android - 使用 Camera2 API 的图片真的很暗

Question

我在 Android 上工作，我试图在不显示任何预览的情况下拍摄图片。我试图通过上课来简化这个过程。它正在工作，但所有图片都非常暗。这是我的课:

public class Cam {
private Context context;
private CameraManager manager;
private CameraDevice camera;
private CameraCaptureSession session;
private ImageReader reader;
public static String FRONT="-1";
public static String BACK="-1";
private boolean available=true;
private String filepath;

private static final String NO_CAM = "No camera found on device!";
private static final String ERR_CONFIGURE = "Failed configuring session";
private static final String ERR_OPEN = "Can't open the camera";
private static final String CAM_DISCONNECT = "Camera disconnected";
private static final String FILE_EXIST = "File already exist";

private static final SparseIntArray ORIENTATIONS = new SparseIntArray();
static {
    ORIENTATIONS.append(Surface.ROTATION_0, 90);
    ORIENTATIONS.append(Surface.ROTATION_90, 0);
    ORIENTATIONS.append(Surface.ROTATION_180, 270);
    ORIENTATIONS.append(Surface.ROTATION_270, 180);
}

public Cam(Context context) throws CameraAccessException {
    this.context = context;
    this.manager = (CameraManager) context.getSystemService(Context.CAMERA_SERVICE);
    String ids[] = manager.getCameraIdList();
    if(ids.length==2){
        BACK=ids[0];
        FRONT=ids[1];
    }
    else if(ids.length==1){
        BACK=ids[0];
    }
    else{
        available=false;
        throw new CameraAccessException(-1, NO_CAM);
    }
}

public void takePicture(String camId, String filepath) throws CameraAccessException {
    if(available){
        this.filepath=filepath;
        StreamConfigurationMap map = manager.getCameraCharacteristics(camId).get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
        Size largest = Collections.max(Arrays.asList(map.getOutputSizes(ImageFormat.JPEG)), new CompareSizesByArea());
        reader=ImageReader.newInstance(largest.getWidth(), largest.getHeight(), ImageFormat.JPEG, 1);
        reader.setOnImageAvailableListener(imageListener, null);
        manager.openCamera(camId, cameraStateCallback, null);
    }
    else
        throwError(NO_CAM);
}

private CameraDevice.StateCallback cameraStateCallback = new CameraDevice.StateCallback() {
    @Override
    public void onOpened(CameraDevice camera) {
        Cam.this.camera=camera;
        try {
            camera.createCaptureSession(Collections.singletonList(reader.getSurface()), sessionStateCallback, null);
        } catch (CameraAccessException e) {
            throwError(e.getMessage());
        }
    }

    @Override
    public void onDisconnected(CameraDevice camera) {
        throwError(CAM_DISCONNECT);
    }

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

private CameraCaptureSession.StateCallback sessionStateCallback = new CameraCaptureSession.StateCallback() {
    @Override
    public void onConfigured(CameraCaptureSession session) {
        Cam.this.session=session;
        try {
            CaptureRequest.Builder request = camera.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE);
            request.set(CaptureRequest.CONTROL_AF_MODE, CaptureRequest.CONTROL_AF_MODE_CONTINUOUS_PICTURE);
            request.addTarget(reader.getSurface());
            int rotation = ((WindowManager)context.getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay().getRotation();
            request.set(CaptureRequest.JPEG_ORIENTATION, ORIENTATIONS.get(rotation));
            session.capture(request.build(), captureCallback, null);
        } catch (CameraAccessException e) {
            throwError(e.getMessage());
        }
    }

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

private CameraCaptureSession.CaptureCallback captureCallback = new CameraCaptureSession.CaptureCallback() {
    @Override
    public void onCaptureFailed(CameraCaptureSession session, CaptureRequest request, CaptureFailure failure) {
        super.onCaptureFailed(session, request, failure);
        throwError(failure.toString());
    }
};

private ImageReader.OnImageAvailableListener imageListener = new ImageReader.OnImageAvailableListener() {
    @Override
    public void onImageAvailable(ImageReader reader) {
        Image image = reader.acquireLatestImage();
        try {
            File file = saveImage(image);
            // Send file via a listener
            closeCamera();
        } catch (IOException e) {
            throwError(e.getMessage());
        }
        reader.close();
    }
};

private File saveImage(Image image) throws IOException {
    File file = new File(filepath);
    if (file.exists()) {
        throwError(FILE_EXIST);
        return null;
    }
    else {
        ByteBuffer buffer = image.getPlanes()[0].getBuffer();
        byte[] bytes = new byte[buffer.remaining()];
        buffer.get(bytes);
        FileOutputStream output = new FileOutputStream(file);
        output.write(bytes);
        image.close();
        output.close();
        return file;
    }
}

static class CompareSizesByArea implements Comparator<Size> {
    @Override
    public int compare(Size lhs, Size rhs) {
        return Long.signum((long) lhs.getWidth() * lhs.getHeight() - (long) rhs.getWidth() * rhs.getHeight());
    }
}

private void closeCamera(){
    if(session!=null) {session.close();}
    if(reader!=null) {reader.close();}
    if(camera!=null) {camera.close();}
}

然后我在我的 Activity 中调用 Cam 对象:

Cam cam = new Cam(MainActivity.this);
cam.takePicture(Cam.BACK, "/sdcard/pic.jpg");

当图片可用时，监听器会阻止 MainActivity，但我删除了代码以清除一点。

我不知道我做错了什么，图片真的很暗。也许是一面旗帜或其他东西......任何帮助将不胜感激。

编辑: worker 类(Class):https://github.com/omaflak/Android-Camera2-Library/blob/master/ezcam/src/main/java/me/aflak/ezcam/EZCam.java

示例:https://github.com/omaflak/Android-Camera2-Library/blob/master/app/src/main/java/me/aflak/libraries/MainActivity.java

Answer 1

如果您发送给相机的唯一捕获请求是最终图片请求，这不足为奇。

相机自动曝光、对焦和白平衡例程通常需要一两秒的流缓冲才能收敛到良好的结果。

虽然您不需要在屏幕上绘制预览，但这里最简单的方法是首先针对虚拟 SurfaceTexture 运行重复请求一两秒钟，然后触发 JPEG 捕获。您可以只流式传输 JPEG 捕获，但 JPEG 捕获速度很慢，因此您需要更长的时间来收敛(此外，与典型的预览相比，相机实现更可能存在重复 JPEG 捕获和获得良好曝光的错误) .

因此，创建一个带有随机纹理 ID 参数的虚拟 SurfaceTexture:

private SurfaceTexture mDummyPreview = new SurfaceTexture(1);
private Surface mDummySurface = new Surface(mDummyPreview);

并将 Surface 包含在您的 session 配置中。配置 session 后，创建一个以虚拟预览为目标的预览请求，并在 N 个捕获结果进来后，提交您想要的 JPEG 的捕获请求。您可能想要尝试使用 N，但大概 ~30 帧就足够了。

请注意，您还没有处理:

• 锁定自动对焦以确保您的 JPEG 图像清晰
• 运行 AE 预捕获以允许闪光测光，如果你想允许使用闪光灯的话
• 通过某种方式让用户知道他们将捕获什么，因为没有预览，他们无法将设备对准任何目标。

AF 锁定和预捕获触发序列包含在此处的 Camera2Basic 示例中:https://github.com/googlesamples/android-Camera2Basic ，所以您可以看看它们的作用。