Grayscale image

UIImage+CIPhotoEffectNoir.swift

extension UIImage {
    var grayscaled: UIImage? {
        guard let openGLContext = EAGLContext(api: .openGLES2) else { return self }
        let ciContext = CIContext(eaglContext: openGLContext)

        guard let currentFilter = CIFilter(name: "CIPhotoEffectNoir") else { return self }
        currentFilter.setValue(CIImage(image: self), forKey: kCIInputImageKey)
        if let output = currentFilter.outputImage,
            let cgImage = ciContext.createCGImage(output, from: output.extent) {
            return UIImage(cgImage: cgImage, scale: scale, orientation: imageOrientation)
        }

        return nil
    }
}