No abstract

No abstract

Aim: In visual cryptography, a secret image is encrypted into two meaningless random images called shares. These two shares can be stacked to recover the secret image without any calculations. However, because of the alignment problem in the decryption phase, risk of poor quality of the restored image exists. Encrypting multiple secrets on two images simultaneously can improve execution efficiency. Methods: Let 7 × 7 pixels be a unit; this paper designs a codebook for any unit in the secret images by using a random grid. Besides, this paper shows a general shifting approach that can embed N (≥ 2) secret images simultaneously with adjustable distortion. Results: This paper provides a visual multi-secret sharing scheme without pixel expansion; the proposed scheme can encrypt more than two secret images into two shares simultaneously. During decoding, aligning the shares precisely is not necessary. Conclusion: Theoretical analysis and simulation results indicate the effectiveness and practicality of the proposed scheme.