Using Modified Digital Halftoning Technique to Design Invisible 2D Barcode by Infrared Detection

2D barcode is an important interface to connect physical environment with virtual (digital) world. It is commonly presented at printing substrates whose embedded information can be captured through optical recognition system. Yet, for human perception, the black-and-white barcode is not only meaningless but also aesthetically displeasing. Therefore, this study utilized a modified digital halftoning technique to make 2D barcode invisible under normal reading condition; however, it can still be detected by infrared devices. The research composes halftone dots of both amplitude modulation (AM) and frequency modulation (FM) to create an infrared watermark due to the different absorption properties between K (black) ink and CMY (cyan, magenta, and yellow) inks under infrared light. The results show that the proposed method successfully avoids 2D barcode distracting people from normal reading. The method conforms to the existing printing process without requiring any special inks or materials. In the future, the technique can be applied to product packaging and brand protection.