func generateBarcode(from string: String) -> UIImage? {
    let data = string.data(using: String.Encoding.ascii)

    if let filter = CIFilter(name: "CICode128BarcodeGenerator") {
      filter.setValue(data, forKey: "inputMessage")
      let transform = CGAffineTransform(scaleX: 3, y: 3)

      if let output = filter.outputImage?.applying(transform) {
        return UIImage(ciImage: output)
      }
    }
    return nil
}