Demonstrate how to use CIFilter.colorAbsoluteDifference() on macOS

CIFilter-colorAbsoluteDifference-demo.swift

import Cocoa
import CoreImage
import CoreImage.CIFilterBuiltins

let nextButtonImage = NSImage(named: "next button")!
let startGameButtonImage = NSImage(named: "start game button")!

computeImageDifference(inputImage: nextButtonImage, inputImage2: startGameButtonImage)

// MARK: -

extension NSImage {
  var ciImage: CIImage? {
    guard let cgImage = cgImage(forProposedRect: nil, context: nil, hints: nil) else { return nil }
    return CIImage(cgImage: cgImage)
  }
}

func computeImageDifference(inputImage: NSImage, inputImage2: NSImage) -> NSImage? {
  guard let inputImage = inputImage.ciImage else { return nil }
  guard let inputImage2 = inputImage2.ciImage else { return nil }

  let context = CIContext()
  let currentFilter = CIFilter.colorAbsoluteDifference()
  currentFilter.inputImage = inputImage
  currentFilter.inputImage2 = inputImage2

  guard let outputImage = currentFilter.outputImage else { return nil }

  guard let result = context.createCGImage(
    outputImage,
    from: outputImage.extent
  ) else { return nil }

  return NSImage(cgImage: result, size: CGSize(width: result.width, height: result.height))
}