UIImageExtension.swift

func addFilter(filterType : FilterType) -> UIImage {
        let filter = CIFilter(name: filterType.rawValue)
        // convert UIImage to CIImage and set as input
        let ciInput = CIImage(image: self)
        filter?.setValue(ciInput, forKey: "inputImage")
        
        if filterType == .Sharpen {
            filter?.setValue(0.8, forKey: "inputIntensity")
            filter?.setValue(8, forKey: "inputRadius")
        }
        if filterType == .Posterize {
            filter?.setValue(15, forKey: "inputLevels")
        }
        if filterType == .MonoChrome {
            filter?.setValue(CIColor(red: 0.8, green: 0.8, blue: 0.8), forKey: "inputColor")
            filter?.setValue(1.0, forKey: "inputIntensity")
        }
        if filterType == .NoiseReduction {
            filter?.setValue(2, forKey: "inputSharpness")
        }
        
        // get output CIImage, render as CGImage first to retain proper UIImage scale
        let ciOutput = filter?.outputImage
        let ciContext = CIContext()
        let cgImage = ciContext.createCGImage(ciOutput!, from: (ciOutput?.extent)!)
        
        return UIImage(cgImage: cgImage!, scale: 1, orientation: imageOrientation)
    }