پنهان سازی داده های زمان واقعی و رمزنگاری ویژوال Special Issue: Real-Time Data Hiding and Visual Cryptography

1 Introduction Data hiding (DH) may embed secret data, copyright information, and annotation into various media such as image, audio, video, or text. The embedded data should be invisible to a watchdog, and meanwhile the secret data have to stay hidden in a cover signal without detection from steganalysis tools. For this reason, we should retain the good visual quality of an image with the high embedding data. However, trade-offs exist between the embedding capacity and the degree of quality to cover media modification. That is, as one increases, the other must decrease. Thus, according to our need, we choose the best way to implement DH. Reversible DH (RDH) was derived from DH for sensitive applications such as military and hospital since 10 year ago. Recent research on RDH has been focused on encrypted domains. Another topic of this special issue is visual cryptography scheme (VCS). In the last two decades, investigations on VCS were widely conducted. A basic model of VC was firstly proposed by Naor and Shamir. They demonstrated VCS, where an image was divided into a number of shared images so that only participants in the qualified set could decrypt the secret image, while participants in the nonqualified set have no information about the secret. In VCS, the appealing property is that the decoding process can be performed directly by the human eyes without any complicated cryptographic computation. This ‘‘stackingto-see’’ property of VCS provides many intended applications, e.g., information hiding, access control, watermarking, authentication, identification, and transmitting passwords. This special issue (SI) of the Springer Journal of RealTime Image Processing (JRTIP) entitled Real-Time DH and VCS highlights the latest research results on various image, pattern recognition, and signal processing algorithms and technologies for real-time approaches in DH, RDH, and VCS based on various multimedia. This SI addresses both theoretical and practical problems along with the real-time theme of JRTIP. It includes fast schemes and hardware implementations, as well as software/hardware co-design based on DH/RDH and VCS. The call for papers resulted in 29 submissions. For each submission, at least two reviewers examined its quality, together with the guest editors and editor-in-chief. Finally, 19 papers were accepted for this special issue. The selected papers outlined below can be divided broadly into the following themes. The first theme involves VCS and image secret sharing schemes to support real-time algorithms. Six papers fall into this theme. The second theme involves DH, RDH, and steganography for high capacity and good image quality with fast encoding algorithm, and another nine papers fall into this theme. The third theme has two papers and consists of watermarking and reversible watermarking implemented with FPGA for supporting real-time processing techniques. The fourth theme has two papers including steganalysis and authentication.