一.Android摄像头预览
Android OpenCV开发过程中，我们有3种可选方式去实现Android摄像头预览功能：
- 使用Android系统Camera API
- 使用CameraX（JetPack组件）
- 使用OpenCV SDK辅助类（JavaCameraView、JavaCamera2View等）
利用Android OpenCV SDK实现相机预览
1.申明权限
<uses-permission android:name="android.permission.CAMERA" />
<uses-feature
android:name="android.hardware.camera"
android:required="false" />
<uses-feature
android:name="android.hardware.camera.autofocus"
android:required="false" />
<uses-feature
android:name="android.hardware.camera.front"
android:required="false" />
<uses-feature
android:name="android.hardware.camera.front.autofocus"
android:required="false" />
2.布局添加JavaCameraView或者JavaCamera2View至布局
<?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"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">
<org.opencv.android.JavaCamera2View
android:id="@+id/camera_view"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
android:layout_width="match_parent"
android:layout_height="match_parent">
</org.opencv.android.JavaCamera2View>
<ImageView
android:id="@+id/image_view"
android:layout_width="match_parent"
android:layout_height="match_parent">
</ImageView>
</androidx.constraintlayout.widget.ConstraintLayout>
3.Activity继承CameraActivity，实现CameraBridgeViewbase.CvCameraViewListener或者CameraBridgeViewbase.CvCameraViewListener2接口，两个接口的差异主要集中在onCameraframe回调。
@Override
public void onCameraViewStarted(int width, int height) {
}
@Override
public void onCameraViewStopped() {
}
@Override
public Mat onCameraframe(CameraBridgeViewbase.CvCameraViewframe inputframe) {
// 获取相机中的图像
Mat rgba = inputframe.rgba();
Core.rotate(rgba, rgba, Core.ROTATE_90_CLOCKWISE);
Bitmap bitmap = Bitmap.createBitmap(rgba.cols(), rgba.rows(), Bitmap.Config.ARGB_8888);
Utils.matToBitmap(rgba, bitmap);
Bitmap location = location(bitmap);
if (location==null){
return null;
}
runonUiThread(() -> image_view.setImageBitmap(location));
return null;
}
4.复写方法getCameraViewList
@Override
protected List<? extends CameraBridgeViewbase> getCameraViewList() {
return Arrays.asList(mCVCamera);
}
二.物体检测
1.在onCameraframe回调中拿到图像后做一次滤镜去除干扰再进行边缘检测，这时候边缘可能并不是连通的所以我们再对图像做一次膨胀操作。最后进行轮廓检测将检测到的轮廓绘制到原图上。
private Bitmap location(Bitmap bmp) {
Mat originMat=new Mat();
Utils.bitmapToMat(bmp,originMat);
Mat resultG = new Mat();
Mat result = new Mat();
Imgproc.GaussianBlur(originMat, resultG, new Size(3.0, 3.0), 0);
Imgproc.Canny(resultG, result, 100.0, 220.0, 3);
// 膨胀，连接边缘
Imgproc.dilate(result, result, new Mat(), new Point(-1,-1), 4, 1, new Scalar(1));
// Bitmap Bmp = Bitmap.createBitmap(result.cols(), result.rows(), Bitmap.Config.ARGB_8888);
// Utils.matToBitmap(result,Bmp);
List<MatOfPoint> contours = new ArrayList<>();
Mat hierarchy = new Mat();
Imgproc.findContours(result, contours, hierarchy, Imgproc.RETR_EXTERNAL, Imgproc.CHAIN_APPROX_SIMPLE);
//有了轮廓之后，为了方便我们先将轮廓给画出来，这里的resultMat其实就是srcMat，为了区分用了Mat resultMat = srcMat.clone();，
// 下面代码的意思是，把contours轮廓列表中的所有轮廓(-1表示所有轮廓)在，resultMat上画用黑色(new Scalar(0, 0, 0))粗细为10的线条画出来。
if (contours.isEmpty()){
return null;
}
Mat resultMat = resultG.clone();
double arcLength=0;
int index=0;
for (int i = 0; i < contours.size(); i++) {
MatOfPoint2f source = new MatOfPoint2f();
source.fromList(contours.get(i).toList());
if (Imgproc.arcLength(source, true)>arcLength){
arcLength=Imgproc.arcLength(source, true);
index=i;
}
}
MatOfPoint matOfPoint = contours.get(index);
MatOfPoint2f tempMat=new MatOfPoint2f();
Imgproc.approxPolyDP(new MatOfPoint2f(matOfPoint.toArray()), tempMat, Imgproc.arcLength(new MatOfPoint2f(matOfPoint.toArray()), true)*0.04, true);
Point[] points = tempMat.toArray();
if (points.length!=4){
return null;
}
List<MatOfPoint> matOfPoints = new ArrayList<>();
matOfPoints.add(new MatOfPoint(tempMat.toArray()));
Imgproc.drawContours(resultMat, matOfPoints, -1, new Scalar(0, 0, 255), 4);
Bitmap resultBmp = Bitmap.createBitmap(resultMat.cols(), resultMat.rows(), Bitmap.Config.ARGB_8888);
Utils.matToBitmap(resultMat,resultBmp);
return resultBmp;
}
三.效果
没办法传视频。https://github.com/jzqCode/OpenCvDemo
111.jpg
