份额重构的变方向灰度渐进视觉密码  

Variable-direction grayscale progressive visual cryptography through share reconstruction

作　　者：王春常 邵利平[1] 李赫然 WANG Chunchang;SHAO Liping;LI Heran(School of Computer Science,Shaanxi Normal University,Xi’an 710119,P.R.China)

机构地区：[1]陕西师范大学计算机科学学院,西安710119

出　　处：《重庆邮电大学学报（自然科学版）》2024年第6期1159-1174,共16页Journal of Chongqing University of Posts and Telecommunications(Natural Science Edition)

基　　金：陕西省自然科学基金项目(2020JM-301);陕西省重点研究计划项目(2020GY-269)。

摘　　要：基于二值模式组合的灰度阶视觉密码可实现灰度阶像素免计算重构,但不能充分利用二值像素点阵且会产生大量拆分份额;而多密图变方向视觉密码需考虑像素重构冲突,构造复杂且缺乏灵活性和普适性。针对以上问题,提出份额重构的变方向灰度渐进视觉密码。将待隐藏灰度密图通过多级半色调转换为降灰度阶密图并直接映射为二值密图,借助(2,2)门限视觉密码来构造公共份额和隐藏不同密图的中间份额,采用主辅对角线融合的方式产生融合份额并通过不透明像素点拆分策略实现不同密图的渐进重构。理论和实验表明,相对于二值模式组合方案,提出的方法可充分利用二值像素点阵提升视觉质量,避免大量份额拆分;相对于变方向视觉密码,提出的方法构造简单灵活,可实现不同方向不同密图重构和渐进重构,具有普适性,可保持较好的灰度阶视觉质量且只在正确的叠加方向下才能恢复密图。Grayscale visual cryptography based on binary pattern combinations can reconstruct grayscale images without computation but fails to fully utilize binary pixel matrices and generates a large number of shares.Multi-grayscale directional visual cryptography,on the other hand,faces pixel reconstruction conflicts,is complex to construct,and lacks flexibility and universality.To address these issues,a directional grayscale progressive visual cryptography scheme based on share reconstruction is proposed.The grayscale secret image is first converted into reduced-grayscale images through multi-level halftoning,which are then directly mapped to binary images.Using a(2,2)threshold visual cryptography scheme,public shares and intermediate shares for hiding different secret images are constructed.By employing a primary-auxiliary diagonal merging method,fused shares are generated,and a transparent pixel-splitting strategy enables progressive reconstruction of different secret images.Theoretical and experimental results demonstrate that compared to binary pattern combination schemes,the proposed method improves visual quality by fully utilizing binary pixel matrices while avoiding excessive share splitting.Compared to directional visual cryptography,the proposed scheme is simpler,more flexible,supports reconstruction in different directions and progressive reconstruction,and maintains good grayscale visual quality.The hidden image can only be reconstructed in the correct overlay direction.

关 键 词：视觉密码 变方向 二值点阵映射 份额融合 份额拆分 多灰度阶 

分 类 号：TP309.7[自动化与计算机技术—计算机系统结构] TN919[自动化与计算机技术—计算机科学与技术]