Image from CIFilter wont display

Question

I'm taking a snapshot of a subview and turning it into an image:

let image = UIImage(view: swiftyDraw)
let scaledImage = scaleImage(image: image, toSize: CGSize(width: 28, height:28))

finalImage is a UIImageView and setting it to display the scaledImage works, I can see it fine:

finalImage.image = scaledImage //this works

However, I want to invert the colors before displaying it:

let filter = CIFilter(name: "CIColorInvert")
filter!.setValue(CIImage(image: scaledImage), forKey: kCIInputImageKey)
let invertedImage = UIImage(ciImage: filter!.outputImage!)
finalImage.image = invertedImage //this does not work

Nothing shows up when I set finalImage.image to invertedImage, but it shows up fine when it's set to scaledImage.

Edit: scaleImage function:

func scaleImage (image: UIImage, toSize size:CGSize) -> UIImage {
    UIGraphicsBeginImageContextWithOptions(size, false, 1.0)
    image.draw(in: CGRect(x: 0, y: 0, width: size.width, height: size.height))
    let newImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return newImage!
}

Answer 1

Let's say your "scaledImage" is an UIImage, so you can directly get an CIImage without creating a new one.

guard let ciImage = scaledImage.ciImage, let filter = CIFilter(name: "CIColorInvert") else {
    fatalError("CIImage conversion fail")
}
//Now access the CIFilter object to filter the image
filter.setValue(ciImage, forKey: kCIInputImageKey)
finalImage.image = UIImage(ciImage: filter.outputImage!)

Update

In case, if you are fatalError means UIImage doesn't exists with CIImage so you need to convert UIImage to CIImage.

extension UIImage {
    var toCIImage: CIImage {
        return self.CIImage ?? CIImage(CGImage: self.CGImage!)
    }
}

guard let filter = CIFilter(name: "CIColorInvert") else {
    fatalError("CIImage conversion fail")
}

let ciImage = scaledImage.toCIImage
//Now access the CIFilter object to filter the image
filter.setValue(ciImage, forKey: kCIInputImageKey)
finalImage.image = UIImage(ciImage: filter.outputImage!)