Capture picture without preview using camera2 API

问题:

What I want to achieve is capturing a picture without showing the preview, sending directly the output to an ImageReader. I have used the Camera2Basic example as a starting point. However, the callback of my ImageReader is never called, hence no image is sent to its Surface. Do I really need to display a preview first?

This is the camera code, which is ordered following the flow of the asynchronous callbacks:

private ImageReader imageReader;
private Handler backgroundHandler;
private HandlerThread backgroundThread;
private String cameraId;
private CameraDevice cameraDevice;
private CameraCaptureSession cameraCaptureSession;
    @Override
    public void onCreate() {
        setupCamera2();
    }

    private void setupCamera2() {
        CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);

        try {

            for (String cameraId : manager.getCameraIdList()) {
            CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);

            if (characteristics.get(CameraCharacteristics.LENS_FACING) != CameraCharacteristics.LENS_FACING_FRONT) {
                continue;
            }

            this.cameraId = cameraId;

            int[] picSize = Settings.getPictureSize();
            int picWidth = picSize[0];
            int picHeight = picSize[1];

            imageReader = ImageReader.newInstance(picWidth, picHeight, ImageFormat.JPEG, 2);
            imageReader.setOnImageAvailableListener(onImageAvailableListener, backgroundHandler);
            }

        } catch (CameraAccessException | NullPointerException e) {
            e.printStackTrace();
        }
    }


    private void openCamera2() {
        CameraManager manager = (CameraManager) getSystemService(Context.CAMERA_SERVICE);
        try {

            manager.openCamera(cameraId, cameraStateCallback, backgroundHandler);

        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }



    private final CameraDevice.StateCallback cameraStateCallback = new CameraDevice.StateCallback() {
        @Override
        public void onOpened(CameraDevice device) {
            cameraDevice = device;
            createCameraCaptureSession();
        }

        @Override
        public void onDisconnected(CameraDevice cameraDevice) {}

        @Override
        public void onError(CameraDevice cameraDevice, int error) {}
    };



    private void createCaptureSession() {
        List<Surface> outputSurfaces = new LinkedList<>();
        outputSurfaces.add(imageReader.getSurface());

        try {

            cameraDevice.createCaptureSession(outputSurfaces, new CameraCaptureSession.StateCallback() {
                @Override
                public void onConfigured(CameraCaptureSession session) {
                    cameraCaptureSession = session;
                }

                @Override
                public void onConfigureFailed(CameraCaptureSession session) {}
            }, null);

        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }


    private final ImageReader.OnImageAvailableListener onImageAvailableListener = new ImageReader.OnImageAvailableListener() {
        @Override
        public void onImageAvailable(ImageReader reader) {
            createCaptureRequest();
        }
    };


    private void createCaptureRequest() {
        try {

            CaptureRequest.Builder requestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
            requestBuilder.addTarget(imageReader.getSurface());

            // Focus
            requestBuilder.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);

            // Orientation
            int rotation = windowManager.getDefaultDisplay().getRotation();
            requestBuilder.set(CaptureRequest.JPEG_ORIENTATION, ORIENTATIONS.get(rotation));

            cameraCaptureSession.capture(requestBuilder.build(), camera2Callback, null);

        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

回答1:

You should capture photos in "onConfigured" function but not onImageAvailable.

public void onConfigured(CameraCaptureSession session) {
            cameraCaptureSession = session;
            createCaptureRequest();
        }

In this function "onImageAvailable",you should save images,

Image image = mImageReader.acquireLatestImage();
ByteBuffer buffer = image.getPlanes()[0].getBuffer();
byte[] bytes = new byte[buffer.remaining()];
buffer.get(bytes);
try {
    save(bytes, file);
} catch (IOException e) {
    e.printStackTrace();
}
image.close();

"onImageAvailable" function will be invoked after session.capture() .

