ios - 捕获完成后从 AVCapturePhotoOutput 获取使用的曝光持续时间和 ISO 值

Question

背景

我使用 AVCaptureSession 和 AVCapturePhotoOutput 将捕获保存为 JPEG 图像。

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...
    }

}

捕获开始于

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)

}

父类设置为 AVCapturePhotoCaptureDelegate 并由其处理 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 ...
    }

}

然而，一切都按其应有的方式进行......

问题

我需要知道每次拍摄时使用的曝光持续时间和 ISO 值。这些值会有所不同，因为相机设置为自动调整曝光，并且必须如此。

我知道捕获的元数据保存这些值，但我不知道如何访问它们。

曝光持续时间和 ISO 值对于微调曝光以获得最佳效果是必要的。微调后，使用这些手动曝光值开始捕捉

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

Answer 1

我没有从捕捉元数据中获取使用的 ISO 和曝光持续时间，而是在捕捉照片之前读取这些值。当这样做时，重要的是检查曝光是否已完成调整。

在调用捕获之前:

检查自动曝光是否未调整

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

读取当前曝光参数

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

然后拍照

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