Get the average color of a UIImage. (Swift 4.2, Xcode 10.0)

UIImage+averageColor.swift

import UIKit

extension UIImage {
    
    var averageColor: UIColor? {
        guard let inputImage = self.ciImage ?? CIImage(image: self) else { return nil }
        guard let filter = CIFilter(name: "CIAreaAverage", parameters: [kCIInputImageKey: inputImage, kCIInputExtentKey: CIVector(extent: inputImage.extent)])
        else { return nil }
        guard let outputImage = filter.outputImage else { return nil }

        var bitmap = [UInt8](repeating: 0, count: 4)
        let context = CIContext(options: [CIContextOption.workingColorSpace : kCFNull])
        let outputImageRect = CGRect(x: 0, y: 0, width: 1, height: 1)

        context.render(outputImage, toBitmap: &bitmap, rowBytes: 4, bounds: outputImageRect, format: CIFormat.RGBA8, colorSpace: nil)

        return UIColor(red: CGFloat(bitmap[0]) / 255, green: CGFloat(bitmap[1]) / 255, blue: CGFloat(bitmap[2]) / 255, alpha: CGFloat(bitmap[3) / 255)
    }
}