Getting a successful build...but triggers an error when I try to change the filter after I try to move the slider...but it worked fine in the step where we just used SepiaTone...stopped working when the other filters were added to the UIAlert.

Thread 1: Exception: "[<CITwirlDistortion 0x600002ccea00> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key inputIntensity."

Solutions?

import CoreImage
import UIKit

class ViewController: UIViewController, UIImagePickerControllerDelegate, UINavigationControllerDelegate {
@IBOutlet var imageView: UIImageView!
@IBOutlet var intensity: UISlider!
var currentImage: UIImage!

var context: CIContext!
var currentFilter: CIFilter!

override func viewDidLoad() {
    super.viewDidLoad()
    title = "Instafilter"
    navigationItem.rightBarButtonItem = UIBarButtonItem(barButtonSystemItem: .add, target: self, action: #selector(importPicture))

    context = CIContext()
    currentFilter = CIFilter(name: "CISepiaTone")
}

@objc func importPicture() {
    let picker = UIImagePickerController()
    picker.allowsEditing = true
    picker.delegate = self
    present(picker, animated: true)
}

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
    guard let image = info[.editedImage] as? UIImage else { return }
    dismiss(animated: true)
    currentImage = image

    let beginImage = CIImage(image: currentImage)
    currentFilter.setValue(beginImage, forKey: kCIInputImageKey)
    applyProcessing()
}

@IBAction func changeFilter(_ sender: UIButton) {
    let ac = UIAlertController(title: "Choose filter", message: nil, preferredStyle: .actionSheet)
    ac.addAction(UIAlertAction(title: "CIBumpDistortion", style: .default, handler: setFilter))
    ac.addAction(UIAlertAction(title: "CIGaussianBlur", style: .default, handler: setFilter))
    ac.addAction(UIAlertAction(title: "CIPixellate", style: .default, handler: setFilter))
    ac.addAction(UIAlertAction(title: "CISepiaTone", style: .default, handler: setFilter))
    ac.addAction(UIAlertAction(title: "CITwirlDistortion", style: .default, handler: setFilter))
    ac.addAction(UIAlertAction(title: "CIUnsharpMask", style: .default, handler: setFilter))
    ac.addAction(UIAlertAction(title: "CIVignette", style: .default, handler: setFilter))
    ac.addAction(UIAlertAction(title: "CANCEL", style: .cancel))

    if let popoverController = ac.popoverPresentationController {
        popoverController.sourceView = sender
        popoverController.sourceRect = sender.bounds
    }
    present(ac, animated: true)
}

func setFilter(action: UIAlertAction) {
    guard currentImage != nil else { return }
    guard let actionTitle = action.title else { return }

    currentFilter = CIFilter(name: actionTitle)
    let beginImage = CIImage(image: currentImage)
    currentFilter.setValue(beginImage, forKey: kCIInputImageKey)

    applyProcessing()
}

@IBAction func save(_ sender: Any) {
}

@IBAction func intensityChange(_ sender: Any) {
    applyProcessing()
}

func applyProcessing() {
    let inputKeys = currentFilter.inputKeys

    if inputKeys.contains(kCIInputIntensityKey) {
        currentFilter.setValue(intensity.value, forKey: kCIInputIntensityKey)
    }

    if inputKeys.contains(kCIInputRadiusKey) {
        currentFilter.setValue(intensity.value * 200, forKey: kCIInputRadiusKey)
    }

    if inputKeys.contains(kCIInputScaleKey) {
        currentFilter.setValue(intensity.value * 10, forKey: kCIInputScaleKey)
    }

    if inputKeys.contains(kCIInputCenterKey) {
        currentFilter.setValue(CIVector(x: currentImage.size.width / 2, y: currentImage.size.height / 2), forKey: kCIInputCenterKey)
    }

    guard let outPutImage = currentFilter.outputImage else { return }
    currentFilter.setValue(intensity.value, forKey: kCIInputIntensityKey)

    if let cgImage = context.createCGImage(outPutImage, from: outPutImage.extent) {
        let processedImage = UIImage(cgImage: cgImage)
        imageView.image = processedImage
    }
  }
}

Solution found...remove the following lines from the changeFilter function:

ac.addAction(UIAlertAction(title: "CIBumpDistortion", style: .default, handler: setFilter))
ac.addAction(UIAlertAction(title: "CIGaussianBlur", style: .default, handler: setFilter))
ac.addAction(UIAlertAction(title: "CIPixellate", style: .default, handler: setFilter))
ac.addAction(UIAlertAction(title: "CITwirlDistortion", style: .default, handler: setFilter))

... these filters must have changed.

...not sure if this is up to date...

Core Image Filter Reference