How to filter images using Core Image and CIFilter

Swift version: 5.1

Paul Hudson @twostraws May 28th 2019

Core Image is the one of the most powerful frameworks available to iOS developers: it makes hardware-accelerated image manipulation ridiculously easy, which means you get to add powerful graphical effects to your apps and games with very little work.

Most of the work is done by choosing the right CIFilter. Apple's official documentation goes into great detail about the various filters you can use, and you can also read Hacking with Swift project 13 for a hands-on tutorial showing off various effects. The code below applies a 50% sepia tone effect to an image:

let inputImage = UIImage(named: "taylor-swift")!
let context = CIContext(options: nil)

if let currentFilter = CIFilter(name: "CISepiaTone") {
    let beginImage = CIImage(image: inputImage)
    currentFilter.setValue(beginImage, forKey: kCIInputImageKey)
    currentFilter.setValue(0.5, forKey: kCIInputIntensityKey)

    if let output = currentFilter.outputImage {
        if let cgimg = context.createCGImage(output, from: output.extent) {
            let processedImage = UIImage(cgImage: cgimg)
            // do something interesting with the processed image
        }
    }
}