回答2:

Since I struggled a lot finding out how this works, here is a minimal working Android Service which can process Image data. It probably needs some time after create before you can call start the service, though!

import android.app.Service;
import android.content.Intent;
import android.graphics.ImageFormat;
import android.hardware.camera2.CameraAccessException;
import android.hardware.camera2.CameraCaptureSession;
import android.hardware.camera2.CameraCharacteristics;
import android.hardware.camera2.CameraDevice;
import android.hardware.camera2.CameraManager;
import android.hardware.camera2.CaptureRequest;
import android.media.Image;
import android.media.ImageReader;
import android.os.IBinder;
import android.util.Log;

import java.util.Arrays;

public class VideoProcessingService extends Service {
    private static final String TAG = "VideoProcessing";
    private static final int CAMERA = CameraCharacteristics.LENS_FACING_FRONT;
    private CameraDevice camera;
    private CameraCaptureSession session;
    private ImageReader imageReader;

    private CameraDevice.StateCallback cameraStateCallback = new CameraDevice.StateCallback() {
        @Override
        public void onOpened(CameraDevice camera) {
            VideoProcessingService.this.camera = camera;
        }

        @Override
        public void onDisconnected(CameraDevice camera) {}

        @Override
        public void onError(CameraDevice camera, int error) {}
    };

    private CameraCaptureSession.StateCallback sessionStateCallback = new CameraCaptureSession.StateCallback() {
        @Override
        public void onConfigured(CameraCaptureSession session) {
            VideoProcessingService.this.session = session;
            try {
                session.setRepeatingRequest(createCaptureRequest(), null, null);
            } catch (CameraAccessException e){
                Log.e(TAG, e.getMessage());
            }
        }

        @Override
        public void onConfigureFailed(CameraCaptureSession session) {}
    };

    private ImageReader.OnImageAvailableListener onImageAvailableListener = new ImageReader.OnImageAvailableListener() {
        @Override
        public void onImageAvailable(ImageReader reader){
            Image img = reader.acquireLatestImage();
            processImage(img);
            img.close();
        }
    };

    @Override
    public void onCreate() {
        CameraManager manager = (CameraManager) getSystemService(CAMERA_SERVICE);
        try {
            manager.openCamera(getCamera(manager), cameraStateCallback, null);
            imageReader = ImageReader.newInstance(320, 240, ImageFormat.YUV_420_888, 30 * 600); //fps * 10 min
            imageReader.setOnImageAvailableListener(onImageAvailableListener, null);
        } catch (CameraAccessException e){
            Log.e(TAG, e.getMessage());
        }
    }

    /**
     *  Return the Camera Id which matches the field CAMERA.
     */
    public String getCamera(CameraManager manager){
        try {
            for (String cameraId : manager.getCameraIdList()) {
                CameraCharacteristics characteristics = manager.getCameraCharacteristics(cameraId);
                int cOrientation = characteristics.get(CameraCharacteristics.LENS_FACING);
                if (cOrientation == CAMERA) {
                    return cameraId;
                }
            }
        } catch (CameraAccessException e){
            e.printStackTrace();
        }
        return null;
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        try {
            camera.createCaptureSession(Arrays.asList(imageReader.getSurface()), sessionStateCallback, null);
        } catch (CameraAccessException e){
            Log.e(TAG, e.getMessage());
        }
        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onDestroy() {
        try {
            session.abortCaptures();
        } catch (CameraAccessException e){
            Log.e(TAG, e.getMessage());
        }
        session.close();
    }

    /**
     *  Process image data as desired.
     */
    private void processImage(Image image){
        //Process image data
    }

    private CaptureRequest createCaptureRequest() {
        try {
            CaptureRequest.Builder builder = camera.createCaptureRequest(CameraDevice.TEMPLATE_RECORD);
            builder.addTarget(imageReader.getSurface());
            return builder.build();
        } catch (CameraAccessException e) {
            Log.e(TAG, e.getMessage());
            return null;
        }
    }

    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }
}

回答3:

Since I've been struggling with CAMERA2 API for a long time, looking for how to take pictures without preview from all available cameras on the device, I've created a project on GitHub that does exactly what you want (and maybe more) https://github.com/hzitoun/android-camera2-secret-picture-taker

Hope that helped :)