android - 使用 Camera2 API 在服务中拍照

Question

我正在使用 camera2 API。我需要在没有预览的情况下在服务中拍照。它有效，但照片曝光不佳。图片很暗或有时很亮。如何修复我的代码以使照片具有高质量？我正在使用前置摄像头。

public class Camera2Service extends Service
{

    protected static final String TAG = "myLog";
    protected static final int CAMERACHOICE = CameraCharacteristics.LENS_FACING_BACK;
    protected CameraDevice cameraDevice;
    protected CameraCaptureSession session;
    protected ImageReader imageReader;

    protected CameraDevice.StateCallback cameraStateCallback = new CameraDevice.StateCallback() {
        @Override
        public void onOpened(@NonNull CameraDevice camera) {
            Log.d(TAG, "CameraDevice.StateCallback onOpened");
            cameraDevice = camera;
            actOnReadyCameraDevice();
        }

        @Override
        public void onDisconnected(@NonNull CameraDevice camera) {
            Log.w(TAG, "CameraDevice.StateCallback onDisconnected");
        }

        @Override
        public void onError(@NonNull CameraDevice camera, int error) {
            Log.e(TAG, "CameraDevice.StateCallback onError " + error);
        }
    };

    protected CameraCaptureSession.StateCallback sessionStateCallback = new CameraCaptureSession.StateCallback() {

        @Override
        public void onReady(CameraCaptureSession session) {
            Camera2Service.this.session = session;
            try {
                session.setRepeatingRequest(createCaptureRequest(), null, null);
            } catch (CameraAccessException e) {
                Log.e(TAG, e.getMessage());
            }
        }


        @Override
        public void onConfigured(CameraCaptureSession session) {

        }

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

    protected ImageReader.OnImageAvailableListener onImageAvailableListener = new ImageReader.OnImageAvailableListener() {
        @Override
        public void onImageAvailable(ImageReader reader) {
            Log.d(TAG, "onImageAvailable");
            Image img = reader.acquireLatestImage();
            if (img != null) {
                processImage(img);
                img.close();
            }
        }
    };

    public void readyCamera() {
        CameraManager manager = (CameraManager) getSystemService(CAMERA_SERVICE);
        try {
            String pickedCamera = getCamera(manager);
            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                return;
            }
            manager.openCamera(pickedCamera, cameraStateCallback, null);
            imageReader = ImageReader.newInstance(1920, 1088, ImageFormat.JPEG, 2 /* images buffered */);
            imageReader.setOnImageAvailableListener(onImageAvailableListener, null);
            Log.d(TAG, "imageReader created");
        } catch (CameraAccessException e){
            Log.e(TAG, e.getMessage());
        }
    }

    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 != CAMERACHOICE) {
                    return cameraId;
                }
            }
        } catch (CameraAccessException e){
            e.printStackTrace();
        }
        return null;
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.d(TAG, "onStartCommand flags " + flags + " startId " + startId);

        readyCamera();

        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onCreate() {
        Log.d(TAG,"onCreate service");
        super.onCreate();
    }

    public void actOnReadyCameraDevice()
    {
        try {
            cameraDevice.createCaptureSession(Arrays.asList(imageReader.getSurface()), sessionStateCallback, null);
        } catch (CameraAccessException e){
            Log.e(TAG, e.getMessage());
        }
    }

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


    private void processImage(Image image){
        //Process image data
        ByteBuffer buffer;
        byte[] bytes;
        boolean success = false;
        File file = new File(Environment.getExternalStorageDirectory() + "/Pictures/image.jpg");
        FileOutputStream output = null;

        if(image.getFormat() == ImageFormat.JPEG) {
            buffer = image.getPlanes()[0].getBuffer();
            bytes = new byte[buffer.remaining()]; // makes byte array large enough to hold image
            buffer.get(bytes); // copies image from buffer to byte array
            try {
                output = new FileOutputStream(file);
                output.write(bytes);    // write the byte array to file
                j++;
                success = true;
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                image.close(); // close this to free up buffer for other images
                if (null != output) {
                    try {
                        output.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }

        }


    }

    protected CaptureRequest createCaptureRequest() {
        try {
            CaptureRequest.Builder builder = cameraDevice.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;
    }
}

Answer 1

谢尔盖，我复制了你的代码，确实我能够重现这个问题。我从 Google Pixel 2 (Android 8.1) 得到全黑的照片。

不过，我已经成功解决黑图问题如下:

首先，如果有人想知道，您实际上不需要任何 Activity 或任何预览 UI 元素，因为许多其他关于 Camera API 的线程声称!这曾经适用于已弃用的 Camera v1 API。现在，有了新的 Camera v2 API，我只需要一个前台服务。

为了开始捕获过程，我使用了这段代码:

CaptureRequest.Builder builder = cameraDevice.createCaptureRequest (CameraDevice.TEMPLATE_VIDEO_SNAPSHOT);
builder.set (CaptureRequest.CONTROL_MODE, CaptureRequest.CONTROL_MODE_AUTO);
builder.set (CaptureRequest.FLASH_MODE, CaptureRequest.FLASH_MODE_OFF);
builder.addTarget (imageReader.getSurface ());
captureRequest = builder.build ();

然后，在 ImageReader.onImageAvailable 中，我跳过了前 N 张图片(意味着我没有保存它们)。我让 session 运行，并在不保存的情况下捕获更多照片。

