How to blur an existing image in a UIImageView with Swift?

for those who ❤️ protocols

protocol Blurable {
    func addBlur(_ alpha: CGFloat)
}

extension Blurable where Self: UIView {
    func addBlur(_ alpha: CGFloat = 0.5) {
        // create effect
        let effect = UIBlurEffect(style: .dark)
        let effectView = UIVisualEffectView(effect: effect)
        
        // set boundry and alpha
        effectView.frame = self.bounds
        effectView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        effectView.alpha = alpha
        
        self.addSubview(effectView)
    }
}

// Conformance
extension UIView: Blurable {}

// use
someImageview.addBlur()

You could simply use UIVisualEffect to achieve blur effect. As you trying to achieve a blur effect using CoreImage.Try below code after import CoreImage to your class.

var context = CIContext(options: nil)

func blurEffect() {

    let currentFilter = CIFilter(name: "CIGaussianBlur") 
    let beginImage = CIImage(image: bg.image!)
    currentFilter!.setValue(beginImage, forKey: kCIInputImageKey)
    currentFilter!.setValue(10, forKey: kCIInputRadiusKey)

    let cropFilter = CIFilter(name: "CICrop")
    cropFilter!.setValue(currentFilter!.outputImage, forKey: kCIInputImageKey)
    cropFilter!.setValue(CIVector(cgRect: beginImage!.extent), forKey: "inputRectangle")

    let output = cropFilter!.outputImage 
    let cgimg = context.createCGImage(output!, from: output!.extent)
    let processedImage = UIImage(cgImage: cgimg!)
    bg.image = processedImage
}

Output:

Note: I recommend you to test the code in real device as Simulator performance is too slow on coreImage.