为什么AVCaptureSession的图像非常暗

Question

我们有Xamarin Forms解决方案，在iOS项目中，我们尝试在按钮点击上创建照片。问题是图像很暗。它几乎是黑色的。为什么会这样？这是一个代码：

var _captureSession = new AVCaptureSession();
var _captureDevice = AVCaptureDevice.GetDefaultDevice(AVMediaType.Video);
var _captureDeviceInput = AVCaptureDeviceInput.FromDevice(_captureDevice);
_captureSession.AddInput(_captureDeviceInput);
_captureSession.StartRunning();

private async void OnButtonClick()
{
    var output = new AVCaptureStillImageOutput { OutputSettings = new NSDictionary(AVVideo.CodecKey, AVVideo.CodecJPEG) };
    _captureSession.AddOutput(output);

    var buffer = await output.CaptureStillImageTaskAsync(output.Connections[0]);
    NSData data = AVCaptureStillImageOutput.JpegStillToNSData(buffer);

    UIImage image = UIImage.LoadFromData(data);
    //image = RotateImage(image);
    NSData imageData = image.AsPNG();
    byte[] byteArray = imageData.ToArray();

    IFolder folder = FileSystem.Current.LocalStorage;
    IFile file = await folder.CreateFileAsync("image.png", CreationCollisionOption.ReplaceExisting);

    using (Stream stream = await file.OpenAsync(PCLStorage.FileAccess.ReadAndWrite))
    {
        stream.Write(image, 0, image.Length);
    }
}

这是图片：

Answer 1

行：

_captureSession.AddOutput(output);

应该在点击按钮之前（在StartRunning之前）。通过该更改，图像具有正常亮度，并且也不需要旋转。