MLkit 人脸检测不适用于 android 的前置摄像头

Question

我正在使用 MLKit 在 android 上进行人脸检测。我正在关注可以在此处找到的官方文档 - https://developers.google.com/ml-kit/vision/face-detection/android。我可以使用后置摄像头成功检测到人脸，但是当我切换到前置摄像头时没有检测到人脸。根据我从this论坛了解到的，问题可能是旋转补偿。为此，我使用了与文档中所示相同的代码-

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);
}

/**
 * Get the angle by which an image must be rotated given the device's current
 * orientation.
 */
@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
private int getRotationCompensation(String cameraId, Activity activity, Context context)
        throws CameraAccessException {
    // Get the device's current rotation relative to its "native" orientation.
    // Then, from the ORIENTATIONS table, look up the angle the image must be
    // rotated to compensate for the device's rotation.
    int deviceRotation = activity.getWindowManager().getDefaultDisplay().getRotation();
    int rotationCompensation = ORIENTATIONS.get(deviceRotation);

    // On most devices, the sensor orientation is 90 degrees, but for some
    // devices it is 270 degrees. For devices with a sensor orientation of
    // 270, rotate the image an additional 180 ((270 + 270) % 360) degrees.
    CameraManager cameraManager = (CameraManager) context.getSystemService(CAMERA_SERVICE);
    int sensorOrientation = cameraManager
            .getCameraCharacteristics(cameraId)
            .get(CameraCharacteristics.SENSOR_ORIENTATION);
    rotationCompensation = (rotationCompensation + sensorOrientation + 270) % 360;

    return rotationCompensation;
}

为了改变相机，我只是改变了一个全局变量cameraID，代码中没有做其他的改变。

编辑- 在前置摄像头的情况下，使用旋转 = getRotationCompensation(...) - 180 生成输入图像，如果后置摄像头对我有用，则不减去 180。不知道为什么会这样。我仍然希望对此或如何避免这种情况的任何解释。

Answer 1

上面代码sn-p的计算可能对前置摄像头效果不好，因为图像翻转。

您能否尝试定义：

static {
  ORIENTATIONS.append(Surface.ROTATION_0, 0);
  ORIENTATIONS.append(Surface.ROTATION_90, 90);
  ORIENTATIONS.append(Surface.ROTATION_180, 180);
  ORIENTATIONS.append(Surface.ROTATION_270, 270);
}

并使用

if (lensFacing == CameraSelector.LENS_FACING_FRONT) {
  rotationCompensation = (sensorOrientation + rotationDegrees) % 360;
} else { // back-facing
  rotationCompensation = (sensorOrientation - rotationDegrees + 360) % 360;
}

替换

rotationCompensation = (rotationCompensation + sensorOrientation + 270) % 360;

我们还将更新开发文档中的代码 sn-p 以反映这一点。