Android中用OpenCV拍照的正确方法？CameraBridgeViewBase无takePicture方法

Hey there, let's sort out this OpenCV camera capture issue you're dealing with. You're right that some old resources mention using a takePicture method on CameraBridgeViewBase, but that method never actually existed on that class—it's designed for real-time preview, not direct capture. Those outdated solutions probably relied on hacky workarounds that don't hold up in modern OpenCV versions. Here's the proper, reliable way to implement capture with CameraBridgeViewBase:

Step 1: Create a Custom Camera View Subclass #

Since CameraBridgeViewBase (and its common subclass JavaCameraView) keeps its internal Camera instance protected, we need to create a subclass to expose it:

public class CustomOpenCVCamera extends JavaCameraView {
    public CustomOpenCVCamera(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    // Expose the internal Camera instance for capture
    public Camera getCameraInstance() {
        return mCamera;
    }
}

Replace the standard JavaCameraView in your layout XML with this custom class:

<com.yourpackage.CustomOpenCVCamera
    android:id="@+id/camera_preview"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    opencv:camera_id="0" />

Step 2: Implement Capture Logic in Your Activity #

In your activity, initialize the custom camera view, grab the exposed Camera instance, and set up a capture trigger (like a button click):

public class OpenCVCameraActivity extends AppCompatActivity implements CvCameraViewListener2 {
    private CustomOpenCVCamera mCameraView;
    private Camera mCamera;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_camera);

        // Request camera permissions (critical for Android 6.0+)
        if (ContextCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.CAMERA}, 100);
        }

        mCameraView = findViewById(R.id.camera_preview);
        mCameraView.setCvCameraViewListener(this);
        mCameraView.enableView();

        // Get the exposed Camera instance
        mCamera = mCameraView.getCameraInstance();
    }

    // Trigger capture on button click
    public void takePicture(View view) {
        if (mCamera == null) return;

        // Use the native Camera API's takePicture method
        mCamera.takePicture(
                null,  // Shutter callback (optional)
                null,  // Raw callback (optional)
                (data, camera) -> {
                    // Convert the captured byte array to an OpenCV Mat
                    Mat capturedMat = Imgcodecs.imdecode(new MatOfByte(data), Imgcodecs.IMREAD_COLOR);

                    // --- Add your OpenCV image processing here ---
                    // Example: Convert to grayscale
                    Mat grayMat = new Mat();
                    Imgproc.cvtColor(capturedMat, grayMat, Imgproc.COLOR_RGB2GRAY);

                    // Save or display the processed image as needed
                    Imgcodecs.imwrite(Environment.getExternalStorageDirectory() + "/captured_gray.jpg", grayMat);

                    // Restart preview after capture (camera stops preview by default)
                    camera.startPreview();

                    // Clean up Mats to avoid memory leaks
                    capturedMat.release();
                    grayMat.release();
                }
        );
    }

    // Required CvCameraViewListener2 methods
    @Override
    public void onCameraViewStarted(int width, int height) {}

    @Override
    public void onCameraViewStopped() {}

    @Override
    public Mat onCameraFrame(CvCameraViewFrame inputFrame) {
        // Return the preview frame for real-time display
        return inputFrame.rgba();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (mCameraView != null) {
            mCameraView.disableView();
        }
    }
}

Key Notes to Avoid Common Issues #

• Permissions: Don't forget to handle runtime permissions for camera access—this is mandatory for Android 6.0 and above.
• Preview Restart: After calling takePicture(), the camera stops preview automatically. Always call camera.startPreview() to resume it.
• Memory Management: Always release OpenCV Mat objects after use to prevent memory leaks.
• OpenCV Version Compatibility: This method works for OpenCV 3.x and 4.x. If you're using a newer version that deprecates JavaCameraView, you can adapt this approach to use the Camera2-based Camera2Renderer, but the core idea of accessing the underlying camera instance remains similar.

内容的提问来源于stack exchange，提问作者Tugay