。在调用您的onCreate()
方法之前,您需要添加以下代码块:
private BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {
@Override
public void onManagerConnected(int status) {
switch (status) {
case LoaderCallbackInterface.SUCCESS:
{
Log.i("TAG", "OpenCV loaded successfully");
mOpenCvCameraView.enableView();
System.loadLibrary("nameOfYourNativeLibrary"); // if you are working with JNI
run();
} break;
default:
{
super.onManagerConnected(status);
} break;
}
}
};
if (!OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_2_4_3, this, mLoaderCallback)){
Log.e("ERR", "Cannot connect to OpenCV Manager");
}else Log.i("SUCCESS", "opencv successfull");
你需要在onCreate()
方法中编辑,但是你真正需要的是重写onResume()
方法:
@Override
public void onResume()
{
super.onResume();
OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_2_4_3, this, mLoaderCallback);
mOpenCvCameraView.enableView();
}
mOpenCvCameraView
是一个JavaCameraView
。如果您对此不熟悉,这是您的MainActivity
的xml
布局:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:opencv="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="com.example.yourapp.MainActivity$PlaceholderFragment" >
<org.opencv.android.JavaCameraView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:visibility="visible"
android:id="@+id/HelloOpenCvView"
opencv:show_fps="false"
opencv:camera_id="any" />
</RelativeLayout>
onCreate()
方法应该像这样:@Override
public void onCreate(Bundle savedInstanceState) {
Log.i("APP", "called onCreate");
super.onCreate(savedInstanceState);
getWindow().addFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
setContentView(R.layout.fragment_main);
mOpenCvCameraView = (CameraBridgeViewBase)findViewById(R.id.HelloOpenCvView);
if (!OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_2_4_3, this, mLoaderCallback)){
Log.e("OPENCV", "Cannot connect to OpenCV Manager");
}else Log.i("OPENCV", "opencv successfull");
}
在缺失的run()
方法中,您应该添加想要执行的图像处理。在这种情况下,我们将把帧转换为灰度并显示它们:
private void run(){
camListener = new CvCameraViewListener2() {
@Override
public void onCameraViewStopped() {
// TODO Auto-generated method stub
}
@Override
public void onCameraViewStarted(int width, int height) {
// TODO Auto-generated method stub
}
@Override
public Mat onCameraFrame(CvCameraViewFrame inputFrame) {
rgb = inputFrame.rgba();
// here you could just return inputframe.gray(), but for illustration we do the following
Mat gray = new Mat();
Imgproc.cvtColor(rgb, gray, Imgproc.COLOR_RGB2GRAY);
return gray;
}
};
mOpenCvCameraView.setVisibility(SurfaceView.VISIBLE);
mOpenCvCameraView.setCvCameraViewListener(camListener);
}
Mat
对象的像素值,你需要像这样做:double mean = 0;
double size = mat.rows()*mat.cols();
for(int k=0; k<mat.rows(); k++){
for(int j=0; j<mat.cols(); j++){
mean += mat.get(k, j)[0]/size;
}
}
Mat
对象只有一个通道(这意味着如果您尝试访问mat.get(k, j)[1]
,您将获得一个数组越界异常
)。对于RGB Mat
对象,您应该能够访问所有的mat.get(k, j)[0]
、mat.get(k, j)[1]
和mat.get(k, j)[2]
。Mat
对象的像素值的示例。具体来说,我正在计算平均值。 - alvaro.delaserna