从AvcapturePhotoOutput完成捕获后，获得使用的曝光持续时间和ISO值

Question

背景

我正在使用avcapturesession和avcapturephotoOutput将捕获作为jpeg图像保存。

let captureSession = AVCaptureSession()
let stillImageOutput = AVCapturePhotoOutput()
var captureDevice : AVCaptureDevice?

...

func setupCamera() {
    captureDevice = AVCaptureDevice.default(AVCaptureDevice.DeviceType.builtInWideAngleCamera, for: AVMediaType.video, position: .back)
    if (captureDevice != nil)  {
        captureSession.addInput(try AVCaptureDeviceInput(device: captureDevice!))
        if captureSession.canAddOutput(stillImageOutput) {
            captureSession.addOutput(stillImageOutput)
        }
    }
}

avcapturedevice设置为自动和连续调整曝光设置

func configureCamera() {
    do {
        try captureDevice?.lockForConfiguration()
        captureDevice?.exposureMode = AVCaptureDevice.ExposureMode.continuousAutoExposure
        captureDevice?.unlockForConfiguration()
    } catch let error as NSError {
        // Errors handled here...
    }
}

捕获是由

开始的

func capture(){
    // Get an instance of AVCapturePhotoSettings class
    let photoSettings = AVCapturePhotoSettings()
    // Set photo settings
    photoSettings.isAutoStillImageStabilizationEnabled = true
    photoSettings.flashMode = .off
    // Call capturePhoto method by passing photo settings and a
    // delegate implementing AVCapturePhotoCaptureDelegate
    stillImageOutput.capturePhoto(with: photoSettings, delegate: self)
}

将父类设置为AVCAPTUREPHOTOCAPTUREDELEGATE，并通过IT处理PhotoOutput

//Delegate
func photoOutput(_ captureOutput: AVCapturePhotoOutput,
                 didFinishProcessingPhoto photoSampleBuffer: CMSampleBuffer?,
                 previewPhoto previewPhotoSampleBuffer: CMSampleBuffer?,
                 resolvedSettings: AVCaptureResolvedPhotoSettings,
                 bracketSettings: AVCaptureBracketedStillImageSettings?,
                 error: Error?) {
    // Make sure there is a photo sample buffer
    guard error == nil,
        let photoSampleBuffer = photoSampleBuffer else {
            //Errors handled here
            return
    }
    // Convert photo same buffer to a jpeg image data by using // AVCapturePhotoOutput
    guard let imageData =
        AVCapturePhotoOutput.jpegPhotoDataRepresentation(forJPEGSampleBuffer: photoSampleBuffer, previewPhotoSampleBuffer: previewPhotoSampleBuffer) else {
            return
    }
    let capturedImage = UIImage.init(data: imageData , scale: 1.0)
    if let image = capturedImage {
        //save photo ...
    }
}

，一切都应该运行，但是...

问题

我需要知道用于每个捕获的曝光持续时间和ISO值。值之所以有所不同，是因为摄像机设置为自动调整曝光，并且必须这样。

我知道捕获的元数据具有这些值，但我不知道如何访问它们。

暴露持续时间和ISO值对于微调暴露以获得最佳结果是必需的。微调后，这些手动曝光值开始捕获

captureDevice?.setExposureModeCustom(duration: customTime, iso: customISO, completionHandler: nil)

Answer 1

，而不是从捕获元数据中获取所用的ISO和曝光持续时间，而是在捕获照片之前读取这些值。这样做时，重要的是检查曝光是否已完成调整。

在调用捕获之前：

检查自动曝光未调整

while ((captureDevice?.isAdjustingExposure)!){
    usleep(100000) // wait 100 msec
}

阅读当前的曝光参数

let current_exposure_duration : CMTime = (captureDevice?.exposureDuration)!
let current_exposure_ISO : Float = (captureDevice?.iso)!

然后拍照

stillImageOutput.capturePhoto(with: photoSettings, delegate: self)