如何以不同的曝光时间拍照

Question

我使用Xcode 10.0和Swift 4.2，我想制作11张具有不同曝光时间的图片。

例如，第一张照片是基本的，但是在我想将曝光时间除以2后，如：last_exposure_time / 2，当我在第5张照片中时，我采用原始的曝光时间，然后乘以2，这样我就得到了原始图片，将5次曝光除以2，将5次曝光乘以2。

实际上我有以下代码：

import UIKit
import AVFoundation

class ViewController: UIViewController {

    var captureSession = AVCaptureSession()
    var backCamera: AVCaptureDevice?
    var frontCamera: AVCaptureDevice?
    var currentCamera: AVCaptureDevice?

    var Arrayimages: Array<UIImage> = []

    var photoOutput: AVCapturePhotoOutput?

    var cameraPreview: AVCaptureVideoPreviewLayer?

    var image: UIImage?
    var lastExifExposureTime: CMTime?
    var pictureNumber: Int = 0
    var imageView: UIImageView?

    override func viewDidLoad() {
        super.viewDidLoad()


        setupCaptureSession()
        setupDevice()
        setupInputOutput()
        setupPreviewLayer()
        startRunningCaptureSession()

    }

    func setupCaptureSession(){
        captureSession.sessionPreset = AVCaptureSession.Preset.photo
    }

    func setupDevice(){
        let deviceDiscoverySession = AVCaptureDevice.DiscoverySession(deviceTypes: [AVCaptureDevice.DeviceType.builtInWideAngleCamera], mediaType: AVMediaType.video, position: AVCaptureDevice.Position.unspecified)

        let devices = deviceDiscoverySession.devices

        for device in devices {
            if device.position == AVCaptureDevice.Position.back{
                backCamera = device
            }else if device.position == AVCaptureDevice.Position.front{
                frontCamera = device
            }
        }

        currentCamera = backCamera
    }

    func setupInputOutput(){
        do{
            let captureDeviceInput = try AVCaptureDeviceInput(device: currentCamera!)
            captureSession.addInput(captureDeviceInput)
            photoOutput = AVCapturePhotoOutput()
        photoOutput?.setPreparedPhotoSettingsArray([AVCapturePhotoSettings(format: [AVVideoCodecKey: AVVideoCodecType.jpeg])], completionHandler: nil)

            if captureSession.canAddOutput(photoOutput!) {
            captureSession.addOutput(photoOutput!)
            }

        }catch{
            print(error)
        }
    }

    func setupPreviewLayer(){
        cameraPreview = AVCaptureVideoPreviewLayer(session: captureSession)
        cameraPreview?.videoGravity = AVLayerVideoGravity.resizeAspectFill
        cameraPreview?.connection?.videoOrientation = AVCaptureVideoOrientation.landscapeRight
        cameraPreview?.frame = self.view.frame
        self.view.layer.insertSublayer(cameraPreview!, at: 0)
    }

    func startRunningCaptureSession(){
        captureSession.startRunning()
    }

    func stoptRunningCaptureSession(){
        captureSession.stopRunning()
    }

    @IBAction func cameraButton_TouchUpInside(_ sender: Any) {
        do{
            try currentCamera?.lockForConfiguration()
        }catch{
            print(error)
        }
        photoOutput?.capturePhoto(with: AVCapturePhotoSettings(), delegate: self)

    }
}

extension ViewController: AVCapturePhotoCaptureDelegate{
    func photoOutput(_ output: AVCapturePhotoOutput, didFinishProcessingPhoto photo: AVCapturePhoto, error: Error?) {

        if pictureNumber  > 11 {
            print("finish")
        }
        else{
            if let imageData = photo.fileDataRepresentation(){

                image = UIImage(data: imageData)

                imageView?.image = image
                Arrayimages.append(image!)
                print(Arrayimages[pictureNumber])
                UIImageWriteToSavedPhotosAlbum(image!, nil, nil, nil)
                //imageView!.image = image
                let newDurationSeconds = Float64(CMTimeGetSeconds(currentCamera!.exposureDuration))
                let timeNanoSeconds = newDurationSeconds * 1000000000.0
                print(newDurationSeconds)
                let newExposureTime = CMTimeMakeWithSeconds(Float64(newDurationSeconds),preferredTimescale: Int32(timeNanoSeconds) / 3 )
                currentCamera?.setExposureModeCustom(duration: newExposureTime, iso: 100, completionHandler: nil)


                photoOutput?.capturePhoto(with: AVCapturePhotoSettings(), delegate: self)
        pictureNumber += 1
            }
        }

    }
}

实际上我得到了我所有的照片，但是只有秒针被修改了，并且曝光时间没有改变。

如何制作原始图片，将曝光时间除以2的5和将曝光时间乘以2的5？

谢谢!!