这让相机有足够的时间自动逐渐调整曝光参数。然后，N张无视照片后，我存了一张，正常曝光，一点都不黑。

N 常量的值取决于您的硬件特性。因此，您需要通过实验为您的硬件确定 N 的理想值。您还可以使用基于直方图的启发式自动化。在实验开始时，不要害怕在经过数百毫秒的校准后才开始保存。

最后，在许多类似的话题中，人们建议等待，例如创建 session 后 500 毫秒，然后才拍摄一张照片。这于事无补。 确实必须让相机运行并让它快速拍摄许多照片(以尽可能快的速度)。为此，只需使用 setRepeatingRequest 方法(就像在您的原始代码中一样)。

希望这对您有所帮助。 :)

编辑添加:跳过最初的 N 张图片时，您还需要为每张跳过的图片调用 ImageReader 的 acquireLatestImage 方法。否则，它不会工作。

包含我的更改的完整原始代码解决了该问题，测试并确认可在 Google Pixel 2、Android 8.1 上运行:

public class Camera2Service extends Service
{
    protected static final int CAMERA_CALIBRATION_DELAY = 500;
    protected static final String TAG = "myLog";
    protected static final int CAMERACHOICE = CameraCharacteristics.LENS_FACING_BACK;
    protected static long cameraCaptureStartTime;
    protected CameraDevice cameraDevice;
    protected CameraCaptureSession session;
    protected ImageReader imageReader;

    protected CameraDevice.StateCallback cameraStateCallback = new CameraDevice.StateCallback() {
        @Override
        public void onOpened(@NonNull CameraDevice camera) {
            Log.d(TAG, "CameraDevice.StateCallback onOpened");
            cameraDevice = camera;
            actOnReadyCameraDevice();
        }

        @Override
        public void onDisconnected(@NonNull CameraDevice camera) {
            Log.w(TAG, "CameraDevice.StateCallback onDisconnected");
        }

        @Override
        public void onError(@NonNull CameraDevice camera, int error) {
            Log.e(TAG, "CameraDevice.StateCallback onError " + error);
        }
    };

    protected CameraCaptureSession.StateCallback sessionStateCallback = new CameraCaptureSession.StateCallback() {

        @Override
        public void onReady(CameraCaptureSession session) {
            Camera2Service.this.session = session;
            try {
                session.setRepeatingRequest(createCaptureRequest(), null, null);
                cameraCaptureStartTime = System.currentTimeMillis ();
            } catch (CameraAccessException e) {
                Log.e(TAG, e.getMessage());
            }
        }


        @Override
        public void onConfigured(CameraCaptureSession session) {

        }

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

    protected ImageReader.OnImageAvailableListener onImageAvailableListener = new ImageReader.OnImageAvailableListener() {
        @Override
        public void onImageAvailable(ImageReader reader) {
            Log.d(TAG, "onImageAvailable");
            Image img = reader.acquireLatestImage();
            if (img != null) {
                if (System.currentTimeMillis () > cameraCaptureStartTime + CAMERA_CALIBRATION_DELAY) {
                    processImage(img);
                }
                img.close();
            }
        }
    };

    public void readyCamera() {
        CameraManager manager = (CameraManager) getSystemService(CAMERA_SERVICE);
        try {
            String pickedCamera = getCamera(manager);
            if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA) != PackageManager.PERMISSION_GRANTED) {
                return;
            }
            manager.openCamera(pickedCamera, cameraStateCallback, null);
            imageReader = ImageReader.newInstance(1920, 1088, ImageFormat.JPEG, 2 /* images buffered */);
            imageReader.setOnImageAvailableListener(onImageAvailableListener, null);
            Log.d(TAG, "imageReader created");
        } catch (CameraAccessException e){
            Log.e(TAG, e.getMessage());
        }
    }

    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 == CAMERACHOICE) {
                    return cameraId;
                }
            }
        } catch (CameraAccessException e){
            e.printStackTrace();
        }
        return null;
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.d(TAG, "onStartCommand flags " + flags + " startId " + startId);

        readyCamera();

        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onCreate() {
        Log.d(TAG,"onCreate service");
        super.onCreate();
    }

    public void actOnReadyCameraDevice()
    {
        try {
            cameraDevice.createCaptureSession(Arrays.asList(imageReader.getSurface()), sessionStateCallback, null);
        } catch (CameraAccessException e){
            Log.e(TAG, e.getMessage());
        }
    }

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


     private void processImage(Image image){
    //Process image data
    ByteBuffer buffer;
    byte[] bytes;
    boolean success = false;
    File file = new File(Environment.getExternalStorageDirectory() + "/Pictures/image.jpg");
    FileOutputStream output = null;

    if(image.getFormat() == ImageFormat.JPEG) {
        buffer = image.getPlanes()[0].getBuffer();
        bytes = new byte[buffer.remaining()]; // makes byte array large enough to hold image
        buffer.get(bytes); // copies image from buffer to byte array
        try {
            output = new FileOutputStream(file);
            output.write(bytes);    // write the byte array to file
            j++;
            success = true;
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            image.close(); // close this to free up buffer for other images
            if (null != output) {
                try {
                    output.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }


}

protected CaptureRequest createCaptureRequest() {
    try {
        CaptureRequest.Builder builder = cameraDevice.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;
}