Why is my CIImage nil after I invert a UIImage? - swift

Question

I have a very peculiar issue here where I convert a UIImage to CIImage after I inverted the UIImage. Here is the code:
let imageFromBuffer1 = self.imageInvert(image: self.imageFromBuffer)
let ciImage = CIImage(image: imageFromBuffer1)
So, in above code ciImage is nil for some bizarre reason. Can anybody explain this, or tell me what else to do to get the UIImage converted to CIImage?
This is the invert function I am using above:
func imageInvert(image: UIImage) -> UIImage{
let beginImage = CIImage(image: image)
var newImage = UIImage()
if let filter = CIFilter(name: "CIColorInvert") {
filter.setValue(beginImage, forKey: kCIInputImageKey)
let ciImage = filter.outputImage
newImage = UIImage(ciImage: ciImage!)
}
else{
print("filter does not exist")
newImage = image
}
return newImage
}

Answer 1

Because when an image is converted from one form to another some data may be modified, lost or not used. For instance when you load a UIImage from assets it may be larger than the view in which it is displayed, The graphics engine does it's best to display the image as true as possible. However some of the underlying image data may not be used, this is especially true for compressed jpeg images. Instead of converting the image back and forth consider transforming the current context the image resides in:
ViewController.swift
import UIKit
class ViewController: UIViewController {
lazy var imageView = UIImageView(frame: self.view.frame)
override func viewDidLoad() {
super.viewDidLoad()
self.view.addSubview(imageView)
let tap = UITapGestureRecognizer(target: self, action: #selector(imageViewTapped))
imageView.addGestureRecognizer(tap)
imageView.isUserInteractionEnabled = true
imageView.contentMode = .scaleAspectFit
// https://en.wikipedia.org/wiki/File:Meisje_met_de_parel.jpg
imageView.image = UIImage(named: "Meisje_met_de_parel.jpg")
}
func invert(image: UIImage) -> UIImage? {
let ciImage = CIImage(image: image)
var newImage:UIImage? = nil
guard let filter = CIFilter(name: "CIColorInvert") else {return image}
filter.setValue(ciImage, forKey: kCIInputImageKey)
let context = CIContext(options: nil)
if let outputImage = filter.outputImage, let cgImage = context.createCGImage(outputImage, from: outputImage.extent) {
newImage = UIImage(cgImage: cgImage)
}
return newImage
}
#objc func imageViewTapped() {
if let image = self.imageView.image {
let invertedImage = self.invert(image: image)
DispatchQueue.main.async {
self.imageView.image = invertedImage
}
}
}
}