java - 相机预览很好，但前置相机产生的照片非常暗

Question

我使用 Camera 1 API 构建了一个自定义相机，由于某种原因，它生成了非常暗的图片(仅在前置摄像头上，后置摄像头工作得很好)。相机预览以正确的亮度显示相机应有的样子 - 只有当图像被捕获并解码为位图时，它才会看起来真的暗。我疯狂地用谷歌搜索了一段时间，发现这个问题被报告了好几次，但找不到有效的解决方案。我使用的设备是三星 J5。

相机预览:

class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {

  private static final String CAMERA = "CAMERA";

  private static Camera mCamera;

  private final CameraActivity cameraActivity;
  private final SurfaceHolder mHolder;

  public CameraPreview(Camera camera, CameraActivity cameraActivity) {
    super(cameraActivity);
    this.cameraActivity = cameraActivity;
    mCamera = camera;
    mHolder = getHolder();
    mHolder.addCallback(this);
    mHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
  }

  public void setCameraDisplayOrientation(int cameraId) {
    Camera.CameraInfo info = new android.hardware.Camera.CameraInfo();
    Camera.getCameraInfo(cameraId, info);
    final int rotation = cameraActivity.getWindowManager().getDefaultDisplay().getRotation();
    int degrees = 0;

    switch (rotation) {
      case Surface.ROTATION_0:
        degrees = 0;
        break;
      case Surface.ROTATION_90:
        degrees = 90;
        break;
      case Surface.ROTATION_180:
        degrees = 180;
        break;
      case Surface.ROTATION_270:
        degrees = 270;
        break;
    }

    int result;
    if (info.facing == cameraId) {
      result = (info.orientation + degrees) % 360;
      result = (360 - result) % 360;
    } else {
      result = (info.orientation - degrees + 360) % 360;
    }

    mCamera.setDisplayOrientation(result);
  }

  @Override
  public void surfaceCreated(SurfaceHolder holder) {
    try {
      mCamera.setPreviewDisplay(holder);
      mCamera.startPreview();
      cameraActivity.isSafeToTakePicture(true);
      Camera.Parameters params = mCamera.getParameters();
      // my attempt at preventing darkness 
      params.setExposureCompensation(params.getMaxExposureCompensation());
      if(params.isAutoExposureLockSupported()) {
        params.setAutoExposureLock(false);
      }

      mCamera.setParameters(params);
    } catch (IOException e) {
      Log.d(CAMERA, "An error occured when setting up the camera preview " + e.getMessage());
    }
  }

  @Override
  public void surfaceDestroyed(SurfaceHolder holder) {
    mCamera.stopPreview();
  }

  @Override
  public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
  }
}

在我的 CameraPictureCallback 上(拍摄图像时)，我将字节发送到此方法，该方法将字节解码为位图，将其放入一个包中并将其传递给下一个 fragment :

 public void openFragmentWithBitmap(byte[] bytes) {
    final BitmapFactory.Options scalingOptions = new BitmapFactory.Options();
    final Bitmap bitmap = BitmapFactory.decodeByteArray(bytes, 0, bytes.length, scalingOptions);
    final Bundle bundle = new Bundle();
    bundle.putParcelable(SELFIE, bitmap);

    mCamera.stopPreview();
    final FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
    final Fragment startChainFragment = new StartChainFragment();
    startChainFragment.setArguments(bundle);
    ft.setCustomAnimations(R.anim.slide_up, R.anim.slide_down)
      .replace(R.id.rlPlaceholder, startChainFragment, StartChainFragment.TAG)
      .addToBackStack(null)
      .commit();
  }

我是不是漏掉了什么技巧？在我的 surfaceCreated() 中，我将曝光补偿设置为最大值，但这似乎没有效果。感谢任何帮助。

编辑:事实证明，添加延迟并没有什么不同，所以这里是结果(相机预览与实际拍摄的图像):

相机预览:

捕获的图像:

当点击捕获按钮时，通过调用 mCamera.takePicture(null, null, pictureCallback) 捕获图像(回调只是将字节传输到上述方法)。

Answer 1

在经历了所有的鲜血、汗水和泪水之后，我找到了解决方案。我注意到预览图片和最终图片看起来分辨率不同(您可以看到预览图片中的瓶子比捕获的图片宽)。所以我试图让它们相同或尽可能接近。我在 surfaceCreated() 中的 startPreview() 之后调用此方法:

private void loadCameraParameters() {
    final Camera.Parameters camParams = mCamera.getParameters();

    final Camera.Size previewSize = getOptimalPreviewSize(camParams.getSupportedPreviewSizes(),  screenWidth, screenHeight);
    camParams.setPreviewSize(previewSize.width, previewSize.height);

    final Camera.Size pictureSize = getOptimalPreviewSize(camParams.getSupportedPictureSizes(), screenWidth, screenHeight);
    camParams.setPictureSize(pictureSize.width, pictureSize.height);

    mCamera.setParameters(camParams);
}

其中 getOptimalPreviewSize() 是:

private Camera.Size getOptimalPreviewSize(List<Size> sizes, int targetWidth, int targetHeight) {
    final double aspectTolerance = 0.05;
    final double targetRatio = (double) targetWidth/targetHeight;

    if (sizes == null) {
      return null;
    }

    Camera.Size optimalSize = null;
    double minDiff = Double.MAX_VALUE;

    for (Camera.Size size : sizes) {
      final double ratio = (double) size.width / size.height;
      if (Math.abs(ratio - targetRatio) > aspectTolerance) continue;
      if (Math.abs(size.height - targetHeight) < minDiff) {
        optimalSize = size;
        minDiff = Math.abs(size.height - targetHeight);
      }
    }

    if (optimalSize == null) {
      minDiff = Double.MAX_VALUE;
      for (Camera.Size size : sizes) {
        if (Math.abs(size.height - targetHeight) < minDiff) {
          optimalSize = size;
          minDiff = Math.abs(size.height - targetHeight);
        }
      }
    }

    return optimalSize;
  }

现在我的图片和预览在我的两台设备上都完美匹配，具有相同的亮度和分辨率。