Windows 8.1 MediaCapture预览聚焦速度较慢

Question

我正在使用MediaCapture实例展示Dell Venue 8专业版平板电脑摄像头的取景器。这款平板电脑运行的是Windows 8.1 Pro。我面临的问题是，相机在对焦和根据房间里的照明进行调整时似乎速度很慢。预览可以在太暗和太亮之间快速闪烁，似乎很难获得最佳的照明设置。使用股票相机应用程序没有问题的对焦。这是我用来初始化相机的代码。

// Attempt to get the back camera if one is available, but use any camera device if not
var cameraDevice = await FindCameraDeviceByPanelAsync(Windows.Devices.Enumeration.Panel.Back);
if (cameraDevice == null)
{
    Debug.WriteLine("No camera device found!");
    return;
}
var settings = new MediaCaptureInitializationSettings { 
    VideoDeviceId = cameraDevice.Id, 
    AudioDeviceId = "",
    StreamingCaptureMode = StreamingCaptureMode.Video, 
    PhotoCaptureSource = PhotoCaptureSource.VideoPreview
};
//setup media capture
mediaCapture = new MediaCapture();
await mediaCapture.InitializeAsync(settings);
mediaCapture.VideoDeviceController.PrimaryUse = CaptureUse.Photo;
ViewFinder.Source = mediaCapture;
mediaCapture.SetPreviewRotation(VideoRotation.Clockwise90Degrees);
await mediaCapture.StartPreviewAsync();

如何优化MediaCapture以快速聚焦？(应用需要MediaCapture来解码二维码)

Answer 1

听起来你想使用连续自动对焦。这段代码应该可以让您开始：

var focusControl = _mediaCapture.VideoDeviceController.FocusControl;

await focusControl.UnlockAsync();

// You may want to use AutoFocusRange.Macro for QR codes. Make sure it's within the supported modes though
var settings = new FocusSettings { Mode = FocusMode.Continuous, AutoFocusRange = AutoFocusRange.FullRange };

focusControl.Configure(settings);
await focusControl.FocusAsync();

还有，我注意到你在用SetPreviewRotation。官方CameraStarterKit sample建议按如下方式轮换预览，以提高效率：

// Rotation metadata to apply to the preview stream and recorded videos (MF_MT_VIDEO_ROTATION)
// Reference: http://msdn.microsoft.com/en-us/library/windows/apps/xaml/hh868174.aspx
readonly Guid RotationKey = new Guid("C380465D-2271-428C-9B83-ECEA3B4A85C1");

// Add rotation metadata to the preview stream to make sure the aspect ratio / dimensions match when rendering and getting preview frames
var props = _mediaCapture.VideoDeviceController.GetMediaStreamProperties(MediaStreamType.VideoPreview);
props.Properties.Add(RotationKey, rotationDegrees);
await _mediaCapture.SetEncodingPropertiesAsync(MediaStreamType.VideoPreview, props, null);

您可以通过//build/ presentation在摄影机会话中了解有关预览旋转的更多信息。